Cyclodextrin-supported sulfide zero-valent iron as PMS activator for simultaneous removing norfloxacin and ARGs in reclaimed water: Activation and controlled release of active components

Abstract

Rapid passivation of nZVI limits its sustained activation of peroxymonosulfate (PMS), hindering its application in environmental pollutant degradation. In this study, a core–shell structured cyclodextrin-loaded sulfur-modified nano-zero-valent iron (S-nZVI@CD) was synthesized, exhibiting high efficiency and durability in activating PMS for the simultaneous degradation of norfloxacin (NOR) and antibiotic resistance genes (ARGs). Sulfur enhanced PMS activation by promoting ferrous ion recycling, while cyclodextrin (CD) improved sulfur dispersion and prevented rapid depletion of active substances, creating an efficient reaction environment. Kinetic studies showed that the S-nZVI@CD/PMS system degraded NOR (k_obs = 0.0313 min⁻¹) and DNA (k_obs = 0.224 min⁻¹) according to pseudo-first-order kinetics, while the nZVI/PMS and S-nZVI/PMS systems were more inclined to exhibit two-stage kinetics. Air exposure tests showed after 60 days of exposure to air, S-nZVI@CD still maintained efficient degradation of NOR (99.5 %) and DNA (99.2 %). Additionally, S-nZVI@CD demonstrated stable PMS activation performance in actual reclaimed water, achieving 100 % removal of NOR, 97.4 % of total ARGs, and 98.2 % of class 1 integron (IntI1). Quenching experiments, quantitative analysis, and EPR tests confirmed that sulfate radicals (SO₄^•−) and hydroxyl radicals (•OH) were the main active species in the S-nZVI@CD/PMS system. Theoretical calculations identified susceptible sites on NOR (quinolone ring) and DNA (C10, C16, N17, and N18) for radical attack, which was the main mechanism behind their effective degradation. This CD modification method utilizing an amphiphilic cavity structure provides a strategy for sustained PMS activation and enhanced contaminant removal.