Optimization of defect distribution in photodegradation of air pollutants via SiO2-shell-enhanced fluorine modification

•Bulk defects were reduced by SiO2-shell-enhanced F modification.•Surface Ti3+ were increased by SiO2-shell-enhanced F modification.•Surface doped F was increased by SiO2-shell-enhanced F modification.•F doping in lattice was inhibited by SiO2-shell-enhanced F modification.•Surface doped F acted as catalytic site whereas lattice F induced bulk defects.

The distribution of bulk and surface defects significantly affects the separation and injection of photogenerated charge carriers. In this study, we provide a strategy of SiO2-shell-enhanced F modification to optimize the distribution of bulk and surface defects. The effects of SiO2 coating and F modification on the physical structure, the separation behavior of photogenerated charge carriers, and the photocatalytic activity of P25 were studied by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and toluene degradation experiments. Results showed that the removal rate of toluene over SiO2-F-modified P25 was significantly higher than those over P25 and F modified P25. The SiO2-shell-enhanced F modification simultaneously increased the content of surface Ti3+ and reduced the bulk defects, thereby enhancing the separation of charge carriers. Furthermore, F doped at surface exerted a strong catalytic effect on the removal of toluene, whereas F doped in lattice caused the recombination of photogenerated charge carriers. The SiO2 coating and calcination treatment significantly increased the amount of F ions doped at TiO2 surface and inhibited F doping in lattice.

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