Correlation between photocatalytic efficacy and electronic band structure in hydrothermally grown TiO₂ nanoparticles

The effects of electronic band structure, electron-hole recombination, and photocatalytic property of N- and/or Fe-doped TiO₂ were systematically explored. Hydrothermal reaction was used to incorporate N and/or Fe into TiO₂ nanoparticles. Structural analysis using Raman spectra, X-ray diffraction, and transmission electron microscope (TEM) indicates that hydrothermally grown TiO₂ particles have anatase phase, and their average size is ∼10 nm. In addition, hydrothermal doping of N and/or Fe was found to significantly modify the electronic band structure. The photocatalytic performance of undoped and doped nanomaterials was examined under UV or visible light. N doping increased the photocatalytic efficacy of TiO₂ under visible light by more than 2 times. In contrast, Fe-doped and N/Fe-codoped TiO₂ show worse photocatalytic performance than pure TiO₂ under both UV and visible light, in spite of their smaller band gaps. Fluorescence of terephthalic acid indicates that a change in the photocatalytic performance of doped TiO₂ is closely related to the amount of photoinduced radical ions. X-ray photoelectron spectroscopy and low-temperature photoluminescence were employed to study the doping mechanism. While both N and Fe facilitate the absorption of the visible light, it is found that only Fe increases the electron-hole recombination rate, leading to the opposite effects of N and Fe doping on the photocatalytic performance of TiO₂.