Electro-activating persulfate via biochar catalytic cathode for sulfamethazine degradation: Performance and mechanism insight

This work prepared biochar particle electrodes (BCPE) from excess sludge and biochar catalytic cathodes (BCCC) synthesized by modifying nickel foam electrodes with BCPE. Then, both of them were constructed as electro-catalytic systems for activating persulfate (PS) to degrade sulfamethazine (SMZ). BCPE demonstrated remarkable electrocatalytic PS performance, in which oxygen-containing functional groups and Fe3O4 are the main active sites. The quenching experiment and electron paramagnetic resonance (EPR) results indicate that free hydroxyl radicals, sulfate radicals and superoxide radicals are generated in solution of the particle electrode system. On the contrary, most of the above radicals generated by BCCC exist on the electrode surface, and the direct electron transfer from the power source to BCCC effectively improves the mass transfer rate and catalytic performance, thus leading to the complete degradation of 50 mg/L SMZ within 60 min. Fe2+/Fe3+ released by BCCC was below the ambient concentration, which constituted a stable cycle in the electrocatalytic system and efficiently acti-vated PS. The calculation results of density functional theory and oxygen reduction reactions verified the mechanism of activation. Electrostatic surface potential distribution calculation showed that Fe and C were the main active site. In silico toxicity assessment by ADMETlab2.0 found a significant decrease in overall toxicity of SMZ degradation products.