多酸的光化学和光催化（上）

综述了多酸光化学研究的发展历程,阐明了多酸光化学的原理及相应的理论模型,总结了各种化合物作为光催化剂在有机反应、环境化学及分解水方面的应用,最后指明了目前正在进行的与多酸光化学相关的前沿研究。     

Fe掺杂g⁃C3N4光催化活化过硫酸钠降解偶氮染料

以硝酸铁为铁源,通过浸渍法制备Fe?C₃N₄复合材料。采用FT?IR对Fe?C₃N₄材料进行了表征分析。结果表明,Fe掺杂不改变g?C₃N₄的骨架结构,可以增加g?C₃N₄材料的光催化性能。以橙黄II为目标污染物,在可见光下Fe?C₃N₄催化活化过硫酸钠降解偶氮染料,考察了过硫酸钠物质的量、Fe?C₃N₄质量浓度、橙黄II质量浓度及pH对降解效果的影响,并对反应进行了动力学研究,分析了所制备的催化材料的稳定性。结果表明,在Fe?C₃N₄质量浓度为2.0 g/L、过硫酸钠与污染物物质的量比为1 200∶1和pH=3的条件下,降解效果最好,降解率为77.8%;Fe?C₃N₄/过硫酸钠体系对偶氮染料的降解满足准二级动力学方程;Fe?C₃N₄材料具有可重复利用性。     

A quantitative evalution of the photocatalytic performance of TiO2 slurries

This paper reports the results of a comparison between two TiO₂ photocatalysts that differ for particle size and absorption/scattering optical properties. The catalyst with larger particles and lower surface area performed better in the degradation of phenol than the specimen with smaller particles and larger surface area. Following carefully designed experiments, it is possible to assess the relative role of light absorption/scattering properties and catalyst-related efficiency by means of a basic kinetic model for the rate of photocatalytic reactions. Explicit relationships are derived in the framework of the steady-state approximation for the quantum yield as a function of one a-dimensional number collecting surface kinetic constants for charge carrier reactions at the interface, absorbed light and surface substrate concentrations. The dimensionality change to volume-defined quantities allows derivation of the explicit dependence of the quantum yield on substrate concentration and partition constants, catalyst concentration, and the rate of volumetric light absorption. Following this approach, the rate expression for slurry systems, valid in the absence of back reactions, is directly derived. Some further simplification of the rate equation for the case of low quantum yield regime leads to analytical relationships able to account for the dependence of the rate on catalyst concentration and absorbed light in the case of stirred and unstirred conditions. The reported properly designed experiments allow the estimation of catalyst-specific micro-kinetic constants.     

Relationship concerning the nature and concentration of Fe(III) species on the surface of TiO2 particles and photocatalytic activity of the catalyst

There have been contradictory results concerning the effect of doping TiO₂ with Fe(III) upon its photocatalytic activity. We believe that this is due to the method used in adding the Fe(III) to TiO₂. This paper addresses this issue by using a precise adsorption process for loading stable aqueous suspensions (sols) of TiO₂ doped with Fe(III). In this manner, we control the speciation of Fe(III) on the surface of TiO₂ and subsequently use these loaded sols to produce stable thin-film photocatalysts. Adsorption isotherms for these systems at different pH (2.0 and 2.5) values showed that both pH and the concentration of Fe(III) in solution influence the adsorption density of Fe(III), the stability of the resulting sols, and the speciation (degree of polymerization) of Fe(III) ions on the surface of the TiO₂ nano-particles. UV-Vis spectroscopy on selected systems was the technique employed to confirm these results. The pore structure of the resulting gels (xerogels) prepared from these sols, as well as thermal stability of porous materials prepared by firing the xerogels have been determined by measuring N₂ adsorption as a function of firing temperature. Thermal analysis (TG–DTA) studies on xerogels obtained from some of these systems showed that the presence of Fe(III) species on the TiO₂ retards the conversion of anatase into rutile and therefore increases the thermal stability of the gel microstructure. Lastly, porous films, resulting from the casting of the sols on glass rings and subsequent firing, were used in photocatalytic studies. In the presence of UV light, these supported films were capable of degrading ethanol in the gas phase. While photocatalytic activity for Fe(III) loaded TiO₂ films is less than for TiO₂ films without Fe(III), the speciation of Fe(III) on the surface directly influences the behavior of the intermediate—acetaldehyde—formed in this reaction. Since we have only evaluated the effect of iron speciation on the degradation of ethanol, other target species may be influenced either advantageously or deleteriously depending upon the state of Fe(III) on the surface of TiO₂ photocatalysts.     

Nanocomposites of SnO2 and g-C3N4: Preparation,characterization and photocatalysis under visible LED irradiation

Tin dioxide nanoparticles were prepared in the presence of graphitized carbon nitride (g-C₃N₄) forming nanocomposites with different contents of SnO₂ up to 40 %. G-C₃N₄ was synthetized by heating of melamine at 550 °C in the open air and Sn²⁺ ions were precipitated by sodium hydroxide in g-C₃N₄ aqueous dispersions. Resulting mixtures were dried by freezing at ?20 °C and calcined at 450 °C to obtain SnO₂/g-C₃N₄ nanocomposites.The nanocomposites were characterized by common characterization methods in solid state and in their aqueous dispersions using dynamic light scattering (DLS) analysis and photocatalysis. SnO₂ nanoparticles in the nanocomposites were found to have an average size of 4 nm, however, those precipitated without g-C₃N₄ had an average size of 14 nm. Separation of photoinduced electron and holes via heterojunction between SnO₂ and g-C₃N₄ was demonstrated by photocatalytic decomposition of Rhodamine B (RhB) under LED visible irradiation (416 nm) and photocurrent measurements. The most photocatalytically active nanocomposite contained 10 % of SnO₂. Graphitized carbon nitride was assumed to serve as a template structure for the preparation of SnO₂ nanoparticles with a narrow size distribution without using any stabilizing additives.     

空调环境中污染物的光催化净化

大多数人大部分时间均处于室内环境之中,因而即使室内很低浓度的污染物,在长期作用于人体之后,也会影响人体健康。本文分析了空调环境中污染物的分布特征,论述了利用TiO2光催化技术净化空调环境中空气污染物的可行性以及要面对的问题。认为TiO2光催化技术是一项能耗低、易操作、安全环保的净化技术,在空调环境污染物净化方面具有广泛的应用前景。     

Photocatalytic hydrogen evolution from aqueous solutions of organophosphorous compounds

Photocatalytic hydrogen production from water solutions of dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), triethyl phosphate (TEP), and radiation protective amine WR 2721, that imitate nerve chemical warfare agents was studied for the first time. Platinized titianium dioxide Degussa P25 was used as catalyst. No significant hydrogen evolution was detected without organic electron donors – sacrificial agents.     

Visible Light Photocatalytic Properties and Thermochromic Phenomena of Nanostructured BiOCl Microspheres

Black nanostructured Bi OCl microspheres were directly synthesized by a hydrothermal method. The black balllike Bi OCl microspheres and black flower-like Bi OCl microspheres were obtained using different surfactant.The color of the Bi OCl microspheres turned from black to white when being annealed at 400℃ in air for 3 h and could be recovered to black by exposure to ultraviolet light for a few hours. The photocatalytic activity of both the black and the white Bi OCl microspheres was characterized by the photo-degradation of methyl orange dye under visible light irradiation. The black ball-like nanostructure Bi OCl displayed the best photocatalytic activity, compared with the white Bi OCl and the black flower-like Bi OCl. It can degrade the methyl orange dye to 20% within 70 min under visible light irradiation. The high activity of the Bi OCl ball-like sphere may own to its special morphology, strong absorption in visible light range and the existence of oxygen vacancies.