Rapid electron transfer-promoted tetracycline hydrochloride degradation: Enhanced activity in visible light-coupled peroxymonosulfate with PdO/g-C3N4/kaolinite catalyst

In this work, a novel highly dispersed PdO/g-C3N4/kaolinite (P/CNK) composite was synthesized to activate peroxymonosulfate (PMS) under visible light for tetracycline hydrochloride (TCH) degradation. The 4 %P/CNK catalyst showed the best catalytic ability for TCH degradation within 20 min (94.5 %) over the vis/PMS system. The favorable specific surface area and pore volume of CNK allowed for the high dispersion of PdO and the adsorption of PMS, while PdO anchoring on CNK endowed the catalyst with channels and acceptors that could accommodate a large number of electrons to achieve rapid transfer between electrons. Furthermore, kaolinite is inexpensive, and the plentiful hydroxyl groups on the kaolinite surface can accelerate the self-decomposition of PMS. The 4 %P/CNK system also showed excellent degradation efficiency under different pH conditions and maintained its catalytic activity (87.1 %) after five cycles. The intermediates produced during the degradation of TCH and the corresponding differences in aquatic toxicity were identified. The results of electron paramagnetic resonance and reactive oxygen species quenching experiments showed that 1O2 was the key reaction species, while O2− and h+ were secondary species during the degradation process. In addition to TCH, 4 %P/CNK also had good degradation and mineralization effects on sulfamethoxazole, chlortetracycline, and carbamazepine. This work provides a deep foresight into the efficient degradation of antibiotic pollutants by kaolinite-based catalytic materials in a photocatalytic coupled PMS system.