WO3纳米管的模板法制备及表征

0引言 WO3纳米材料具有光致变色、电致变色、气致变色等特性,可用于光学信息和储存显示器、pH值探测器、气敏传感器、灵敏窗口等[1,2];并且在太阳能的储存与利用、光电转换、光催化降解大气和水中的污染物等方面有着广阔的应用前景[3,4],成为近几年重点研究的半导体材料之一.以前纳米WO3的制备主要集中在薄膜上,其薄膜的制备工艺已经相当成熟,主要包括蒸发法、溅射法、CVD法、喷涂法、阳极氧化法、溶胶-凝胶法等[3].     

W(100) c(2×2)表面的STM图像

用基于第一性原理的密度泛函理论研究了W(100) c(2×2)再构表面的表面弛豫以及扫描隧道显微镜(STM)图像和衬底偏压的关系. 计算所得到的表面原子沿[-110]方向的畸变位移δ为0.027 nm, 畸变能⊿E为80.6 meV·atom-1, 表面原子的弛豫分别为-7.6%(⊿d12/d0)和+0.8%(⊿d23/d0), 功函数Φ为4.55 eV. STM图像模拟表明, 由于表面原子沿[-110]方向的位移, 会导致出现平行于[110]方向的亮暗带状条纹. STM图像中突起所对应的并不是表面或次表面的钨原子, 而是zig-zag型W 原子链中线位置; 而STM暗区对应于原子位置畸变形成的相邻zig-zag型W原子链中间区域. 当衬底负偏压时, STM针尖典型起伏高度大约在0.008-0.013 nm之间; 而当衬底正偏压时, 针尖起伏高度在0.019-0.024 nm之间变化.     

Inter-orbital interference in STM tip during electron tunneling in tip–sample system: influence on STM images

We present a theoretical study of the influence of interference effects connected with the tunneling through s and p_z orbitals of the apex atom in STM tip on the formation of STM image. The results show that such an interference may modify significantly the tunneling current by changing the current contributions from the different orbitals in the tip–sample system. STM simulations have been performed for the Al(0 0 1) surface and different fcc-metal tips: they clearly indicate that the height and type of the STM corrugation depend considerably on this interference.     

WC/CNT纳米复合材料制备及其对甲醇氧化的电催化性能

采用表面修饰技术将碳纳米管(CNT)表面羧基化, 通过羧基将钨离子基团修饰到碳纳米管的外表面, 再通过原位还原碳化技术, 将钨离子基团还原成碳化钨(WC)纳米微粒, 制备出WC/CNT纳米复合材料. 采用FTIR、XRD、SEM、HRTEM和N2吸附等分析测试手段对样品的形貌、晶相组成和微观结构特征进行了表征. FTIR和N2吸附结果表明, 硝化后, 在碳纳米管表面羧基化的同时比表面积增加; XRD结果表明, WC/CNT样品由碳纳米管、WC以及非化学计量比的氧化钨组成; SEM和HRTEM结果表明, WC纳米颗粒均匀地分散于碳纳米管的外表面,并与碳纳米管构成了复合材料. 采用循环伏安法测试了样品在碱性条件下对甲醇氧化的电催化性能, 结果表明, 复合材料对甲醇氧化的电催性能明显强于WC 和碳纳米管, 并在实验结果的基础上探讨了复合材料催化性能提高的原因.     

Encapsulated Pd nanocrystals supported by nanoline-structured SrTiO3(001)

Palladium nanocrystals were grown on a nanostructured SrTiO(3)(001) surface and annealed in ultrahigh vacuum at 620 degrees C. This leads to the so-called strong metal-support interaction (SMSI) state, characterized by encapsulation of the metal clusters with an oxide layer. Scanning tunneling microscopy (STM) of the oxide adlayer on the Pd(111) cluster surface reveals two superstructures with different lattice parameters and crystallographic rotations. Interpretation of the STM images is most readily achieved via noncommensurate TiO(x)() surface layers which result in two distinct Moiré patterns.     

Nanoparticle-modified monolithic pipette tips for phosphopeptide enrichment

We have developed nanoparticle-modified monoliths in pipette tips for selective and efficient enrichment of phosphopeptides. The 5 μL monolithic beds were prepared by UV-initiated polymerization in 200 μL polypropylene pipette tips and either iron oxide or hydroxyapatite nanoparticles were used for monolith modification. Iron oxide nanoparticles were prepared by a co-precipitation method and stabilized by citrate ions. A stable coating of iron oxide nanoparticles on the pore surface of the monolith was obtained via multivalent electrostatic interactions of citrate ions on the surface of nanoparticles with a quaternary amine functionalized poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) monolith. Hydroxyapatite nanoparticles were incorporated into the poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) monolith by simply admixing them in the polymerization mixture followed by in situ polymerization. The nanoparticle-modified monoliths were compared with commercially available titanium dioxide pipette tips. Performance of the developed and commercially available sorbents was demonstrated with the efficient and selective enrichment of phosphopeptides from peptide mixtures of α-casein and β-casein digests followed by off-line MALDI/MS analysis.     

Chromium wheels quasi-hexagonal 2D assembling by direct UHV sublimation

Chromium(III)-based wheels close-pack on the Ag(110) surface forming a quasi-hexagonal 2D network following direct sublimation in ultra high vacuum (UHV). Wheels organization and chemical integrity have been proved through in situ Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS) studies.     

Interaction of CO with palladium supported on oxidized tungsten

A model catalyst system, palladium on tungsten oxide, has been examined by temperature-programmed desorption and photoemission spectroscopy. The samples were prepared by evaporation of palladium onto an oxidized tungsten foil under ultrahigh vacuum conditions. Mostly three-dimensional (3-D) palladium (Pd) clusters were found to be present on oxidized tungsten (WOx) surfaces at room temperature. Upon annealing to 670 K, the palladium clusters are redispersed and decorated by the WOx surface layer. The nature of the WOx phase on top of the palladium clusters is dependent on the mode of oxidation of the tungsten foil prior to palladium deposition. Mainly W(2+) species decorate palladium deposits on tungsten oxidized at room temperature, while mainly W(4+) species are on top of palladium deposits on the surface oxidized at 1300 K. The appearance of a Pd(n+)-O-W(4+) mixed oxide phase with n < 2 was observed on the oxidized tungsten surface. The substantial reduction (relative to nonannealed samples) of molecular CO coverage induced by annealing is discussed in terms of the changes in chemical composition and morphology of the outermost surface.     

DC-plasma polymerization of pyrrole

DC-plasma-polymerized pyrrole (PP-Py) films deposited on metals were extensively characterized by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Reflection-Absorption IR Spectroscopy (RAIR), X-ray Photoelectron Spectroscopy (XPS), Scanning Tunneling Microscopy (STM), Glow Discharge Optical Spectroscopy (GDOS), electrical conductivity (ASTM Franklin test), and contact angle measurements. TOF-SIMS and RAIR showed no spectroscopic evidence of the presence of the pyrrole ring structure in any of the plasmadeposited films. The major parameter that affected their composition was found to be the pressure. Films deposited at low pressure were less hydrogenated than those polymerized at high pressure or in remote plasma conditions. Although all deposits oxidized slowly in air, their surface energy remained low over an extended period of time. The electrical conductivity of the PP-Py films was in the range of 10⁻³–10⁻⁴ S/cm, i.e., higher than that of amorphous carbon films.     

Reaction Intermediates on TiO2(110) Identified by Time-Lapse Scanning Tunneling Microscopy

The present account describes first time examples of scanning tunneling microscope (STM) visualization of reaction intermediates on a metal oxide surface. The topographic response of reactant-adsorbed TiO₂(110) surfaces to a temperature increment or to a pressure increment was monitored as a sequence of STM images. Acetates thermally decomposing to ketene were resolved in a temperature-jump STM observation. The kinetics of the acetate consumption was determined on the number of acetates resolved in the microscope images and agreed with the macroscopic rate law of ketene production. A pressure-jump study revealed how a chemisorbed carboxylate (RCOO^-) is exchanged by another carboxylate (R'COO^-) supplied from the ambient vapor phase. An impinging R'COOH was immobilized on the top of a RCOO^- and then squeezed itself into the monolayer of the RCOO^-. One of the carboxylates in the squeezed state returned to the vapor phase via the immobilized state.     

Metathesis of butene to propene on WO<Subscript>3</Subscript> supported on MTS-9 titanium-silica: effect of loading on selectivity of product and yield of propene

An advanced heterogeneous catalyst for olefin disproportion was prepared by supporting WO₃ on titanium-silica sieve (MTS-9). The nature of the surface tungsten oxide species present in these catalysts was determined as a function of tungsten oxide loading by X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance spectra (UV–DRS) and ultraviolet–visible Raman (UV-Raman). The catalyst showed high activity for the metathesis of butene to propene. The active centers are not crystallites of WO₃ but rather surface tungsten oxide species. The conversion of butene varies with the degree of catalyst loading.     

CrOx-CeO2二元氧化物表面NO的NH3催化还原反应机理

利用原位漫反射红外光谱法研究了473 K下在CrOx-CeO₂二元氧化物表面NO的NH₃催化还原反应的机理。研究了CrO-CeO₂二元氧化物表面在反应过程中的表面吸附物种。为了更加清晰的了解反应过程, 在SCR反应过程中分别切断NH₃和NO的气流, 并采集了所生成的原位漫反射红外光谱图, 通过研究以上结果得出结论:当前状态下的SCR反应过程可能服从E-R机理。     

Single crystal WO3 nanoflakes as quartz crystal microbalance sensing layer for ultrafast detection of trace sarin simulant

Tungsten oxide (WO₃) nanoflakes were synthesized, and characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Thermogravimetry and X-ray photoelectron spectroscopy demonstrate the existence of strongly bound surface water molecules on the surface of tungsten oxide nanoflakes. WO₃ nanoflake functionalized quartz crystal microbalance sensors were fabricated, and firstly used for detection of trace sarin simulant, dimethyl methylphosphonate (DMMP). The sensors have better reproducibility and stability as well as much shorter response (30 s) and recovery time (73 s) than those functionalized by conventional hydrogen-bond acidic branched copolymers. The strongly bound surface water molecules on the surface of WO₃ nanoflakes are believed to play a key role in achieving such excellent DMMP sensing characteristics.     

Distribution and thickness of the surface contaminations on STM tungsten tips,studied by AES/SEM and ARXPS

The combination of Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and angle resolved X-ray photoelectron spectroscopy (ARXPS) has been applied to the analysis of the distribution of elements at the surface region of electrochemically etched tungsten tips and the determination of the thickness of a layer with oxygen and carbon contamination. Auger line profiling revealed a homogeneous distribution of oxygen and significant enrichment of carbon on the W tip between 0 and 1.5 m from the top. The thickness of the contamination layer on various W materials, electrochemically etched, was found to be 1.35±0.15 nm as measured using ARXPS, and was estimated to be about 1–3 nm as measured by AES.     

Thermochemical hole burning on a triethylammonium bis-7,7,8,8-tetracyanoquinodimethane charge-transfer complex using single-walled carbon nanotube scanning tunneling microscopy tips

The present article describes a thermochemical hole burning (THB) effect on a charge-transfer complex triethylammonium bis-7,7,8,8-tetracyanoquinodimethane (TEA(TCNQ)(2)) using single-walled carbon nanotube (SWNT) scanning tunneling microscopy (STM) tips, which demonstrates the possibility of optimizing the THB storage materials and the writing tips for ultrahigh-density data storage. TEA(TCNQ)(2) is proven to be a high-performance THB storage material, which gives deeper holes and larger hole depth-to-diameter ratio as compared to the previous materials dipropylammonium bis-7,7,8,8-tetracyanoquinodimethane and N-methyl-N-ethylmorpholinium bis-7,7,8,8-tetracyanoquinodimethane. Instead of conventional Pt/Ir STM tips, SWNT tips made by a unique chemical assembly technique we developed have been shown to be excellent writing tips for greatly decreasing the hole sizes and increasing the storage density. Possible reasons for the improvements on the storage performance were discussed.     

Solid sampling electrothermal atomic absorption spectrometry for analysis of high-purity tungsten trioxide and high-purity tungsten blue oxide

A solid sampling ETAAS method for the direct determination of Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni and Zn in high-purity tungsten trioxide and tungsten blue oxide powders using a modern spectrometer with transversely heated graphite tube and a solid sampling system is described. The extremely high background caused by the vaporizing tungsten oxides could be eliminated by the reduction to tungsten metal using hydrogen as purge gas during pyrolysis. Quantification of all elements was performed using calibration curves measured with aqueous standard solutions. The analyte contents determined were between 0.033 (Cu) and 12.6 (Fe) μg/g for tungsten trioxide and between 0.001 (Co) and 0.5 (Na) μg/g for tungsten blue oxide. The accuracy was checked by comparing the results with those obtained by ETAAS in analysis of HF/HNO₃ sample digests and by other methods. Extremely low limits of detection being between 0.07 (Mg, Na, Zn) - 2 (Ni) and 0.01 (Mg, Na, Ni) - 1.7 (Fe) ng/g for tungsten trioxide and tungsten blue oxide, respectively, could be achieved due to almost complete freedom of blank and unusually high applicable sample amounts (5–15 mg for tungsten trioxide and 5–70 mg for tungsten blue oxide).     

CrOx-CeO2二元氧化物表面NO的NH3催化还原反应机理

利用原位漫反射红外光谱法研究了473 K下在CrOx-CeO2二元氧化物表面NO的NH3催化还原反应的机理。研究了CrOx-CeO2二元氧化物表面在反应过程中的表面吸附物种。为了更加清晰的了解反应过程,在SCR反应过程中分别切断NH3和NO的气流,并采集了所生成的原位漫反射红外光谱图,通过研究以上结果得出结论:当前状态下的SCR反应过程可能服从ER机理。     

A green route for microwave synthesis of sodium tungsten bronzes NaxWO3 (0<x<1)

A green route has been developed for microwave synthesis of sodium tungsten bronzes Na_xWO₃ (0<x<1) from Na₂WO₄, WO₃ and tungsten powder. The hybrid microwave synthesis was carried out in argon atmosphere using CuO powder as the heating medium. Tungsten powder is used as the reducing agent instead of the alkali metal iodides previously used for the microwave synthesis of oxide bronzes. The prepared samples were characterized by powder X-ray diffraction, energy-dispersive X-ray analysis and scanning electron microscopy, and their phase constitutions, crystal structures and morphologies are in consistence with that in the literature. This synthesis method is simple, green and atom economic, and promising for preparation of other oxide bronzes and related compounds.     

Microgravimetric study of electrochemical properties of PEDOT/WO3 composite films in diluted sulfuric acid

Journal of Solid State Electrochemistry - Poly-3,4-ethylenedioxythiophene composite films with tungsten oxide (PEDOT/WO3) were obtained by potentiodynamic deposition of tungsten oxide from acidic...     

碳化钨/碳化二钨核壳结构纳米复合材料的制备及电化学性能

以偏钨酸铵为钨源, 铁黄(FeOOH)为载体, 将表面包覆法与原位还原碳化技术相结合, 制备出了具有核壳结构的碳化钨(WC)/碳化二钨(W₂C)纳米复合材料; 应用X射线衍射(XRD)分析、透射电子显微镜(TEM)和X射线能量散射谱(EDS)等手段对不同阶段样品的晶相、形貌、微结构和化学组成等特征进行了表征. 结果表明, 负载体经煅烧后, 载体及包裹层的物相均发生了变化, 形貌也相应地发生了改变; 经盐酸处理及还原碳化后, 样品由WC和W₂C纳米颗粒构成, 并构成了以W₂C为壳, 以WC为核的典型核壳结构; 结合表征结果对核壳结构的形成机理进行了探讨. 采用三电极体系循环伏安法测试了样品在酸性、中性和碱性溶液中对甲醇的电催化氧化活性. 结果表明, 与颗粒状碳化钨和介孔空心球状碳化钨相比, 样品的电催化活性有了明显的提高. 这说明W₂C与WC构成核壳结构纳米复合材料后, 其电化学性能有了明显的提升, 核壳结构纳米复合材料是提高碳化钨催化材料活性的有效途径之一.