负载型复合半导体V2O5-TiO2/SiO2表面V2O5和TiO2的相互修饰作用

 采用表面改性法制备了负载型复合半导体材料V2O5-TiO2/SiO2,并用X射线衍射、比表面积测定、拉曼光谱、程序升温还原和紫外-可见漫反射光谱等技术对固体材料的结构和光响应性能进行了表征. 结果表明,V2O5和TiO2在负载型复合半导体V2O5-TiO2/SiO2表面有相互修饰的作用. 一方面,V2O5能扩展TiO2的光响应范围,使TiO2的吸光区域由紫外光区拓宽至可见光区,从而提高了复合半导体对光能的利用率; 另一方面,TiO2则有助于提高V2O5在载体表面的分散程度,抑制VOx的聚合,减小V2O5的微晶尺寸,提高固体材料的能隙值和氧化还原能力.     

Vertically aligned mixed V2O5-TiO2 nanotube arrays for supercapacitor applications

Highly ordered mixed V(2)O(5)-TiO(2) nanotubes can be formed by self-organizing anodization of Ti-V alloys with vanadium content of up to 18 at%. In the resulting oxide nanotube arrays, the vanadium is electrochemically switchable leading to a specific capacitance that can reach up to 220 F g(-1) and an energy density of 19.56 Wh kg(-1) with perfect reversibility and long-term stability. Thus these mixed oxide nanotubes may be considered as a promising candidate for supercapacitors.     

Electron microscopy of V2O5 microcrystals in the V2O5-NH3-H2O colloid system

Summary The formation of V₂O₅ fibrous microcrystals in the V₂O₅-NH₃-H₂O system has been investigated by electron microscopy. The morphology of these microcrystals is dependent on the concentration of the particular components in the colloidal system and on the time of aging. In some colloid systems the orientation of V₂O₅ fibrous crystals with their long axes parallel to one another is also possible. The microcrystal growth in these systems can be attributed to very effective conditions for the recrystallization of vanadium pentoxide crystals in equilibrium with ammonium vanadate in solution.With 3 figures     

A DFT study on the hydrated V2O5-TiO2-anatase catalyst: stability of monomeric species

A combined cluster and periodic study has been carried out to elucidate the stability of hydrated species on the vanadia/titania catalyst. First, the hydration of a V₂O₅ cluster was analyzed for the successive adsorption of one to four water molecules. The dimeric skeleton is found to be preserved at a low water concentration. However, after the adsorption of four water molecules on the dimer, it is found to break to generate stable monomeric OV(OH)₃ units. The two moieties are related by the equation: Such OV(OH)₃ units have been taken as a monomer model for the periodic representation of the vanadia/titania catalyst. On the (100) surface, the OV(OH)₃ moieties are anchored by three V–O–Ti bonds to the support surface in a pyramidal arrangement. The vanadyl V=O bond is found to be very stable.     

高能机械球磨法制备V-Ti-O超细微粒催化剂

负载型V2O5/TiO2氧化物催化剂因具有优良的催化性能而广泛地用于烃类选择性氧化[1,2]和氮氧化物选择性催化还原(SCR)[3]. 迄今,所研究的负载型V2O5/TiO2氧化物催化剂大多是采用浸渍法制备的[2,4～6],通过调整催化剂的组成[2,5]、引入适当的助剂组分[2,6]和选择适宜的反应操作条件[2,5]可进一步优化其催化性能.     

Phase equilibria in the V2O5-Cr2O3 system

The phase equilibria in the total range of component concentrations in the V₂O₅-Cr₂O₃ system up to 1000 °C were studied by means of phase powder diffraction and DTA. Two compounds exist in the system: CrVO₄, melting incongruently at 860±5 °C, and Cr₂V₄O₁₃, which decomposes in the solid state at 640±5 °C to CrVO_4(s) and V₂O_5(s). At 645±5 °C, CrVO₄ and V₂O₅ form a eutectic mixture with the CrVO₄ content not exceeding 2% mol.

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Zusammenfassung Mittels DTA und Pulverdiffraktionsaufnahmen wurde das Phasengleichgewicht des Systems V₂O₅-Cr₂O₃ bis 1000 °C im gesamten Konzentrationsbereich untersucht. Innerhalb des Systemes existieren zwei Verbindungen: CrVO₄ mit einem inkongruentem Schmelzpunkt bei 860±5 °C und Cr₂V₄O₁₃, das sich in festem Zustand bei 640±5 °C in CrVO_4(s) und V₂O_5(s) zersetzt. Bei 645±5 °C bilden CrVO₄ und V₂O₅ ein eutektisches Gemisch mit einem maximalen CrVO₄-Gehalt von 2 mol%.

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DTA V₂₅-Cr₂₃ 1000° . : CrVO₄, 860±5° Cr₂V₄O₁₃, 640±5° CrVO₄ V₂O₅, 645±5° CrVO₄, 2 %.

     

Structural, optical, physical and electrical properties of V2O5.SrO.B2O3 glasses

The present work aims to study the structure and variation of optical band gap, density and dc electrical conductivity in vanadium strontium borate glasses. The glass systems xV2O5.(40-x)SrO.60B2O3 and xV2O5.(60-x)B2O3.40SrO with x varying from 0 to 20 mol% were prepared by normal melt quench technique. Structural studies were made by recording IR transmission spectra. The fundamental absorption edge for all the glasses was analyzed in terms of the theory proposed by Davis and Mott. The position of absorption edge and hence the value of the optical band gap was found to depend on the semiconducting glass composition. The absorption in these glasses is believed to be associated with indirect transitions. The origin of Urbach energy is associated with the phonon-assisted indirect transitions. The change in both density and molar volume was discussed in terms of the structural modifications that take place in the glass matrix on addition of V2O5. dc conductivity of the glass systems is also reported. The change of conductivity and activation energy with composition indicates that the conduction process varies from ionic to polaronic one.     

Studies on the system Al2O3-V2O5-MoO3

Studies on the three-component system Al₂O₃-V₂O₅-MoO₃ have shown the existence of a new compound with molecular formula AlVMoO₇. The synthesis conditions and X-ray characteristics of this compound and its melting temperature, 690±10°C, are reported.

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Zusammenfassung Einleitende Untersuchungen am Dreikomponentensystem Al₂O₃-V₂ O₅-MoO₃ zeigten die Existenz einer neuen, noch nicht publizierten Verbindung der Formel AlVMoO₇. Die Synthese der Verbindung sowie ihre röntgenographischen Eigenschaften wurden beschrieben. Ihr Schmelzpunkt beträgt 690±10°C.

     

Phase diagram of the V2O5-MoO3-Ag2O system

The phase diagram of the MoO₃-Ag₂O system was constructed. A comparison of the phase diagram presented here with the phase diagram of MoO₃-Ag₂MoO₄ system presented in [2] revealed some discrepancies.It was found that phase equilibrium in MoO₃-Ag₂O system could be reached only after cooling the previously melted mixtures of silver and molybdenum oxides.

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Zusammenfassung Es wurde das Phasendiagramm des Systemes MoO₃-Ag₂O erstellt. Der Vergleich dieses Phasendiagrammes mit dem des in (2) beschriebenen Systemes MoO₃-Ag₂MoO₄, ergeben sich einige Unterschiede.Man fand, da\ ein Phasengleichgewicht im System MoO₃-Ag₂O nur nach Abkühlen des zuvor geschmolzenen Gemisches aus Silber- und MolybdÄnoxides erreicht werden kann.

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The author wishes to thank Professor M. Figlarz from Université de Picardie, Amiens for giving the possibility of carrying out in his laboratory a part of the experiments described.     

Studies on conjugated fluoro-polymers Ⅱ. Characterization and electrical conductivity of polyperfluorobutyne-2

Polyperfluorobutyne-2 (PPFB), a conjugated polymer, was characterized with IR, UV-VIS,fluorescence spectra etc. The electrical conductivities of the polymer doped with various dopants wereinvestigated. The effect of the molecular structure of PPFB on the electrical properties was discussed.     

制备方法对V2O5/WO3-TiO2催化剂脱除柴油车尾气中NOx的影响

分别采用普通浸渍法(VWTi-con)和超声辅助浸渍法(VWTi-HUST)制备了V2O5/WO3-TiO2催化剂,并用X射线衍射、扫描电镜、拉曼光谱和X射线光电子能谱等技术对催化剂进行了表征,评价了水热老化前后两种催化剂的NH3-SCR脱除模拟柴油车尾气中NOx的反应活性,并与国外成熟商品催化剂进行了比较.结果表明,制备方法可影响V2O5/WO3-TiO2催化剂的水热稳定性,VWTi-con催化剂老化后几乎完全失活,而VWTi-HUST具有优异的水热稳定性,与国外成熟商品催化剂性能相当.与传统浸渍法相比,超声辅助浸渍法增强了活性物种和载体的相互作用,提高了活性组分的分散性等.采用该法制备的VWTi-HUST催化剂将具有较强的商业应用性;台架试验正在进行中,以期满足柴油车国IV排放标准的要求.     

V2O5/TiO2 Catalytic Xerogels Raman and EPR Studies

Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V₂O₅/TiO₂ catalysts prepared by a modified sol-gel method in order to identify the vanadium species. Two species of surface vanadium were identified by Raman measurements, monomeric vanadyls and polymeric vanadates. Monomeric vanadyls are characterized by a narrow Raman band at 1030 cm^–1 and polymeric vanadates by two broad bands in the region from 900 to 960 cm^–1 and 770 to 850 cm^–1. The Raman spectra do not exhibit characteristic peaks of crystalline V₂O₅. These results are in agreement with those of X-ray Diffractometry (XRD) and Fourier Transform Infrared (FT-IR) previously reported (C.B. Rodella et al., J. Sol-Gel Sci. Techn., submitted). At least three families of V⁴⁺ ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V⁴⁺ ions are located in sites with octahedral symmetry substituting for Ti⁴⁺ ions in the rutile structure. Magnetically interacting V⁴⁺ ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V₂O₅, a partial oxidation of V⁴⁺ to V⁵⁺ is apparent from the EPR results.     

Phase equilibria in the P2O5-rich part of the system Y2O3−Na2O−P2O5

In the ternary system Y₂O₃?Na₂O?P₂O₅, the partial system Y(PO₃)₃?NaPO₃?P₂O₅ was examined by means of differential thermal analysis and X-ray powder diffraction; its phase diagram is given.     

Phase equilibria in the V2O5-FeVMoO7 system

The progress of the reactions of water with brownmillerite (C₄AF⁺) and its mixtures with gypsum (C¯SH₂) and calcium sulphoaluminate (C₄A₃¯S) was investigated by means of calorimetric measurements in situ and X-ray diffractometry to determine the reaction heat and the conversion of the solid reactants as functions of time up to 50 h. The rapid reaction of C₄AF with water and the modifying effect of sulphates on the composition of the hydrated phases were confirmed. The presence of sulphates causes the induction period during the reactions of aluminium and iron-containing clinker phases with water. These phenomena are important technologically too, especially in cements with increased contents of C₄AF and of sulphate-yielding phases (C¯SH₂ and C₄A₃¯S).

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Zusammenfassung Der Verlauf der Hydratation von Brownmillerit Ca₄AF^* bzw. seinen Mischungen mit Gips (C¯SH₂) und Calcium-sulfat-aluminat (C₄A₃¯S) wurde durch kalorimetrische Messungen in situ und Röntgendiffraktometrie verfolgt, um die Abhängigkeit der Reaktionswärme und des Umsatzes der festen Reaktanden von der Zeit (bis 50 h) zu bestimmen. Die schnelle Reaktion von C₄AF mit Wasser und der modifizierende Effekt der Sulfate auf die Zusammensetzung der hydratisierten Phase wird bestätigt. Die Anwesenheit von Sulfat bewirkt eine Induktionsperiode bei der Reaktion von alumimum- und eisenhaltigen Klinkerphasen mit Wasser. Diese Erscheinungen sind von technischer Bedeutung, insbesondere für Zemente mit erhöhtem Gehalt an C₄AF und sulfatbildenden Phasen wie C¯SH₂ und C₄A₃¯S.

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(4 · l23 · Fe2O3) (4 · 3l23 · SO3) ( 50 ). . - . , , - .

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Dedicated to F. Hanic, D. Sc. on the occasion of his 60th birthday     

Reactivity of T-Nb2O5 or H-Nb2O5 towards V2O5. Synthesis in the solid state and properties of V4Nb18O55

The IR spectrum of V₄Nb₁₈O₅₅ has been compared with the IR spectra of selected niobates of known structures to show structural relations between these compounds. This comparison shows that V₄Nb₁₈O₅₅ has crystal structure related to T-Nb₂O₅, W16Nb18O94 and Ba₂NaNb₅O₁₅. On the other hand, reaction between V₂O₅ and H-Nb₂O₅ yields a solid solution of V₂O₅ in VNb₉O₂₅. It has been proposed two models of synthesized solid solution with formulas V_1+xNb_9-xO₂₅ or V_1+xNb₉O_25+5x/2.Independently of Nb₂O₅ polymorph, used for synthesis, the metastable compound VNbO5 cannot be synthesized in the solid state below 650°C      

Subsolidus area of the system CdO - V2O5 - Fe2O3

Phase diagrams in the subsolidus area of the systems FeVO₄ - CdO and FeVO₄ - Cd₂V₂O₇ have been deduced using the results of XRD and DTA analyses. On the basis of these diagrams and some additional verifying research, a projection of the subsolidus area of the CdO - V₂O₅ - Fe₂O₃ system onto the plane that comprises the components’ concentration triangle has been presented. The H-type phase is the only phase formed in this system. It co-exists at equilibrium with other phases in six subsidiary subsystems.      

Novel non-hydrolytic synthesis of a V2O5-TiO2 xerogel for the selective catalytic reduction of NOx by ammonia

A vanadia-titania mesoporous xerogel (10.5 wt% V(2)O(5)) was prepared from chloride precursors using a one-step non-hydrolytic sol-gel route and subsequent drying at ambient pressure; after calcination at 773 K for 5 h no crystalline V(2)O(5) was detected and the resulting mixed oxide exhibited remarkable activity in the selective reduction of NO with NH(3).     

Temperature-programmed reduction of V2O5 and coprecipitated V2O5−TiO2 by hydrogen

Temperature-programmed reductions (TPR) with H₂ of both pure V₂O₅ and coprecipitated V₂O₅?TiO₂ systems with different titanium concentrations was performed. The original and the reduced samples following each TPR step were characterized by X-ray diffraction, Fourier transform infrared analysis and scanning electron microscopy. Within the temperature range in which TPR analysis was carried out (100–600°C) the V₂O₅ phase was reduced in two or three steps, while no variation in the TiO₂ phase (anatase or rutile) was observed. In the first reduction step only superficial reduction of the oxides was detected. In the following steps, the H₂ reacted with oxygen atoms of the V=O and V?O?V bonds. This led to important changes in the structure and morphology of the system. The experimental evidence allowed the conclusion that titanium stabilizes certain phases of vanadium oxides in which vanadium appears as V(+4) or as a mixture of V(+4) and V(+5). Moreover, when moderate and high titanium concentrations were used, the reduction temperature of the bulk V₂O₅ decreased markedly.     

V2O5-TiO2催化剂光催化降解2,4-二氯苯酚：催化剂载体和表面活性剂的影响

采用固态分散法成功制备了表面活性剂修饰的不同V2O5含量的二元氧化物催化剂,运用X射线衍射、漫反射光谱、红外光谱、扫描电镜和N2吸附-脱附法对该纳米复合物进行了表征,并在紫外光照射下考察了其光催化降解2,4-二氯苯酚的性能.结果表明,50 wt%, V2O5-TiO2(记为50V2O5-TiO2)表现出比单纯V2O5, TiO2和P25更高的光催化活性, V2O5和TiO2之间的相互作用会影响二元氧化物催化剂的光催化效率. CTAB和HTAB的修饰显著增加了50V2O5-TiO2样品的催化效率,其中(50V2O5-TiO2)-CTAB催化剂在反应30 min后表现出最高的2,4-二氯苯酚降解率(100%)和反应速率(2.22 mg/(L·min)).表面活性剂的加入能修饰二元氧化物中V2O5和TiO2的光学和电子性质,从而显著提高其光催化活性.