Photoredox coupling of carbon dioxide reduction with tetracycline oxidation using excited-state bismuth and cobalt dual sites over cobalt-tailored bismuth oxychloride.

Photocatalytic carbon dioxide (CO) conversion and simultaneous pollutant oxidation in a single system are promising approaches to mitigate energy and environmental challenges. However, the limited availability of active photocatalyst sites led to slow reaction kinetics and poor selectivity. Current research has predominantly focused on ground-state reactive sites of semiconductors, with less emphasis on active sites in their excited states. Therefore, gaining insights into the active sites in the excited state of semiconductors could provide a significant breakthrough in understanding the photocatalytic reaction mechanism. In this study, cobalt-doped bismuth oxychloride nanosheets containing abundant oxygen vacancies (OVs) were used as a model to investigate the active sites in excited states. These nanosheets were used to integrate CO reduction with tetracycline (TC) oxidation. Combining theoretical calculations with in situ characterizations revealed that under excited-state conditions photogenerated electrons transfer from cobalt (Co) dopants to OVs and subsequently to bismuth (Bi) atoms, forming Bi sites enriched with excited electrons. These excited-electron-rich Bi sites and electron-deficient Co sites contribute to CO reduction and TC oxidation, respectively. This study provides a comprehensive understanding of active sites in the excited state in doped semiconductors at the atomic level, reinforcing their potential for synergistic CO reduction and pollutant degradation.