Study On Degradation Of Organic Pollutants In Water By Iron-nitrogen-doped Carbon Materials Activation Of Peroxymonosulfate

The development of highly efficient and environmentally friendly water treatment technologies has been one of the most important and greatly challenging task in the face of the problem of removing refractory organic pollutants in water in the environmental field.In recent years,sulfate radical-based advanced oxidation processes（SR-AOPs）have gained more and more attention because of their advantages such as strong oxidizing ability,high degree of mineralization,and wide effective pH range.Iron-based catalysts are considered as the promising approach to activate PMS due to their excellent activation performance,cheap preparation method,and green environmental benefits.In addition,some nitrogen-doped carbon materials（eg,nitrogen-doped carbon nanotubes,nitrogen-doped graphene,etc.）have been reported to be capable of supporting metal nanoparticles as heterogeneous SR-AOPs catalysts for the removal of organic contaminants,and nitrogen-doping carbon matrix also show excellent performance in activating PMS.Therefore,we have meticulously constructed three heterogeneous catalysts of Fe-N-doped carbon heterogeneous catalyst for the activation of PMS to produce SO₄^·-to remove refractory organic pollutants.The major contents are described as follows:Using polydopamine-metal ions complex as precursor,hollow mesoporous N-dopedcarbonmicrospheresencapsulatingspinelferritesnanocrystals（HM-NC/CoFe₂O₄）were facilely prepared with the aim of creating a novel heterogeneous catalyst for sulphate radical-based oxidation of organic contaminants.The surface morphology,structure,composition,thermal stability and magnetization of the HM-NC/CoFe₂O₄ hybrids were studied in detail through a series of characterization methods.During the catalytic reactions,MB was adopted as a model pollutant,a series of catalysts were compared for activation of peroxymonosulfate,besides,the influence of some parameters like the dosages of catalysts and oxidant,MB initial concentrations and pH were analyzed systemically.Under the same conditions,different model pollutants were selected to systematically evaluate the suitability of the catalyst.Outstanding efficiency and excellent reusability were achieved due to the unique structure and composition of HM-NC/CoFe₂O₄.The HM-NC scaffold with high porosity and surface area not only stabilizes the CoFe₂O₄nanoparticles but also greatly facilitates the accessibility and adsorption of substrates to the active sites.In addition,both HM-NC and CoFe₂O₄ on the material surface can act as active sites.Sulfate radicals and hydroxyl radicals are identified as main active species and a possible enhancement mechanism of catalytic performance is also proposed.Additionally,the Fe/Fe₃C@NC hybrids can be facilely fabricated through one-pot pyrolysis Fe,N-contained nano-scale metal-organic framework（MOF）,combining cost-effective iron-based nanoparticles（Fe/Fe₃C）with nitrogen-doped porous carbon（NC）as an excellent heterogeneous SR-AOPs catalyst.Benefiting from the excellent enrichment ability of NC matrix and abundant accessible sites arising from NPs and catalyst support,Fe/Fe₃C@NC outperformed common oxides such as Co₃O₄ and Fe₃O₄ for PMS activation and organic compound degradation.The applicability of this catalyst was also systematically assessed by means of the influence of the main factors and extent of mineralization.It is worth mentioning that VSM characterization shows that Fe/Fe₃C@NC has a higher saturation magnetization,and the catalyst can then be easily recycled for next runs without significant capacity or activity loss.Through the mechanistic study,the active species in the system are identified as sulfate radicals(SO₄^·-)and hydroxyl radicals（OH·）,and the variable chemical valences of Fe NPs as well as pyridinic N and graphitic N in support contribute to the outstanding catalytic activity.In addition,using an in situ replication and transformation strategy,porous Fe₃O₄microspheres were facilely converted into novel Fe-and N-codoped large-pore mesoporous carbon spheres（M-Fe/NC）as PMS activators.Benefiting from the abundance of dual heteroatom doping induced active sites and unique mesoporous structures to enhance active site exposure,the derived M-Fe/NC strikingly outperformed the pristine Fe₃O₄ for PMS activation and organics degradation and was efficient over a wide pH range（2-9）.In contrast to the previously proposed mechanisms,both radical(surface-bound SO₄^·-and^·OH)and nonradical（¹O₂ and direct oxidation）pathways are involved in the M-Fe/NC/PMS system.Experimental observations in combination with DFT calculations reveal that graphitic N and Fe-N₄complex sites played a key role in the catalysis.These new findings open an avenue for development of novel multidoped carbocatalysts in the field of SR-AOPs.