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, BiOxTCN 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.