Dual role of oxygen vacancies in TiO₂/Bi₂O₃ for enhanced carrier separation and PDS activation: A combined experimental and DFT study

A layered solvothermal method to control the distribution of oxygen vacancies (O_V) in TiO₂-O_V/Bi₂O₃ was proposed. This composite was used to degrade four typical synthetic organic chemicals, and exhibited excellent degradation efficiency and stability in the photoelectrocatalysis (PEC)/peroxydisulfate (PDS) system. To clarify the mechanism of improving the PEC efficiency of this system, the O_V inward migration energy barriers, theoretical band gap, and adsorption energy (E_ads) of PDS were simulated by density functional theory (DFT); at the same time, the types and contributions of the main oxidizing species were investigated by quenching experiments. These results indicated the presence of O_V not only reduced the bandgap and enhanced light absorption, but also formed oxygen vacancy levels that could capture electrons to suppress the recombination of photogenerated carriers. With the increase in O_V content, the positions of oxygen vacancy levels moved closer to the conduction band to avoid becoming the recombination centre. Also, O_V were beneficial to the adsorption and activation of PDS, which could promote the degradation of synthetic organic chemicals by acting as an electron acceptor. Apart from that, the inward migration behavior of O_V and the corresponding driving force were discussed. Specifically, the surface oxygen vacancies (SOV) were generated first and migrated inward into bulk oxygen vacancies (BOV) under the influence of O_V concentration gradient. This work provided an idea for designing a reasonable and simple preparation method to control the O_V distribution and improve the PEC degradation efficiency.