Enhanced visible-light photocatalytic activity of carbonate-doped anatase TiO2 based on the electron-withdrawing bidentate carboxylate linkage

Carbonate-doped anatase TiO2 photocatalysts were prepared by a conventional sol-gel method and subsequent xerogel carbonization process in hypoxic atmosphere. Acetic acid was used as the hydrolysis inhibitors of titanium butoxide (TBOT) and the carbon source was the organic species produced during the synthesis of TiO2 particles. Via a low-temperature (≤300 °C) carbonization process, the carboxylate ligands from the chelated acetic acid molecules can be retained and transformed into the bidentate carboxylate linkage between the amorphous carbonate dopants and TiO2 lattice. The strong electron-withdrawing bidentate carboxylate ligands can induce valence band (VB) tail states to narrow the bandgap of TiO2, as confirmed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. Moreover, the carbonate dopants can serve as photosensitizer to absorb visible-light and help to promote the charge carriers’ separation through cooperation with bulk/surface defects of TiO2. The synergistic effects can significantly enhance the visible-light photocatalytic activities of TiO2 for phenol degradation (λ ≥ 420 nm). The band structure and possible photocatalytic mechanism of the carbonate-doped TiO2 were thus elucidated.