Triphenyltin hydroxide as a precursor for the synthesis of nanosized tin‐doped TiO2 photocatalysts

¹H and ¹¹⁹Sn NMR results indicate that, when Ph₃SnOH is dissolved in CD₂Cl₂, it dehydrates to (Ph₃Sn)₂O, only a small amount of Ph₃SnOH remaining in equilibrium at room temperature. As a result, the reaction of TiCl₄ with Ph₃SnOH in CH₂Cl₂ proceeds via hydrolysis of the halide to precipitate amorphous TiO₂ that contains adsorbed organotin species. Calcination of the amorphous precursor to 723 K yields nanoparticles of tin‐doped TiO₂ photocatalysts, that contain anatase and rutile phases, and may also contain a segregated SnO₂ phase. The reaction conditions that lead to the formation of a SnO₂ phase have been studied and we have found that it is formed when the amorphous precipitate is not thoroughly washed with CH₂Cl₂ or when non‐recrystallized commercial Ph₃SnOH is used as a starting material. The catalysts obtained have a high activity for the photooxidation of toluene in the gas phase. In particular, a material obtained from non‐recrystallized Ph₃SnOH is particularly promising because the toluene photooxidation rate is more than twice as high as when using Degussa P25. Copyright © 2005 John Wiley & Sons, Ltd.     

金红石型TiO_2中四种点缺陷态研究

利用第一性原理计算方法研究了金红石型TiO_2中四种缺陷的电子态.这四种缺陷包括氧空位(O_v)、钛空位(Ti_V)、钛间隙(Ti_S)以及氧空位O_v与钛间隙态Ti_S共存态.氧空位的存在导致禁带内施主缺陷能级较浅,而深施主能级与Ti间隙态有关.预测了氧空位更倾向于与钛间隙结合,主要通过钛间隙态的3d电子部分转移到近邻近氧空位的部分形成O_V-Ti_S对缺陷.具有O_v、Ti_S或O_V-Ti_S缺陷的体系都出现间隙态,促进体系出现红外吸收.     

Expanding the Applications of the Ilmenite Mineral to the Preparation of Nanostructures: TiO2 Nanorods and their Photocatalytic Properties in the Degradation of Oxalic Acid

The mineral ilmenite is one of the most abundant ores in the Earth′s crust and it is the main source for the industrial production of bulk titanium oxide. At the same time, methods to convert ilmenite into nanostructures of TiO₂ (which are required for new advanced applications, such as solar cells, batteries, and photocatalysts) have not been explored to any significant extent. Herein, we describe a simple and effective method for the preparation of rutile TiO₂ nanorods from ball‐milled ilmenite. These nanorods have small dimensions (width: 5–20 nm, length: 50–100 nm, thickness: 2–5 nm) and possess large specific surface areas (up to 97 m² g^?1). Dissolution/hydrolysis/precipitation is proposed as a growth mechanism. The nanorods were found to have attractive photocatalytic properties in the degradation of oxalic acid. Their photocatalytic activity is close to that of the benchmark Degussa P25 material and better than that of a commercial high‐surface‐area rutile powder.     

Ab initio study of the high‐temperature phase transition in crystalline GeO2

Germanium dioxide (GeO₂) takes two forms at ambient pressure: a thermodynamically stable rutile‐type structure and a high‐temperature quartz‐type polymorph. Here, we investigate the phase stability at finite temperatures by ab initio phonon and thermochemical computations. We use gradient‐corrected density‐functional theory (PBE‐GGA) and pay particular attention to the modeling of the “semicore” germanium 3d orbitals (ascribing them either to the core or to the valence region). The phase transition is predicted correctly in both cases, and computed heat capacities and entropies are in excellent agreement with thermochemical database values. Nonetheless, the computed formation energies of α‐quartz‐type GeO₂ (and, consequently, the predicted transition temperatures) differ significantly depending on theoretical method. Remarkably, the simpler and cheaper computational approach produces seemingly better results, not worse. In our opinion, GeO₂ is a nice test case that illustrates both possibilities and limitations of modern ab initio thermochemistry. © 2013 Wiley Periodicals, Inc.     

Molecular‐Level Understanding of the Photocatalytic Activity Difference between Anatase and Rutile Nanoparticles

The generation of oxidants on illuminated photocatalysts and their participation in subsequent reactions are the main basis of the widely investigated photocatalytic processes for environmental remediation and selective oxidation. Here, the generation and the subsequent diffusion of ^.OH from the illuminated TiO₂ surface to the solution bulk were directly observed using a single‐molecule detection method and this molecular phenomenon could explain the different macroscopic behavior of anatase and rutile in photocatalysis. The mobile ^.OH is generated on anatase but not on rutile. Therefore, the photocatalytic oxidation on rutile is limited to adsorbed substrates whereas that on anatase is more facile and versatile owing to the presence of mobile ^.OH. The ability of anatase to generate mobile ^.OH is proposed as a previously unrecognized key factor that explains the common observations that anatase has higher activity than rutile for many photooxidative reactions.     

Synthesis of TiO2/ZnSn（OH）6 Hollow Nano-composite via a Simultaneous Crystallization-etching Route as Photocatalyst

We report the synthesis of TiO2/ZnSn（OH）6 as a novel nano-composite material via a simultaneous crystallization-etching route with cubic nano-ZnSn（OH）6 and TiF4 as the precursors. The structure, composition and morphology of the composite were characterized by XRD, EDS, FETEM and FESEM, which showed the prepared TiO2/ZnSn（OH）6 had a unique morphology of hollow cubic nano-ZnSn（OH）6 attached with rutile TiO2 nanoparticles. The results of photocatalytic activity measurement indicated the photocatalytic activity of the prepared composite was better than that of nano-ZnSn（OH）6. This study may be helpful for the design and fabrication of functional comoosite materials.     

Electronic structure and optical properties of rutile RuO2 from first principles

The systematic trends of electrionic structure and optical properties of rutile (P42 /mnm) RuO2 have been calculated by using the plane-wave norm-conserving pseudopotential density functional theory (DFT) method within the generalised gradient approximation (GGA) for the exchange-correlation potential.The obtained equilibrium structure parameters are in excellent agreement with the experimental data.The calculated bulk modulus and elastic constants are also in good agreement with the experimental data and available theoretical calculations.Analysis based on electronic structure and pseudogap reveals that the bonding nature in RuO2 is a combination of covalent,ionic and metallic bonds.Based on a Kramers-Kronig analysis of the reflectivity,we have obtained the spectral dependence of the real and imaginary parts of the complex dielectric constant (ε1 and ε2,respectively) and the refractive index (n);and comparisons have shown that the theoretical results agree well with the experimental data as well.Meanwhile,we have also calculated the absorption coefficient,reflectivity index,electron energy loss function of RuO2 for radiation up to 30 eV.As a result,the predicted reflectivity index is in good agreement with the experimental data at low energies.     

Anisotropy of magnetization-induced surface optical second harmonic generation from Co doped rutile TiO2

We have investigated the surface magnetization anisotropy of 5 at% Co doped rutile TiO₂ (1 1 0) using magnetization-induced optical second harmonic generation (MSHG) in the longitudinal Kerr configuration with an incident beam angle of 4°. The MSH intensity pattern from the Co:TiO₂ without surface Co clusters showed two anisotropic lobes at the second harmonic photon energy of 2?ω=3.13 eV. Since MSH intensity is proportional to surface magnetization, the result indicates an anisotropy of the surface magnetization of Co:rutile TiO₂ (1 1 0). This confirms the possibility that 5 at% Co:rutile TiO₂ (1 1 0) is a ferromagnetic dilute magnetic semiconductor at its surface, as proposed in our previous paper.     

Al-N共掺杂金红石相TiO_2的第一性原理研究

本文采用了基于密度泛函理论的第一性原理平面波超软赝势法对金红石相TiO_2进行了计算,其中内容包括未掺杂与单掺杂Al、单掺杂N以及共掺杂Al-N这四种不同情况下TiO_2的能带结构与态密度和光吸收系数的研究.计算结果表明:单掺杂Al和N时,均不同程度地改变了其能带结构,光吸收能力均有提高但效果不佳.在共掺杂Al-N时,TiO_2晶格常数产生了改变,并出现了新的杂质能级.由于杂质能级存在于TiO_2禁带范围内,减小了电子跃迁至导带所需能量,从而提高了其光吸收能力,其效果相对于单掺杂来说更有明显提高.     

N-Mo-W共掺杂金红石相TiO_2的第一性原理研究

基于密度泛函理论第一性原理与平面波超软赝势法是目前对物质光学性质计算的成熟手段,本文利用MS软件采取该方法对金红石相TiO_2进行了不同掺杂情况下的模拟计算.内容包括未掺杂与单掺杂Mo、单掺杂N、共掺杂Mo-N以及共掺杂N-Mo-W这五种不同情况下TiO_2的能带结构、电子态密度与光学性质分析,通过对计算得出的数据分析有以下结论:单掺杂能改变TiO_2禁带宽度,但相对于共掺杂Mo-N和W-N以及N-Mo-W来说效果欠佳.其中,掺杂W时由于在导带底中出现新的杂质能级,并出现了导带下降幅度大于价带下降幅度的情况,禁带宽度变窄,使得在单掺杂情况中效果明显.而共掺杂中N-Mo-W的价带出现清晰的杂质能级,并且由于该能级介于费米能级附近的关系使得价电子跃迁至导带更为容易,并且此时能级密度较大也是掺杂效果明显的一个重要原因.