Generation of singlet oxygen over CeO2/K,Na-codoped g-C3N4 for tetracycline hydrochloride degradation over a wide pH range

Singlet oxygen (1O2) species have been widely studied in catalytic oxidation and photodynamic therapy (PDT) and so on due to their unique properties, such as their long lifetime, wide pH tolerance, relative long migration distance, and high selectivity. In this work, 1O2 could be generated over CeO2/K,Na-codoped g-C3N4 heterojunction (CeO2/CN) fabricated using a molten salt method in the presence of H2O2 in dark for the first time, which was used as a Fenton-like catalyst to degrade the emerging tetracycline hydrochloride (TCH) pollutant through a Fenton-like reaction. A significantly-enhanced catalytic activity was observed over CeO2/CN compared with g-C3N4 and commercial CeO2. The Ce4+/Ce3+ redox system was found to play a vital role in the formation of 1O2 from the disproportionation of superoxide radical (·O2−). The 1O2 and ·O2− radicals were observed as the main active species in the highly-efficient degradation of TCH over a wide pH range (1.20–11.20). The strong interfacial interaction of CeO2/CN promoted the Ce4+/Ce3+ redox and the generation of active species. The catalytic mechanism of TCH decomposition was also proposed. This finding introduces an efficient and promising approach for the preparation of the highly-effective Fenton-like catalysts for water purification.