A biochar-based catalyst prepared by potassium ferrate oxidation coupled high-temperature pyrolysis and its application for the activation of peroxymonosulfate towards the degradation of norfloxacin: Performance and mechanism insight

Developing an efficient catalyst for persulfate activation is critical to the high-efficiency degradation of organic pollutants in an aqueous solution using a persulfate-based advanced oxidation method. A biochar-based catalyst, 800Fe2BC2, was prepared using a novel technology of potassium ferrate oxidation coupled with high-temperature pyrolysis based on the biomass raw material of waste branches pruned from apple trees in an orchard. Batch tests were conducted to degrade norfloxacin using 800Fe2BC2 to activate peroxymonosulfate (PMS). Norfloxacin was almost completely degraded within 10 min. The reactive oxygen species (ROS), for instance, •OH, SO4•−, O2•−and 1O2, were generated in the 800Fe2BC2/PMS system. The iron oxides, defective structures, and CO groups in 800Fe2BC2 served as catalytic sites for generating free radicals. However, the recombination of superoxide radicals, the interaction of CO groups on the catalyst surface with PMS, and the self-decomposition of PMS contributed to generating 1O2. The quenching test showed that the degree of the contribution of •OH, SO4•−, O2•−and 1O2 to NOR degradation was approximately 1O2 > O2•− > SO4•− > •OH, respectively. We proposed three potential NOR degradation pathways: piperazine ring opening (P), quinolone ring oxidation (Q), and benzene ring defluorination (F). Then part of these intermediates was completely mineralized into inorganics like CO2, H2O, NO3− and F−. The acute and chronic toxicity of the degradation products were estimated, and the evolution of toxicity in the present catalytic system could not be ignored and should be overcome by deeper mineralization. The prepared 800Fe2BC2 demonstrated a good application prospect with good stability, recyclability, low metal leaching, and versatility to various refractory pollutants. Therefore, this study offered a new way of producing biochar-based catalysts for activating PMS using biomass wastes.