Nitrogen doping mediated oxygen vacancy and Ti valence regulation to enhance photocatalytic H2 generation

Abstract

The band gap width has always been the main reason for the low photocatalytic performance of TiO2 semiconductors. “Band gap engineering” is often used to change the band gap width of TiO2. On this basis, the impurity band gap was induced below the TiO2 conduction band by regulating N element. What's interesting was that N element adjusted the valence state of adjacent Ti element and caused the generation of oxygen vacancy. This is due to the extraction of neutral oxygen atoms, resulting in electron transfer to the Ti cation band structure. The 300-N-T catalyst exhibited the best photocatalytic hydrogen production performance under visible light, which was 307.65 μmol/(g·h) and was 61.53 times higher than that of anatase. And the concentration of Ti3+ defects and oxygen vacancy reduced with decreasing of N content in TiO2. According to Kubelke Munk formula, the band gap of 300-N-T photocatalyst was narrowed to 2.73 eV, which indicated that there are impurity energy levels near the CB and VB of TiO2 material. The Ti3+ ions as the active site of the photocatalytic reaction was confirmed by instantaneous photocurrent response and EIS characteristic. This study revealed the structure-activity relationship between the content of N element, Ti3+ ions and oxygen vacancy in TiO2 materials, as well as the decisive process of defect induced visible light catalysis.