Net-zero strategies through valorization of nylon-6 and steel slag: production of syngas and an environmental catalyst for bisphenol A remediation

Abstract

The rapid growth of the global population and industrial activities has resulted in the excessive generation of plastic and industrial waste, posing serious environmental challenges due to their limited compatibility with conventional waste management practices. This study proposes a novel thermochemical co-pyrolysis strategy for nylon-6 and steel slag to simultaneously produce syngas and a char composite capable of removing bisphenol A (BPA) from aqueous solution. Incorporation of steel slag into nylon-6 pyrolysis markedly enhanced syngas generation owing to the catalytic activity of Fe species present in the slag. The resulting char comprised a carbon composite embedded with Fe mineral phases of low oxidation states, as revealed by X-ray diffraction and X-ray photoelectron spectroscopy analyses. The composite achieved ≥99% BPA removal within 10 min under optimized reaction conditions by effectively activating persulfate through surface iron active sites, while the graphitic carbon nitride layer functions as an electron shuttle to facilitate pollutant oxidation. In this synergistic process, the zero-valent iron core continuously regenerates surface Fe2+ species via electron donation, thereby sustaining radical generation and enhancing structural stability. Radical quenching experiments verified the generation of SO4•−, •OH, O2•−, and 1O2 species, with SO4•− and •OH playing dominant roles in BPA degradation. Life cycle assessment demonstrated that the proposed co-pyrolysis approach reduced global warming potential by 34% compared to conventional nylon-6 pyrolysis. This work demonstrates a promising and sustainable route for transforming dual waste streams into valuable gaseous fuels and high-performance environmental catalysts, thereby advancing circular economic practices.