Visible light induced hydrogen evolution over the heterosystem Bi2S3/TiO2

A new photochemical heterosystem Bi2S3/TiO2 immersed in solutions of X2- (=S2- or S2O32-) as reducing agents for generated minorities is proposed. Bi2S3, synthesized via solvent thermal process, has a good crystallinity and exhibits n-type conduction as evidenced from photocurrent-potential characteristics. The flat band potential of Bi2S3 (-0.83V(SCE)) is pH-insensitive and shifts negatively with increasing S2- concentration by similar to 53 mV/pS. The heterosystem shows a much higher activity than Bi2S3 alone where efficient H-2-photoevolution can be realized with concomitant oxidation of X2-. The optimal value of the mass ratio (Bi2S3/TiO2) was equal to unity. In S2O32- electrolyte, the photoactivity peaks at pH similar to 13.7 with an evolution rate of 2.9 mu mol mg(-1) h(-1) and decreases gradually to zero near pH 7. The competitive back reduction of end products S4O62- and S2(2-) slows down the H-2-evolution. The regression of the photoactivity over time is also due to the decrease of band bending at the interface TiO2/electrolyte. (c) 2007 Elsevier B.V. All rights reserved.