Effect of organic acid reductants on photocatalytic reduction of selenate solutions using a TiO2 catalyst

Abstract

The effect of organic acid reductants including formic acid, citric acid, oxalic acid, and tartaric acid, on the photocatalytic reduction of aqueous Se (VI) solutions was studied using TiO2 catalyst. Among the organic acids examined, formic acid was found most effective in accelerating photocatalytic reduction of Se(VI). Although tartaric acid seemed to be another important acid, it failed to complete the reduction of Se(VI). Although these organic acids were photocatalytically oxidized, their oxidation rates and amounts were small. To reduce Se(VI) to H2Se, 4∼5 molar equivalent organic acid was oxidized. However, simple chemical reduction of Se(VI) by organic acid did not occur. It is thought that the photocatalytic reduction of Se(VI) by efficient use of electrons formed on TiO2 catalyst was accelerated by the consumption of positive holes by organic acid.