Check out our New Publishers' Select for Free Articles

Applied Surface Science (v.258, #11)

Surface studies of hydroxylated multi-wall carbon nanotubes by Robert H. Bradley; Kelby Cassity; Rodney Andrews; Mark Meier; Susan Osbeck; Aurik Andreu; Colin Johnston; Alison Crossley (pp. 4835-4843).

► The surface oxygen levels of MWCNTs have been increased from 4.3 to 22.3at.% using the Fenton hydroxylation reaction. ► No significant structural disruption to the MWCNTs is detected but their surface chemical properties are significantly improved. ► The hydroxylated materials have an enthalpy of immersion in water of −193mJm⁻², this gives enhanced water wettability and dispersion. ► Water vapour adsorption, which occurs by hydrogen bonding at polar surface oxygen groups, is also increased. ► Using graphitized MWCNTs evidence supporting direct attack at the graphene ring as one possible hydroxylation mechanism is presented.CVD grown MWCNTs, of typical diameter 5 to 50nm and with approximately 15–20 concentric graphene layers in the multi-walls, have been surface functionalised using the Fenton hydroxylation reaction. HRTEM reveals little physical difference between the treated and untreated materials; images from both exhibit similar multi-wall structure and contain evidence for some low-level disruption of the very outermost layers. Raman spectra from the two types of nanotubes are almost identical displaying the disorder (D) peaks at approximately 1350cm⁻¹ and graphite (G) peaks at approximately 1580cm⁻¹, characteristic of graphene-based carbon materials, in approximately equal intensity ratios. Equilibrium adsorption data for nitrogen at 77K leads to BET surface areas of 60.4m²g⁻¹ for the untreated and 71.8m²g⁻¹ for the hydroxylated samples; the increase in area being due to separation of the tube-bundles during functionalization. This is accompanied by a decrease in measured porosity, mostly at high relative pressures of nitrogen, i.e. where larger (meso 2–5nm and macro >5nm) pores are being filled, which is consistent with an attendant loss of inter-tube capillarity. X-ray photoelectron spectroscopy (XPS) shows that hydroxylation increases the nanotube surface oxygen level from 4.3at.% to 22.3at.%; chemical shift data indicate that approximately 75% of that oxygen is present as hydroxyl (–OH) groups. Water vapour adsorption by the hydroxylated surfaces leads to Type II isotherms which are characteristic of relatively high numbers of hydrogen bonding interactions compared to the untreated materials which exhibit Type III curves. This difference in polar surface energy is confirmed by calorimetric enthalpies of immersion in water which are −54mJm⁻² for the untreated and −192mJm⁻² for the hydroxylated materials. The treated materials therefore have significantly increased water wettability/dispersivity and a greater potential for cross-linking with matrix compounds. The mechanism by which hydroxylation occurs i.e. free radical (OH) attack and subsequent electrophilic addition at CC bonds in the graphene basal planes, is discussed.

Keywords: Multi-wall carbon nanotubes; Functionalization; XPS; Raman; HRTEM; Adsorption; Surface energy

Transparent conductive CuFeO₂ thin films prepared by sol–gel processing by Hong-Ying Chen; Jia-Hao Wu (pp. 4844-4847).

► Delafossite CuFeO₂ thin films are successfully deposited by low-cost sol–gel processing. ► The bandgap of delafossite CuFeO2 thin films is 3.1eV. ► The electrical conductivity of delafossite CuFeO₂thin films is 0.358Scm⁻¹.In this study, transparent conductive CuFeO₂ thin films were deposited onto a quartz substrate using a low-cost sol–gel process and sequential annealing in N₂. The sol–gel derived films were annealed at 500°C for 1h in air and then annealed at 700°C in N₂ for 2h. The CuO and CuFe₂O₄ phases appeared as the film annealed in air, and a single CuFeO₂ phase (delafossite, R3 m) appeared as the film annealed in N₂. X-ray photoelectron spectroscopy showed that the chemical composition of the CuFeO₂ thin films was similar to the stoichiometry. The optical bandgap of the CuFeO₂ thin films was 3.1eV. The p-type characteristics of the films were verified by Hall-effect measurements. The electrical conductivity and carrier concentration of the CuFeO₂ thin films were 0.358Scm⁻¹ and 5.34×10¹⁸cm⁻³, respectively. These results show that the proposed low-cost sol–gel process provides a feasible method of depositing transparent CuFeO₂ thin films.

Keywords: Delafossite; Thin films; CuFeO; ₂; Sol–gel; Annealing

Identification of the monolayer oxygen structure onRu(101¯0) by means of directional elastic peak electron spectroscopy (DEPES) by I. Morawski; J. Brona; M. Nowicki (pp. 4848-4851).

► Mono-atomic O layer on Ru is detected by elastic scatterings of primary electrons. ► Experimental result straightforwardly reveals O adatom position within unit cell. ► Presented method substantially extends application of the retarding field analyzer.The investigation of 1 monolayer of oxygen on theRu(101¯0) surface by directional elastic peak electron spectroscopy (DEPES) reveals high sensitivity of this surface method to light gases. The presentation of the experimental data as the anisotropy DEPES pattern shows an angular orientation of the oxygen adsorbate with respect to the substrate atoms. The straightforward identification of the oxygen structure is supported by a quantitative analysis providing oxygen atom coordinates within the unit cell.

Keywords: Elastic electron scattering; Retarding field analyzer; Ruthenium; Oxygen adsorbate

Surface treatment of nickel substrate for the preparation of BSCCO film through sol–gel method by Huazhe Yang; Xiaoming Yu; Yang Ji; Yang Qi (pp. 4852-4856).

► A modified degreasing-oxidization process was applied to treat Nickel substrate. ► Wettability of the surface to BSCCO precursor sol can be remarkably enhanced. ► BSCCO tapes with preferential orientation were prepared on treated substrates via sol–gel process. ► The preferential orientation is attributed to the spontaneous orientation rotation growth of BSCCO to decrease lattice mismatch energy.A modified degreasing-oxidization process was devised and settled to treat the surface of nickel (Ni) substrates, and BSCCO films were prepared on the treated NiO/Ni substrates by sol–gel method. X-ray diffraction (XRD) and optical microscopy were adopted to clarify the function of different treatment on phase formation and wettability of NiO/Ni substrates. Differential thermal analysis and thermal gravimetry analysis were adopted to confirm the desirable heat treatment process. XRD and scanning electron microscopy were adopted to investigate the phase constituent and surface morphology of BSCCO films. Results demonstrate that both the surface wettability of the substrate to sol and the lattice matching between the substrate and BSCCO can be improved through the modified treatment, which are favorable for the preparation of BSCCO films.

Keywords: BSCCO; Nickel substrate; Sol; Wettability

Growth mode transition of Ni thin films on nanopatterned substrate: Kinetic Monte Carlo simulations by Shuhan Chen; Jingshu Liang; Yuan Zhu; Shaoji Jiang (pp. 4857-4860).

► A uniform arranged triangular prism structure is introduced to mimic the nanopatterned substrate. ► The transition from continuous growth to the anisotropic columnar growth has been demonstrated. ► The growth mode transition is assumed to be attributed to difference in the relative importance of diffusion and shadowing. ► The modulation of nanopatterned substrate is assumed to reduce more quickly when the film thickness is larger than 70ML in our model.A three-dimension (3D) kinetic Monte Carlo (KMC) model with Ehrlich–Schwoebel barrier is presented. A uniform arranged triangular prism structure is introduced to mimic the nanopatterned substrate. The transition from continuous growth to anisotropic columnar growth has been demonstrated. The kinetic process and the growth exponent are discussed by our KMC model. Results show that the growth exponent is smaller than 0.5 when the film thickness surpasses 70ML under normal deposition but larger than 0.5 under high oblique angle deposition, such as 77°. We assume that the modulation of nanopatterned substrate reduces more quickly when the film thickness is larger than 70ML in our model. The growth mode transition can be mainly attributed to difference in the relative importance of diffusion and shadowing with normal and high oblique angle deposition conditions. Besides, the competition and vanishing process during oblique angle deposition are also demonstrated.

Keywords: Growth mode; Nanopatterned substrate; Ni film; Kinetic Monte Carlo simulation

ZnO and ZnS microrods coated on glass and photocatalytic activity by İlknur Altın; İsmail Polat; Emin Bacaksız; Münevver Sökmen (pp. 4861-4865).

► Production of ZnO and ZnS microrods on glass surface employing simple coating method. ► Determination of the structural properties of produced materials. ► Photocatalytic degradation ability of ZnO or ZnS films. ► Stability of ZnO or ZnS films.In this study, the large-scale ZnO and ZnS rods at sub-micrometer were prepared on soda lime glass substrate using a spray pyrolysis method. The microstructure of the rods was characterized by X-ray diffractometry and scanning electron microscopy with the energy dispersive X-ray spectroscopy, and the optical properties were investigated. XRD and SEM results show that the wurtzite structure and rod-like ZnO and ZnS at micro scale were obtained. The optical band gap values were 3.22 and 3.44eV for ZnO and ZnS microrods, respectively. The obtained samples were tested for their photocatalytic ability using them for the degradation of methylene blue (MB, 1×10⁻⁵M). Results show that the dye can be degraded at quite high rate (74.0±3.7% for ZnO and 65.0±5% for ZnS) by both films under a 365nm UV light after a 60min exposure period. The materials were re-checked after the treatment and microstructures were observed mainly unchanged.

Keywords: ZnO coating; ZnS coating; Spray pyrolysis; Photocatalysis

Simple chemical solution coating and gas sensing properties of α-Fe₂O₃/chrysotile fibrous composites by Haifeng Liu; Tongjiang Peng; Guohua Ma; Hongjuan Sun; Hailong Hu (pp. 4866-4870).

► α-Fe₂O₃ nanoparticles were coated on fibrous chrysotile by a simple solution method. ► α-Fe₂O₃ particles were compact and well-proportioned on the surface of chrysotile. ► The sensitivity of α-Fe₂O₃ to H₂ or CH₄ was improved by such coating treatment. ► There is no relevant report on improving gas sensitivity by such coating treatment.α-Fe₂O₃/chrysotile fibrous composites were prepared by a simple chemical solution coating method for the gas sensitivity improvement of α-Fe₂O₃. X-ray diffraction (XRD) and atomic force microscope (AFM) analyses indicate that corundum-type α-Fe₂O₃ nanoparticles with a mean particle size ∼20nm are dense and well-proportioned on the surface of chrysotile fibers due to the mechanism that positively charged Fe(OH)₃ particles can be adsorbed onto the negatively charged chrysotile fibers in acidic liquids. The fabricated sensor devices were characterized for their electrical and gas sensing properties, it is found that the sensitivities of α-Fe₂O₃/chrysotile fibrous composites to H₂ and CH₄ all increase by ∼35% than those of the single α-Fe₂O₃ nanoparticles. Such simple coating treatment is an effective way in improving the continuities and gas sensing properties of nanogranular thick films.

Keywords: Composite; Coating; Gas sensor; Thick film

Correlations between the optical emission spectra and microstructure of microplasma coatings on aluminum 2024 alloy by A.B. Rogov; V.R. Shayapov (pp. 4871-4876).

► Optical emission of microdischarges during microplasma synthesis on 2024 alloy. ► Simple well-known alkaline-silicate electrolyte as a model system was chosen. ► Changes in coating microstructure correlate with plasma composition evolution.The microplasma synthesis of the surface layers on aluminum alloy 2024 was studied by optical emission spectroscopy in situ. The evolutions of atomic line intensities in emission spectra and the properties of obtained coatings are discussed. The evolution in the chemical composition of plasma microdischarges and coatings layer structure in the light of previously obtained data on the dynamics of phase transformation by EPR and semi-quantitative X-ray analysis were compared. In the early stages of the synthesis of the plasma consists mainly of the substrate components, but with coating thickness increasing the electrolyte components become dominant. The formation of a dense layer enriched with α-Al₂O₃ requires specific conditions, which can be found from the changes in the emission spectra of microdischarges radiation.

Keywords: Microplasma electrochemical process; Aluminum 2024 alloy; Optical emission spectrum; Coating microstructure

Synthesis of free standing carbon nanosheet using electron cyclotron resonance plasma enhanced chemical vapor deposition by Rajesh Thomas; G. Mohan Rao (pp. 4877-4880).

In this study we have shown the growth of carbon nanosheets of several micrometer wide on Cu substrates using electron cyclotron resonance (ECR) plasma. Thick folded carbon-sheets and a semi transparent freestanding CNSs have been observed by scanning electron microscopy (A–C show different zones on the sheets).Display Omitted► The carbon films were synthesized from the acetylene using microwave assisted electron cyclotron resonance plasma enhanced CVD. ► Carbon nanosheets (CNSs) were grown over the Cu substrate having several micrometer wide in area. ► The growth rate of CNSs was very high.Carbon nanosheets (CNSs) have been synthesized by electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD) using a mixture of acetylene and argon gases on copper foil as the substrate. Micrometer-wide carbon sheets consisting of several atomic layers thick graphene sheets have been synthesized by controlled decomposition of carbon radicals in ECR-PECVD. Raman spectroscopy of these films revealed characteristics of a disordered graphitic sheet. Thick folded carbon-sheets and a semi transparent freestanding CNSs have been observed by scanning electron microscopy. This is a promising technique to synthesize free standing CNSs and can be used in the fabrication of nanoelecronic devices in future.

Keywords: Carbon nanosheet; Microwave-ECR plasma deposition; Electron microscopy; Infrared spectroscopy; Photoelectron spectroscopy

Synthesis and characterization of polyaniline/MnWO₄ nanocomposites as electrodes for pseudocapacitors by S. Saranya; R. Kalai Selvan; N. Priyadharsini (pp. 4881-4887).

► Polyaniline/MnWO₄ nanocomposites were prepared by in situ polymerization method, whereas MnWO₄ nanocrystals were prepared by surfactant assisted ultrasonication method. ► The characterization of composite and individual counter parts was studied using TG/DTA, XRD, FT-IR, SEM, TEM, Cyclic Voltammetry, Charge discharge and Electrochemical impedance spectroscopy. ► PAni/MnWO₄ nanocomposites with 50% of MnWO₄ loading have a high specific capacitance of 481F/g when compared with the pristine polyaniline and PAni/MnWO₄ nanocomposites with 25% and 75% of MnWO₄. ► The charge transfer resistance was less for the in-situ polymerized PAni/MnWO₄ nanocomposite compared with its physical mixture.Polyaniline (PAni)/MnWO₄ nanocomposite was successfully synthesized by in situ polymerization method under ultrasonication and the MnWO₄ was prepared by surfactant assisted ultrasonication method. The thermal stability of PAni was determined by TG/DTA (Thermo Gravimetric/ Differential thermal analysis). The structural and morphological features of PAni, MnWO₄ and PAni/MnWO₄ composite was analyzed using Fourier transform infrared spectrometry, X-ray diffraction (XRD), scanning electron microscope (SEM) and Transmission electron microscope (TEM) images. The electro-chemical properties of PAni, MnWO₄ and its composites with different weight percentage of MnWO₄ loading were studied through cyclic voltammetry (CV) for the application of supercapacitors as active electrode materials. From the cyclic voltammogram, 50% of MnWO₄ impregnated PAni showed a high specific capacitance (SC) of 481F/g than their individual counterparts of PAni (396F/g) and MnWO₄ (18F/g). The galvanostatic charge–discharge studies indicate the in situ polymerized composite shows greater specific capacitance (475F/g) than the physical mixture (346F/g) at a constant discharge current of 1mA/cm² with reasonable cycling stability. The charge transfer resistance ( R_ct) of PAni/MnWO₄ composite (22ohm) was calculated using electrochemical impedance spectroscopy (EIS) and compared with its physical mixture (58ohm).

Keywords: Polyaniline; MnWO; ₄; Composites; X-ray diffraction; Electrochemical properties

Thermoresponsive PNIPAAm-modified cotton fabric surfaces that switch between superhydrophilicity and superhydrophobicity by Cheng Jiang; Qihua Wang; Tingmei Wang (pp. 4888-4892).

► PNIPAAm was grafted onto cotton fabric by ATRP. ► The density of PNIPAAm chains can be adjusted by introducing PFDTS to the surface. ► The as-prepared surface had controllable wettability by changing temperature. ► The prepared cotton fabric may find application in functional textiles.Thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto the cotton fabric by atom transfer radical polymerization (ATRP). Introducing 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTS) onto the surface, the density of PNIPAAm chains can be adjusted because of the competitive reactions of (3-aminopropyl) triethoxysilane (APS) and PFDTS. With the appropriate ratio of APS and PFDTS, the cotton fabric can be switched from superhydrophilic to superhydrophobic by controlling temperature. The prepared cotton fabric may find application in functional textiles, soft and folding superhydrophobic materials.

Keywords: Thermoresponsive; Cotton fabric; Superhydrophobic surface; ATRP

Influence of Ni doping on phase transformation and optical properties of TiO₂ films deposited on quartz substrates by sol–gel process by Jianjun Tian; Hongmei Deng; Lin Sun; Hui Kong; Pingxiong Yang; Junhao Chu (pp. 4893-4897).

Display Omitted► Ni doping catalyzes the anatase-to-rutile transformation of TiO₂ films. ► Optical properties of Ni-doped TiO₂ films were studied according to Adachi's model. ► Optical band gap of TiO₂ decreases from 3.64eV to 3.51eV with increasing Ni content.The Ni-doped TiO₂ films were synthesized on quartz substrates by the sol–gel method. Results from X-ray diffraction and Raman spectra indicate that Ni doping catalyzes the anatase-to-rutile transformation. When Ni content is up to 10mol%, the transformation has been finished. The dielectric functions of Ni-doped TiO₂ films were extracted by fitting transmittance spectra according to the Adachi's dielectric function model. The optical band gap decreases from 3.64eV to 3.51eV with increasing Ni content. The results suggest that the acceleration of phase change and variation of optical properties may be related to defects due to Ni doping.

Keywords: PACS; 81.40.Ef; 74.62.Dh; 67.80.bf; 64.70.Nd; 78.20.CiTiO; ₂; Doping; Growth kinetics; Phase transition; Optical property

Influence of process parameters on surface plasmon resonance characteristics of densely packed gold nanoparticle films grown by pulsed laser deposition by Shweta Verma; B. Tirumala Rao; Sanjay Rai; V. Ganesan; L.M. Kukreja (pp. 4898-4905).

► Growth of densely packed gold nanoparticle films using pulsed laser deposition. ► Laser fluence and substrate temperature strongly influence surface plasmon resonance. ► Same plasmon resonance wavelength can be obtained in films of different thicknesses. ► Modeling of optical responses using modified Yamaguchi model. ► Volume filling fraction and aspect ratio of nanoparticles tune the plasmon resonance.The optical responses of gold nanoparticle films and thin continuous films grown by pulsed laser deposition (PLD) in a wide range of process parameters were studied. The growth conditions for obtaining strong surface plasmon resonances (SPR) were optimized. Laser fluence and substrate temperature were found to play key roles in the SPR characteristics of the grown films. The SPR wavelength was tuned in the range of 580–720nm by varying number of pulses and target-to-substrate distance during the PLD. Atomic force microscopic analysis revealed that the size of metal nanoparticles systematically increased with increasing number of pulses and decreasing target-to-substrate distance. Morphology of the films, which exhibited strong SPR showed densely packed spheroid nanoparticles of gold. Theoretical calculations of SPR wavelengths for the presently studied densely packed gold nanoparticle films were carried out using modified Yamaguchi model which incorporate particle–substrate and particle–particle interactions. From these calculations it was found that the observed SPR responses and their tuning arise from the combination of high volume filling fraction and aspect ratios of the gold nanoparticles.

Keywords: Gold nanoparticles; Pulsed laser deposition; Film morphology; Surface plasmon resonance

Superhydrophobic silver surface with dendrites structure on steel substrate by a facile electroless galvanic deposition process by Feng Guo; Xunjia Su; Genliang Hou; Ping Li (pp. 4906-4910).

► A facile electroless galvanic deposition method is proposed to fabricate superhydrophobic surface on steel substrate. ► A two-tier roughness structure composed of silver dendrites and silver nanoparticles is obtained. ► The as-prepared superhydrophobic surface possesses a water contact angle of 158° and a sliding angle of about 2°.A simple electroless galvanic deposition process to prepare superhydrophobic surface on steel substrate is presented here. Micro- and nano roughness structure is generated on steel surface by the deposition of silver dendrites with nanoscale leaves. After modified with stearic acid, the as-prepared surface shows a remarkable superhydrophobicity with a high water contact angle (WCA) of 158° and a low sliding angle of about 2°. The surface also shows non-sticking properties to a 4μL water droplet. The cooperation of dendrites structure and stearic acid modification is responsible for the superhydrophobicty of the as-prepared surface. This simple and reliable method is of great significance to the large scale fabrication of superhydrophobic surfaces on steel substrate.

Keywords: Superhydrophobicity; Dendrites structure; Electroless galvanic deposition; Crystal growth; XPS

First-principles study of the adsorption of lysine on hydroxyapatite (100) surface by Zhaoyang Lou; Qun Zeng; Xiang Chu; Fang Yang; Duanwei He; Mingli Yang; Mingli Xiang; Xingdong Zhang; Hongsong Fan (pp. 4911-4916).

Display Omitted► Conformers of Lys on HA (100) surface are identified. ► Multiple interactions that favor the Lys adsorption are revealed. ► Strong ionic bonding is formed between carbonyl-O in Lys and Ca ion on HA surface. ► Both Lys and HA structures are subjected to changes upon adsorption.The adsorption of lysine (Lys) on hydroxyapatite (HA) (100) surface was studied using density functional theory calculations within the generalized gradient approximation framework. The optimal adsorption pattern was identified from a number of interactive Lys–HA structures. The carbonyl-O, amine-H and C_ɛ–H atoms are active sites in Lys that interact directly with the Ca ion and phosphate-O atoms on the HA (100) surface, respectively. Multiple interactions were noted between Lys and HA surface. The adsorption is mainly stabilized by the CaO ionic bonding, followed by hydrogen bond and/or van der Waals interaction between phosphate-O and Lys–HA. Both the Lys and HA surface structures are subjected to some changes upon adsorption. The zwitterionic form of Lys was found more stable on the HA (100) surface than its neutral form. Our calculations reveal the structural characteristics and their variations for the Lys–HA systems, which are essential for understanding the interaction mechanism of biomolecules with inorganic biomaterials.

Keywords: Hydroxyapatite; Lysine; Density functional theory calculations; Adsorption

Flower-like SnO₂/graphene composite for high-capacity lithium storage by Hongdong Liu; Jiamu Huang; Xinlu Li; Jia Liu; Yuxin Zhang; Kun Du (pp. 4917-4921).

SEM image of (c) low-magnification of flower-like SnO₂/graphene composite, (d) high-magnification of flower-like SnO₂/graphene.Display Omitted► Flower-like SnO₂/graphene composite and bare flower-like SnO₂ are synthesized by a simple hydrothermal method. ► The SEM images show that the flower-like SnO₂ nanorod clusters are 800nm in size and homogeneously adhere on graphene sheets. ► This flower-like SnO₂/graphene composite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance and good rate capability.Flower-like SnO₂/graphene composite is synthesized by a simple hydrothermal method for high-capacity lithium storage. The as-prepared products are characterized by XRD, FTIR, FESEM, TGA and Nitrogen adsorption/desorption. The electrochemical performance of the flower-like SnO₂/graphene composite is measured by cyclic voltammetry and galvanostatic charge/discharge cycling. The results show that the flower-like SnO₂ nanorod clusters are 800nm in size and homogeneously adhere on graphene sheets. The flower-like SnO₂/graphene composite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance and good rate capability.

Keywords: Flower-like SnO; ₂; Graphene; Lithium-ion batteries; Anode

Preparation and characterization of Ni–Zr–O nanoparticles and its catalytic behavior for ethane oxidative dehydrogenation by Ying Wu; Jing Gao; Yiming He; Tinghua Wu (pp. 4922-4928).

► Uniform Ni–Zr–O nanoparticles obtained by modified sol–gel method. ► Catalysts for oxidative dehydrogenation of ethane to ethylene. ► An interaction between Ni and Zr results in the change of reducibility and adsorption oxygen species distribution. ► The doping of Zr increases the selectivity to ethylene and deactivation temperature.Ni–Zr–O nanoparticles with various Zr contents were prepared by a modified sol–gel method and characterized by X-ray diffraction (XRD), scanning/high-resolution transmission electron microscope (SEM/HRTEM), BET surface area analysis, H₂ temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and O₂ temperature-programmed desorption (O₂-TPD). The oxidative dehydrogenation of ethane (ODHE) to ethylene was applied to evaluate catalytic performance of the samples. The results show that the doping of Zr affected the cell parameter and the chemical environment of the catalysts, indicating the existence of strong interaction between Ni and Zr. The interaction plays an important role in the lessened reducibility and the distribution of adsorbed oxygen species, consequently influence their catalytic performance. The best yield to ethylene was obtained over the 10% Ni–Zr–O catalyst with 60% ethane conversion and 66% ethylene selectivity.

Keywords: Nanoparticles; Modified sol–gel method; Interaction; Ethane oxidative dehydrogenation

Fabrication of Bi³⁺-doped ZnO with enhanced photocatalytic performance by Jun bo Zhong; Jian zhang Li; Yan Lu; Xi yang He; Jun Zeng; Wei Hu; Yue cheng Shen (pp. 4929-4933).

In general, the strong SPS response corresponds to the high separation rate of photoinduced charge carriers on the basis of the SPS principle. The photovoltage of Bi³⁺-doped ZnO is higher than that of ZnO, thus, it can be confirmed that the Bi³⁺-doped ZnO has a higher charge separation rate than the ZnO sample. Among these samples, 5%Bi has the highest charge separation rate.Display Omitted► Bi³⁺ increases the BET surface area and changes the morphology of ZnO. ► Bi³⁺ induces binding energy value of Zn 2p_3/2 shift. ► The photoinduced charge separation rate has been changed. ► The photocatalytic activity has been greatly influenced.ZnO and Bi³⁺-doped ZnO photocatalysts with different molar ratio of Bi/Zn were prepared by a parallel flaw precipitation method. The photocatalysts prepared were characterized by BET surface area, X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopic techniques (XPS), UV/Vis diffuse reflectance spectroscopy (DRS) and surface photovoltage spectroscopy (SPS), respectively. The results show that doping Bi into ZnO increases the BET surface area. The XRD spectra of the Bi³⁺-doped ZnO photocatalysts calcined at 573K show only the characteristic peaks of wurtzite-type. Doping Bi³⁺ into ZnO influences the response to the light and the photoinduced charge separation rate, changes the morphology of ZnO and induces binding energy value of Zn2p_3/2 shift. The photocatalytic activity of Bi³⁺-doped ZnO photocatalysts for decolorization of methyl orange (MO) solution was evaluated, of all the photocatalysts prepared, the Bi³⁺-doped ZnO with 5%Bi possesses the best photocatalytic activity among the experimented compositions and the possible reason was discussed.

Keywords: ZnO; Photocatalytic performance; Doping; Bi

Synergy effect over electrodeposited submicron Cu₂O films in photocatalytic degradation of methylene blue by Ling Xu; Haiyan Xu; Shibiao Wu; Xinyi Zhang (pp. 4934-4938).

► Cu₂O films have been prepared by electrodeposition. ► A strong effect between H₂O₂ and Cu₂O films has been observed. ► Cu₂O films can be used as a reliable platform for environmental remediation.In the study, we report a simple method to fabricate semiconductor Cu₂O films by using a potentiostatic method. The obtained thin films have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM). The obtained Cu₂O films are composed of submicron particles with sizes in the range from tens to several hundreds of nanometers. The photocatalytic activity over the Cu₂O films was investigated under simulated solar light. A strong synergy effect between H₂O₂ and Cu₂O films in the photocatalytic degradation of methylene blue has been observed. The binary H₂O₂/Cu₂O systems exhibit high catalytic ability under the solar irradiation. The results show that Cu₂O films can be used as a reliable platform for environmental remediation by using solar energy.

Keywords: Electrodeposition; Submicron Cu; ₂; O film; Photocatalytic degradation; Methylene blue

The effect of plasma pre-treatment on NaHCO₃ desizing of blended sizes on cotton fabrics by Xuming Li; Yiping Qiu (pp. 4939-4944).

► The dissolubility of the blend of PVA and starch phosphate treated by plasma and subsequent NaHCO₃ treatment is studied. ► The change of surface morphology and surface chemical composition of blends treated by plasma were studied. ► The influence of plasma treatment time on the NaHCO₃ desizing is investigated. ► The influence of NaHCO₃ treatment time and temperature on the PDR of the samples with plasma treatment.The influence of the He/O₂ atmospheric pressure plasma jet pre-treatment on subsequent NaHCO₃ desizing of blends of starch phosphate and poly(vinyl alcohol) on cotton fabrics is investigated. Atomic force microscopy and scanning electron microscopy analysis indicate that the surface topography of the samples has significantly changed and the surface roughness increases with an increase in plasma exposure time. X-ray photoelectron spectroscopy analysis shows that a larger number of oxygen-containing polar groups are formed on the sized fabric surface after the plasma treatment. The results of the percent desizing ratio (PDR) indicate that the plasma pretreatment facilitated the blended sizes removal from the cotton fabrics in subsequent NaHCO₃ treatment and the PDR increases with prolonging plasma treatment time. The plasma technology is a promising pretreatment for desizing of blended sizes due to dramatically reduced desizing time.

Keywords: Atmospheric pressure plasma jet (APPJ); Starch phosphate; Poly(vinyl alcohol) (PVA); NaHCO; ₃; desizing; AFM; XPS; SEM

Thermodynamic stability, magnetism and half-metallicity of Heusler alloy Co₂MnX(X=Si, Ge, Sn)(100) surface by Bo Wu; Hongkuan Yuan; Anlong Kuang; Hong Chen; Yu Feng (pp. 4945-4951).

► Stability, magnetism and half-metallicity of Co₂Mn[Si, Ge, Sn](100) are studied. ► CoCo termination of Co₂MnSn(100) is excluded from thermodynamic equilibrium region. ► Surface Co or Mn atomic magnetic moment is enhanced by compared with the bulk. ► The minority-spin gap in Co₂MnSn(100) has been destroyed by the surface states.The thermodynamic stability, magnetism and half-metallicity of Heusler alloy Co₂MnX(X=Si, Ge, Sn)(100) surface are comprehensively investigated from the first-principles calculations. The calculated phase diagram indicates that with increasing core electrons of X atoms in Co₂MnX(100) the CoCo termination will be faded out of the thermodynamic equilibrium region gradually. Due to the difference of CoX bonding the surface Co and Mn atoms prefer to move towards the slab and vacuum, respectively. By comparing with the bulk, the surface Co and Mn atomic magnetic moments (AMMs) are enhanced obviously because of the significant surface d-electronic localization. Further investigations of the partial density of states (PDOS) show that the half-metallicity observed in bulk has been destroyed by the surface states in deficient-Mn atomic terminated surface, only the terminations capped pure Mn atoms in Co₂MnSi(100) and Co₂MnGe(100) surfaces preserve spin-polarization of 100% instead of the Co₂MnSn(100) surface, which is a possible explanation for low experimental tunnel magnetoresistance (TMR) value in Co₂MnSn(100)-based magnetic tunnel junctions (TMJs).

Keywords: Heusler alloy; Structure stability; Magnetism; Spin-polarization

One-step hydrothermal synthesis of magnetic Fe₃O₄ nanoparticles immobilized on polyamide fabric by Hui Zhang; Guoqing Zhu (pp. 4952-4959).

Display Omitted► We employed a facile and efficient process to immobilize the Fe₃O₄ nanoparticles on the surface of polyamide fiber. ► We fabricated the magnetic polyamide fabric. ► We characterized the fiber by using SEM, TEM, XRD, TG, DSC, VSM and XPS techniques. ► Magnetite (Fe₃O₄) nanoparticles are grafted on the fiber surface. ► The modification method may be suitable for the potential applications.A thin film of nanosized Fe₃O₄ particles prepared by hydrothermal method was immobilized on the surface of polyamide 6 fiber using ferric trichloride and ferrous chloride as the precursor, N,N-dimethyl formamide as the swelling agent and sodium dodecyl sulfate as the dispersant agent. The morphology, crystalline phase, thermal stability, magnetization properties and chemical structure of polyamide 6 fabric before and after treatments were characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), vibrating sample magnetometer (VSM) and X-ray photoelectron spectroscopy (XPS) techniques. The tensile properties and abrasion resistance were also measured. It was found that the inverse cubic spinel phase of Fe₃O₄ nanoparticles with an average size 50nm were synthesized, and synchronously grafted onto polyamide fiber surface. As compared with the original fabric, the onset decomposition temperature of the Fe₃O₄-coated fabric decreased slightly. The saturation magnetization was measured to be 3.8emu/g at temperature of 300K. The tensile properties were enhanced to some extent mainly due to the fabric shrinkage. The abrasion resistance of the Fe₃O₄-coated fabric behaved well.

Keywords: Polyamide 6 fabric; Hydrothermal method; Fe; ₃; O; ₄; nanoparticle

Assessments on friction and wear behaviors of P110 steel and chromizing coating sliding against two counterparts under dry and wet conditions by Naiming Lin; Faqin Xie; Huijun Yang; Wei Tian; Hefeng Wang; Bin Tang (pp. 4960-4970).

► Continuous chromizing coating was synthesized on P110 steel by pack cementation. ► The obtained coating consisted of M_xC_y and minor Cr₂N. ► The tested samples showed different wear mechanisms in the sliding tests. ► The coating significantly improved hardness and wear resistance of P110 steel.Chromizing coating was fabricated on P110 oil casing tube steel by employ of pack cementation to improve the performance and increase the life-time during operation. Scanning electron microscope (SEM), X-ray diffraction (XRD), glow discharge optical emission spectroscope (GDOES) and microhardness tester were used to investigate the surface morphology, cross-sectional microstructure, phase constitutions, element distribution and microhardness distribution of the coating. Friction and wear behaviors of P110 steel and chromizing coating were measured using a ball-on-disc type tribometer under sliding against two counterparts in dry and wet conditions. The variations in friction coefficient, mass loss and surface morphologies of the tested samples were systemically investigated and analyzed. Energy dispersive spectrometer (EDS) and SEM were employed to elucidate the wear mechanisms of the tested samples. The results showed that the obtained coating was uniform and compact, mainly consisted of M_xC_y and reached a thickness of 55μm. Chromizing coating had higher surface hardness and lower mass losses than that of P110 steel. When sliding against GCr15, chromizing coating showed no obvious friction–reduction effect, but indicated certain anti-friction property in sliding against Si₃N₄. The tested samples varied with surface hardness values and surface compositions have shown different wear mechanisms in the sliding tests. Chromizing treatment makes it possible to create on the working surface of P110 steel with enhanced surface hardness and wear resistance.

Keywords: P110 steel; Chromizing coating; Friction; Wear

Photoemission and energy gap of MgWO₄ particles connecting as nanofibers synthesized by electrospinning–calcination combinations by Surangkana Wannapop; Titipun Thongtem; Somchai Thongtem (pp. 4971-4976).

► MgWO₄ fibers as a semiconducting material. ► A lab-made electrospinning equipment enables us to form as-spun fibrous precursor. ► The precursor was further calcined at 700°C for 3h to synthesize MgWO₄. ► It was composed of particles with different sizes connecting as fibrous assemblies. ► A promising material for a number of technological applications.Mixtures of magnesium acetate tetrahydrate ((CH₃COO)₂Mg·4H₂O), ammonium tungstate tetrahydrate ((NH₄)₆W₇O₂₄·4H₂O), and poly(vinyl alcohol) with the molecular weight of 72,000 were electrospun through a +15kV direct voltage to form fibers on ground flat aluminum foils. The electrospun fibers of 1.5, 3.0, and 4.5mmol of each starting material containing 1.3g poly(vinyl alcohol) were further calcined at 500–700°C for 3h constant length of time. At 500 and 600°C calcination, both monoclinic and anorthic phases of MgWO₄ particles with different sizes connecting as fibrous assemblies were detected. Upon increasing the calcination temperature to 700°C, only monoclinic phase of facet nanoparticles interconnecting along the fibrous axes with 4.19eV indirect band gap and 461nm photoemission was synthesized. In the present research, formation of MgWO₄ molecules as well as nucleation and growth of nanoparticles was also proposed.

Keywords: MgWO; ₄; nanofibers; Electrospinning; Indirect band gap

A superficial coating to improve oxidation and decarburization resistance of bearing steel at high temperature by Xiaojing Wang; Lianqi Wei; Xun Zhou; Xiaomeng Zhang; Shufeng Ye; Yunfa Chen (pp. 4977-4982).

► Coating to improve oxidation and decarburization resistance was coated onto bearing steel. ► The coating material consisted of dolomite, bauxite and silicon carbide mixture. ► The newly densified coating comprised of spinels improved corrosion resistance. ► The reducing atmosphere made the coating much effective at high temperature.The coating material consisted of aqueous slurry of dolomite, bauxite and silicon carbide mixture. Such a coating material when applied superficially on the steel surface not only enhances oxidation resistance but also helps in inhibiting the decarburization even up to 1250°C. Metalloscope, XRD and TG-DTA thermal analysis revealed that the formation of a newly densified coating comprised of spinels and the reducing atmosphere formed by the oxidation of SiC improved the resistance of oxidation and decarburization.

Keywords: Bearing steel; High temperature oxidation; Decarburization; Coatings

Microporous gel electrolytes based on amphiphilic poly(vinylidene fluoride- co-hexafluoropropylene) for lithium batteries by Shicheng Yu; Lie Chen; Yiwang Chen; Yongfen Tong (pp. 4983-4989).

Display Omitted► Amphiphilic poly(vinylidene fluoride- co-hexafluoropropylene) grafted poly(poly(ethylene glycol) methyl ether methacrylate) are simply prepared directly via atom transfer radical polymerization. ► The strong affinity of PPEGMA segments dramatically improves the electrolyte uptakes and ion conductivities of the graft copolymer membranes. ► The highest ion conductivity at room temperature is 2.01×10⁻³Scm⁻¹.Poly(vinylidene fluoride- co-hexafluoropropylene) grafted poly(poly(ethylene glycol) methyl ether methacrylate) (PVDF-HFP- g-PPEGMA) is simply prepared by single-step synthesis directly via atom transfer radical polymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate (PEGMA) from poly(vinylidene fluoride- co-hexafluoropropylene) (PVDF-HFP). Thermal, mechanical, swelling and electrochemical properties, as well as microstructures of the prepared polymer electrolytes, are evaluated and the effects of the various contents and average molecular weights of PEGMA on those properties are also been investigated. By phase inversion technique, the copolymer membranes tend to form well-defined microporous morphology with the increase of content and average molecular weight of PEGMA, due to the competition and cooperation between the hydrophilic PEGMA segments and hydrophobic PVDF-HFP. When these membranes are gelled with 1M LiCF₃SO₃ in ethylene carbonate (EC)/propylene carbonate (PC) (1:1, v/v), their saturated electrolyte uptakes (up to 323.5%) and ion conductivities (up to 2.01×10⁻³Scm⁻¹) are dramatically improved with respect to the pristine PVDF-HFP, ascribing to the strong affinity of the hydrophilic PEGMA segments with the electrolytes. All the polymer electrolytes are electrochemically stable up to 4.7V versus Li/Li⁺, and show good mechanical properties. Coin cells based on the polymer electrolytes show stable charge–discharge cycles and deliver discharge capacities to LiFePO₄ is up to 156mAhg⁻¹.

Keywords: Polyelectrolytes; Atom transfer radical polymerization; Ionic conductivity

Field emission from ZnO whiskers under intervalley electron redistribution by O. Yilmazoglu; J.-P. Biethan; A. Evtukh; M. Semenenko; D. Pavlidis; H.L. Hartnagel; V. Litovchenko (pp. 4990-4993).

► Study of the conduction band of nano-structured ZnO whiskers. ► Electron transfer effect between the conduction band valleys in ZnO. ► Very low electron affinity from upper valley. ► Model for explanation of unusually large field enhancement factors for ZnO emitter.ZnO field-emitter whiskers with nanometer diameter were fabricated by metal-organic chemical vapor deposition (MOCVD) growth on Si substrates. Their electron field emission properties and electron transfer effect between the valleys were investigated in a high vacuum chamber. The Fowler–Nordheim (F–N) plots of the emission current show different slopes for the small and high electric field regions. A model based on the electron-emission from valleys having different specific electron affinities is proposed to explain the experimental results. The paper presents a study of the conduction band of nano-structured ZnO with the help of field emission experiments. The energy difference between the lower and upper valleys was determined to be between 3.02eV and 3.3eV. The effective work function from the satellite valley is much lower than from the Γ-valley. These results can explain the usually obtained large discrepancies between extremely high field enhancement factors by fitting using F–N equation with known work function Φ from the Γ-valley and the geometrical estimated field enhancement factors for ZnO emitter. These functional field emitters based on ZnO materials and their ternaries can also be used as ultraviolet photodetector and find new applications for miniaturized photo-field assisted vacuum devices.

Keywords: PACS; 85.45.−w; 85.45.Bz; 81.15.Gh; 71.20.Nr; 72.20.HtZnO; Field emission; Electron transfer effect; Spectroscopy

Sections

Personal tools

Applied Surface Science (v.258, #11)

Sections

Personal tools

Local resources

Applied Surface Science (v.258, #11)