Optimizing optical absorption of TiO2 by alloying with TiS2

TiO2 is an attractive material for photocatalytic water splitting, but its band gap is too large to allow for efficient absorption of solar photons. We present a comprehensive first-principles investigation of band-structure modifications induced by alloying TiO2 with TiS2. The band gap of TiO2(1-x)S2x alloys exhibits a dramatic decrease upon addition of even a low concentration of S. The optical absorption of visible light is attainable with sulfur concentrations less than x=0.25. We have verified that the band alignment in these alloys is favorable for photocatalytic applications: in particular, the conduction band exhibits only small shifts, while the majority of the band-gap change is due to an upward shift of the valence band