Effects of colloid stabilizer and pH on photoinduced electron transfer from colloidal titanium dioxide to methylviologen

Abstract The effects of a colloid stabilizer (stabilization against the flocculation of the colloid) and pH on the photoinduced electron transfer from colloidal TiO 2 to methylviologen (MV 2+ ) were investigated by laser flash photolysis. The photoinduced electron transfer reaction was accelerated when polyvinyl alcohol (PVA), known to act as a hole scavenger, was used as colloid stabilizer; it was inhibited by stabilizers with negative charge, such as sodium dodecylsulphate (SDS) and sodium hexametaphosphate (HMP). Furthermore, the pH of the solutions also has an influence on the electron transfer reactions. The transient absorption due to the methylviologen cation radical (MV* + ), produced by electron transfer, appeared at zero charge of TiO 2 , and increased in intensity with increasing pH. The rate of electron transfer also increased with increasing pH. When HMP was used as colloid stabilizer, very rapid electron transfer was observed even around pH 6–7, although the transient absorption was very weak compared with that observed for PVA.