Synthesis of Ti3+ self-doped mesoporous TiO2 cube with enhanced visible-light photoactivity by a simple reduction method

Abstract

Through a simple reduction method, mesoporous anatase TiO2 cube was synthesized and the Ti3+ species and oxygen vacancies were successfully introduced into the anatase TiO2. CO2 and CO gases were produced by the thermal decomposition of oxalic acid and acted as a soft template to form the mesoporous structure, wherein CO acted as a reducing agent for reducing Ti4+ to Ti3+. The X-ray photoelectron spectroscopy spectra confirmed the presence of Ti3+ and oxygen vacancies in the samples. The UV–vis diffuse reflection spectra showed that the Ti3+ and oxygen vacancies shift the absorption edges of TiO2 from UV to the visible light region, which leaded to the enhanced photocatalytic activity. The charge carrier recombination rates of as-prepared samples were monitored by PL spectroscopy. The results showed that the trend was TiO2-3.70 < TiO2-1.85 < TiO2-0 < TiO2-7.41 < TiO2-11.11 (The X in the sample number TiO2-X refers to the ratio of the amount of H2C2O4 to Ti(SO4)2 (mole ratio)), implying that the charge carrier recombination rate of TiO2-3.70 was the lowest, which was responsible for enhancing the photocatalytic activity in the degradation of methylene orange under visible light irradiation. The Ti3+ and oxygen vacancies content, crystal size, specific area were strongly affected by the amount of oxalic acid. The oxalic acid content had an optimum value for the highest photocatalytic activity. It was worth noting that the sample exhibits excellent photocatalytic stability even after five recycles. This work demonstrates a new way to fabricate Ti3+ self-doped mesoporous TiO2 cube that have multiple channel structure and has potential to be used as in environmental photocatalysis.