Enhanced persulfate activation by ethylene glycol-mediated bimetallic sulfide for imidacloprid degradation

Abstract

CuFeS₂ is regarded as a promising catalyst for heterogeneous activation to remove organic contaminants in wastewater. However, effects of solvents in regulating material synthesis and catalytic activity are still not clear. Herein, we reported the role of water, ethanol, ethylene glycol (EG), glycerol, and polyethylene glycol 200 on the synthesis of CuFeS₂ micro-flowers and their performance in activating persulfate (PS) to remove imidacloprid (IMI) pesticide. The results showed that the solvent had an effect on the morphology, crystallinity, yields, specific surface areas and unpaired electrons of CuFeS₂ micro-flowers. The degradation experiments revealed the efficient catalytic activity of EG-mediated CuFeS₂ for heterogeneous PS activation. SO₄^•- and •OH were identified in EG-CuFeS₂/PS system and •OH (90.4%) was the dominant reactive species. Meanwhile, stable 20% of η[PMSO₂] (the molar ratio of PMSO₂ generation to PMSO consumption) was achieved and demonstrated that Fe(IV) was also involved in the degradation process. Moreover, S^2- promoted the cycling of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺, enhancing the synergistic activation and reusability of the catalyst. Density functional theory (DFT) calculations verified that PS was adsorbed by Fe atom and electron transfer occurred on the catalyst surface. Three possible degradation pathways of IMI were proposed by analysis of the degradation intermediates and their toxicities were evaluated by ECOSAR. This study not only provides a theoretical foundation for catalyst design, but also promotes the industrial application of bimetallic sulfide Fenton-like catalysts for water management.

Keywords: Activation mechanism; EG-CuFeS(2); Fe(IV); Persulfate; Pesticides; Theoretical calculation.