Photocatalytic reduction of selenite and selenate using TiO2 photocatalyst

The fate of selenite (Se(IV)) and selenate (Se(VI)) ions in illuminated TiO2 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 TiO2 particles. UV–vis reflectance measurements showed that the Se–TiO2 powders were red-shifted relative to pure TiO2 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 TiO2 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.