Semiconducting and photoelectrochemical properties of the ilmenite CoTiO3 prepared by wet method and its application for O2 evolution under visible light

The ilmenite CoTiO3 was synthesized by chemical route, and the decomposition of nitrates was followed by thermal analysis (TG/DTA). The intermediate products and single-phase were identified by X-ray diffraction (XRD). CoTiO3 was characterized by the Fourier transform infrared (FTIR) spectrum. The BET measurements indicated a small specific surface area (~ 2 m2 g−1). The microstructure, visualized by scanning electron microscopy (SEM), showed medium grains (200–300 nm diameter), and the crystallite size (~ 10 nm) was evaluated from the broadening of XRD peaks. The UV–Vis diffuse reflectance spectroscopy gave a direct optical transition at 1.88 eV, due to the crystal field splitting of Co3+ octahedrally coordinated. The electrical properties of CoTiO3 are characteristics of a semiconducting behavior with activation energy of 0.02 eV. The electrochemical characterization was undertaken to build the energy diagram of CoTiO3 which predicted the photocatalytic performance for the O2-evolution (~ 205 mmol h−1) upon visible light (27 mW cm−2). Indeed, the valence band (1.67 VREH) is more anodic than the O2 level, yielding spontaneous O2 evolution.