Synergistic activation of peroxymonosulfate by nitrogen-doped biochar loaded with mixed-valence iron nanoparticles for tetracycline degradation

Biochar prepared from waste biomass has attracted increasing attention due to its excellent performance in treating wastewaters containing organic pollutants. In this study, a nitrogen-doped corn cob-based biochar loaded with mixed-valence iron nanoparticles (FeOx@N-BC) was synthesized via a two-step pyrolysis method, and its physicochemical characteristics, catalytic capacity and mechanism for activating PMS toward tetracycline (TC) degradation were systematically studied. The results indicated that a 91.8% removal of TC (100 mg/L) could be achieved in 10 min with a 0.2 g/L dose of FeOx@N-BC. The nitrogen atoms that were introduced into the biochar framework not only inhibited the agglomeration of iron nanoparticles but also produced defects that served as bridges to accelerate electron transfer, thus enhancing the catalyst's synergetic effect toward the iron nanoparticles and efficiently promoting Fe(Ⅱ)/Fe(Ⅲ) cycling. A non-radical degradation pathway with singlet oxygen (1O2) was dominant, and radical-initiated degradation with sulfate radicals (SO4•−), superoxide radicals (O2•−) and hydroxyl radicals (•OH) was involved. Four probable degradation pathways were proposed by identifying intermediates via LC−MS. Moreover, the FeOx@N-BC composite exhibited high stability, good reusability, and a very low iron leaching rate.