Copper-catalyzed Reductant Degrades Organic Pollutants In Water From An Oxidation System

For the emerging organic pollutants that are difficult to be degraded,the treatment effect of traditional water treatment process is limited,and advanced oxidation technology should be introduced.Compared with the traditional Fenton advanced oxidation technology,Cu(?)catalytic reductant self-oxidation system has the advantages of low consumption of transition metals,less metal precipitations and no need to add additional strong oxidants.However,there is no systematic study on the degradation of organic pollutants catalyzed by Cu(?)in different reductant systems.In this study,common reducing agents such as sodium sulfite(Na₂SO₃),hydroxylamine(NH₂OH)and ascorbic acid(C₆H₈O₆)were selected to explore the reaction mechanism,degradation kinetics and degradation mechanism of different reducing agents catalyzed by Cu(?)for carbamazepine(CBZ),iodipanol(IPM)and benzoic acid(BA).(1)The degradation rate of CBZ in Cu(?)/Na₂SO₃ system could reach 100%under alkaline conditions.Quenching experiment and ESR detection showed that SO₄^·-and HO^·were the main active components for the degradation of CBZ,and SO₃^·-was an important precursor for the production of strong active free radicals.In addition,ultraviolet spectroscopy detection confirmed that Cu(?I)was formed in the system,but its role in the degradation of CBZ was weak and limited.The increase of p H was beneficial to the degradation of CBZ.The degradation rate of CBZ increased first and then stabilized with the increase of Cu(?)concentration,and increased first and then decreased with the increase of Na₂SO₃ concentration.HCO₃^-,Cl^-and humic acid had inhibitory effect on CBZ degradation.The degradation rate of Cu(?)/Na₂SO₃ system for CBZ could reach 41.77%in actual water background.Ten degradation products of CBZ were detected by UPLC-MS,and the possible degradation paths of CBZ were speculated as follows:dehydrogen hydroxylation,dehydrogen epoxygenation,deamidation carboxylation,hydroxyl ring-opening,carboxylation or aldehyde,heterocyclic recombination,amide group shedding,amide group cracking,etc.(2)The degradation of CBZ by Cu(?)/NH₂OH system reached the best at neutral p H and decreased in acidic or alkaline environment.Through the quenching experiment and the formation of active oxidizing substances and Cu(?I),it was proved that Cu(?I)and HO^·were the main active components for the degradation of CBZ in the system.However,Cu(?)/NH₂OH system achieved the best degradation rate of IPM under alkaline conditions,indicating that Cu(?)/NH₂OH system had different degradation mechanisms for the two pollutants.The quenching experiments,dissolved oxygen and redox potential measurements showed that the degradation of IPM was more favorable in anoxic reduction environment,and Cu(I)was the main active component.The increase of p H was conducive to the degradation of IPM.With the increase of Cu(?)concentration and NH₂OH concentration,the degradation rate of IPM increased first and then stabilized.In Cu(?)/NH₂OH system,HCO₃^-had a significant inhibitory effect on IPM degradation,humic acid had a weak inhibitory effect and Cl^-had the least inhibition.The degradation rate of Cu(?)/NH₂OH system for IPM could reach 64.04%in actual water background.Twelve degradation products of IPM were detected by UPLC-MS,and the possible degradation paths of IPM were speculated as follows:amide group fracture into amino,amide group fracture into amide,hydrogen substitution of iodine,hydroxyl substitution of iodine,etc.(3)The degradation rates of CBZ and BA in Cu(?)/C₆H₈O₆ system under acidic conditions could reach 72.99%and 60.74%respectively.The quenching experiment and the formation of H₂O₂ and Cu(?I)showed that Cu(?I)and HO^·were the main active components for the degradation of CBZ and BA in the system.The degradation rates of CBZ and BA increased first and then decreased with the increase of p H value,and reached the maximum value at p H 4.The degradation rates of CBZ and BA increased first and then stabilized with the increase of Cu(?)concentration,and increased first and then decreased with the increase of C₆H₈O₆ concentration.HCO₃^-,Cl^-and humic acid had little effect on the degradation of CBZ and BA.The degradation rate of Cu(?)/C₆H₈O₆ system for CBZ and BA could reach 58.26%and 39.93%in actual water background respectively.It was found that the optimum p H values of Cu(?)/reductant system for the degradation of CBZ were different.The optimum p H of Cu(?)/Na₂SO₃,Cu(?)/NH₂OH and Cu(?)/C₆H₈O₆systems were 10,7 and 4 respectively.The main reason was that the main active components of the three systems were different.The main active components of Cu(?)/Na₂SO₃ system were SO₄^·-and HO^·produced by chain reaction of oxysulfur radicals.The main active components of Cu(?)/NH₂OH and Cu(?)/C₆H₈O₆ systems were Cu(?I)and HO^·produced by the conversion of different valence copper.