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

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 SiO 2 -shell-enhanced F modification to optimize the distribution of bulk and surface defects. The effects of SiO 2 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 SiO 2 -F-modified P25 was significantly higher than those over P25 and F modified P25. The SiO 2 -shell-enhanced F modification simultaneously increased the content of surface Ti 3+ 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 SiO 2 coating and calcination treatment significantly increased the amount of F ions doped at TiO 2 surface and inhibited F doping in lattice.