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

Self-doped SrTiO3-delta 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 degrees 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 SrTiO3-delta, 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 SrTiO3-delta leads to the absence of oxygen evolution which therefore results in the oxidation of SrTiO3-delta (Ti3+ -> Ti4+).