摘要
采用XPS和ESR表征技术研究表明，Cr（Ⅵ）离子在TiO2表面的光催化还原过程中，有Ti3+物种生成并参与了Cr（Ⅵ）离子的还原反应。实验结果表明，Cr（Ⅵ）离子的光催化还原主要以从Ti3+上得到电子的间接还原为主，同时也存在着从TiO2导带捕获先激发电子发生直接还原的可能性。
Semiconductor photocatalysis has been widely studied as an efficient means for treatment of environmental pollution. Toxic heaVy metal ions can be reduced and detoxified by getting photo-induced electrons. Cr(Ⅳ) pollution has caused much attention because of its high toxicity. Photocatalytic reduction of Cr(Ⅳ) ion has been investigated in many papers. But the mechanism of this reduction process is still not very clear.The experimental results showed that Cr(Ⅵ) ion is reduced efficiently on P-25 TiO2semiconductor particles in acidic suspension under UV irradiation. Kinetic studies showed that photocatalytic reduction of Cr(Ⅵ) is in accordance with Langmuir-Hinshelwood law. The mechanism of photocatalytic Cr(Ⅵ) reduction is studied in this paper with ESR and XPS methods. ESR results showed that Ti3+ is produced at the beginning of the reaction, but disappears along with the reaction time. It is pointal out that Ti3+ is involved in the reaction as an intermediate from which Cr(Ⅵ) gets electrons. Photo-induced conduction band electrons is captured by Ti4+ at the beginning of the reaction, and Ti3+ is formed. Then Cr(Ⅵ)gets electrons from Ti3+ and is reduced. So Cr(Ⅵ) ion is mainly reduced indirectly by getting elevtrons from Ti3+. At the same time, Cr(Ⅵ) reduCtion by directly capturing photo-induced conduction band electrons is possible. XPS results showed that Cr(Ⅵ) ions adsorbed at the surface of TiO2 is totally redued to Cr(Ⅲ). Cr(Ⅴ) and Cr(Ⅵ) may be produced as the reaction intermediates. The remarkable inhibition of phosphate ion on Cr(Ⅵ) reduction meantthat Cr(Ⅵ) adsorption on the surface of TiO2 is the elementary step for Cr(Ⅵ) reduction.The decrease in Cr(Ⅵ) reduction in the presence Mn2+ ions may results from the reoxidation of the possible intermediate Cr(Ⅵ) spedes.
关键词
还原
机理
铬离子
光催化剂
二氧化钛
Cr(Ⅵ) ion Photocatalytic reduction Mechanism Ti^(3+)
