Applied Surface Science (v.393, #C)

To develop high-performance halloysite nanotube (HNT)-based nanocomposites, the two key issues need to be considered: precise interface control and the dispersal of HNTs. This study presents an efficient way to functionalize halloysite nanotubes with 3-aminophenoxy-phthalonitrile, followed by compounding with poly(arylene ether nitrile) (PEN), to prepare functional nanocomposite films. The surface functionalization of HNTs was characterized and confirmed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Compared with neat PEN, the tensile strength and modulus of the resulting PEN nanocomposites with 3 wt% functionalized HNTs were found to increase by 25.7% and 20.7%, respectively. The good dispersion and high capacitance of the dielectric layer resulted in PEN/HNTs nancomposites with enhanced dielectric permittivity and relatively low dielectric loss. Moreover, the addition of functional HNTs greatly improved the thermal stability of PEN, which could be further enhanced through the chemical cross-linking reaction between the functional HNTs and the PEN matrix. This work provides a new path toward obtaining advanced polymer-based nanocomposites with functional properties.
Keywords: Halloysite nanotubes; Poly(arylene ether nitrile); Functionalization; Tensile properties; Dielectric permittivity; Thermal stability;

Gas phase propylene epoxidation over Au supported on titanosilicates with different Ti chemical environments by Xuan-Ye Chen; Shi-Long Chen; Ai-Pin Jia; Ji-Qing Lu; Wei-Xin Huang (11-22).
Display OmittedThree Ti-containing porous materials − a mesoporous Ti-MCM-41 with distorted tetrahedral framework Ti sites (denoted as Ti-MCM-41-C), a microporous titanium silicate (TS-1) with tetrahedral framework Ti sites and a hybrid Ti-MCM-41 containing TS-1 microstructure (denoted as Ti-MCM-41-H) were used to prepare supported Au catalysts for gas phase propylene epoxidation in the presence of H2 and O2. Both catalyst structures and catalytic reaction kinetics were investigated in detail. The kinetic results show that the apparent activation energies for both PO and CO2 formation follow the order of Au/Ti-MCM-41-C < Au/Ti-MCM-41-H < Au/TS-1. Besides, the adsorption behaviors of propylene on the catalysts were strongly affected by the chemical environment of the framework Ti sites and pore structure in the supports. The adsorption capacity follows the order of Au/Ti-MCM-41-H > Au/TS–1 > Au/Ti-MCM-41-C, in consistence with the order of propylene conversion rate, and the adsorption stability follows the order of Au/TS–1 > Au/Ti-MCM-41-H > Au/Ti-MCM-41-C, in consistence with the order of apparent activation energy. These results demonstrated that the adsorption strength of propylene on the titanosilicates supports strongly affected the catalytic behavior, and implied that the support with balanced defective Ti sites and mesoporous/microporous structure may be a promising approach in the preparation of high-performance supported Au catalysts.
Keywords: Propylene epoxidation; Au catalysts; Defective Ti sites; Porous structure; Kinetics;

Au-assisted fabrication of nano-holes on c-plane sapphire via thermal treatment guided by Au nanoparticles as catalysts by Mao Sui; Puran Pandey; Ming-Yu Li; Quanzhen Zhang; Sundar Kunwar; Jihoon Lee (23-29).
Display OmittedNanoscale patterning of sapphires is a challenging task due to the high mechanical strength, chemical stability as well as thermal durability. In this paper, we demonstrate a gold droplet assisted approach of nano-hole fabrication on c-plane sapphire via a thermal treatment. Uniformly distributed nano-holes are fabricated on the sapphire surface guided by dome shaped Au nanoparticles (NPs) as catalysts and the patterning process is discussed based on the disequilibrium of vapor, liquid, solid interface energies at the Au NP/sapphire interface induced by the Au evaporation at high temperature. Followed by the re-equilibration of interface energy, transport of alumina from the beneath of NPs to the sapphire surface can occur along the NP/sapphire interface resulting in the formation of nano-holes. The fabrication of nano-holes using Au NPs as catalysts is a flexible, economical and convenient approach and can find applications in various optoelectronics.
Keywords: Sapphire patterning; Au nanoparticles; Thermal treatment; Nano-holes; Porous;

Display OmittedMonoclinic Li3V2(PO4)3 compound is gathering significant interest as cathode material for lithium-ion batteries at the moment because of its high theoretical capacity, good safety and low cost. However, it suffers from bad rate capability and short cycling performance duo to the intrinsic low electronic conductivity. Herein, we report a design of Li3V2(PO4)3 particles coated by conducting polymer PEDOT through a facile method. When the cell is tested between 3.0 and 4.3 V, the core-shell Li3V2(PO4)3@PEDOT electrode delivers a capacity of 128.5 mAh g−1 at 0.1C which is about 96.6% of the theoretical capacity. At a high rate of 8C, it can still maintain a capacity of 108.6 mAh g−1 for over 15 cycles with capacity decay rate of only 0.049% per cycle. The impressive electrochemical performance could be attributed to the coated PEDOT layer which can provide a fast electronic connection. Therefore, it can be make a conclusion that the core-shell Li3V2(PO4)3@PEDOT composite is a promising cathode material for next-generation lithium-ion batteries.
Keywords: Li3V2(PO4)3 cathode; Conducting polymer; PEDOT; Lithium-ion batteries; Electrochemical performance;

Display OmittedFree-standing hierarchical macro/mesoporous flexible graphene foam have been constructed by rational intergration ofwell dispersed graphene oxide sheets and amino-modified polystyrene (PS) spheres through a facile “templating and embossing” technique. The three dimensional (3D) macro/mesoporous flexible graphene foam not only inherits the uniform porous structures of graphene foam, but also contains hierarchical macro/mesopores on the struts by sacrificing PS spheres and the activation of KOH, which could providing rapid pathways for ionic and electronic transport to high specific capacitance. Vertically polyaniline (PANI) nanowire arrays are then uniformly deposited onto the hierarchical macro/mesoporous graphene foam(fRGO-F/PANI) by a simple in situ polymerization, which show a high specific capacitance of 939 F g−1. Thanks to the synergistic function of 3D bicontinuous hierarchical porous structure of graphene foam and effective immobilization of PANI nanowires on the struts, the assembled symmetric supercapctior with fRGO-F/PANI as electrodes exhibits a maximum energy density and power density of 20.9 Wh kg−1 and 103.2 kW kg−1, respectively. Moreover, it also displays an excellent cyclic stability with a 88.7% retention after 5000 cycles.
Keywords: Hierarchical porous structure; Graphene foam; Polyaniline; Supercapacitors; Flexible;

Carbon as amorphous shell and interstitial dopant in mesoporous rutile TiO2: Bio-template assisted sol-gel synthesis and photocatalytic activity by Mohamad Azuwa Mohamed; Wan Norharyati Wan Salleh; Juhana Jaafar; Mohamad Saufi Rosmi; Zul Adlan Mohd. Hir; Muhazri Abd Mutalib; Ahmad Fauzi Ismail; Masaki Tanemura (46-59).
Display OmittedRegenerated cellulose membrane was used as bio-template nanoreactor for the formation of rutile TiO2 mesoporous, as well as in-situ carbon dopant in acidified sol-gel system. The effects of calcination temperature on the physicochemical characteristic of core-shell nanostructured of bio-templated C-doped mesoporous TiO2 are highlighted in this study. By varying the calcination temperature, the thickness of the carbon shell coating on TiO2, crystallinity, surface area, and optical properties could be tuned as confirmed by HRTEM, nitrogen adsorption/desorption measurement, XRD and UV–vis-NIR spectroscopy. The results suggested that increment in the calcination temperature would lead to the band gap narrowing from 2.95 to 2.80 eV and the thickness of carbon shell increased from 0.40 to 1.20 nm. The x-ray photoelectron spectroscopy showed that the visible light absorption capability was mainly due to the incorporation of carbon dopant at interstitial position in the TiO2 to form O―Ti―C or Ti―O―C bond. In addition, the formation of the carbon core-shell nanostructured was due to carbonaceous layer grafted onto the surface of TiO2 via Ti―O―C and Ti―OCO bonds. The result indicated that bio-templated C-doped core-shell mesoporous TiO2 prepared at 300 °C exhibited the highest photocatalytic activity. It is worthy to note that, the calcination temperature provided a huge impact towards improving the physicochemical and photocatalytic properties of the prepared bio-templated C-doped core-shell mesoporous TiO2.
Keywords: Mesoporous C-TiO2; Bio-template assisted; Rutile; Carbon shell; Interstitial carbon doping; Photocatalysis;

Carbon nanohoops as attractive toughening and lubricant agents in TiN porous films by Jianyun Zheng; Xiaodong Ren; Junying Hao; Ang Li; Weimin Liu (60-66).
Hoop-shaped conjugated macrocycles (or carbon nanohoops) are eliciting significant interest from theoretical and synthetic scientists on account of their eminent physical and chemical properties. Herein, carbon nanohoops firstly fabricated by CH4 plasma treatment serve as toughening and lubricant agents in TiN porous films. The formation mechanism of carbon nanohoops is explained through a tandem Suzuki coupling/macrocyclization sequence of the charged multiple hydrocarbon molecules. The essential features of carbon nanohoops ensure that the TiN porous films with carbon nanohoops successfully possess flexible, hard, lubricant and antiwear effects.
Keywords: Carbon nanohoops; TiN porous films; CH4 plasma treatment; Modifying properties;

Fenton-like degradation of Bisphenol A catalyzed by mesoporous Cu/TUD-1 by Muthusamy P. Pachamuthu; Sekar Karthikeyan; Rajamanickam Maheswari; Adam F. Lee; Anand Ramanathan (67-73).
Display OmittedA family of copper oxide catalysts with loadings spanning 1–5 wt% were dispersed on a three dimensional, mesoporous TUD-1 silica through a hydrothermal, surfactant-free route employing tetraethylene glycol as a structure-directing agent. Their bulk and surface properties were characterized by N2 physisorption, XRD, DRUVS, EPR, TEM and Raman spectroscopy, confirming the expected mesoporous wormhole/foam support morphology and presence of well-dispersed CuO nanoparticles (∼5–20 nm). The catalytic performance of Cu/TUD-1 was evaluated as heterogeneous Fenton-like catalysts for Bisphenol A (BPA) oxidative degradation in the presence of H2O2 as a function of [H2O2], and CuO loading. Up to 90.4% of 100 ppm BPA removal was achieved over 2.5 wt% Cu/TUD-1 within 180 min, with negligible Cu leaching into the treated water.
Keywords: Copper; TUD-1; Fenton-like oxidation; Mesoporous solid; Bisphenol A; Excitation-emission matrix;

Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3 (001) by O. Lobacheva; Y.M. Yiu; N. Chen; T.K. Sham; L.V. Goncharova (74-81).
Local surface structure of single crystal strontium titanate SrTiO3 (001) samples implanted with Fe in the range of concentrations between 2 × 1014 to 2 × 1016  Fe/cm2 at 30 keV has been investigated. In order to facilitate Fe substitution (doping), implanted samples were annealed in oxygen at 350 °C. Sr depletion was observed from the near-surface layers impacted by the ion-implantation process, as revealed by Rutherford Backscattering Spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), X-ray Absorption Near Edge Spectroscopy (XANES), and Atomic Force Microscopy (AFM). Hydrocarbon contaminations on the surface may contribute to the mechanisms of Sr depletion, which have important implications for Sr(Ti1-xFex)O3-δ materials in gas sensing applications.
Keywords: XPS; XANES; Fe-doped SrTiO3; Ion implantation;

Functionalization of CoCr surfaces with cell adhesive peptides to promote HUVECs adhesion and proliferation by Maria Isabel Castellanos; Carlos Mas-Moruno; Anna Grau; Xavier Serra-Picamal; Xavier Trepat; Fernando Albericio; Michael Joner; Francisco Javier Gil; Maria Pau Ginebra; Jose María Manero; Marta Pegueroles (82-92).
Display OmittedBiomimetic surface modification with peptides that have specific cell-binding moieties is a promising approach to improve endothelialization of metal-based stents. In this study, we functionalized CoCr surfaces with RGDS, REDV, YIGSR peptides and their combinations to promote endothelial cells (ECs) adhesion and proliferation. An extensive characterization of the functionalized surfaces was performed by XPS analysis, surface charge and quartz crystal microbalance with dissipation monitoring (QCM-D), which demonstrated the successful immobilization of the peptides to the surface. Cell studies demonstrated that the covalent functionalization of CoCr surfaces with an equimolar combination of RGDS and YIGSR represents the most powerful strategy to enhance the early stages of ECs adhesion and proliferation, indicating a positive synergistic effect between the two peptide motifs. Although these peptide sequences slightly increased smooth muscle cells (SMCs) adhesion, these values were ten times lower than those observed for ECs. The combination of RGDS with the REDV sequence did not show synergistic effects in promoting the adhesion or proliferation of ECs. The strategy presented in this study holds great potential to overcome clinical limitations of current metal stents by enhancing their capacity to support surface endothelialization.
Keywords: CoCr alloy; Surface functionalization; Cell adhesive peptides; HUVEC proliferation; Endothelialization; SMCs adhesion;

Enhancing performance and surface antifouling properties of polysulfone ultrafiltration membranes with salicylate-alumoxane nanoparticles by Samaneh Mokhtari; Ahmad Rahimpour; Ahmad Arabi Shamsabadi; Setareh Habibzadeh; Masoud Soroush (93-102).
To improve the hydrophilicity and antifouling properties of polysulfone (PS) ultrafiltration membranes, we studied the use of salicylate-alumoxane (SA) nanoparticles as a novel hydrophilic additive. The effects of SA nanoparticles on the membrane characteristics and performance were investigated in terms of membrane structure, permeation flux, solute rejection, hydrophilicity, and antifouling ability. The new mixed-matrix membranes (MMMs) possess asymmetric structures. They have smaller finger-like pores and smoother surfaces than the neat PS membranes. The embedment of SA nanoparticles in the polymer matrix and the improvement of surface hydrophilicity were investigated. Ultrafiltration experiments indicated that the pure-water flux of the new MMMs initially increases with SA nanoparticles loading followed by a decrease at high loadings. Higher BSA solution flux was achieved for the MMMs compared to the neat PS membranes. Membranes with 1 wt.% SA nanoparticles exhibit the highest flux recovery ratio of 87% and the lowest irreversible fouling of 13%.
Keywords: Salicylate-alumoxane nanoparticles; PS ultrafiltration membranes; Surface hydrophilicity; Surface antifouling properties;

Display OmittedTitanium dioxide nanoparticles are widely used for photocatalysis, and the relative fraction of titanium dioxide polymorph, i.e. anatase, rutile, or brookite, significantly affects the final performance. Even though conventional phase diagrams indicate a higher stability for the rutile polymorph, it is well established that nanosizes benefit the anatase phase due to its smaller surface energy. However, doping elements are expected to change this behavior, once changes in both surface and bulk energies may occur. Nb2O5 is commonly added to TiO2 to allow property control. However, the effect of niobium on the relative stability of anatase and rutile phases is not well understood from the thermodynamic point of view. The objective of this work was to build a new predictive nanoscale phase diagram for Nb2O5-doped TiO2. Water adsorption microcalorimetry and high temperature oxide melt solution were used to obtain the surface and bulk enthalpies. The phase diagram obtained shows the stable titania polymorph as a function of the composition and size.
Keywords: Titanium dioxide; Anatase; Rutile; Surface energy; Enthalpy; Phase diagram; Nanoparticles;

Herein, we designed the p-type CuxO (x  = 1 or 2) nanoparticles deposited on SiO2 spherical particle inside and coated with thin layered n-type TiO2 semiconductors outside for reduction purpose. The composite material, abbreviated as SiO2@CuxO@TiO2, was characterized. The catalytic performance of the composite was tested for the reductions of 4-nitrophenol (4-NP) and 2-nitroaniline (2-NA). Complete reductions of 4-NP and 2-NA took, 210 and 150 s, respectively. The catalytic efficiency of the composite material may be associated with electron and hole separation resulted from the p-n junction formation between p-type CuxO and n-type TiO2 and the built-in electric field. Moreover, the hydride ion and electrons released from NaBH4 together with outward electrons from n-type TiO2, synergistically, are also responsible for the reduction of nitro aromatic compounds. Our design of composite material from low-priced metal oxides was successful towards reduction of nitro-aromatic compounds.
Keywords: 4-Nitrophenol; Reduction; Nitro-aromatic; p-n Junction;

Germanium nitride and oxynitride films for surface passivation of Ge radiation detectors by G. Maggioni; S. Carturan; L. Fiorese; N. Pinto; F. Caproli; D.R. Napoli; M. Giarola; G. Mariotto (119-126).
Display OmittedThis work reports a detailed investigation of the properties of germanium nitride and oxynitride films to be applied as passivation layers to Ge radiation detectors. All the samples were deposited at room temperature by reactive RF magnetron sputtering. A strong correlation was found between the deposition parameters, such as deposition rate, substrate bias and atmosphere composition, and the oxygen and nitrogen content in the film matrix. We found that all the films were very poorly crystallized, consisting of very small Ge nitride and oxynitride nanocrystallites, and electrically insulating, with the resistivity changing from three to six orders of magnitude as a function of temperature. A preliminary test of these films as passivation layers was successfully performed by depositing a germanium nitride film on the intrinsic surface of a high-purity germanium (HPGe) diode and measuring the improved performance, in terms of leakage current, with respect to a reference passivated diode. All these interesting results allow us to envisage the application of this coating technology to the surface passivation of germanium-based radiation detectors.
Keywords: Germanium nitride layer; Germanium oxynitride layer; Room temperature deposition; Electrical resistivity; Surface passivation; Hyperpure germanium detector;

Morphology control in thin films of PS:PLA homopolymer blends by dip-coating deposition by Alexane Vital; Marylène Vayer; Thomas Tillocher; Rémi Dussart; Mohamed Boufnichel; Christophe Sinturel (127-133).
Display OmittedIn this work, smooth polymer films of PS, PLA and their blends, with thicknesses ranging from 20 nm up to 400 nm and very few defects on the surface were obtained by dip-coating. In contrast to the process of spin-coating which is conventionally used to prepare thin films of polymer blends, we showed that depending on the deposition parameters (withdrawal speed and geometry of the reservoir), various morphologies such as layered films and laterally phase-separated domains could be formed for a given blend/solvent pair, offering much more opportunities compared to the spin-coating process. This diversity of morphologies was explained by considering the superposition of different phenomena such as phase separation process, dewetting and vitrification in which parameters such as the drying time, the compatibility of the polymer/solvent pairs and the affinity of the polymer towards the interfaces were suspected to play a significant role. For that purpose, the process of dip-coating was examined within the capillary and the draining regimes (for low and high withdrawal speed respectively) in order to get a full description of the thickness variation and evaporation rate as a function of the deposition parameters.
Keywords: Polymer blend; Dip-coating; Morphology; Thin polymer film; Phase separation;

Effect of synthesis route on electrical and ethanol sensing characteristics for LaFeO3-δ nanoparticles by citric sol-gel method by Ensi Cao; Yuqing Yang; Tingting Cui; Yongjia Zhang; Wentao Hao; Li Sun; Hua Peng; Xiao Deng (134-143).
LaFeO3-δ nanoparticles were prepared by citric sol-gel method with different raw material choosing and calcination process. The choosing of polyethylene glycol instead of ethylene glycol as raw material and additional pre-calcination at 400 °C rather than direct calcination at 600 °C could result in the decrease of resistance due to the reduction of activation energy Ea. Meanwhile, the choosing of ethylene glycol as raw material and additional pre-calcination leads to the enhancement of sensitivity to ethanol. Comprehensive analysis on the sensitivity and XRD, SEM, TEM, XPS results indicates that the sensing performance of LaFeO3-δ should be mainly determined by the adsorbed oxygen species on Fe ions, with certain contribution from native active oxygen. The best sensitivity of 46.1–200 ppm ethanol at prime working temperature of 112 °C is obtained by the sample using ethylene glycol as raw material with additional pre-calcination, which originates from its uniformly-sized and well-dispersed particles as well as high atomic ratio of Fe/La at surface region.
Keywords: LaFeO3; Sol-gel; XPS; Ethanol sensing; Gas sensor;

This work demonstrates an example for turning rubbish into valuable products and addresses the disposal issue of waste biomass simultaneously for environment clean. And the typical sample exhibits excellent catalytic performance toward ORR, which is similar to that of commercial Pt/C.Display OmittedDeveloping efficient and economical catalysts for the oxygen reduction reaction (ORR) is important to promote the commercialization of fuel cells. Here, we report a simple and environmentally friendly method to prepare nitrogen (N) –doped hierarchical porous carbon (HPC)/reduced graphene oxide (RGO) composites by reusing waste biomass (pomelo peel) coupled with graphene oxide (GO). This method is green, low-cost and without using any acid or alkali activator. The typical sample (N-HPC/RGO-1) contains 5.96 at.% nitrogen and larger BET surface area (1194 m2/g). Electrochemical measurements show that N-HPC/RGO-1 exhibits not only a relatively positive onset potential and high current density, but also considerable methanol tolerance and long-term durability in alkaline media as well as in acidic media. The electron transfer number is close to 4, which means that it is mostly via a four-electron pathway toward ORR. The excellent catalytic performance of N-HPC/RGO-1 is due to the synergistic effect of the inherent interwoven network structure of HPC, the good electrical conductivity of RGO, and the heteroatom doping for the composite. More importantly, this work demonstrates a good example for turning discarded rubbish into valuable functional products and addresses the disposal issue of waste biomass simultaneously for environment clean.
Keywords: Oxygen reduction reaction; Waste biomass; N-HPC/RGO; Synergistic effect; Valuable functional products;

Controllable synthesis of nitrogen-doped hollow mesoporous carbon spheres using ionic liquids as template for supercapacitors by Aibing Chen; Yunqian Li; Lei Liu; Yifeng Yu; Kechan Xia; Yuying Wang; Shuhui Li (151-158).
We demonstrate a facile sol-gel process for the synthesis of the N-HMCSs with tailorable size and morphology using resorcinol/formaldehyde resin as a carbon precursor, tetraethyl orthosilicate as a structure-assistant agent, ionic liquids simultaneously as template, partial carbon source and nitrogen source.Display OmittedWe have demonstrated a facile and controllable synthesis of monodispersed nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) using resorcinol/formaldehyde resin as a carbon precursor, tetraethyl orthosilicate as a structure-assistant agent, ionic liquids (ILs) as soft template, partial carbon sources, and nitrogen sources. The sizes and the architectures including hollow and yolk-shell of resultant carbon spheres can be efficiently controlled through the adjustment of the content of ILs. Alkyl chain length of the ILs also has an important effect on the formation of N-HMCSs. With proper alkyl chain length and content of ILs, the resultant N-HMCSs show monodispersed hollow spheres with high surface areas (up to 1158 m2  g−1), large pore volumes (up to 1.70 cm3  g−1), and uniform mesopore size (5.0 nm). Combining the hollow mesoporous structure, high porosity, large surface area, and nitrogen functionality, the as-synthesized N-HMCSs have good supercapacitor performance with good capacitance (up to 159 F g−1) and favorable capacitance retention (88% capacitive retention after 5000 cycles).
Keywords: Mesoporous; Carbon nanospheres; ILs; Hollow; Nitrogen-doped; Supercapacitors;

Display OmittedSurface compositional disorder were discovered in ZnWO4 nanocrystals prepared by solvothermal method.Present work focuses on the surface composition disorder, its origin and relevance to photoluminescent and photocatalytic properties of ZnWO4 nanocrystals. ZnWO4 nanoparticles were synthesized under solvothermal conditions, in which formic acid was employed for both the nonstoichiometry and kinetic size control. Nonstoichiometry ranging from 1.05 to 1.18 was originated from the surface Zn-rich disorder layer, as reflected by an excess of cation Zn2+ in the X-ray photoelectron spectroscopy and a new Raman vibration mode at about 930 cm−1 and HR-TEM images. Surface Zn-rich disorder layer has shown a great impact on the structure and properties, including lattice expansion, band-gap narrowing, luminescence enhancement, as well as photocatalytic weakening effect. The investigation on surface composition disorder of multi-component oxides is helpful to deeply understand their formation process and further to find a new functionality optimizing approach.
Keywords: Zn rich ZnWO4; Solvothermal synthesis; Formic acid; Surface disordered; Photoluminescence; Photocatalysis;

Display OmittedProperties of the SiC(0001) surface under various Si coverage were studied using density functional theory (DFT) calculations. It was shown that the clean SiC(0001) surface has the Fermi level pinned by the Si broken bond state, located 0.8 eV below the conduction band minimum (CBM). The single Si atom is adsorbed in the H3 site, saturating broken bonds of the three neighboring Si atoms and that leads to the 2 3 × 2 3 reconstruction. The energy of Si atom adsorption at the clean SiC(0001) surface is equal to 7.1 eV for single atom. It is reduced to approximately 6.7 eV and 5.0 eV, for the coverage below and above 0.25 monolayer (ML), respectively. The adsorption energy jump of about 1.7 eV is due to electron transfer in which Si adatom states accommodate four electrons from Si broken bonds states. In addition adsorption of Si atoms at coverage exceeding 0.4 ML leads to occupation of H3 sites that share Si surface top atoms with other Si adatoms which further reduces the adsorption energy to 4.2 eV. The Si on-top position has the same energy which indicates on transition to this occupation for higher coverage. Accordingly, the vapor-surface equilibrium shows decrease of Si pressure by 3 orders of magnitude in the 0.25–0.40 Si ML coverage range. It is therefore expected that in typical SiC vapor growth, the Si coverage of the SiC(0001) surface is close to 0.3 ML.
Keywords: Silicon carbide; Adsorption; Surface;

Display OmittedA direct Z-scheme type photocatalyst WO3/Ag3PO4 composite (molar ration 1:1, 1W/1Ag) was prepared by hydrothermal method. The 1W/1Ag was characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), UV–vis diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and photoluminescence emission spectroscopy (PL) etc. technologies. The photocatalytic performances were evaluated by degradation of methylene blue (MB) and methyl orange (MO), and their removal rates were up to 95% after 60 min and 90% after 180 min, respectively. The prepared 1W/1Ag exhibits a much higher photocatalytic activity than pure Ag3PO4 and pure WO3 under visible light irradiation. The apparent rate constants of MB and MO degradation on 1W/1Ag are about 2.4 and 2.5 times that of pure Ag3PO4, respectively. The enhanced performance of the 1W/1Ag is attributed to a synergistic effect including relatively high surface area, strong light absorption, matched energy band structure, and the improved separation of photogenerated charge carriers between the two components. A reasonable Z-scheme mechanism referring to directed migration of photoinduced carriers was proposed. Thus, it can be suggested that the 1W/1Ag can serve as a promising photocatalyst for environmental purification and clean energy utilization.
Keywords: Z-scheme photocatalyst; Silver orthophosphate; Nanocomposites; Organic dye degradation;

Electrodeposition of nano-sized bismuth on copper foil as electrocatalyst for reduction of CO2 to formate by Weixin Lv; Jing Zhou; Jingjing Bei; Rui Zhang; Lei Wang; Qi Xu; Wei Wang (191-196).
Display OmittedElectrochemical reduction of carbon dioxide (CO2) to formate is energetically inefficient because high overpotential is required for reduction of CO2 to formate on most traditional catalysts. In this paper, a novel nano-sized Bi-based electrocatalyst deposited on a Cu foil has been synthesized, which can be used as a cathode for electrochemical reduction of CO2 to formate with a low overpotential (0.69 V) and a high selectivity (91.3%). The electrocatalyst can show excellent catalytic performance toward reduction of CO2 which can probably be attributed to the nano-sized structure and the surface oxide layer. The energy efficiency for reduction of CO2 to formate can reach to 50% when an IrxSnyRuzO2/Ti electrode is used as anode, it is one of the highest values found in the literatures and very practicable for sustainable fuel synthesis.
Keywords: Nano-sized bismuth; Electrocatalysis; Low overpotential; Tafel slope; Energy efficiency;

Display OmittedHierarchical Ag mesostructures with highly rough surface morphology have been synthesized at room temperature through a simple seed-mediated approach. Electron microscopy characterizations indicate that the obtained Ag mesostructures exhibit a textured surface morphology with the flower-like architecture. Moreover, the particle size can be tailored easily in the range of 250–500 nm. For the growth process of the hierarchical Ag mesostructures, it is believed that the self-assembly mechanism is more reasonable rather than the epitaxial overgrowth of Ag seed. The oriented attachment of nanoparticles is revealed during the formation of Ag mesostructures. Single particle surface enhanced Raman spectra (sp-SERS) of crystal violet adsorbed on the hierarchical Ag mesostructures were measured. Results reveal that the hierarchical Ag mesostructures can be highly sensitive sp-SERS substrates with good reproducibility. The average enhancement factors for individual Ag mesostructures are estimated to be about 106.
Keywords: Hierarchical; Silver; Seed-mediated growth; Mesostructure; SERS;

Display OmittedThin films of U1− xThxO2 (x = 0 to 1) have been deposited via reactive DC sputter technique and characterized by X-ray/Ultra-violet Photoelectron Spectroscopy (XPS/UPS), X-ray Powder Diffractometer (XRD) and Cyclic Voltammetry (CV) in order to understand the effect of Thorium on the oxidation mechanism. During the deposition, the competition between uranium and thorium for oxidation showed that thorium has a much higher affinity for oxygen. Deposition conditions, time and temperature were also the subject of this study, to look at the homogeneity and the stability of the films. While core level and valence band spectra were not altered by the time of deposition, temperature was affecting the oxidation state of uranium and the valence band due to the mobility increase of oxygen through the film. X-ray diffraction patterns, core level spectra obtained for U1 − xThxO2 versus the composition showed that lattice parameters follow the Vegard's law and together with the binding energies of U-4f and Th-4f are in good agreement with literature data obtained on bulk compounds. To study the effect of thorium on the oxidation of U1 − xThxO2 films, we used CV experiments at neutral pH of a NaCl solution in contact with air. The results indicated that thorium has an effect on the uranium oxidation as demonstrated by the decrease of the current of the oxidation peak of uranium. XPS measurements made before and after the CV, showed a relative enrichment of thorium at the extent of uranium at the surface supporting the formation at a longer term of a thorium protective layer at the surface of uranium-thorium mixed oxide.
Keywords: Thin film; Mixed oxide; Electrochemistry; Corrosion; Actinide oxide;

Hydrogenation of o-cresol on platinum catalyst: Catalytic experiments and first-principles calculations by Yaping Li; Zhimin Liu; Wenhua Xue; Steven P. Crossley; Friederike C. Jentoft; Sanwu Wang (212-220).
Display OmittedCatalytic experiments were performed for the hydrogenation of o-cresol in n-dodecane over a platinum catalyst. Batch reactions analyzed with an in-situ ATR IR probe suggest that the hydrogenation results in the formation of the final product, 2-methyl-cyclohexanol, with 2-methyl-cyclohexanone as the intermediate product. Ab initio density-functional theory was employed to investigate the atomic-scale mechanism of o-cresol hydrogenation on the Pt(111) surface. The formation of 2-methyl-cyclohexanone was found to involve two steps. The first step is a hydrogen abstraction, that is, the H atom in the hydroxyl group migrates to the Pt surface. The second step is hydrogenation, that is, the pre-existing H atoms on Pt react with the carbon atoms in the aromatic ring. On the other hand, 2-methyl-cyclohexanonol may be produced through two paths, with activation energies slightly greater than that for the formation of 2-methyl-cyclohexanone. One path involves direct hydrogenation of the aromatic ring. Another path involves three steps, with the partial hydrogenation of the ring as the first step, hydrogen abstraction of the ―OH group as the second, and hydrogenation of remaining C atoms and the O atom the last.
Keywords: Hydrogenation; Cresol; Platinum catalyst; ab initio calculations; Activation energies;

The function of an In0.17Al0.83N interlayer in n-ZnO/In0.17Al0.83N/p-GaN heterojunctions by Xiao Wang; Xuewei Gan; Guozhen Zhang; Xi Su; Meijuan Zheng; Zhiwei Ai; Hao Wu; Chang Liu (221-224).
ZnO thin films were deposited on p-type GaN with a thin In0.17Al0.83N interlayer, forming double heterostructural diodes of n-ZnO/In0.17Al0.83N/p-GaN. The crystalline quality of the ZnO films was improved and its orientation was kept along < 70 7 ¯ 4 > that was perpendicular to ( 10 1 ¯ 1 ) plane. The reverse leakage current was reduced by introducing the In0.17Al0.83N interlayer. The electroluminescence spectra of the n-ZnO/In0.17Al0.83N/p-GaN heterojunctions were dominated by p-GaN emissions under forward biases and n-ZnO emissions under reverse biases. The valence-band offset and conduction-band offset between the ZnO and In0.17Al0.83N were determined to be −0.72 and 1.95 eV, respectively.
Keywords: ZnO/InAlN/GaN hetrojunction; InAlN interlayer; Light emitting diode; Electroluminescence; Band alignment;

Equilibrium CO2 adsorption on zeolite 13X prepared from natural clays by Vahid Garshasbi; Mansour Jahangiri; Mansoor Anbia (225-233).
Display OmittedZeolite 13X was successfully synthesized by hydrothermal treatment using natural clays extracted from Iranian resources. The preliminary natural materials and the final zeolite 13X samples were characterized by X-ray Diffraction (XRD), Fourier-Transfer Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and N2 adsorption–desorption isotherm. The effects of various factors such as NaOH addition amount and aging time on the crystalline products were studied during the synthesis process. The optimum conditions related to the synthesis of zeolite 13X were set. Accordingly, NaOH concentration was equal to 4 M. It was further crystallized at 65 °C for 72 h after its homogenization by agitation at room temperature for 120 h. In this study, the zeolite 13X prepared from natural kaolin (13X-K) showed a high BET surface area of 591 m2/g with higher micropore volume (0.250 cm3/g) than other materials. Adsorption equilibrium isotherms of CO2 were investigated using a static, volumetric method. In addition, pressures for the pure component data extended up to 20 bar. The adsorption equilibrium data of CO2 was fitted to Langmuir, Freundlich, Lamgmuir-Freundlich, Toth and BET isotherm models. It was found that the Langmuir-Freundlich model was more suitable than other models for CO2 description. The results showed that the synthetic zeolite has higher equilibrium selectivity for CO2. Also, the CO2 uptake by zeolite 13X-K was equal to 6.9 mmol/g.
Keywords: Zeolite 13X; Hydrothermal synthesis; Adsorption isotherms; Kaolin; Bentonite; Feldspath;

Nano-structure and optical properties (plasmonic) of graded helical square tower-like (terraced) Mn sculptured thin films by Hadi Savaloni; Mahsa Fakharpour; Araz Siabi-Garjan; Frank Placido; Ferydon Babaei (234-255).
Display OmittedGraded helical square tower-like terraced sculptured Mn thin films (GHSTTS) are produced in three stages with different number of arms using oblique angle deposition together with rotation of substrate holder about its surface normal, plus a shadowing block fixed at the centre of the substrate holder. The structural characterization of the produced samples was obtained using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). Results showed a structural gradient with distance from the edge of the shadowing block, which in turn is responsible for the decrease in the volume of void fraction and increase of grain size. Plasmon absorption peaks observed in the optical analysis of these nano-structures showed that their wavelength region and intensity depend on the polarization and the incident angle of light, as well as the distance from the edge of the shadowing block. According to our model and discrete dipole approximation (DDA) calculations, when the number of parallel nano-rods of different lengths and radii are increased the peak in the spectrum shifts to shorter wavelengths (blue shift). Also when the diameters of the nano-rods increases (a situation that occurs with increasing film thickness) the results is again a blue shift in the spectrum. The presence of defects in these sculptured structures caused by the shadowing effect is predicted by the theoretical DDA investigation of their optical spectra. Good agreement is obtained between our theoretical results and the experimental observations in this work.
Keywords: Graded helical; Square sculptured thin films; Manganese; Extinction spectra; Optical properties; Electric near-field distribution;

Producing ZnFe2O4 thin films from ZnO/FeO multilayers by Karen L. Salcedo Rodríguez; Martin Hoffmann; Federico Golmar; Gustavo Pasquevich; Peter Werner; Wolfram Hergert; Claudia E. Rodríguez Torres (256-261).
Display OmittedThe present work investigates the structural and magnetic properties of ZnFe2O4 thin films obtained from ZnO/FeO multilayers deposited on MgO substrate by DC reactive sputtering. We show that this method is good to grow efficiently ordered ZnFe2O4 films. The quality of the thin films is ensured by TEM measurements, which showed a well ordered film of ZnFe2O4. The magnetic properties of these thin films present still minimal differences when compared to bulk ZnFe2O4 powders. They exhibit a ferromagnetic-like behavior at low temperatures, whereas ZnFe2O4 is expected to be antiferromagnetic. We found that the magnetic signal originated from the film surface, where cation inversion was visible from grazing incidence X-ray fluorescence measurements. The inversion of Fe ions with Zn ions caused a magnetic spin glass state, which created then the ferromagnetic-like behavior differently to bulk ZnFe2O4. These facts point to possible routes in order to improve the growing process of ZnFe2O4 via ZnO/FeO multilayers.
Keywords: ZnFe2O4; DC-sputtering; Cation inversion; Spin glass;

Display OmittedA novel synthesis process was used to prepare TiO2 microspheres, TiO2 P-25, SrTiO3 and KTaO3 decorated by CdTe QDs and/or Pt NPs. The effect of semiconductor matrix, presence of CdTe QDs and/or Pt NPs on the semiconductor surface as well as deposition technique of Pt NPs (photodeposition or radiolysis) on the photocatalytic activity were investigated. The as-prepared samples were characterized by X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) with energy-dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), photoluminescence spectrometry (PL), Fourier transform infrared (FT-IR) and Raman spectra, diffuse reflectance spectroscopy (DRS) and BET surface area analysis. The photocatalytic decomposition of toluene in gas phase, activated by light-emitting diodes (LEDs), with the CdTe/Pt nanoparticles-modified TiO2 microspheres, P25, SrTiO3 and KTaO3 semiconductors was investigated under UV–vis and visible irradiation.The results showed that the photoactivity depends on semiconductor matrix. The highest photoactivity under Vis light was observed for KTaO3/CdTe-Pt(R) sample (56% of toluene was decompose after 30 min of irradiation). The efficiency of the most active sample was 3 times higher than result for P25 and two times higher than for unmodified KTaO3.
Keywords: TiO2; KTaO3; SrTiO3; CdTe quantum dots; Pt nanoparticles; Nanocomposites;

Green synthesis of nitrogen-doped graphitic carbon sheets with use of Prunus persica for supercapacitor applications by Raji Atchudan; Thomas Nesakumar Jebakumar Immanuel Edison; Suguna Perumal; Yong Rok Lee (276-286).
Display OmittedNitrogen-doped graphitic carbon sheets (N-GCSs) were prepared from the extract of unripe Prunus persica fruit by a direct hydrothermal method. The synthesized N-GCSs were examined by high resolution transmission electron microscopy (HRTEM), nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR) spectroscopy. HRTEM showed that the synthesized carbon sheets were graphitic with lattice fringes and an inter-layer distance of 0.36 nm. Doping with the nitrogen moiety present over the synthesized GCSs was confirmed by XPS, FT-IR spectroscopy, and energy dispersive X-ray spectroscopy elemental mapping. The fruit extract associated with hydrothermal-carbonization method is economical and eco-friendly with a single step process. The resulting carbon sheets could be modified and are promising candidates for nano-electronic applications, including supercapacitors. The synthesized N-GCSs-2 provided a high specific capacitance of 176 F g−1 at a current density of 0.1 A g−1. This electrode material has excellent cyclic stability, even after 2000 cycles of charge-discharge at a current density of 0.5 A g−1.
Keywords: Prunus persica; Hydrothermal; Carbonization; Graphitic carbon sheet; Carbon cloth; Supercapacitor;

Effects of 3D microlens transfer into fused silica substrate by CF4/O2 dry etching by Viktoras Grigaliūnas; Dalius Jucius; Algirdas Lazauskas; Mindaugas Andrulevičius; Jolita Sakaliūnienė; Brigita Abakevičienė; Vitoldas Kopustinskas; Saulius Smetona; Sigitas Tamulevičius (287-293).
Display OmittedNowadays, 3D microoptical elements find a variety of applications from light emitting diodes and household appliances to precise medical endoscopes. Such elements, fabricated in a fused silica substrate by combining 3D e-beam patterning and dry etching, can be used as a mold for the high throughput replication in polymeric materials by UV nanoimprint technique. Flexible and precise control of 3D shape in the resist layer can be achieved by e-beam patterning, but it is also very important to know peculiarities of 3D pattern transfer from resist layer into the fused silica substrate. This paper reports on the effects of PMMA 3D microlens pattern transfer into fused silica substrate by CF4/O2 dry etching. It is demonstrated that etching rate ratio between PMMA and fused silica changes during plasma treatment. Thus, the resulting shape of transferred 3D profile is different from the shape in PMMA and this variation must be assessed during the design phase.
Keywords: Microlens; e-Beam patterning; PMMA; Dry etching; Fused silica;

Atomic nature of the Schottky barrier height formation of the Ag/GaAs(001)-2 × 4 interface: An in-situ synchrotron radiation photoemission study by Chiu-Ping Cheng; Wan-Sin Chen; Keng-Yung Lin; Guo-Jhen Wei; Yi-Ting Cheng; Yen-Hsun Lin; Hsien-Wen Wan; Tun-Wen Pi; Raymond T. Tung; Jueinai Kwo; Minghwei Hong (294-298).
Display OmittedThe Interface of Ag with p-type α2 GaAs(001)-2 × 4 has been studied to further understand the formation mechanism of the Schottky barrier height (SBH). In the initial phase of Ag deposition, high-resolution core-level data show that Ag adatoms effectively passivate the surface As-As dimers without breaking them apart. The Ag(+)-As(−) dipoles are thus generated with a maximal potential energy of 0.26 eV; a SBH of 0.38 eV was measured. Greater Ag coverage causes elemental segregation of As/Ga atoms, reversing the direction of the net dipole. The band bending effect near the interface shows a downward shift of 0.08 eV, and the final SBH is similar to the value as measured at the initial Ag deposition. Both parameters are secured at 0.25 Å of Ag thickness prior to the observation of metallic behavior of Ag. Inadequacy of the metal-induced gap-state model for explaining SBH is evident.
Keywords: Schottky barrier height; III–V semiconductor; Synchrotron radiation photoemission;

Preparation of paclitaxel/chitosan co-assembled core-shell nanofibers for drug-eluting stent by Jing Tang; Yongjia Liu; Bangshang Zhu; Yue Su; Xinyuan Zhu (299-308).
Display OmittedThe paclitaxel/chitosan (PTX/CS) core-shell nanofibers (NFs) are easily prepared by co-assembly of PTX and CS and used in drug-eluting stent. The mixture solution of PTX (dissolved in ethanol) and CS (dissolved in 1% acetic acid water solution) under sonication will make the formation of NFs, in which small molecule PTX co-assembles with biomacromolecular CS through non-covalent interactions. The obtained NFs are tens to hundreds nanometers in diameter and millimeter level in length. Furthermore, the structure of PTX/CS NFs was characterized by confocal laser scanning microscopy (CLSM), zeta potential, X-ray photoelectron spectroscopy (XPS) and nanoscale infra-red (nanoIR), which provided evidences demonstrated that PTX/CS NFs are core-shell structures. The ‘shell’ of CS wrapped outside of the NFs, while PTX is located in the core. Thus it resulted in high drug loading content (>40 wt.%). The well-controlled drug release, low cytotoxicity and good haemocompatibility were also found in drug carrier system of PTX/CS NFs. In addition, the hydrophilic and flexible properties of NFs make them easily coating and filming on stent to prepare drug-eluting stent (DES). Therefore, this study provides a convenient method to prepare high PTX loaded NFs, which is a promising nano-drug carrier used for DES and other biomedical applications. The possible molecular mechanism of PTX and CS co-assembly and core-shell nanofiber formation is also explored.We develop a convenient and efficient approach to fabricate core-shell nanofibers (NFs) through the co-assembly of paclitaxel (PTX) and chitosan (CS). Results indicate that the co-assembled PTX/CS NFs have high drug loading content (>40 wt.%), low cytotoxicity, well-sustained drug release and good haemocompatibility. The PTX/CS NFs coated easily on stents with substrate surface uneven and irregular. Findings from this work provide a novel drug/polymer system, which would have potential application for drug-eluting stent (DES).
Keywords: Co-assembly; Paclitaxel; Chitosan; Core-shell nanofibers; Drug-eluting stent;

Synthesis of graphene oxide and reduced graphene oxide by needle platy natural vein graphite by R.M.N.M. Rathnayake; H.W.M.A.C. Wijayasinghe; H.M.T.G.A. Pitawala; Masamichi Yoshimura; Hsin-Hui Huang (309-315).
Display OmittedAmong natural graphite varieties, needle platy vein graphite (NPG) has very high purity. Therefore, it is readily used to prepare graphene oxide (GO) and reduced graphene oxide (rGO). In this study, GO and rGO were prepared using chemical oxidation and reduction process, respectively. The synthesized materials were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. XRD studies confirmed the increase of the interlayer spacing of GO and rGO in between 3.35 to 8.66 A°. AFM studies showed the layer height of rGO to be 1.05 nm after the reduction process. TEM micrographs clearly illustrated that the prepared GO has more than 25 layers, while the rGO has only less than 15 layers. Furthermore, the effect of chemical oxidation and reduction processes on surface morphology of graphite were clearly observed in FESEM micrographs. The calculated RO/C of GO and rGO using XPS analysis are 5.37% and 1.77%, respectively. The present study revealed the successful and cost effective nature of the chemical oxidation, and the reduction processes for the production of GO and rGO out of natural vein graphite.
Keywords: Needle platy graphite; Reduced graphene oxide; Graphene oxide; Chemical oxidation; Chemical reduction;

Enhanced aerobic degradation of 4-chlorophenol with iron-nickel nanoparticles by Wenjuan Shen; Yi Mu; Bingning Wang; Zhihui Ai; Lizhi Zhang (316-324).
Display OmittedIn this study, we demonstrate that the bimetallic iron-nickel nanoparticles (nZVIN) possessed an enhanced performance in comparison with nanoscale zero-valent iron (nZVI) on aerobic degradation of 4-chlorophenol (4-CP). The 4-CP degradation rate constant in the aerobic nZVIN process (nZVIN/Air) was 5 times that in the classic nZVI counterpart system (nZVI/Air). Both reactive oxygen species measurement and inhibition experimental results suggested that hydroxyl radicals were the major active species contributed to aerobic 4-CP degradation with nZVI, on contrast, superoxide radicals predominated the 4-CP degradation in the nZVIN/Air process. High performance liquid chromatography and gas chromatography-mass spectrometer analysis indicated the intermediates of the nZVI/Air system were p-benzoquinone and hydroquinone, which were resulted from the bond cleavage between the chlorine and carbon atom in the benzene ring by hydroxyl radicals. However, the primary intermediates of 4-CP found in the nZVIN/Air system were phenol via the direct dechlorination by superoxide radicals, accompanying with the formation of chloride ions. On the base of experimental results, a superoxide radicals mediated enhancing mechanism was proposed for the aerobic degradation of 4-CP in the nZVIN/Air system. This study provides new insight into the role of bimetallic nickel on enhancing removal of organic pollutants with nZVI.
Keywords: Iron-nickel bimetallic nanoparticles; Molecular oxygen activation; 4-Chlorophenol; Reactive oxygen species;

Light regulated I–V hysteresis loop of Ag/BiFeO3/FTO thin film by Lujun Wei; Bai Sun; Wenxi Zhao; Hongwei Li; Peng Chen (325-329).
A hysteresis loop of current–voltage characteristics based multiferroic BiFeO3 nanoribbons memory device is observed. Moreover, the white-light can greatly regulate both the current–voltage hysteresis loop and the ferroelectric hysteresis loop. The stored space charges within the electrodes/BiFeO3 interface can lead to hysteresis-type I–V characteristics of Ag/BiFeO3/FTO devices. The white-light controlled I–V loop and ferroelectric loop result from photon-generated carries. Since the I–V hysteresis loop and ferroelectric hysteresis loop have a potential application prospect to the memory devices, these two white-light controlled the hysteresis loops curves are likely to provide promising opportunity for developing the multi-functional memory devices.
Keywords: BiFeO3 nanoribbons; Ag/BiFeO3/FTO; Hysteresis loop; Current–voltage characteristics;

Sub-surface microstructure of single and polycrystalline tungsten after high flux plasma exposure studied by TEM by A. Dubinko; D. Terentyev; A. Bakaeva; M. Hernández-Mayoral; G. De Temmerman; L. Buzi; J.-M. Noterdaeme; B. Unterberg (330-339).
We have performed high flux plasma exposure of tungsten and subsequent microstructural characterization using transmission electron microscopy (TEM) techniques. The aim was to reveal the nanometric features in the sub-surface region as well as to compare the microstructural evolution in tungsten single crystal and ITER-relevant specification. In both types of samples, TEM examination revealed the formation of a dense dislocation network and dislocation tangles. The estimated dislocation density in the sub-surface region was of the order of 1014  m−2 and it gradually decreased with a depth position of the examined sample. Besides individual dislocation lines, networks and tangles, the interstitial dislocation loops have been observed in all examined samples only after the exposure. Contrary to that, examination of the pristine single crystal W and backside of the plasma-exposed samples did not reveal the presence of dislocation loops and tangles. This clearly proves that high flux plasma exposure induces severe plastic deformation in the sub-surface region irrespective of the presence of initial dislocations and sub-grains, and the formation of dislocation tangles, networks and interstitial loops is a co-product of thermal stress and intensive plasma particles uptake.
Keywords: High flux plasma; Tungsten; Single crystal; Dislocations;

Corrosion of Ti6Al4V pins produced by direct metal laser sintering by J.J. de Damborenea; M.A. Arenas; Maria Aparecida Larosa; André Luiz Jardini; Cecília Amélia de Carvalho Zavaglia; A. Conde (340-347).
Display OmittedDirect Metal Laser Sintering (DMLS) technique allows the manufacturing a wide variety of medical devices for any type of prosthetic surgery (HIP, dental, cranial, maxillofacial) as well as for internal fixation devices (K-Wires or Steinmann Pins). There are a large number of research studies on DMLS, including microstructural characterization, mechanical properties and those based on production quality assurance but the influence of porosity in the corrosion behavior of these materials not been sufficiently considered.In the present paper, surgical pins of Ti6Al4V have been produced by DMLS. After testing in a phosphate buffered saline solution, the surface of the titanium alloy appeared locally covered by a voluminous white oxide. This unexpected behavior was presumably due to the existence of internal defects in the pins as result of the manufacturing process. The importance of these defects—that might act as crevice nucleation sites- has been revealed by electrochemical techniques and confirmed by computed tomography.
Keywords: Internal fixation device; Ti6Al4V; Cyclic voltammetry; SEM; Tomography;

Novel chromium doped perovskites A2ZnTiO6 (A = Pr, Gd): Synthesis, crystal structure and photocatalytic activity under simulated solar light irradiation by Hekai Zhu; Minghao Fang; Zhaohui Huang; Yan’gai Liu; Kai Chen; Ming Guan; Chao Tang; Lina Zhang; Meng Wang (348-356).
Display OmittedDouble perovskite related oxides A2ZnTiO6 (A = Pr, Gd) have been successfully synthesized by solid state reaction and investigated as photocatalysts for the first time. The two layered titanates mainly demonstrate absorbances under UV irradiation, except for several sharp absorption bands above 400 nm for Pr2ZnTiO6. Therefore, a series of photocatalysts by doping A2ZnTiO6 (A = Pr, Gd) with Cr have been developed in the hope to improve their absorption in the visible light region. The successful incorporation of Cr was detected by XRD and XPS, and the prepared samples have also been characteriazed by SEM, UV–vis DRS and PL. The characterization results suggested that Cr was present mainly in the form of Cr3+, with only a small amount of Cr6+ species. It served as an efficient dopant for the extension of visible light absorbance and improved photocatalytic activities under solar light irradiation. For both Pr2ZnTiO6 and Gd2ZnTiO6, the valence band (VB) was composed of hybridized states of the Zn 3d, O 2p and the conduction band (CB) has major contribution from Zn 4s, Ti 3d orbitals. For Cr doped samples, the newly formed spin-polarized valence band in the middle of the band gap that primarily arises from Cr 3d orbitals was responsible for the improved optical and photocatalytic properties.
Keywords: Double perovskite; Chromium doping; Photocatalyst; Photocatalytic degradation;

Broadening molecular weight polyethylene distribution by tailoring the silica surface environment on supported metallocenes by Eliana Galland Barrera; Fernanda C. Stedile; Rodrigo Brambilla; João H.Z. dos Santos (357-363).
Display OmittedThe synthesis of nonporous monodisperse chemically modified spherical silica particles was carried out according to the Stöber method. The resulting hybrid silicas were employed in the preparation of supported Cp2ZrCl2. The resulting metal loading, determined by Rutherford Backscattering Spectrometry (RBS), was between 0.15 and 0.48 wt% Zr/SiO2. The systems were evaluated in ethylene polymerization with MAO as the co-catalyst. The presence of ligands can increase catalyst activity and the nature of the employed organosilane ligand on the hybrid silicas were shown to affect the molecular weight distribution leading to polyethylenes with broad polydispersity (Mw/Mn = 3.8) and even with bimodality (Mw/Mn = 12.6).
Keywords: Supported metallocene; Organosilane; Sol-gel; Bimodal polyethylene;

A temperature-dependent surface free energy model for solid single crystals by Tianbao Cheng; Daining Fang; Yazheng Yang (364-368).
The surface free energy of Pb from 0 K to melting point given by the present model, the previous theories, simulations, and experiments.Display OmittedA temperature-dependent theoretical model for the surface free energy of the solid single crystals is established. This model relates the surface free energy at the elevated temperatures to that at the reference temperature, the temperature-dependent specific heat at constant pressure and coefficient of the linear thermal expansion, the heat of phase transition, the melting heat, and the vapor heat. As examples, the surface free energies of Fe, Cu, Al, Ni, and Pb from 0 K to melting points are calculated and are in reasonable agreement with these from Tyson’s theories and the experimental results. This model has obvious advantages compared to Tyson’s semi-empirical equations from the aspect of physical meaning, applicable condition, and accuracy. The study shows that the surface free energy of the solid single crystals firstly remains approximately constant and then decreases linearly as temperature increases from 0 K to melting point.
Keywords: Surface free energy; Solid single crystal; High temperature; Modeling; Metal;

Antimony sulfide thin films prepared by laser assisted chemical bath deposition by S. Shaji; L.V. Garcia; S.L. Loredo; B. Krishnan; J.A. Aguilar Martinez; T.K. Das Roy; D.A. Avellaneda (369-376).
Display OmittedAntimony sulfide (Sb2S3) thin films were prepared by laser assisted chemical bath deposition (LACBD) technique. These thin films were deposited on glass substrates from a chemical bath containing antimony chloride, acetone and sodium thiosulfate under various conditions of normal chemical bath deposition (CBD) as well as in-situ irradiation of the chemical bath using a continuous laser of 532 nm wavelength. Structure, composition, morphology, optical and electrical properties of the Sb2S3 thin films produced by normal CBD and LACBD were analyzed by X-Ray diffraction (XRD), Raman Spectroscopy, Atomic force microscopy (AFM), X-Ray photoelectron spectroscopy (XPS), UV–vis spectroscopy and Photoconductivity. The results showed that LACBD is an effective synthesis technique to obtain Sb2S3 thin films for optoelectronic applications.
Keywords: Sb2S3 thin films; Chemical bath deposition; XRD; XPS; Optoelectronic properties;

Zn doped MoO3 nanobelts and the enhanced gas sensing properties to ethanol by Shuang Yang; Yueli Liu; Tao Chen; Wei Jin; Tingqiang Yang; Minchi Cao; Shunshun Liu; Jing Zhou; Galina S. Zakharova; Wen Chen (377-384).
Display OmittedZn doped MoO3 nanobelts with the thickness of 120–275 nm, width of 0.3–1.4 μm and length of more than 100 μm are prepared by hydrothermal reaction. The operating temperature of sensors based on Zn doped MoO3 nanobelts is 100–380 °C with a better response to low concentration of ethanol. The highest response value of sensors based on Zn doped MoO3 to 1000 ppm ethanol at 240 °C is 321, which is about 15 times higher than that of pure MoO3 nanobelts. The gas sensors based on Zn doped MoO3 nanobelts possess good selectivity to ethanol compared with methanol, ammonia, acetone and toluene, which implies that it would be a good candidate in the potential application. The improvement of gas sensing properties may be attributed to the increasing absorbed ethanol, the decreasing probability of ethoxy recombination, the promoted dehydrogenation progress at lower temperature, and the narrowed band gap by Zn doping.
Keywords: MoO3 nanobelts; Zn doping; Gas sensor; Ethanol;

Display OmittedA new check-patterned CuSx–TiO2 film was designed to improve the photoreduction of CO2 to CH4. The check-patterned CuSx–TiO2 film with a 3D-network microstructure was fabricated by a facile squeeze method. The as-synthesized TiO2 and CuSx powders, as well as the patterned film, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, cyclic voltammetry (CV), and photoluminescence (PL) spectroscopy, as well as photocurrent density and CO2 temperature-programmed desorption (TPD) measurements. Compared to pure CuSx and TiO2, the check-patterned CuSx–TiO2 film exhibited significantly increased adsorption of CO2 on its networked microstructure, attributed to the enlarged interfaces between the microparticles. The check-patterned CuSx–TiO2 film exhibited superior photocatalytic behavior, with 53.2 μmolgcat −1  L−1 of CH4 produced after 8 h of reaction, whereas 18.1 and 7.3 μmolgcat −1  L−1 of CH4 were produced from pure TiO2 and CuSx films under the same reaction conditions, respectively. A model for enhanced photoactivity over the check-patterned CuSx  − TiO2 film was proposed. Results indicated that the check-patterned CuS–TiO2 material is quite promising as a photocatalyst for the reduction of CO2 to CH4.
Keywords: Checks-patterned CuSx-TiO2 film; Carbon dioxide photoreduction; Methane production; Electron-rich pool;

The present work provides a comparative study on the corrosion protection efficiency of defect free sol-gel hybrid coating containing ceria nanoparticles and cerium nitrate ions as corrosion inhibitors. Less explored organically modified alumina-silica hybrid sol-gel coatings are synthesized from 3-glycidoxypropyltrimethoxysilane and aluminium-tri-sec-butoxide. The microemulsion derived nanoparticles and the hybrid coatings are characterized and compared with coatings containing cerium nitrate. Corrosion inhibiting capability is assessed using electrochemical impedance spectroscopy. Scanning Kelvin probe measurements are also conducted on the coatings for identifying the apparent corrosion prone regions. Detailed X-ray photoelectron spectroscopy (XPS) analysis is carried out to comprehend the bonding and corrosion protection rendered by the hybrid coatings.
Keywords: Sol-gel; Corrosion; EIS; Ceria nanoparticles; XPS; Scanning Kelvin probe;

Display OmittedThree-dimension molecular dynamics (MD) simulations is employed to investigate the ultraprecision machining of single crystal silicon with structured nanoscale diamond tool fabricated by laser. The advantages and disadvantages of diamond machining using structured tools are discussed in comparison with those of using non-structured tools. The von Mises stress distribution, hydrostatic stress distribution, atomic displacement, stress, the radial distribution function, cutting forces, frictional coefficient, subsurface temperature and potential energy during the nanometric machining process are studied. A theoretical analysis model is also established to investigate the subsurface damage mechanism by analyzing the distribution of residual stress during the nanoscale machining process. The results show that a structured nanoscale tool in machining brittle material silicon causes a smaller hydrostatic stress, a less compressive normal stress σ x x and σ y y , a lower temperature and a smaller cutting force. However, the structured nanoscale tool machining results in smaller chip volume and more beta-silicon phase. Besides, the friction coefficient for tool with V-shape groove is smaller than those for non-structured tools and other structured nanoscale tools. This means that the tool with V-shape groove can reduce the resistance to cutting during the nanoscale machining process. In addition, the results also point out that the potential energy of subsurface atoms and the number of other atoms for pyramid-structured tool are much smaller than those of using non-structured tools and other structured nanoscale tools.
Keywords: Molecular dynamics; Phase transformation; Laser nano-structured diamond tool; Subsurface damage; Ultraprecision machining;

The energy level alignment at the CH3NH3PbI3/pentacene interface by Gengwu Ji; Bin Zhao; Fei Song; Guanhaojie Zheng; Xiaonan Zhang; Kongchao Shen; Yingguo Yang; Shi Chen; Xingyu Gao (417-421).
Pentacene thin film on CH3NH3PbI3 was studied by in-situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy to determine their interfacial energy level alignment. A 0.2 eV downward band bending together with a 0.1 eV interfacial dipole was found at the pentacene side, whereas there was no band bending found at the CH3NH3PbI3 side. The offset between CH3NH3PbI3 Valance Band Maximum (VBM) and pentacene Highest Occupied Molecular Orbital (HOMO) and that between CH3NH3PbI3 Conduction Band Minimum (CBM) and pentacene Lowest Unoccupied Molecular Orbital (LUMO) was determined to be 0.7 and 1.35 eV, respectively. The band alignment at this interface is favor of efficient hole transfer, which suggests pentacene as a viable HTL candidate to be explored in perovskite solar cells.
Keywords: Perovskite solar cell; Interface electronic structure; Energy level alignment;

Novel structures of oxygen adsorbed on a Zr(0001) surface predicted from first principles by Bo Gao; Jianyun Wang; Jian Lv; Xingyu Gao; Yafan Zhao; Yanchao Wang; Haifeng Song; Yanming Ma (422-427).
The structures of O atoms adsorbed on a metal surface influence the metal properties significantly. Thus, studying O chemisorption on a Zr surface is of great interest. We investigated O adsorption on a Zr(0001) surface using our newly developed structure-searching method combined with first-principles calculations. A novel structural prototype with a unique combination of surface face-centered cubic (SFCC) and surface hexagonal close-packed (SHCP) O adsorption sites was predicted using a single-layer adsorption model (SLAM) for a 0.5 and 1.0 monolayer (ML) O coverage. First-principles calculations based on the SLAM revealed that the new predicted structures are energetically favorable compared with the well-known SFCC structures for a low O coverage (0.5 and 1.0 ML). Furthermore, on basis of our predicted SFCC + SHCP structures, a new structure within multi-layer adsorption model (MLAM) was proposed to be more stable at the O coverage of 1.0 ML, in which adsorbed O atoms occupy the SFCC + SHCP sites and the substitutional octahedral sites. The calculated work functions indicate that the SFCC + SHCP configuration has the lowest work function of all known structures at an O coverage of 0.5 ML within the SLAM, which agrees with the experimental trend of work function with variation in O coverage.
Keywords: First principle; O-adsorbed Zr surface; Structure prediction;

Influence of copper foil polycrystalline structure on graphene anisotropic etching by Kamal P. Sharma; Rakesh D. Mahyavanshi; Golap Kalita; Masaki Tanemura (428-433).
Hexagonal hole formation with anisotropic etching independent of the stripes and wrinkles in the synthesized graphene. We also observed variation in etched pattern of the graphene depending on the base Cu grain orientations, attributing to difference in nucleation and growth process.Display OmittedAnisotropic etching of graphene and other two dimensional materials is an important tool to understand the growth process as well as enabling fabrication of various well-defined structures. Here, we reveal the influence of copper foil polycrystalline structure on anisotropic etching process of as-synthesized graphene. Graphene crystals were synthesized on the polycrystalline Cu foil by a low-pressure chemical vapor deposition (LPCVD) system. Microscopic analysis shows difference in shape, size and stripes alignment of graphene crystals with dissimilar nucleation within closure vicinity of neighboring Cu grains. Post-growth etching of such graphene crystals also significantly affected by the crystallographic nature of Cu grains as observed by the field emission scanning electron microscope (FE-SEM) and electron back scattered diffraction (EBSD) analysis. Hexagonal hole formation with anisotropic etching is observed to be independent of the stripes and wrinkles in the synthesized graphene. We also observed variation in etched pattern of the graphene depending on the base Cu grain orientations, attributing to difference in nucleation and growth process. The findings can facilitate to understand the nature of microscopic etched pattern depending on metal catalyst crystallographic structure.
Keywords: Anisotropic etching; Orientations; Microscopic;

Synthesis of NiCo2O4 nanostructures with different morphologies for the removal of methyl orange by Yaxi Tian; Haizhen Li; Zhongyuan Ruan; Guijia Cui; Shiqiang Yan (434-440).
Aiming to investigate the adsorption removal performance of NiCo2O4 as water purification adsorbents, magnetic materials NiCo2O4 with six different morphologies were successfully synthesized by a facile method. NiCo2O4 with six different morphologies were characterized by scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, N2 adsorption-desorption, vibrating sample magnetometry and X-ray energy dispersive spectrometry. In this study, we mainly explored the effect of specific surface area, pore volume and pore size on the performance for the removal of methyl orange, and the adsorption capacity followed an order of (b) NiCo2O4 nanorods > (e) balsam-like NiCo2O4  > (f) rose-like NiCo2O4  > (d) NiCo2O4 nanoribbons > (a) NiCo2O4 flowerlike nanostructures > (c) dandelion-like NiCo2O4 spheres. The results indicated that NiCo2O4 nanorods exhibited better adsorption performance. The reasons for the excellent adsorption capacity of NiCo2O4 nanorods were also discussed in depth by analyzing scale and surface characteristics. Besides, NiCo2O4 could be easily recovered from solution, which may avoid potential secondary pollution. Moreover, adsorption kinetics, the influence of pH and adsorption mechanism were comprehensively investigated. This finding indicated that NiCo2O4 were promising adsorbents for water purification.
Keywords: NiCo2O4; Different morphologies; Methyl orange; Adsorption;

Functionalization of cotton fabrics through thermal reduction of graphene oxide by Guangming Cai; Zhenglin Xu; Mengyun Yang; Bin Tang; Xungai Wang (441-448).
Display OmittedGraphene oxide (GO) was in-situ reduced on cotton fabrics by a simple heat treatment, which endowed cotton fabrics with multi-functions. GO was coated on the surface of cotton fabric through a conventional “dip and dry” approach. Reduced graphene oxide (RGO) was obtained from GO in the presence of cotton by heating under the protection of nitrogen. Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy were employed to characterize the complexes of RGO and cotton (RGO/cotton). The RGO/cotton fabrics showed good electrical conductivity, surface hydrophobicity and ultraviolet (UV) protection properties. These properties did not deteriorate significantly after repeated fabric bending and washing.
Keywords: Functional fiber; Graphene oxide; Thermal reduction; Surface modification; Conductive fabric;

Display OmittedSuperhydrophobic surfaces with extremely low wettability have attracted attention globally along with their remarkable characteristics such as anti-icing, anti-sticking, and self-cleaning. In this study, a facile and cost-effective approach of fabricating patternable superhydrophobic surfaces, which can be applied on various substrates (including large area and 3D curvilinear substrates), is proposed with a salt-dissolution-assisted etching process. This novel proposal is environmentally benign (entirely water-based and fluorine-free process). The only required ingredients to realize superhydrophobic surfaces are commercially available salt particles, polydimethylsiloxane (PDMS), and water. No expensive equipment or complex process control is needed. The fabricated superhydrophobic surface shows high static contact angle (∼151°) and a low sliding angle (∼6°), which correspond to the standards of superhydrophobicity. This surface also shows corrosive liquids (acid/alkali)-resistant characteristics. Moreover, the self-cleaning ability of the fabricated surfaces is explored. As a proof-of-concept application of the present approach, the spatially controllable superhydrophobic patterns on flat/curvilinear substrates are directly drawn with a minimum feature size of 500 μm without the use of expensive tooling, dies, or lithographic masks.
Keywords: Superhydrophobic surface; Polydimethylsiloxane; Cost-effective fabrication; Salt-dissolution-assisted etching;

Display OmittedA novel hybrid material was fabricated using mercaptoamine-functionalised silica-coated magnetic nanoparticles (MAF-SCMNPs) and was effective in the extraction and recovery of mercury and lead ions from wastewater. The properties of this new magnetic material were explored using various characterisation and analysis methods. Adsorbent amounts, pH levels and initial concentrations were optimised to improve removal efficiency. Additionally, kinetics, thermodynamics and adsorption isotherms were investigated to determine the mechanism by which the fabricated MAF-SCMNPs adsorb heavy metal ions. The results revealed that MAF-SCMNPs were acid-resistant. Sorption likely occurred by chelation through the amine group and ion exchange between heavy metal ions and thiol functional groups on the nanoadsorbent surface. The equilibrium was attained within 120 min, and the adsorption kinetics showed pseudo-second-order (R2  > 0.99). The mercury and lead adsorption isotherms were in agreement with the Freundlich model, displaying maximum adsorption capacities of 355 and 292 mg/g, respectively. The maximum adsorptions took place at pH 5–6 and 6–7 for Hg(II) and Pb(II), respectively. The maximum adsorptions were observed at 10 mg and 12 mg adsorbent quantities for Hg(II) and Pb(II), respectively. The adsorption process was endothermic and spontaneous within the temperature range of 298–318 K. This work demonstrates a unique magnetic nano-adsorbent for the removal of Hg(II) and Pb(II) from wastewater.
Keywords: MAF-SCMNPs; Mercaptoamine modification; Wastewater; Mercury and lead ions;

Self-enhanced plasma discharge effect in the deposition of diamond-like carbon films on the inner surface of slender tube by Yi Xu; Liuhe Li; Sida Luo; Qiuyuan Lu; Jiabin Gu; Ning Lei; Chunqin Huo (467-473).
Enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PIII&D) have been proved to be highly effective for depositing diamond-like carbon (DLC) films on the inner surface of the slender quartz tube with a deposition rate of 1.3 μm/min. Such a high-efficiency DLC films deposition was explained previously as the short electrons mean free path to cause large collision frequency between electrons and neutral particles. However, in this paper, we found that the inner surface material of the tube itself play a vital role on the films deposition. To disclose the mechanism of this phenomenon, the effect of different inner surface materials on plasma discharge was experimentally and theoretically investigated. Then a self-enhancing plasma discharge is discovered. It is found that secondary electrons emitted from the inner surface material, whatever it is the tube inner surface or deposited DLC films, can dramatically enhance the plasma discharge to improve the DLC films deposition rate.
Keywords: Enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PIII&D); Diamond-like carbon (DLC); Inner surface; Self-enhanced plasma discharge;

Experiments for improving fabrication, recovery and surface-protection of Cs3Sb photocathode by Takayoshi Kimoto; Yoshihiro Arai; Kuniak Nagayama (474-485).
We examined 1) the photocurrent from Cs3Sb photocathode as a function of anode voltage below 200 V, 2) the relationship between the quantum efficiency of photoemission and the conditions for fabrication by the sandwich method, 3) recovery of the photoemission by additional Cs deposition, and 4) the effects of surface protection of Cs3Sb photocathodes by WO3 and Cr2O3 films in the passive state. The photocurrent had a maximum at approximately 68 V except when we increased the anode voltage extraordinarily slowly. Cs3Sb photocathodes were fabricated by increasing the temperature of sandwiched layers of Sb, Cs and Sb deposited on the fine tips of eight cathodes at less than −12 °C. Cs3Sb photocathodes having higher quantum efficiency were fabricated by smoothly increasing the temperature of the layers quickly after we deposited the second Sb layer. The photocurrent from the Cs3Sb photocathodes was significantly higher when Cs was deposited at temperatures of 50–70 °C. Deposition of a one- to three- atomic-layer W or Cr film extended the photoemission lifetime after the layers were oxidized to WO3 or Cr2O3 in the passive state due to oxidation. The WO3 or Cr2O3 in the passive state provided more surface protection as their thickness increased.
Keywords: Cs3Sb photocathode; Sandwich method; Additional Cs deposition; Cr2O3 in passive state; WO3 in passive state; Lifetime test;

Preparation, characterization of Sb-doped ZnO nanocrystals and their excellent solar light driven photocatalytic activity by Ramzi Nasser; Walid Ben Haj Othmen; Habib Elhouichet; Mokhtar Férid (486-495).
Display OmittedIn the present study, undoped and antimony (Sb) doped ZnO nanocrystals (NCs) were prepared by a simple and economical sol-gel method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the purity of the obtained phase and its high crystallinity. Raman analysis confirms the hexagonal Wurtzite ZnO structure. According to the diffuse reflectance results, the band gap was found to decrease up to 3% of Sb doping (ZSb3 sample). The results of X-ray photoelectron spectroscopy (XPS) measurements reveal that Sb ions occupied both Zn and interstitials sites. The successful substitution of antimony in ZnO lattice suggests the formation of the complex (SbZn–2 VZn) acceptor level above the valence band. Particularly for ZSb3 sample, the UV photoluminescence (PL) band presents an obvious red-shift attributed to the formation of this complex. Rhodamine B (RhB) was used to evaluate the photocatalytic activity of Sb-doped ZnO NCs under sunlight irradiation. It was found that oxygen vacancies play a major role in the photocatalytic process by trapping the excited electrons and inhibiting the radiative recombination. During the photocatalytic mechanism, the Sb doping, expressed through the apparition of the (SbZn–2 VZn) correspondent acceptor level, enhances the sunlight absorption within the ZnO band gap, which stimulates the generation of hydroxyl radicals and promotes the photocatalytics reaction rates. Such important contribution of the hydroxyl radicals was confirmed experimentally when using ethanol as scavenger in the photocatalytic reaction. The photodegradation experiments reveal that ZSb3 sample exhibits the highest photocatalytic activity among all the prepared samples and presents a good cycling stability and reusability. The influence of the initial pH in the photodegradation efficiency was also monitored and discussed.
Keywords: ZnO; Sb doping; Modified sol-gel method; Photoluminescence; Acceptor complex; Photocatalysis;

Photocatalytic activity of Bi2WO6/Bi2S3 heterojunctions: the facilitation of exposed facets of Bi2WO6 substrate by Long Yan; Yufei Wang; Huidong Shen; Yu Zhang; Jian Li; Danjun Wang (496-503).
Display OmittedBi2S3/Bi2WO6 hybrid architectures with exposed (020) Bi2WO6 facets have been synthesized via a controlled anion exchange approach. X-ray photoelectron spectroscopy (XPS) reveals that a small amount of Bi2S3 was formed on the surface of Bi2WO6 during the anion exchange process, thus leading to the transformation from the Bi2WO6 to Bi2S3/Bi2WO6. A rhodamine B (RhB) aqueous solution was chosen as model organic pollutants to evaluate the photocatalytic activities of the Bi2S3/Bi2WO6 catalysts. Under visible light irradiation, the Bi2S3/Bi2WO6-TAA displayed the excellent visible light photoactivities compared with pure Bi2S3, Bi2WO6 and other composite photocatalysts. The efficient photocatalytic activity of the Bi2S3/Bi2WO6-TAA composite microspheres was ascribed to the constructed heterojunctions and the inner electric field caused by the exposed (020) Bi2WO6 facets. Active species trapping experiments revealed that h+ and O2 are the main active species in the photocatalytic process. Furthermore, the as-obtained photocatalysts showed good photocatalytic activity after four recycles. The results presented in this study provide a new concept for the rational design and development of highly efficient photocatalysts.
Keywords: Bi2S3/Bi2WO6; Heterujunciton; Exposed facet; Inner electric field; Photocatalysis;