Photocatalytic reduction of selenite and selenate using TiO 2 photocatalyst

Abstract

The fate of selenite (Se(IV)) and selenate (Se(VI)) ions in illuminated TiO 2 suspensions was studied. In the presence of formic acid as a hole scavenger, both Se(IV) and Se(VI) were photoreduced to Se(0). The Se(0) deposited as either separate particles or a film on the TiO 2 particles. UV–vis reflectance measurements showed that the Se–TiO 2 powders were red-shifted relative to pure TiO 2 with an additional absorbance band at around 680 nm, attributed to Se(0). The photocatalytic reduction mechanism of selenium ions, with focus on selenite photoreduction, is discussed. It is proposed that direct reduction of Se(IV) by the electrons photogenerated in TiO 2 resulted in the formation of a Se(0) film while the formation of Se(0) particles was due to a chemical reaction between Se(IV) and Se(2−). The Se(2−) is believed to have been generated from the six electron photoreduction of Se(IV) and/or further photoreduction of Se(0) deposits.