Research On The Degradation Of Azo Dyes By Cobalt Activated Peracetic Acid

Peracetic acid?PAA?is widely used as a conventional disinfectant forits excellent sterilization and non-toxic properties.In the past three decades,with the gradual application of PAA in water treatment,it has been found that PAA can be used as an oxidant to remove pollutants.However,the research on the activation and its mechanism of PAA is still not enough.The transition metal cobalt has excellent activation properties for inorganic peroxides such as persulfate?PMS?.Even atrace amount of cobalt can rapidly activate the peroxy linkage of PMS to produce highly active sulfate radicals?SO₄^-??.In this study,the transition metal cobalt was used to activate PAA to degrade the azo dyes.As well the homogeneous and heterogeneous systems were used to activate PAA.Based on these studies,the activation effect of transition metal cobalt on the peroxygen bond of the organic peroxide PAA has been confirmed.Furthermore,the type of free radicals and the related influencing factors have been clarifiedThe main work and conclusions of this study are as following:?1?In the homogeneous system,the degradation of acid orange?AO7?was studied by Co²⁺activated PAA.The oxidation performance of Co²⁺/PAA was evaluated and the related effects on dye degradation were investigated.The results showed that Co²⁺/PAA system could effectively decolorize organic dyes,and its oxidation capacity was comparable to that of Co²⁺/PMS system and was superior to that of Fenton system.Decolorization of AO7 increased with the increase of PAA or Co²⁺concentration.The decolorization rate of AO7 could reach 92%after 60 min with 0.01mM of Co²⁺dosage and 4/1 of PAA/AO7 molar ratio.Weak acidic and neutral pHs were favourable for the decolorization of AO7.The presence of Cl^-and HA could slightly inhibite AO7decolorization.Using the quenchers,such as ascorbic acid,tert-butanol,and methanol,CH₃COO·and CH₃COOO·were speculated to be the main radicals responsible for AO7decolourization in the Co²⁺/PAA system.UV-Vis spectra analysis showed that the radicals mainly attacked the azo bond and naphthalene ring structure in AO7 molecules.?2?Based on the homogeneous system,the degradation of Orange G?OG?was researched by Co₃O₄ activated PAA in the heterogeneous system.The oxidation performance of Co₃O₄/PAA was evaluated,as well as the related effects on dye degradation and the stability of the catalyst were investigated.The results showed that decolorization efficiency of OG increased with the increase of PAA concentration and Co₃O₄ dosage.Near neutral pHs were favourable for the decolourization of OG,and the presence of anions?such as Cl^-and HCO₃^-?could inhibited OG decolourization,implying the possibility of applying Co3O4/PAA process under environmental realistic conditions.Results of the quenching tests,electron paramagnetic resonance?EPR?experiments,and X-Ray photoelectron spectroscopy?XPS?analysis revealed that CH3C?=O?O·and CH3C?=O?OO·also played a critical role in the degradation process.The conversion of?Co²⁺-?Co³⁺,the changes in the content of lattice oxygen and adsorbed oxygen also were involved in this process.The analysis of scanning electron microscope?SEM?and X-ray diffraction?XRD?showed that Co3O4 had good catalytic performance,excellent reusability and long-term stability.No changes in Co3O4 before and after the reaction were observed,either in terms of morphology or structural properties.The maximum leaching amount of cobalt ions was determined by ICP-MS to be 0.105 mg/L,which was lower than the standard?1.0 mg/L?.Trivalent cobalt was the predominant form of cobalt in the filtrate and had little effect on PAA during OG degradation.Additionally,the Co3O4-PAA system also had distinguished oxidative degradation of other contaminants?such as the other 12 contaminants selected in this work?.This study represented that transition metal cobalt and its oxides could efficiently activate PAA to generate organic free radicals,which could effectively decolor organic dyes and selectively degrade other organic pollutants under mild conditions.The research results enriched the advanced oxidation process of PAA and its related mechanisms.Therefore,new technologies and necessary scientific evidence were provided in the area of environmental pollution control and water treatment research.