The bifunctional Lewis acid site improved reactive oxygen species production: a detailed study of surface acid site modulation of TiO₂ using ethanol and Br^-

Modulation of surface acid sites (SAS) can effectively enhance the efficiency of reactive oxygen species (ROS) production. However, the role of SAS has been neglected for photoreduction reactions. Here, we report a Lewis acid site (L-acid) rich TiO2 prepared using the synergistic effect of ethanol and halogen ions. The formation of L-acid improves the adsorption and mobility of O-2, which facilitates its reduction into a superoxide radical (O-2(-)). L-acid may lift the population of photogenerated electrons (e(-)), which is concluded from the presence of a CH3 signal in the DMPO-O-2(-) ESR spectrum of only L-acid rich TiO2. In addition, L-acid enhances the migration of photogenerated holes (h(+)) to the surface of the catalyst, which induces a continuous photooxidation reaction of H2O or -OH. Therefore, L-acid simultaneously enhances the photoredox ROS generation reaction, resulting in higher photocatalytic activity. This work illustrates a dual function of L-acid and provides a useful strategy for improving the photocarrier separation and surface reaction efficiency.