ZrW2O8 photocatalyst and its visible-light sensitization via sulfur anion doping for water splitting

ZrW2O8 prepared by hydrothermal reaction was found to act as a photocatalyst for water splitting under UV light irradiation. It has good activity for water splitting to evolve H2 and O2 steadily in the presence of CH3OH and AgNO3 as electron donor and electron scavenger respectively. With respect to the band structure for photocatalytic water splitting, ZrW2O8 (4.0 eV) was found to be superior to ZrO2 (5.0 eV) with a wider band gap and WO3 (2.7 eV) with CB bottom more positive than the reduction potential of H+ to H2. The improvement of the band structure was attributed to the hybridization of W5d and Zr4d in conduction band (CB) as well as the change in crystal structure. Moreover, the absorption edge of ZrW2O8 was significantly extended to visible-light region by sulfur anion doping, and H2 could be evolved over Pt/S-ZrW2O8 under irradiation up to 360 nm in the presence of CH3OH while O2 could be evolved over S-ZrW2O8 under irradiation up to 510 nm in the presence of AgNO3. The visible-light sensitization was attributed to the S3p states, which increased the width of the VB itself and caused the decrease in the band gap energy.