The Activation Of Peroxymonosulfate And Degradation Of Pollutants By Nitrogen Doped Carbon-based Catalysts

Advanced oxidation process is a kind of way for alleviating water pollution issues,among which,peroxymonosulfate（PMS）based technology aroused much interests because this process can generate strong oxidative sulfate radicals（SO₄·-,with the potential of 2.5-3.1 V）.In view of the excessive metal ions leaching in metal-based catalytic systems and subsequent secondary pollution to the environment,N doped carbon in terms of PMS activation is very popular recently.However,the controlled synthesis and profound activation mechanism still need to be studied.Based on this,this paper focused on the fabrication of N doped carbon materials,and we obtained a series of N doped carbon with high performance by adjusting the species and doping level of heteroatoms,the graphitization degree of carbon,and pore structures.Then,systematic characterization and deep understanding about PMS activation were analyzed.Zeolitic imidazolate frameworks（ZIFs）derived strategy was employed to prepare N doped porous carbon（NPC）.Herein,ZIF-8 derived NPC has very high N doping level and considerable specific surface areas.As the change of calcination temperature,N doping level and existing forms also change.NPC exhibits excellent performance for Rh B and phenol removal.Mechanism studies indicated that after the introduction of N,radical and non-radical processes both existed in PMS activation.To further enhance the catalytic activity,multiple heteroatoms doping method was explored.Different amounts of polymer PZS containing N,P and S atoms were coated onto the surface of ZIF-67,and proportion of three heteroatoms could be modulated by the reaction between Co and P.After washing the metal species,N,P and S doped hollow carbon shells（NPSC）with the thickness of 15 nm were obtained,and the porosity was developed.The elevation of temperature facilitated S doping,and suppressed the introduction of N and P.When the polymer coating was excessive,the obtained N and S amount within NPSC increase and P amount decreased accordingly.For the activation of PMS,three heteroatoms doping in carbon shells exhibits synergistic effects.Radical quenching experiments manifested that radical species were ·OH、SO₄·-and O₂·-,and part of non-radical process was still involved.The pore structures are much important for catalytic activities.This study used biomass human hair with multiple amino acids as the sole source,and transformed the hair into N、S co-doped carbon（NSC）through reaction between KOH and carbon.The specific surface areas were as high as 2937 m²/g,and micro pores were the main existing forms of pores.Adsorption models were fitted to elucidate the adsorption process between NSC and BPA,it turned out that adsorption mechanism was multiple layers adsorption on the heterogeneous surface.NSC/PMS could remove 98.4% of BPA with adsorption and degradation effects.The interconnected microporous networks served as fast electron transportation bridges,and pollutants and PMS could be enriched onto the surface,generate ¹O₂ and then effectively degrade pollutants.The graphitization degree of carbon can affect the PMS activation.Considering of that transition metal could catalyze the growth of graphitic carbon,ZIF-67 was utilized as the precursor to synthesize N doped graphitic carbon.ZIF-67 was calcined under H₂/N₂ atmosphere,during this process,carbon grew along the surface of Co,then gradually formed the tubular structures.After washing the exposed Co,interconnected N doped carbon frameworks（NCNTFs）were obtained,and the diameter was 4 nm.This material owned evident graphitic structures,and NCNTFs-800/PMS had high degradation efficiency for BPA.GC-MS detected 8 intermediates and catalytic mechanism was deduced.Electron paramagnetic resonance（EPR）and quenching tests proved that the reaction followed non-radical pathways,and reactive species was ¹O₂.K₄Fe（CN）₆ was chosen as the precursor to fabricate N doped graphitic carbon.Six CN-coordinate with one Fe²⁺,which supplied abundant carbon and N sources.When the coordination compound was calcined under 900 ℃,Fe directed the production of carbon nanotubes and graphitic nanosheets,after washing it with acid,carbon nanotubes encapsulated with Fe₃ C and graphitic nanosheets assemblies（Fe₃C/NCNTs/GNS）were prepared.This material had extremely high graphitization degree,and when coupled with PMS,about 97.8% of BPA was removed in 30 min.Similarly,the produced species were ¹O₂.Through a comparative study about the mechanism of N doped amorphous carbon,graphitic carbon and N doped graphitic carbon,it was found that radical and non-radical mechanism both existed in carbon/PMS systems.The graphitic N within materials may promote the circulation of electrons on the surface of the whole carbon skeletons,nonradical was prone to occur.Graphitic degree and N doping exert great synergistic effects for the generation of non-radical mechanisms.