Effective peroxymonosulfate activation using electrified nanohybrid filter towards one-step decontamination of roxarsone: Performance and mechanism

An electrochemical filtration technology was rationally developed toward effective one-step roxarsone (ROX) decontamination. A bifunctional electroactive nanohybrid filter of carbon nanotube (CNT) and iron(III) oxide (Fe3O4) species is the key to this technology. ROX (91.8%) was simultaneously adsorbed and oxidized by passing through a functional filter together with peroxymonosulfate (PMS) under an electric field (τ < 2 s). Several critical operational parameters of the system performance (applied voltage, PMS concentration, solution pH and aqueous competitive anions) were identified and optimized. The underlying mechanism was proposed based on the experimental evidence. Mechanistic studies have demonstrated that carbonyl group (C=O) of CNT can serve as electron donor to activate PMS to generate singlet oxygen (1O2) and Fe can provide electrons to PMS to produce hydroxyl radical (HO•) and sulfate radical (SO4•-). This suggests that both radicals and non-radical pathways contribute to the effective oxidation of ROX during the electrochemical filtration process. These reactions can transform highly toxic arsenite (As(III)) to less toxic arsenate (As(V)) by cleavage of the arsenic-carbon bond (As-C). The applied electric field facilitated the cycling of the ferric/ferrous (Fe3+/Fe2+) pairs and induced the electro-PMS activation to generate aggressive radical species. Meanwhile, the carbonyl groups of CNT provided essential active sites for the generation of 1O2. The synergistic interplays of the electrochemical reactivity, high porosity, flow-through configuration and abundant active sites for effective ROX decontamination were highlighted. The findings of this study are dedicated to providing a viable solution to remove organic arsenic and related species from water.