有机物/TiO2电荷转移复合物的形成及其在可见光下的催化活性

以TiO2（Degussa P25）为光催化剂，可见光为激发光源，分别对甲醇/TiO2、甲醛/TiO2、甲酸/TiO2体系中光催化还原Cr6+的情况进行了研究. 结果表明，有机醇和羧酸能与TiO2形成电荷转移复合物. 这种复合物能够吸收400 nm以上的可见光，并通过LMCT（ligand-to-metal charge transfer）机制引发光催化还原反应. 不同的有机物/TiO2体系中，Cr6+的光催化还原反应表现出极大的差异，这种差别与有机物的结构密切相关. 当体系中不存在有机物时，可见光下TiO2几乎不能将Cr6+还原；当加入甲酸，经光照80 min后，Cr6+的还原率即可达100%；而在甲醛/TiO2和甲醇/TiO2体系中，光照6 h后，Cr6+的还原率分别可达93.63%和22.69%. 体系的pH对Cr6+的光催化还原反应有显著影响. 有机物/TiO2体系中，光催化还原Cr6+的反应符合一级动力学规律.

The Formation of Charge-Transfer-Complex of Organics/TiO2 and Their Effects on Photocatalytic Reduction of Cr6 + Under Visible Light Irradiation

The photocatalytic reductions of Cr6+ in methanol/TiO2,methanal/TiO2 and formic acid/TiO2 systems under visible light irradiation were investigated.The results showed that alcohols and carboxylic acid with TiO2 could form the charge-transfer-complexes which were able to absorb visible light.The photocatalytic reductions of Cr6+ were carried out through ligand-to-metal charge transfer(LMCT) mechanism and their photocatalytic activities were related to the structure of organics.Cr6+ could hardly be reduced by TiO2 without organics under visible light irradiation.The Cr6+conversion was 100% in formic acid/TiO2 systems after 80 min.For the methanal and methanol systems,the Cr6+conversion were 93.63% and 22.69% after 6 h,respectively.The pH value of system significantly affect on the photocatalytic reduction of Cr6+.In organics/TiO2 systems,the photocatalytic reduction of Cr6+ conformed to the first-order kinetic equation.