Applied Surface Science (v.317, #C)
Editorial Board (ii).
Thermal stability study of Cr/Au contact formed on n-type Ga-polar GaN, N-polar GaN, and wet-etched N-polar GaN surfaces by Yunju Choi; Yangsoo Kim; Kwang-Soon Ahn; Hyunsoo Kim (1-5).
The electrical characteristics and thermal stability of a Cr/Au contact formed on n-type Ga-polar (0 0 0 1) GaN, N-polar GaN, and wet-etched N-polar GaN were investigated. As-deposited Cr/Au showed a nearly ohmic contact behavior for all samples, i.e., the specific contact resistance was 3.2 × 10−3, 4.3 × 10−4, and 1.1 × 10−3 Ω cm2 for the Ga-polar, flat N-polar, and roughened N-polar samples, respectively. However, thermal annealing performed at 250 °C for 1 min in a N2 ambient led to a significant degradation of contact, i.e., the contact resistance increased by 186, 3260, and 2030% after annealing for Ga-polar, flat N-polar, and roughened N-polar samples, respectively. This could be due to the different disruption degree of Cr/Au and GaN interface after annealing, i.e., the insignificant interfacial reaction occurred in the Ga-polar sample, while out-diffusion of Ga and N atoms was clearly observed in N-polar samples.
Keywords: GaN; N-polar; Contact degradation; Polarization;
Evolution of plasticity in nanometric cutting of Fe single crystals by Yu Gao; Herbert M. Urbassek (6-10).
Using molecular dynamics simulation we study the generation and evolution of plasticity and defects in orthogonal cutting of an Fe single-crystalline workpiece. We focus on the (1 1 1)[11 2 ¯ ] cutting geometry. Dislocations are generated at the primary shear zone with Burgers vector b = 1/2〈11 1〉 and the dislocation line oriented parallel to the cutting edge. They are emitted along their glide systems deep into the material. The chip – beyond the primary shear zone – is initially defect-free; upon continued cutting point defects and threading dislocations enter the chip. Besides the emitted dislocations, an extended defect (twin boundary) is created immediately below the cutting edge in the workpiece. The cut surface strongly roughens and deviates from the original (1 1 1) orientation.
Keywords: Molecular dynamics; Nanocutting; Iron; Dislocations; Nanomachining;
The oxidization behavior and mechanical properties of ultrananocrystalline diamond films at high temperature annealing by Kai Huang; Xiaojun Hu; Hui Xu; Yaogen Shen; Alex Khomich (11-18).
Ultrananocrystalline diamond (UNCD) films prepared by hot filament chemical vapor deposition (HFCVD) were annealed at 1000 °C in low degree vacuum under a pressure of 4000 Pa. The correlation between the mechanical and structural properties was investigated to understand the oxidization behavior of UNCD films after high temperature annealing. At the early stage of annealing (∼30 min), the amorphous carbon and graphite in grain boundaries are selectively oxidized firstly along the clusters’ gaps, with the Young's modulus and hardness decreasing rapidly revealed by nanoindentation results. A special annealing time of ∼30–60 min is found to exist as a turning point that the mechanical properties changing trend has a transition, because of the diamond grains starting to be oxidized. With the annealing time increasing to 180 min, the nanoindentation depth increases from ∼70 to ∼90 nm and the Young's modulus and hardness decrease more slowly with almost keeping constant of ∼383 and ∼35 GPa, respectively. X-ray photoelectron spectroscopy (XPS) results show that a steady 30-nm-thick oxidized layer has been formed on the top-surface and keeps a balance of the speed between films being oxidized and the carbon oxidation being broken down.
Keywords: Ultrananocrystalline diamond films; Annealing; Microstructure; Mechanical properties; Selective thermal oxidation;
Nanostructured ZnO thin films prepared by sol–gel spin-coating by E. Heredia; C. Bojorge; J. Casanova; H. Cánepa; A. Craievich; G. Kellermann (19-25).
ZnO thin films deposited on silica flat plates were prepared by spin-coating and studied by applying several techniques for structural characterization. The films were prepared by depositing different numbers of layers, each deposition being followed by a thermal treatment at 200 °C to dry and consolidate the successive layers. After depositing all layers, a final thermal treatment at 450 °C during 3 h was also applied in order to eliminate organic components and to promote the crystallization of the thin films. The total thickness of the multilayered films – ranging from 40 nm up to 150 nm – was determined by AFM and FESEM. The analysis by GIXD showed that the thin films are composed of ZnO crystallites with an average diameter of 25 nm circa. XR results demonstrated that the thin films also exhibit a large volume fraction of nanoporosity, typically 30–40 vol.% in thin films having thicknesses larger than ∼70 nm. GISAXS measurements showed that the experimental scattering intensity is well described by a structural model composed of nanopores with shape of oblate spheroids, height/diameter aspect ratio within the 0.8–0.9 range and average diameter along the sample surface plane in the 5–7 nm range.
Keywords: ZnO; Nanostructured thin films; XR; AFM; FESEM; GISAXS;
Adsorption kinetics of NO on ordered mesoporous carbon (OMC) and cerium-containing OMC (Ce-OMC) by Jinghuan Chen; Feifei Cao; Songze Chen; Mingjiang Ni; Xiang Gao; Kefa Cen (26-34).
Ordered mesoporous carbon (OMC) and cerium-containing OMC (Ce-OMC) were prepared using evaporation-induced self-assembly (EISA) method and used to adsorb NO. N2 sorption, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to confirm their structures. The results showed that the ordered and uniform structures were successfully synthesized and with the introduction of cerium pore properties were not significantly changed. The NO adsorption capacity of OMC was two times larger than that of activated carbon (AC). With the introduction of cerium both the adsorption capacity and the adsorption rate were improved. The effects of residence time and oxygen concentration on NO adsorption were also investigated. Oxygen played an important role in the NO adsorption (especially in the form of chemisorption) and residence time had small influence on the NO adsorption capacity. The NO adsorption kinetics was analyzed using pseudo-first-order, pseudo-second-order, Elovich equation and intraparticle diffusion models. The results indicated that the NO adsorption process can be divided into rapid adsorption period, slow adsorption period, and equilibrium adsorption period. The pseudo-second-order model was the most suitable model for NO adsorption on OMC and Ce-OMC. The rate controlling step was the intraparticle diffusion together with the adsorption reaction.
Keywords: Ordered mesoporous carbon (OMC); NO adsorption; Ce-OMC; Adsorption kinetics;
Synthesis of organic rectorite with novel Gemini surfactants for copper removal by Guocheng Han; Yang Han; Xiaoying Wang; Shijie Liu; Runcang Sun (35-42).
Three Gemini surfactants showed stronger rapid intercalation capacity into rectorite and behaved better on Cu2+ removal than two single-chain surfactants, which were positive to their increasing amount and chain length.Three novel Gemini surfactants were used to prepare organic rectorite (OREC) under microwave irradiation, in comparison with single-chain surfactant ester quaternary ammonium salt (EQAS) and cetyltrimethyl ammonium bromide (CTAB). The structure and morphology of OREC were characterized by XRD, BET, FT-IR, TEM and TGA. The removal of Cu2+ on OREC from aqueous solution was performed. The results reveal that Gemini surfactants modified REC had larger interlayer distance and higher surface area than single-chain surfactants EQAS and CTAB, and the increasing amount or chain length of Gemini surfactants led to larger layer spacing and higher adsorption capacities. The adsorption behavior of Gemini surfactant modified REC can be better described by Freundlich adsorption isotherm model, with a maximum adsorption capacity of 15.16 mg g−1. The desorption and regeneration experiments indicate good reuse property of Gemini modified REC adsorbent. Therefore, this study may widen the utilization of Gemini surfactants modified layered silicates.
Keywords: Gemini surfactant; Rectorite; Copper; Adsorption; Regeneration;
One-dimensional mesoporous Fe2O3@TiO2 core–shell nanocomposites: Rational design, synthesis and application as high-performance photocatalyst in visible and UV light region by Xiao Zhang; Yaping Xie; Haoxin Chen; Jinxue Guo; Alan Meng; Chunfang Li (43-48).
An ideal photocatalyst for degradation of organic pollutants should combine the features of efficient visible light response, fast electron transport, high electron–hole separation efficiency, and large specific surface area. However, these requirements usually cannot be achieved simultaneously in the present state-of-the-art research. In this work, we develop a rational synthesis strategy for the preparation of one-dimensional (1D) mesoporous Fe2O3@TiO2 core–shell composites. In this strategy, FeOOH nanorods are firstly coated by TiO2 shell, followed by a calcination process. The as-prepared composites are thoroughly investigated with X-ray powder diffraction, scanning electron microscope, energy dispersive spectroscopy, transmission electron microscope, N2 adsorption–desorption isotherms, UV–visible diffuse-reflectance spectra, and photoluminescence spectra. Endowed with the advantages of its composition and specific structural features, the presented sample possesses the combined advantages mentioned above, thus delivering evidently enhanced photocatalytic activity for the degradation of methyl orange under UV light irradiation and Rhodamine B under visible light irradiation. And the possible mechanism of the enhanced photocatalytic performance is proposed.
Keywords: TiO2; Fe2O3; Core–shell structures; Mesoporous structures; Photocatalysis;
Synthesis of silver nanoparticles on surface-functionalized multi-walled carbon nanotubes by ultraviolet initiated photo-reduction method by Yanhua Lei; Guanhui Gao; Wechao Liu; Tao Liu; Yansheng Yin (49-55).
In this article, we described a new, facile method on fabrication of multi-walled carbon nanotubes (MWNTs) with silver nanoparticles by an ultraviolet initiated method. MWNTs were functionalized with acrylic acid to introduce carboxylic acid groups, and then the Ag nanoparticles were synthesized on the functionalized MWNTs by using of ultraviolet irradiation without adding of any protective or reductive agent. The obtained MWNTs/Ag composites were analyzed with Fourier transform infrared spectrometer (FT-IR) spectroscopy, transmission electron microscope (TEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It was confirmed that Ag nanoparticles with diameters in a region of 5–10 nm were anchored on the surface of MWNTs by an interaction of Ag and oxygen in the carboxyl group.
Keywords: MWNTs; Silver nanoparticles; PAA; XPS;
Long-term antibiotic delivery by chitosan-based composite coatings with bone regenerative potential by F. Ordikhani; A. Simchi (56-66).
Composite coatings with bone-bioactivity and drug-eluting capacity are considered as promising materials for titanium bone implants. In this work, drug-eluting chitosan-bioactive glass coatings were fabricated by a single-step electrophoretic deposition technique. Drug-loading and -releasing capacity of the composite coatings were carried out using the vancomycin antibiotic. Uniform coatings with a thickness of ∼55 μm containing 23.7 wt% bioactive glass particles and various amounts of the antibiotic (380–630 μg/cm2) were produced. The coatings were bioactive in terms of apatite-forming ability in simulated body fluid and showed favorable cell adhesion and growth. In vitro biological tests also indicated that the composite coatings had better cellular affinity than pristine chitosan coatings. The in vitro elution kinetics of the composite coating revealed an initial burst release of around 40% of the drug within the first elution step of 1 h and following by a continuous eluting over 4 weeks, revealing long-term drug-delivering potential. Antibacterial tests using survival assay against Gram-positive Staphylococcus aureus bacteria determined the effect of vancomycin release on reduction of infection risk. Almost no bacteria were survived on the coatings prepared from the EPD suspension containing ≥0.5 g/l vancomycin. The developed chitosan-based composite coatings with bone bioactivity and long-term drug-delivery ability may be potentially useful for metallic implants to reduce infection risk.
Keywords: Chitosan; Bioactive coating; Drug eluting; Antibacterial; Cell response;
Removal of brownish-black tarnish on silver–copper alloy objects with sodium glycinate by João Cura D’Ars de Figueiredo; Samara Santos Asevedo; João Henrique Ribeiro Barbosa (67-72).
This article has the principal aim of presenting a new method of chemical cleaning of tarnished silver–copper alloy objects. The chemical cleaning must be harmless to the health, selective to tarnish removal, and easy to use. Sodium glycinate was selected for the study. The reactions of sodium glycinate with tarnish and the silver–copper alloy were evaluated. Products of the reaction, the lixiviated material, and the esthetics of silver–copper alloy coins (used as prototypes) were studied to evaluate if the proposed method can be applied to the cleaning of silver objects.Silver–copper alloys can be deteriorated through a uniform and superficial corrosion process that produces brownish-black tarnish. This tarnish alters the esthetic of the object. The cleaning of artistic and archeological objects requires more caution than regular cleaning, and it must take into account the procedures for the conservation and restoration of cultural heritage. There are different methods for cleaning silver–copper alloy objects, chemical cleaning is one of them. We studied two chemical cleaning methods that use sodium glycinate and sodium acetylglycinate solutions. Silver–copper alloy coins were artificially corroded in a basic thiourea solution and immersed in solutions of sodium glycinate and sodium acetylglycinate. After immersion, optical microscopy and scanning electron microscopy of the surfaces were studied. The sodium glycinate solution was shown to be very efficient in removing the brownish-black tarnish. Absorption spectroscopy measured the percentage of silver and copper lixiviated in immersion baths, and very small quantities of these metals were detected. Infrared absorption spectroscopy and X-ray fluorescence characterized the obtained products. The greater efficiency of the sodium glycinate solution compared to the sodium acetylglycinate solution was explained by chelation and Hard–Soft Acid–Base Theory with the aid of quantum chemical calculations.
Keywords: Silver–copper alloy; Tarnish; Glycinate; Scanning electron microscopy; X-ray fluorescence; Infrared absorption spectroscopy;
Surface and bulk characterization of an ultrafine South African coal fly ash with reference to polymer applications by E.M. van der Merwe; L.C. Prinsloo; C.L. Mathebula; H.C. Swart; E. Coetsee; F.J. Doucet (73-83).
South African coal-fired power stations produce about 25 million tons of fly ash per annum, of which only approximately 5% is currently reused. A growing concern about pollution and increasing landfill costs stimulates research into new ways to utilize coal fly ash for economically beneficial applications. Fly ash particles may be used as inorganic filler in polymers, an application which generally requires the modification of their surface properties. In order to design experiments that will result in controlled changes in surface chemistry and morphology, a detailed knowledge of the bulk chemical and mineralogical compositions of untreated fly ash particles, as well as their morphology and surface properties, is needed. In this paper, a combination of complementary bulk and surface techniques was explored to assess the physicochemical properties of a classified, ultrafine coal fly ash sample, and the findings were discussed in the context of polymer application as fillers. The sample was categorized as a Class F fly ash (XRF). Sixty-two percent of the sample was an amorphous glass phase, with mullite and quartz being the main identified crystalline phases (XRD, FTIR). Quantitative carbon and sulfur analysis reported a total bulk carbon and sulfur content of 0.37% and 0.16% respectively. The spatial distribution of the phases was determined by 2D mapping of Raman spectra, while TGA showed a very low weight loss for temperatures ranging between 25 and 1000 °C. Individual fly ash particles were characterized by a monomodal size distribution (PSD) of spherical particles with smooth surfaces (SEM, TEM, AFM), and a mean particle size of 4.6 μm (PSD). The BET active surface area of this sample was 1.52 m2/g and the chemical composition of the fly ash surface (AES, XPS) was significantly different from the bulk composition and varied considerably between spheres. Many properties of the sample (e.g. spherical morphology, small particle size, thermal stability) appeared to be suitable for its applicability as filler in polymers, although the wide variation in surface composition between individual particles may challenge the development of a suitable surface modification technique. The observation that the bulk and surface compositions of the particles were so intrinsically different, strongly suggested that surface characterization is important when considering compatibility between matrices when applying fly ash as filler in polymers.
Keywords: Coal fly ash; Bulk properties; Surface properties; Characterization;
Graphite coated with manganese oxide/multiwall carbon nanotubes composites as anodes in marine benthic microbial fuel cells by Yubin Fu; Jian Yu; Yelong Zhang; Yao Meng (84-89).
Improving anode performance is of great significance to scale up benthic microbial fuel cells (BMFCs) for its marine application to drive oceanography instruments. In this study, manganese oxide (MnO2)/multiwall carbon nanotubes (MWCNTs) composites are prepared to be as novel anodes in the BMFCs via a direct redox reaction between permanganate ions (MnO4 −) and MWCNTs. The results indicate that the MnO2/MWCNTs anode has a better wettability, greater kinetic activity and higher power density than that of the plain graphite (PG) anode. It is noted that the MnO2 (50% weight percent)/MWCNTs anode shows the highest electrochemical performance among them and will be a promising material for improving bioelectricity production of the BMFCs. Finally, a synergistic mechanism of electron transfer shuttle of Mn ions and their redox reactions in the interface between modified anode and bacteria biofilm are proposed to explain its excellent electrochemical performance.
Keywords: Manganese oxide; Modified anodes; Kinetic activity; Electron transfer mechanism;
Influence of chitosan–PEG binary template on the crystallite characteristics of sol–gel synthesized mesoporous nano-titania photocatalyst by T. Preethi; B. Abarna; G.R. Rajarajeswari (90-97).
Nano-titania is by far, the most studied material for its photocatalytic application in air and water pollution abatement. In this study, we have demonstrated the advantage offered by using a binary template of PEG and chitosan for the sol–gel synthesis of titania. Nano-titania samples were prepared using PEG, chitosan and the binary combination of these two as templates. XRD showed that all synthesized samples preserved the anatase structure. Titania sample prepared on 1% PEG and 3% chitosan as template (P1-C3 titania) possessed spherical shaped particles with an average particle size of 12.3 nm, a surface area of 82.9 m2/g and uniform dispersion. DRS UV–Vis spectra indicated that, P1-C3 titania showed blue shift in its absorption profile due to decrease in particle size. Consistent with the characteristics, the P1-C3 titania exhibited the highest photocatalytic activity for the degradation of 4-chlorophenol under UV irradiation, in comparison with all the synthesized photocatalytic systems and Degussa-P25. The chitosan bio template is believed to offer controlled growth of titania through Lewis base type interaction with Ti metallic centers in TiO2. Such controlled growth route will be significant in synthesizing custom-made titania for its advanced applications in catalytic processes.
Keywords: Titania; Photocatalysis; Templates; Chitosan–PEG; 4-Chlorophenol;
Spatially selective Er/Yb-doped CaF2 crystal formation by CO2 laser exposure by Dong-Seon Kim; Jin-Ho Lee; Ki-Soo Lim (98-102).
We report the glass–ceramic precipitation on the oxyfluoride glass surface by spatially selective annealing with a CO2 laser and a heat gun exposure. X-ray diffraction analysis showed the formation of major CaF2 and miner Ca2SiO4 nanoparticles. We observed ∼100 nm nanoparticle aggregation by tunneling electron microscopy and element distribution in glass and crystal phases. Spatial distribution of glass ceramics near the glass surface was probed by confocal fluorescence microscope by using much enhanced emission from the Er ions in the laser-treated area. Strong emissions at 365 nm excitation and visible up-conversion emissions at 980 nm excitation also indicated well incorporation of Er and Yb ions into a crystalline environment.
Keywords: CaF2; Nanocrystals; Glass–ceramics; CO2 laser; Er; Upconversion;
Surface properties and hydrophobic recovery of polymers treated by atmospheric-pressure plasma by C. Borcia; I.L. Punga; G. Borcia (103-110).
This paper provides an analysis on the relation between plasma effects on polymers exposed to inert gas atmospheric-pressure plasma, polymer structure characteristics and surface recovery during post-processing ageing. Polymers offering variety of structure, functionality, degree of oxidation, polarity, crystallinity are tested, using contact angle, XPS, XRD and solvent absorption measurement, thus exploring the relationship linking the surface polarity, the chemical structure and composition contribution in the combined functionalization/crosslinking surface modification mechanisms of plasma-exposed polymers. The limiting level of modification attainable, the surface stability and the factors controlling these are examined, concluding on the plasma capacity to provide operational stability for modified polymer surfaces.
Keywords: Atmospheric-pressure plasma; Polymer; Crosslinking; Functionalization; Ageing;
The poisoning effect of Na and K on Mn/TiO2 catalyst for selective catalytic reduction of NO with NH3: A comparative study by Rui-tang Guo; Qing-shan Wang; Wei-guo Pan; Wen-long Zhen; Qi-lin Chen; Hong-lei Ding; Ning-zhi Yang; Chen-zi Lu (111-116).
Mn/TiO2 catalyst is of high activity for low temperature selective catalytic reduction (SCR) of NO with NH3. And the deposition of alkali metal would lead to the deactivation of Mn/TiO2 catalyst. In this paper, the poisoning effect of Na and K on Mn/TiO2 was investigated based on experimental and theoretical study. It was found that K had a stronger poisoning effect than that of Na. The bad performance of K–Mn/TiO2 may be due to its small surface area, high crystallinity, weak surface acidity, low content of Mn4+ and chemisorbed oxygen, and bad redox ability. The interpretation of the experimental results is supported by DFT calculations.
Keywords: Mn/TiO2 catalyst; Alkali metal; Deactivation; Characterization; DFT;
Hydrogen gas sensing feature of polyaniline/titania (rutile) nanocomposite at environmental conditions by Hossain Milani Moghaddam; Shahruz Nasirian (117-124).
The resistance-based sensors of polyaniline/titania (rutile) nanocomposite (TPNC) were prepared by spin coating technique onto an epoxy glass substrate with Cu-interdigited electrodes to study their hydrogen (H2) gas sensing features. Our findings are that the change of the surface morphology, porosity and wt% of titania in TPNCs have a significant effect on H2 gas sensing of sensors. All of the sensors had a reproducibility response toward 0.8 vol% H2 gas at room temperature, air pressure and 50% relative humidity. A sensor with 40 wt% of titania nanoparticles had better response/recovery time and the response than other sensors. Moreover, H2 gas sensing mechanism of TPNC sensors based contact areas and the correlation of energy levels between PANI chains and the titania grains were studied.
Keywords: Polyaniline; Titania; Nanocomposite; Hydrogen gas sensing; Environmental conditions;
The effects of cold rolling temperature on corrosion resistance of pure iron by Lv Jinlong; Luo Hongyun (125-130).
The effects of cold rolling temperature on grain size and grain orientation of pure iron were investigated. Comparing with sample rolled at room temperature, the grain refinement was facilitated in sample obtained by cryogenic cold rolling at liquid-nitrogen temperature. However, the grain orientation changed little for two samples. It was shown that cathodic hydrogen evolution reaction could govern the corrosion reaction for pure iron in sulfuric acid solution. The grain refinement obtained by rolling improved the corrosion resistance of iron in sulfuric acid solution, borate buffer solution and borate buffer solution with chloride ion. However, comparing with iron rolled at room temperature, the corrosion resistance of iron obtained by cryogenic temperature rolling was lower. Comparing with iron rolled at room temperature, higher dislocation density in iron rolled at cryogenic temperature reduced its corrosion resistance.
Keywords: Grain size; Microstructure; Corrosion resistance; Cryogenic cold rolling;
Chemical, mechanical and antibacterial properties of silver nanocluster/silica composite coated textiles for safety systems and aerospace applications by S. Ferraris; S. Perero; M. Miola; E. Vernè; A. Rosiello; V. Ferrazzo; G. Valletta; J. Sanchez; M. Ohrlander; S. Tjörnhammar; M. Fokine; F. Laurell; E. Blomberg; S. Skoglund; I. Odnevall Wallinder; M. Ferraris (131-139).
This work describes the chemical, mechanical and antibacterial properties of a novel silver nanocluster/silica composite coating, obtained by sputtering, on textiles for use in nuclear bacteriological and chemical (NBC) protection suites and for aerospace applications.The properties of the coated textiles were analyzed in terms of surface morphology, silver concentration and silver release in artificial sweat and synthetic tap water, respectively. No release of silver nanoparticles was observed at given conditions.The water repellency, permeability, flammability and mechanical resistance of the textiles before and after sputtering demonstrated that the textile properties were not negatively affected by the coating.The antibacterial effect was evaluated at different experimental conditions using a standard bacterial strain of Staphylococcus aureus and compared with the behavior of uncoated textiles.The coating process conferred all textiles a good antibacterial activity. Optimal deposition conditions were elaborated to obtain sufficient antibacterial action without altering the aesthetical appearance of the textiles.The antibacterial coating retained its antibacterial activity after one cycle in a washing machine only for the Nylon based textile.
Keywords: Antibacterial coating; Sputtering; Silver nanoclusters; Textiles; Protective garments;
Wetting of polycrystalline SiC by molten Al and Al−Si alloys by Xiao–Shuang Cong; Ping Shen; Yi Wang; Qichuan Jiang (140-146).
The wetting of α-SiC by molten Al and Al–Si alloys was investigated using a dispensed sessile drop method in a high vacuum. In the Al–SiC system, representative wetting stages were identified. The liquid spreading was initially controlled by the deoxidation of the SiC surface and then by the formation of Al4C3 at the interface. The intrinsic contact angle for molten Al on the polycrystalline α-SiC surface was suggested to be lower than 90̊ provided that the oxide films covering the Al and SiC surfaces were removed, i.e., the system is partial wetting in nature. An increase in the Si concentration in liquid Al weakened the interfacial reaction but improved the final wettability. The role of the Si addition on the wetting was presumably attributed to its segregation at the interface and the formation of strong chemical bonds with the SiC surface.
Keywords: Wetting; Interfaces; Microstructures;
Preparation of silane-functionalized silica films via two-step dip coating sol–gel and evaluation of their superhydrophobic properties by Maedeh Ramezani; Mohammad Reza Vaezi; Asghar Kazemzadeh (147-153).
Schematic illustration of the surface modification of the silica nanoparticle by iso-OTMS on the glass substrate.In this paper, we study the two-step dip coating via a sol–gel process to prepare superhydrophobic silica films on the glass substrate. The water repellency of the silica films was controlled by surface silylation method using isooctyltrimethoxysilane (iso-OTMS) as a surface modifying agent. Silica alcosol was synthesized by keeping the molar ratio of ethyltriethoxysilane (ETES) precursor, ethanol (EtOH) solvent, water (H2O) was kept constant at 1:36:6.6 respectively, with 6 M NH4OH throughout the experiment and the percentages of hydrophobic agent in hexane bath was varied from 0 to 15 vol.%. The static water contact angle values of the silica films increased from 108° to 160° with an increase in the vol.% of iso-OTMS. At 15 vol%. of iso-OTMS, the silica film shows static water contact angle as high as 160°. The superhydrophobic silica films are thermally stable up to 440 °C and above this temperature, the silica films lose superhydrophobicity. By controlling the primer particle size of SiO2 about 26 nm, leading to decrease the final size of silica nanoparticles after modification of nanoparticles by isooctyltrimethoxysilane about 42 nm. The films are transparent and have uniform size on the surface. The silica films have been characterized by atomic force microscopy (AFM), fourier transform infrared spectroscopy (FT-IR), transparency, contact angle measurement (CA), Zeta-potential, Thermal stability by TG–DTA analysis.
Keywords: Superhydrophobic surfaces; Silica film; Sol–gel process; Contact angle;
Impact of annealing on the electrodeposited WS2 thin films: Enhanced photodegradation of coupled semiconductor by Sumanta Jana; Pulakesh Bera; Biswajit Chakraborty; Bibhas Chandra Mitra; Anup Mondal (154-159).
Polycrystalline WS2 thin films were electrodeposited on ITO coated glass substrate using sodium tungastate (Na2WO4·2H2O) and thioacetamide (CH3C(S)NH2) as metal and sulfur sources. The deposited WS2 thin films were air annealed at different temperatures and the changes in phase, morphology, optical property were studied. It has been observed that annealing WS2 films at 450 °C generates a mix phase of WS2/WO3 and annealing the same film at 650 °C results 100% conversion of WS2 to WO3. These phases are absolutely different from each other. Their applicability has also been tested by photodegradation of phenol. It has been found that among the different phases, mix phase i.e WS2/WO3 shows better catalytic activity. Presence of two semiconductors with different energy levels in conduction and valence bands enhance displacement of electrons and holes from one semiconductor to another. The better charge separation in the coupled semiconductor is the key factor for interfacial charge transfer to the adsorbed substrate.
Keywords: Thin films; Electrodeposited; Mix phase; Coupled semiconductor; Photodegradation;
Sol–gel preparation and characterization of SiO2 coated VO2 films with enhanced transmittance and high thermochromic performance by Dezeng Li; Yongkui Shan; Fuqiang Huang; Shangjun Ding (160-166).
Vanadium dioxide (VO2) films prepared at low-temperature with a low cost are considerable for energy-saving applications. Here, SiO2 coated VO2 films with clearly enhanced visible transmittance by introducing antireflection coatings (ARCs) and excellent thermochromic performance were present. The VO2 films have been prepared via a stable and low-cost sol–gel synthesis route using vanadium pentaoxide powder as precursor, and their structural, morphological, optical and electrical properties and thermochromic performance were systemically characterized. The resistance of VO2 films varies by 4 orders of magnitude and the transmittance changes from 11.8% to 69.3% at 2500 nm while no significant deviation appears in the visible region during metal–insulator transition (MIT). Nanoporous SiO2 coating with good optical transparency was coated on the surface of VO2 film via sol–gel dip-coating technique to enhance its optical transmittance, and the visible transmittance is increased by 14.6% due to the significantly decreased reflectance. The critical transition temperature (63 °C) and infrared switching properties of VO2 films are not much deteriorated by applying SiO2 layer. The synergistic effect of antireflection and thermochromism on SiO2 coated VO2 films was investigated.
Keywords: Vanadium dioxide; Thermochromic; Metal–insulator transition; Sol–gel process; Antireflection coating;
Investigation of the particle size distribution of the ejected material generated during the single femtosecond laser pulse ablation of aluminium by Han Wu; Nan Zhang; Xiaonong Zhu (167-171).
Single femtosecond laser pulses are employed to ablate an aluminium target in vacuum, and the particle size distribution of the ablated material deposited on a mica substrate is examined with atomic force microscopy (AFM). The recorded AFM images show that these particles have a mean radius of several tens of nanometres. It is also determined that the mean radius of these deposited nanoparticles increases when the laser fluence at the aluminium target increases from 0.44 J/cm2 to 0.63 J/cm2. The mechanism of the laser-induced nanoparticle generation is thought to be photomechanical tensile stress relaxation. Raman spectroscopy measurements confirm that the nanoparticles thus produced have the same structure as the bulk aluminium.
Keywords: Femtosecond laser deposition; Nanoparticle generation; Particle size distribution;
Fabrication, ultra-structure characterization and in vitro studies of RF magnetron sputter deposited nano-hydroxyapatite thin films for biomedical applications by Maria A. Surmeneva; Roman A. Surmenev; Yulia A. Nikonova; Irina I. Selezneva; Anna A. Ivanova; Valery I. Putlyaev; Oleg Prymak; Matthias Epple (172-180).
A series of nanostructured low-crystalline hydroxyapatite (HA) coatings averaging 170, 250, and 440 nm in thickness were deposited onto previously etched titanium substrates through radio-frequency (RF) magnetron sputtering. The HA coatings were analyzed using infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning and transmission electron microscopy (SEM and TEM). Cross sections of the thin specimens were prepared by FIB to study the microstructure of the coatings by TEM. The deposition process formed nano-scale grains, generating an amorphous layer at the substrate/coating interface and inducing the growth of a columnar grain structure perpendicular to the substrate surface. A microstructural analysis of the film confirmed that the grain size and crystallinity increased when increasing the deposition time. The nanostructured HA coatings were not cytotoxic, as proven by in vitro assays using primary dental pulp stem cells and mouse fibroblast NCTC clone L929 cells. Low-crystallinity HA coatings with different thicknesses stimulated cells to attach, proliferate and form mineralized nodules on the surface better than uncoated titanium substrates.
Keywords: Hydroxyapatite; Radio-frequency magnetron sputtering; Functionally graded material; Bioactivity;
1,10-Phenanthroline as an accelerator for Ag nanoparticle-catalysed electroless copper deposition by Chia-Ru Liu; Nan-Kuang Chou; Cheng-Hsing Li; Ho-Rei Chen; Chien-Liang Lee (181-187).
1,10-Phenanthroline (phen) can be successfully used as an accelerator for Ag-catalysed electroless copper deposition (ECD) processes. Electrochemical quartz crystal microbalance analyses indicate that the mass activity in terms of thickness of deposited Cu layer and average ECD rate within a deposition time of 110 s for Ag nanoparticles activated by phen are 7.86 × 10-3 μm μg-1 and 1.43 × 10-4 μm μg-1 s-1, respectively, whereas Ag nanoparticles without phen cannot catalyse the reaction. Furthermore, Tafel and cyclic voltammetric results show that the addition of phen to the ECD bath significantly enhances the ability of the Ag nanoparticles to catalyse the oxidation of HCHO and suppresses the formation of CuO.
Keywords: Activation; Printed circuit board; XPS; XRD; EQCM;
Comparison of interface mechanics characteristics of DLC coating deposited on bearing steel and ceramics by Chongyang Nie; Dezhi Zheng; Le Gu; Xiaoli Zhao; Liqin Wang (188-197).
The load response of a coating and substrate system was built using interface mechanics theory. The characteristics of interface mechanics of diamond-like carbon (DLC) coatings deposited on bearing steel (M50) and ceramics (silicon nitride, Si3N4) were calculated, where the results showed that Si3N4 substrate could bear greater stresses along the interface than M50 under similar surface load and DLC coating conditions. Since the elastic modulus of ceramics is greater than that of the steel's, when a thicker coating is deposited, there will be a greater increase of interface normal stress for ceramics than for steel, as well as a greater elastic modulus of coatings meaning a greater interface normal stress. The interface transverse stress can be small when the difference of elastic modulus between coating and substrate is minor, meaning a better match. From the scratch test results, the interface bonding capacity of DLC coating with Si3N4 and M50 substrate were verified.
Keywords: Interface mechanics; DLC coating; Bearing steel; Ceramics;
Role of electrolyte composition on structural, morphological and in-vitro biological properties of plasma electrolytic oxidation films formed on zirconium by Sandhyarani M; Prasadrao T; Rameshbabu N (198-209).
Development of oxide films on metallic implants with a good combination of corrosion resistance, bioactivity and cell adhesion can greatly improve its biocompatibility and functionality. Thus, the present work is aimed to fabricate oxide films on metallic Zr by plasma electrolytic oxidation (PEO) in methodically varied concentrations of phosphate, silicate and KOH based electrolyte systems using a pulsed DC power source. The oxide films fabricated on Zr are characterized for its phase composition, surface morphology, chemical composition, roughness, wettability, surface energy, corrosion resistance, apatite forming ability and osteoblast cell adhesion. Uniform films with thickness varying from 6 to 11 μm are formed. XRD patterns of all the PEO films showed the predominance of monoclinic zirconia phase. The film formed in phosphate + KOH electrolyte showed superior corrosion resistance, which can be ascribed to its pore free morphology. The films formed in silicate electrolyte showed higher apatite forming ability with good cell adhesion and spreading over its surface which is attributed to its superior surface roughness and wettability characteristics. Among the five different electrolyte systems employed in the present study, the PEO film formed in an electrolyte system with phosphate + silicate + KOH showed optimum corrosion resistance, apatite forming ability and biocompatibility.
Keywords: Zirconium implant; Plasma electrolytic oxidation; Electrolyte chemistry; Corrosion; Bioactivity; Cell adhesion;
Enhancing antibiofouling performance of Polysulfone (PSf) membrane by photo-grafting of capsaicin derivative and acrylic acid by Jian Wang; Haijing Sun; Xueli Gao; Congjie Gao (210-219).
Biofouling is a critical issue in membrane water and wastewater treatment. Herein, antibiofouling PSf membrane was prepared by UV-assisted graft polymerization of acrylic acid (AA) and a capsaicin derivative, N-(5-methyl-3-tert-butyl-2-hydroxy benzyl) acrylamide (MBHBA), on PSf membrane. AA and MBHBA were used as hydrophilic monomer and antibacterial monomer separately. The membranes were characterized by FTIR-ATR, contact angle, SEM, AFM, cross-flow filtration unit, antifouling and antibacterial measurements. Verification of MBHBA and AA that photo-chemically grafted onto the PSf membrane surface is confirmed by carbonyl stretching vibration at ∼1655 cm−1 and ∼1730 cm−1, separately. The increasing AA concentration accelerates the graft-polymerization of MBHBA and resulted in a more hydrophilic surface. Consequently, antifouling property of the membranes was improved on a large level. The flux recovery rate can achieve 100% during the cyclic test, which may be attributed to the more hydrophilic and smooth surface, as well as the decreased membrane pore size. Most importantly, the presence of AA in graft co-polymer does not affect the antibacterial activity of MBHBA. That may be induced by the increasing chain length and flexibility of the grafted polymer chains.
Keywords: UV-assisted graft polymerization; Surface modification; Capsaicin derivative; Hydrophilicity; Antibiofouling;
Highly controllable and reproducible ZnO nanowire arrays growth with focused ion beam and low-temperature hydrothermal method by Kaidi Diao; Jicheng Zhang; Minjie Zhou; Yongjian Tang; Shuxia Wang; Xudong Cui (220-225).
In this work, high-quality ZnO nanowire arrays with controllable degrees over size, orientation, uniformity and periodicity are fabricated on GaN substrates with focused ion beam etching and low-temperature hydrothermal method. Experimental results revealed that the patterned holes (i.e., shape, depth, size and period) have decisive impacts on the morphology of resulting arrays. Optimal conditions and ordered arrays are obtained in terms of functionality analysis for both patterned holes and hydrothermal method. A possible mechanism is proposed to interpret the growth process in and out of the pattern holes. Results show that this hybrid method exhibits good reproducibility for the fabrication of high-quality ZnO nanowire arrays with great potentials.
Keywords: ZnO; Nanowire arrays; FIB; Hydrothermal method; ZnO nanodevices;
Surface functionalized magnetic PVA microspheres for rapid naked-eye recognizing of copper(II) ions in aqueous solutions by Zulin Hua; Bei Yang; Wei Chen; Xue Bai; Quanjun Xu; Haixin Gu (226-235).
We proposed a robust method for surface-functionalizing magnetic polyvinyl alcohol microspheres to detect heavy metal ions in aqueous solutions. The prepared chemosensor (PAR-MPVA) was characterized through scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectra (XPS). In neutral solutions, PAR-MPVA selectively recognized diatomic heavy metal ions, as indicated with a color change from earth yellow to red; in strong acidic solutions, the chemosensor only selectively detected Cu2+. PAR-MPVA microspheres had a detection limit as low as 0.5 μM by naked-eye and 0.16 μM by UV–vis spectrometer for Cu2+. Moreover, the sensor possessed magnetism for effective recovery, could easily be regenerated by a solution of EDTA, and also displayed perferable stability. The PAR-MPVA microspheres possessed preeminent properties of detecting copper (II) ions in aqueous solutions.
Keywords: Functionalization; Magnetism; PVA microspheres; Detection;
Synthesis of ZnSe nanocrystals (NCs) using a rapid microwave irradiation method and investigation of the effect of copper (Cu) doping on the optical properties by M. Molaei; A.R. Khezripour; M. Karimipour (236-240).
ZnSe nanocrystals (NCs) were synthesized using a microwave activated method. Synthesized NCs were characterized by means of X-ray diffraction (XRD), UV–visible (UV–vis) optical spectroscopy and photoluminescence (PL). XRD analysis demonstrated cubic zinc blende NCs. TEM image indicated round shape NCs and most of the particles had diameters of about 3 nm. Band gap of the NCs was obtained about 3.15 eV and PL spectra indicates a broad emission with two peaks located about 415 and 500 nm related to band edge and trap state respectively. For ZnSe:Cu NCs, PL intensity of band gap emission of ZnSe NCs at 415 nm decreased gradually with the increase in the concentration of Cu dopant ions and for precursor ratio of Cu:Zn 1% band gap emission at 415 nm disappeared completely. At the same conditions, PL QY was obtained about 2% and 8% for ZnSe and ZnSe:Cu (1%) NCs, respectively.
Keywords: ZnSe; Nanocrystals (NCs); Microwave; Cu doping;
Pyridine adsorption on NiSn/MgO–Al2O3: An FTIR spectroscopic study of surface acidity by Anna Penkova; Luis F. Bobadilla; Francisca Romero-Sarria; Miguel A. Centeno; José A. Odriozola (241-251).
The acid–base properties of MgO–Al2O3 supports and NiSn/MgO–Al2O3 catalysts were evaluated by IR spectroscopy using pyridine as a probe molecule. The results indicate that only Lewis acid sites were detected on the surface of the supports as well as on the catalysts. Nevertheless, Brønsted acid sites were not detected. In the support without MgO three kinds of coordinatively unsaturated acid sites were detected: Al3+ cations occupying octahedral, tetrahedral and tetrahedral with cationic vacancy in the neighbourhood. The last sites appear as the strongest. Moreover, they are able to activate the pyridine molecules leading to the formation of an intermediate α-pyridone complex. When MgO or NiO were added to the alumina, the number and strength of the Lewis acid sites decreased and significant changes were observed in the tetrahedral sites with adjoining cation vacancies. The incorporation of the Mg2+ cations into the alumina's structure takes place on the vacant tetrahedral positions, forming spinel MgAl2O4. As a result, the fraction of tetrahedral sites with adjoining cationic vacancy diminished and the intermediate α-pyridone complex in the support with the highest MgO loading was hardly detected. The addition of Ni2+ cations leads to the filling of the free octahedral positions, resulting in the formation of a NiAl2O4 spinel structure and the thermal stability of the α-pyridone species decreases. In the catalysts, the progressive reduction of the number and strength of the Lewis acid sites is due to a competitive formation of the two types of MgAl2O4 and NiAl2O4 spinels. In the catalyst NiSn/30MgO–Al2O3 no cationic vacancies were detected and the surface reaction with α-pyridone formation did not occur.
Keywords: FTIR spectroscopy; Probe molecules; Pyridine; Lewis acidity; Cation vacancy; α-Pyridone;
Improvement of aluminum drilling efficiency and precision by shaped femtosecond laser by Ying Qi; Hongxia Qi; Anmin Chen; Zhan Hu (252-256).
Shaped femtosecond laser pulses with the plain phase (transform-limited pulse) and sine phase (A = 1.2566, T = 30, T = 10, and T = 5) were used to drill Al sheet in vacuum. Using different phase, the number of pulses required to drill through the sheet was different. With lower laser pulse energy, the ablation rate was the highest when plain phase (corresponding to transform limited pulse) was used. With higher laser energy, the optimized ablation rate can be achieved by increasing the time separation between the subpulses of pulse train produced from the sine phase function. And, with the shaped femtosecond laser, the diameter of ablation holes produced was smaller, the ablation precision was also improved. The results showed that shaped femtosecond laser pulse has great advantages in the context of femtosecond laser drilling.
Keywords: Shaped femtosecond laser; Laser drilling; Drilling efficiency; Drilling precision;
Multi-layered nanostructure Bi2Se3 grown by chemical vapor deposition in selenium-rich atmosphere by Mei Liu; Fu Yan Liu; Bao Yuan Man; Dong Bi; Xue You Xu (257-261).
High quality multi-layered nanostructured bismuth selenide (Bi2Se3) with an asymmetric, elongated hexagonal morphology were obtained in a selenium-rich atmosphere by chemical vapor deposition (CVD) using high purity Se and Bi2Se3 powder as source materials. The measurement results reveal that Au particles only serve as the initial stage nucleation of the Bi2Se3 nanostructures at a low temperature. The Se powder in the source materials is helpful to ensure the stoichiometry and decrease the selenium vacancies, and causes the wide Bi2Se3 nanoribbons to grow along the lateral direction.
Keywords: Topological insulator; Bismuth selenide; Multi-layered nanostructure; Chemical vapor deposition;
Copper ion implanted aluminum nitride dilute magnetic semiconductors (DMS) prepared by molecular beam epitaxy by A. Shah; Jamil Ahmad; Ishaq Ahmad; Mazhar Mehmood; Arshad Mahmood; Muhammad Asim Rasheed (262-268).
Diluted magnetic semiconductor (DMS) AlN:Cu films were fabricated by implanting Cu+ ions into AlN thin films at various ion fluxes. AlN films were deposited on c-plane sapphire by molecular beam epitaxy followed by Cu+ ion implantation. The structural and magnetic characterization of the samples was performed through Rutherford backscattering and channeling spectrometry (RBS/C), X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometer (VSM) and SQUID. Incorporation of copper into the AlN lattice was confirmed by RBS, while XRD revealed that no new phase was formed as a result of ion implantation. RBS also indicated formation of defects as a result of implantation process and the depth and degree of damage increased with an increase in ion fluence. Raman spectra showed only E 2 (high) and A 1 (LO) modes of wurtzite AlN crystal structure and confirmed that no secondary phases were formed. It was found that both Raman modes shift with Cu+ fluences, indicating that Cu ion may go to interstitial or substitutional sites resulting in distortion or damage of lattice. Although as implanted samples showed no magnetization, annealing of the samples resulted in appearance of room temperature ferromagnetism. The saturation magnetization increased with both the annealing temperature as well as with ion fluence. FC/ZFC measurements indicated that the ferromagnetic effect was not related with superparamagnetic phase formation. In spite, it was due to the formation of AlN based DMS material. The Curie temperature (T C) of the sample prepared at an ion fluence of 5 × 1015 cm−2 and an annealing temperature of 950 °C was found to lie above 340 K.
Keywords: Cu+-implanted AlN; Diluted magnetic semiconductor; Rutherford back scattering; Ferromagnetism; FC/ZFC;
Influence of Zr alloying on the mechanical properties, thermal stability and oxidation resistance of Cr–Al–N coatings by W.Z. Li; Q.Z. Chen; T. Polcar; R. Serra; A. Cavaleiro (269-277).
Cr–Al–N coatings with Zr alloying (Zr contents from 0 to 29.5 at.%) were deposited by d.c. reactive magnetron sputtering. The chemical composition and the morphology of as-deposited coatings were characterized, and the phase structure, mechanical properties and wear resistance of the coatings before and after thermal annealing were analyzed and evaluated. With the increase of Zr content, both Cr and N contents decrease whereas Al shows a growing trend. Low Zr (<26.9 at.%) coatings are stoichiometric and present a fcc NaCl-type B1 structure with columnar morphology, while high Zr (≥26.9 at.%) coatings are in N deficiency and have low crystallinity degree. The alloying of low contents of Zr improves the coating hardness and H/E ratio; however, for low ordered coatings these properties decrease significantly. After thermal annealing, fcc structure is kept in low Zr films whereas the crystalline degree is improved in the high Zr ones and their mechanical properties were slightly improved. Two coatings were selected for further testing, representatives of low (CrAlZr5N) and high (CrAlZr27N) Zr contents. The onset oxidation temperature is ∼900 °C and 600 °C for CrAlZr5N and CrAlZr27N coatings, respectively. Mainly Cr2O3 is formed on low Zr coatings whereas mixed oxides of ZrO2 and Cr2O3 are detected on CrAlZr27N sample after thermal exposure. In all tribological tests, low Zr coating presents lower wear rate than the CrAlZr27N coating. In general, the addition of very high Zr contents (>20 at.%) with N deficiency markedly weakens the mechanical properties and the oxidation resistance of Cr–Al–Zr–N coatings.
Keywords: Cr–Al–(Zr–)N coatings; Mechanical properties; Thermal stability; Wear resistance; Oxidation resistance;
Evaluation of PHBV/calcium silicate composite scaffolds for cartilage tissue engineering by Jun Wu; Junying Sun; Jinbo Liu (278-283).
In our previous studies, composite scaffolds containing poly (hydroxybutyrate-co-hydroxyvalerate) (PHBV) and calcium silicate (CS) have been prepared and well characterized as cell scaffolds. Here, we evaluated these composite scaffolds for cartilage tissue engineering through in vitro experiments of cell-scaffold interactions and in vivo observation of cartilage formation. Rabbit articular chondrocytes were seeded into PHBV and PHBV/CS scaffolds. A short-term in vitro culture followed by a long-term in vivo transplantation was performed to evaluate the difference of cartilage regeneration in PHBV and PHBV/CS scaffolds. Results showed that, as compared to pure PHBV scaffolds, the addition of CS into PHBV improved the cell adhesion on the scaffolds and further promoted the cell penetration into scaffolds. In vivo results indicated that the PHBV/CS composite scaffolds enhanced the formation of cartilage-like tissue as thicker and stronger cartilage matrix was found in PHBV/CS group as compared to those in PHBV group. These results demonstrated that the PHBV/CS scaffolds may be more suitable for applications in cartilage tissue engineering that pure PHBV scaffolds.
Keywords: PHBV; Calcium silicate; Cartilage tissue engineering;
Synthesis of boron and nitrogen doped graphene supporting PtRu nanoparticles as catalysts for methanol electrooxidation by Jiming Lu; Yingke Zhou; Xiaohui Tian; Xiao Xu; Hongxi Zhu; Shaowei Zhang; Tao Yuan (284-293).
In this study, we demonstrate a single-step heat treatment approach to synthesize boron and nitrogen doped graphene supporting PtRu electrocatalysts for methanol electro-oxidation reaction. The reduction of graphene oxide, boron or nitrogen doping of graphene and loading of PtRu nanoparticles happened simultaneously during the reaction process. The morphologies and microstructures of the as-prepared catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic methanol oxidation activity and durability of the obtained catalysts were evaluated by the cyclic voltammetry and chronoamperometric techniques. The results reveal that the boron and nitrogen doped graphene supporting PtRu electrocatalysts can be successfully prepared by the single step heat treatment technique, and the introduction of boron or nitrogen containing function groups into the reduced graphene sheets could modulate the particle size and dispersion of the supporting PtRu nanoparticles and improve the electrocatalytic performance of methanol oxidation reaction. The optimal annealing temperature is 800 °C, the preferable heat treatment time is 60 min for the nitrogen-doped catalysts and 90 min for the boron-doped catalysts, and the catalysts prepared under such conditions present superior catalytic activities for methanol oxidation than those prepared under other heat treatment conditions.
Keywords: Doped graphene; PtRu nanocatalyst; Single-step synthesis; Methanol electro-oxidation;
An investigation of ruthenium coating from LiCl–KCl eutectic melt by G. Kartal Sireli (294-301).
In this study, electrodeposition of ruthenium (Ru) from LiCl–KCl eutectic melt was investigated in a systematic manner and the effects of process parameters namely current density, time and agitation of electrolyte on the thickness and morphology of Ru layer were explored. The presence of Ru on graphite substrates was confirmed by thin film X-ray diffraction method. The Ru coatings formed at all electrodeposition conditions appeared as a white/gray deposit. The typical “faceted structure” was observed on the surface of Ru deposited at 3 and 7 mA/cm2. Fracture cross-section examinations revealed the columnar morphology of Ru which was twinned with boundaries. The smooth appearance of Ru coating became uneven and rough with coarse nodules at 12 mA/cm2. The thickness of Ru increased with increasing both current density and time at stationary electrodeposition conditions. A dense and 7.5 μm thick Ru coating was possible to grow on graphite without any agitation at 3 mA/cm2 for 2 h. The highest cathodic current efficiency (η), 99.68%, was achieved at 3 mA/cm2 after 2 h of electrodeposition time with the rotating cathode speed of 50 rpm. The cross sectional micro-indentation studies indicated that the Ru layer has hardness as high as 450 ± 10 HV.
Keywords: Electrodeposition; LiCl–KCl eutectic; Ruthenium coating; Molten salt;
Novel high potential visible-light-active photocatalyst of CNT/Mo, S-codoped TiO2 hetero-nanostructure by M. Hamadanian; M. Shamshiri; V. Jabbari (302-311).
The current study deals with synthesize of novel nanophotocatalysts of CNT/Mo,S-codoped TiO2 by reacting between titanium isopropoxide (Ti(OC3H7)4) and CNT in aqueous ammonia and subsequent calcining of hydrolysis of the products. The prepared catalysts were characterized by N2 adsorption–desorption measurements, XRD, SEM, TEM, EDX, FT-IR, and UV–vis DRS spectroscopy. SEM and TEM images exhibited uniform coverage of CNT with anatase TiO2 nanoclusters. It was also demonstrated that the presence of S and Mo within the TiO2 acts as electrons traps and prevents the charge recombination and also enables the TiO2 photocatalyst to be active in visible-light region. Moreover, the CNT/Mo,S-doped TiO2 nanohybrids has been proven to has a excellent photocatalytic performance in photodecomposition of Congored (CR), at which the rate of decomposition reaches 100% in only 20 and 30 min under UV and visible-light irradiation, respectively. The enhanced photocatalytic activity was ascribed to the synergetic effects of excellent electrical property of CNT and metal–non-metal codoping. Finally, which to best of our knowledge is done for the first time, we have demonstrated that Mo- and S-doped TiO2 decorated over CNT, or CNT/Mo,S-codoped TiO2, may have high potential applications in photocatalysis and environmental protection with superior catalytic activity under visible-light illumination.
Keywords: TiO2; CNT; CNT/Mo,S-codoped TiO2; Nanocomposite; Nano-catalyst;
Fe–0.4 wt.%C–6.5 wt.%Cr hardfacing coating: Microstructures and wear resistance with La2O3 additive by Xiaoru Hou; Bin Zhao; Jian Yang; Xiaolei Xing; Yefei Zhou; Yulin Yang; Qingxiang Yang (312-318).
Flux-cored wires with different La2O3 additives were developed. The microstructures of the hardfacing coatings were observed by optical microscopy (OM) and field emission scanning electron microscope (FESEM). The phase structures were determined by X-ray diffraction (XRD). The hardness, wear resistance and friction coefficient of the hardfacing coatings were measured by Rockwell hardness tester, unilateral abrasive belt wear testing machine and CETR reciprocating wear testing machine, respectively. At last, the worn morphologies of the hardfacing coatings were observed by FESEM.The results indicate that, the microstructures of the hardfacing coatings consist of needle-like martensite, high alloy matensite and retained austenite. With the increase of La2O3 additive, the high alloy matensite dissolves in the matrix gradually and the amount of retained austenite is not changed basically after it is increased firstly. When La2O3 addition is 0.70 wt.%, the grain size of the hardfacing coating is the smallest, which is 18 μm and the average hardness is the highest. Unidirectional abrasive belt wear test shows that the high alloy martensite can be as wear-resistance phase during the wear process of the hardfacing coatings. When the La2O3 addition is 0.35 wt.%, the unidirectional wear resistance of the hardfacing coating is the highest. Reciprocating wear test shows that with the increase of the La2O3 additives, the friction coefficient is decreased and the reciprocating wear resistance is increased. When La2O3 addition is 0.70 wt.% the reciprocating wear resistance is the highest.
Keywords: Fe–Cr–C alloy; Hardfacing coating; Microstructure; Wear resistances; La2O3;
Preparation and properties of red inorganic hollow nanospheres for electrophoretic display by Yi Fang; Shirong Wang; Yin Xiao; Xianggao Li (319-324).
The Fe-doped TiO2 and Fe/Co/Al-doped TiO2 red hollow nanospheres was prepared via template method and two-step hydrolysis process. It exhibit a bright color and hollow structures with uniform size and shape, which also present excellent performance and a quick response of electrophoretic display.An effective approach had been developed for the preparation of Fe-doped TiO2 red hollow nanospheres via template method using PMMA-BA copolymers as the core template by a two-step hydrolysis process. The nanospheres were rarely displayed fragmentation and exhibited hollow structures with uniform size and shape. Then, the multicomponent Fe/Co/Al-doped TiO2 hollow nanospheres were produced with Co and Al as tinting metal ions so as to endow them with higher color saturation and brightness. The average diameter of the hollow spheres coated with a layer of α-Fe2O3 was approximately 300 nm and the thickness of the layer was roughly 50 nm. The electrophoretic mobility and zeta potential of two kinds of hollow particles were about −1.0 × 10−5 cm2 v−1 s−1 and −100 mV, respectively. Finally, the electrophoretic inks prototype device was successfully assembled using dispersion of the obtained red hollow nanospheres in a mixed dielectric solvent with TiO2 white particles as contrast. Under an applied bias voltage of 30 V, the response time of the simple EPD device was 1121 ms and the max contrast was 3.173, which had shown great potential for practical application in a vivid chromatic electrophoretic display.
Keywords: Hollow nanospheres; Electrophoretic mobility; Zeta potential; Electrophoretic display;
Study on the mechanism of surface modification of magnesium oxysulfate whisker by Li Dang; Xueying Nai; Donghai Zhu; Yanwei Jing; Xin Liu; Yaping Dong; Wu Li (325-331).
Hydrophobic-lipophilic magnesium oxysulfate whisker (MOSw) was prepared by surface modification with lauric acid and the surface morphology of MOSw was examined with field emission scanning electron microscope (FESEM). X-ray powder diffraction (XRD) was used to characterize the crystalline degree of MOSw and modified MOSw (MOSw-LA). Both FESEM and XRD suggested that modification occurred on the surface of MOSw exclusively. The inexistence of physisorbed lauric acid was proved by Fouier transform infrared (FT-IR) spectroscopy. Thermogravimetric analyses ruled out the possibility that magnesium laurate (LA-Mg) physisorbed on the surface of MOSw-LA. Solid state 13C nuclear magnetic resonance (13C NMR) further verified the formation of COO–Mg< bonds based on the significant changes of chemical shift and decrease in intensity. Hence, we confirmed that the type of surface modification of MOSw with lauric acid was chemical adsorption taken place between lauric acid and Mg<. In order to study the dynamic state approach of this reaction, a pH meter was employed to monitor the reaction process synchronously, and then we proposed a reaction mechanism which was similar to the “acid-base neutralization”. This research provides a detailed explanation for a kind of surface modification, which may be further used in the performance of whisker/polymer matrix composites.
Keywords: Magnesium oxysulfate whisker; Surface modification; “Acid-base neutralization”;
Effect of ionic strength on ruthenium CMP in H2O2-based slurries by Liang Jiang; Yongyong He; Yuzhuo Li; Jianbin Luo (332-337).
With the development of ultra-large scale integrated circuits, ruthenium has been selected as one of the most promising barrier metals for copper interconnects to replace traditional Ta/TaN bilayer. This paper mainly investigated the effect of ionic strength on the chemical mechanical polishing performance of ruthenium in H2O2-based slurries. The results show that, the ruthenium removal rate (RR) increases with the increasing concentration of H2O2 due to the formation of ruthenium oxides like Ru(OH)3, RuO2·2H2O and even RuO4 2−; additionally, the ruthenium RR can be further enhanced with the increase of K+ ionic strength. It is revealed that the added K+ can intensify the electrochemical reactions between H2O2 and the ruthenium surface by increasing the conductivity, meanwhile can also result in the neutralization of the zeta potentials of both silica particles and the ruthenium surface, and thus can lead to the decrease of the electrostatic repulsive force and the increase of the mechanical abrasion intensity between silica particles and the ruthenium surface. Therefore, the ruthenium RR increases with the increase of K+ ionic strength. Furthermore, the effects of K+ ionic strength on the material removal rate (MRR) selectivity of Ru vs. Cu and the galvanic corrosion of Cu/Ru couple are studied. It is found that, in order to achieve higher MRR selectivity than 1.0, KNO3 is preferred for the K+ source; and with H2O2 as the oxidizer, copper galvanic corrosion problem can be effectively suppressed.
Keywords: Ruthenium chemical mechanical polishing; Ionic strength; Material removal rate selectivity; Galvanic corrosion;
Effects of thermal efficiency in DCMD and the preparation of membranes with low thermal conductivity by Zhehao Li; Yuelian Peng; Yajun Dong; Hongwei Fan; Ping Chen; Lin Qiu; Qi Jiang (338-349).
The effects of the membrane characteristics and operational conditions on the vapor flux and thermal efficiency in a direct contact membrane distillation (DCMD) process were studied with a mathematical simulation. The membrane temperature, driving force of vapor transfer, membrane distillation coefficient, etc. were used to analyze the effects. The operating conditions that increased the vapor flux improved the thermal efficiency. The membrane characteristics of four microporous membranes and their performances in DCMD were compared. A polysulfone (PSf) membrane prepared via vapor-induced phase separation exhibited the lowest thermal conductivity. The PSf and polyvinylidene difluoride (PVDF) membranes were modified using SiO2 aerogel blending and coating to reduce the thermal conductivity of the membrane. The coating process was more effective than the blending process toward this end. The changes in the structure of the modified membrane were observed with a scanning electron microscope. Si was found on the modified membrane surface with an energy spectrometer. The PVDF composite and support membranes were tested during the DCMD process; the composite membrane had a higher vapor flux and a better thermal efficiency than the support. A new method based on a 3ω technique was used to measure the thermal conductivity of the membranes.
Keywords: Membranes distillation; Mathematical simulation; Thermal conductivity; Thermal efficiency; 3ω technique;
Oxidative-reforming of model biogas over NiO/Al2O3 catalysts: The influence of the variation of support synthesis conditions by Yvan J.O. Asencios; Kariny F.M. Elias; Elisabete M. Assaf (350-359).
In this study, nickel catalysts (20 wt%) supported on γ-Al2O3 were prepared by the impregnation method. The γ-Al2O3, was synthesized by precipitation of bayerite gel obtained from aluminum scrap. The synthetic conditions of the bayerite gel varied as follows: precipitation pH ranging from 6 to 7; ageing temperature ranging from 25 to 80 °C, the calcination temperature for all samples was 500 °C. The catalysts and the supports were analyzed by temperature programmed reduction (H2-TPR), X-ray diffraction (XRD), physisorption of N2 (BET), X-ray absorption near-edge structure (XANES) and scanning electron microscopy (SEM). Isopropanol decomposition reactions over the catalysts were carried out to evaluate their acidity. SEM images of the spent catalysts showed that the morphology of the carbon formed during the reaction is of the filamentous type. The TPR analysis of the catalysts showed the presence of NiO species weakly interacted with the support as well as stoichiometric and non-stoichiometric nickel aluminate, the reduction of these species was also observed by XANES analysis. XRD analysis of the fresh catalyst showed peaks assigned to NiO, NiAl2O4 and γ-Al2O3. The best catalysts (samples NiAl7-25 and NiAl7-80) synthesized in this report showed high stability and high conversion values (CH4 (70%) and CO2 (78%)). These catalysts showed better performance than the catalyst supported on commercial γ-Al2O3, which showed a high coke formation which affected the course of the reaction. The γ-Al2O3 synthesized from bayerite obtained at neutral pH conditions was the best support for nickel catalysts in the oxidative-reforming of model biogas.
Keywords: Alumina; Synthetic-conditions; Bayerite; Nickel catalysts; Biogas; Oxidative-reforming; Syngas;
Isothermal oxidation behaviour of thermal barrier coatings with CoCrAlY bond coat irradiated by high-current pulsed electron beam by Jie Cai; Qingfeng Guan; Xiuli Hou; Zhiping Wang; Jingxin Su; Zhiyong Han (360-369).
Thermal sprayed CoCrAlY bond coat irradiated by high-current pulsed electron beam (HCPEB) and thermal barrier coatings (TBCs) prepared with the irradiated bond coat and the ceramic top coat were investigated. The high temperature oxidation resistance of these specimens was tested at 1050 °C in air. Microstructure observations revealed that the original coarse surface of the as-sprayed bond coat was significantly changed as the interconnected bulged nodules with a compact appearance after HCPEB irradiation. Abundant Y-rich alumina particulates and very fine grains were dispersed on the irradiated surface. After high temperature oxidation test, the thermally grown oxide (TGO) in the initial TBCs grew rapidly and was comprised of two distinct layers: a large percentage of mixed oxides in the outer layer and a relatively small portion of Al2O3 in the inner layer. Severe local internal oxidation and extensive cracks in the TGO layer were discovered as well. Comparatively, the irradiated TBCs exhibited thinner TGO layer, slower TGO growth rate, and homogeneous TGO composition (primarily consisting of Al2O3). The results indicate that TBCs with the irradiated bond coat have a much higher oxidation resistance.
Keywords: Thermal barrier coatings (TBCs); Air plasma spraying (APS); High current pulsed electron beam (HCPEB); Microstructure; Oxidation; Thermally grown oxide (TGO);
In situ formation of Ni(OH)2 nanoparticle on nitrogen-doped reduced graphene oxide nanosheet for high-performance supercapacitor electrode material by Huidi Liu; Jinglin Zhang; Dongdong Xu; Bin Zhang; Lei Shi; Langhuan Huang; Shaozao Tan (370-377).
A nitrogen-doped reduced graphene oxide/Ni(OH)2 (N-rGO/Ni(OH)2) composite is prepared by in situ formation of Ni(OH)2 nanoparticle on the surface of N-rGO nanosheet under easy one-step hydrothermal condition. With the improved electrochemical activity upon nitrogen doping and positive synergetic effect between N-rGO and Ni(OH)2, the obtained composite exhibits high capacitance, excellent rate capability, good cycle life, etc. A new hybrid material consisting of nickel hydroxide and nitrogen-doped reduced graphene oxide (N-rGO/Ni(OH)2) for supercapacitor electrode material is prepared via an easy one-step hydrothermal method, where the reduction and nitrogen doping of graphene oxide (GO) and the in situ formation of Ni(OH)2 are achieved simultaneously. The results show the improved electrochemical activity of N-rGO/Ni(OH)2 upon nitrogen doping. Moreover, thanks to the positive synergetic effect between N-rGO and Ni(OH)2, the synthesized N-rGO/Ni(OH)2 composite shows superior electrochemical performance, including high capacitance, excellent rate capability and good cycle life. Hence, the facile preparation approach in this work will be considered as a new way to obtain metal oxide or hydroxide/N-rGO material which can be used as advanced electrode material in high-performance supercapacitors.
Keywords: Reduced graphene oxide; Nickel hydroxide; Nitrogen doping; Hydrothermal; Supercapacitor;
Microstructure and elevated temperature wear behavior of induction melted Fe-based composite coating by Ge Hu; Huimin Meng; Junyou Liu (378-384).
Fe-based composite coating prepared onto the component of guide wheel using ultrasonic frequency inductive cladding (UFIC) technique has been investigated in terms of microstructure, phase constitutions, microhardness and elevated temperature wear behavior by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), X-ray diffraction (XRD), Vickers microhardness tester and ball-on-disc wear tester. The results indicated that the primary phase in the coating contained austenite γ-Fe, eutectic γ-Fe/(Cr,Fe)2B, boride (Cr,Fe)2B and precipitation enriched in Mo. The average microhardness of the coating was 760 ± 10 HV0.2, which was three times higher than that of the substrate. With increasing temperature, the friction coefficients of the coating and high-chromium cast iron decreased gradually while the wear rates increased during dry sliding wear condition. The relative wear resistance of the coating was 1.63 times higher than that of the high-chromium cast iron at 500 °C, which was ascribed to the hard borides with high thermal stability uniformly embedded in the coating and the formation of dense transfer layer formed onto the worn surface. The high temperature wear mechanism of the coating was dominated by mild abrasive wear. The study revealed that Fe-based composite coating had excellent high temperature wear resistance under dry sliding wear condition.
Keywords: Inductive cladding; Composite coating; Microstructure; Microhardness; High temperature wear resistance;
Effects of UV weathering on surface properties of polypropylene composites reinforced with wood flour, lignin, and cellulose by Yao Peng; Ru Liu; Jinzhen Cao; Yu Chen (385-392).
In this study, the influence of accelerated weathering on polypropylene composites reinforced with wood flour (WF), lignin, and cellulose at different loading levels were evaluated. Six groups of samples were exposed in a QUV accelerated weathering tester for a total of 960 h. The surface color, surface gloss, contact angle and flexural properties of the samples were tested. Besides, the weathered surface was characterized by SEM and ATR-FTIR. The results revealed that (1) the discoloration of composites was accelerated by the presence of lignin, especially at high content; (2) composites containing lignin showed less loss of flexural strength and modulus, less cracks, and better hydrophobicity on weathered surface than other groups, confirming its functions of stabilization and antioxidation; (3) cellulose-based composites exhibited better color stability but more significant deterioration in flexural properties after weathering compared to other composites, suggesting that such kind of composites could not be used as load-bearing structure in outdoor applications.
Keywords: Wood flour/polypropylene composites; Cellulose; Lignin; Weathering; Surface properties;
Preparation and characterization of crystalline titania film on polyimide substrate by SILAR by Yaping Shi; Yiyong Wu; Chengyue Sun; Mingxue Huo (393-399).
Crystalline titania films were prepared by SILAR technique on polyimide substrates at room temperature and the photo catalytic degradation performance of MB solution can reach 87%.Crystalline titania films were prepared on the flexible polyimide (Kapton) substrates using the successive ionic layer adsorption and reaction (SILAR) technique modified with mixed organic amine template agents at room temperature. The titania film with the organic amine template agents presents orderly stacked morphology with cross linked V-shaped strips, and it composes of mainly anatase and minor rutile phases with N doping. Structural and morphology analysis indicates that there includes two parallel deposition growth processes: One is adsorption of the template agents and reaction with Ti4+ ions on the constraint region; and the other is a normal SILAR process of including the adsorption of Ti4+ ions and reaction with hydroxyl groups. The organic amine templates and their specific adsorption induce and direct the crystallization of the titania films. Crystal structure of the titania film was confirmed by its excellent photo catalytic property of the films, detected by the degradation test of MB.
Keywords: Flexible Kapton substrate; SILAR at room temperature; Crystalline TiO2 film; Template agent; Photo catalytic degradation;
Preparation and optical properties of Mg-doped ZnO nanorods by N. Guo; X.Q. Wei; R.R. Zhao; X.J. Xu (400-404).
Doped ZnO nanorods with different magnesium (Mg) concentrations have been successfully fabricated on Si (1 1 1) substrates via two-step method. The influence on the nanorods morphologies and crystallinities of the Mg concentrations was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) spectra. The SEM results show that it is beneficial to grow regular ZnMgO nanorods with the increase of Mg concentrations, and the XRD results indicate that the nanorods possess the preferential orientation along the c-axis when the molar ratio of Mg/Zn is 0.5, which possess the best crystalline. The photoluminescence (PL) spectra show that the UV emissions have the obvious blue shift with the increase of Mg concentrations. ZnMgO has a wider bandwidth with increase in Mg-content.
Keywords: Chemical vapor deposition (CVD); Hydrothermal; Nanorods; ZnMgO; Doping;
Heat treatment effect on erosion behavior of poly(methylmethacrylate) for optical transmittance efficiency by Onur Çoban (405-413).
Influence of heat treatment on optical transmittance of poly(methyl methacrylate) (PMMA) samples was investigated under solid particle erosion. Heat treatment was employed at 85 °C for 1, 2 and 3 h. Effect of heat treatment on physical, chemical, mechanical and thermal properties of PMMA samples was investigated by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, Vickers microhardness measurement methods. After these analysis, both pristine and heat treated PMMA samples were eroded at 15°, 30°, 45°, 60°, 75° and 90° impingement angles. Then, optical transmittance of all eroded PMMA samples was inspected by a UV–Vis spectrometer. Scanning electron microscopy (SEM) was used to explain the erosion mechanisms and to compare the roughness and optical transmittance of eroded PMMA surfaces.Heat treatment under glass transition temperature of PMMA increased the T g and hardness values. According to erosion test results, both pristine and heat treated PMMA samples were showed ductile erosion behavior. However; maximum and minimum optical transmittance values of eroded pristine PMMA samples were obtained for the angles of 15° and 90°, respectively. A positive effect of heat treatment on optical transmittance of PMMA was obtained for all impingement angles, but most pronounced effect was seen for 15°.
Keywords: PMMA; Fresnel lens; Optical transmittance; Heat treatment; Solid particle erosion;
Fabrication of nanostructured CuO films by electrodeposition and their photocatalytic properties by Yongqian Wang; Tingting Jiang; Dawei Meng; Jun Yang; Yinchang Li; Qun Ma; Jun Han (414-421).
Monoclinic nanostructured CuO films with star-like morphology on indium tin oxide (ITO)-coated glass substrates were successfully synthesized by electrodeposition method in acidic solution with the pH of 5.7. The as-synthesized films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis. The influence of different electrodeposition parameters and annealing temperature on the growth of CuO films were investigated. The results showed that the nanostructured CuO film was well-crystallized and electrodeposition voltage is the main factor to control its morphology. Moreover, good photocatalytic activity was exhibited and photo-degradation rate to methylene blue can reach 95%. Its optical energy band gap is 3.3 eV. The plausible growth mechanism for the formation of CuO film with star-like structure is also proposed for the first time.
Keywords: CuO film; Electrodeposition; Photocatalytic activity; Growth mechanism;
Fabrication and characterization of mesoporous activated carbon from Lemna minor using one-step H3PO4 activation for Pb(II) removal by Yang Huang; Shunxing Li; Haibin Lin; Jianhua Chen (422-431).
A low cost and locally available material, Lemna minor, was used to fabricate activated carbon using H3PO4 activation. After H3PO4 activation, the L. minor activated carbons (LACs) possess high mesoporosity (92.2%) and a surface area of 531.9 m2/g according to Brunauer–Emmett–Teller (BET) analysis. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectrometer (XPS) analyses reveal the presence of rich hydroxyl, carboxyl, amide and phosphate functional groups on the LACs surface, leading to facile Pb(II) binding to the surface through strong chemisorptive bonds or ion-exchange. The kinetic and equilibrium data were well described by pseudo-first-order model and Langmuir isotherm, with the maximum monolayer adsorption capacity (q m) 170.9 mg/g at 25 °C. The intra-particle diffusion mechanism was partially responsible for the adsorption. The adsorption process was spontaneous and endothermic with negative ΔG and positive ΔH. The Pb(II)-loaded LACs could be easily regenerated using 0.1-M HCl and reused for seven cycles without significant adsorption capacity reduction. The maximum percentage removal rate for Pb(II) (20 mg/L) was found to be 91.8% within 30 min, at optimum conditions of pH 6.0 and 25 °C. These suggested that the low-cost LACs could be used as a potential adsorbent in the treatment of lead-contaminated water.
Keywords: Lead; Activated carbon; Lemna minor; Mesoporous; Adsorption;
Molecular dynamics simulations of nanometric cutting mechanisms of amorphous alloy by Peng-Zhe Zhu; Chen Qiu; Feng-Zhou Fang; Dan-Dan Yuan; Xue-Cen Shen (432-442).
Molecular dynamics simulations are employed to study the nanometric cutting process of Cu50Zr50 amorphous alloy. The effects of cutting depth, cutting speed and tool edge radius on the cutting force, workpiece pile-up and temperature of the cutting region are studied to investigate the mechanisms of the material removal and surface formation in the nanometric cutting process. It is found that the material removal of amorphous alloy workpiece is mainly based on extrusion at the nanoscale instead of shearing at the macroscale. The plastic deformation of amorphous alloy is mainly due to the formation of shear transformation zones during the nanometric cutting process. The results also suggest that bigger cutting depth and cutting speed will lead to larger tangential force and normal force. However, the tool edge radius has a negligible effect on the tangential force although the normal force increases with the increase of tool edge radius. The workpiece pile-up increases with an increase of the cutting depth, but decreases with an increase of the edge radius of the tool. The workpiece pile-up is not significantly affected by the cutting speed. It is also found that larger cutting depth and cutting speed will result in higher temperature in the cutting region of workpiece and the average Newtonian layer temperature of the tool. Tool edge radius has no significant effect on the temperature distribution of the workpiece and the average Newtonian layer temperature of the tool.
Keywords: Amorphous alloy; nanometric cutting; molecular dynamics;
Fabrication of sulfur-functionalized DLC films by photochemical modification and attachment of gold nanoparticles by Takako Nakamura; Tetsuo Tsuchiya; Tsuguyori Ohana (443-448).
The direct sulfurization of diamond-like carbon (DLC) film surfaces by a photochemical reaction with elemental sulfur was realized. The surface modification of DLC films with thiol functional group was confirmed by X-ray photoelectron spectroscopy (XPS) with the maintenance of DLC bulk structure characterized by Raman spectroscopy. The exposure of gold nanoparticles to the thiol-modified DLC films led to the attachment of gold nanoparticles onto DLC films by self-assembly, confirming by XPS and scanning electron microscopy (SEM). The gold-modified DLC film was also observed to act as a substrate for DNA immobilization by hybridization. The gold nanoparticles on the DLC surfaces were embedded by the deposition of an additional DLC layer onto the gold-modified DLC film to form a sandwich structure, and the resulting structure acted as a substrate exhibiting surface-enhanced Raman scattering.
Keywords: Chemical modification; Diamond-like carbon; Sulfur; Gold; Photochemistry;
Features of the formation of nanoparticles based on copper in thin-layer systems by A.V. Ragachev; Jiang Xiaohong; Liu Xiaoheng; M.A. Yarmolenko; A.A. Rogachev; D.L. Gorbachev; Zhubo Liu (449-456).
The paper covers the mechanism of the formation of nanoparticles in thin-layer systems based on citric acid, organic and inorganic copper compounds. It shows the possibility to form copper clusters in the hydrocarbon matrix during heat treatment of the composite layer based on polyethylene and copper acetate.
Keywords: Copper oxide nanoparticles; Copper clusters; Low–energy electron beam evaporation; Citric acid; Thin-layer systems;
High rate dry etching of (BiSb)2Te3 film by CH4/H2-based plasma by Junqiang Song; Xun Shi; Lidong Chen (457-461).
Etching characteristics of p-type (BiSb)2Te3 films were studied with CH4/H2/Ar gas mixture using an inductively coupled plasma (ICP)-reactive ion etching (RIE) system. The effects of gas mixing ratio, working pressure and gas flow rate on the etch rate and the surface morphology were investigated. The vertical etched profile with the etch rate of 600 nm/min was achieved at the optimized processing parameters. X-ray photoelectron spectroscopy (XPS) analysis revealed the non-uniform etching of (BiSb)2Te3 films due to disparate volatility of the etching products. Micro-masking effects caused by polymer deposition and Bi-rich residues resulted in roughly etched surfaces. Smooth surfaces can be obtained by optimizing the CH4/H2/Ar mixing ratio.
Keywords: Dry etching; Thermoelectric film; CH4/H2/Ar; Inductively coupled plasma;
Optimization of functionalization conditions for protein analysis by AFM by María Arroyo-Hernández; Rafael Daza; Jose Pérez-Rigueiro; Manuel Elices; Jorge Nieto-Márquez; Gustavo V. Guinea (462-468).
Activated vapor silanization (AVS) is used to functionalize silicon surfaces through deposition of amine-containing thin films. AVS combines vapor silanization and chemical vapor deposition techniques and allows the properties of the functionalized layers (thickness, amine concentration and topography) to be controlled by tuning the deposition conditions. An accurate characterization is performed to correlate the deposition conditions and functional-film properties. In particular, it is shown that smooth surfaces with a sufficient surface density of amine groups may be obtained with this technique. These surfaces are suitable for the study of proteins with atomic force microscopy.
Keywords: Surface modification; Atomic force microscopy; Amino groups; Infrared spectroscopy; Protein adsorption;
Insights into the microstructural and physical properties of colloidal Fe:ZnSe nanocrystals by Ruishi Xie; Yuanli Li; Linhai Jiang; Xingquan Zhang (469-475).
Here, we present a facile and environmentally friendly synthetic protocol to fabricate highly luminescent and water-soluble Fe:ZnSe nanocrystals in aqueous solution at low temperature. The microstructure and various physical properties (e.g., crystal structure, interplanar spacing, lattice parameter, crystalline size, lattice microstrain, intrinsic stress, X-ray density, specific surface area, dislocation density, porosity, agglomeration number) of the Fe:ZnSe nanocrystals were systematically investigated using X-ray diffraction. The particle size and morphology of the Fe:ZnSe nanocrystals were determined by transmission electron microscopy. The optical properties (e.g., absorption and photoluminescence) of the fabricated nanocrystals were explored using ultraviolet–visible absorption and photoluminescence spectroscopies, respectively. The surface functionalization of the Fe:ZnSe nanocrystals by mercaptoacetic acid ligand was evidenced by Fourier transform infrared spectroscopy. To confirm the elementary composition of the obtained nanocrystals, Energy dispersive X-ray spectroscopy was performed. To further shed light upon elemental distribution of the resulting nanocrystals, elemental mapping measurements were conducted. Moreover, the underlying mechanisms were also elucidated. As a consequence, the current investigation not only provides a deep insight into exploring the physical properties of doped nanocrystals, but also demonstrates a useful synthetic strategy for producing water-soluble and highly fluorescent doped nanocrystals.
Keywords: Nanostructured materials; Chemical synthesis; Microstructure; Physical properties;
Medium energy Ar+-ion induced ripple formation: Role of ion energy in pattern formation by S.K. Garg; D.P. Datta; J. Ghatak; S.R. Tripathy; D. Kanjilal; T. Som (476-479).
We show that the energy scaling of the ion beam induced depth of amorphization and ripple wavelength in the medium energy regime can be understood in terms of dominant nuclear energy loss in this energy regime. Specifically, thickness of amorphous layer developed under 60 keV Ar+-ion bombardment of Si at an incidence angle of 60° as determined by micro-Raman Spectrometry and cross-sectional transmission electron microscopy is shown to be consistent with the assumption of only nuclear energy loss mediated evolution. Further, the variation of ripple wavelength with ion energy is estimated using SRIM. Estimated variation of ripple wavelength with ion energy under this assumption is found to be in qualitative agreement with experimental observations in the medium energy range.
Keywords: Ion irradiation; Micro-Raman; SRIM simulation; Nuclear energy loss; Ion-induced ripple pattern;
LaF3 nanoparticles surface modified with tryptophan and their optical properties by Anatoly Safronikhin; Heinrich Ehrlich; Georgy Lisichkin (480-485).
LaF3 nanoparticles were synthesized by the double-jet precipitation technique in presence of tryptophan (Trp). The product was investigated by TEM, IR, absorption, and luminescence spectroscopies. Interaction of Trp with the nanoparticles results in formation of complexes between Trp and La3+ ions on the nanoparticle surface. Surface density of Trp was found as 0.7 molecule nm−2. It is shown that the modifier effects on LaF3 nanoparticle growth and stability of the surface modified LaF3 colloids. Luminescent properties of LaF3 nanoparticles modified with Trp (Trp@LaF3) are investigated. It is determined that Trp@LaF3 and Trp have the same profiles of excitation and photoluminescence spectra. Effects of pH, ionic strength, and Trp concentration on luminescence intensity are studied. At the same Trp amounts in the systems, Trp@LaF3 luminescence intensity is about 6 times less than Trp luminescence intensity. Such products can be used as luminescent labels.
Keywords: Tryptophan; Lanthanum fluoride; Surface modification; Nanoparticles; Luminescence; Surface complexes;
One-step, simple, and green synthesis of tin dioxide/graphene nanocomposites and their application to lithium-ion battery anodes by Zaixing Jiang; Dongjie Zhang; Yue Li; Hao Cheng; Mingqiang Wang; Xueqin Wang; Yongping Bai; Haibao Lv; Yongtao Yao; Lu Shao; Yudong Huang (486-489).
Graphene with extraordinary thermal, mechanical and electrical properties offers possibilities in a variety of applications. Recent advances in the synthesis of graphene composites using supercritical fluids are highlighted. Supercritical fluids exhibit unique features for the synthesis of composites due to its low viscosity, high diffusivity, near-zero surface tension, and tunability. Here, we report the preparation of tin dioxide (SnO2)/graphene nanocomposite through supercritical CO2 method. It demonstrates that the SnO2 nanoparticles are homogeneously dispersed on the surface of graphene sheets with a particle size of 2.3–2.6 nm. The SnO2/graphene nanocomposites exhibit higher lithium storage capacity and better cycling performance compared to that of the similar CNT nanocomposites. The reported synthetic procedure is straightforward, green and inexpensive. And it may be readily adopted to produce large quantities of graphene based nanocomposites.
Keywords: Graphene; Tin dioxide; Supercritical CO2; Lithium-battery anode;
Ti1−x Ag x electrodes deposited on polymer based sensors by S.M. Marques; N.K. Manninen; Stanislav Ferdov; S. Lanceros-Mendez; S. Carvalho (490-495).
Piezoelectric materials are interesting for the development of sensors and actuators for biomedical applications in areas such as smart prosthesis, implantable biosensors and biomechanical signal monitoring, among others. For acquiring or applying the electrical signal from/to the piezoelectric material, suitable electrodes can be produced from Ti based coatings with tailored multifunctional properties: conductivity and antibacterial characteristics through Ag inclusions. This work reports on Ti1−x Ag x electrodes with different Ag/Ti atomic ratios deposited by dc and pulsed magnetron sputtering at room temperature on poly(vinylidene fluoride), PVDF. The X-ray diffraction (XRD) results revealed that the deposition conditions preserve the polymer structure and suggested the presence of crystalline Tiβ phase in pure titanium coating and fcc-Ag phase in pure silver coating. According to the results obtained from scanning electron microscopy (SEM) analysis, the coatings are homogeneous and no clusters were found; since β-PVDF is anisotropic, the deposited coatings replicate the underlying substrate surface. Sheet resistivity values show a typical behavior of a binary alloy system, with low resistivity values for coatings of zone 1 (Ti rich) and zone 3 (Ag rich) and a slightly higher resistivity values in zone 2. The piezoelectricity of the different samples show similar values.
Keywords: Sensors; Ag nanoparticles; Piezoelectric polymers; Sputtering;
Pt catalysts on PANI coated WC/C nanocomposites for methanol electro-oxidation and oxygen electro-reduction in DMFC by Maryam Yaldagard; Mohsen Jahanshahi; Naser Seghatoleslami (496-504).
In the present study a Pt/PANI/WC/C electrocatalyst was developed to increase the methanol electro-oxidation and oxygen electro-reduction activity and stability of commercial Pt/C electrocatalyst. WC/C was coated with protonated polyaniline (PANI) in situ during the polymerization of aniline. Fourier transform infrared (FTIR) results illustrate the presence of PANI in the composite. The conductivity of PANI coated – WC/C has been compared with the conductivity of the corresponding mixtures of WC/C and Vulcan XC-72. X-ray diffraction results showed that Pt particles were dispersed on the support with mean particle size of about 10.56 nm. Transition electron microscopy images showed that the nanosized WC/C were successfully coated by PANI. Based on the electrochemical properties characterized by cyclic voltammetry, CO stripping and rotating disk electrode measurements it was found that the as prepared Pt/PANI/WC/C electrocatalyst exhibited a comparable activity for methanol oxidation reaction and oxygen reduction reaction with respect to the commercial one. A significant reduction in the potential of CO electro-oxidation peak from 0.75 V for Pt/C to 0.52 V for Pt/PANI/WC/C electrocatalyst indicates that an increase in the activity for CO electro-oxidation is achieved by replacing the carbon support by PANI coated WC/C. Chronoamerometry results also showed, in the presence of methanol the Pt/PANI/WC/C electrocatalyst still maintains a higher current density than Pt/WC/C and Pt/C.
Keywords: Methanol electro-oxidation; Oxygen electro-reduction; PANI; WC/C nanocomposites; Activity and stability; Microwave heating;
A facile fabrication of multifunctional knit polyester fabric based on chitosan and polyaniline polymer nanocomposite by Xiaoning Tang; Mingwei Tian; Lijun Qu; Shifeng Zhu; Xiaoqing Guo; Guangting Han; Kaikai Sun; Xili Hu; Yujiao Wang; Xiaoqi Xu (505-510).
Knit polyester fabric was successively modified and decorated with chitosan layer and polyaniline polymer nanocomposite layer in this paper. The fabric was firstly treated with chitosan to form a stable layer through the pad-dry-cure process, and then the polyaniline polymer nanocomposite layer was established on the outer layer by in situ chemical polymerization method using ammonium persulfate as oxidant and chlorhydric acid as dopant. The surface morphology of coated fabric was characterized by scanning electron microscopy (SEM), and the co-existence of chitosan layer and granular polyaniline polymer nanocomposite was confirmed and well dispersed on the fabric surface. The resultant fabric was endowed with remarkable electrical conductivity properties and efficient water-repellent capability, which also have been found stable after water laundering. In addition, the photocatalytic decomposition activity for reactive red dye was observed when the multifunctional knit polyester fabric was exposed to the illumination of ultraviolet lamp. These results indicated that chitosan and polyaniline polymer nanocomposite could form ideal multifunctional coatings on the surface of knit polyester fabric.
Keywords: Chitosan; Polyaniline; Multifunctional fabric; Water-repellent; Electrical conductivity; Photocatalytic activities;
DFT study of adsorption and dissociation behavior of H2S on Fe-doped graphene by Hong-ping Zhang; Xue-gang Luo; Hong-tao Song; Xiao-yan Lin; Xiong Lu; Youhong Tang (511-516).
Understanding the interaction mechanisms of hydrogen sulfide (H2S) with graphene is important in developing graphene-based sensors for gas detection and removal. In this study, the effects of doped Fe atom on interaction of H2S with graphene were investigated by density functional theory calculations. Analyses of adsorption energy, electron density difference, and density of states indicated that the doped Fe atom can significantly improve the interaction of H2S gas molecules with graphene, as well as Pt-doped graphene. The location of the sulfur atom is important in the interactions between H2S and Fe-doped graphene. The influence of the Fe―S distance can be very weak within a certain distance, as simulated in this study.
Keywords: DFT; Fe-doped graphene; Hydrogen sulfide;
RhB-sensitized effect on the enhancement of photocatalytic activity of BiOCl toward bisphenol-A under visible light irradiation by Xiaoming Mao; Caimei Fan; Yawen Wang; Yunfang Wang; Xiaochao Zhang (517-525).
A bismuth oxychloride (BiOCl) photocatalyst with visible light activity was successfully synthesized using NaBiO3 and HCl as raw materials. The crystal structure, morphology, and UV–vis diffuse reflectance spectra of the as-synthesized BiOCl were characterized. Rhodamine B (RhB), as a photosensitizer, can remarkably enhance light utilization and improve the photocatalytic activity of BiOCl toward bisphenol-A (BPA). The effects of BiOCl dosage, RhB dosage, BPA initial concentration and initial solution pH on the photocatalytic performance of BiOCl were studied. The photocatalytic oxidation of BPA followed pseudo first-order kinetics, and the highest photodegradation efficiency of BPA was observed using a BiOCl dosage of 1.5 g L−1 and RhB dosage of 5 mg L−1 in BPA solution (c 0 = 20 mg L−1, pH = 6) under visible light irradiation for 30 min. Under these conditions, the reaction rate constant of the system was 11.3 times greater than that of BiOCl without RhB. The superior photocatalytic activity observed was attributed to the sensitization effect of RhB. Experimental scavenging results revealed that h + and O2 • − are the main active species involved in BPA degradation. The as-synthesized BiOCl exhibited good photocatalytic stability during photodegradation, which suggests promising prospects in the practical application of organic pollutant photodegradation.
Keywords: BiOCl; Rhodamine B dye; Sensitization effect; Visible light photocatalysis; Bisphenol-A;
Modeling the impact, flattening and solidification of a molten droplet on a solid substrate during plasma spraying by Y.Z. Zheng; Q. Li; Z.H. Zheng; J.F. Zhu; P.L. Cao (526-533).
It is quite important to clearly understand the dynamic process of single splat formation for optimizing the plasma spraying process. In present study, a three-dimensional model including heat transfer and phase change was developed on Ansys Fluent 14 platform to simulate the impact, flattening and solidification of a molten droplet on a solid substrate during plasma spraying. The phase, contact pressure, temperature and velocity fields at different spreading times were presented to gain an insight into splat formation mechanism. The predicted splat morphology was in good agreement with the experimental photos. The effect of mushy zone constant, a parameter dominating the solidification behavior of fluid in Fluent, on the flattening of droplet was further investigated. Through comparing the calculated spread factor from present model with the experimental value, a mushy zone constant of 108 or 109 was found to be more appropriate for simulation on the solidification problem occurring in high-speed impact and flattening process, instead of the range of 104–107 recommended in Fluent.
Keywords: Numerical modeling; Plasma spraying; Splat; Solidification;
The freezing process of continuously sprayed water droplets on the superhydrophobic silicone acrylate resin coating surface by Jianlin Hu; Ke Xu; Yao Wu; Binhuan Lan; Xingliang Jiang; Lichun Shu (534-544).
This study conducted experiments on freezing process of water droplets on glass slides covered with superhydrophobic coatings under the continuous water spray condition in the artificial climatic chamber which could simulate low temperature and high humidity environments. The freezing mechanism and freezing time of water droplets under the condition of continuous spray were observed by the microscope and were compared with those of the single static droplet. Then, differences of freezing process between continuously sprayed droplets and single static droplet were analyzed. Furthermore, the effects of static contact angle (CA), contact angle hysteresis (CAH) and roughness of the superhydrophobic coating surface on the freezing time of continuously sprayed droplets were explored. Results show that the freezing process of the continuously sprayed droplets on the superhydrophobic coating started with the homogeneous nucleation at gas–liquid interfaces. In addition, the temperature difference between the location near the solid–liquid interface and the location near the gas–liquid interface was the key factor that influenced the ice crystallization mechanism of water droplets. Moreover, with the larger CA, the smaller CAH and the greater roughness of the surface, droplets were more likely to roll down the surface and the freezing duration on the surface was delayed. Based on the findings, continuous water spray is suggested in the anti-icing superhydrophobic coatings research.
Keywords: Superhydrophobic surface; Silicone acrylate resin coating; Droplet freezing process;
Fabrication of hierarchical structures with ZnO nanowires on micropillars by UV soft imprinting and hydrothermal growth for a controlled morphology and wettability by Jie Hu; Yongjiao Sun; Wendong Zhang; Fanqin Gao; Pengwei Li; Dong Jiang; Yong Chen (545-551).
Hierarchical structures of ZnO nanowires (NWs) with different lengths on well-defined micropillars are fabricated by UV soft imprinting and hydrothermal growth. X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS) are employed to characterize the crystal structure, morphology and chemical composition of the hierarchical structures of ZnO nanowires on micropillars. By varying the growth time, ZnO NWs of different lengths and morphology were obtained, showing distinct wettability which can be further modified by surface coating with octadecyltrichlorosilane (OTS). Our results show that under optimal growth conditions, the water contact angle (CA) and contact angle hysteresis (CAH) of the fabricated hierarchical structures after OTS surface treatment can reach 159 ± 1° and 6°, respectively.
Keywords: ZnO nanowires; Hierarchical structures; UV soft imprinting; Wettability;
Synthesis and properties of a magnetic core–shell composite nano-adsorbent for fluoride removal from drinking water by Chang Zhang; Lin Chen; Ting-Jie Wang; Chao-Li Su; Yong Jin (552-559).
A novel Fe–Ti/Fe3O4 composite nano-adsorbent with a core–shell structure was prepared for rapid adsorption of fluoride from drinking water and complete solid–liquid separation after adsorption. The superparamagnetic composite nano-adsorbent has high absorption capacity and can be used in a fluidized system.An adsorbent for fluoride removal from drinking water was prepared by coating Fe–Ti bimetallic oxide on magnetic Fe3O4 particles by co-precipitation. The adsorbent was a nanosized composite with a core–shell structure comprising a magnetic Fe3O4 core of 10–20 nm in diameter and an amorphous adsorbent shell of several nanometer thickness. The synthesis parameters were optimized to give high adsorption capacity and high magnetization. The optimized mass ratio of the Fe–Ti bimetallic oxide shell to Fe3O4 core was 2.72. The adsorption isotherm was well fitted with the Langmuir isotherm and the saturation adsorption capacity 57.22 mg/g adsorbent. Adsorption was fast and reached equilibrium within 2 min. The nano-adsorbent was superparamagnetic with a saturation magnetization of 18.4 emu/g, which allowed rapid separation of the adsorbent from the water solution by an external magnet.
Keywords: Fluoride removal; Nano-adsorbent; Coating; Core–shell structure; Magnetic separation;
Analysis of moving surface structures at a laser-induced boiling front by R.S. Matti; A.F.H. Kaplan (560-567).
Recently ultra-high speed imaging enabled to observe moving wave patterns on metal melts that experience laser-induced boiling. In laser materials processing a vertical laser-induced boiling front governs processes like keyhole laser welding, laser remote fusion cutting, laser drilling or laser ablation. The observed waves originate from temperature variations that are closely related to the melt topology. For improved understanding of the essential front mechanisms and of the front topology, for the first time a deeper systematic analysis of the wave patterns was carried out. Seven geometrical shapes of bright or dark domains were distinguished and categorized, in particular bright peaks of three kinds and dark valleys, often inclined. Two categories describe special flow patterns at the top and bottom of the front. Dynamic and statistical analysis has revealed that the shapes often combine or separate from one category to another when streaming down the front. The brightness of wave peaks typically fluctuates during 20–50 μs. This variety of thermal wave observations is interpreted with respect to the accompanying surface topology of the melt and in turn for governing local mechanisms like absorption, shadowing, boiling, ablation pressure and melt acceleration. The findings can be of importance for understanding the key process mechanisms and for optimizing laser materials processing.
Keywords: Wave structure; Pattern; Image analysis; Shape; Topology; Molten metal;
Defects improved photocatalytic ability of TiO2 by Lei Li; Hong-Wei Tian; Fan-Ling Meng; Xiao-Ying Hu; Wei-Tao Zheng; Chang Q. Sun (568-572).
Defect generation forms an important means modulating the photocatalytic ability of TiO2 with mechanisms that remain yet unclear. Here we show that a spectral distillation clarifies the impact of defect on modulating the band gap, electroaffinity, and work function of the substance. Firstly, by analyzing XPS measurements, we calibrated the 2p3/2 level of 451.47 eV for an isolated Ti atom and its shifts by 2.14 and 6.94 eV, respectively, upon Ti and TiO2 bulk formation. Spectral difference between the defected and the un-defected TiO2 skin revealed then that the 2p3/2 level shifts further from 6.94 to 9.67 eV due to the defect-induced quantum entrapment. This entrapment is associated with an elevation of the upper edges of both the 2p3/2 and the conduction band by polarization. The shortening and strengthening of bonds between undercoordinated atoms densify and entrap the core electrons, which in turn polarize the dangling bond electrons of defect atoms. The entrapment and polarization mediate thus the band gap, the electroaffinity, the work function, and the photocatalytic ability of TiO2.
Keywords: Photocatalysis; XPS; TiO2; Defect; Surface; Nanostructures;
Thermal degradation of TiO2 nanotubes on titanium by Anish Shivaram; Susmita Bose; Amit Bandyopadhyay (573-580).
The objective of this research was to study thermal degradation behavior of TiO2 nanotubes on titanium (Ti). TiO2 nanotubes were grown via anodization method on commercially pure Ti (Cp-Ti) discs using two different electrolytes, 1 vol. % HF in deionized (DI) water and 1 vol. % HF + 0.5 wt. % NH4F + 10 vol. % DI water in ethylene glycol, to obtain nanotubes with two different lengths, 300 nm and 950 nm keeping the nanotube diameter constant at 100 ± 20 nm. As grown TiO2 nanotubes were subjected to heat treatment to understand thermal degradation as a function of both temperature and hold time. The signs of degradation were observed mainly when amorphous nanotubes started to crystallize, however the crystallization temperature varied based on TiO2 nanotubes length and anodizing condition. Overall, 300 nm nanotubes were thermally stable at least up to 400 °C for 12 h, while the 950 nm long nanotubes show signs of degradation from 400 °C for 6 h only. Clearly, length of nanotubes, heat treatment temperature as well as hold times show influence toward degradation kinetics of TiO2 nanotubes on titanium.
Keywords: TiO2 nanotubes; Thermal degradation; Phase transformation; Surface energy;
Tribological properties of amorphous hydrogenated (a-C:H) and hydrogen-free tetrahedral (ta-C) diamond-like carbon coatings under jatropha biodegradable lubricating oil at different temperatures by H.M. Mobarak; H.H. Masjuki; E. Niza Mohamad; M.A. Kalam; H.K. Rashedul; M.M. Rashed; M. Habibullah (581-592).
The application of diamond-like carbon (DLC) coatings on automotive components is emerging as a favorable strategy to address the recent challenges in the industry. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, thereby improving their fuel efficiency and durability. The lubrication of ferrous materials can be enhanced by a large amount of unsaturated and polar components of oils. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetable oil should be investigated. A ball-on-plate tribotester was used to run the experiments. Stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC that slide against 440C stainless steel ball were used to create a ball-on-plate tribotester. The wear track was investigated through scanning electron microscopy. Energy dispersive and X-ray photoelectron spectroscopies were used to analyze the tribofilm inside the wear track. Raman analysis was performed to investigate the structural changes in the coatings. At high temperatures, the CoF in both coatings decreased. The wear rate, however, increased in the a-C:H but decreased in the ta-C DLC-coated plates. The CoF and the wear rate (coated layer and counter surface) were primarily influenced by the graphitization of the coating. Tribochemical films, such as polyphosphate glass, were formed in ta-C and acted as protective layers. Therefore, the wear rate of the ta-C DLC was lower than that of the-C:H DLC.
Keywords: Diamond-like carbon (DLC) coatings; Friction; Wear; Graphitization;
Kinetics of nitrogen incorporation at the SiO2/4H-SiC interface during an NO passivation by Zengjun Chen; Yi Xu; Eric Garfunkel; Leonard C. Feldman; Temel Buyuklimanli; Wei Ou; Jeff Serfass; Alan Wan; Sarit Dhar (593-597).
Nitridation of the SiO2-4H-SiC interface using post-oxidation annealing in nitric oxide (NO) is the most established process for obtaining high quality 4H-SiC MOS interfaces. In this paper, a detailed study of the interfacial nitrogen uptake kinetics is reported for the (0 0 0 1) Si-terminated and (0 0 0-1) C-terminated crystal faces of 4H-SiC. The results indicate a significantly faster kinetics for the C-face compared to the Si-face. For the first time, the correlation between N-uptake and the interface trap density reduction was observed on the C-face. First-order kinetics models are used to fit the nitrogen up-take. Empirical equations predicting N coverage at the SiO2-4H-SiC interface via NO annealing have been established. The result also shows that the N-uptake rate is associated with the oxidation rate.
Keywords: Silicon carbide; Interface; Nitridation; Kinetics;
Microstructure and thermal shock resistance of the peg-nail structured TBCs treated by selective laser modification by Fa Chang; Kesong Zhou; Xin Tong; Liping Xu; Xiaofeng Zhang; Min Liu (598-606).
The surface of the discrete peg-nail structured laser modified units shows resolidification with network segmented cracks perpendicular to the surface and columnar grains on the surface. The interface between top coating and bond coating exhibits a metallurgical bond to some degree after the peg-nail structured laser modification. It can be noted that lifetime of the peg-nail structured laser modified coatings, relative to that of the as-sprayed coating, exhibit 3–5 improvement.In this study, a peg-nail structured laser modification was implemented on thermal barrier coatings (TBCs) by a pulsed Nd:YAG laser. The effects of the peg-nail structured laser modified units on microstructure and thermal shock resistance of the TBCs were investigated. The results indicated that the surface roughness of the peg-nail structured laser modified units was less than that of the as-sprayed coating. The laser modified region, which penetrated the whole YSZ top coating and the partial NiCoCrAlYTa bond coating, consisted of a network of segmented cracks perpendicular to surface and a dense dendritic columnar structure associating with a thin discontinuous equiaxed grains on its surface. The interface between the top coating and the bond coating exhibited a metallurgical bond to some degree after the peg-nail structured laser modification. XRD analysis revealed that the as-sprayed coating was composed of nonequilibrium tetragonal (T′) phase, cubic (C) phase and a small amount of monoclinic (M) phase, however, the last phase disappeared after laser modification. The thermal shock tests indicated that the cyclical lifetime of the as-sprayed TBCs were enhanced around 3–5 times by the peg-nail structured laser modification after 130 thermal shock cycles. The TBCs’ failure was due to the oxide scale growth of bond coating and the thermal expansion mismatch stress during thermal shock cycles. Furthermore, both improvement on strain accommodation and delay of cracks propagation resulting from network segmented cracks perpendicular to the surface and dendritic columnar structure in the peg-nail structured units, formation of metallurgical bonding which enhances bonding strength, creating the lamellar and columnar alternate microstructure with toughness and rigidity hybrid characteristics for providing more compliance to the coating, were all considered as the main reasons of improving thermal shock lifetime of peg-nail structured laser modified TBCs.
Keywords: Thermal barrier coatings; Peg-nail structure; Laser modification; Thermal shock resistance;
Structural and optical properties investigation of DC magnetron sputtered β-TiO2 thin film by Shakil Khan; Ishaq Ahmed; A. Shah (607-613).
Thin films of monoclinic titanium oxide phase (β-TiO2) have been grown on glass substrate using DC magnetron sputtering technique. The effect of oxygen conditions on the films stoichiometry, growth rate, structure, molecular mode of vibration and optical properties has been investigated. An improvement in stoichiometric ratio (O/Ti) has been observed with the increase of oxygen content in the synthesized chamber. XRD patterns demonstrated the polycrystalline nature of the deposited films with ( 2 ¯ 11 ) preferential orientation of β-TiO2 phase. In the FTIR analysis, a dominant peak at 868 cm−1 wavenumbers corresponding to the longitudinal optical (LO) mode of monoclinic TiO2 phase was observed at 10% oxygen condition. It shifted to 880 cm−1 wavenumbers at higher oxygen fractions, illustrated the rise of oxygen concentration in the grown films. The influence of various oxygen conditions on transmittance/extinction coefficient, band gap and refractive index of TiO2 (B) phase is reported.
Keywords: TiO2; DC magnetron sputtering; XRD; FTIR; UV–vis spectroscopy;
Wear and corrosion resistance of anti-bacterial Ti–Cu–N coatings on titanium implants by Haibo Wu; Xiangyu Zhang; Xiaojing He; Meng Li; Xiaobo Huang; Ruiqiang Hang; Bin Tang (614-621).
Anti-bacterial coatings with excellent wear and corrosion resistance play a vital role in ensuring the durability of implant materials in constant use. To this end, a novel anti-bacterial surface modification by combining magnetron sputtering with plasma nitriding was adopted in this paper to fabricate Cu-bearing Ti-based nitrides coatings (Ti–Cu–N) on titanium surface. The anti-bacterial properties of Ti–Cu–N coatings were evaluated. The microstructures and composition of the coatings were investigated by using FESEM, EDS, GDOES, XRD. The wear and corrosion resistance of the coatings were investigated. The results confirmed that an anti-bacterial Ti–Cu–N coating with a thickness of 6 μm and good adhesive strength to substrate was successfully achieved on titanium surface. As implied by XRD, the coatings were consisted of TiN, Ti2N, TiN0.3 phases. The surface micro-hardness and wear resistance of Ti–Cu–N coatings were significantly enhanced after plasma nitriding treatment. The analysis of potentiodynamic polarization curves and Nyquist plots obtained in 0.9 wt.% NaCl solution suggested that the Ti–Cu–N coatings also exhibited an excellent corrosion resistance. As mentioned above, it can be concluded that the duplex-treatment reported here was a versatile approach to develop anti-bacterial Ti–Cu–N coatings with excellent comprehensive properties on titanium implants.
Keywords: Anti-bacterial coatings; S. aureus; Wear; Corrosion resistance; Plasma nitriding;
Polypyrrole–ZnFe2O4 magnetic nano-composite with core–shell structure for glucose sensing by Zohreh Shahnavaz; Farnaz Lorestani; Yatimah Alias; Pei Meng Woi (622-629).
An amperometric enzymeless glucose sensor using core–shell nanocomposite based on chemical oxidative polymerization of pyrrole on ZnFe2O4 nanoparticles surface was investigated in this study. ZnFe2O4 nanoparticles and ZnFe2O4/PPy nanoparticles showed electrocatalytic activity for the oxidation of glucose in alkaline solution. The electrochemical performance of the modified electrodes was investigated by cyclic voltammetry (CV) method. The results demonstrated that this nanocomposite with the proper concentration of PPy displayed enhanced electrocatalytic activity toward the oxidation of glucose in 0.1 M NaOH solution. The modified sensor possesses good linear response in glucose concentration with an appropriate linear range up to 8.0 mM (R 2 = 0.9943) and good sensitivity to glucose (145.36 μA mM−1) with a detection limit of 0.1 mM, at room temperature.
Keywords: Non-enzymatic sensor; Zinc ferrite; Core–shell structure; Glucose;
Synthesis and processing of ELISA polymer substitute: The influence of surface chemistry and morphology on detection sensitivity by Samira Hosseini; Fatimah Ibrahim; Ivan Djordjevic; Hussin A. Rothan; Rohana Yusof; Cees van der Marel; Leo H. Koole (630-638).
Despite the known drawbacks of enzyme-linked immunosorbent assay (ELISA), one of the deficiencies that have relatively been ignored is the performance of ELISA substrate itself. Polystyrene (PS), as the cost effective material of choice for mass production of ELISA well-plates, has shown obvious lacks of suitable physical and chemical properties for protein attachment. The general concept of this work was to develop a potential substrate that can be suggested as a material of choice for production of a new generation of ELISA analytical kits. Spin-coated thin films of polymethyl methacrylate-co-methacrylic acid (PMMA-co-MAA) on silicon surfaces were designed and processed for detection of dengue virus. Coated surfaces of different molar ratios have been investigated as carboxyl-functionalized layers for obtaining platform for biomolecule immobilization with high level of protein activity. To improve the sensitivity of detection, we have used amine functional “spacers”, hexamethylenediamine (HMDA) and polyethyleneimine (PEI), which were covalently bonded to the surfaces of PMMA-co-MAA coatings. Results demonstrate that the variation of surface concentration of carboxyl groups of PMMA-co-MAA can be used to control the amine surface concentration after carbodiimide coupling with HMDA and PEI spacers. The presence of amine spacers increases hydrophilicity of the coatings and significantly impacts the polymer surface morphology. In particular, protein immobilization via amine-bearing spacers has been achieved in two effective steps: (1) carbodiimide bonding between amine spacer molecules and PMMA-co-MAA polymer coatings; and (2) covalent immobilization of antibody via glutaraldehyde reaction with amine groups from amine-treated surfaces. The application of PEI spacer in comparison to HMDA has shown much higher intensity of detection signal in ELISA experiment, indicating better immobilization efficiency and preservation of antibody activity upon attachment to the polymer surface.
Keywords: Protein immobilization; Polyacrylate coatings; ELISA substrate; Dengue virus detection;
Investigation of optical and morphological properties of metalized nanocomposites by Sandra Varnaitė-Žuravliova; Virginija Jankauskaitė; Asta Guobienė; Igoris Prosyčevas (639-647).
Nanoparticles play an important role in scientific and technological fields, because they significantly affect the polymer matrix and lead to new properties. A combination of PMMA (poly-methylmethacrylate) with metal nanoparticles can offer very wide application field in medicine, because metals may act on a broad range of microbial targets, and many mutations may occur for microorganisms to resist their antimicrobial activity. Usually metal and other nanoparticles are coated onto surfaces of substrates. Unfortunately, the durability of such nanocomposites normally is very poor, because coatings are quite sensitive to different damages. Therefore the main target of this research was to apply nanoparticles on the surface of PMMA substrate and to affect them with microwave heating that nanoparticles intervene into the polymer matrix and form permanent damage resistance metal nanolayer. It was determined that the application of the metal nanolayer on the PMMA and the partial insertion of nanoparticles into the polymer were successful. Although Cu nanoparticles mostly formed deep elements than Ag nanoparticles in the nanocomposites, they both molded grains on the surface of nanocomposites. The incorporation of metal nanoparticles into the PMMA allowed expanding the application field of nanocomposites with more durable metal nanolayers.
Keywords: Nanocomposite; Nanoparticle; PMMA; Ag; Cu; Microwave heating;
Water-phase strategy for synthesis of TiO2–graphene composites with tunable structure for high performance photocatalysts by Changyuan Hu; Fei Chen; Tiewen Lu; Chengjiang Lian; Shizheng Zheng; Quanhong Hu; Shuwang Duo; Rongbin Zhang (648-656).
The controllable synthesis of strongly coupled TiO2/graphene composites has been a long-standing challenge for developing advanced photocatalysts. Here, we report a facile water-phase protocol for synthesis of TiO2–graphene composites using GO aqueous suspension and TiO2 aqueous nanosols as precursors. By controlling the ratio of GO to TiO2, both high-/low-dense TiO2 nanoparticles across graphene and graphene–TiO2–graphene sandwich structured composites are successfully achieved through electrostatic attraction between negatively charged GO nanosheets and positively charged TiO 2 nanosols. The TiO2–graphene composites show an enhanced photocatalytic activity for the degradation of methylene blue (MB) under UV light. Interestingly, the sandwich structured TiO2–graphene composite exhibits the best photocatalytic activity and the highest photocurrent density, which is 12.2 and 35.46 times as that of pure TiO2, respectively. The outstanding photocatalytic activity of sandwich structured composite is likely due to the following two reasons, two-channel electron conduction path between TiO2 and graphene, as well as the better adsorption capability of MB molecule.
Keywords: TiO2; Graphene; Electrostatic attraction; Photocatalysis;
An investigation on the inhibitory action of benzazole derivatives as a consequence of sulfur atom induction by Z. Moradi; M.M. Attar (657-665).
The inhibitory action of three benzazole based molecules namely 2-methyl benzimidazole (2-MBI), 2-methyl benzothiazole (2-MBT) and 2-mercapto benzthiazole (2-SHBT) in 1 M HCl solution was studied by gravimetric analysis and electrochemical impedance spectroscopy (EIS). Results showed that the inhibitor adsorption on the iron surface was according to Langmuir adsorption isotherm for 2-MBI and 2-MBT and Flory Huggins Isotherm for 2-SHBT. Surface roughness obtained by Atomic Forced Microscopy (AFM) revealed that a good inhibitor decreases the surface roughness significantly which can be related to the formation of more integrated molecular film of inhibitor on steel surface. Based on contact angle (CA) measurements as the efficiency of the inhibitor molecules improve the hydrophobicity increases. These three molecules were chosen to see the effect of introducing sulfur atom into the structure the main effect of which would be on electronic parameters. To better understand this effect, the quantum chemical descriptors including: E HOMO, E LUMO, energy gap (ΔE), dipole moment (μ), hardness (η), softness (σ), electronegativity index (χ), fraction of electrons transferred (ΔN), that are most relevant to the potential action of a molecule as corrosion inhibitor, have been calculated in water and vacuum. Electronic parameters of these three inhibitors have been studied using DFT/B3LYP, and HF methods with 6-31G (d,p) basis set.
Keywords: Benzazole inhibitor; Weight loss; EIS; AFM; Contact angle; Quantum chemistry;
Morphological features of silicon substrate by using different frequency laser ablation in air and water by J.Y. Xu; H. Hu; Y.L. Lei (666-671).
The interaction of the nanosecond laser (FWHM = 30 ns, λ = 355 nm) and monocrystalline silicon is investigated in air and water. Conventional optical and scanning electron microscopes are used to characterize surface ablation of the monocrystalline silicon. A numerical model is used to ascertain the time of the bubble motion in water. Morphological features of the laser-induced crater are different under various environments and frequencies. More debris is found when using high frequency ablation, and a larger zone is affected by heat when using low frequency ablation in air.There is no debris found in water, and the morphology of craters is better in low frequency ablation than that in high frequency ablation because bubbles generated by high frequency ablation affect laser transmission.
Keywords: Laser frequency; Morphological features; Nanosecond laser; Ablation;
Controllable electrodeposition of ZnO nanorod arrays on flexible stainless steel mesh substrate for photocatalytic degradation of Rhodamine B by Hui Lu; Mei Zhang; Min Guo (672-681).
Well-aligned single-crystalline ZnO nanorod arrays were first prepared on flexible stainless steel mesh substrate in large-scale by using a direct electrodeposition method and showed enhanced photocatalytic performance.Well-aligned single-crystalline ZnO nanorod arrays (ZNRAs) were prepared on flexible stainless steel mesh (SSM) substrate in large-scale by using a direct electrodeposition method. The effects of electrochemical parameters, such as applied potential, applied nucleation potential time, substrate pretreatment, electrodeposition duration and times, on the orientation, morphology and density of ZNRAs were systematically studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and the selected area electron diffraction (SAED). The results showed that ZNRAs on SSM substrate with [0 0 1] preferred orientation and well crystallization were obtained by controlling the applied potential in the range of −0.9 to −1.1 V. The density of ZNRAs could be increased obviously by applying a nucleation potential (−1.3 V for more than 10 s before deposition) or by means of substrate pretreatment (the SSM immersed in zinc acetate colloid for more than 10 min before deposition), meanwhile, the deposited ZNRAs also had small average diameter (<46 ± 4 nm), narrow size distribution and good orientation. In addition, it was also found that the average diameter of ZNRAs could be increased from 89 to 201 ± 5 nm by extending the electrodeposition duration from 1800 to 7200 s, and the length of rods was from 0.8 to 2.2 ± 0.1 μm when the times of the electrodeposition from one to six times. Furthermore, the band gap energy (E g) of as-prepared ZNTAs was not closely related to the electrodeposition times (only changed from 3.30 to 3.32 eV). The ZNRAs prepared with more electrodeposition times showed enhanced photocatalytic performance under the UV-lamp for degradation of Rhodamine B. The degradation efficiency of ZNRAs improved from 89.4% to 98.3% with the deposition times from one to six times.
Keywords: ZnO nanorod arrays; Flexible stainless steel mesh; Controllable electrodeposition; Photocatalytic degradation;
One-pot synthesis of ZnO/ZnGa2O4 heterojunction with X/XY structure for improved photocatalytic activity by Ma Baojun; Lin Keying; Su Weiguang; Liu Wanyi (682-687).
A large scale one-pot coprecipitation method is developed for synthesis of ZnO/ZnGa2O4 heterojunction photocatalysts. XRD and Raman spectra show that ZnO and ZnGa2O4 are formed. SEM images indicate the particle size of ZnO/ZnGa2O4 heterojunction composites is about 20 nm. The HRTEM images show a close contact between ZnO and ZnGa2O4. The activities of photocatalysts are evaluated by photocatalytic degradation of methyl orange (MO) in the aqueous solution. The efficiency of MO degradation on the optimum photocatalysts ZnO/ZnGa2O4-0.2 shows about 82% in 70 min, which is greatly higher than that of ZnO (6%) and ZnGa2O4 (47%). It is proposed that the heterojunctions between ZnO and ZnGa2O4 promote the charge separation and is responsible for the improved photocatalytic activity. The synthetic method of ZnO/ZnGa2O4 heterojunction has potential commercial value and can be applied to other semiconductors heterojunctions with similar structure of X/XY.
Keywords: One-pot; Coprecipitation; Photocatalytic; Heterojunction; ZnGa2O4; ZnO;
Noteworthy impacts of polyurethane-urea ionomers as the efficient polar coatings on adhesion strength of plasma treated polypropylene by Mohammad. R. Chashmejahanbin; Hamed Daemi; Mehdi Barikani; Ali Salimi (688-695).
In present research, polypropylene (PP) was selected as a model nonpolar substrate for chemical modification using plasma. In the first step, the PP samples were treated using oxygen and argon atmospheres, individually. The prepared samples were analyzed using both FTIR and AFM techniques. The output of these techniques revealed that the carbonyl, carboxylic acid and its derivatives have been formed on the surface of PP. Afterward, a series of aqueous polyurethane-urea dispersions were synthesized as the novel polar coating for modified nonpolar polymers and characterized by different techniques including FTIR, DSC, TGA, mechanical properties and contact angle. Finally, the plasma treated samples were coated by prepared polyurethane ionomer. The results of pull-off analysis confirmed the significant role of the polyurethane as an extremely polar coating to create hydrogen bonding with functional groups on the surface of treated PP. The adhesion strength of polypropylenes increased from 0.04 MPa to 0.61 MPa for neat and oxygen-based plasma treated samples, respectively.
Keywords: Polypropylene; Polyurethane-urea ionomer; Coating; Adhesion; Plasma treatment;
High temperature thermal stability investigations of ammonium sulphide passivated InGaAs and interface formation with Al2O3 studied by synchrotron radiation based photoemission by Lalit Chauhan; Durga Rao Gajula; David McNeill; Greg Hughes (696-700).
High resolution synchrotron radiation core level photoemission measurements have been used to undertake a comparative study of the high temperature thermal stability of the ammonium sulphide passivated InGaAs surface and the same surface following the atomic layer deposition (ALD) of an ultrathin (∼1 nm) Al2O3 layer. The solution based ex situ sulphur passivation was found to be effective at removing a significant amount of the native oxides and protecting the surface against re-oxidation upon air exposure. The residual interfacial oxides which form between sulphur passivated InGaAs and the ultrathin Al2O3 layer can be substantially removed at high temperature (up to 700 °C) without impacting on the InGaAs stoichiometry while significant loss of indium was recorded at this temperature on the uncovered sulphur passivated InGaAs surface.
Keywords: Passivation; InGaAs; Photoemission; Sulphur; Synchrotron;
Fabrication of superhydrophobic surface on aluminum by continuous chemical etching and its anti-icing property by Ruijin Liao; Zhiping Zuo; Chao Guo; Yuan Yuan; Aoyun Zhuang (701-709).
Aluminum is extensively used metals in transmission lines, and the accumulation of ice on aluminum may inflict serious damage such as tower collapse and power failure. In this study, micro/nanostructured aluminum surface was fabricated using a continuous chemical etching method. The static and dynamic anti-icing behaviors of the as-prepared aluminum surface in different conditions were systematically investigated with a self-made device and artificial climate laboratory. Results showed that the as-prepared surface can mitigate freezing in glaze ice. Only several isolated ice points formed on the surface in glaze ice after 50 min. Due to the superhydrophobicity of the as-prepared aluminum surface, cold water sprayed on the surface aggregated into large drops and rolled off the surface before freezing, thus protecting the surface against excessive ice accumulation. The surface morphology and crystal structure of the samples were also characterized by scanning electron microscopy/energy-dispersive spectrometry and X-ray diffraction. This study offers insight into understanding the anti-icing behavior of the superhydrophobic aluminum surface and may favor the application of structured aluminum surface in power transmission lines against ice accumulation.
Keywords: Anti-icing behavior; Continuous chemical etching; Aluminum; Superhydrophobic; Glaze ice;
Nano-adhesion influenced by atomic-scale asperities: A molecular dynamics simulation study by Lina Si; Xiaoli Wang (710-717).
The effect of atomic-scale surface roughness on the adhesion between a spherical tip and single asperities with varying radii and heights situated on a flat surface has been investigated by using the molecular dynamics (MD) simulation method in this work. The simulation results are also compared with the theoretical predications, i.e., Rumpf and Rabinovich models. The normal forces versus separation curves are analyzed thoroughly, from which the van der Waals (vdW) force (F vdW) and the adhesive force (F adh) are obtained. The effects of the indentation velocity and the silicon crystallographic orientation on the contact processes have also been discussed. The results indicate that both F vdW and F adh decrease dramatically with the introduction of nano-asperity in comparison to the smooth substrate without the asperity, e.g., more than 90% drop in both F vdW and F adh when asperity radius/tip radius (r/R) is 0.05. The influence of the asperity height on F vdW and F adh can be very important when height/radius of spherical cap asperity (y max/r 0) is less than 0.5. Furthermore, the discrepancies between the adhesion forces obtained through MD simulation and these calculated with existing Rumpf and Rabinovich models have been discussed.
Keywords: Nanoadhesion; Roughness; MEMS/NEMS; Molecular dynamics simulation;
Theoretical study of heavy metal Cd, Cu, Hg, and Ni(II) adsorption on the kaolinite(0 0 1) surface by Jian Zhao; Man-Chao He (718-723).
Heavy metal pollution is currently of great concern because it has been recognized as a potential threat to air, water, and soil. Adsorption was one of the most popular methods for the removal of heavy metal. The adsorption of heavy metal Cd, Cu, Hg, and Ni(II) atoms on the hydroxylated (0 0 1) surface of kaolinite was investigated using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics were systematically studied for a wide range of coverage Θ [from 0.11 to 1.0 monolayers (ML)] and adsorption sites. The most stable among all possible adsorption sites for Cd(II) atom was the two-fold bridge site followed by the one-fold top site, and the top site was the most favorite adsorption site for Cu and Ni(II) atoms, while the three-fold hollow site was the most stable adsorption site for Hg(II) atom followed by the two-fold bridge site. The adsorption energy increases with the coverage for Cd, Cu, and Hg(II) atoms, thus indicating the higher stability of surface adsorption and a tendency to the formation of adsorbate islands (clusters) with increasing the coverage. However, the adsorption energy of Ni(II) atoms decreases when increasing the coverage. The adsorption capabilities of the kaolinite clay for the heavy metal atoms were in the order of Ni > Cu > Cd > Hg(II). The other properties of the Cd, Cu, Hg, and Ni(II)/kaolinite(0 0 1) system including the different charge distribution, the lattice relaxation, and the electronic density of states were also studied and discussed in detail.
Keywords: DFT calculations; Kaolinite; Heavy metal; Adsorption;
Uniform surface modification of diatomaceous earth with amorphous manganese oxide and its adsorption characteristics for lead ions by Song Li; Duanyang Li; Fei Su; Yuping Ren; Gaowu Qin (724-729).
A novel method to produce composite sorbent material compromising porous diatomaceous earth (DE) and surface functionalized amorphous MnO2 is reported. Via a simple in situ redox reaction over the carbonized DE powders, a uniform layer of amorphous MnO2 was anchored onto the DE surface. The hybrid adsorbent was characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. The batch method has been employed to investigate the effects of surface coating on adsorption performance of DE. According to the equilibrium studies, the adsorption capacity of DE for adsorbing lead ions after MnO2 modification increased more than six times. And the adsorption of Pb2+ on the MnO2 surface is based on ion-exchange mechanism. The developed strategy presents a novel opportunity to prepare composite adsorbent materials by integrating nanocrystals with porous matrix.
Keywords: Diatomaceous earth; MnO2; Adsorption; Heavy metal ions;
Preparation, and characterizations of a novel luminescence Lu2WO6:Eu3+ film as potential scintillator by Xiang-Yang Chen; Zhi-Jun Zhang; Lin-Lin Zhu; Meng Xu; Hong Wang; Ai-Guo Li; Jing-Tai Zhao (730-736).
Novel Lu2WO6:Eu3+ films with excellent luminescence performance were successfully prepared by Pechini method for the first time and characterized with X-ray diffraction (XRD), micro X-ray fluorescence imaging (μ-XRF), atomic force microscope (AFM), and X-ray excited luminescence (XEL), etc. Eu3+-doped films emitted strong red light peak wavelength at 612 nm under both UV light or X-ray excitation. The optimal annealing temperature and Eu3+-doped concentration are around 950 °C and 10 mol%, respectively. In addition, luminescence mechanism associated with Eu3+ site occupation and possible energy transfer of Lu2WO6:Eu3+ films have also been proposed. The optimized thin film shows great potential for applications as a candidate for X-ray imaging due to its high density, suitable emission wavelength and high light yield.
Keywords: Luminescence; Lu2WO6:Eu3+ film; X-ray imaging; Energy transfer;
Surface modification of carbon fibers by a polyether sulfone emulsion sizing for increased interfacial adhesion with polyether sulfone by Haojie Yuan; Shouchun Zhang; Chunxiang Lu (737-744).
Interests on carbon fiber-reinforced thermoplastic composites are growing rapidly, but the challenges with poor interfacial adhesion have slowed their adoption. In this work, a polyether sulfone (PES) emulsion sizing was prepared successfully for increased interfacial adhesion of carbon fiber/PES composites. To obtain a high-quality PES emulsion sizing, the key factor, emulsifier concentration, was studied by dynamic light scattering technique. The results demonstrated that the suitable weight ratio of PES to emulsifier was 8:3, and the resulting PES emulsion sizing had an average particle diameter of 117 nm and Zeta potential of −52.6 mV. After sizing, the surface oxygen-containing functional groups, free energy and wettability of carbon fibers increased significantly, which were advantageous to promote molecular-level contact between carbon fiber and PES. Finally, short beam shear tests were performed to evaluate the interfacial adhesion of carbon fiber/PES composites. The results indicated that PES emulsion sizing played a critical role for the enhanced interfacial adhesion in carbon fiber/PES composites, and a 26% increase of interlaminar shear strength was achieved, because of the improved fiber surface wettability and interfacial compatibility between carbon fiber and PES.
Keywords: Carbon fiber; Emulsion sizing; Interfacial adhesion; Polyether sulfone; Thermoplastic composite;
Defect formation in single layer graphene under extreme ultraviolet irradiation by A. Gao; E. Zoethout; J.M. Sturm; C.J. Lee; F. Bijkerk (745-751).
We study extreme ultraviolet (EUV) radiation induced defects in single-layer graphene. Two mechanisms for inducing defects in graphene were separately investigated: photon induced chemical reactions between graphene and background residual gases, and breaking sp2 bonds, due to photon and/or photoelectrons induced bond cleaving. Raman spectroscopy shows that D peak intensities grow after EUV irradiation with increasing water partial pressure in the exposure chamber. Temperature-programmed desorption (TPD) experiments prove that EUV radiation results in water dissociation on the graphene surface. The oxidation of graphene, caused by water dissociation, is triggered by photon and/or photoelectron induced dissociation of water. Our studies show that the EUV photons break the sp2 bonds, forming sp3 bonds, leading to defects in graphene.
Keywords: EUV; Irradiation; Graphene; Defect;
Density functional theory study on the interaction of CO with the Fe3O4(0 0 1) surface by Pengyan Xue; Zhaoming Fu; Xingli Chu; Yanxing Zhang; Zongxian Yang (752-759).
The adsorption properties of CO on the nondefective and defective (with an oxygen vacancy) B-layer Fe3O4(0 0 1) surfaces (an octahedral environment of iron ions) at different coverages are studied using the spin-polarized density functional theory with the inclusion of on-site Coulomb interaction by introducing Hubbard U parameter (DFT + U) method. It is found that the CO adsorption energy in general increases with the CO coverage. Both types of B-layer Fe3O4(0 0 1) surfaces have the excellent ability for CO oxidation. Comparatively, the defective B-layer Fe3O4(0 0 1) surface has a much stronger CO adsorption ability and a lower CO oxidation ability than the nondefective B-layer Fe3O4(0 0 1) surface. The density of state reveals the bonding mechanism of CO on the two surfaces. The effects of the ambient conditions on the CO adsorption processes are analyzed.
Keywords: Fe3O4(0 0 1) surface; CO adsorption; CO oxidation; DFT + U;
Influence of ion/atom arrival ratio on structure and optical properties of AlN films by ion beam assisted deposition by Jian-ping Meng; Zhi-qiang Fu; Xiao-peng Liu; Wen Yue; Cheng-biao Wang (760-764).
In order to improve the optical properties of AlN films, the influence of the ion/atom arrival ratio on the structure and optical characteristics of AlN films deposited by dual ion beam sputtering was studied by using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry and UV–vis spectroscopy. The films prepared at the ion/atom arrival ratio of 1.4 are amorphous while the crystalline quality is improved with the increase of the ion/atom arrival ratio. The films deposited at the ion/atom arrival ratio of no less than 1.8 have an approximately stoichiometric ratio and mainly consist of aluminum nitride with little aluminum oxynitride, while metallic aluminum component appears in the films deposited at the ion/atom arrival ratio of 1.4. When the ion/atom arrival ratio is not less than 1.8, films are smooth, high transmitting and dense. The films prepared with high ion/atom arrival ratio (≥1.8) display the characteristic of a dielectric. The films deposited at the ion/atom arrival ratio of 1.4 are coarse, opaque and show characteristic of cermet.
Keywords: Ion beam assisted deposition; Ion/atom arrival ratio; Optical constants; Aluminum nitride;
Ni2O3 decoration of In2O3 nanostructures for catalytically enhanced methane sensing by Nguyen Minh Vuong; Nguyen Minh Hieu; Dojin Kim; Byunh Il Choi; Myungbae Kim (765-770).
The explosive limit of methane (CH4) gas concentration is 5%. However, detection of CH4 gas at lower concentrations is essential for prevention and warning purposes in leaking gas systems. In this study, a simple method for fabricating thin films of granular indium oxide (In2O3) particles decorated with nickel oxide (Ni2O3) nanoparticles was developed for high response CH4 gas sensor. The In2O3 granular film was fabricated by sputter deposition of indium, followed by oxidation. Ni2O3 nanoparticles were deposited onto the In2O3 film by arc-discharge deposition of single-wall carbon nanotubes (SWCNTs) with Ni catalyst nanowires, followed by burning the carbon nanotubes. The Ni nanoparticle catalysts deposited on the SWCNTs were then oxidized to Ni2O3.The Ni2O3 nanoparticles on the surface exhibited a catalytic role in methane gas reactions, resulting in reduction of operation temperature. The sensors showed relatively high response percentage per 100 ppm methane gas concentration.
Keywords: Indium oxide; Nickel oxide; Nanowire gas sensor; Methane;
Investigation on surface structure of potassium permanganate/nitric acid treated poly(tetrafluoroethylene) by Congli Fu; Shuling Liu; Tianlong Gong; Aiqun Gu; Zili Yu (771-775).
In the previous articles concerning the treatment of poly(tetrafluoroethylene) (PTFE) with potassium permanganate/nitric acid mixture, the conversion of a hydrophobic to a hydrophilic surface was partially assigned to the defluorination of PTFE and then the introduction of carbonyl and hydroxyl groups into the defluorinated sites. In the present work, PTFE sheets were treated with potassium permanganate/nitric acid, and the surfaces before and after treatment were comparatively characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The surface sediments of the treated PTFE were also determined by atomic absorption spectroscopy (AAS). The results indicate that the conversion of the hydrophobicity to the hydrophilicity on the modified PTFE surface is mainly due to the deposition of hydrophilic manganese oxides which covered the fluorocarbon surface, and no detectable chemical reactions of PTFE occur in the treating process.
Keywords: Poly(tetrafluoroethylene); Potassium permanganate/nitric acid; Manganese oxide; Surface structure;
Covalent co-immobilization of heparin/laminin complex that with different concentration ratio on titanium surface for selectively direction of platelets and vascular cells behavior by Jian Wang; Yuan Chen; Tao Liu; Xue Wang; Yang Liu; Yuan Wang; Junying Chen; Nan Huang (776-786).
Surface biofunctional modification of coronary artery stent to improve the hemocompatibility and selectively accelerate endothelium regeneration but prevent restenosis have been become a new hotspot. For this, a novel method was developed in this work by co-immobilization of Ln and heparin complex on poly-l-lysine modified Ti surface. Take the advantage of the specific interaction between Ln and heparin, Ln and heparin complexes with different concentration ratios were set up for creating different exposure density of these two types of biomolecules. According to biocompatibility evaluation results, the Hep/Ln complexes modified surface displayed less platelet adhesion and activation. Especially, on L(150)H and L(200)H surface, the AT III binding quantity, APTT value and anti-coagulation property of modified surface were significantly promoted. Furthermore, the adherent density and proliferation activity of ECs and EPCs were positively correlated with Ln concentration. Notably, the proliferation of both ECs and EPCs on L(100)H, L(150)H and L(200)H surface were greatly promoted. Another hand, the proliferation activity of SMCs was significantly inhibited on Hep/Ln modified surfaces, which was considered mainly due to the inhibitory effect of heparin to SMCs. According to the existing results, this study demonstrated that in a certain range of heparin and laminin concentration ratio, the biological behavior of platelets, ECs, EPCs and SMCs could be selectively directed. We suggested that this article provided a potential method to construct an adequate platform on a stent surface for accelerate endothelialization with low side effects.
Keywords: Heparin; Laminin; Endothelial cell; Re-endothelialization; Hemocompatibility;
Synthesis of P (St-DVB)/Fe3O4 microspheres and application for oil removal in aqueous environment by Jianyu Mao; Wei Jiang; Junjun Gu; Shuai Zhou; Yue Lu; Tan Xie (787-793).
In this article, magnetic P (St-DVB)/Fe3O4 microspheres with hollow and porous structure were successfully fabricated by a seed swelling polymerization process for fast and selective absorption of oils from water surface. These microspheres, with unsinkable, magnetic, hydrophobic and oleophilic properties, were used to absorb different oils up to 8.42 times of the particles’ weight while repelling water completely. More importantly, the oil-absorbed microspheres could be removed from water surface efficiently via introducing an external magnetic field. This material also shows excellent reusability after washing with ethanol and the oil-absorption capacity of the material was not sharply reduced even after the 10th cycle. The discoveries presented in this study might provide a low-cost, effective, and environmental-friendly approach for the clean-up of oils and organic solvents on the water.
Keywords: Magnetic; Hollow; Porous; P (St-DVB)/Fe3O4 microspheres; Oil removal;
A role of nanotube dangling pyrrole and oxygen functions in the electrochemical synthesis of polypyrrole/MWCNTs hybrid materials by Katarzyna Krukiewicz; Artur P. Herman; Roman Turczyn; Katarzyna Szymańska; Krzysztof K.K. Koziol; Sławomir Boncel; Jerzy K. Zak (794-802).
The effect of the functionalization of multi-walled carbon nanotubes (MWCNTs) on the process of electrochemical co-deposition of MWCNTs and polypyrrole (PPy), as well as the morphology of obtained composites have been demonstrated. As the nanotube components of the hybrids, three types of MWCNT were used, namely c-CVD derived (pristine) MWCNTs, their oxidized counterparts MWCNT-Ox and pyrrole-modified MWCNT-Py. The stability of pristine and functionalized MWCNTs (f-MWCNT) dispersions in tetrahydrofuran and water was studied together with the description of the process of formation PPy/(f-)MWCNT hybrid materials via electrochemical co-deposition. The structural and morphological properties of the hybrids were characterized by Raman spectroscopy, scanning electron microscopy and atomic force microscopy revealing substantial differences among hybrid materials in their surface morphology and the influence of MWCNT functionalization on the orientation of growing PPy chains.
Keywords: Conducting polymer; Polypyrrole; Multi-walled carbon nanotubes; Functionalization of carbon nanotubes; Composites; Hybrid materials;
Bias voltage dependence of molecular orientation of dialkyl ketone and fatty acid alkyl ester at the liquid–graphite interface by Masahiro Hibino; Hiroshi Tsuchiya (803-810).
Molecular orientations of self-assembled 18-pentatriacontanone (as ketone) and stearyl stearate (as ester) monolayers adsorbed on a graphite surface were studied by scanning tunneling microscopy (STM) at the liquid–solid interface. At a positive sample bias, the central areas of the dialkyl ketone and fatty acid alkyl ester molecules in the STM images appeared as two bright regions on both sides of a dim spot and a bright region on one side of a dim spot, whereas at a negative sample bias, the areas appeared dim. This contrast variation indicates that a perpendicular carbon skeleton-plane orientation with the CO pointing down on the surface is favorable for a substrate with positive charge and vice versa because of the greater electronegativity of the oxygen atom. Upon the bias voltage reversal, the delay time for the STM image contrast change in the region was observed on a time scale of minutes. The difference between the delay time lengths for the direction of bias polarity change indicates that the perpendicular configuration with CO pointing up is more stable than that with CO pointing down. These results indicate that the use of an electric field along a direction vertical to the monolayer on the substrate provides control over the orientations of the molecules between two stable states at the liquid–solid interface.
Keywords: Alkyl chain; Carbonyl group; Dipole moment; Scanning tunneling microscopy; Self-assembly;
High-fluence hyperthermal ion irradiation of gallium nitride surfaces at elevated temperatures by A. Finzel; J.W. Gerlach; J. Lorbeer; F. Frost; B. Rauschenbach (811-817).
Wurtzitic GaN films deposited on 6H-SiC(0001) substrates by ion-beam assisted molecular-beam epitaxy were irradiated with hyperthermal nitrogen ions with different fluences at different substrate temperatures. In situ observations with reflection high energy electron diffraction showed that during the irradiation process the surface structure of the GaN films changed from two dimensional to three dimensional at elevated temperatures, but not at room temperature. Atomic force microscopy revealed an enhancement of nanometric holes and canyons upon the ion irradiation at higher temperatures. The roughness of the irradiated and heated GaN films was clearly increased by the ion irradiation in accordance with x-ray reflectivity measurements. A sole thermal decomposition of the films at the chosen temperatures could be excluded. The results are discussed taking into account temperature dependent sputtering and surface uphill adatom diffusion as a function of temperature.
Keywords: Hyperthermal ions; Ion irradiation; Topography; Gallium nitride;
Polyamide–thallium selenide composite materials via temperature and pH controlled adsorption–diffusion method by Remigijus Ivanauskas; Linas Samardokas; Marius Mikolajunas; Darius Virzonis; Jonas Baltrusaitis (818-827).
Single phase polyamide–thallium selenide hybrid functional materials were synthesized for solar energy conversion.Composite materials based on III–VI elements are promising in designing efficient photoelectronic devices, such as thin film organic–inorganic solar cells. In this work, TlSe composite materials were synthesized on a model polymer polyamide using temperature and pH controlled adsorption–diffusion method via (a) selenization followed by (b) the exposure to the group III metal (Tl) salt solution and their surface morphological, chemical and crystalline phase information was determined with particular focus on their corresponding structure–optical property relationship. XRD analysis yielded a complex crystalline phase distribution which correlated well with the optical and surface morphological properties measured. pH 11.3 and 80 °C yielded well defined, low structural disorder composite material surface. After annealing in N2 at 100 °C, polycrystalline PA-Tl x Se y composite materials yielded a single TlSe phase due to the enhanced diffusion and reaction of thallium ions into the polymer. The method described here can be used to synthesize variety of binary III–VI compounds diffused into the polymer at relatively low temperatures and low overall cost, thus providing for a flexible synthesis route for novel composite solar energy harvesting materials.
Keywords: Thallium selenide; Surface properties; Functional materials; XPS; AFM;
Effects of ultrathin AlAs interfacial layer on the structure and optical properties of GaInP epilayer grown on germanium by S.P. Jia; G.F. Chen; W. He; P. Dai; J.X. Chen; S.L. Lu; H. Yang (828-832).
Structure and optical properties of GaInP epilayer with the ultrathin interfacial layers grown on germanium by metal–organic vapor-phase epitaxy (MOVPE) were characterized by high resolution transmission electron microscopy (HRTEM), photoluminescence (PL), Raman as well as surface morphology measurement. A five angstroms (5 Å) AlAs interfacial layer results in the decrease of PL intensity arising from the emission of [Ge(Ga,In) − V (Ga,In)] complex. With the incorporation of AlAs interfacial layer, an increased ordered degree of GaInP epilayer is observed. On the basis of the combination of step–terrace-reconstruction (STR) mode with the dimer-induced-stress model, a CuPt-B type ordering of GaInP which is related to AlAs reconstruction with 2× periodicity process is proposed to explain this effect. Long range order occurs as a consequence of the minimization of the strain energy with increased interfacial layer thickness from 5 Å to 5 nm.
Keywords: Ge/GaInP; Interfacial layer; Diffusion; Degree of order;
Ag3PO4/TiO2 composite for efficient photodegradation of organic pollutants under visible light by Feng-Min Zhao; Lun Pan; Siwen Wang; Qinyi Deng; Ji-Jun Zou; Li Wang; Xiangwen Zhang (833-838).
Photocatalytic degradation of organic pollutants attracts much attention in environment remediation, and it is still a challenge to develop highly efficient and stable visible-light-response photocatalyst. Herein, we synthesized Ag3PO4/TiO2 (P-25) composite via a facile in situ precipitation method to enhance the activity and stability of Ag3PO4. SEM and TEM characterizations indicate TiO2 particles are dispersed on Ag3PO4 surface, resulting in heterojunction interfaces. UV–vis DRS spectra show that TiO2 in the composite does not interfere the absorption of visible light, while the photoluminescence spectra confirm TiO2 inhibits the recombination of photo-induced charges. Therefore, during the photodegradation of organic pollutants under visible light, the composites are much more active than pure Ag3PO4. Moreover, XPS and XRD analysis show the reduction of Ag3PO4 to Ag0 is retarded during the photoreaction. Furthermore, the effect of TiO2 amount in the composites was studied, and AP12 is the most active with the reaction rate being 1.43 times higher than pure Ag3PO4. The strategy of using TiO2 as activity and stability promoter to construct the composite may be useful in developing highly active and stable visible-light photocatalyst for pollutants removal.
Keywords: Photocatalysis; Ag3PO4/TiO2 composite; Visible light; Pollutant removal;
Effects of substrate preheating on the thin-wall part built by laser metal deposition shaping by Kai Zhang; Shijie Wang; Weijun Liu; Risheng Long (839-855).
Laser metal deposition shaping (LMDS) is a state-of-the-art technology that combines rapid prototyping and laser processing. There are many factors affecting the quality, precision, microstructure and performance of the LMDS-deposited parts. Among these factors, substrate preheating is a significant one because it can change the heat history of the LMDS process. Preheating is generally adopted to reduce the residual stresses and the risk of thermal distortion and cracking. However, it changes the heat transfer conditions and affects the final microstructure and properties. In this work a numerical simulation model was established to analyze the heat transfer characteristics between deposited material and substrate, the influence rules of substrate preheating on the thermal behavior during LMDS, and the distribution characters of temperature and stress field. And then, the experimental methods were used to evaluate the effects of substrate preheating on the surface quality, microstructure, composition, hardness distribution, and mechanical properties of as-built thin-wall parts. The experimental results primarily agree with the theoretical analysis and numerical model, which indicates that in terms of the varied thermo-mechanical coupled field, the investigated microstructure and properties of formed components depend considerably on the initial temperature of the substrate, so the LMDS process can be effectively adjusted and controlled by means of substrate preheating.
Keywords: Laser metal deposition shaping (LMDS); Substrate preheating; Thin-wall part; Rapid prototyping; Microstructure and performance; Thermo-mechanical analysis;
Controlling the synergetic effects in (3-aminopropyl) trimethoxysilane and (3-mercaptopropyl) trimethoxysilane coadsorption on stainless steel surfaces by Leena Vuori; Markku Hannula; Kimmo Lahtonen; Petri Jussila; Harri Ali-Löytty; Mika Hirsimäki; Rainer Pärna; Ergo Nõmmiste; Mika Valden (856-866).
A versatile and economic method of preparing covalently-bound and uniform bifunctional silane monolayers on stainless steel is presented. Stainless steel is first electrochemically hydroxylated to enable the formation of a bifunctional overlayer via simultaneous liquid-phase deposition of two organofunctional silanes: (3-aminopropyl)trimethoxysilane (APS) and (3-mercaptopropyl)trimethoxysilane (MPS). The chemical composition, in-depth distribution, molecular orientation and chemical bonds in APS, MPS and APS/MPS layers over a range of APS/MPS mixing ratios are studied with synchrotron radiation mediated photoelectron spectroscopy (SR-PES), conventional X-ray photoelectron spectroscopy (XPS) and energy filtered X-ray photoemission electron microscopy (EF-XPEEM). Inelastic electron energy-loss background (IEEB) analysis is employed to determine the surface morphology of the silanized samples. Coadsorption is shown to produce a covalently-bound and highly ordered monolayer with a controllable MPS surface concentration within APS matrix. The results show evidence of strong synergistic effects during simultaneous adsorption of MPS and APS from liquid phase. While the uptake of MPS alone is low, the coadsorption of MPS and APS strongly enhances both the uptake of MPS and ordering in the APS/MPS overlayer. Results from PES, EF-XPEEM and IEEB analysis reveal that the surface is predominantly covered by a well-ordered APS/MPS monolayer with only slight degree of clustering. Clustering is attributed to different hydrolysis rates in solution and structural irregularities on the substrate. Our results conclusively invalidate the assumption that APS/MPS ratio in a deposited overlayer should correlate linearly with the mixing ratio in solution. The reported insights into the chemical bonds, molecular orientation and morphology in APS/MPS overlayers facilitate site-selective coupling of functional molecules to amino and thiol groups with controllable spatial distribution and, in general, knowledge-based development of novel surface functionalities for stainless steel and other metal (alloy) oxides.
Keywords: Aminopropyl trimethoxysilane; Mercaptopropyl trimethoxysilane; Stainless steel; Synchrotron radiation mediated photoelectron spectroscopy; Bifunctional monolayer;
Effect of direct current density on microstructure of tungsten coating electroplated from Na2WO4-WO3-NaPO3 system by Fan Jiang; Yingchun Zhang; Ningbo Sun; Zhi’ang Liu (867-874).
Pure tungsten coating with body-centered cubic (bbc) structure was successfully electrodeposited from Na2WO4-WO3-NaPO3 molten salt at 1153 K in atmosphere. The coatings comprised an inner layer of tooth-like grains and an outer layer of columnar grains with a thin diffusion layer of tungsten in the Cu substrate. The effects of current density and electrodeposition duration on the morphology and microstructure of the coatings were investigated in this paper. With increasing of current density from 50 to 80 mA cm−2, the grain size of the tungsten coating increased from 7.01 μm to 12.44 μm. With the increase of the current density, the thickness of the coating changed from 25.92 μm to 34.40 μm, and then dropped to 29.72 μm. The preferred orientation of the coatings changed from (2 2 0) to (2 1 1). With the increasing of duration, the grain size and thickness of tungsten coatings increased while the (2 1 1) favored orientation dot not changed. Because of the low current efficiency at long duration of direct current electrodeposition, it should not be suitable for the electroplating of thick tungsten coating.
Keywords: Tungsten coating; Electrodeposition; Molten salt; Microstructure;
Novel lubricated surface of titanium alloy based on porous structure and hydrophilic polymer brushes by Kun Wang; Dangsheng Xiong; Yuxiang Niu (875-883).
On the purpose of improving the tribological properties of titanium alloy through mimicking natural articular cartilage, porous structure was prepared on the surface of Ti6Al4V alloy by anodic oxidation method, and then hydrophilic polymer brushes were grafted onto its surface. Surface morphology of porous oxidized film was investigated by metalloscope and scanning electron microscope (SEM). The composition and structure of modified surface were characterized by Fourier-transform infrared spectroscopy with attenuated total reflection (FTIR/ATR), and the wettability was also evaluated. Friction and wear properties of modified alloys sliding against ultra-high molecular weight polyethylene (UHMWPE) were tested by a pin-on-disc tribometer in physiological saline. The results showed that, the optimum porous structure treated by anodic oxidation formed when the voltage reached as high as 100 V. Hydrophilic monomers [Acrylic acid (AA) and 3-dimethyl-(3-(N-methacrylamido) propyl) ammonium propane sulfonate (DMMPPS)] were successfully grafted onto porous Ti6Al4V surface to form polymer brushes by UV radiation. The change of contact angle showed that wettability of modified Ti6Al4V was improved significantly. The friction coefficient of modified Ti6Al4V was much lower and more stable than untreated ones. The lowest friction coefficient was obtained when the sample was anodized at 100 V and grafted with DMMPPS, and the value was 0.132. The wear of modified samples was also obviously improved.
Keywords: Ti6Al4V alloy; Porous structure; Hydrophilic polymer brush; Friction and wear;
A novel coating onto LiMn2O4 cathode with increased lithium ion battery performance by Jiesheng Zeng; Minsi Li; Xifei Li; Chen Chen; Dongbin Xiong; Litian Dong; Dejun Li; Andrew Lushington; Xueliang Sun (884-891).
A sol–gel method was employed to synthesize LiMn2O4 cathode for lithium ion batteries. Calcination treatment with citric acid results in the reduction of external active materials of the cathode, finally a novel layer coating of MnO was proposed on the surface of LiMn2O4. The structures and morphologies of the as-prepared samples were characterized by XRD, Raman, SEM and HRTEM techniques. It was found that the reaction between LiMn2O4 and citric acid derived carbon occurred during coating process, and the resultant layer was verified to be MnO uniformly coated onto the cathode. Electrochemical performances show that the amount of coating exhibits a significant effect on LiMn2O4 performance, and the optimized MnO coating could exhibit improved battery performance of the LiMn2O4 cathode. The obtained improvement is attributed to decreased Mn dissolution into electrolyte upon cycling resulting from the MnO coating.
Keywords: LiMn2O4; MnO; Cycling performance; Mn dissolution;
A comparative investigation on catalytic oxidation of CO, benzene, and toluene over birnessites derived from different routes by Qing Ye; Heng Lu; Jun Zhao; Shuiyuan Cheng; Tianfang Kang; Dao Wang; Hongxing Dai (892-901).
Catalytic oxidation of CO, benzene, and toluene was studied over the octahedral layered birnessites (OL-1, OL-2, OL-3, and OL-4) derived from different routes. Physicochemical properties of the samples were characterized by a number of different analytical techniques. It is found that all of the samples have birnessite-type octahedral layered structure and an interlayer spacing of ca. 0.72 nm. Surface areas and pore volumes of the OL-3 and OL-4 samples were much higher than those of the OL-1 and OL-2 samples. There was co-presence of Mn3+, Mn4+ and/or Mn2+ on the surface of these samples. Based on the manganese ion contents, the average oxidation states of surface Mn species in the birnessite samples were in the range of 3.2–3.5, which was lower than those (3.5–3.9) obtained from the H2-TPR studies. The amounts of oxygen vacancies and lattice oxygen mobility of the OL-1 and OL-4 samples were higher than those of the OL-2 and OL-3 samples. Either in CO oxidation or in benzene or toluene oxidation, the catalytic activity decreased in the order of OL-1 > OL-4 >> OL-3 > OL-2, with the OL-1 sample showing the best performance (T 50% = 115 and T 100% = 150 °C for CO oxidation at 15,000 mL/(g h), T 50% = 200 °C and T 95% = 240 °C for benzene oxidation, and T 50% = 190 °C and T 95% = 230 °C for toluene oxidation at 40,000 mL/(g h)). We conclude that catalytic performance of the octahedral layered birnessite samples was associated with the Mn oxide nature, surface lattice oxygen mobility, and reducibility.
Keywords: Octahedral layered birnessite catalyst; Oxygen mobility; Reducibility; CO oxidation; Volatile organic compound removal;
Thermal and stress studies of the 30.4 nm Mo/Si multilayer mirror for the moon-based EUV camera by Yunpeng Li; Hongji Zhang; Haifeng Wang; Fei He; Xiaodong Wang; Yang Liu; Suli Han; Xin Zheng; Xiaoduo Wang; Bin Chen; Haibo Li; Bo Chen; Jianlin Cao (902-907).
To investigate the environmental adaptability of the Mo/Si multilayers on lunar surface, we studied the stability and stress of Mo/Si multilayers under the low and high temperature environment. The in-situ X-ray diffraction (XRD) and the ex-situ intrinsic stress are measured in the temperature range from −135 °C to 600 °C and from −190 °C to 600 °C, respectively. The results demonstrate that the periodic structure of Mo/Si multilayers is stable between −135 °C and 300 °C. The stress is unaffected under low temperature and it gradually increases from −260 MPa to 1G MPa when the temperature changes from room temperature to 600 °C. Above 600 °C, large tensile stress leads to folds and cracks in the film. Thus, the large temperature range on lunar surface has little effect on the structure, performance and stress of the Mo/Si multilayers and the high temperature in lunar day releases the stress of the multilayer mirror.
Keywords: X-rays; Soft X-ray; Extreme ultraviolet (EUV); Multilayers; Thermal stability; Residual stress;
Interface bonding between particle and substrate during HVOF spraying by Ce Sun; Lei Guo; Guanxiong Lu; Yanbing Lv; Fuxing Ye (908-913).
The impact processes of Ni particles at initial temperature of 900 K on Al, Cu and Steel substrates were numerically analyzed by using ANSYS/LS-DYNA. Initial kinetic energy of the particle dissipated to particle and substrate simultaneously, the proportion of which was defined as energy distribution coefficient (K). The K values for Ni/Al, Ni/Cu and Ni/steel combinations were approximated to 4, 0.4 and 0.1, respectively. Individual Ni60 particles were deposited experimentally onto 6061–T6 aluminum alloy, copper and 304 stainless steel by High Velocity Oxy-fuel (HVOF) spraying. The contact between Ni particles and three substrates was not perfect. The bonding ratio, which is the effective contact area divided by total area, for Ni/Cu combination is 55.41%, larger than those for Ni/Al (40.78%) and Ni/steel (32.70%) combinations, indicating that moderate K value is beneficial for interface bonding between particle and substrate.
Keywords: Deposition behavior; Energy distribution; Impact model; HVOF;
Synthesis and characterization of amoxicillin derived silver nanoparticles: Its catalytic effect on degradation of some pharmaceutical antibiotics by Y. Junejo; A. Güner; A. Baykal (914-922).
We synthesized novel amoxicillin derived silver nanoparticles (Amp-Ag (0) NPs) in aqueous solution by one-pot simple synthetic method by reducing silver nitrate by the help of amoxicillin antibiotic as a reducing/capping agent and NaOH as the catalyst for reaction enhancement. The formation of the Amp-Ag (0) NPs was monitored using UV–Vis absorption spectroscopy which confirmed the formation of Amp-Ag (0) NPs by exciting the typical surface plasmon absorption maxima at 404 nm. Transmission electron microscopy (TEM) confirmed the spherical morphology and monodispersed Amp-Ag (0) NPs with particle size 6.87 ± 2.2 nm. The antibacterial activities of the antibiotics were evaluated against Gram-negative bacteria Escherichia coli, Salmonella enteritidis, Pseudomonas aeruginosa and Gram-positive bacteria Streptococcus pneumonia, Streptococcus pyogenes, Staphylococcus aureus by the disk diffusion method. Whereas standard antibiotics showed normal zone of inhibition, the reduced ones with Amp-Ag (0) NPs showed no inhibition zone. The antimicrobial results therefore reveal that newly synthesized Amp-Ag (0) NPs had an excellent catalytic activity as catalyst for the 100% reduction of antibiotics i.e. cefdinir, cefditoren, cefiximee, ceftriaxone sodium and doxycycline, which was carried out in just 2–5 min. They were recovered easily from reaction medium and reused with enhanced catalytic potential five times. Based upon these results it has been concluded that Amp-Ag (0) NPs are novel, rapid, and highly cost-effective for environmental safety against pollution by antibiotics in wastewater and extendable for control of other reducible contaminants as well.
Keywords: Antibiotics; Silver nanoparticles; Reducing agent; Antimicrobial activity; Wastewater;
Effects of metal elements in catalytic growth of carbon nanotubes/graphene: A first principles DFT study by Jingde Li; Eric Croiset; Luis Ricardez-Sandoval (923-928).
Role of metals in the catalytic Chemical Vapor Deposition (CVD) growth of carbon nanotubes (CNTs) or graphene was investigated using DFT. Crucial processes involved in the growth of CNTs/graphene: methane dissociation to produce C, C diffusion and nucleation kinetics were studied on the (1 1 1) surface of different transition metals, i.e., Fe, Co, Ni, and Cu. Based on the DFT calculation results, the present study explains why Ni-based catalyst is a suitable CVD substrate for growing CNTs: it has a moderate reactivity towards methane dissociation; low energy barrier for C atom surface diffusion, which makes C to diffuse easily to the metal/CNTs edges and contribute to CNTs growth; relatively high nucleation barriers, making it more resistant for deactivation caused by the cover of carbon clusters. Meanwhile, this study also shows that Cu may be an appropriate catalyst for graphene synthesis due to the particularly low diffusion and nucleation barriers of C atoms on Cu, which suggest that C atoms tend to be more uniformly distributed and nucleate easily on the Cu surface. Key limitation of Cu is the low reactivity of this metal towards methane dissociation. Since Fe and Ni are very reactive towards C―H bond breaking, Cu based alloys, e.g. Cu8Ni, were proposed as a suitable catalyst for graphene production.
Keywords: Carbon nucleation; DFT; Diffusion; Methane; Transition metal;
Surface chemical and photocatalytic consequences of Ca-doping of BiFeO3 as probed by XPS and H2O2 decomposition studies by Mohamed I. Zaki; Wegdan Ramadan; Ali Katrib; Abdallah I.M. Rabee (929-934).
Pure and Ca-doped Bi1−x Ca x FeO3 samples were prepared with x = 0.0–0.2, adopting a sol–gel method. Previously reported studies performed on similarly composed and prepared samples revealed that Ca-doping, above solubility limit (namely at ≥10%-Ca), results in phase separation and formation of BiFeO3/α(γ)-Fe2O3 nanocomposite particles. Hetero p/n nanojunctions thus established were considered to help separating photo-generated electron–hole pairs and, therefore, explain consequent promotion of photo-Fenton catalytic activity of BiFeO3 towards methylene blue degradation in presence of H2O2 additive. However, the encompassed decomposition of H2O2 was not addressed. To bridge this gap of knowledge, the present investigation was designed to assess Ca-doping-effected surface chemical modifications and gauge its impact on the heterogeneous photo-/thermo-catalytic activity of BiFeO3 towards H2O2 decomposition, by means of X-ray photoelectron spectroscopy (XPS) and H2O2 decomposition gravimetry. XPS results revealed generation of high binding energy Bi 4f and Fe 2p states, as well as enhancement of the surface basicity, upon doping to 10%-Ca. These surface chemical consequences are rendered hardly detectable upon further increase of the dopant magnitude to 20%-Ca. In parallel, the H2O2 decomposition activity of the ferrite, under natural visible light, is enhanced to optimize upon Ca-doping at 10%, and, then, decreased on further doping to 20%. H2O2 decomposition experiments carried out in absence of light indicate that the doping promoting impact is reflected essentially in the photocatalytic activity. Accordingly, the observed surface chemical consequences of Ca-doping are considered to consolidate the p/n nanojunctions consequently established in the material bulk, by retarding recombination of visible light generated electron–hole pairs, thus enhancing the heterogeneous photocatalytic activity of BiFeO3.
Keywords: Bismuth ferrite; Calcium-doping; Surface chemical consequences; Visible-light photocatalytic consequences; X-ray photoelectron spectroscopy; H2O2 decomposition gravimetry;
Structural evolution of yttrium nanolayer inserted in FeNi/Y nanomultilayered film by Wei Li; Ping Liu; Ke Zhang; Fengcang Ma; Xinkuan Liu; Xiaohong Chen; Daihua He (935-939).
The FeNi/Y nanomultilayered films with different Y layer thickness (t Y) were synthesized by magnetron sputtering. The structural evolution of Y nanolayer with increase in t Y was investigated. When t Y was less than 2 nm, Y layers transformed to fcc structure under the template effect of FeNi layers and grew epitaxially with FeNi. With t Y of 3 nm, Y layers could not maintain the epitaxial growth, but present a transient amorphous state. As t Y further increases to 4 nm, Y layers transformed into the stable hcp structure. The microstructural evolution sequence of Y layers was fcc→amorphous→hcp structure, which could be explained by a thermodynamic model.
Keywords: FeNi/Y nanomultilayered film; Structural evolution; Interface structure; Amorphization; Thermodynamic model;
Detection of explosives by surface enhanced Raman scattering using substrate with a monolayer of ordered Au nanoparticles by T.F. Chen; S.H. Lu; A.J. Wang; D. Zheng; Z.L. Wu; Y.S. Wang (940-945).
Monolayers with different structures arranged by 5 nm Au nanoparticles were grown using a self-assembly method on Si substrates. Raman spectra of ammonium nitrate (NH4NO3) and cyclotrimethylenetrinitramine (RDX) explosives adsorbed on bare and Au nanoparticle covered Si substrates were measured. Effects of Au monolayers and their structures on surface enhanced Raman scattering (SERS) of NH4NO3 and RDX were investigated. The monolayer arranged by Au nanoparticles into linear arrays is more sensitive to the explosives than that arranged into hexagonal close-packed structure. The detection limit using the substrate covered by a monolayer of Au nanoparticle linear arrays is about 7.7 ppm for NH4NO3 and 0.19 ppm for RDX. The integrated intensity of the vibration peak increases linearly with an increase in explosive concentration in log–log scales for both NH4NO3 and RDX. The enhancement factor is 7.0 × 104 for RDX. Monolayers of Au nanoparticles arranged into linear arrays have potential applications in detecting or identifying explosives at very low levels of concentration.
Keywords: Self-assembly; Ordered Au nanoparticles; Linear arrays; SERS; Explosives;
Optimizing production of hydroxyapatite from alkaline residue for removal of Pb2+ from wastewater by Yubo Yan; YanPeng Wang; Xiuyun Sun; Jiansheng Li; Jinyou Shen; Weiqing Han; Xiaodong Liu; Lianjun Wang (946-954).
Alkaline residue, a common solid waste generated from the ammonia-soda process for the production of soda ash, has been converted into hydroxyapatite for Pb2+ removal from wastewater. Response surface methodology was used to optimize the preparation conditions which were Ca/P (molar ratio), reaction temperature and reaction time, with the Pb2+ removal percentage as targeted response. The optimum conditions were identified to be Ca/P of 1.29, reaction temperature of 165.87 °C and reaction time of 14.5 h. Batch tests were conducted to evaluate the adsorption performance of optimum adsorbent (O-HAP), and the adsorption data were analyzed with different kinetic and isotherm models. The results showed that the pseudo-second order kinetic model and Langmuir isotherm model could best describe the adsorption of Pb2+ on O-HAP. The maximum adsorption capacity calculated from Langmuir equation was 1429 mg/g, which was greater than other familiar adsorbents. The MINTEQ results predicted that the formation of different Pb precipitates was the main mechanism in Pb2+ removal process, which was in good agreement with the kinetic and thermodynamic studies and were confirmed by the SEM-EDS and XRD analysis. In addition to aqueous medium, the O-HAP also could efficiently immobilize Pb2+ from contaminated soil.
Keywords: Alkaline residue; Response surface methodology; Hydroxyapatite; Lead ion; Mechanism;
Surface characterization studies of CuO-CeO2-ZrO2 catalysts for selective catalytic reduction of NO with NH3 by Qiulin Zhang; Lisi Xu; Ping Ning; Junjie Gu; Qingqing Guan (955-961).
The SCR activities, morphology, particles dimension, and the surface chemical state of CeO2-ZrO2-CuO catalysts were obviously influenced by the preparation method. The high surface area, the synergistic effect between copper and ceria, and the highly dispersed copper species were responsible for the high SCR activity of the CeO2-ZrO2-CuO catalyst.A series of CuO-CeO2-ZrO2 catalysts were prepared by different methods and applied to the selective catalytic reduction of NO with NH3 reaction at low temperature. The results showed that the SCR activities, morphology, particles dimension, and the surface chemical state of CuO-CeO2-ZrO2 catalysts were obviously influenced by the preparation method. The SCR performance results showed that the CuO-CeO2-ZrO2 catalyst prepared by co-precipitation method presented the best activity in the temperature range of 125–180 °C. The characterization results showed that the Ce4+, Ce3+, Cu2+ and Cu+ species were coexistence in the CuO-CeO2-ZrO2 catalysts, and the Cu species mainly existed as Cu2+. It was also found that the high surface area, the synergistic effect between copper and ceria, enhanced acidity and the highly dispersed copper species were responsible for the high SCR activity of the CuO-CeO2-ZrO2 catalyst.
Keywords: Selective catalytic reduction; Synergistic effect; CuO-CeO2-ZrO2; Highly dispersed;
Effect of surface nanostructuring of aluminum alloy on post plasma electrolytic oxidation by H.R. Masiha; H.R. Bagheri; M. Gheytani; M. Aliofkhazraei; A. Sabour Rouhaghdam; T. Shahrabi (962-969).
AA1230 aluminum alloy samples were coated by plasma electrolytic oxidation (PEO). The samples with and without surface mechanical attrition treatment (SMAT) were coated in phosphate- and silicate-based electrolytes and in the presence of Si3N4 nanoparticles. Besides, morphology and properties of the produced coatings were examined. To determine the corrosion resistance of the coatings, potentiodynamic polarization technique was used. All coated samples were subjected to wear test in order to compare coating wear properties of the SMATed and unSMATed samples. Then the effects of SMAT preprocessing and its duration on the properties of the coatings prepared by PEO were investigated. The results indicated that the mean coefficient of friction of the coated samples decreased by near 83% with respect to the uncoated (raw) samples. Furthermore, the SMATed samples showed thicker coatings as compared to unSMATed samples due to an increase in their matrix reactivity.
Keywords: Aluminum; Corrosion; Plasma electrolytic oxidation; Nanocrystallization; Wear;
Humidity sensing properties of morphology-controlled ordered silicon nanopillar by Wei Li; Mingyue Hu; Pengpeng Ge; Jing Wang; YanYan Guo (970-973).
Ordered silicon nanopillar array (Si-NPA) was fabricated by nanosphere lithography. The size of silicon nanopillars can be easily controlled by an etching process. The period and density of nanopillar arrays are determined by the initial diameter of polystyrene (PS) spheres. It was studied as a sensing material to detect humidity. Room temperature current sensitivity of Si-NPA sensor was investigated at a relative humidity (RH) ranging from 50 to 70%. As a result, the measured current showed there was a significant increase at 70% RH. The response and recovery time was about 10 s and 15 s. These excellent sensing characteristics indicate that Si-NPA might be a practical sensing material.
Keywords: Ordered silicon nanoillar; Morphology-controlled; Humidity sensing;
Effect of titanium nitride/titanium coatings on the stress corrosion of nickel–titanium orthodontic archwires in artificial saliva by Jia-Kuang Liu; I-Hua Liu; Cheng Liu; Chen-Jung Chang; Kuan-Chen Kung; Yen-Ting Liu; Tzer-Min Lee; Jin-Long Jou (974-981).
The purpose of this investigation was to develop titanium nitride (TiN)/titanium (Ti) coating on orthodontic nickel–titanium (NiTi) wires and to study the stress corrosion of specimens in vitro, simulating the intra-oral environment in as realistic a manner as possible. TiN/Ti coatings were formed on orthodontic NiTi wires by physical vapor deposition (PVD). The characteristics of untreated and TiN/Ti-coated NiTi wires were evaluated by measurement of corrosion potential (E corr), corrosion current densities (I corr), breakdown potential (E b), and surface morphology in artificial saliva with different pH and three-point bending conditions. From the potentiodynamic polarization and SEM results, the untreated NiTi wires showed localized corrosion compared with the uniform corrosion observed in the TiN/Ti-coated specimen under both unstressed and stressed conditions. The bending stress influenced the corrosion current density and breakdown potential of untreated specimens at both pH 2 and pH 5.3. Although the bending stress influenced the corrosion current of the TiN/Ti-coated specimens, stable and passive corrosion behavior of the stressed specimen was observed even at 2.0 V (Ag/AgCl). It should be noted that the surface properties of the NiTi alloy could determine clinical performance. For orthodontic application, the mechanical damage destroys the protective oxide film of NiTi; however, the self-repairing capacity of the passive film of NiTi alloys is inferior to Ti in chloride-containing solutions. In this study, the TiN coating was found able to provide protection against mechanical damage, while the Ti interlayer improved the corrosion properties in an aggressive environment.
Keywords: TiN/Ti coating; Orthodontic; Nickel–titanium (NiTi); Stress corrosion; Bending stress; Localized corrosion;
Impacts of Au-doping on the performance of Cu/HfO2/Pt RRAM devices by Tingting Tan; Tingting Guo; Xi Chen; Xiaojing Li; Zhengtang Liu (982-985).
The impact of Au-doping on the resistive switching properties of a Cu/HfO2/Pt resistive random access memory (RRAM) device is investigated. The significantly enhanced performances are achieved in the Cu/HfO2: Au/Pt device, including low set voltages, improved uniformity of switching parameters, enough ON/OFF ratio. This performance improvement in Cu/HfO2: Au/Pt is clarified to the suppressed stochastic formation of oxygen vacancy conducting filaments in the HfO2 film by Au―O bond effect. The validity of the trivalent dopants in future application of HfO2-based RRAM devices is also identified.
Keywords: Au-doping HfO2; Oxygen vacancy; Conducting filament;
Sputtered titanium oxynitride coatings for endosseous applications: Physical and chemical evaluation and first bioactivity assays by Oksana Banakh; Mira Moussa; Joel Matthey; Alessandro Pontearso; Maria Cattani-Lorente; Rosendo Sanjines; Pierre Fontana; Anselm Wiskott; Stephane Durual (986-993).
Titanium oxynitride coatings (TiN x O y ) are considered a promising material for applications in dental implantology due to their high corrosion resistance, their biocompatibility and their superior hardness. Using the sputtering technique, TiN x O y films with variable chemical compositions can be deposited. These films may then be set to a desired value by varying the process parameters, that is, the oxygen and nitrogen gas flows. To improve the control of the sputtering process with two reactive gases and to achieve a variable and controllable coating composition, the plasma characteristics were monitored in-situ by optical emission spectroscopy.TiN x O y films were deposited onto commercially pure (ASTM 67) microroughened titanium plates by reactive magnetron sputtering. The nitrogen gas flow was kept constant while the oxygen gas flow was adjusted for each deposition run to obtain films with different oxygen and nitrogen contents. The physical and chemical properties of the deposited films were analyzed as a function of oxygen content in the titanium oxynitride. The potential application of the coatings in dental implantology was assessed by monitoring the proliferation and differentiation of human primary osteoblasts.
Keywords: Titanium oxynitride coating; Reactive magnetron sputtering; Bioactivity; Dental implant;
Band alignment studies of Al2O3/CuGaO2 and ZnO/CuGaO2 hetero-structures grown by pulsed laser deposition by R.S. Ajimsha; Amit. K. Das; M.P. Joshi; L.M. Kukreja (994-999).
We have studied the band offset and alignment of pulsed laser deposited Al2O3/CuGaO2 and ZnO/CuGaO2 hetero-structures using photoelectron spectroscopy. Al2O3/CuGaO2 interface exhibited a type I band alignment with valance band offset (VBO) of 4.05 eV whereas type II band alignment was observed in ZnO/CuGaO2 hetero-structure with a VBO of 2.32 eV. Schematic band alignment diagram for the interface of these hetero-structures has been constructed. Band offset and alignment studies of these heterojunctions are important for gaining insight to the design of various optoelectronic devices based on such hetero-structures.
Keywords: PLD; Oxide thin film; Band offset;
Preparation and characterization of high-transmittance AZO films using RF magnetron sputtering at room temperature by Jian Chen; Yihua Sun; Xin Lv; Derong Li; Liang Fang; Hailin Wang; Xiaohua Sun; Caihua Huang; Haizhou Yu; Ping Feng (1000-1003).
Aluminum-doped zinc oxide (AZO) thin films with 250 nm thickness had been prepared on soda-lime glass substrate without heated by RF magnetron sputtering using a ceramic target. The microstructure, surface morphology, electrical and optical properties of AZO thin films had been investigated by X-ray diffraction, scanning electron microscope, four-point probe method and optical transmission spectroscopy. The results indicated that all of the films obtained were polycrystalline with a hexagonal structure and oriented with the c-axis perpendicular to the substrate. The resistivity decreased and transmittance improved with the sputtering power increase. The minimum resistivity of 2.55 × 10−3 Ω cm combined with highest transmittance of 91% was obtained at a sputtering power of 400 W. The optical bandgap at different sputtering power varied among 3.81–4.04 eV.
Keywords: AZO thin films; Room temperature; Optoelectronic properties; RF magnetron sputtering;
Multi- and few-layer graphene on insulating substrate via pulsed laser deposition technique by Indrajeet Kumar; Alika Khare (1004-1009).
In this paper, multilayer and few layer graphene (FLG) fabricated on fused silica substrate by pulsed laser deposition (PLD) technique without using any catalyst is reported. The effect of deposition temperature onto the formation of graphene layers is investigated. Raman spectra showed the characteristic features of sp2 bonded carbon atoms; G band, D band and 2D band. The line shape of 2D band structure and the relative intensities of G and 2D bands were used to estimate the number of graphene layers. The graphene layers deposited via PLD at room temperature has I 2D/I G ratio ∼0.33, confirming the formation of multilayer whereas that of deposited at substrate temperature 700 °C is ∼0.47 confirming the formation of less than five layers of graphene; few layers graphene. The decrease in separation of subpeaks of 2D band with deposition temperature further confirms the reduction in the number of layers of graphene from ∼10 deposited at room temperature to less than 5 layers at that of 700 °C. The surface morphology of the deposited samples was recorded by field emission scanning electron microscope and transmission electron microscope.
Keywords: Graphene; Pulsed laser deposition; Raman spectroscopy;
Low fraction of hexagonal inclusions in thick and bulk cubic GaN layers by S.N. Waheeda; N. Zainal; Z. Hassan; S.V. Novikov; A.V. Akimov; A.J. Kent (1010-1014).
We report present a study of the formation of hexagonal inclusions in thick (∼5 μm) and bulk (∼50 μm) cubic GaN (c-GaN) layers grown on GaAs (0 0 1) substrates. Surface analysis of both samples revealed the evidence of hexagonal grains on the surface. However, larger grains were formed in the bulk sample. In the XRD measurement, the signature of the h-GaN in the bulk sample was more visible than the thick sample. This is consistent with the PL measurement, of which the h-GaN peak emission was found to be more intense in the bulk sample with respect to the thick sample. Such observations showed that the fraction of hexagonal inclusions had increased by increasing the thickness of the c-GaN layer. As presented in the Raman spectroscopy, the signals of the h-GaN were dominant, but the transverse optical (TO) and longitudinal optical (LO) modes of c-GaN were still observable at ∼559 cm−1 and ∼739 cm−1, respectively. Finally, a micro-PL measurement showed that the average content of the hexagonal inclusions in the c-GaN layer up to ∼50 μm was less than 22%, suggesting that our samples have a lower hexagonal GaN content than some reported thin c-GaN samples.
Keywords: Hexagonal inclusions; Thick cubic GaN; Bulk cubic GaN;
Effect of pH on the synthesis and characteristics of RGO–CdS nanocomposites by Fatima Tuz Johra; Woo-Gwang Jung (1015-1021).
The effect of pH on the synthesis of reduced graphene oxide (RGO)–CdS nanocomposites via a hydrothermal method was investigated. Higher pH is more favorable for the formation of good quality RGO–CdS nanocomposites. The photocatalytic performance of the composites was investigated by measuring the reduction of Cr(VI), and the composite synthesized at high pH (=11) exhibited a 76% removal rate of Cr(VI). At high pH, the development of CdS particles of smaller sizes and the maximum number of π-electrons available in RGO increased the effective surface area available for light absorption, fast electron transport, and enhanced light absorption intensity. The staircase band structure of CdS in combination with RGO helped to inhibit electron–hole recombination, which enhanced photocatalytic activity.
Keywords: Reduced graphene oxide; Cadmium sulfide; pH; Photocatalyst; Staircase band structure;
Characterization of interface and border traps in ALD Al2O3/GaN MOS capacitors with two-step surface pretreatments on Ga-polar GaN by S. Gu; E.A. Chagarov; J. Min; S. Madisetti; S. Novak; S. Oktyabrsky; A.J. Kerr; T. Kaufman-Osborn; A.C. Kummel; P.M. Asbeck (1022-1027).
Atomic layer deposited (ALD) Al2O3/Ga-polar GaN(0001) metal–oxide–semiconductor (MOS) capacitors have been prepared with surface pretreatments including ex-situ wet sulfide passivation and in-situ cyclic trimethylaluminum (TMA)/hydrogen plasma exposure. Capacitance–voltage characterization showed that the two-step surface preparation led to reductions in the densities of both interface traps and border traps. The influence of the pretreatments on interfacial bonding was investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). DFT calculations correlate the electronic properties with the interfacial bonding from the two-step surface preparation. The results are consistent with the surface preparations influencing the nucleation density of the ALD films and, therefore, the defect density of the interface and neighboring oxide.
Keywords: Atomic layer deposition (ALD); Gallium nitride (GaN); High-k dieletrics; Interface trap density; Border trap density;
One-step synthesis of water-dispersible cysteine functionalized magnetic Fe3O4 nanoparticles for mercury(II) removal from aqueous solutions by Xiaofang Shen; Qin Wang; WenLing Chen; Yuehong Pang (1028-1034).
Using Fe2+ as precursors, air as oxidant and cysteine as protectant, this novel cysteine functionalized Fe3O4 magnetic nanoparticles (Cys-Fe3O4 MNPs) was facilely one-pot synthesized at room temperature by oxidation–precipitation method with the assistance of sonication. Then the Cys-Fe3O4 MNPs were demonstrated as an inexpensive and quite efficient magnetic nano-adsorbent for as high as 95% Hg(II) removal efficiency. These results indicated that Cys-Fe3O4 MNPs is a potentially attractive material for the removal of Hg(II) from water.Cysteine functionalized Fe3O4 magnetic nanoparticles (Cys-Fe3O4 MNPs) were prepared facilely for Hg(II) removal from aqueous solutions. Using Fe2+ as precursors, air as oxidant and Cys as protectant, this novel material was one-pot synthesis at room temperature by oxidation–precipitation method with the assistance of sonication. The MNPs were characterized by TEM, VSM, FTIR, X-ray powder diffraction analysis (XRD) and TGA methods. Under the optimum experimental conditions, the removal efficiency was as high as 95% and the maximum sorption capacity is found to be 380 mg/mol for Hg(II). Study on adsorption kinetics shows that adsorption of Hg(II) onto Cys-Fe3O4 MNPs follows pseudo-first-order kinetic model and the adsorption rate constant was 0.22 min−1. Additionally, the Hg(II)-loaded Cys-Fe3O4 MNPs could be easily regenerated up to 95% using 1.0 M acetic acid. These results indicated that Cys-Fe3O4 MNPs is a potentially attractive material for the removal of Hg(II) from water.
Keywords: Mercury(II) removal; Cysteine modified; Fe3O4 nanoparticles; Magnetic separation;
Preparation and characterization of heat-assisted PbS/TiO2 thin films by Yanyan Xu; Miao Zhang; Jianguo Lv; Miaocui Zhang; Xishun Jiang; Xueping Song; Gang He; Zhaoqi Sun (1035-1040).
Heat-assisted PbS/TiO2 thin films with different reaction temperatures were prepared. Microstructure, morphology, optical and photoelectron-chemical properties of the as-synthesized thin films were investigated systematically. For the PbS/TiO2 thin films with reaction temperature changing from 10 to 95 °C, PbS particles obtained by successive ionic layer adsorption and reaction are galena phase, the mean size of PbS particles decreases firstly and then increases, the coverage of PbS particles on surface increases. At the same time, red shift in the adsorption edges from 416 to 594 nm has been detected, and the optical band gap E g decreases from 3.58 to 2.88 eV. What's more, the intensity of photoluminescence increases firstly and then decreases. The photochemistry measurement suggests that the sample prepared at 60 °C possesses the highest photocurrent in the first test cycle. However, the value of photocurrent decreases immediately with increasing the test cycle. The effect of the reaction temperature on the microstructure, morphology, optical and photoelectron-chemical properties of PbS/TiO2 thin films have been discussed in detail.
Keywords: PbS/TiO2; UV–vis; Photoluminescence; Photoelectron-chemical;
Plasmonic properties of silver nanoparticles embedded in diamond like carbon films: Influence of structure and composition by Š. Meškinis; A. Čiegis; A. Vasiliauskas; A. Tamulevičienė; K. Šlapikas; R. Juškėnas; G. Niaura; S. Tamulevičius (1041-1046).
In the present study optical properties of hydrogenated diamond like carbon nanocomposite films containing silver nanoparticles (DLC:Ag) deposited by direct current (DC) unbalanced reactive magnetron sputtering were studied in 180–1100 nm range. Different substrate bias was used during deposition of the films. Structure of the films was investigated by multiwavelength Raman scattering spectroscopy and X-ray diffractometry (XRD). Chemical composition of the samples was studied by X-ray photoelectron spectroscopy (XPS), surface morphology was investigated by atomic force microscopy (AFM). Red shift of the surface plasmon resonance peak of DLC:Ag films with the increase of Ag atomic concentration was observed. It was found that high atomic concentration of oxygen in DLC:Ag films results in some redshift of the plasmonic peak, too. Such a behavior is explained by increase of the refractive index of the dielectric medium surrounding silver nanoparticle due to possible presence of the silver oxide interlayer at the Ag nanocluster and diamond like carbon matrix interface. It was demonstrated that influence of the increased Ag atomic concentration on position of the surface plasmon resonance peak of DLC:Ag films clearly prevails influence of the increased sp3/sp2 ratio of the diamond like carbon matrix. Correlation between the structure of Ag nanocrystallites studied by XRD and position of the surface plasmon resonance peak position was observed.
Keywords: Diamond like carbon films containing silver; Reactive magnetron sputtering; Optical properties; Surface plasmon resonance; Raman scattering spectroscopy; Chemical composition;
Step-by-step self-assembly of manganese phthalocyanine on Bi(1 1 1) surface: From single molecule to two-dimensional domains by Ting-Ting Zhang; Chun-Jie Wang; Kai Sun; Hong-Kuan Yuan; Jun-Zhong Wang (1047-1051).
The adsorption and self-assembly of manganese phthalocyanine (MnPc) molecules on Bi(1 1 1) are investigated by means of low-temperature scanning tunneling microscope (STM). At low temperature (4.6 K), isolated MnPc molecules adsorb flatly on Bi(1 1 1) with the two opposing lobes aligned in the direction of surface base vectors. When temperature is increased to 78 K, individual MnPc molecules rotate around the central Mn ion until they meet other MnPc molecules forming self-assembled structures. With the coverage increasing, MnPc molecules show a structural evolution from single molecules to molecular chains, and finally to 2-D domains. In particular, high-resolution STM images reveal there are two mirrored molecular chains with alternating arrangement in the 2-D domains. Annealing the sample to room temperature leads to a phase separation such that each molecule chains appeared only in the respective domains.
Keywords: STM; MnPc; Semimetallic Bi(1 1 1); Molecular chains; Self-assembly; Phase-separation;
Synthesis of green nano iron particles (GnIP) and their application in adsorptive removal of As(III) and As(V) from aqueous solution by Kumar Suranjit Prasad; Pooja Gandhi; Kaliaperumal Selvaraj (1052-1059).
The present study reports a new approach to synthesise nano iron particles using leaf extract of Mint (Mentha spicata L.) plant. The synthesised GnIPs were subjected to detailed adsorption studies for removal of arsenite and arsenate from aqueous solution of defined concentration. Iron nanoparticles synthesised using leaf extract showed UV–vis absorption peaks at 360 and 430 nm. TEM result showed the formation of polydispersed nanoparticles of size ranging from 20 to 45 nm. Nanoparticles were found to have core–shell structure. The planer reflection of selected area electron diffraction (SAED) and XRD analysis suggested that iron particles were crystalline and belonged to fcc (face centred cubic) type. Energy-dispersive X-ray analysis (EDAX) shows that Fe was an integral component of synthesised nanoparticles. The content of Fe in nanoparticles was found to be 40%, in addition to other elements like C (16%), O (19%) and Cl (23%). FT-IR study suggested that functional groups like ―NH, ―C＝O, ―C＝N and ―C＝C were involved in particle formation. The removal efficiency of GnIP-chitosan composite for As(III) and As(V) was found to be 98.79 and 99.65%. Regeneration of adsorbent suggested that synthesised green GnIP may work as an effective tool for removal of arsenic from contaminated water.
Keywords: Arsenite; Arsenate; Adsorption; Iron nanoparticles; M. spicata L.; Kinetics;
Lewis basicity, adhesion thermodynamic work and coordinating ability on aminated silicon surfaces by M. Alejandra Sánchez; Sergio A. Paniagua; Ignacio Borge; Christian Viales; Mavis L. Montero (1060-1067).
Silicon(1 0 0) surfaces have been modified with three different amines (aniline, benzylamine and dodecylamine) and diamines (4-aminopyridine, 4-aminomethylpyridine, 1,12-dodecyldiamine). The surface energy was measured by contact angle technique. For Si-diamine surfaces, Lewis basicity (using Fowkes–van Oss–Chaudhury–Good surface tension model) and adhesion thermodynamic work (using chemical force microscopy) were determined. We related these data, the amine/diamine nature and their geometry on the surface (via DFT calculations) with the consequent ability to coordinate copper(II) acetate. Finally, copper(II) acetate monolayers behavior was studied by cyclic voltammetry.
Keywords: Silicon; Diamines; Copper(II) acetate; Chemical force microscopy; DFT calculation; Electrochemistry;
Topographical length scales of hierarchical superhydrophobic surfaces by P.K. Dhillon; P.S. Brown; C.D. Bain; J.P.S. Badyal; S. Sarkar (1068-1074).
The morphology of hydrophobic CF4 plasma fluorinated polybutadiene surfaces has been characterised using atomic force microscopy (AFM). Judicious choice of the plasma power and exposure duration leads to formation of three different surface morphologies (Micro, Nano, and Micro + Nano). Scaling theory analysis shows that for all three surface topographies, there is an initial increase in roughness with length scale followed by a levelling-off to a saturation level. At length scales around 500 nm, it is found that the roughness is very similar for all three types of surfaces, and the saturation roughness value for the Micro + Nano morphology is found to be intermediate between those for the Micro and Nano surfaces. Fast Fourier Transform (FFT) analysis has shown that the Micro + Nano topography comprises a hierarchical superposition of Micro and Nano morphologies. Furthermore, the Micro + Nano surfaces display the highest local roughness (roughness exponent α = 0.42 for length scales shorter than ∼500 nm), which helps to explain their superhydrophobic behaviour (large water contact angle (>170°) and low hysteresis (<1°)).
Keywords: Hydrophobicity; Dynamic scaling theory; Length scales; Roughness;
Influence of thermal annealing and ion irradiation on zinc silicate phases in nanocomposite ZnO–SiO x thin films by Venkata Siva Kumar Valiveti; F. Singh; S. Ojha; D. Kanjilal (1075-1079).
The formation of zinc silicate phase in nanocomposite (nc) ZnO–SiO x thin films, its dilution by ion irradiation and subsequent developments were investigated. The nc ZnO–SiO x thin films used in the study were grown using rf magnetron sputter deposition on silicon (Si) substrates. Thin films were also grown on transmission electron microscopy (TEM) grids in identical conditions. The as-deposited films on Si substrates were annealed at 750 and 900 °C in air for growth of crystalline zinc silicate phase. The as-deposited and 750 °C annealed films were irradiated with 50 MeV oxygen ions in the fluence range from 5 × 1011 to 1 × 1014 ions cm−2. The presence of zinc silicate was observed by X-ray diffraction (XRD) analysis of the annealed films and by Fourier transform infrared (FT-IR) spectroscopy measurements. XRD and FT-IR analyses of the films show increase in zinc silicate phase with annealing and dilution of zinc silicate phase with irradiation. Photoluminescence (PL) analysis of irradiated as-deposited films show change in defects of ZnO. The results are explained in terms of possible ion irradiation induced modifications in the material.
Keywords: Nc ZnO–SiO x ; XRD; Crystalline Zn2SiO4 phase; Visible PL; FT-IR;
Deposition of nano Fe3O4@mZrO2 onto exfoliated graphite oxide sheets and its application for removal of amaranth by Hualin Jiang; Pinghua Chen; Weibo Zhang; Shenglian Luo; Xubiao Luo; Chaktong (Peter) Au; Menglin Li (1080-1089).
Herein we report a novel method to exfoliate graphite to thin structure by depositing nanoparticles. Graphite was oxidated to graphite oxide (GO), and then nano Fe3O4@mZrO2 was loaded and inserted between GO sheets as GO being reduced to reduced graphite oxide (rGO) in one step by hydro-thermal co-precipitation. As-obtained nanocomposite Fe3O4@mZrO2/rGO was characterized by SEM, TEM, AFM, FT-IR, BET, XRD, VSM and EDX techniques. The microscopic studies show the thickness of Fe3O4@mZrO2/rGO sheet is significant thinner than that of rGO sheet. Evidences indicate the presence of nano Fe3O4@mZrO2 effectively preserves rGO sheets from stacking and forming thick structure. Amaranth was used as a model contamination to investigate the adsorption ability of the nanocomposite due to its hazardness. It shows effective adsorption ability. Based on all the evidence shown in studies, a possible mechanism for the adsorbent composing and its amaranth adsorption was postulated.
Keywords: Adsorption; Graphite oxide; Nanocomposite; Removal; Mechanism;
Preparation and characterization of bioactive and degradable composites containing ordered mesoporous calcium-magnesium silicate and poly(l-lactide) by Jiajin Ji; Xieping Dong; Xuhui Ma; Songchao Tang; Zhaoying Wu; Ji Xia; Quanxiang Wang; Yutao Wang; Jie Wei (1090-1099).
Polylactide (PLA) and its copolymers have been widely used for bone tissue regeneration. In this study, a bioactive composite of ordered mesoporous calcium–magnesium silicate (m-CMS) and poly(l-lactide) (PLLA) was fabricated by melt blending method. The results indicated that the m-CMS particles were entrapped by polymer phase, and crystallinity of PLLA significantly decreased while the thermal stability of the m-CMS/PLLA composites was not obviously affected by addition of the m-CMS into PLLA. In addition, compared to PLLA, incorporation of the m-CMS into PLLA significantly improved the hydrophilicity, in vitro degradability and bioactivity (apatite-formation ability) of the m-CMS/PLLA composite, which were m-CMS content dependent. Moreover, it was found that incorporation of the m-CMS into PLLA could neutralize the acidic degradation by-products and thus compensated for the decrease of pH value. In cell culture experiments, the results showed that the composite enhanced attachment, proliferation and alkaline phosphatase activity (ALP) of MC3T3-E1 cells, which were m-CMS content dependent. The results indicated that the addition of bioactive materials to PLLA could result in a composite with improved properties of hydrophilicity, degradability, bioactivity and cytocompatibility.
Keywords: Mesoporous materials; Polymer; Degradability; Bioactivity; Cytocompatibility;
Synthesis of chemical vapor deposition graphene on tantalum wire for supercapacitor applications by Mingji Li; Wenlong Guo; Hongji Li; Sheng Xu; Changqing Qu; Baohe Yang (1100-1106).
This paper studies the synthesis and electrochemical characterization of graphene/tantalum (Ta) wires as high-performance electrode material for supercapacitors. Graphene on Ta wires is prepared by the thermal decomposition of methane under various conditions. The graphene nanosheets on the Ta wire surface have an average thickness of 1.3–3.4 nm and consist typically of a few graphene monolayers, and TaC buffer layers form between the graphene and Ta wire. A capacitor structure is fabricated using graphene/Ta wire with a length of 10 mm and a diameter of 0.6 mm as the anode and Pt wire of the same size as the cathode. The electrochemical behavior of the graphene/Ta wires as supercapacitor electrodes is characterized by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy in 1 M Na2SO4 aqueous electrolyte. The as-prepared graphene/Ta electrode has highest capacitance of 345.5 F g−1 at current density of 0.5 A g−1. The capacitance remains at about 84% after 1000 cycles at 10 A g−1. The good electrochemical performance of the graphene/Ta wire electrode is attributed to the unique nanostructural configuration, high electrical conductivity, and large specific surface area of the graphene layer. This suggests that graphene/Ta wire electrode materials have potential applications in high-performance energy storage devices.
Keywords: Electrochemical supercapacitor; Graphene; Tantalum carbide; Tantalum wire; Hot-filament chemical vapor deposition;
Low temperature self-cleaning properties of superhydrophobic surfaces by Fajun Wang; Taohua Shen; Changquan Li; Wen Li; Guilong Yan (1107-1112).
Outdoor surfaces are usually dirty surfaces. Ice accretion on outdoor surfaces could lead to serious accidents. In the present work, the superhydrophobic surface based on 1H, 1H, 2H, 2H-Perfluorodecanethiol (PFDT) modified Ag/PDMS composite was prepared to investigate the anti-icing property and self-cleaning property at temperatures below freezing point. The superhydrophobic surface was deliberately polluted with activated carbon before testing. It was observed that water droplet picked up dusts on the cold superhydrophobic surface and took it away without freezing at a measuring temperature of −10 °C. While on a smooth PFDT surface and a rough surface base on Ag/PDMS composite without PFDT modification, water droplets accumulated and then froze quickly at the same temperature. However, at even lower temperature of −12 °C, the superhydrophobic surface could not prevent the surface water from icing. In addition, it was observed that the frost layer condensed from the moisture pay an important role in determining the low temperature self-cleaning properties of a superhydrophobic surface.
Keywords: Superhydrophobic; Anti-icing; Self-clean; Contaminant;
Structure of anodized Al–Zr sputter deposited coatings and effect on optical appearance by Visweswara Chakravarthy Gudla; Stela Canulescu; Rajashekhara Shabadi; Kristian Rechendorff; Kai Dirscherl; Rajan Ambat (1113-1124).
The mechanism of interaction of light with the microstructure of anodized layer giving specific optical appearance is investigated using Al–Zr sputter deposited coating as a model system on an AA6060 substrate. Differences in the oxidative nature of various microstructural components result in the evolution of typical features in the anodized layer, which are investigated as a function of microstructure and correlated with its optical appearance. The Zr concentration in the coating was varied from 6 wt.% to 23 wt.%. Heat treatment of the coated samples was carried out at 550 °C for 4 h in order to evolve Al–Zr based second phase precipitates in the microstructure. Anodizing was performed using 20 wt.% sulphuric acid at 18 °C with an intention to study the effect of anodizing on the Al–Zr based precipitates in the coating. Detailed microstructural characterization of the coating and anodized layer was carried out using high resolution scanning and transmission electron microscopy, grazing incidence X-ray diffraction analysis, glow discharge optical emission spectroscopy, and optical appearance using spectrophotometry. The evolution of microstructure in the anodized layer as a function of anodizing parameters and their influence on the interaction of light is investigated and the results in general are applicable to discolouration of anodized layer on recycled aluminium alloys due to intermetallics.
Keywords: Magnetron sputtering; Aluminium; Microstructure; Anodizing; Optical appearance; TEM;
Magnetic solid base catalyst CaO/CoFe2O4 for biodiesel production: Influence of basicity and wettability of the catalyst in catalytic performance by Pingbo Zhang; Qiuju Han; Mingming Fan; Pingping Jiang (1125-1130).
A novel magnetic solid base catalyst CaO/CoFe2O4 was successfully prepared with CoFe2O4 synthesized by hydrothermal method as the magnetic core and applied to the transesterification of soybean oil for the production of biodiesel. The magnetic solid base catalysts were characterized by a series of techniques including CO2-TPD, powder XRD, TGA, TEM and the contact angle measurement of the water droplet. It was demonstrated that CaO/CoFe2O4 has stronger magnetic strength indicating perfect utility for repeated use and better basic strength. Compared with CaO/ZnFe2O4 and CaO/MnFe2O4, solid base catalyst CaO/CoFe2O4 has better catalytic performance, weaker hydroscopicity and stronger wettability, demonstrating that catalytic performance was relative to both basicity of catalyst and the full contact between the catalyst and the reactants, but the latter was a main factor in the catalytic system.
Keywords: Biodiesel; Transesterification; Basicity; Wettability; Magnetic solid base catalyst;
Visible light photoactivity of TiO2 loaded with monometallic (Au or Pt) and bimetallic (Au/Pt) nanoparticles by Anna Gołąbiewska; Wojciech Lisowski; Marcin Jarek; Grzegorz Nowaczyk; Anna Zielińska-Jurek; Adriana Zaleska (1131-1142).
TiO2 modified with monometallic (Au or Pt) and bimetallic (Au/Pt) nanoparticles have been prepared using a water-in-oil microemulsion system (water/AOT/cyclohexane) followed by calcination step. The effect of metal ratio, reducing agent type (NaBH4 or N2H4), TiO2 matrix type (P-25, ST-01, TiO-5, TiO2 nanotubes or TiO2 obtained by TIP hydrolysis) as well as calcination temperature (from 350 to 650 °C) were systematically investigated. Obtained photocatalysts were characterized by UV–vis diffuse-reflectance spectroscopy (DRS), BET surface area measurements, scanning transmission microscopy (STEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). Photocatalytic activity under visible light (λ > 420 nm) has been estimated in phenol degradation reaction in aqueous phase. The results showed that phenol degradation rate under visible light in the presence of TiO2 loaded with Au/Pt nanoparticles differed from 0.7 to 2.2 μmol dm−3 min−1 for samples prepared using different reducing agent. Sodium borohydride (NaBH4) favors formation of smaller Au/Pt nanoparticles and higher amount gold in Au/Pt is in the form of electronegative species (Au δ−) resulted in higher photoactivity. TiO2 obtained by TIP hydrolysis in microemulsion system seems to be the best support for Au/Pt nanoparticles from all among investigated matrix. It was also observed that enhancement of calcination temperature from 450 to 650 °C resulted in rapid drop of Au/Pt-TiO2 photoactivity under visible light due to surface area shrinkage, crystal structure change and probably change in Au/Pt nanoparticles morphology.
Keywords: Au/Pt-TiO2 nanoparticles; Photocatalysis; Visible light photoactivity;
Study of the corrosion behavior and the corrosion films formed on the surfaces of Mg–xSn alloys in 3.5 wt.% NaCl solution by Jingfeng Wang; Yang Li; Song Huang; Xiaoen Zhou (1143-1150).
The corrosion behavior and the corrosion films formed on the surfaces of Mg–xSn (x = 0.5, 1.0, 1.5, and 2.0 wt.%) alloys in 3.5 wt.% NaCl solution were investigated by immersion tests, electrochemical measurements, corrosion morphology observations, and X-ray diffraction analysis. Immersion tests and electrochemical measurements illustrated that the best corrosion resistance was reported for the Mg–1.5Sn alloy. Both Mg(OH)2/SnO2 corrosion product film and Mg(OH)2/MgSnO3 clusters formed on Mg–1.5Sn alloy surface. Mg(OH)2/MgSnO3 clusters were compact and suppressed the cathodic effect of the impurity inclusions greatly. The Mg–xSn (x = 0.5, 1.0, and 2.0 wt.%) alloys only formed loose Mg(OH)2/SnO2 corrosion product film during the corrosion process.
Keywords: Magnesium; Polarization; Hydrogen evolution; Corrosion;