Novel CoFe2Px derived from CoFe2O4 for efficient peroxymonosulfate activation: Switching the reaction route and suppressing metal leaching

In this study, bimetallic phosphides were reported to be novel, efficient, and stable activators of peroxymonosulfate (PMS). CoFe2Px was synthesized by phosphorization of CoFe2O4 and applied in PMS activation for sulphachloropyridazine sodium (SCP) degradation. The SCP removal reached up to 94.2% in 30 min, with a reaction rate of 0.090 min−1. Particularly, CoFe2Px exhibited much lower cobalt ion leaching (0.082 mg L−1) than the reported cobalt-containing catalysts, due to the more intimate Co-Fe interaction and the surrounding of metals by phosphorus. Different from the free radical pathway in CoFe2O4/PMS system, a radical-nonradical coupling process was detected in CoFe2Px/PMS system, which was confirmed by quenching tests, electron paramagnetic resonance (EPR) measurements, and transformation intermediate analyses. Moreover, CoFe2Px demonstrates favorable durability for PMS activation and potential practicability for realistic wastewater treatment. This work provides new insights for rational design and mechanism exploration of transition-metal phosphides (TMPs) in the environmental catalysis field.