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.