A novel N/C co-modified FeS2 nanocomposite synthesized by wet-mechanochemical method for efficient peroxymonosulfate activation and nearly 100% SO4●─ selective generation

Abstract

Sulfate radical (SO₄^●─) is a strong reactive oxygen species for efficiently oxidizing refractory organics. Nevertheless, its effective and selective generation in peroxymonosulfate (PMS) system maintain a great challenge. Herein, a novel N/C co-modified FeS₂ nanocomposite (FeS₂-20@N(C)) with high activity, selectivity, and stability was prepared through a simple wet-mechanochemical method. The FeS₂-20@N(C)/PMS system exhibited nearly 100 % SO₄^●─ selective generation with faster PMS utilization rate, and achieved 100 % sulfadiazine (SDZ) removal within 6 min with a k_obs (0.931 min⁻¹) approaching 2 times that of pristine FeS₂. The multiple active sites (S^2─, S_n^2─, C=O, N components, Fe₃N and Fe-C bonds) as electron donors/shuttles expedited Fe²⁺/Fe³⁺ redox-cycle for performance improvement. The experimental results and DFT calculation demonstrated that the newly formed CN (different N components, especially pyrrole N) could not only availably enhance the PMS adsorption and exogenous electron transfer to PMS, but also offer endogenous electrons for PMS to generate SO₄^●─. Furthermore, the abundant iron species including Fe(II)-S, Fe₃N and fast Fe²⁺/Fe³⁺ redox-cycle all contributed to the efficient PMS activation and SO₄^●─ generation. This work highlighted the essential role of CN species in efficient and selective generation of SO₄^●─, and provided a new way for the rational regulation of efficient ROS production with selectivity in FeS₂-based system.