β-Cyclodextrin-modified NiCo2S4 promotes peroxymonosulfate activation by regulating interfacial electron transfer for efficient ofloxacin degradation: Mechanism, degradation pathways, and toxicity assessment

Abstract

Interface modification strategies are of great significance in heterogeneous catalysis for the efficient removal of refractory organic pollutants, though numerous challenges remain. In this study, β-cyclodextrin (β-CD)-modified NiCo₂S₄ composite catalysts (NCS@CD) were synthesized via a hydrothermal method. For the first time, β-CD was introduced into the NiCo₂S₄ bimetallic sulfide to regulate interfacial electron transfer and enhance the activation efficiency of peroxymonosulfate (PMS), thereby achieving efficient removal of ofloxacin (OFX). Under optimal conditions, the NCS@CD/PMS system achieved an OFX removal rate of 86.23% within 10 min, significantly higher than of NiCo₂S₄/PMS (78.43%). Notably, β-CD introduction effectively suppressed catalyst aggregation and metal ion leaching, while increased the specific surface area of the catalyst (37.21%), thereby providing additional active sites. Moreover, EIS and CV further confirmed a markedly reduced charge transfer resistance and enhanced interfacial electron transfer efficiency upon β-CD modification, which facilitated PMS activation. Mechanistic studies revealed that the excellent catalytic performance of the system stems from accelerated interfacial electron transfer, which promotes the synergistic involvement of radical and non-radical pathways. The multivalent cycling of Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ and the synergistic effect with sulfur species significantly enhanced PMS activation. Furthermore, based on DFT and ESP calculations combined with LC-MS analysis, possible degradation pathways of OFX were proposed, and the ecotoxicity of the intermediates was systematically assessed. Overall, this study reveals an interfacial regulation strategy for β-CD-modified bimetallic sulfides, offering a novel approach for constructing highly efficient, stable, and environmentally friendly catalytic systems to remove recalcitrant organic pollutants from wastewater.

Keywords: Interfacial electron transfer; NiCo(2)S(4); Ofloxacin; Peroxymonosulfate; β-cyclodextrin.