Generation of singlet oxygen over CeO 2 /K,Na-codoped g-C 3 N 4 for tetracycline hydrochloride degradation over a wide pH range.

Singlet oxygen ( ¹ O ₂ ) 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, ¹ O ₂ could be generated over CeO ₂ /K,Na-codoped g-C ₃ N ₄ heterojunction (CeO ₂ /CN) fabricated using a molten salt method in the presence of H ₂ O ₂ 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 CeO ₂ /CN compared with g-C ₃ N ₄ and commercial CeO ₂ . The Ce ⁴⁺ /Ce ³⁺ redox system was found to play a vital role in the formation of ¹ O ₂ from the disproportionation of superoxide radical (˙O ₂ ^- ). The ¹ O ₂ and ˙O ₂ ^- 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 CeO ₂ /CN promoted the Ce ⁴⁺ /Ce ³⁺ 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.