Unveiling the mechanism on photocatalytic singlet oxygen generation over rationally designed carbonylated carbon nitride

Singlet oxygen (¹O₂) with electrical neutrality and long lifetime exhibits great potential in environmental remediation. However, the production of ¹O₂ from O₂ is greatly limited by spin-forbidden transitions. Herein, we elaborate on carbonylated carbon nitride (Ox-CN), which exhibits excellent ability for ¹O₂ generation. Based on the characterization results and theoretical calculations, the introduced carbonyl functional group improved the spin-orbit coupling (SOC) inside polymer carbon nitride (PCN) to reduce the energy gap between singlet states (S) and triplet states (T), thus promoting the intersystem-crossing (ISC) process. As a result, the excitons inside PCN achieved a fast transition from S to T, and the generated T excitons underwent energy transfer with O₂ to produce ¹O₂. Therefore, Ox-CN presents outstanding photocatalytic performance for sulfamethoxazole degradation under different water environmental conditions, thus holding great promise for water treatment. This work provides a theoretical basis for designing a photocatalytic system to generate ¹O₂ for water environmental remediation. © 2024 The Royal Society of Chemistry.