Study On Preparation And Photocatalytic Properties Of Graphite Phase Carbon Nitride-Based Photocatalyst

In recent years,with the acceleration of industrialization and the rapid growth of population,a large number of organic pollutants have been discharged,which makes environment pollution,especially in water pollution,more and more serious.Therefore,it is urgent to overcome technical barriers and develope effective solutions.Among all kinds of environmental purification technologies,semiconductor photocatalysis technology has a series of advantages and shows great application prospects.It has attracted wide attention of scholars around the world.Compared with many precious metal semiconductor materials,graphite phase carbon nitride?g-C₃N₄?has become one of the most popular materials in semiconductor photocatalytic technology due to its advantages of low cost,simple synthesis process,catalytic activity under visible light and great product stability.However,it still possesses the narrow light response range,low photogenerated electron-hole separation and migration efficiency,which can not meet the requirements of practical application.In order to solve the above problems,different composite photocatalytic systems have been constructed basing on g-C₃N₄,which is a semiconductor polymer material with excellent physical and chemical properties.The intrinsic relationship between the structure and properties of the as-developed composite has been systematically studied.The mechanism of synergistic photocatalysis has also been discussed.The main contents are presented as follows:?1?Preparation,properties and mechanism of boron nitride nanosheets?BNNS?/bulk g-C₃N₄?BNNS/g-C₃N₄?composite photocatalytic materials.BNNS/g-C₃N₄ composites were prepared by using a two-step method with loading BNNS on the surfaces of bulk g-C₃N₄ via an in-situ composite technology The structure and photocatalytic properties of the samples were characterized by X-ray diffraction?XRD?,projection electron microscopy?TEM?,ultraviolet-visible diffuse reflectance spectroscopy?UV-Vis DRS?and electrochemical impedance spectroscopy?EIS?.The experimental results show that the photocatalytic degradation efficiency of the samples for Rhodamine B?RhB?increases first and then decreass with increasing the BNNS content under visible light irradiation.When the mass ratio of BNNS to g-C₃N₄ is 8%,the photocatalytic efficiency reaches the optimum value of 73%.Morover,compared with the pure sample,the electronic migration efficiency of the composite is obviously improved.?2?Construction of AgBrO₃/flaky g-C₃N₄ composite photocatalytic system and study on its synergistic photocatalytic mechanism.AgBrO₃/flaky g-C₃N₄ composite photocatalyst was prepared by an in-situ synthesis of loading AgBrO₃ on flaky g-C₃N₄.XRD,TEM,UV-Vis DRS,EIS,Mott-Schottky potential spectroscopy?MS?,X-ray photoelectron spectroscopy?XPS?and other methods were used to characterize the structure,morphology,light response range,separation efficiency of the samples,respectively.The mechanism of synergistic photocatalytic degradation of the composites was also analyzed.The experimental results show that the photocatalytic activity of the composite samples increases first and then decreases with increasing the AgBrO₃ content under visible light irradiation.When the mass ratio of AgBrO₃ to g-C₃N₄ is 4:3,the photocatalytic degradation efficiency of tetracycline?TC?reaches the maximum of 79%,which is 45%and 21%higher than that of pure AgBrO₃ and flake g-C₃N₄,respectively.In addition,the separation and migration efficiency of the electron-hole pairs have been significantly improved,and superoxide radicals?·O₂^-?and holes?h⁺?are the dominant active species in the photocatalytic process.?3?Construction of silver bromide?CdS?/spherical g-C₃N₄ composite photocatalytic system and study on its synergistic photocatalytic mechanism.Similar to previous ones,CdS/spherical g-C₃N₄ composite photocatalytic materials were prepared by an in-situ synthesis of loading CdS nanoparticles onto the surface of spherical g-C₃N₄.By means of XRD,TEM,UV-Vis DRS,EIS,XPS and other measuring methods,the microscopic and macroscopic properties of the samples,such as phase,morphology and structure,were comprehensively analyzed.The experimental results show that under visible light irradiation the photocatalytic activity of the composite samples increases first and then decreases with increasing the CdS content.When the mass ratio of CdS to g-C₃N₄ is 7:1,the photocatalytic degradation efficiency for TC reaches the best of 93%.In addition,a matched energy level was formed at the interface of the composites to inhibit the recombination of photogenerated carriers and improve the photocatalytic degradation efficiency.In addition,·O₂^-is the main active species affecting the efficiency of CdS/spherical g-C₃N₄ composite photocatalysts during the photocatalytic degradation process.