有机物/TiO_2电荷转移复合物的形成及其在可见光下的催化活性

The Formation of Charge-Transfer-Complex of Organics/TiO_2 and Their Effects on Photocatalytic Reduction of Cr^(6+) Under Visible Light Irradiation

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.其吸收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,与有机物结构密切相关.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影响Cr6+的光催化还原反应.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 photocatalytic reductions of Cr^6＋ 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 Cr^6＋ were carried out through ligand - to - metal charge transfer （LMCT） mechanism and their photocatalytic ac- tivities were related to the structure of organics. Cr^6＋ could hardly be reduced by TiO2 without organics under visi- ble light irradiation. The Cr^6＋ conversion was 100% in formic acid/TiO2 systems after 80 min. For the methanal and methanol systems, the Cr^6＋ conversion were 93.63% and 22.69% after 6 h, respectively. The pH value of system significantly affect on the photocatalytic reduction of Cr^6＋. In organics/TiO2 systems, the photocatalytic re- duction of Cr^6＋ conformed to the first - order kinetic equation.