TiO2/H2O/空气O2光催化氧化降解有机污染物的速率限制步骤

金属氧化物如TiO2、ZnO和WO3等在H2O/空气O2介质中，光生空穴及其与表面吸附H2O产生的OH自由基，是光催化降解水中有机物污染物的初始氧化物种。过去总认为这些物种的进攻是扩散控制步骤，难以用动力学同位素效应（H/D KIE）等手段区分。本项目分别以极性不同的各种有机芳香污染物羟基化反应为模型氧化反应，合成环上部分氢被氘取代的底物，研究环上C-H/D键在羟基化中出现逆动力学同位素效应（inverse H/D KIE）与底物极性的关系；研究1,2-NIH shift (1,2-氢迁移效应)的对应关系；以及溶液条件对氧化侧是否是限速步的影响；用低温（4K）ESR和ATR-FTIR跟踪OH自由基加合物的衰减动力学。本项目研究结论将改变过去对光催化氧化一侧不分底物对象笼统概括成扩散控制的片面认识，对修饰、控制氧化物光催化剂降解水中有机污染物，特别是非极性和憎水性强的有机物提供机理上的依据。

The primary oxidative species in photocatalytic degradation of organic pollutants in aqueous environment is photo-induced hole and hydroxyl radical generated from surface-adsorbed H2O in metal oxide semiconductors such as TiO2, ZnO and WO3 in H2O/air or O2 medium. It was often considered the main pathways for these species attacking pollutants was through diffusion-controlled mechanism and was difficult to differentiate the related radical reaction pathways by kinetic isotope effects (KIE). This research is based on the pre-study of using polar, non-polar and hydrophobic organic aromatic pollutants hydroxylation as the model oxidation reaction, synthesizing partial deuterated substrates in aromatic ring, studying the relation between substrate polarity and 1,2-NIH shift (1, 2- neighboring group induced hydrogen shift effect)；studying the relation between the inverse H/D kinetic isotope effect (inverse H/D KIE) in C-H/D bond in hydroxylation and substrate polarity and metal oxide semiconductor surface polarity, and the influence of solvent, dissolved dioxygen and conductive-band electron sacrificial reagents to the rate-determination step of oxidation. And low-temperature ESR (4K) and ATR-FTIR technique would follow the decay kinetics of OH radical adduct. The conclusion of this research would change the past understandings of diffusion-controlled mechanism for photocatalytic oxidation, and provide mechanistic evidences for modifying and controlling metal oxide photocatalyst to degrade organic pollutants especially non-polar and hydrophobic substrates in aqueous solution.