氢氧根离子在TiO_2薄膜电极上的吸附行为和光氧化动力学

Adsorption Behavior and Photooxidation Kinetics of OH at TiO_2 Thin Film Electrodes

在醇的水溶液中,应用电化学方法研究了OH-在TiO2薄膜电极上的吸附行为和光氧化动力学.实验结果表明,OH-在TiO2表面的吸附模型符合Langmuir等温吸附方程式,其光氧化动力学行为能用Lang-muir-Hinshelwood动力学方程来描述.在光强足够大时,光电流和OH-在TiO2表面的吸附浓度成正比,这表明,光生空穴仅氧化吸附于TiO2表面的OH-,同时吸附的水分子则不能被氧化.在醇浓度足够高的溶液中,自由基OH和电子之间的复合反应几乎不发生,这时整个光氧化反应的速控步骤是光生自由基OH的生成.

The adsorption behavior and photooxidation kinetics of OH- at TiO2 thin film electrodes in solution of alcohols have been studied by electrochemical measurements. The results show that the adsorption model of OH- on TiO2 surface corresponds to the Langmuir isotherm and under high enough applied bias potential the photooxidation kinetics can be described by Langmuir-Hinshelwood expression. Hydroxide ions are regarded to be the reactant with photogenerated holes and adsorbed water could not be captured by the holes and, consequently, the photocurrent is proportional to the density of OH- adsorbed on TiO2 surface under the condition of high enough light intensity. In solution with high content of alcohols, the recombining reaction between OH. radical and photogenerating electron can hardly occur, where the rate-limiting step is the formation of photo-driven OH. radical.