Photo-oxidation of water sensitized by TiO2 and WO3 in presence of different electron acceptors

The photo-oxidation of water is studied in presence of UV-light (lambda < 400 nm) using titanium dioxide (TiO2) and tungsten oxide (WO3 , micro- and nano-crystalline) semiconductors in presence of different sacrificial electron acceptors (SEA): Fe(NO3)(2), Na2S2O8, Ce(SO4)(2), Co[(NH3)(5)Cl]Cl-2, AgNO3, HgCl2 and Cu(NO3)(2). TiO2 is 5 to 10 times more photoactive than WO3 with reference to oxygen evolution. Ag ions are the best of the SEAs, for all the semiconductors tested in the photo-redox process. No oxygen evolution is observed when Hg2+ or Cu2+ ions are used as SEAs. The effect of high (10(-2) Mol dm(-3)) and low (10(-3) mol dm(-3)) SEA concentrations is also studied but no common trend is observed. Instead, each system (i.e., SEA+H2O+Semiconductor) exhibits a different behaviour and the results are rationalised in terms of the spectral and redox potential features of the system