Atrazine removal by peroxymonosulfate activated with magnetic CoFe alloy@N-doped graphitic carbon encapsulated in chitosan carbonized microspheres

Abstract

Magnetic CoFe alloy@N-doped graphitic carbon (CoFe@NC) encapsulated in chitosan carbonized microspheres (CoFe@NC/CCM) was synthesized, then coupled with peroxymonosulfate (PMS) for atrazine (ATZ) removal. CoFe@NC derived from Co-Fe Prussian blue analogues were embedded into CCM by the alkaline gel-carbonization process, in which CCM formed a protective layer for CoFe@NC. The morphology, crystal structure, and material composition of CoFe@NC/CCM were characterized. The effects of catalyst dosages, PMS dosages, initial pH, temperature, coexisting anions, natural organic matter (NOM), and different practical water matrices were systematically investigated. The productivity test was performed under the conditions of [PMS] = 0.4 mM, pHi = 5.9, T = 25 °C, ATZ = 30 mg/L and [CoFe@NC-600/CCM] = 4 mg/L, the stability upon reuse for 8 days was studied and the accumulated turnover number was determined to be 46.8 after an 8-day cycle. Electron paramagnetic resonance (EPR) technology and radical quenching tests revealed ·OH and SO4·- were major radicals, with contribution rates of 49.2% and 42.9%, respectively. Fe0 → ≡FeII ↔ ≡FeIII and Co0 → ≡CoII ↔ ≡CoIII redox cycles were involved in the catalytic reaction. The toxicity effect of transformation products (TPs) on activated sludge was also evaluated. Based on quantitative structure–activity relationship model prediction, the comprehensive toxicity of ATZ and TPs was analyzed and compared by the toxicity estimation software tool. Results showed that most TPs toxicity decreased or disappeared. This work proposes an environmentally friendly and easy-to-recycle heterogeneous catalyst to remove refractory organics by activating PMS.