Activation Of Peroxymonosulfate By Nitrogen-sulfur Doped Carbon-based Catalyst For Degradation Of Chlorophenols

Advanced oxidation technology based on activated permonosulfate degradation of organic pollutants is not only efficient and simple,but also the chemical properties of permonosulfate before activation is stable,easy to transport and storage,and it has been widely used with the development of industry.Activation of permonosulfate by carbon-based catalyst,which could avoid secondary pollution,reduce operating cost and simplified reaction process,has been attracted more and more attention in the environmental research.The key to gain the most improvement of carbon-based catalysts is to introduce proper amounts of nonmetallic elements on their surface.In order to solve the problems such as uneven heteroatom distribution,element loss and complex process in the doping process,this study obtained in situ doped nitrogen and sulfur carbon-based catalytic by carbonizing polypyrrole and polythiophene mixture,and studied the activation efficiency and activation mechanism of the prepared catalyst.It was found that the surface microstructure and functional group structure of the catalyst changed obviously by different morphological and structural characterization methods.99% 2,4-DCP can be removed in 30 min and 60% mineralization rate can be achieved under the conditions of initial pollutant concentration of 50 mg/L,catalyst dosage of 0.1 g/L,PMS dosage of 1 g/L,and initial solution p H of 7.0,which illustrated the nitrogen-sulfur doped carbon-based catalyst prepared by polypyrrole and polythiophene can effectively activate permonosulfate.The graphitization structure and active nitrogen-sulfur functional groups on the surface of the catalyst are the key factors affecting the activation performance of the catalyst.The higher the calcination temperature,the more graphitized structures are formed,and the doping ratio of high nitrogen and low sulfur will introduce more effective active nitrogen and sulfur functional groups.Singlet oxygen was found to be the main active oxidizing substance in the system by quenching experiments and electron paramagnetic resonance(EPR)trapping of free radicals.The non-free radical oxidation process with singlet oxygen as the main active substance also has a good ability to degrade pollutants under a wide p H range and different anion interference background.Singlet oxygen in the system can be formed by the broken peroxygen bond of PMS after activation,or can be formed by the recombination of superoxide radicals and water molecules.The synergistic effect of nitrogen and sulfur doping enhanced the electron transfer ability on the surface of the carbon-based catalyst,and the electrons lost by pollutants on the surface of the catalyst were transferred to PMS to promote it activation by breaking of the peroxy bond.In order to study the universality of system degradation,the degradation ability and degradation pathways of aromatic compounds with different types and numbers of substituents during non-free radical oxidation process were further analyzed combined with GC-MS technology.The non-free radical oxidation process can selectively degrade the pollutants with high electron density in the benzene ring.The substituents which have the effect of pushing electron conjugation on the benzene ring are favorable to the degradation reaction.The intermediate products produced by degrading different number of chlorinesubstituteds pollutants were studied,and it was found that the pollutants could lost electrons on the surface of the catalyst to form benzene ring free radical cations,which could be rapidly dechlorinated and dehydrogenated to form hydroquinone compounds.Then it could further oxidize to form benzoquinone compounds,and finally mineralized by opening the ring to form carbon dioxide and water.With the increase of chlorinated substituents,the para-substituted chlorinated substituents are shed faster.However,the increase of chlorinated substituents on the benzene ring resulted in the formation of stable chlorinated intermediates,which affected the further mineralization.In conclusion,the system is more suitable for degrading chlorophenols with low chlorine substitutions.