Bi modified oxidized tubular carbon nitride with high-yield singlet oxygen for propylparaben degradation: Implication for a novel oxygen activation mechanism

The separation of electron-hole was the challenge in photocatalytic oxidation technology. In this study, Bi-OxTCN photocatalyst was prepared by introducing oxygen-containing functional groups and Bi metal into tubular g-C₃N₄ (TCN) to explore energy transfer mediated oxygen activation mechanism. Compared with TCN, the apparent rate constant of propylparaben (PrP) degradation on 0.8-Bi-OxTCN improved approximately 5.9 times. The installed Bi metal and oxygen-containing functional groups could improve spin-orbit coupling and narrow energy barrier between singlet and triplet state (decreasing from 0.310 eV to 0.168 eV), resulting in selective generation of high-yield singlet oxygen (¹O₂). The ¹O₂ yield in 0.8-Bi-OxTCN was increased by 18 times in comparison with TCN. According to the density function theory calculations, the ¹O₂ mainly attacked the benzene ring, hydroxyl and carboxyl group of PrP to form p-hydroxybenzoic acid, phenols, and benzoquinones. In summary, the study provides a novel oxygen activation pathway for photocatalytic oxidation technology in water treatment.