Preparation And Photocatalytic Properties Of Porous G-C₃N₄ Doped With Phosphorus/Oxygen Atoms And Nitrogen Rich Vacancy

With the rapid development of urban industrialization,the problem of environmental organic pollution is becoming more and more serious.Photocatalysis technology has attracted much attention because of its effective treatment of organic pollutants.Among many photocatalysts,graphite phase carbon nitride（g-C₃N₄）,as a non-metallic semiconductor material,has been widely used in the field of photocatalysis due to its advantages such as suitable energy band structure（Eg=2.7e V）,visible light response,good thermal stability,simple preparation method and low raw material cost.However,the development of g-C₃N₄ in the field of photocatalysis is limited due to its small specific surface area,easy recombination of photogenerated electron-hole and weak utilization of visible light.Based on the above analysis,methods such as incorporation of different impurity atoms and construction of vacancy were used to optimize the structure of g-C₃N₄ photocatalyst,improve the photocatalytic activity of g-C₃N₄ photocatalyst,inhibit the photogenerated electron-hole recombination and enhance the visible light response ability,thus improving its photodegradation performance as a photocatalyst of organic pollutants.Specific research contents and results are as follows:（1）Porous g-C₃N₄（W-A-CN）rich in nitrogen vacancies and heteroatoms was prepared by one-pot polymerization.In this method,urea and ammonium bicarbonate molecules were homogenized,urea recrystallization,polycondensation and thermal stripping were used to form porous g-C₃N₄ with abundant exposed edges,interconnected open diffusion channels,and abundant nitrogen vacancies and oxygen heteroatoms.This unique structure and composition facilitates the exposure of active sites and the migration of substrates and products.The construction of nitrogen vacancies and oxygen heteroatoms in porous g-C₃N₄ modulates its electronic structure,thus accelerating the photogenic carrier separation and further promoting the production of active substances under light irradiation.The optimized g-C₃N₄photocatalyst was used to photodegrade Rhodamine B（C₀=50 mg/L）under visible light and sunlight,respectively.After 90 min,the photodegradation efficiency of Rhodamine B reached 97.5%and 99%,respectively.（2）An ultra-thin g-C₃N₄（P-NCN）photocatalyst rich in nitrogen vacancy and phosphorus/oxygen atom co-doping was successfully prepared by one-pot forging and gas phase deposition.The g-C₃N₄ structure was optimized by nitrogen vacancy and phosphorus/oxygen atom,which effectively widened the range of light absorption,suppressed the recombination of photogenerated electron-hole pairs and extended the life of photogenerated carriers.P-NCN has excellent photocatalytic degradation of Rhodamine B.The maximum rate constant K(0.077 min^-1)for g-C₃N₄（P-NCN）rich in nitrogen vacancy and phosphorus/oxygen dopant atoms under visible light is g-C₃N₄（NCN）rich in nitrogen vacancy and oxygen atom(0.030 min^-1)and original g-C₃N₄（CN）(0.027 min^-1)2.6 times and 2.9 times.（3）Through radical quenching experiment and EPR test,it was found that W-A-CN and P-NCN photocatalysts degraded Rhodamine B mainly by generating superoxide free radical（·O₂^-）under light conditions.The conductance potential of W-A-CN and P-NCN photocatalysts is more negative than that of O₂/·O₂^-,which is conducive to the generation of superoxide radical（·O₂^-）,thus accelerating the whole process of photodegradation of Rhodamine B.