W18O49 nanorods decorated with Ag/AgCl nanoparticles as highly-sensitive gas-sensing material and visible-light-driven photocatalyst

A novel gas-sensing material and photocatalyst was successfully obtained by decorating Ag/AgCl nanoparticles on the W₁₈O₄₉ nanorods through a clean photochemical route. The as-prepared samples were characterized using combined techniques of X-ray diffractometry, electron microscopy, energy dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. Gas-sensing measurements indicate that the Ag/AgCl/W₁₈O₄₉ NRs sensors exhibit superior reducing gas-sensing properties to those of bare W₁₈O₄₉ NRs, and they are highly selective and sensitive to NH₃, acetone, and H₂S with short response and recovery times. The Ag/AgCl/W₁₈O₄₉ NRs photocatlysts also possess higher photocatalytic performance than bare W₁₈O₄₉ NRs for degradation of methyl orange under simulated sunlight irradiation. Possible mechanisms concerning the enhancement of gas-sensing and photocatalytic activities of the Ag/AgCl/W₁₈O₄₉ NRs composite were proposed.     

Electron microscopy studies of W18O49. 2. Defects and disorder introduced by partial oxidation

W₁₈O₄₉ was oxidized in air at about 500K for different intervals of time. Defects of various kinds, related to structures of higher oxides, were observed. These were a coherent intergrowth of W₁₂O₃₄, {102}, and {103} crystallographic shear, and WO₃-type structures. A new type of TTB structure was also observed as a defect. Its formation mechanism is proposed and discussed.     

Electrochemical zinc insertion into W18O49: Synthesis and characterization of new bronzes

Divalent zinc ions have been electrochemically inserted into W₁₈O₄₉, producing zinc bronzes. Under our experimental conditions, W₁₈O₄₉ accepts zinc reversibly as a guest up to 0.9 ions per formula. The reaction seems to proceed through the formation of a solid solution in which the W-O framework of the parent oxide is maintained. The location of the Zn²⁺ ions in the framework of W₁₈O₄₉ has been determined by neutron diffraction on a chemically prepared sample having the composition Zn_0.34W₁₈O₄₉. As a main result, we found that Zn prefers to insert in one of the four types of quadrangular tunnels. More precisely, it is displaced from the center to occupy a low coordination site. This result indicates that a significant covalent character exists in the Zn-O bond.     

一维纳米材料Cs0.2WO3和W18O49长度与红外吸收关联性的Mie散射理论推导及实验验证

研究表明二元、三元钨基氧化物的红外吸收性能具有尺寸和形貌依赖性,但还没有普适性的物理学机理及计算方法。本工作基于Mie散射理论,推导了一维材料的长度与光吸收性能之间的关系,通过理论推导计算和实验验证,探究了纳米钨基氧化物的红外吸收性能与颗粒长度的关联性。首先,基于Mie散射理论的推演和计算,揭示了增加纳米Cs_(0.2)WO_3和W_(18)O_(49)材料长度可适度提高其近红外吸收性能的规律。其次,测试了合成的不同长度Cs_(0.2)WO_3纳米棒和W_(18)O_(49)纳米线的红外吸收性能,结果与理论计算及模拟相吻合。其中在2 500～20 000 nm波长范围内Cs_(0.2)WO_3纳米棒和W_(18)O_(49)纳米线随长度的变化趋势不同,Cs_(0.2)WO_3纳米棒的红外吸收性能随长度的增加而增加,而W_(18)O_(49)纳米线的红外吸收性能随长度的增加而减弱。Cs_(0.2)WO_3纳米棒和W_(18)0O_9纳米线的光热效应均随长度的增加而增加,增幅分别达18.5%和12.7%,再次验证了长度效应。     

H_6P_2W_(18)O_(62)/SiO_2:用模板剂制备及光催化降解二甲酚橙的性能

分别采用非离子表面活性剂(C_3H_6OC_2H_4O)_x(P123),阴离子表面活性剂C_(12)H_(25)NaO_4S(SDS)和C_(18)H_(29)NaO_3S(SDBS)作为模板剂,通过溶胶-凝胶再结合程序升温溶剂热一步法制备了一系列固载杂多酸光催化材料-H_6P_2W_(18)O_(62)/SiO_2。通过傅立叶-红外光谱(FTIR)、X-射线衍射(XRD)、电感耦合等离子体原子发射光谱(ICP-AES)、氮气吸附-脱附测定、透射电子显微镜(TEM)以及扫描电子显微镜配合X-射线能量色散谱仪(SEM-EDS)等测试手段对不同模板剂作用下合成产物进行了对比表征分析。结果表明,不同模板剂作用下的系列固载杂多酸-H_6P_2W_(18)O_(62)/SiO_2产物中母体多酸的Dawson基本结构均未发生明显变化,但固载后比表面积显著不同,其中,经模板剂P123和SDS作用合成的H_6P_2W_(18)O_(62)/SiO_2(P123)和H_6P_2W_(18)O_(62)/SiO_2(SDS)的比表面积高达916和634m~2·g~(-1),且显示为有序介孔材料。以二甲酚橙为模型分子,在微波场作用下,该系列固载多酸光催化性能研究结果显示,它们的光催化活性可被微波显著增强,其中,采用P123作用合成产物的光催化活性最高,60 min内对二甲酚橙的降解率达99%以上。     

Structural and conductivity studies of Y10−xLaxW2O21

The aim of this work was to determine structural parameters of the Y_10−xLa_xW₂O₂₁ (x=0-10) solid solution series and investigate their electric properties. Crystallographic data shows a gradual increase in symmetry with increasing La content, as the structure evolves from orthorhombic, Y₁₀W₂O₂₁, towards the pseudo-cubic structure of Y₅La₅W₂O₂₁. The solubility limit of La₂O₃ was found to be 50% (x=5). Above this level two phases were observed, La₆W₂O₁₅ and (La,Y)_10+xW_2−xO_21−δ. The conductivity of Y rich samples was very low, with σ of the order 2×10⁻⁵-5×10⁻⁵ S cm⁻¹ at 1000 °C, whilst ionic conductivity was observed for most La rich doped samples. The highest conductivity was observed for La₁₀W₂O₂₁ and its doped analogues, at 1×10⁻³-5×10⁻³ S cm⁻¹ at 1000 °C. Unit cell parameters were determined as a function of temperature from 0 to 1000°C, and thermal expansion of these materials was determined from temperature studies carried out at the Australian Synchrotron facility in Melbourne, Victoria, Australia.     

Reactivity in the solid state between CoWO4 and RE2WO6 where RE = Sm, Eu, Gd

Reactivity in the solid state between CoWO₄ and some rare-earth metal tungstates RE₂WO₆ (RE = Sm, Eu, Gd) was investigated by the XRD method. Two families of new isostructural cobalt and rare-earth metal tungstates, Co₂RE₂W₃O₁₄ and CoRE₄W₃O₁₆, were synthesized. The Co₂RE₂W₃O₁₄ phases are formed by heating in air the CoWO₄ and RE₂WO₆ compounds mixed at the molar ratio 2:1, while the CoRE₄W₃O₁₆ phases are synthesized at the molar ratio of CoWO₄/RE₂WO₆ equals to 1:2. The Co₂RE₂W₃O₁₄ phases as well as the CoRE₄W₃O₁₆ compounds crystallize in the orthorhombic system. The Co₂RE₂W₃O₁₄ and CoRE₄W₃O₁₆ compound melt above 1150 °C. A melting manner of the Co₂RE₂W₃O₁₄ and CoRE₄W₃O₁₆ compounds was determined in an inert atmosphere. The formation of CoWO_4−x phase was observed during heating in an inert atmosphere.     

Dawson型磷钨杂多阴离子P2W18O626-的电化学性质和对O2还原的电催化作用

用循环伏安、交流伏安和交流阻抗法对Dawson型磷钨杂多阴离子P₂W₁₈O₆₂^6-的电化学性质进行了详细研究, 循环伏安结果显示, P₂W₁₈O₆₂^6-在pH 2.52的0.1 mol·L^-1 Na₂SO₄+NaHSO₄溶液中有两对可逆的单电子还原-氧化波和两对可逆的双电子还原-氧化波. 单电子波的峰电位和电流与溶液的pH无关, 双电子波的峰电位则随溶液pH的增加而负移, 峰电流降低, 表明双电子电极过程有H⁺参与, 其数目为2. 交流阻抗谱表明P₂W₁₈O₆₂^6-的电极过程完全受扩散控制, 实验测定其扩散系数(D_O)为2.5×10^-6 cm²·s^-1. 循环伏安结果表明P₂W₁₈O₆₂^6-的第III对波对O₂还原为H₂O₂具有显著的电催化作用, 催化效率约达300%. 将P₂W₁₈O₆₂^6-应用于PW₁₁O₃₉Fe(III)(H₂O)^4-构成的类电-芬顿过程, 使该过程对硝基苯的降解效率显著提高.     

Dilatometric studies of Y2W3O12 with added Al2O3

Y₂W₃O₁₂ exhibits negative thermal expansion along the three crystallographic directions due to the transverse thermal vibrations perpendicular to the Y-O-W linkage. It is highly hygroscopic and forms a trihydrate structure at room temperature. Dilatometric studies of Y₂W₃O₁₂ show large thermal expansion hysteresis due to large grain size and a large initial positive thermal expansion due to the removal of water molecules. Al₂O₃ has been added to Y₂W₃O₁₂ upto 10 wt% in an attempt to overcome the hygroscopicity and reduce the particle size and thereby the thermal expansion hysteresis. Thermo gravimetric, dilatometric and electron microscopic studies are presented to support these observations. Dedicated to Professor C N R Rao on his 70th birthday     

High-resolution electron microscopy of defects in W4Nb26O77

Several different kinds of planar defects have been observed by means of high-resolution electron microscopy in W₄Nb₂₆O₇₇, such as disordered intergrowth of WNb₁₂O₃₃ and W₃Nb₁₄O₄₄ structural slabs, locally ordered intergrowth with a sequence of AABAAB, two separate microdomains of WNb₁₂O₃₃ and W₃Nb₁₄O₄₄ coexisting with W₄Nb₂₆O₇₇ and a complicated intergrowth of W₄Nb₂₆O₇₇, NNb₂O₅, W₃Nb₁₄O₄₄, and Nb₃₁O₇₇F types of structure.     

Synthesis and characterization of hybrid materials based on 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and Dawson-type tungstophosphate K7[H4PW18O62]·18H2O and K6[P2W18O62]·13H2O

In this study, we synthesized hybrid materials using well-Dawson polyoxometalates (POMs), K₇[H₄PW₁₈O₆₂]·18H₂O or K₆[P₂W₁₈O₆₂]·13H₂O and a room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]). K, W, P and CHN elemental analysis showed that one mole of [H₄PW₁₈O₆₂]⁷⁻ reacts with 6 moles of BMIM⁺ and one mole of [P₂W₁₈O₆₂]⁶⁻ reacts with 4 moles of BMIM⁺ to form, respectively, K[BMIM]₆H₄PW₁₈O₆₂ and K₂[BMIM]₄P₂W₁₈O₆₂. X-ray diffraction illustrated amorphous structure of the hybrid materials. FT-IR spectra showed the presence of both 1-butyl-3-methylimidazolium cation and the Dawson anion. TG analysis displayed a relative thermal stability of the hybrid materials compared to the parents Dawson POMs. Cyclic voltammetry showed that the reduction peak potentials of the Dawson anion in the hybrid materials shift towards negative values and the shift is more pronounced for K[BMIM]₆H₄PW₁₈O₆₂ compared to K₂[BMIM]₄P₂W₁₈O₆₂. This was attributed to a decrease in the acidity of the Dawson POM anion in the hybrid material.     

Study on mechanism of hydrogen adsorption on WO3, W20O58, and W18O49

The density functional theory (DFT) calculation of hydrogen adsorption on tungsten oxides and calculation of the crystal structure of WO₃, W₂₀O₅₈, and W₁₈O₄₉ were performed_. These calculations suggest that the length of W-O bonds in WO₃ are 1.913 Å, the length of 66% W-O bonds in W₂₀O₅₈ is 1.8 to 1.9 Å, and the length of 43.48% W-O bonds in W₁₈O₄₉ is longer than 2.0 Å. The hydrate (WO₂[OH]₂), as an autocatalyst in the hydrogen reduction process, was found in the particular adsorption configuration of W₁₈O₄₉. The WO₃ and W₂₀O₅₈ were completely reduced within 40 to 60 minutes at a temperature of 1000°C and at a hydrogen flow rate of 200 mL/min, while W₁₈O₄₉ was completely reduced within 20 to 40 minutes. The phase composition and micromorphology of raw material and production were studied by both X-ray diffraction analysis (XRD) and FE-SEM technology. The differences of the mechanism of hydrogen adsorption on WO₃, W₂₀O₅₈, and W₁₈O₄₉ were explored based on the density functional theory calculation and the hydrogen reduction experiments.     

Crystal-chemistry of mullite-type aluminoborates Al18B4O33 and Al5BO9: A stoichiometry puzzle

Orthorhombic Al₂O₃-rich aluminoborate is an important ceramic material for which two slightly different compositions have been assumed: Al₅BO₉ (5Al₂O₃:B₂O₃) and Al₁₈B₄O₃₃ (9Al₂O₃:2B₂O₃). The formula Al₁₈B₄O₃₃ (=Al_4.91B_1.09O₉) was derived from results of chemical analyses when crystal structure data were not yet available. Subsequent structural investigations indicated Al₅BO₉ composition. Nevertheless, Al₁₈B₄O₃₃ was still accepted as the correct stoichiometry assuming that additional B replaces 9% Al.Powder samples of both compositions and ones with excess boron were prepared by solid state reactions between α-Al₂O₃ and B₂O₃/H₃BO₃ at temperatures above 1100 °C and single-crystals were grown from flux at 1100 and 1550 °C. Products were investigated by single-crystal and powder XRD, ¹¹B and ²⁷Al solid-state MAS-NMR, Raman and FTIR spectroscopy as well as Laser-ablation ICP-MS. No indication of the predicted 9% B→Al substitution was found. LA ICP-MS indicated 12.36(27) wt% B₂O₃ corresponding to Al_4.97B_1.03O₉. Hence, the suggested Al₁₈B₄O₃₃ stoichiometry can be excluded for all synthesized samples. A very low amount of Al vacancies at a five-fold coordinated site are likely, charge balanced by an additional nearby three-fold coordinated B site. All evidences indicate that the title compound should be reported as Al_5−xB_1+xO₉ with x<0.038(6), which is close to Al₅BO₉.     

Phase relations in the K2W2O7-K2WO4-KPO3-Bi2O3 system and structure of K6.5Bi2.5W4P6O34

The phase relations in the cross-section of the K₂W₂O₇-K₂WO₄-KPO₃ containing 15 mol% Bi₂O₃ were undertaken using flux method. Crystallization fields of K_6.5Bi_2.5W₄P₆O₃₄, K₂Bi(PO₄)(WO₄), Bi₂WO₆, KBi(WO₄)₂ and their cocrystallization areas were identified. Novel phase K_6.5Bi_2.5W₄P₆O₃₄ was characterized by single-crystal X-ray diffraction: sp. gr. P−1, a=9.4170(5), b=9.7166(4), c=17.6050(7) Å, α=90.052(5)°, β=103.880(5)° and γ=90.125(5)°. It has a layered structure, which contains {K₇Bi₅W₈P₁₂O₆₈}_∞ layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K₇Bi₅W₈P₁₂O₆₈}_∞ layers are assembled from [W₂P₂O₁₃]_∞ and [BiPO₄]_∞ building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K₂Bi(PO₄)(WO₄) and K_6.5Bi_2.5W₄P₆O₃₄ were discussed on the basis of factor group theory.     

水热法合成双金属多元型的Mo1.8W16.2O49纳米棒

近年来,纳米材料在电子学[1]、光电子学[2]和存储元件[3]等技术的发展方面起到至关重要的作用。在纳米材料的合成中,过渡金属氧化物的合成越来越受到人们的重视[4,5]。一维过渡金属氧化物纳米材料具有特殊的光学、磁学和电学特性。其中,一维氧化钨(WO3-x,0≤x<3)纳米材料具有很     

Growth and characterization of ZnO (microdisks)/W18O49 (nanorods) heterostructures

ZnO (microdisks)/W₁₈O₄₉ (nanorods) heterostructures were grown on a Si(111) substrate using a thermal evaporation method. X-ray diffraction of the products indicated two separate phases belong to monoclinic W₁₈O₄₉ and hexagonal ZnO structures. Field emission scanning electron microscope (FESEM) images showed W₁₈O₄₉ nanorods with approximately uniform diameters (∼20 nm) on ZnO microdisk. Field emission Auger electron spectroscopy (FEAES) also confirmed two separate elemental characteristics of W₁₈O₄₉ and ZnO. The Raman and photoluminescence (PL) studies demonstrated that the ZnO microdisks have a good crystallinity with excellent optical properties. The Raman results of the ZnO(microdisks)/W₁₈O₄₉(nanorods) heterostructures indicated only W₁₈O₄₉ structure and the PL results of the heterostructures showed two peaks, one in the ultraviolet region at 374 nm and another in the visible region at 500 nm, which both belong to W₁₈O₄₉ nanorods.     

Preparation and properties of potassium pentafluorodioxo-tungstate (VI) K3WO2F5 and potassium octafluoropentaoxo-ditungstate (VI) K6W2O5F8

The potassium salts of two new hepta coordinated oxyfluoro anions of tungsten (VI) are reported in this paper. The monomer, K₃WO₂F₅ was obtained from the aqueous solution while the dimer, K₆W₂O₅F₈ was isolated from alcohol. The absorption peak of K₆W₂O₅F₈ at 830 cm^-1 has been attributed to W-O-W link. The W-O-W angle is found to be 155° and the force constant is 4.44 mdyn/A°. The d values obtained from x-ray powder diffraction studies are given.     

氧化钨纳米棒团簇的制备及电催化性能

以氯化钨为前驱体,通过溶剂热法制备了WO₃和W₁₈O₄₉并将其应用在染料敏化太阳能电池(dye-sensitized solar cells,DSSCs)和电解水析氢反应(hydrogen evolution reaction,HER)中。通过X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)和透射电子显微镜(TEM)对WO₃和W₁₈O₄₉的结构和形貌进行表征。结果表明：WO₃和W₁₈O₄₉均为单斜相,其形貌表现为定向排列的纳米棒组成的团簇。X射线光电子能谱(XPS)和电子顺磁共振(EPR)表明W₁₈O₄₉中含有丰富的氧空位。基于氧空位优异的电化学特性,W₁₈O₄₉对电极组装的DSSC获得了7.41%的光电能量转换效率(power conversion efficiency,PCE),高于WO     

(Nb2W4O19), TMA2, Na4(OH2)14(SO4): a new layered structure with Lindqvist heteropolyanions, XAS characterization of the HPAs

The new (Nb₂W₄O₁₉),TMA₂, Na₄(OH₂)₁₄(SO₄) has been evidenced as a minor phase during the Nb₂W₄O₁₉TMA (tetramethylammonium) salt synthesis. Its crystal structure has been refined from single crystal X-ray diffraction data, system monoclinic, a=10.166(5) Å, b=17.93(1) Å, c=24.81(1) Å, β=93.057(7)°, space group (S.G.) C2/c, Z=4, R₁=3.96%, wR₁=4.50%. It shows the stacking of cationic and anionic bidimensional layers. The anionic layer of formula [(Nb₂W₄O₁₉), TMA₂ ]²⁻ is formed of isolated Lindqvist HPAs surrounded by TMA groups. The isolated layers adopt a trigonal symmetry that is lost in the crystal by the association of the cationic sheets. These later, of formula [Na₄(OH₂)₁₄(SO₄)]²⁺ form porous net-like sheets with nearly circular cavities of diameter 7.5 Å. groups host the available cavities in a disordered manner. The cohesion between the sheets is performed by both electrostatic interactions and a set of hydrogen bonds. In the cationic layers, the highly symmetrical surrounding of HPAs by TMA groups yields a homogeneous electrostatic field at their external surface leading to a statistic Nb/W disorder over the three available independent metallic positions. Then, XAS experiments at the L₁/L₃-W edge complementarily helped to highlight the preferential cis configuration of (Nb₂W₄O₁₉)⁴⁻ anions, help to the strong Nb vs W contrast in their contribution to the backscattering paths. Previously to these experiments, it was of course checked that both the two phases present in the prepared sample contain Nb₂W₄O₁₉ anions with nearly unchanged geometry.     

Novel perovskite-related barium tungstate Ba11W4O23

Ba₁₁W₄O₂₃ was synthesized at 1300 °C, followed by quenching with liquid nitrogen. The crystal structure, which was known to be cryolite-related but has remained unclear, was initially determined by single-crystal X-ray diffraction for the isostructural Ru-substituted compound Ba₁₁(W_3.1Ru_0.9)O_22.5, which was discovered during exploratory synthesis in the Ba-Ru-O system. The structure of Ba₁₁W₄O₂₃ was refined by a combined powder X-ray and neutron Rietveld method (Fd-3m, a=17.1823(1) Å, Z=8, R_p=3.09%, R_wp=4.25%, χ²=2.8, 23 °C). The structure is an example of A-site vacancy-ordered 4×4×4 superstructure of a simple perovskite ABO₃, and it may be written as (Ba_1.75□_0.25)BaWO_5.75□_0.25, emphasizing vacancies on both metal and anion sites. The local structure of one of two asymmetric tungsten ions is the WO₆ octahedron, typical of perovskite. The other tungsten, however, is surrounded by oxygen and anionic vacancies statistically distributed over three divided sites to form 18 partially occupied oxygen atoms (∼30% on average), represented as WO_18/3. The A-site cation-vacancies are ordered at the 8a (, , ) site in between adjoining WO_18/3 polyhedra which form 1-D arrangements along [110] and equivalent directions. In situ high-temperature XRD data have shown that the quenched Ba₁₁W₄O₂₃ at room temperature is isostructural to the high-temperature phase at 1100 °C.