The photocatalytic reduction of aqueous Se(VI) solution was studied using t
wo types of TiO2 powders with different specific surface areas and disperse
d particle sizes as a catalyst, and HCOOH as a reductant. The principal red
uction products were Se degrees and H2Se: Se(IV) was not detected. The redu
ction rate of Se(VI) was mainly controlled by the amount of Se(VI) adsorbed
onto each type of the TiO2 powders. When different TiO2 powders were used,
the energy conversion ratio of TiO2 played the more important role in the
photocatalytic reduction of Se(VI) or Se degrees. Using a TiO2 catalyst wit
h a high conversion ratio, the time required for the reductions of Se(VI) t
o Se degrees and of Se degrees to H2Se differed by a ratio of 3 : 1, as exp
ected from reaction equations. The reduction rates for Se(VI) can be approx
imated from the amount of Se(VI) adsorbed onto TiO2 powders and the energy
conversion ratios. The pH of solution, amount of TiO2 and concentrations of
Se(VI) and HCOOH were additionaly recognized as important factors.