Applied Surface Science (v.406, #C)
Editorial Board (ii).
Oxidation behavior of Ru–Al multilayer coatings by Yung-I Chen; Zhi-Ting Zheng; Wu Kai; Yu-Ren Huang (1-7).
Ru0.63Al0.37 coatings were deposited through a cyclical gradient concentration deposition at 400 °C with a substrate-holder rotation speed of 1 rpm by direct current magnetron cosputtering. Scanning electron microscopy revealed that the as-deposited coatings exhibited a multilayer structure along with the columnar structure. The oxidation behavior of the Ru0.63Al0.37 coatings was examined through X-ray diffraction, Auger electron spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Oxidation kinetics was measured using a thermogravimetric analyzer. Internal oxidation was observed for Ru0.63Al0.37 coatings annealed in a 1% O2–99% Ar atmosphere at 400–600 °C accompanied with activation energies of 72–84 kJ/mol. By contrast, external oxidation was observed after annealing at 700–800 °C, resulting in the formation of a continuous alumina scale consisting of crystalline δ-Al2O3 domains, which can be attributable to the outward diffusion of Al.
Keywords: Auger electron spectroscopy; Kinetics; Multilayer coatings; Nanostructure; Oxidation; X-ray photoelectron spectroscopy;
Understanding the interfacial properties of graphene-based materials/BiOI heterostructures by DFT calculations by Wen-Wu Dai; Zong-Yan Zhao (8-20).
Heterostructure constructing is a feasible and powerful strategy to enhance the performance of photocatalysts, because they can be tailored to have desirable photo-electronics properties and couple distinct advantageous of components. As a novel layered photocatalyst, the main drawback of BiOI is the low edge position of the conduction band. To address this problem, it is meaningful to find materials that possess suitable band gap, proper band edge position, and high mobility of carrier to combine with BiOI to form hetertrostructure. In this study, graphene-based materials (including: graphene, graphene oxide, and g-C3N4) were chosen as candidates to achieve this purpose. The charge transfer, interface interaction, and band offsets are focused on and analyzed in detail by DFT calculations. Results indicated that graphene-based materials and BiOI were in contact and formed van der Waals heterostructures. The valence and conduction band edge positions of graphene oxide, g-C3N4 and BiOI changed with the Fermi level and formed the standard type-II heterojunction. In addition, the overall analysis of charge density difference, Mulliken population, and band offsets indicated that the internal electric field is facilitate for the separation of photo-generated electron-hole pairs, which means these heterostructures can enhance the photocatalytic efficiency of BiOI. Thus, BiOI combines with 2D materials to construct heterostructure not only make use of the unique high electron mobility, but also can adjust the position of energy bands and promote the separation of photo-generated carriers, which provide useful hints for the applications in photocatalysis.
Keywords: Photocatalysis; Heterostructure constructing; Graphene-based materials; DFT calculations;
Preparation and performance characterization of AlF3 as interface stabilizer coated Li1.24Ni0.12Co0.12Mn0.56O2 cathode for lithium-ion batteries by Jingjing Ding; Zhongpei Lu; Manman Wu; Cong Liu; Hongmei Ji; Gang Yang (21-29).
Li1.24Ni0.12Co0.12Mn0.56O2 (LNCM) with high specific capacity is a potential cathode for commercial lithium-ion batteries (LIBs). To improve the high-rate capacity and cyclic stability, LNCM sample is successfully coated by minor AlF3. The crystal structure and electrochemical properties of the bare and coated samples are investigated by X-ray diffractometry (XRD), scanning and transmission electron microscopy (SEM, TEM), cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), and charge/discharge measurements. The coating layer AlF3 efficiently plays a positive role in enhancing rate performance and cyclic stability of LNCM. At 0.5 A g−1, the specific discharge capacity of LNCM@2%AlF3 is 149 mAh g−1 much higher than 35 mAh g−1 in bare LNCM. At 20 mA g−1, the specific discharge capacity of LNCM@2%AlF3 is 223 mAh g−1 at the 60th cycle in comparison with 203 mAh g−1 in bare LNCM. Moreover, a proper AlF3 coating layer efficiently ensures the stability of LNCM cathode operated at higher temperature. LNCM@2%AlF3 operated at 55 °C remains 219 mAh g−1 at the 50th cycle, much higher than bare LNCM only remains 99 mAh g−1 at the 40th cycle.
Keywords: Lithium-ion batteries; Cathode material; Surface coating; Electrochemical performance;
Carbon and nitrogen co-doping self-assembled MoS2 multilayer films by Xiaoqin Zhang; Jiao Xu; Liqiang Chai; Tengfei He; Fucheng Yu; Peng Wang (30-38).
Display OmittedMo–S–C–N composite films were prepared using reactive magnetron sputtering of graphite and MoS2 targets in argon and nitrogen atmospheres. The effects of carbon/nitrogen co-doping and carbon concentration on the composition, microstructure, mechanical and tribological properties of deposited films have been investigated by various characterization techniques. The results show that the deposited films comprise MoS2 nanocrystalline and amorphous carbon, and the incorporating nitrogen forms Mo-N and C–N chemical bonds. Increasing carbon concentration leads to the increase of sp2 carbon fraction in the films. Furthermore, the high-resolution transmission electron microscopy reveals that a self-assembled multilayer structure with periodicity in the nanometer scale is formed in the Mo–S–C–N film. Benefiting from the composite and self-assembled multilayer structures, the hardness of Mo–S–C–N film deposited at optimized parameter reaches up to 9.76 GPa, and corresponding friction experiment indicates that this composite films display low friction coefficient and high wear resistance both in vacuum and ambient air conditions.
Keywords: Composite film; Self-assembled multilayer; Mechanical properties; Tribological properties;
Surface flashover performance of epoxy resin microcomposites improved by electron beam irradiation by Yin Huang; Daomin Min; Shengtao Li; Zhen Li; Dongri Xie; Xuan Wang; Shengjun Lin (39-45).
The influencing mechanism of electron beam irradiation on surface flashover of epoxy resin/Al2O3 microcomposite was investigated. Epoxy resin/Al2O3 microcomposite samples with a diameter of 50 mm and a thickness of 1 mm were prepared. The samples were irradiated by electron beam with energies of 10 and 20 keV and a beam current of 5 μA for 5 min. Surface potential decay, surface conduction, and surface flashover properties of untreated and irradiated samples were measured. Both the decay rate of surface potential and surface conductivity decrease with an increase in the energy of electron beam. Meanwhile, surface flashover voltage increase. It was found that both the untreated and irradiated samples have two trap centers, which are labeled as shallow and deep traps. The increase in the energy and density of deep surface traps enhance the ability to capture primary emitted electrons. In addition, the decrease in surface conductivity blocks electron emission at the cathode triple junction. Therefore, electron avalanche at the interface between gas and an insulating material would be suppressed, eventually improving surface flashover voltage of epoxy resin microcomposites.
Keywords: Electron beam irradiation; Epoxy resin microcomposite; Surface trap; Surface flashover;
Ultrathin mesoporous Co3O4 nanosheets-constructed hierarchical clusters as high rate capability and long life anode materials for lithium-ion batteries by Shengming Wu; Tian Xia; Jingping Wang; Feifei Lu; Chunbo Xu; Xianfa Zhang; Lihua Huo; Hui Zhao (46-55).
Ultrathin mesoporous Co3O4 nanosheets-constructed hierarchical clusters (UMCN-HCs) have been successfully synthesized via a facile hydrothermal method followed by a subsequent thermolysis treatment. When tested as anode materials for LIBs, UMCN-HCs achieve high reversible capacity, good long cycling life, and rate capability.Display OmittedHerein, Ultrathin mesoporous Co3O4 nanosheets-constructed hierarchical clusters (UMCN-HCs) have been successfully synthesized via a facile hydrothermal method followed by a subsequent thermolysis treatment at 600 °C in air. The products consist of cluster-like Co3O4 microarchitectures, which are assembled by numerous ultrathin mesoporous Co3O4 nanosheets. When tested as anode materials for lithium-ion batteries, UMCN-HCs deliver a high reversible capacity of 1067 mAh g−1 at a current density of 100 mA g−1 after 100 cycles. Even at 2 A g−1, a stable capacity as high as 507 mAh g−1 can be achieved after 500 cycles. The high reversible capacity, excellent cycling stability, and good rate capability of UMCN-HCs may be attributed to their mesoporous sheet-like nanostructure. The sheet-layered structure of UMCN-HCs may buffer the volume change during the lithiation-delithiation process, and the mesoporous characteristic make lithium-ion transfer more easily at the interface between the active electrode and the electrolyte.
Keywords: Oxides; Nanostructures; Lithium-ion batteries; Anode materials; Electrochemical performance;
Surface-conduction electron-emitter characteristics and fabrication based on vertically aligned carbon nanotube arrays by Yi-Ting Shih; Kuan-Wei Li; Shin-ichi Honda; Pao-Hung Lin; Ying-Sheng Huang; Kuei-Yi Lee (56-61).
The pattern design provides a new structure of surface-conduction electron-emitter display (SED). Delta-star shaped vertically aligned CNT (VACNT) arrays with 20o tips can simultaneously provide three emitters to bombard the sides of equilateral triangles pattern of VACNT, which produces numerous secondary electrons and enhance the SED efficiency.Display OmittedThe carbon nanotube (CNT) has replaced palladium oxide (PdO) as the electrode material for surface-conduction electron-emitter (SCE) applications. Vertically aligned CNT arrays with a delta-star arrangement were patterned and synthesized onto a quartz substrate using photolithography and thermal chemical vapor deposition. Delta-star shaped VACNT arrays with 20° tips are used as cathodes that easily emit electrons because of their high electrical field gradient. In order to improve the field emission and secondary electrons (SEs) in SCE applications, magnesium oxide (MgO) nanostructures were coated onto the VACNT arrays to promote the surface-conduction electron-emitter display (SED) efficiency (η). According to the definition of η in SCE applications, in this study, the η was stably maintained in the 75–85% range. The proposed design provides a facile new method for developing SED applications.
Keywords: Surface-conduction electron-emitter; Carbon nanotube; MgO; Chemical vapor deposition; e-Beam evaporation; Photolithography;
Deposition of titanium coating on SiC fiber by chemical vapor deposition with Ti-I2 system by Xian Luo; Shuai Wu; Yan-qing Yang; Na Jin; Shuai Liu; Bin Huang (62-68).
Titanium coating was prepared on SiC fiber using titanium-iodine (Ti-I2) mixture by hot-wall chemical vapor deposition. Thermodynamic analysis and experimental observation were carried out in this work. The thermodynamic analysis of the reactions in the Ti-I2 system indicates that Ti and I2 raw powder materials transform to titanium coating as follows: Ti + I2 → (TiI2, TiI3), and (TiI2, TiI3) → Ti. In theory, the conversions of TiI3 and TiI2 reach the maximum when Ti:I2 is 1:1.5, while in actual experiment that reached the maximum when Ti:I2 was 1:2, as there existed the waste of I2 due to sublimation. Typical deposited coating is relatively flat and uniform. However, as SiC is prone to react with Ti at high temperatures, the obtained coating contained some Si and C elements except for Ti. So the coating was not a pure Ti coating but contained some carbides and silicides. Deposition rate of the coating increased with the increase of temperature. The deposited thickness increased with the increase of heat preservation time, and achieved the maximum thickness at 90 min.
Keywords: Chemical vapor deposition; Titanium coating; SiC fiber; Titanium iodide; Iodine;
High performance and durability of order-structured cathode catalyst layer based on TiO2@PANI core-shell nanowire arrays by Ming Chen; Meng Wang; Zhaoyi Yang; Xindong Wang (69-76).
Display OmittedIn this paper, an order-structured cathode catalyst layer consisting of Pt-TiO2@PANI core-shell nanowire arrays that in situ grown on commercial gas diffusion layer (GDL) are prepared and applied to membrane electrode assembly (MEA) of proton exchange membrane fuel cell (PEMFC). In order to prepare the TiO2@PANI core-shell nanowire arrays with suitable porosity and prominent conductivity, the morphologies of the TiO2 nanoarray and electrochemical polymerization process of aniline are schematically investigated. The MEA with order-structured cathode catalyst layer is assembled in the single cell to evaluate the electrochemical performance and durability of PEMFC. As a result, the PEMFC with order-structured cathode catalyst layer shows higher peak power density (773.54 mW cm−2) than conventional PEMFC (699.30 mW cm−2). Electrochemically active surface area (ECSA) and charge transfer impedance (Rct) are measured before and after accelerated degradation test (ADT), and the corresponding experimental results indicate the novel cathode structure exhibits a better stability with respect to conventional cathode. The enhanced electrochemical performance and durability toward PEMFC can be ascribed to the order-structured cathode nanoarray structure with high specific surface area increases the utilization of catalyst and reduces the tortuosity of transport pathways, and the synergistic effect between TiO2@PANI support and Pt nanoparticles promotes the high efficiency of electrochemical reaction and improves the stability of catalyst. This research provides a facile and controllable method to prepare order-structured membrane electrode with lower Pt loading for PEMFC in the future.
Keywords: Proton exchange membrane fuel cell; TiO2@PANI core-shell nanowires; Order-structured cathode catalyst layer; Performance; Durability;
Modifying friction between ultra-high molecular weight polyethylene (UHMWPE) yarns with plasma enhanced chemical vapour deposition (PCVD) by Yanyan Chu; Xiaogang Chen; Lipeng Tian (77-83).
Ultra-high molecular weight polyethylene (UHMWPE) yarns are widely used in military applications for protection owing to its high modulus and high strength; however, the friction between UHMWPE yarns is too small, which is a weakness for ballistic applications. The purpose of current research is to increase the friction between UHMWPE yarns by plasma enhanced chemical vapour deposition (PCVD). The changes of morphology and chemical structure were characterised by SEM and FTIR individually. The coefficients of friction between yarns were tested by means of Capstan method. Results from tests showed that the yarn–yarn coefficient of static friction (CSF) has been improved from 0.12 to 0.23 and that of kinetic friction (CSF) increased from 0.11 to 0.19, as the samples exposure from 21 s to 4 min. The more inter-yarn friction can be attributed to more and more particles and more polar groups deposited on the surfaces of yarns, including carboxyl, carbonyl, hydroxyl and amine groups and compounds containing silicon. The tensile strength and modulus of yarns, which are essential to ballistic performance, keep stable and are not affected by the treatments, indicating that PCVD treatment is an effective way to improve the inter-yarn friction without mechanical property degradation.
Keywords: Fibre; Inter-yarn friction; Ballistic impact; Plasma; PCVD; UHMWPE;
Growth of a WSe2/W counter electrode by sputtering and selenization annealing for high-efficiency dye-sensitized solar cells by Sajjad Hussain; Supriya A. Patil; Dhanasekaran Vikraman; Alvira Ayoub Arbab; Sung Hoon Jeong; Hak-Sung Kim; Jongwan Jung (84-90).
A chemically active and stable WSe2/W structure was prepared by sputtering and selenization annealing in order to replace a high-cost Pt counter electrode in dye-sensitized solar cells. The CV, EIS analysis, and Tafel curve measurements indicated that the WSe2/W electrode possesses high conductivity, low charge transfer resistance at the electrolyte-electrode interface, good electrocatalytic activity, and fast reaction kinetics for the a iodide/triiodide redox reaction, which are due to the synergistic effect of W and WSe2 in combination. The DSSC with a novel WSe2/W counter electrode achieved a high power conversion efficiency of 8.22% under standard light illumination, which is comparable to that with a platinum (Pt)-coated FTO electrode (8.20%).
Keywords: WSe2; Sputtering; Counter electrode; DSSC;
An investigation on 800 nm femtosecond laser ablation of K9 glass in air and vacuum by Shi-zhen Xu; Cai-zhen Yao; Hong-qiang Dou; Wei Liao; Xiao-yang Li; Ren-jie Ding; Li-juan Zhang; Hao Liu; Xiao-dong Yuan; Xiao-tao Zu (91-98).
Ablation rates of K9 glass were studied as a function of femtosecond laser fluences. The central wavelength was 800 nm, and pulse durations of 35 fs and 500 fs in air and vacuum were employed. Ablation thresholds of 0.42 J/cm2 and 2.1 J/cm2 were obtained at 35 fs and 500 fs, respectively, which were independent with the ambient conditions and depend on the incident pulse numbers due to incubation effects. The ablation rate of 35 fs pulse laser increased with the increasing of laser fluence in vacuum, while in air condition, it slowly increased to a plateau at high fluence. The ablation rate of 500 fs pulse laser showed an increase at low fluence and a slow drop of ablation rate was observed at high fluence in air and vacuum, which may due to the strong defocusing effects associated with the non-equilibrium ionization of air, and/or the shielding effects of conduction band electrons (CBEs) produced by multi-photon ionization and impact ionization in K9 glass surface. The typical ablation morphologies, e.g. smooth zone and laser-induced periodic surface structures (LIPSS) were also presented and illustrated.
Keywords: Femtosecond laser; K9 glass; Laser ablation; Ablation rate; Laser-induced damage threshold; Laser materials processing;
Non-parabolic isothermal oxidation kinetics of low pressure plasma sprayed MCrAlY bond coat by Bang-Yan Zhang; Guan-Jun Yang; Cheng-Xin Li; Chang-Jiu Li (99-109).
Display OmittedThe non-parabolic isothermal oxidation kinetics of low pressure plasma sprayed MCrAlY bond coat was investigated. To qualitatively explain the abnormal growth phenomenon of thermally grown oxides (TGO), the changes that occurred to their microstructure during the oxidation process were studied. Based on these observations, a modified model was developed to understand and quantitatively predict the non-parabolic oxidation and growth kinetics of TGO. This modified model, which fits well with experimental results, provides a novel method to quantitatively predict the long-term growth behaviour of TGO, and thereby benefits the development of long-life and highly reliable thermal barrier coatings.
Keywords: Bond coat; Isothermal oxidation kinetics; Thermally grown oxide; Grain structure; Oxygen diffusion rate;
Magnetic properties of Co-N films deposited by ECR nitrogen/argon plasma with DC negative-biased Co target by H. Li; Y.C. Zhang; K. Yang; H.X. Liu; X.D. Zhu; H.Y. Zhou (110-114).
By introducing DC negative-biased Co target in the Electron Cyclotron Resonance (ECR) nitrogen/argon plasma, the Co-N films containing Co4N phase were synthesized on Si(100) substrate. Effects of processing parameters on magnetic properties of the films are investigated. It is found that magnetic properties of Co-N films vary with N2/Ar flow ratio, substrate temperature, and target biasing voltage. The saturation magnetization Ms decreased by increasing the N2/Ar gas flow ratio or decreasing target biasing voltage, while the coercive field Hc increased, which is ascribed to the variation of relative concentration for N or Co active species in plasma vapor. The magnetic properties present complex dependency with growth temperature, which is related to the atom mobility on the substrate affected by the growth temperature. This study exhibits a potential of ECR plasma chemical vapor deposition to synthesize the interstitial compounds and tune magnetic properties of films.
Keywords: Co-N films; ECR plasma; Magnetic properties;
New immobilisation protocol for the template used in solid-phase synthesis of MIP nanoparticles by Lu Chen; Turghun Muhammad; Burabiye Yakup; Sergey A. Piletsky (115-121).
Display OmittedAs a novel imprinting method, solid-phase synthesis has proven to be a promising approach to prepare polymer nanoparticles with specific recognition sites for a template molecule. In this method, imprinted polymer nanoparticles were synthesized using template immobilized on a solid support. Herein, preparation of immobilized templates on quartz chips through homogeneous route was reported as an efficient alternative strategy to heterogeneous one. The template molecule indole-3-butyric acid (IBA) was reacted with 3-aminopropyltriethoxysilane (APTES) to produce silylated template (IBA-APTES), and it was characterized by IR, 1H NMR and GC–MS. Then, the silylated template molecule was grafted onto the activated surfaces of quartz chip to prepare immobilized template (SiO2@IBA-APTES). The immobilization was confirmed by contact angle, XPS, UV and fluorescence measurement. Immobilization protocol has shown good reproducibility and stability of the immobilized template. MIP nanoparticles were prepared with high selectivity toward the molecule immobilized onto the solid surface. This provides a new approach for the development of molecularly imprinted nanoparticles.
Keywords: Molecularly imprinted polymers; Solid-phase synthesis; Nanoparticles; Homogeneous route; Characterization; Chip surface;
Adsorbate-induced modification of electronic band structure of epitaxial Bi(111) films by A.V. Matetskiy; L.V. Bondarenko; A.Y. Tupchaya; D.V. Gruznev; S.V. Eremeev; A.V. Zotov; A.A. Saranin (122-127).
Display OmittedChanges of the electronic band structure of Bi(111) films on Si(111) induced by Cs and Sn adsorption have been studied using angle-resolved photoemission spectroscopy and density functional theory calculations. It has been found that small amounts of Cs when it presents at the surface in a form of the adatom gas leads to shifting of the surface and quantum well states to the higher binding energies due to the electron donation from adsorbate to the Bi film. In contrast, adsorbed Sn dissolves into the Bi film bulk upon heating and acts as an acceptor dopant, that results in shifting of the surface and quantum well states upward to the lower binding energies. These results pave the way to manipulate with the Bi thin film electron band structure allowing to achieve a certain type of conductivity (electron or hole) with a single spin channel at the Fermi level making the adsorbate-modified Bi a reliable base for prospective spintronics applications.
Keywords: Electron photoemission; Bismuth ultrathin films; Spin-splitting; Rashba effect;
Hydrogen release at metal-oxide interfaces: A first principle study of hydrogenated Al/SiO2 interfaces by Jianqiu Huang; Eric Tea; Guanchen Li; Celine Hin (128-135).
The Anode Hydrogen Release (AHR) mechanism at interfaces is responsible for the generation of defects, that traps charge carriers and can induce dielectric breakdown in Metal-Oxide-Semiconductor Field Effect Transistors. The AHR has been extensively studied at Si/SiO2 interfaces but its characteristics at metal-silica interfaces remain unclear. In this study, we performed Density Functional Theory (DFT) calculations to study the hydrogen release mechanism at the typical Al/SiO2 metal-oxide interface. We found that interstitial hydrogen atoms can break interfacial Al―Si bonds, passivating a Si sp 3 orbital. Interstitial hydrogen atoms can also break interfacial Al―O bonds, or be adsorbed at the interface on aluminum, forming stable Al―H―Al bridges. We showed that hydrogenated O―H, Si―H and Al―H bonds at the Al/SiO2 interfaces are polarized. The resulting bond dipole weakens the O―H and Si―H bonds, but strengthens the Al―H bond under the application of a positive bias at the metal gate. Our calculations indicate that Al―H bonds and O―H bonds are more important than Si―H bonds for the hydrogen release process.
Keywords: Hydrogen release; Interface; Point defect; Dielectric breakdown;
Investigation of transient dynamics of capillary assisted particle assembly yield by D. Virganavičius; M. Juodėnas; T. Tamulevičius; H. Schift; S. Tamulevičius (136-143).
Display OmittedIn this paper, the transient behavior of the particle assembly yield dynamics when switching from low yield to high yield deposition at different velocity and thermal regimes is investigated. Capillary force assisted particle assembly (CAPA) using colloidal suspension of green fluorescent 270 nm diameter polystyrene beads was performed on patterned poly (dimethyl siloxane) substrates using a custom-built deposition setup. Two types of patterns with different trapping site densities were used to assess CAPA process dynamics and the influence of pattern density and geometry on the deposition yield transitions. Closely packed 300 nm diameter circular pits ordered in hexagonal arrangement with 300 nm pitch, and 2 × 2 mm2 square pits with 2 μm spacing were used. 2-D regular structures of the deposited particles were investigated by means of optical fluorescence and scanning electron microscopy. The fluorescence micrographs were analyzed using a custom algorithm enabling to identify particles and calculate efficiency of the deposition performed at different regimes. Relationship between the spatial distribution of particles in transition zone and ambient conditions was evaluated and quantified by approximation of the yield profile with a logistic function.
Keywords: Capillary force assisted assembly; Polystyrene beads; Ordered arrays; Fluorescence; Deposition yield dynamics;
Angle resolved XPS for selective characterization of internal and external surface of porous silicon by Anna Lion; Nadhira Laidani; Paolo Bettotti; Chiara Piotto; Giancarlo Pepponi; Mario Barozzi; Marina Scarpa (144-149).
Display OmittedSelective functionalization of the external/internal pore surface of porous silicon is of interest for the numerous potential applications of this material, in particular in pharmacology. With the aim of obtaining porous silicon platforms compatible with the aqueous environment and providing hydrophobic pores to load poorly water soluble molecules, we set-up a three step functionalization procedure consisting in two hydrosilylation reactions separated by the selective etching of the external surface. This procedure was applied both, to porous layers and porous microparticles. The characterization of the functionalized material by conventional techniques such as contact angle and FTIR showed a change of the properties of porous structures in line with the expected surface modifications. However, these techniques do not permit to clearly distinguish between internally and externally grafted functional groups. For this reason, an innovative procedure based on angle-resolved XPS was set-up and applied to differently functionalized pSi layers. By this technique, we obtained indications of prevalent grafting of hydrophilic moieties on the external surface and hydrophobic ones inside the pores.
Keywords: Porous silicon; Porous silicon microparticles; Space selective functionalization; Angle resolved XPS; Surface hydrophilicity; Hydrophobic cavities;
Covalent layer-by-layer grafting (LBLG) functionalized superhydrophobic stainless steel mesh for oil/water separation by Bin Jiang; Hongjie Zhang; Yongli Sun; Luhong Zhang; Lidong Xu; Li Hao; Huawei Yang (150-160).
Display OmittedA superhydrophobic and superoleophilic stainless steel (SS) mesh for oil/water separation has been developed by using a novel, facile and inexpensive covalent layer-by-layer grafting (LBLG) method. Hierarchical micro/nanostructure surface was formed through grafting the (3-aminopropyl) triethoxysilane (SCA), polyethylenimine (PEI) and trimesoyl chloride (TMC) onto the mesh in sequence, accompanied with SiO2 nanoparticles subtly and firmly anchored in multilayers. Superhydrophobic characteristic was realized by self-assembly grafting of hydrophobic groups onto the surface. The as-prepared mesh exhibits excellent superhydrophobicity with a water contact angle of 159°. Moreover, with a low sliding angle of 4°, it shows the “lotus effect” for self-cleaning. As for application evaluation, the as-prepared mesh can be used for large-scale separation of oil/water mixtures with a relatively high separation efficiency after 30 times reuse (99.88% for n-octane/water mixture) and a high intrusion pressure (3.58 kPa). More importantly, the mesh exhibited excellent stability in the case of vibration situation, long-term storage as well as saline corrosion conditions, and the compatible pH range was determined to be 1–13. In summary, this work provides a brand new method of modifying SS mesh in a covalent LBLG way, and makes it possible to introduce various functionalized groups onto the surface.
Keywords: Layer-by-layer grafting (LBLG); Oil/water separation; Superhydrophobic; Superoleophilic; Stainless steel (SS) mesh;
Design lithium storage materials by lithium adatoms adsorption at the edges of zigzag silicene nanoribbon: A first principle study by Gang Guo; Yuliang Mao; Jianxin Zhong; Jianmei Yuan; Hongquan Zhao (161-169).
Display OmittedFirst-principles spin-polarized calculations are performed to design lithium storage materials using the active edges of zigzag silicene nanoribbon (ZSiNR). We predict that edge-adsorption of Li adatoms on zigzag silicene nanoribbon is preferred in energy to form new type lithium storage materials. Significant charge transfer from Li adatoms to Si atoms at the edges of ZSiNR is found, indicating the main ionic interactions. It is found that the band structures of ZSiNR with Li adsorptions are sensitive with the variation of sites of adatoms at the two edges. Ferro-magnetic to antiferro-magnetic change is found in ZSiNR with symmetrical adsorption of Li adatoms at its two edges. Other unsymmetrical Li adsorptions at the edges of ZSiNR prefer to stay in ferro-magnetic state as that in narrow pristine ZSiNR.
Keywords: Silicene nanoribbon; Electronic and magnetic property; First-principles; Edge-adsorption;
Horseradish peroxidase immobilized on copper surfaces and applications in selective electrocatalysis of p-dihydroxybenzene by Chuntao Wang; Xiaoxiao Luo; Zehui Jia; Qinghua Shi; Ritao Zhu (170-177).
Cyclic voltammograms of Cu/L-Cys/HRP electrodes in o, m, p-dihydroxybenzene solutions.HRP was immobilized on copper surfaces with the linker of L-Cys self-assembled films to form Cu/L-Cys/HRP electrodes. The oxidation—reduction active sites, heme, in the HRP can be exposed by linking HRP with L-Cys on the Cu surfaces. Cyclic voltammograms revealed that p-dihydroxybenzen can be selective electrocatalysis by the Cu/L-Cys/HRP electrodes. The selective electrocatalysis to p-dihydroxybenzen by the Cu/L-Cys/HRP electrodes can be explained by the DFT calculation. For the three structural isomers of o-dihydroxybenzen, m-dihydroxybenzen, p-dihydroxybenzen, p-Dihydroxybenzen has the best molecular structure symmetry and the minimum space steric hindrance, it has most advantage to combine with HRP by conjugate Л―Л bonds between the plane of porphyrin ring and benzene ring. Moreover, p-dihydroxybenzen has the lowest energy of LUMO and negative charges of oxygen atom on hydroxyl group than m-dihydroxybenzen, and it has the highest ability of losing the hydrogen atom on hydroxyl group to be oxided.Display OmittedHorseradish Peroxidase (HRP) was immobilized on copper surfaces with the linker of L-Cysteine (L-Cys) self-assembled films to form Cu/L-Cys/HRP electrodes. The activity of HRP can be preserved by the Cu/L-Cys self-assembled films. The Cu/L-Cys/HRP electrodes can be used for the selective electrocatalytic oxidase of p-dihydroxybenzen in absent of H2O2. The optimum pH for electrocatalyzing p-dihydroxybenzen was 5.5 or 7.0, which corresponds to the isoelectric points of L-Cys and HRP, respectively. X-ray photoelectron spectroscopy (XPS) provided the evidence that L-Cys linked with Cu surface by the Cu― S bond. Fourier transform infrared spectroscopy (FTIR) analyses indicated that aromatic plane of p-dihydroxybenzen was connected parallel to porphyrin ring of heme in HRP. Quantum chemical calculation of density functional theory (DFT) revealed that symmetry of molecular structure and minimum space steric hindrance for p-dihydroxybenzen were benefit to combination with HRP. Moreover, the lowest energy of LUMO and most negative charges of oxygen atom on hydroxyl group of p-dihydroxybenzen were advantage to lose the hydrogen atom of hydroxyl group to be oxided.
Keywords: Horseradish peroxidase; Electrocatalytic oxidation; p-Dihydroxybenzene;
Micromechanism of oxygen transport during initial stage oxidation in Si(100) surface: A ReaxFF molecular dynamics simulation study by Yu Sun; Yilun Liu; Xuefeng Chen; Zhi Zhai; Fei Xu; Yijun Liu (178-185).
Display OmittedThe early stage oxidation in Si(100) surface has been investigated in this work by a reactive force field molecular dynamics (ReaxFF MD) simulation, manifesting that the oxygen transport acted as a dominant issue for initial oxidation process. Due to the oxidation, a compressive stress was generated in the oxide layer which blocked the oxygen transport perpendicular to the Si(100) surface and further prevented oxidation in the deeper layer. In contrast, thermal actuation was beneficial to the oxygen transport into deeper layer as temperature increases. Therefore, a competition mechanism was found for the oxygen transport during early stage oxidation in Si(100) surface. At room temperature, the oxygen transport was governed by the blocking effect of compressive stress, so a better quality oxide film with more uniform interface and more stoichiometric oxide structure was obtained. Indeed, the mechanism presented in this work is also applicable for other self-limiting oxidation (e.g. metal oxidation) and is helpful for the design of high-performance electronic devices.
Keywords: ReaxFF MD; Oxygen transport; Oxidation; Thermal actuation;
Crystallography facet tailoring of carbon doped ZnO nanorods via selective etching by Xiangyang Duan; Guangde Chen; Peihong Gao; Wentao Jin; Xiaoman Ma; Yuan Yin; Lu’an Guo; Honggang Ye; Youzhang Zhu; Jinying Yu; Yelong Wu (186-191).
Display OmittedUsing a facile hydrothermal method, we have successfully synthesized carbon doped (C-doped) ZnO nanorods with standard hexagonal column shapes. To modify their photocatalytic activities by tailoring the surfaces, a post etching process under ammonia atmosphere was used, and these nanorods could be converted into hexagonal porous nanorods (at 750 °C), and porous nanorods with corrugated surface structures covered by alternant ( 11 2 ¯ 1 ) and ( 11 2 ¯ 1 ¯ ) planes (at 850 °C and 950 °C). Energy Dispersion Spectrum and Raman spectra are used to carefully study the concentration and vibration modes of the doped carbon species. It explicitly shows that there is a carbonation process around 750 °C and some organic aldehyde molecules transform into carbon with flake form. After investigating their photoluminescence spectra and photocatalytic activities, we conclude that an appropriate etching temperature is the key point to obtain high photocatalytic performance.
Keywords: Corrugated nanorods; Selective etch; Doping; Carbonization; Raman; Porous materials;
Solution-processed n-ZnO nanorod/p-Co3O4 nanoplate heterojunction light-emitting diode by Jong-Woo Kim; Su Jeong Lee; Pranab Biswas; Tae Il Lee; Jae-Min Myoung (192-198).
Display OmittedA heterojunction light-emitting diode (LED) based on p-type cobalt oxide (Co3O4) nanoplates (NPs)/n-type zinc oxide (ZnO) nanorods (NRs) is demonstrated. Using a low-temperature aqueous solution process, the n-type ZnO NRs were epitaxially grown on Co3O4 NPs which were two-dimensionally assembled by a modified Langmuir-Blodgett process. The heterojunction LEDs exhibited a typical rectifying behavior with a turn-on voltage of about 2 V and emitted not only reddish-orange light at 610 nm but also violet light at about 400 nm. From the comparative analyses of electroluminescence and photoluminescence, it was determined that the reddish-orange light emission was related to the electronic transitions from zinc interstitials (Zni) to oxygen interstitials (Oi) or conduction-band minimum (CBM) to oxygen vacancies (VO), and the violet light emission was attribute to the transition from CBM to valence-band maximum (VBM) or Zni to zinc vacancies (VZn).
Keywords: p-type Co3O4 nanoplate; n-type ZnO nanorod; Heteroepitaxial p-n junction; Solution process; Light-emitting diode;
Laser micropolishing of AISI 304 stainless steel surfaces for cleanability and bacteria removal capability by Chiara De Giorgi; Valentina Furlan; Ali Gökhan Demir; Elena Tallarita; Gabriele Candiani; Barbara Previtali (199-211).
Display OmittedIn this work, laser micropolishing (LμP) was employed to reduce the surface roughness and waviness of cold-rolled AISI 304 stainless steel sheets. A pulsed fibre laser operating in the ns regime was used and the influence of laser parameters in a N2-controlled atmospheres was evaluated. In the optimal conditions, the surface remelting induced by the process allowed to reduce the surface roughness by closing cracks and defects formed during the rolling process. Other conditions that did not improve the surface quality were analysed for defect typology. Moreover, laser treatments allowed the production of more hydrophobic surfaces, and no surface chemistry modification was identified. Surface cleanability was investigated with Escherichia coli (E. coli), evaluating the number of residual bacteria adhering to the substrate after a washing procedure. These results showed that LμP is a suitable way to lower the average surface roughness by about 58% and average surface waviness by approximately 38%. The LμP process proved to be effective on the bacteria cleanability as approximately five times fewer bacteria remained on the surfaces treated with the optimized LμP parameters compared to the untreated surfaces.
Keywords: Laser micropolishing; Antibacterial surface; Antifouling; Bacteria repelling; Surface functionalization;
Oxygen-dependent epitaxial growth of Pt(001) thin films on MgO(001) by magnetron sputtering by X.Y. Qiu; R.X. Wang; G.Q. Li; T. Zhang; L.T. Li; M.L. Wei; X.S. Meng; H. Ji; Z. Zhang; C.H. Chan; J.Y. Dai (212-217).
Display OmittedThe roles of oxygen gas in crystal orientation, surface morphology and electrical resistivity of Pt thin films grown on MgO(001) substrate by magnetron sputtering are studied. With a well-controlled oxygen ratio (15% oxygen) during sputtering deposition with Ar-O2 mixture ambient, (001) epitaxial growth of Pt film on MgO substrate is achieved with an epitaxial orientation relationship of (001)Pt//(001)MgO and Pt//MgO. Microstructural and electrical characterizations reveal that the (001) Pt thin films possess very smooth surface and good conductivity. The formation and subsequent decomposition of platinum oxides in the Pt films grown with more than 30% oxygen result in an increase of surface roughness and electrical resistivity. The high-quality Pt(001) film has large potential for integrated electronic device applications.
Keywords: Pt film; Epitaxial growth; Oxygen ratio; Microstructure;
Selective catalytic reduction of NO x with NH3 over iron-cerium-tungsten mixed oxide catalyst prepared by different methods by Zhi-bo Xiong; Jing Liu; Fei Zhou; Dun-yu Liu; Wei Lu; Jing Jin; Shi-fa Ding (218-225).
A series of magnetic Fe0.85Ce0.10W0.05O z catalysts were synthesized by three different methods(Co-precipitation(Fe0.85Ce0.10W0.05O z -CP), Hydrothermal treatment assistant critic acid sol-gel method(Fe0.85Ce0.10W0.05O z -HT) and Microwave irradiation assistant critic acid sol-gel method(Fe0.85Ce0.10W0.05O z -MW)), and the catalytic activity was evaluated for selective catalytic reduction of NO with NH3. The catalyst was characterized by XRD, N2 adsorption-desorption, XPS, H2-TPR and NH3-TPD. Among the tested catalysts, Fe0.85Ce0.10W0.05O z -MW shows the highest NO x conversion over per gram in unit time with NO x conversion of 60.8% at 350 °C under a high gas hourly space velocity of 1,200,000 ml/(g h). Different from Fe0.85Ce0.10W0.05O z -CP catalyst, there exists a large of iron oxide crystallite(γ-Fe2O3 and α-Fe2O3) scattered in Fe0.85Ce0.10W0.05O z catalysts prepared through hydrothermal treatment or microwave irradiation assistant critic acid sol-gel method, and higher iron atomic concentration on their surface. And Fe0.85Ce0.10W0.05O z -MW shows higher surface absorbed oxygen concentration and better dispersion compared with Fe0.85Ce0.10W0.05O z -HT catalyst. These features were favorable for the high catalytic performance of NO reduction with NH3 over Fe0.85Ce0.10W0.05O z -MW catalyst.
Keywords: Selective catalytic reduction of NO x ; Iron-cerium-tungsten mixed oxide; Co-precipitation; Critic acid sol-gel; Hydrothermal treatment; Microwave irradiation;
2,3-diaminopyridine functionalized reduced graphene oxide-supported palladium nanoparticles with high activity for electrocatalytic oxygen reduction reaction by Sabina Yasmin; Yuri Joo; Seungwon Jeon (226-234).
Display OmittedThe electrochemical deposition of Pd nanoparticles (Pd NPs) on 2,3 diamino pyridine functionalized reduced graphene oxide (2,3 DAP-rGO/Pd) has been investigated for the oxygen reduction reaction (ORR) in alkaline media. First, 2,3 diaminopyridine functionalized graphene oxide (2,3 DAP-rGO) has been synthesized via simple hydrothermal method. Then, palladium is directly incorporated into the 2,3 DAP-rGO by electrochemical deposition method to generate 2,3 DAP-rGO/Pd composites. The as-prepared material 2,3 DAP-rGO/Pd has been characterized by various instrumental methods. The morphological analysis shows the cluster-like Pd nanoparticles are dispersed onto the 2,3 diamino pyridine functionalized reduced graphene oxide (2,3 DAP-rGO). The electrocatalytic activities have been verified using cyclic voltammetry (CV) and hydrodynamic voltammetry and chronoamperometry techniques in 0.1 M KOH electrolyte. The as-synthesized 2,3 DAP-rGO/Pd shows higher catalytic activity toward ORR with more positive onset potential and cathodic current density, superior methanol/ethanol tolerance and excellent stability in alkaline medium. It is also noteworthy that the 2,3 DAP-rGO/Pd exhibits a four-electron transfer pathway for ORR with lower H2O2 yield.
Keywords: Oxygen reduction reaction; 2,3 diaminopyridine; Fuel cell; Nanoparticles; Electrochemical deposition;
Nanoparticle string formation on self-assembled copolymer films by J. Jenczyk; M. Woźniak-Budych; M. Jarek; M. Grzeszkowiak; G. Nowaczyk; S. Jurga (235-244).
Display OmittedNanoparticles (NP) string formations on self-assembled copolymeric substrates has been observed. These ”thread of beads” like structures develop via simple colloidal droplet evaporation during meniscus rim withdrawal on polystyrene-block-poly(ethylene oxide) (PS-PEO) copolymer surfaces. It is shown that the process is triggered by the presence of the substrate impurities, which lead to NP aggregate formations serving as string initiation sites. The growth mechanism of these linear structures seems to be capillarity-driven. Moreover, there is an exceptional alignment coupling between NP strips and the block copolymer (BC) domains observed. BC directed NP assembly stems from a gold nanocrystal surface functionalization, which introduces selective affinity for one particular type of BC domain. The presented results reveal a potential fabrication method of NP wires characterized by remarkably low width and thickness comparable with the size of the individual constituent NP.
Keywords: Copolymer thin films; Copolymer directed NPs assembly; Self-assembling phenomenon;
The monolithic transition metal oxide crossed nanosheets used for diesel soot combustion under gravitational contact mode by Chunmei Cao; Lingli Xing; Yuexi Yang; Ye Tian; Tong Ding; Jing Zhang; Tiandou Hu; Lirong Zheng; Xingang Li (245-253).
The multiporous Co3O4 nanosheets on the monolithic three-dimensional macroporous Ni foam exhibits the high catalytic performance for soot combustion, because of the high intrinsic activity (TOF), the large amount of active oxygen species, the high reducibility and ability of oxidation NO to NO2.Display OmittedCrossed nanosheets of transition metal oxide (TMO-NS: Co-NS, Mn-NS and Fe-NS) were synthesized by a facile hydrothermal method and employed for soot combustion in the NO/O2/N2 and O2/N2 atmosphere under gravitational contact mode (GCM). They show high catalytic activities for soot combustion due to the macroporous structure of the as-prepare catalysts increasing the soot-catalyst contact efficiency. The XRD and XPS results reveal that the active phases in the corresponding catalysts exist as Co3O4, Mn2O3 and Fe2O3, respectively. Among these catalysts, the Co-NS shows the best activity for soot combustion, especially in the presence of NO, whose catalytic activity of T50 (391 °C) and S CO2 (100%) is as good as that of the Pt/Al2O3 catalyst. The excellent performance of the Co-NS catalyst results from several factors: the highest intrinsic activity (TOF = 1.77 × 10−5 s−1); the highest redox property as revealed by H2-TPR and soot-TPR; the largest amount of active oxygen species as clarified by XPS; the highest ability of NO oxidation to NO2 supported by NO-TPO. In addition, the multiporous structure of Co3O4 nanosheets is facilitated for the mass transfer. In the O2 atmosphere, soot particulates are directly oxidized by the surface adsorbed oxygen. After introducing of NO, the soot particulates are readily oxidized by NO2 at the low temperature (< 330 °C); with the increase of the reaction temperature (330–450 °C), both the active oxygen species and NO2 involve in soot combustion.
Keywords: Transition metal oxides; Nanosheets; Three-dimensionally macroporous Ni foam; Soot combustion; Crossed macropores;
Facile synthesis of the flower-like ternary heterostructure of Ag/ZnO encapsulating carbon spheres with enhanced photocatalytic performance by Xiaohua Zhao; Shuai Su; Guangli Wu; Caizhu Li; Zhe Qin; Xiangdong Lou; Jianguo Zhou (254-264).
Display OmittedTo utilize sunlight more effectively in photocatalytic reactions, the flower-like ternary heterostructure of Ag/ZnO encapsulating carbon spheres (Ag/ZnO@C) was successfully synthesized by a green and facile one-pot hydrothermal method. The carbon spheres (CSs) were wrapped by ZnO nanosheets, forming flower-like microstructures, and Ag nanoparticles (Ag NPs) were deposited on the surface of the ZnO nanosheets. The Ag/ZnO@C ternary heterostructure exhibited enhanced photocatalytic activity compared to those of Ag/ZnO, ZnO@C and pure ZnO for the degradation of Reactive Black GR and metronidazole under sunlight and visible light irradiation. This was attributed to the enhanced visible light absorption and effective charge separation based on the synergistic effect of ZnO, Ag NPs, and CSs. Due to the surface plasmon resonance effect of Ag NPs and surface photosensitizing effect of CSs, Ag/ZnO@C exhibited enhanced visible light absorption. Meanwhile, Ag NPs and CSs can both act as rapid electron transfer units to improve the separation of photogenerated charge carriers in Ag/ZnO@C. The primary active species were determined, and the photocatalytic mechanism was proposed. This work demonstrates an effective way to improve the photocatalytic performance of ZnO and provides information for the facile synthesis of noble metal/ZnO@C ternary heterostructure.
Keywords: Ag/ZnO encapsulating carbon spheres; Flower-like microstructure; Hydrothermal method; Photocatalysis; Organic dye; Metronidazole;
Fabrication of binder-free graphene-SnO2 electrodes by laser introduced conversion of precursors for lithium secondary batteries by Xiaoxiao Lu; Guolong Wu; Qinqin Xiong; Haiying Qin; Weibin Wang; Fang Luo (265-273).
Binder-free graphene-SnO2 electrodes were prepared by laser introduced conversion of precursor (mixture of graphene oxide and stannic oxide sol) coatings on a copper film. The evolution of the microstructure, thermal stability, morphologies and sheet resistance has been studied as a function of laser fluences. It was shown that the conversion of precursors is mainly attributed to the photothermic effect, and a laser fluence of 69.3 J cm−2 is the best condition for sample preparation. When the as-prepared electrode used as an anode for lithium ion batteries, it has been demonstrated with a high lithium storage capacity and good cycling stability. A high capacity of around 700 mAh g−1 can be retained after 50 cycles at a current density of 100 mA g−1, and even after 400 cycles the specific capacity steadied to around 690 mAh g−1. Such electrodes have a short preparing procedure and good electrochemical performance, so the fabrication method adopted here could be referable for industrial continuous production.
Keywords: Binder-free; Graphene; SnO2; Lithium battery;
Study on microstructure of transition zone and its strong contrast of single T700 carbon fibers by Xinshuang Guo; Kexiang Zhang; Zhen Fan; Zhihai Feng; LianLong He (274-276).
Display OmittedThe transition zone (TZ) between the skin and core of Toray T700 carbon fiber was investigated by transmission electron microscopy. The higher basal-plane orientation was identified in the TZ compared with the skin and core, but it disappeared after heat treatment at 2800 °C. Plasmon peak energy in the TZ was higher than that in the skin and core about 0.7–0.8 eV, indicating the TZ with higher density. No element concentration existed in the TZ. The TZ with strong contrast manifests itself before and after heat treatment, and formation mechanism of its strong contrast was proposed.
Keywords: Carbon fiber; Interface; Orientation; Density; Strong contrast;
Simulation study of temperature-dependent diffusion behaviors of Ag/Ag(001) at low substrate temperature by Danyun Cai; Yunjie Mo; Xiaofang Feng; Yingyou He; Shaoji Jiang (277-284).
Display OmittedIn this study, a model based on the First Principles calculations and Kinetic Monte Carlo simulation were established to study the growth characteristic of Ag thin film at low substrate temperature. On the basis of the interaction between the adatom and nearest-neighbor atoms, some simplifications and assumptions were made to categorize the diffusion behaviors of Ag adatoms on Ag(001). Then the barriers of all possible diffusion behaviors were calculated using the Climbing Image Nudged Elastic Band method (CI-NEB). Based on the Arrhenius formula, the morphology variation, which is attributed to the surface diffusion behaviors during the growth, was simulated with a temperature-dependent KMC model. With this model, a non-monotonic relation between the surface roughness and the substrate temperature (decreasing from 300 K to 100 K) were discovered. The analysis of the temperature dependence on diffusion behaviors presents a theoretical explanation of diffusion mechanism for the non-monotonic variation of roughness at low substrate temperature.
Keywords: Ag/Ag(001); Diffusion barrier; Temperature dependence; Surface roughness; First Principles calculations; Kinetic Monte Carlo simulation;
A simple technique for direct growth of Au into a nanoporous alumina layer on conductive glass as a reusable SERS substrate by Jiajie Yu; Muzhong Shen; Siyu Liu; Feng Li; Dongping Sun; Tianhe Wang (285-293).
A simple technique for direct growth of gold nanoparticles (GNPs) into a nanostructured porous alumina layer on conductive glass slide (PAOCG). Gold was uniformly distributed in porous alumina layer. Au/PAOCG can serve as a portable, durable and reusable SERS substrate.Display OmittedIn this paper, we describe a simple technique for direct growth of gold nanoparticles (GNPs) into a nanostructured porous alumina layer on conductive glass slide (PAOCG). PAOCG was attached firmly with a small piece of steel and was then immersed in a HAuCl4 solution. Electro-induced electrons from steel were employed to reduce AuCl4 − on PAOCG. The galvanic replacement reaction (GRR) was adopted as the fundamental mechanism for reducing metal precursors. This mechanism was further studied by open circuit potential-time (OCP-t) experiment and the result demonstrated that steel induced the continuous proceeding of this reaction. This strategy presents a simple and general protocol for preparation of metal nanoparticles (MNPs) on conductive glass substrates. The SERS properties of Au/PAOCG were investigated using aqueous crystal violet (CV) and 4-mercaptopyridine (4-Mpy) as probe molecules. Au/PAOCG allowed as low as 10−9 M CV and 10−8 M 4-Mpy to be detected. The reusability of this substrate was achieved by measuring the SERS spectrum of the probe molecules followed with a 400 °C heat treatment for 10 min to remove the residuals. This substrate could be reused for at least ten cycles without any significantly reduced SERS performance. Therefore, this surface can serve as a portable, durable and reusable SERS substrate and has a potential for commercial applications.
Keywords: Galvanic replacement reaction; Gold nanoparticles; Porous alumina layer; FTO; SERS;
UV irradiation assisted growth of ZnO nanowires on optical fiber surface by Bo Gong; Tielin Shi; Guanglan Liao; Xiaoping Li; Jie Huang; Temgyuan Zhou; Zirong Tang (294-300).
Display OmittedIn this paper, a novel approach was developed for the enhanced growth of ZnO nanowires on optical fiber surface. The method combined a hydrothermal process with the efficient UV irradiation from the fiber core, and the effects of UV irradiation on the growth behavior of ZnO nanowires were investigated. The results show that UV irradiation had great effects on the preferred growth orientation and the quality of the ZnO nanowires. The crystallization velocity along the c-axis would increase rapidly with the increase of the irradiation power, while the growth process in the lateral direction was marginally affected by the irradiation. The structure of ZnO nanowires also shows less oxygen vacancy with UV irradiation of higher power. The developed approach is applicable for the efficient growth of nanowires on the fiber surface, and the ZnO nanowires/optical fiber hybrid structures have great potentials for a wide variety of applications such as optical fiber sensors and probes.
Keywords: UV irradiation assisted growth; ZnO nanowires; Optical fiber; Irradiation power effect; Growth mechanism;
Theoretical insight into an empirical rule about organic corrosion inhibitors containing nitrogen, oxygen, and sulfur atoms by Lei Guo; Ime Bassey Obot; Xingwen Zheng; Xun Shen; Yujie Qiang; Savaş Kaya; Cemal Kaya (301-306).
Display OmittedSteel is an important material in industry. Adding heterocyclic organic compounds have proved to be very efficient for steel protection. There exists an empirical rule that the general trend in the inhibition efficiencies of molecules containing heteroatoms is such that O < N < S. However, an atomic-level insight into the inhibition mechanism is still lacked. Thus, in this work, density functional theory calculations was used to investigate the adsorption of three typical heterocyclic molecules, i.e., pyrrole, furan, and thiophene, on Fe(110) surface. The approach is illustrated by carrying out geometric optimization of inhibitors on the stable and most exposed plane of α-Fe. Some salient features such as charge density difference, changes of work function, density of states were detailedly described. The present study is helpful to understand the afore-mentioned experiment rule.
Keywords: Density functional theory; Corrosion inhibitor; Steel; Adsorption;
Local monitoring of atomic steps on GaAs(001) surface under oxidation, wet removal of oxides and thermal smoothing by I.O. Akhundov; D.M. Kazantsev; V.L. Alperovich; D.V. Sheglov; A.S. Kozhukhov; A.V. Latyshev (307-311).
Display OmittedThe GaAs(001) step-terraced surface relief is studied under oxidation, wet oxide removal and thermal smoothing by ex situ atomic force microscopy with local monitoring of specific atomic steps using lithographic marks for surface area localization. Oxidation in the air and wet oxide removal lead to the formation of monatomic dips on terraces, while atomic steps keep their position and shape. Monitoring step mean position under thermal smoothing allows us to determine the deviation from equilibrium. The experimental smoothing kinetics is well described by Monte Carlo simulation.
Keywords: Atomic steps; Surface smoothing; Local oxidation; GaAs; Monte Carlo simulation;
Green synthesis of silver nanoparticle-reduced graphene oxide using Psidium guajava and its application in SERS for the detection of methylene blue by Prajwal Chettri; V.S. Vendamani; Ajay Tripathi; Manish Kumar Singh; Anand P. Pathak; Archana Tiwari (312-318).
Here we present the synthesis of reduced graphene oxide and silver nanoparticle-reduced graphene oxide composites using aqueous extract of dry leaves of Psidium guajava by one pot reflux method. Psidium guajava extract simultaneously reduces silver nitrate and graphene oxide in the reaction mixture which is confirmed by various spectroscopic techniques. Variable concentrations of silver nitrate solution are used to obtain reduced graphene oxide with different dosage of silver nanoparticles and the resultant composites are examined using surface enhanced Raman scattering measurements. Considering methylene blue as a probe molecule, it is found that the surface enhanced Raman scattering activity increases with the increase in the dose of silver nanoparticles. Our as-synthesised silver nanoparticle-reduced graphene oxide composite shows remarkable performance in detecting methylene blue with concentration as low as 10−8 M for which the enhancement factor is 4.6 × 105. In addition, we report that the reduced graphene oxide quenches the photoluminescence of methylene blue more efficiently than silver nanoparticle-reduced graphene oxide composite. The charge transfer states have been extracted which are mainly responsible for the quenching processes.
Keywords: Silver nanoparticle-reduced graphene oxide; Psidium guajava; SERS; Methylene blue; Fluorescence quenching; Charge transfer;
Effect of electrochemical corrosion on the subsurface microstructure evolution of a CoCrMo alloy in albumin containing environment by Zhongwei Wang; Yu Yan; Yanjing Su; Lijie Qiao (319-329).
Display OmittedThe subsurface microstructures of metallic implants play a key role in bio-tribocorrosion. Due to wear or change of local environment, the implant surface can have inhomogeneous electrochemical corrosion properties. In this work, the effect of electrochemical corrosion conditions on the subsurface microstructure evolution of CoCrMo alloys for artificial joints was investigated. Transmission electron microscope (TEM) was employed to observe the subsurface microstructures of worn areas at different applied potentials in a simulated physiological solution. The results showed that applied potentials could affect the severity of the subsurface deformation not only by changing the surface passivation but also affecting the adsorption of protein on the alloy surface.
Keywords: Cobalt; Bio-tribocorrosion; AES; EIS; TEM; Interfaces;
Removal of aqueous Pb(II) by adsorption on Al2O3-pillared layered MnO2 by Haipeng Zhang; Liqin Gu; Ling Zhang; Shourong Zheng; Haiqin Wan; Jingya Sun; Dongqiang Zhu; Zhaoyi Xu (330-338).
Display OmittedIn the present study, Al2O3-pillared layered MnO2 (p-MnO2) was synthesized using δ-MnO2 as precursor and Pb(II) adsorption on p-MnO2 and δ-MnO2 was investigated. To clarify the adsorption mechanism, Al2O3 was also prepared as an additional sorbent. The adsorbents were characterized by X-ray fluorescence analysis, powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and N2 adsorption-desorption. Results showed that in comparison with pristine δ-MnO2, Al2O3 pillaring led to increased BET surface area of 166.3 m2 g−1 and enlarged basal spacing of 0.85 nm. Accordingly, p-MnO2 exhibited a higher adsorption capacity of Pb(II) than δ-MnO2. The adsorption isotherms of Pb(II) on δ-MnO2 and Al2O3 pillar fitted well to the Freundlich model, while the adsorption isotherm of Pb(II) on p-MnO2 could be well described using a dual-adsorption model, attributed to Pb(II) adsorption on both δ-MnO2 and Al2O3. Additionally, Pb(II) adsorption on δ-MnO2 and p-MnO2 followed the pseudo second-order kinetics, and a lower adsorption rate was observed on p-MnO2 than δ-MnO2. The Pb(II) adsorption capacity of p-MnO2 increased with solution pH and co-existing cation concentration, and the presence of dissolved humic acid (10.2 mg L−1) did not markedly impact Pb(II) adsorption. p-MnO2 also displayed good adsorption capacities for aqueous Cu(II) and Cd(II). Findings in this study indicate that p-MnO2 could be used as a highly effective adsorbent for heavy metal ions removal in water.
Keywords: Manganese oxides; Al2O3 pillaring; Pillared MnO2; Lead adsorption; Heavy metal removal;
ZnO nanoparticles via Moringa oleifera green synthesis: Physical properties & mechanism of formation by N. Matinise; X.G. Fuku; K. Kaviyarasu; N. Mayedwa; M. Maaza (339-347).
The research work involves the development of better and reliable method for the bio-fabrication of Zinc oxide nanoparticles through green method using Moringa Oleifera extract as an effective chelating agent. The electrochemical activity, crystalline structure, morphology, isothermal behavior, chemical composition and optical properties of ZnO nanoparticles were studied using various characterization techniques i.e. Cyclic voltammetry (CV), X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), Selected area electron diffraction (SEAD), Differential scanning calorimetry/thermogravimetric analysis (DSC/TGA), Fourier Transform Infrared analysis (FTIR) and Ultraviolet spectroscopy studies (UV–vis). The electrochemical analysis proved that the ZnO nano has high electrochemical activity without any modifications and therefore are considered as a potential candidate in electrochemical applications. The XRD pattern confirmed the crystallinity and pure phase of the sample. DSC/TGA analysis of ZnO sample (before anneal) revealed three endothermic peaks around 140.8 °C, 223.7 °C and 389.5 °C. These endothermic peaks are attributed to the loss of volatile surfactant, conversion of zinc hydroxide to zinc oxide nanoparticles and transformation of zinc oxide into zinc nanoparticles. Mechanisms of formation of the ZnO nanoparticles via the chemical reaction of the Zinc nitrate precursor with the bioactive compounds of the Moringa oleifera are proposed for each of the major family compounds: Vitamins, Flavonoids, and Phenolic acids.
Keywords: ZnO; Nanoparticles; Green chemistry; Electrochemical; Moringa oleifera;