Study of Congo Red removal from aqueous solution by using the deficient perovskite SrTiO3-δ under solar light

Abstract

The deficient perovskite SrTiO3-δ (STO) synthesized by nitrate route was identified by X-ray diffraction (XRD) and characterised by BET analysis, Attenuated Total Reflectance (ATR) and X-ray photoelectron spectroscopy (XPS). The latter enables us to determine the valence states of Sr2+, Ti4+ and O2−. A band gap of 3.32 eV was determined from the diffuse reflectance, assigned to the charge transfer O2−: 2p → Ti4+: 4s and white coloration of STO. The conduction band (−0.60 VSCE) and the valence band (2.72 VSCE) derived respectively from O2−: 2p and Ti4+: 4s orbitals are within the gap region of STO, thus generating O2·− and ·OH radicals responsible for the photo oxidation of Congo Red (CR), a hazardous dye. The photo-catalytic efficiency of STO was confirmed by the CR adsorption and degradation under solar light. Various physical parameters like the catalyst dose, dye concentration, initial pH, irradiation source and inhibitory effect of anions were studied. The synergetic effect of the electron injection from Congo Red into the STO-conduction band was confirmed by the electrochemical measurements through the photocurrent-potential plots and contribute to the photoactivity. An abatement of 62% and 97% are obtained under UV light and solar irradiation respectively.