Modification of TiO2 with sulfate and phosphate for enhanced eosin Y-sensitized hydrogen evolution under visible light illumination.

TiO2 was modified with sulfate and phosphate (denoted as S/TiO2 and P/TiO2) through a simple sulfuric or phosphoric acid treatment. A strong coordination bond forms between sulfate or phosphate and Ti(4+) of TiO2. Eosin Y (EY)-sensitized S/TiO2 and P/TiO2 (Pt as a co-catalyst and triethanolamine as a sacrificial electron donor) exhibit enhanced photocatalytic activity for hydrogen evolution under visible light illumination (λ > 420 nm) compared to that of EY-sensitized TiO2. The conduction band (CB) edges of S/TiO2 and P/TiO2 shift toward the negative, and the hydrogen bond interaction between the reduced radical EY˙-H and S/TiO2 or P/TiO2 is enhanced due to the inducing effect of the bound sulfate and phosphate. Thus, the photocatalytic hydrogen evolution is promoted. The effects of the concentration of the sulfuric or phosphoric acid as well as concentration of EY on the sensitization hydrogen evolution were investigated. The possible mechanism was discussed.