Origin of visible-light-driven photocatalysis: A comparative study on N/F-doped and N-F-codoped TiO2 powders by means of experimental characterizations and theoretical calculations

An overall comparative study was carried out on N-doped, F-doped, and N-F-codoped TiO₂ powders (NTO, FTO, NFTO) synthesized by spray pyrolysis in order to elucidate the origin of their visible-light-driven photocatalysis. The comparisons in their experimentally obtained characteristics were based on the analysis of XPS, UV-Vis, PL, NH₃-TPD and ESR spectra. The comparisons in their theoretically predicted properties were based on the analysis of the calculated electronic structures. As the results, N-doping into TiO₂ resulted in not only the improvement in visible-light absorption but also the creation of surface oxygen vacancies. F-doping produced several beneficial effects including the creation of surface oxygen vacancies, the enhancement of surface acidity and the increase of Ti³⁺ ions. Doped N atoms formed a localized energy state above the valence band of TiO₂, whereas doped F atoms themselves had no influence on the band structure. The photocatalytic tests indicated that the NFTO demonstrated the highest visible-light activity for decompositions of both acetaldehyde and trichloroethylene. This high activity was ascribed to a synergetic consequence of several beneficial effects induced by the N-F-codoping.     

Ag改性提高TiO2对Cr(VI)的光催化还原活性机理

在消除了质子缺乏、光生电子-空穴复合对Cr6＋光催化还原负效应影响下，比较了TiO2和Ag/TiO2（Ag质量分数 1.0％）光催化还原活性.结果表明，相同条件下Ag/TiO2表现出比TiO2更高的催化活性. EPR分析表明，对于Ag/TiO2，UV照射后Ag表面有活性物种生成，在TiO2上有活性中心表相Ti3＋生成.光生电子通过表相Ti3＋向Cr6＋传递电子是Cr6＋光催化还原的速度控制步骤.较多的表相Ti3＋参与还原反应是Ag/TiO2表现出较高催化活性的主要原因，担载Ag上积聚光生电子的较强流动性对反应也起到一定促进作用.     

Fluorine-doped TiO2 powders prepared by spray pyrolysis and their improved photocatalytic activity for decomposition of gas-phase acetaldehyde

F-doped TiO₂ (FTO) powders were synthesized by spray pyrolysis (SP) from an aqueous solution of H₂TiF₆. The resulting FTO powders possessed spherical particles with a rough surface morphology and a strong surface acidity. The fluorine concentrations in the FTO powders calculated from XPS spectra significantly depended on SP temperature and ranged from 2.76 to 9.40 at.%. The FTO powder prepared at SP temperature of 1173 K demonstrated the highest photocatalytic activity for the decomposition of gas-phase acetaldehyde under both ultraviolet (UV) and visible light (vis) irradiations, and it was higher than that of commercial P 25. This high photocatalytic activity was ascribed to several beneficial effects produced by F-doping: enhancement of surface acidity, creation of oxygen vacancies, and increase of active sites. It was interesting to point out that the vis photocatalytic activity of FTO powders was achieved by the creation of surface oxygen vacancies rather than the improvement of optical absorption property of bulk TiO₂ in vis region.     

丙烯环氧化反应中失活钛硅分子筛的无氧脱附研究

采用无氧脱附方法对丙烯环氧化中失活的薄层钛硅分子筛(即Spent EPO-4)和环氧丙烷(PO)与丙二醇单甲醚(MME)浸渍的TS-1催化剂(即PO／TS-1和MME／TS-1)进行了研究，脱附产物由气相色谱定性分析，无氧脱附后的催化剂以丙烯环氧化为探针反应进行再生性能评价，同时在无氧条件下考察了TS-1在300℃时催化裂化PO反应．实验结果表明：PO浸渍TS-1可使其活性明显下降，PO在TS-1上不是简单的弱吸附，存在着化学强吸附和自聚．失活催化剂(Spent EPO-4和PO／TS-1)经无氧脱附后，其催化活性可显著恢复．通过对失活催化剂脱附产物的比较，推测了丙烯环氧化反应过程中钛硅分子筛失活原因．     

钛硅分子筛挤条成型催化剂热稳定性能的研究

采用在空气中程序升温焙烧的方式考察了钛硅分子筛挤条成型催化剂的热稳定性能．对不同温度焙烧得到的样品进行了XRD、IR、UV Raman和SEM表征．结果表明，在高温焙烧时，由于载体结构的改变引起载体与分子筛之问相互作用发生变化，导致成型催化剂中分子筛骨架破坏．随着焙烧温度的提高，IR谱图中960cm^-1处代表钛进入骨架的特征峰的强度迅速减弱，当焙烧温度达到1000℃时，960cm-1处的骨架钛特征峰移至948cm^-1．在紫外拉曼谱图中，骨架位钛物种的特征拉曼谱峰-1125cm^-1谱峰在加入SiO2载体后，高温下峰强度明显降低，这说明载体的加入降低了钛硅分子筛挤条成型催化剂的热稳定性能．     

Ti基IrO2＋Ta2O5阳极在H2SO4溶液中的电解时效行为

研究了450 ℃制备所得Ti/70％IrO2 30％Ta2O5（摩尔分数）高寿命阳极在H2SO4溶液电解过程中电极的物理、化学及电化学性能的时效行为.结果发现，整个电解过程可分为“活化”、“稳定”及“失效”三个阶段.在“活化”及“稳定”区内主要发生电极表面活性氧化物的溶解，涂层中IrO2金红石相的（110）、（101）晶面择优取向随电解时间延长而减弱，而（002）晶面择优增强.但是在“失效区”内，各晶面的择优程度却不随电解时间的变化而变化，这表明在“失效区”内氧化物的损失机制发生了变化.电化学阻抗谱测试表明，电极的析氧电化学反应电阻随电解时间的延长发生缓慢而连续的上升，而整个电极的物理阻抗在“失效区”内却发生突升现象.X射线衍射分析（XRD）表明，随电解时间的延长TiO2金红石相的衍射强度增大，达“失效区”时衍射强度发生突升.根据实验现象特别是“失效区”内阳极的时效行为提出高寿命Ti基氧化物涂层阳极的失效机制.     

Freon (CHF<Subscript>3</Subscript>)-assisted atomization for the determination of titanium using ultrasonic slurry sampling–graphite furnace atomic absorption spectrometry (USS–GFAAS): a simple and advantageous method for solid samples

A simple and advantageous method for the determination of titanium using graphite furnace atomic absorption spectrometry with slurry sampling has been developed. Titanium is one of the refractory elements that form thermally stable carbides in the graphite tube, which leads to severe memory effects. Trifluoromethane (Freon-23) was applied in the purge gas during the atomization step or alternatively just prior to the atomization to successfully eliminate the problems of carbide formation and increase the lifetime of the furnace tube which could be used for more than 600 heating cycles. A flow rate of 40 mL min^–1 (5% of Freon in argon) was used to obtain symmetrical peaks with no tailing. However, when the gas flow rate was too high (250 mL min^–1) the peak-tailing and memory effects reappeared. Ti was determined in various materials covering a wide range of concentrations, from 2.8 g g^–1 to 12% (m/m) Ti. The accuracy of the method was confirmed by analyzing certified reference materials (CRMs) or by comparing the results with those obtained using inductively coupled plasma–atomic emission spectrometry (ICP–AES) after decomposition of the samples. The materials analyzed were soil, plant, human hair, coal, urban particulate matters, toothpaste, and powdered paint.     

Caesium Heptaiodo‐Dititanate(III), CsTi2I7

Caesium heptaiodo‐dititanate(III), CsTi₂I₇, is obtained from CsI, Ti and TiI₄ at 250 °C in a sealed tantalum ampoule as dark red single crystals. The crystal structure (trigonal, R‐3, a = 1706.6(3), c = 2088.3(5) pm, Z = 12, R1 = 0.0619) contains [TiI₄] tetrahedra sharing common vertices (with Ti—I—Ti angles of 180°) to isolated ditetrahedra [Ti₂I₇]^—. It may also be described as a cubic closest packing of alternating CsI₃ and I₄ layers between which neighbouring tetrahedra are occupied in a way that [Ti₂I₇]^— ditetrahedra are achieved. http://www.gerdmeyer.de     

Titanium and zirconium complexes with novel phenoxy-phosphinimine ligands

A series of novel phenoxy-phosphinimine ligands (L): L = 2-(Ph₂PNR), 4, 6-(CMe₃)₂-C₆H₂OH [2, R = SiMe₃; 3, R = Ph] have been prepared in the yield of 65-71%. And bis(phenoxy-phosphinimide) group 4 complexes of the type L₂MCl₂ [4, M = Ti, R = SiMe₃; 5, M = Zr, R = SiMe₃; 6, M = Ti, R = Ph; 7, M = Zr, R = Ph] have been synthesized by the reaction of the ligands with TiCl₄ and ZrCl₄. The structure of complex 7 has been determined by X-ray crystallography. The complexes 4-7 showed inactive to ethylene polymerization in the presence of modified methylaluminoxane (MMAO) and i-Bu₃Al/Ph₃CB(C₆ F₅)₄. These results should be caused by overdoing the steric congestion around central metal.     

Hydrothermal synthesis and intercalation behavior of a layered titanium phosphate Ti2(H2PO4)(HPO4)(PO4)2 · 0.5C6N2H16, with an extended γ-phase intercalated into organic amine

With a hydrothermal technique, a layered titanium phosphate with the formula Ti₂(H₂PO₄)(HPO₄)(PO₄)₂ · 0.5C₆N₂H₁₆ (denoted TP-J2) has been prepared by treating the Ti/H₃PO₄/H₂O/1-methylpiperazine system directly. The as-synthesized products were characterized by powder X-ray diffraction, CP-MAS solid-state ³¹P NMR spectroscopy, thermogravimetric and differential thermal analyses (TG-DTA). The structure was solved by single-crystal X-ray diffraction analysis and it presents an extended γ-phase intercalated with organic amine. Crystal data: triclinic, , a = 8.106 (2) Å, b = 8.197 (2) Å, c = 11.658 (2) Å.  = 78.32 (3)°, β = 80.85 (3)°, γ = 77.90 (3)°, Z = 2. Additionally, the intercalation behavior of TP-J2 with n-alkyl monoamine (n = 2, 3, 4, 6, 8, 10 and 12) was investigated. Owing to the strong brønsted base, N,N′-dimethylpiperazine, resides in the interlayer, it presented unusual features of TP-J2 in contrast with that of γ-Tip.