Endogenous Mn/Fe biochar derived from algae-rich floc sludge for enhanced peroxymonosulfate activation: Improved surface collision oxidation and role of synergic path

Flocs sludge disposal and resource recycling are now global issues. In this study, a novel biochar activator (FeMn-NBCK) with multi-active sites and more persistent free radicals (PFRs) was synthesized using algae-rich floc sludge as a raw material. FeMn-NBCK possessed an efficient activation for peroxymonosulfate (PMS) to achieve rapid degradation for pollutants. Results showed that the removal rate of 10 mg/L BPA reached 100 % within 20 min by the FeMn-NBCK/PMS system with the reaction rate constant K_obs was 0.1309 min⁻¹. The captured and adsorption PMS on FeMn-NBCK surface to form surface-activated PMS with high potential, collided with surrounding organic pollutants and directly grabbed electron from them to complete pollutant oxidation, making the biochar proposed more effective activation performance through more reactive oxygen species (ROSs), active sites and enhanced electron transfer. And the endogenous Fe/Mn from enhanced coagulation and the rich N/C elements contained in algae made the FeMn-NBCK improved surface collision oxidation path during PMS activation process. Fe/Mn reduced the energy barrier of O-O bond cleaving of PMS, and the presence of Mn provided more electrons, enhanced the electron transport and PMS adsorption at the –CO-Mn sites, making to produce more ROSs. The formation of more persistent free radicals (PFRs) not only acted as active sites, but also facilitated the cleavage of O-O bonds and promoted the formation of free radicals. Furthermore, FeMn-NBCK exhibited good reusability and applicability in water purification. This work would make significant contributions to the utilization of solid waste and the development of biochar in the future.