Z-scheme water splitting by microspherical Rh-doped SrTiO₃ photocatalysts prepared by a spray drying method

Abstract

　Microspherical particles of Rh-doped SrTiO₃ (SrTiO₃:Rh) having size of 1–2 μm were synthesized by a spray drying (SD) method employing a water-soluble ammonium trilactatotitanate. When the calcination temperature increased up to 1200 °C, primary particles grew significantly while the microspherical morphology of the secondary particles was kept. Dynamic light scattering analysis proved well-dispersive nature of the SD sample. Photocatalytic activities of SrTiO_b:Rh synthesized by the SD method, solid state reaction (SSR), and a polymerizable complex (PC) method were evaluated for H₂ evolution using an electron donor such as methanol, Fe²⁺, or [Co(bpy)₃]²⁺ and Z-scheme water splitting combined with BiVO₄ of an O₂^- evolving photocatalyst and either Fe^3+/2+, [Co(bpy)₃]^3+/2+, or reduced graphene oxide as an electron mediator. SrTiO₃:Rh prepared by the SD method showed much higher activities for all Z-scheme water splitting than the samples synthesized by the SSR method. Activities of the SD sample for Z-scheme water splitting using electron shuttles, Fe^3+/2+ and [Co(bpy)₃]^3+/2+, were slightly higher or comparable to those of the PC sample whereas the SD sample achieved higher activity in Z-scheme water splitting based on interparticle electron transfer. In addition, even when the mass of SrTiO₃:Rh used for the Z-scheme system with Fe^3+/2+ was decreased from 50 mg to 30 mg, the SD sample still showed high activity while the activity decreased for the SSR and PC samples. Thus, usefulness of the SD method to obtain highly active SrTiO₃:Rh with well-dispersive nature has been demonstrated.