Study On Modification Of Graphite Carbon Nitride And Synergistic Oxidation System With Sulfate Radical

In recent years,with the rapid growth of the global population and social economy,a large number of pharmaceuticals and personal care products（PPCPs）have been developed and used increasingly,resulting in them being frequently detected in various environmental water bodies such as surface water,groundwater,sewage treatment plant effluent and drinking water,etc.They will cause potential ecological and human health risks through bioaccumulation or biomagnification.And there are related research reports that long-term exposure to certain PPCPs can cause endocrine disorders,carcinogenesis,genotoxicity,and fetal development.Advanced oxidation processes（AOP）has been widely used in recent years to remove PPCPs due to its high efficiency,wide application range and high stability.Among them,the green and sustainable characteristics of photocatalysis technology have attracted wide attention from researchers,and the development of more efficient photocatalysts is its main research direction.Graphite carbon nitride（g-C₃N₄）has received wide attention due to its visible light response,thermochemical stability,wide source of raw materials,excellent controllability and other advantages,but the performance of the original g-C₃N₄ photocatalytic performance is still not satisfactory the requirements of practical applications.Therefore,this paper improves the removal effect of PPCPs in water by modifying its materials and optimizing the oxidation system.The main research contents are as follows:（1）The carbon and oxygen co-doped stalactite-like carbon nitride（COCN）is prepared by the co-thermal polymerization of dicyandiamide and methylamine hydroiodide.The doping of carbon and oxygen not only greatly improves its absorption in the visible light area,but also promotes a more efficient separation of electrons and holes.Under visible light,compared with the pristine g-C₃N₄,the modified COCN has a 5.9-fold increase in the degradation efficiency of indomethacin（IDM）.The quenching experiment proves that O₂^·-and ¹O₂ are the dominant active species in the photocatalytic degradation system.In addition,by testing the energy band of COCN,it is found that the position of the valence band has shifted downward,and electron spin resonance（ESR）spectroscopy proves that the photo-generated holes of COCN have the ability to directly oxidize hydroxide ions to generate hydroxyl radicals.Subsequently,based on the identification of intermediate products by HRAM LC-MS/MS and the total organic carbon（TOC）,the degradation pathway of IDM was proposed.（2）We synthesized the g-C₃N₄ nanobelt（CNNB）through melamine and cyanuric chloride under hydrothermal conditions.Through field emission scanning electron microscopy（SEM）and transmission electron microscopy（TEM）analysis,the morphology of CNNB is uniform and the nanometer bandwidth is about 50nm and CNNB is intertwined to form a three-dimensional bird’s nest shape.In view of its unique nanostructure,it can be combined with peroxydisulfate（PDS）to enhance the photocatalytic degradation of organic pollutants.In this oxidation system,PDS acts as an electron acceptor,and organic pollutants act as a hole trap,thus realizing an external double transfer mechanism and greatly improving the utilization of photogenerated electrons and holes.Therefore,the CNNB/PDS system has excellent photocatalytic removal of sulfamethazine（SMT）performance under blue LED irradiation,which is about 17 times higher than the efficiency of the pristine g-C₃N₄/PDS.In addition,the potential SMT degradation pathway was deduced based on the detection of degradation intermediates and theoretical calculations.Finally,the SMT removal effect of various influencing factors and various types of actual water bodies shows that the CNNB/PDS system maintains an efficient SMT removal effect.Therefore,this coordinated external double transfer mechanism can be used as a promising organic pollutant removal technology.