Electrochemical potential controlling preparation of oxygen vacancies modified SrTiO3 with Ti3+ and Ti2+ self-doping in molten salt

Abstract Self-doping of Ti3+ and Ti2+ in oxygen vacancies modified SrTiO3 crystal could significantly improve its photocatalytic properties. In this paper, a series of dark gray oxygen vacancies modified SrTiO3 with self-doping of Ti3+ and Ti2+ were synthesized by electrochemical reduction of SrTiO3 in molten SrCl2–NaCl. The samples were characterized by XRD, SEM, and UV–vis diffuse reflectance spectroscopy, respectively. The valence state of Ti ions on the surface of sample and its oxygen vacancies types were analyzed by XPS spectrum. XRD patterns showed that the diffraction angle (2θ) of samples shifted towards higher 2 theta as the increased cell voltage and the volume of the crystal decreased. XPS spectra indicated that the concentration of Ti3+ ions and oxygen vacancies in SrTiO3 increased as the increased cell voltage. The concentration of Ti3+ and oxygen vacancies in SrTiO3 obtained at cell voltage of 2.9 ​V were 66% and 24%, respectively. The absorption characteristic peak of the self-doping of Ti2+ in SrTiO3 was showed when the cell voltage exceeded 2.7 ​V. The optical absorption of the SrTiO3 extended to the visible light and its bandgap energy narrowed.