Preparation And Photocatalytic Properties Of Self-Assembled Carbon Nitride

Industrial dye wastewater has great harm,and the harmless treatment of industrial dye wastewater is of great significance to the sustainable development of human society.Photocatalysis is driven by sunlight,which is not only environmentally friendly but also can achieve complete degradation of dye molecules.It has great development potential for organic sewage treatment.Photocatalyst is the core of photocatalytic technology.g-C₃N₄ is a kind of photocatalyst with low price of raw materials,simple preparation,visible light activity and easy regulation of energy band structure.Improving the photocatalytic performance of g-C₃N₄ is of great significance for the development of photocatalytic degradation technologies.In this paper,based on a typical self-assembly of melamine-cyanuric acid for constructing g-C₃N₄ ,a third monomer was introduced into the self-assembly system to regulate the structure and morphology of carbon nitride and improve its photocatalytic degradation performance.In order to further enhance the adsorption and photocatalytic properties of carbon nitride,the treatment process was also investigated.The main research contents are as follows:（1）g-C₃N₄ photocatalysts with different morphologies were prepared by introducing different organic acids（oxalic acid,citric acid）and urea as self-assembly intervention agents to intervene in the self-assembly process.The morphology of the samples changed from bulk g-C₃N₄ to flower-like one,but the skeleton structure of g-C₃N₄ did not change significantly.The specific surface area and porosity of the samples were analyzed.Compared with the compact bulk g-C₃N₄ ,the specific surface area of the self-assembled g-C₃N₄ material was significantly increased,up to 15 times of that of the bulk g-C₃N₄ ,and it has abundant mesopores and macropores.The porosity of g-C₃N₄ obtained was further improved by introducing the self-assembly intervention agent.The results show that oxalic acid and citric acid can further improved the in-plane crystal regularity of g-C₃N₄ ,urea can diversify structure of g-C₃N₄ .The optical properties of the samples are reflected by UV-vis diffuse reflectance and photoluminescence spectra.Compared with bulk g-C₃N₄ and self-assembled g-C₃N₄ without intervening agents,the photon absorption capacity of g-C₃N₄ was enhanced through intervening the self-assembly process by using intervention agent（oxalic acid,citric acid and urea）,and the recombination of photogenerated carriers was greatly suppressed.The photocatalytic activity of the catalyst was evaluated by the effect of photocatalytic degradation of the organic dye molecule rhodamine B（RhB）,and the photocatalytic ability of the sample was significantly enhanced and the sample had cycle stability.Compared with the carbon nitride（CN）obtained without the addition of a self-assembly intervention agent,it not only exhibits stronger dark adsorption to RhB,but also exhibits enhanced photocatalytic activity.（2）Based on the melamine-cyanuric acid self-assembly system mediated by oxalic acid,the effects of different drying methods on the structure and properties of self-assembled g-C₃N₄ were investigated,and it was found that the freeze-drying method can significantly increase the specific surface area of carbon nitride,thereby significantly improving the adsorption capacity for RhB.The effect of catalyst input on the adsorption process was further explored,and the effects of different light sources（Xe lamp and UV LED lamp）and catalyst input on the photocatalytic degradation of RhB were also investigated.The results showed that the freeze-drying treatment enhanced the adsorption capacity and photocatalytic performance of carbon nitride.Therefore,by adjusting the self-assembly and changing the drying method of the assembly,the morphology of g-C₃N₄ can be improved,the specific surface area can be increased,the electron-hole recombination rate can be significantly reduced,the energy band structure can be adjusted,and the adsorption capacity and photocatalysis of g-C₃N₄ can be improved effectively.The prepared carbon nitride will show great application prospects in the treatment of organic wastewater.