Photo-oxidation of water sensitized by TiO$_2$ and WO$_3$ in presence of different electron acceptors

Abstract

The photo-oxidation of water is studied in presence of UV-light ($\lambda <$ 400 nm) using titanium dioxide (TiO$_{2})$ and tungsten oxide (WO$_{3, }$micro- and nano-crystalline) semiconductors in presence of different sacrificial electron acceptors (SEA): Fe(NO$_{3})_{2}$, Na$_{2}$S$_{2}$O$_{8}$, Ce(SO$_{4})_{2}$,\linebreak Co[(NH$_{3})_{5}$Cl]Cl$_{2}$, AgNO$_{3}$, HgCl$_{2}$ and Cu(NO$_{3})_{2}$. TiO$_{2}$ is 5 to 10 times more photoactive than WO$_{3}$ 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 Hg$^{2 + }$ or Cu$^{2 + }$ 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+H$_{2}$O+Semiconductor) exhibits a different behaviour and the results are rationalised in terms of the spectral and redox potential features of the system.