Preparation,Photocatalytic Properties And Mechanisms Of Graphitic Carbon Nitride-Based Composites For The Degradation Of Tetracycline Hydrochloride

In recent decades,antibiotics have been widely used in the fields of medicine,veterinary medicine,animal husbandry and so on.Antibiotics can only be partially metabolized in the living body,and most of them will be discharged into the environment.Water pollution has become one of the major environmental problems facing the world.As a new generation of sustainable organic pollutant treatment technology,photocatalytic oxidation method has a potential application prospect.Graphite carbon nitride（g-C₃N₄）is a kind of extremely potential applications of photocatalyst.It is widely used in the photocatalytic degradation of pollutants antibiotics which has good visible light response ability,excellent chemical stability and thermal stability.However,g-C₃N₄’s small specific surface area,narrow solar spectral response range and low carrier separation efficiency are still the key obstacle to its practical application.Therefore,in this thesis,2D g-C₃N₄ nanosheets are prepared by simple thermal polymerization method,and then 2D/2D Ti₃C₂/g-C₃N₄,3D/2D Fe₂O₃/g-C₃N₄ and 2D/3D CN/CC composite light are designed and constructed.Their microstructure,morphology and physicochemical properties are systematically studied,and their performance and mechanism of degrading tetracycline hydrochloride（TC-HCl）in water are discussed in detail,as follows:1.2D/2D Ti₃C₂/g-C₃N₄ heterojunction photocatalyst is prepared by thermal polymerization in a semi-closed system.The interaction between 2D Ti₃C₂ and 2D g-C₃N₄ heterojunction photocatalyst not only make it have excellent stability,but also generates active sites on the boundary edge of 2D Ti₃C₂ nanosheets.The introduction of 2D Ti₃C₂ improves the visible light response capability of 2D g-C₃N₄ nanosheets,and it can be used as an electronic collector to improve the transmission and separation efficiency of charge carriers,thus greatly enhancing the photocatalytic performance.Under visible light,2D/2D Ti₃C₂/g-C₃N₄-3 heterojunction can not only degrade TC-HCl pollutants in water efficiently,of which TOC removal rate of 79.0%is 3.48 times that of the original g-C₃N₄ sample,but also shows excellent hydrogen production performance,with the hydrogen production rate(26.7 mol h^-1)being about 2.13 times that of the original g-C₃N₄.The study of photocatalytic reaction mechanism shows that h⁺and·O₂^-play a major role in the degradation of TC-HCl,and the influence of·OH is relatively weak.2.The 3D/2Dγ-Fe₂O₃/g-C₃N₄ heterojunction photocatalyst is prepared by simple solvent heat method by anchored mesoporous 3Dγ-Fe₂O₃ nanospheres on the surface of 2D g-C₃N₄ nanosheets.The mesoporous characteristic significantly increases the specific surface area and provides abundant reactive sites for TC-HCl molecules.Particularly,Z-scheme heterostructure is formed between 3Dγ-Fe₂O₃ nanospheres and2D g-C₃N₄ nanosheets,which accelerates the transfer and separation of photogenerated charge carriers between interfaces,thus significantly enhancing the photocatalytic performance.The maximum rate constant of TC-HCl degradation of 3D/2Dγ-Fe₂O₃/g-C₃N₄ heterojunction reaches 0.0134 min^-1,which is much higher than that of 0.0020min^-1 of the original g-C₃N₄ sample.The photocatalytic reaction mechanism study shows that·O₂^-,·OH and h⁺are the main active species,which play an important role in the degradation of TC-HCl,and the order of influence is·OH>·O₂^->h⁺.3.The 2D/3D CN/CC homojunction is prepared by the in-situ surface polymerization strategy and the 3D CC microspheres are anchored tightly on the surface of 2D CN nanosheets by simple solvothermal method.The synergy between the structural coupling and energy band control of 3D CC microspheres and 2D CN nanosheets significantly improves the transfer and separation efficiency of photogenerated charge carriers,thereby greatly enhancing the photocatalytic performance.The maximum rate constant of degradation of TC-HCl over 2D/3D CN/CC homojunction reaches 0.0104 min^-1,which is 4.52 and 5.20 times of the original2D CN and 3D CC,and the TOC removal rate of degradation of TC-HCl within 120min is up to 64.0%,showing excellent mineralization ability.Research on photocatalytic reaction mechanism shows that·OH and h⁺are the main active species in the process of TC-HCl degradation,and the effect of·OH is slightly higher than that of h⁺,while·O₂^-plays a relatively weak role.