Singlet-Oxygen-Driven CeO ₂ Quantum Dots/Hollow Spherical g-C ₃ N ₄ S-Scheme Heterojunction Photocatalyst for the Degradation of Tetracycline

Antibiotics in water have an important impact on human health, and the advanced oxidation process (AOP) is an environmentally friendly method to solve the problem of antibiotics in water. Still, research lacks the main active substances for photocatalytic degradation and their generation mechanism. In this article, cerium oxide quantum dots (CeO₂-QDs)/hollow spherical carbon nitride (CNHS) photocatalysts were synthesized to evaluate the photocatalytic activity through the degradation of tetracycline (TC). Copula CeO₂-QDs with CNHS to form S-scheme heterojunctions enhance photogenerated carrier migration and diffusion and broaden the photoresponsivity range. 5% CeO₂-QDs/CNHS had the best photocatalytic performance and reached tetracycline degradation equilibrium within 10 min. The theoretical system of degrading TC with single oxygen (¹O₂) as the main active substance was also established, and it was confirmed that the combination of •O₂^- and H₂O was the main pathway to produce ¹O₂ by this catalyst. A mechanism of TC degradation with ¹O₂ as the main active substance was proposed to provide a reference for constructing g-C₃N₄-based photocatalysts with efficient photodegradation activity.