Insights into Dynamic Dual-Defect Sites in I-Doped BiOCl for Synergistic Metronidazole Oxidation and CO₂ Reduction

To achieve high-efficiency photocatalytic CO₂ reduction coupled with antibiotic oxidation, it is crucial to design photocatalysts with dual active sites for the corresponding half-reactions. Most studies have focused on ground-state active sites but have often overlooked the dynamic active sites that emerge during the photocatalytic reaction process. Consequently, gaining a deep understanding of the mechanisms governing these dynamic active sites remains a significant challenge. Herein, I-doped BiOCl with oxygen vacancies was employed as a model photocatalyst to visualize the evolution of real active sites during the photocatalytic coupling of CO₂ reduction with the oxidation of metronidazole (MNZ). A series of in situ characterizations and theoretical calculations accurately elucidated the formation and evolution mechanisms of the dynamic active sites associated with the dual defects. Additionally, the correlation between the activity and photoexcited defect evolution revealed that the photoexcited defects serve as the true active sites that determine the photocatalytic redox activity. Detailed results demonstrated that photoinduced electrons migrate from I-substitutional defects to oxygen vacancies (OVs), leading to the activation of OVs and I-substitutional defects as reduction and oxidation sites for the photoreduction of CO₂ and photooxidation of MNZ, respectively. This study offers fresh perspectives on the characteristics of dynamic active sites, offering a deeper understanding of photocatalytic redox reactions.