Preparation Of Graphite Phase Carbon Nitride-based Composite Photocatalyst And Its Performance For Production Of Hydrogen Peroxide

Hydrogen peroxide（H₂O₂）,as a common chemical substance,has strong oxidizing properties and is widely used in actual production and daily life.The production methods of H₂O₂ mainly include anthraquinone method,electrolysis method,hydrogen and oxygen direct synthesis method and air cathode oxidation method.Among them,the anthraquinone method is the mainstream,and the output accounts for more than 95%.However,the synthesis process of the anthraquinone method has terrible safety hazards,and will cause serious environmental pollution problems,which does not meet the requirements of sustainable development.The photocatalytic H₂O₂ production program has the characteristics of mild conditions and environmental friendliness,made it has great development potential.In this paper,a series of K-CNX composites（X represents the doping amount of K⁺）were prepared by doping graphite phase carbon nitride（g-C₃N₄）with different contents of potassium ions（K⁺）.Characterization methods such as XRD,FT-IR,XPS,TEM,SEM,UV-Vis DRS and EIS were used to characterize the composite,and the structure,morphology,optical and electrochemical properties of the composite K-CNX were studied.The EIS results show that the doping of K⁺can significantly enhance the electron transport ability of g-C₃N₄,which is beneficial to the progress of the photocatalytic reaction.Through a series of experiments on the photocatalytic production of from the K-CNX complex under simulated sunlight,the optimal doping amount of K⁺was determined.Among them,K-CN10 showed the best photocatalytic performance.After 6 hour of photocatalytic H₂O₂ reaction,the equilibrium concentration of H₂O₂ reached 1.0mmol/L,which was 20 times that of pure g-C₃N₄.Through the decomposition experiment of H₂O₂ and the cycle experiment of H₂O₂ production by K-CN10,the stability of the composite during the continuous photocatalytic production of H₂O₂ was studied.Through the capture of free radicals and the quantitative determination of superoxide radicals（·O₂^-）,the possible mechanism of the photocatalytic H₂O₂ production of K-CN10 complexes was clarified.In order to further improve the efficiency of the photocatalytic H₂O₂production of K-CN10 complex,this paper uses tungsten trioxide（WO₃）to compound K-CN10.A series of K-CN10/WO₃（X%）composite photocatalysts were prepared by hydrothermal method and mixed with K-CN10,and a series of K-CN10/WO₃（X%）composite photocatalysts were prepared through various characterization methods.The structure,morphology,optics and electrochemistry were studied.Performance,etc.The EIS results also show that the composite of WO₃ further improves the electron transport capability of K-CN10.Through a series of experiments of the K-CN10/WO₃（X%）composite photocatalyst in the photocatalytic production of H₂O₂ under simulated sunlight,the optimal composite amount of WO₃ was determined.Among them,K-CN10/WO³（10%）showed the best H₂O₂ production effect.After 6 hour of photocatalytic H₂O₂reaction,the equilibrium concentration of H₂O₂ reached 1.33 mmol/L,which was1.33 times that of pure K-CN10.At the same time,through H₂O₂ decomposition experiments and K-CN10/WO₃（10%）H₂O₂ production cycle experiments,the stability of the composite photocatalyst in the process of continuous photocatalytic H₂O₂ production was studied.In addition,the valence band positions of K-CN10 and K-CN10/WO₃（10%）were measured and compared by XPS valence band spectroscopy and UV-Vis DRS.The results show that K-CN10/WO₃（10%）has a corrected valence band position.Simultaneously,combined with the free radical capture experiment and the quantitative determination of·O₂^-and hydroxyl radicals（·OH）,it is clarified that the pathway of K-CN10/WO₃（10%）to produce H₂O₂ has changed from a single channel（conduction band electron reduction）of K-CN10 to a dual channel.（Reduction of conduction band electrons and synthesis of hydroxyl radicals generated in valence band）,which improves the ability of photocatalytic production of H₂O₂.In summary,this article prepared K-CNX composites by doping g-C₃N₄ with K⁺to improve the photocatalytic H₂O₂ production capacity of g-C₃N₄.On this basis,K-CN10/WO₃（X%）was successfully prepared by compounding with WO₃.The composite photocatalyst further improves the efficiency of K-CNX’s photocatalytic H₂O₂ production.Through a series of tests,characterization and experimental comparative studies,the paths of the two composite photocatalytic materials for photocatalytic H₂O₂ production were explored,and their possible mechanisms for photocatalytic H₂O₂ production were respectively proposed.The research in this thesis provides a new idea for the improvement of H₂O₂ produced by photocatalytic materials based on g-C₃N₄,and provides a certain theoretical basis for the realization of the clean production of g-C₃N₄.