Effects of Mo sources on Mo doped SrTiO₃ powder prepared by spray pyrolysis for H₂ evolution under visible light irradiation

Highlights: • Three types of molybdenum ions (Mo⁶⁺, Mo⁴⁺, and Mo²⁺) were doped into SrTiO₃. • Molybdenum oxidation states were changed by photocatalyst preparation process. • Hydrogen was evolved by molybdenum doped SrTiO₃ under visible light. • SrTiO₃ doped with Mo⁴⁺ and Mo⁶⁺ showed the best photocatalytic activity. - Abstract: SrTiO₃ was doped with three types of molybdenum ions (Mo⁶⁺, Mo⁴⁺, and Mo²⁺) by spray pyrolysis. The molybdenum ions narrowed the band gap of SrTiO₃ to allow hydrogen evolution under visible-light irradiation. The molybdenum-doped SrTiO₃ photocatalyst prepared from MoO₂ (0.4 mol%) exhibited hydrogen evolution up to a rate of 1410.3 μmol g⁻¹ h⁻¹ with an induction period of 1 h. The use of MoO₂ resulted in SrTiO₃ doping by Mo⁶⁺ and Mo⁴⁺ ions, which enhanced the hydrogen evolution by forming 4d-like states under the conduction band. The ionic structure of SrTiO₃ doped with Mo⁴⁺ and Mo⁶⁺ could be expressed as Sr[Ti⁴⁺_1−x−y(Mo⁴⁺_xMo⁶⁺_y)]O₃ from the X-ray photoelectron spectra.