Preparation Of Carbon Nitride/Iron Based Photo-fenton Catalytic System And Degradation Of Organic Pollutants In Water

In view of the increasingly serious environmental pollution,the importance of water pollution treatment becomes prominent.The heterogeneous photo-Fenton degradation technology shows great potential in this field.In order to achieve better water pollution treatment effect,the development of photo-Fenton catalyst is very important.Graphite carbon nitride（g-C₃N₄）can be used as catalyst or carrier for heterogeneous photo-Fenton degradation,due to its two-dimensional planar structure,narrow band gap,good stability.In this thesis,a series of carbon nitride-based catalysts were designed and developed to achieve efficient and stable heterogeneous photo-Fenton degradation technology.With the elucidation of the structure-activity relationship as the core,the structural design,photoelectric properties,degradation activity and reaction mechanism were discussed in depth.The g-C₃N₄ nanosheets with larger specific surface area,stronger visible light capturing ability and more negative conduction band position were successfully synthesized by a simple rapid cooling treatment in liquid nitrogen.During the rapid cooling treatment,the unsteady inter-layer van der Waals forces at high temperature were broken by the shrinkage force,which generated by the sudden drop in temperature.Moreover,its specific surface area enhanced the adsorption capacity of methylene blue,which can react with photogenerated holes to further promote the separation of photogenerated carriers.On this basis,the generation of superoxide free radicals can be significantly promoted.Compared with bulk g-C₃N₄,the prepared g-C₃N₄nanosheets showed a significant improved degradation activity for MB(100 mg L^-1),with the degradation and mineralization efficiency reaching 99.6%and 77.2%in 120 min,respectively.The Co Fe₂O₄@carbon microspheres-250/g-C₃N₄ photo-Fenton catalyst（CFO@C-250/CN）with three-dimensional structure was prepared by the combination of g-C₃N₄ and Co Fe₂O₄ and the introduction of carbon microsphere shells.Among them,the existence of incomplete carbon microsphere shell can avoid the ineffective charge transfer caused by direct contact between Co Fe₂O₄ and g-C₃N₄,and induce the heterogeneous Fenton degradation reaction of Co Fe₂O₄,for constructing the heterogeneous photo-Fenton degradation system.In addition,the further adjustment in the coating degree of carbon microsphere shell can balance the enhancement of carbon microspheres and Co Fe₂O₄ on the photoelectric performance,which can promote the separation and transfer of photogenerated carriers to the greatest extent.The heterogeneous photo-Fenton degradation system contained both hydroxyl radical and superoxide radical,which made an excellent degradation activity to 500 mg L^-1 MB by CFO@C-250/CN,reaching 99.6%degradation efficiency in 360 min,and mineralization efficiency of organic carbon in water increased from 9.5%to 68.6%.The carbon-based material/carbon nitride/Fe photo-Fenton catalyst（H-r GO-Fe-C₃N₄-CQD）with different Fe coordination environment was prepared by calcination,using carbon quantum dots,graphene oxide and melamine as precursors for complexation with Fe.This catalyst integrated both oxidation sites of organic pollutants（Organic→Organic^*+H⁺+e^-）and reduction sites producing active free radicals（H₂O₂+e^-→·OH+OH^-,O₂+e^-→·O₂^-）.In the highly conductive carbon substrate,the electrons obtained from the oxidation site were transferred to the reduction site of hydrogen peroxide and oxygen,respectively.Based on the self-cycling of Fe（Ⅱ）/Fe（Ⅲ）,the continuous generation of superoxide free radicals and hydroxyl free radicals can be ensured.Subsequently,the degradation of organic pollutants was accelerated under the synergistic ring-opening effect of superoxide free radical and hydroxyl free radical.In addition,the photogenerated carriers produced under visible light irradiation can further promote the electron transfer,and participate in the degradation process to construct the heterogeneous photo-Fenton degradation system.This catalyst showed mineralization efficiency of 85-96%for various pollutants in water within 30-60 min and wide p H application range（2.98-12.28）,indicating great practical application potential.