Self-doped SrTiO3−δ photocatalyst with enhanced activity for artificial photosynthesis under visible light

Abstract

Self-doped SrTiO_3−δ was prepared through a carbon-free one-step combustion method followed by a series of heat treatments in Ar at temperatures ranging from 1200 to 1400 °C. X-Ray Photoelectron Spectroscopy (XPS), Electron Paramagnetic Resonance (EPR) and High-Resolution TEM confirm the presence of Ti³⁺ in samples with oxygen vacancy accommodated in perovskite by forming Ruddlesden–Popper crystallographic shears. The UV-vis spectra and electronic structure calculations show that the oxygen vacancy and Ti³⁺ together induce an in-gap band to enhance the visible light absorption. Pulsed Adsorption of CO₂ and Temperature Programmed Desorption (TPD) experiments show that the higher oxygen deficiency tends to improve the chemical adsorption of CO₂ on the surface as well as in the bulk of SrTiO_3−δ, especially the accommodation of CO₂ molecule in the oxygen vacancy. It is the synergetic effect of visible light absorption and chemical adsorption of CO₂ that improves the artificial photosynthesis to generate hydrocarbon fuels from CO₂/H₂O under visible light irradiation. We also demonstrated that the incorporation of oxygen from CO₂/H₂O into the oxygen vacancy of SrTiO_3−δ leads to the absence of oxygen evolution which therefore results in the oxidation of SrTiO_3−δ (Ti³⁺ → Ti⁴⁺).