Efficient degradation of sulfonamides by high-valence cobalt-oxo species in Co(OH)2@chitosan activated peracetic acid advanced oxidation system

The generation of high-valent cobalt-oxo species Co(IV)=O for the removal of organic pollutants has been challenging due to the low conversion efficiency of Co(III)/Co(II) and the high activation energy barrier of Co(II)-oxidant complexes. Here, we introduced oxygen vacancies into the material by incorporating Co(OH) 2 with chitosan to achieve a nano-complex Co(OH) 2 @CS, which was applied in the activation of peracetic acid (PAA) as oxygen vacancies could optimize the Co 3d orbital, improve the electron distribution in Co(OH) 2 , and accelerate activation of PAA. The reactive species were characterized by reactive oxygen species quenching, phenylmethylsulfoxide probing, and electron paramagnetic resonance (EPR), and the results confirmed that the Co(IV)=O was the predominant substance for the degradation process. After a systematical investigation of the reaction conditions, complete degradation of 4 typical SAs (10 mg/L) was achieved in 8 min. In addition, the system showed remarkable resistance towards inorganic (Cl - , H 2 PO 4 - and NO 3 - ) and organic compounds (humic acid) in real water (pond water and seawater). The degradation products/intermediates from sulfamethoxazole (SMX) were identified using liquid chromatography-high resolution tandem mass spectrometry, and the toxicity of these products was investigated by computational toxicology. It was found that the toxicity of most products was lower than their precursor SMX in terms of acute (all) and chronic toxicity (6 out of 7), indicating that this Co(OH) 2 @CS/PAA system was an environment-friendly approach for the treatment of SAs-containing wastewater.