Upcycling waste sericin into Fe₃O₄-anchored N-doped biochar for efficient peroxymonosulfate activation toward azo dye...

Developing sustainable catalysts from waste biomass for advanced oxidation processes is highly desirable for wastewater treatment. Herein, a waste-to-resource strategy was proposed to upcycle silk-industry waste sericin into Fe₃O₄-anchored N-doped porous biochar Fenton-like catalysts (Fe-NC) for peroxymonosulfate (PMS) activation. Distinct from conventional biomass-derived Fe/carbon catalysts that often require external nitrogen dopants or post-loading of metal species, sericin served simultaneously as a carbon source, intrinsic nitrogen precursor, and Fe³⁺-binding biopolymer, enabling the coordination-assisted formation of Fe₃O₄/N-doped carbon interfacial active sites after controlled pyrolysis. The optimized 0.1Fe-NC possessed a high specific surface area of 477.9 m² g^-1 and uniformly dispersed Fe₃O₄ nanoparticles, enabling rapid removal of Acid Orange 7 (AO-7) over a wide pH range of 4-11. Nearly complete degradation of AO-7 (99.3%) was achieved within 30 min, with a pseudo-first-order rate constant (k_obs) of 0.266 min^-1. Mechanistic investigations revealed that multiple reactive oxygen species, including Fe(IV)=O, SO₄-, OH, and ¹O₂, jointly contributed to pollutant degradation. In addition, the catalyst exhibited excellent magnetic recoverability and stability, maintaining 89.7% removal efficiency after five cycles. Continuous-flow experiments further demonstrated stable performance (>98% removal for 720 min), highlighting its practical applicability. This work provides a sustainable strategy for converting protein-rich sericin waste into efficient Fe-based biochar catalysts and offers insights into designing biomass-derived PMS activation systems with integrated heteroatom doping, metal anchoring, and interfacial electron-transfer regulation.