Synthesis of one-dimensional potassium tungsten bronze with excellent near-infrared absorption property

Potassium tungsten oxide nanofibers were successfully synthesized via a facile hydrothermal reaction route in the presence of sulfate. After reduction under a reductive atmosphere of H(2)(5 vol %)/N(2), the potassium tungsten oxide transformed to potassium tungsten bronze. Because of the lack of free electrons, the potassium tungsten oxide (K(x)WO(3+x/2)) showed no NIR shielding performance; however, the potassium tungsten bronze (K(x)WO(3)) showed promising optical characteristics such as high transmittance for visible light, as well as high shielding performance for near-infrared lights, indicating its potential application as a solar filter. Meanwhile, the potassium tungsten bronze (K(x)WO(3)) showed strong absorption of near-infrared light and instantaneous conversion of photoenergy to heat.     

Size-controlled synthesis and gas sensing application of tungsten oxide nanostructures produced by arc discharge

Several different synthetic methods have been developed to fabricate tungsten oxide (WO(3)) nanostructures, but most of them require exotic reagents or are unsuitable for mass production. In this paper, we present a systematic investigation demonstrating that arc discharge is a fast and inexpensive synthesis method which can be used to produce high quality tungsten oxide nanostructures for NO(2) gas sensing measurements. The as-synthesized WO(3) nanostructures are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), finger-print Raman spectroscopy and proton induced x-ray emission (PIXE). The analysis shows that spheroidal-shaped monoclinic WO(3) crystal nanostructures were produced with an average diameter of 30?nm (range 10-100?nm) at an arc discharge current of 110?A and 300?Torr oxygen partial pressure. It is found that the morphology is controlled by the arc discharge parameters of current and oxygen partial pressure, e.g.?a high arc discharge current combined with a low oxygen partial pressure results in small WO(3) nanostructures with improved conductivity. Sensors produced from the WO(3) nanostructures show a strong response to NO(2) gas at 325?°C. The ability to tune the morphology of the WO(3) nanostructures makes this method ideal for the fabrication of gas sensing materials.     

Preparation of highly dispersed tungsten oxide on MCM-41 via atomic layer deposition and its application to butanol dehydration

Highly dispersed tungsten oxide on MCM-41 was synthesized using a novel atomic layer deposition (ALD) method. BET, XRD, XPS, NH3-TPD, and pyridine-IR were used to study the physicochemical properties of the supported tungsten oxides. In this study, the maximum loading of tungsten oxide on MCM-41 that could be prepared using the modified ALD method was 27.0 wt%. It was confirmed that the textural properties of the mesoporous silica were maintained after tungsten oxide loading. The NH3-TPD and Py-IR results indicated that weak acid sites, mainly Lewis acid sites, were produced over the WO3/MCM-41 samples. Moreover, 2-butanol dehydration was performed to demonstrate the potential advantages of the WO3/MCM-41 catalysts. The WO3/MCM-41 catalyst with 27.0 wt% tungsten oxide loading showed the highest activity in the dehydration of 2-butanol, which was attributed to the highest overall number of acid sites among the WO3/MCM-41 catalysts. The highly dispersed tungsten oxide on MCM-41 prepared via ALD can be an effective catalyst for producing butenes through 2-butanol dehydration.     

Growth of tungsten oxide nanorods with carbon caps

Hybrid nanostructures consisting of tungsten oxide nanorods with mushroom-shaped carbon caps were grown on electrochemically etched tungsten tips by thermal chemical vapor deposition with methane and argon. These nanorods grow along the radial direction and are very straight and smooth. Electron microscopy revealed a dominant diameter and length of approximately 50 nm and approximately 0.6 microm, respectively. High-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS) revealed the presence of crystalline monoclinic W18O49 in the nanorods, and the cap was entirely amorphous carbon. A plausible growth mechanism involves the reduction of tungsten oxide WO3, present on the tungsten surface, by methane at 900 degrees C.     

SnO2/WO3 core-shell nanorods and their high reversible capacity as lithium-ion battery anodes

WO(3) nanorods are uniformly coated with SnO(2) nanoparticles via a facile wet-chemical route. The reversible capacity of SnO(2)/WO(3) core-shell nanorods is 845.9 mA h g(-1), higher than that of bare WO(3) nanorods, SnO(2) nanostructures, and traditional theoretical results. Such behavior can be attributed to a novel mechanism by which nanostructured metallic tungsten makes extra Li(2)O (from SnO(2)) reversibly convert to Li(+). This mechanism is confirmed by x-ray diffraction results. Our results open a way for enhancing the reversible capacity of alloy-type metal oxide anode materials.     

Effect of suitable surfactant on the large scale preparation of WO3 nanorods for the synthesis of WS2 nanoparticles

WO3 nanorods with average dimension about 23 x 145 nm have been synthesized in gram quantities by a hydrothermal method. Effect of various surfactants on the WO3 nanorods morphology was investigated. The results demonstrated that the application of suitable surfactant (such as Triton X-100), leads to obtain obviously individual morphology for WO3 nanorods (with average dimensions about 15 x 100 nm) and decrease the reaction time from 7 days to 3 days. With a very suitable and safe method, the as-prepared WO3 nanorods, will turn to WS2 nanoparticles by mixing them with Sulfur (S) powder, under reducing H2 atmosphere and high temperature. Therefore, application of the harmful and poisonous H2S gas was eliminated.     

Resistive switching behavior and multiple transmittance states in solution-processed tungsten oxide

In this work, a tungsten oxide (WO(x)) film is prepared using a thiourea-assisted solution process. We demonstrate a device composed of fluorine doped tin oxide (FTO)-glass/WO(x)/electrolyte/indium-tin oxide (ITO)-glass stacking electrochromic (EC) structure and Al electrodes that are locally patterned and interposed between the WO(x) film and electrolyte, which form an Al(top electrode)/WO(x)/FTO(bottom electrode) resistance random access memory (RRAM) unit. According to transmission electron microscopy and X-ray photoelectron spectroscopy analyses, the WO(x) film contains nanosize pores and metallic-tungsten nanoclusters which are scattered within the tungsten oxide layer and concentrated along the interface between the Al electrode and WO(x) film. With application of voltage to the ITO electrode, multiple transmittance states are achieved for the EC unit due to the different quantity of intercalated Li ions in the WO(x) film. As for the Al/WO(x)/FTO RRAM unit, a bipolar nonvolatile resistive switching behavior is attained by applying voltage on the Al top electrode, showing electrical bistability with an ON/OFF current ratio up to 1 × 10(4).     

Structure and ionic conduction in the Ag2O·WO3·TeO2 glass system

Preparation, characterization by X-ray diffraction, differential scanning calorimetry, X-ray photoelectron spectroscopy (XPS), Raman and Fourier transform–infrared (FT–IR) spectroscopy and electrical conductivity studies have been carried out on the yAg2O · (1–y) [xWO3·(1–x) TeO2] glass system. The compositional variation of the glass transition temperature and the calculated oxygen packing density values have been correlated. The conductivity at ambient temperature shows two maxima for the compositions corresponding to y = 0.30 and 0.40 at x = 0.2 and 0.4, respectively. The observed conductivity enhancement is about an order of magnitude and it is correlated to the structural modifications due to the WO3 incorporation into the TeO2 glass network. From the XPS spectra, the binding energies (BEs) of the Ag 3d, Te 3d, W 4f and O 1s core-levels have been determined. The O 1s spectrum is found to consist of two peaks due to the presence of Te–eqOax–Te, W–O–W, W–O, Te = O, Te–O–1 and W–O–1 oxygen species. The tungsten ions appear to exist in 5+ and 6+ oxidation states in these glasses. The proportion of the reduced tungsten ion is found to decrease with an increase in the WO3 concentration, while that of the Te–eqOax–Te species decreases as x increases. The FT–IR and Raman spectra of these samples reveal that the glass network consists of TeO4, TeO3, WO4 and WO6 polyhedra.     

Nanostructured mesoporous tungsten oxide films with fast kinetics for electrochromic smart windows

A potential driven self-assembly of sodium dodecyl sulfate/tungsten oxide aggregates at the electrolyte-electrode interface followed by template extraction and annealing yielded mesoporous thin films of electrochromic tungsten oxide (WO(3)). Electron microscopy images revealed that the films are characterized by a hitherto unreported hybrid structure comprising nanoparticles and nanorods with a tetragonal crystalline phase of WO(3) with the measured lattice parameters: a = 0.53?nm and c = 0.37?nm. In addition to pentagonal voids characteristic of the tetragonal WO(3) phase at the lattice scale, open channels and pores of 5-10?nm in diameter lie between the nanoparticles, which cumulatively promote rapid charge transport through the film. This resulted in colouration efficiency (η(max)～90?cm(2)?C(-1) at λ = 900?nm) and switching kinetics (colouration time = 3?s and bleaching time = 2?s for a 50% change in transmittance) higher and faster than previously reported values for mesoporous WO(3) films. Repetitive cycling between the clear and blue states has no deleterious effect on the electrochromic performance of the film, which is suggestive of its potential as a cathode in practical electrochromic windows.     

新型SnO2/WO3双层薄膜NO2敏感性能研究

采用射频磁控反应溅射锡(Sn)靶和钨(W)靶的方法制备了SnO2/WO3双层薄膜材料,通过XRD和XPS实验研究了双层薄膜的物相结构和组份,结果表明,SnO2/WO3双层薄膜经过热处理后形成了SnWO4化合物.在此基础之上,制作了相应的NO2气体敏感薄膜传感器,研究了双层薄膜传感器的制备工艺参数及工作条件对传感器性能的影响,研究了传感器的敏感特性,包括灵敏度、选择性、响应恢复等特性.结果表明,传感器对NO2气体有较好的敏感性,对其他干扰气体不敏感.     

Amorphous tungstate precursor route to nanostructured tungsten oxide film with electrochromic property

Electrochromic tungsten oxide (WO3) films on ITO glass were fabricated by spin-coating with a tungsten peroxy acid solution, which was prepared by adding an equivolume mixture of hydrogen peroxide and glacial acetic acid to tungsten metal powder. The structural evolution of the tungstate precursor upon heat treatment was studied by X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) analyses, which indicated that the as-synthesized tungstate transformed into nanocrystalline WO3 upon heating. It is, therefore, quite clear that as-synthesized tungstate can be a good precursor for electrochromic WO3 films. A series of WO3 thin films were prepared on ITO glass by spin-coating with different concentrations of tungsten peroxy acid solution and then post-annealing at various temperatures. Depending on the concentration of the tungstate coating solution (200-500 mg mL(-1)) and the annealing temperature (100-300 degrees C), the thickness and WO3 content as well as the electrochromic properties of WO3 films can be controlled. As a result, the optimum fabrication conditions were determined to be a tungstate solution concentration of 300-400 mg mL(-1) and a post-annealing temperature of 200 degrees C. Finally, an inorganic-inorganic hybrid electrochromic device (ECD) composed of optimized WO3 and Prussian Blue (PB) with desirable coloration efficiency was successfully developed.     

Synthesis of nanometal oxides and nanometals using hot-wire and thermal CVD

We report the synthesis of nano-oxides of molybdenum, tungsten, and zinc. Molybdenum oxide (MoO₃) and tungsten oxide (WO_x) were produced by hot-wire CVD with molybdenum and tungsten filaments, respectively while zinc oxide (ZnO) was produced by thermal CVD. When high purity molybdenum wire was oxidized at ambient system atmosphere, nanorods and nanostraws of MoO₃ with length ranging from ∼ 20-80 nm and diameters ranging from ∼ 5-15 nm were produced. Also, the oxidation of the tungsten filament led to the deposition of tungsten oxide nanorods (10-25 nm diameter and 75-90 nm long) and nanospheres with diameters of ∼ 60 nm. Each oxide was reduced to its metallic form by annealing in a hydrogen environment to produce metallic nanoparticles. Nanorods and nanoribbons of ZnO with diameters ranging from 20-65 nm and lengths up to 2 μm were also produced.     

Synthesis and photocatalytic activity of WO(3) nanoparticles prepared by the arc discharge method in deionized water

In this paper, we discuss the synthesis and characterization of tungsten trioxide nanoparticles prepared by the arc discharge method in deionized (DI) water. The size and morphology of WO(3) nanoparticles prepared using different arc currents (25, 35 and 45?A) were studied. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) results indicate that at an arc current of 25?A, the size of the particles is about 30?nm, and this increases to 64?nm by increasing the arc current. This size increase caused a decrease of optical band gap from 2.9 to 2.6?eV. X-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) spectra demonstrate the formation of the WO(3) phase. Photodegradation of Rhodamine B shows that samples prepared at the lowest current have more photocatalytic activity due to having the smallest particle size and highest surface area. The results demonstrate the ability of the arc discharge method for direct formation of WO(3) nanoparticles in DI?water medium.     

超细钨粉的制取及其氧化钨原料和钨粉的粒度测量

选取相成分单一的氢钨青铜（H0.33WO3）、铵钨青铜（NH4）0.5WO3）和紫钨（WO2.72）作为原料，研究钨原料对制取超细钨粉的影响，对氧化钨原料和超细钨粉的粒度测量方法作了比较，研究结果表明，紫钨由于有着特殊的结构，其制得的钨粉细而均匀，分散性好，可适合于做微晶硬质合金的原料。氧化钨原料的粒度（伪同晶颗粒尺寸，即二次颗粒）测量，推荐使用激光衍射法，超细钨粉粒度（一次颗粒）的炉前测量，BET法测球形当量径相当理想。     

Large-scale, hot-filament-assisted synthesis of tungsten oxide and related transition metal oxide nanowires

A scalable and versatile method for the large-scale synthesis of tungsten trioxide nanowires and their arrays on a variety of substrates, including amorphous quartz and fluorinated tin oxide, is reported. The synthesis involves the chemical-vapor transport of metal oxide vapor-phase species using air or oxygen flow over hot filaments onto substrates kept at a distance. The results show that the density of the nanowires can be varied from 10(6)-10(10) cm(-2) by varying the substrate temperature. The diameter of the nanowires ranges from 100-20 nm. The results also show that variations in oxygen flow and substrate temperature affect the nanowire morphology from straight to bundled to branched nanowires. A thermodynamic model is proposed to show that the condensation of WO(2) species primarily accounts for the nucleation and subsequent growth of the nanowires, which supports the hypothesis that the nucleation of nanowires occurs through condensation of suboxide WO(2) vapor-phase species. This is in contrast to the expected WO(3) vapor-phase species condensation into WO(3) solid phase for nanoparticle formation. The as-synthesized nanowires are shown to form stable dispersions compared to nanoparticles in various organic and inorganic solvents.     

Defects Induced Magnetism in WO<Subscript>3</Subscript> and Reduced Graphene Oxide-WO<Subscript>3</Subscript> Nanocomposites

A series of reduced graphene oxide (rGO)-WO₃ nanocomposites were prepared by hydrothermal method using GO and tungsten complex. The nanocomposites were characterized by powder XRD, Raman spectroscopy, FT-IR spectroscopy, HRTEM, XPS, photoluminescence (PL), and magnetic studies. The structural analysis confirms the hexagonal crystal structure and formation of rGO-WO₃ nanocomposites. HRTEM images show rod-like shape WO₃ distributed on the wrinkle structure of rGO sheets. XPS results confirm the oxidation state and oxygen vacancies present in the samples. PL spectra of the samples show blue emission and indicate the existence of surface defects and oxygen vacancies. The M–H loop of rGO-WO₃ nanocomposites reveal that the co-existence of both ferro and antiferromagnetism at room temperature. The incorporation of rGO sheets notably increase magnetic behavior of composites due to extended C–C bond conducts much stronger coupling between the 5d and 6s orbitals of tungsten and carbon atoms.     

Photoconductive characteristic in individual WO(3-x) nanowire

Tungsten Oxide nanowires, with their natural excellent structure, possess unique physical and chemical properties. In this paper, photoconductivity of single tungsten trioxide nanowire (WO3 NW) and single tungsten suboxide nanowire (WO(3-x) NW) have been studied respectively on a photoconductivity testing system. Under 514 nm wavelength laser illumination, an unsaturated photocurrent and a slow photoconductive responsivity could be expressed in single WO3 NW device. In WO(3-x) NW device, photoconductive responsivity was determined by the illuminating position. About 100 nA photocurrent could be generated and a fast optoelectric responsivity with a recover time about 90 ms from the device was observed. Not only photoconductive effect but also the photovoltaic effect was obtained from individual WO(3-x) NW device. According to the results of X-ray photoelectron spectroscopy, the mechanisms of photoconductive and photovoltaic effects in these two kinds of devices have been discussed and the oxygen vacancy played an important role in the photoconductive phenomenon. All these effects could be of practical use in the design and fabrication of photodetectors based on single tungsten oxide nanowire.     

Epitaxial growth of WOx nanorod array on W(001)

Nanorods of substoichiometric tungsten oxide (WO_x) were grown on W(001) substrates. Two methods for the growth of nanorods were used: oxidation of the substrate under appropriate conditions and the deposition of tungsten oxide from a tungsten foil heated in the presence of oxygen. The grown nanorods were observed using a scanning electron microscope and an atomic force microscope. The diameters of the nanorods were 5–20 nm. The nanorods were slightly inclined from the directions parallel or normal to the surface. The inclination of nanorods was explained in terms of the epitaxial relationship between WO₃ crystals and the W(001) substrate. The WO₃ crystals formed at the initial stage of growth act as the nuclei of WO_x nanorods. We observed selective enhancement of the growth in a certain epitaxial direction depending on the method of growth, and an array of WO_x nanorods was produced on the W(001) substrate.     

Epitaxial growth of WOx nanorod array on W(001)

Nanorods of substoichiometric tungsten oxide (WO_x) were grown on W(001) substrates. Two methods for the growth of nanorods were used: oxidation of the substrate under appropriate conditions and the deposition of tungsten oxide from a tungsten foil heated in the presence of oxygen. The grown nanorods were observed using a scanning electron microscope and an atomic force microscope. The diameters of the nanorods were 5–20 nm. The nanorods were slightly inclined from the directions parallel or normal to the surface. The inclination of nanorods was explained in terms of the epitaxial relationship between WO₃ crystals and the W(001) substrate. The WO₃ crystals formed at the initial stage of growth act as the nuclei of WO_x nanorods. We observed selective enhancement of the growth in a certain epitaxial direction depending on the method of growth, and an array of WO_x nanorods was produced on the W(001) substrate.     

WO_3薄膜的微观结构与电致变色机制研究

采用直流反应磁控溅射方法在ITO导电玻璃上沉积了WO3薄膜,研究了靶基距对其微结构和电致变色性能的影响,利用XRD、SEM和XPS对薄膜的微结构和成分进行了表征。通过可见光透射谱对样品的电致变色性能进行了研究,并且讨论了WO3薄膜电致变色性能与其微结构、价态变化之间的关系。发现靶基距为7cm的情况下沉积得到的WO3薄膜呈非晶态,薄膜有更多的孔隙,有利于Li+的抽取,进而显示出较好的电致变色性能。反应溅射制备的WO3薄膜中W是W6+价态,颜色为透明状,当发生着色反应时,随着薄膜中Li+成分增加,薄膜颜色变为蓝色,薄膜中W原子为W6+和W5+的混合价态。认为其电致变色的行为是由于Li+和e-在薄膜中的注入和拉出引起的W6+和W5+发生转化所致。