Preparation of new sulfur-doped and sulfur/nitrogen co-doped CsTaWO6 photocatalysts for hydrogen production from water under visible light

Wide band gap semiconductor photocatalyst CsTaWO6 (3.8 eV) was anion-doped via simple gas-solid reactions to extend its absorption into the visible light range. Sulfur doping and sulfur/nitrogen co-doping were performed, using sulfur powder and ammonia as precursors, resulting in decreased band gaps of doped CsTaWO6 down to 2.06 eV. The resulting materials CsTaWO6-xSx and CsTaWO6-x-ySxNy were investigated concerning their chemical and electronic structures via experimental characterizations and first principle calculations. Sulfur and sulfur/nitrogen doped CsTaWO6 crystals showed a clear red shift in absorption, and the anionic dopants were detected using X-ray photoelectron spectroscopy. Photocatalytic performance tests for the doped materials evaluated the capability of generating (OH)-O-center dot radicals for photocatalytic reactions. Water splitting tests of the photocatalysts using a new type of setup including quadrupole mass spectrometry revealed that the doped materials were more efficient in H-2 production under simulated solar irradiation, in contrast to the undoped CsTaWO6 or P25. Co-doped CsTaWO6-x-ySxNy turned out to be the best material for H2 production, due to its capability in efficiently utilizing the visible light in the solar spectrum.