The Degradation Of Synthetic Organic Contaminants In Water By Peracetic Acid Activated With Cobalt Based Catalysts

With the progress of detection technology,researchers have realized that amounts of synthetic organic compounds（SOCs）,such as drugs,endocrine disruptors and dyes,can be emitted into natural environment via the discharge of domestic wastewater,industrial sewage or agricultural runoff,endangering the ecological environment and human health.However,the existing sewage treatments in China are usually designed only for traditional nutrient pollutants and can hardly remove SOCs.Therefore,the development of efficient,economical,environmentally-friendly SOCs treatment technologies should be accelerated.Peracetic acid（PAA）is an efficient,green and economical disinfectant.PAA has been included in the list of commonly used disinfectants for COVID-19 by the Ministry of Ecology and Environment of the People’s Republic of China.Except the successful applications of PAA in the field of disinfection,PAA-based advanced oxidation technologies（AOPs）have received increasing attention.In this paper,a varity of SOCs are selected as the target contaminants and the degradation efficiency of those SOCs in zero-valent cobalt（ZVCo）,cobalt ferrite（Co Fe₂O₄）,bimetal metal-organic framework material（MIL-100（Fe-Co））or magnetic bimetal metal-organic frame material（MIL-100（Fe-Co）@Fe₃O₄）active PAA system was investigated.（1）The removal of several selected SOCs by ZVCo/PAA was invstigated.Sulfamethoxazole（SMX）was selected as a representative SOCs,and the mechanism of PAA activation and SOCs removal in ZVCo/PAA system was explored.The results showed that ZVCo could activate PAA to produce reactive species for SOCs degradation,and the ZVCo/PAA system exhibited a selectivity for different contaminants.According to the characterization results of ZVCo before and after reaction by scanning electron microscopy（SEM）,ZVCo was corroded to provide Co²⁺which was primarily responsible for the activation of PAA.The results of adical scavenging experiments and electron paramagnetic resonance test（EPR）indicated that organic radicals（i.e.,CH₃C（O）O^·and CH₃C（O）OO^·）were the dominant reactive species for SMX degradation in ZVCo/PAA system.SMX could be degraded well in a wide p H range（p H 3–p H 7）especially at near-neutral p H.Increasing PAA or ZVCo dosage could enhance SMX removal,while excess ZVCo inhibited its degradation.ZVCo still presented an excellent activation ability for PAA to degrade SMX after 4 cycles,indicating its good stability and reusability.The probable reaction sites in SMX molecular structure were predicted by density functional theory（DFT）calculation and wave function analysis.Combining the results of DFT calculation and five identified transformation products,four possible degradation pathways of SMX in ZVCo/PAA system were proposed,including oxidation of amino,cleavage of S-N bond,coupling reaction and hydroxylation.（2）In order to avoid the secondary pollution of leached Co²⁺,Co Fe₂O₄was prepared in this study by sol-gel method.The degradation of SOCs by Co Fe₂O₄/PAA was investigated systematicly.And rhodamine B（Rh B）was selected as a representative SOCs and the mechanism of PAA activation and SOCs removal in Co Fe₂O₄/PAA system was explored.The results showed that Co Fe₂O₄could activate PAA to produce reactive species for SOCs degradation,and the Co Fe₂O₄/PAA system exhibited a selectivity for different SOCs.Radical scavenging experiments indicated that organic radicals（i.e.,CH₃COO^·and CH₃COOO^·）were also the dominant reactive species for Rh B degradation.The X-ray photoelectron spectroscopy（XPS）analysis for the fresh and used catalysts and the inductively coupled plasma mass spectrometry（ICP-MS）analysis suggested that the catalytic reaction mainly occurred on the surface of the catalyst,and Co Fe₂O₄could reduce the leaching of Co²⁺efficiently.Increasing PAA dosage and Co Fe₂O₄dosage could enhance the removal of Rh B,while excess Co Fe₂O₄dosage inhibited its degradation probably due to the clumping effect of magnetic nanoparticles.Four degradation products of Rh B by Co Fe₂O₄/PAA were identified and two degradation pathways of Rh B were subsequently proposed,including bond cleavage and hydroxylation.Co Fe₂O₄exhibited an excellent stability and reusability after four cycles.（3）Meatal organic frameworks（MOFs）,a new class of porous crystalline materials usually possess amounts of transition metal ion constituents.MIL-100（Fe-Co）was synthesized via a solvothermal method,and its performance on SOCs removal in PAA-based AOPs was evaluated.Sulfamethoxazole（SMX）was selected as a representative SOCs,and the mechanism of PAA activation and SOCs removal in MIL-100（Fe-Co）/PAA system was investigated.The results showed that MIL-100（Fe-Co）could activate PAA to produce reactive species for SOCs degradation,and the MIL-100（Fe-Co）//PAA system exhibited a selectivity for different SOCs.Organic radicals（i.e.,CH₃C（O）O^·and CH₃C（O）OO^·）were proved to be the dominant reactive species for SMX removal in MIL-100（Fe-Co）/PAA system through radical scavenging experiments.XPS and ICP-MS analysis suggested that the catalytic reaction mainly occurred on the surface of MIL-100（Fe-Co）.Increasing PAA concentration could enhance SMX removal,while the variation of MIL-100（Fe-Co）dosage had negligible effect on SMX degradation.MIL-100（Fe-Co）maintained an excellent activation ability for PAA to remove SMX after 3cycles,indicating its good stability and reusability.Based on identified transformation products and density functional theory（DFT）calculation,four possible SMX transformation pathways were proposed,including oxidation of amino,cleavage of S-N bond,coupling reaction and hydroxylation.（4）In order to improve the recoverability of MIL-100（Fe-Co）,MIL-100（Fe-Co）was synthesised on the mercaptoacetic acid（MAA）-functionalized Fe₃O₄to prepare a magnetic recyclable MIL-100（Fe-Co）@Fe₃O₄,and its cabality of PAA activation for SOCs degradation was investigated in this study.Sulfamethoxazole（SMX）was selected as a representative SOCs,and the mechanism of PAA activation for SOCs removal in MIL-100（Fe-Co）@Fe₃O₄/PAA system was studied.The results showed that MIL-100（Fe-Co）@Fe₃O₄could activate PAA to produce reactive species for SOCs degradation,and the MIL-100（Fe-Co）@Fe₃O₄//PAA system also exhibited a selectivity for different SOCs.Organic radicals（i.e.,CH₃C（O）O^·and CH₃C（O）OO^·）were also proved to be the dominant reactive species for SMX removal in this system.XPS and ICP-MS analysis suggested that the catalytic reaction mainly occurred on the surface of MIL-100（Fe-Co）@Fe₃O₄.Increasing PAA concentration and MIL-100（Fe-Co）@Fe₃O₄dosage in a certain range could enhance SMX removal.MIL-100（Fe-Co）@Fe₃O₄maintained an excellent activation ability for PAA to remove SMX after 4 cycles,indicating its good stability and reusability.