Roles of photo-generated holes and oxygen vacancies in enhancing photocatalytic performance over CeO₂ prepared by molten salt method

A series of CeO₂ photocatalysts were synthesized through the molten salt method. The photocatalytic activity was evaluated through the degradation of methyl orange (MO). Systematic characterizations including X-ray diffraction, Scanning electron microscopy, Fourier transformed infrared, X-ray photoelectron spectroscopy, Raman spectroscopy, electron spin-resonance spectroscopy, UV–vis diffuse reflectance spectroscopy, photoluminescence spectrometry, photocurrent response and electrochemical impedance spectroscopy were conducted to study the as-prepared CeO₂ samples. It was found that, under ultraviolet light irradiation, the apparent rate constants of CeO₂ prepared at 800 °C for degradation of MO was about 3.4 times higher than CeO₂ prepared at 500 °C. CeO₂ prepared at 800 °C held the higher oxygen vacancies concentration. According to the trapping experiments, it was demonstrated that photo-generated holes played a dominant role in this photocatalytic system. Furthermore, the possible photocatalytic mechanism which showed the roles of photo-generated holes and oxygen vacancies was proposed.