Enhanced degradation of clothianidin in peroxymonosulfate/catalyst system via core-shell FeMn @ N-C and phosphate surrounding

FeMn bimetallic nanoparticles coated with nitrogen-doped graphene shells (FeMn@N-C) were prepared to decompose clothianidin (CTD) through activation of peroxymonosulfate (PMS). The redox cycles of encapsulated FeMn bimetallic nanoparticles with multiple valence states could accelerate the radical generation and ensure the stability of FeMn@N-C with continuous PMS activation. Coexisting NaH2PO4 could unusually accelerate CTD degradation through facilitating reactive oxygen species (ROS) generation and decreasing bonding dissociation energies of CTD molecule. DFT calculation indicated that the C-Cl bond in CTD molecule was weakened after being surrounded by NaH2PO4. Two main degradation pathways were proposed in the absence of phosphate and a new dechlorination pathway was first reported after CTD molecule bonding with phosphate, which was confirmed by DFT. This work provides a feasible strategy of PMS activation by graphene coated bimetallic nanoparticles and give a new insight into accelerated degradation of recalcitrant pollutants with phosphate surrounding.