Activation Of Peroxymonosulfate By Cobalt-nitrogen Double-modified Porous Carbon Nanomaterials For Degradation Of Sulfonamide Antibiotics

Sulfonamides（SAs）,as a class of important synthetic sulfanilamide derivatives,have been used in the treatment of various bacterial,protozoal,and fungal infections.Substantial use of SAs results in SAs entering terrestrial and aquatic environments by various means.Excess SAs not only affect the microorganisms in the soi,but also indirectly enter the human body to destroy the immune system.The development of effective treatment methods in which SAs can be converted into less harmful intermediates or even fully mineralized into CO₂ and H₂O has become a major research objective.The commonly used methods for removing SAs include biodegradation,physical adsorption,and advanced oxidation.Among them,advanced oxidation technology based on sulfate（SR-AOPs）has the advantages of strong oxidation ability,simple operation,high selectivity,and wide applicable p H range,which is an emerging technology for the effective treatment of organic pollutants.Free radicals,including hydroxyl radicals（·OH）,sulfate radicals(SO₄^·-),superoxide anion radicals(O₂^·-),and non-radical species,such as single oxygen（¹O₂）,surface-activated complexes,and electron transfer,are common active pathways in SR-AOPs.Recent research showed that SR-AOPs exhibited notable performance in removing antibiotic contaminants.These active substances can completely degrade or mineralize most organic matter and play an important role in the degradation of pollutants.The active species in SR-AOPs can be generated by activating peroxymonosulfate（PMS）or persulfate（PS）.Compared with thermal activation,ultraviolet activation,alkali activation,and other activation methods,transition metal ions(Fe²⁺,Co²⁺,Mn²⁺,Cu²⁺,etc.)are widely used as the homogeneous catalysts to activate PS/PMS in the presence of their high efficiency and mild reaction conditions.Among them,Co²⁺exhibits the best activation performance for PMS.Moreover,carbon-based nanomaterials（nanotubes（CNTs）,activated carbon（AC）,activated carbon fibers（ACFs）,graphene oxide（GO）,etc.）with a large surface area,an abundant porous structure,excellent physical and chemical properties,good biocompatibility,acid and alkali resistance,have become excellent heterogeneous catalysts for PS/PMS activation.Moreover,the doping of heteroatoms such as N into the carbon matrix produces defects to adjust the physical and chemical properties of the material,thereby improving the activation performance of the carbon-based nanomaterials for PS/PMS.The introduction of transition metals（such as Co or Fe）into N-doped carbon materials to form metal-nitrogen double-modified porous carbon nanomaterials（M-N-C,M=Co or Fe）as the heterogeneous catalysts to activate PS/PMS shows great research prospects.In this paper,three main sulfonamide antibiotics,including sulfamethoxazole（SMX）,sulfamerazine（SMZ）,and sulfathiazole（STZ）,were selected as the target pollutants,and three kinds of cobalt-nitrogen double-modified porous carbon nanomaterials were prepared.These materials were employed to activate PMS to generate active species,eventually achieving the efficient and rapid removal of sulfonamide antibiotics in water.Various factors affecting the catalytic performance were investigated,including the concentration of PMS,the initial p H of the solution,and inorganic ions.The active species generated in the degradation system were verified,and a possible catalytic mechanism was proposed.The main research contents of the thesis are as follows:（1）Porous 3D superstructure of nitrogen doped carbon decorated with ultrafine cobalt nanodots as peroxymonosulfate activator for the degradation of sulfonamidesSuperstructures have attracted attention because of their potential applications in chemistry and materials science.In this work,a porous 3D superstructure of nitrogen doped carbon decorated with ultrafine cobalt nanodots（Co@NCSS）was prepared.The modified ultrafine cobalt nanodots served as the main catalytically active sites,and the excellent quality and electron transport efficiency generated by this 3D porous superstructure,Co@NCSS exhibited excellent catalytic performance as a PMS activator towards the degradation of several sulfonamides.Based on radical scavenging tests and electron paramagnetic resonance（EPR）,¹O₂ was the dominant oxidative species.Furthermore,the pathway of SMX degradation by Co@NCSS/PMS was analyzed through the identification of degradation intermediates by HPLC-MS and DFT calculations.The possible catalytic mechanism of Co@NCSS/PMS for SMX degradation was also proposed in this thesis.（2）Low temperature decorated atomically dispersed cobalt-nitrogen-carbon layers on carbon nanotubes as peroxymonosulfate activator for the degradation of sulfamerazine through electron transfer pathwaySingle-atom catalysts have attracted increasing attention in heterogeneous catalysis owing to the atomic dispersion of active sites and high catalytic activities.Herein,carbon nanotubes（CNTs）were decorated with nano-thick carbon-nitrogen（Co NC）layers containing atomically dispersed cobalt atoms on carbon nanotubes（CNTs）via the solvothermal reaction.The as-prepared Co NC-CNTs composite was directly used as the catalyst to activate PMS without pyrolyzis and exhibited high catalytic performance for the degradation of SMZ.The Co sites with atomic dispersion in Co NC-CNTs were confirmed to be active sites.The nonradical mechanism of electron transfer played an important role in the degradation of SMZ by Co NC-CNTs/PMS.Furthermore,the degradation intermediates and pathway of sulfamerazine were also analyzed by HPLC-MS and DFT.（3）Nitrogen-doped hierarchically ordered carbon tube-sheet superstructures decorated with cobalt and Mo O₂ nanoparticles as peroxymonosulfate activators for the degradation of sulfonamidesA layered ordered carbon tube sheet superstructure（CTSS）was successfully prepared by a template-directed self-assembly method using Mo O₃ as the template and PIs as the carbon source.The transition metal cobalt was introduced to increase the degradation performance of the material.Nitrogen-doped hierarchically ordered carbon tube-sheet superstructures decorated with cobalt and Mo O₂ nanoparticles（Mo O₂@CTSS@Co）were successfully prepared after high-temperature carbonization.Mo O₂@CTSS@Co activated PMS to efficiently degrade sulfonamides,The effects of PMS concentration,catalyst loading,initial p H of the solution,inorganic anions,and humic acids on the degradation of STZ by Mo O₂@CTSS@Co/PMS were investigated.The active species generated in Mo O₂@CTSS@Co/PMS were also verified by the quenching experiments and EPR analysis,and the possible catalytic mechanism of Mo O₂@CTSS@Co was proposed.Finally,the pathway of STZ degradation by Mo O₂@CTSS@Co/PMS was analyzed by HPLC-MS.