Study On Preparation Of Hybrid G-C₃N₄-based Photocatalyst And Degradation Performance Of Azo Dyes

Photocatalysis is a green technology with important application prospects in the fields of energy and the environment.The key of its research is to develop efficient,stable and sustainable photocatalysts.Among many semiconductor photocatalysts that have been studied,graphite-phase carbon nitride（g-C₃N₄）with two-dimensional lamellar structure has attracted much attention in pollutant degradation due to its advantages of simple preparation,low cost,good stability and easy adjustment of energy band structure.However,the shortcomings of the original g-C₃N₄,such as narrow visible light absorption range,small specific surface area,low photogenerated carrier mobility,poor separation ability,and inability to generate hydroxyl radical（·OH）,limited its photocatalytic activity.Based on a hybrid modification strategy,the use of metallic or non-metallic elements as dopants to regulate the molecular and electronic structure of g-C₃N₄ to promote the process of light absorption and charge transfer will help to improve its photocatalytic activity.Therefore,this paper designed and prepared two kinds of hybrid g-C₃N₄-based photocatalysts,and realized the efficient catalytic degradation of azo dye molecules（amaranth,Rhodamine B,methylene blue）.The specific research contents are as follows:（1）g-C₃N₄ photocatalyst（CN-x）with different C-doped content was prepared by hot polymerization of urea and citric acid.Through the characterization of its morphology,structure,chemical composition and photoelectric properties,it is found that C can replace the bridging N atom,forming delocalized large bond,improving the visible-light absorption and promoting the transfer of photogenerated charge.After further optimizing the C-doped content,the photocatalytic degradation rates of Rhodamine B,methylene blue and amaranth reached 97.2%,94.2%and 91.2%,respectively,within 40 min,which were 1.1 times,1.3 times and 2 times of the unmodified g-C₃N₄.Sacrificant experiments showed that·O₂^-and·OH were the main active substances for photocatalytic degradation of Rh B and amaranth.·O₂^-and h⁺were the main active substances in the degradation of methylene blue.（2）The protonated g-C₃N₄（Fe-g-C₃N₄）doped with Fe³⁺was prepared by hot polymerization method with melamine as precursor and a certain amount of HNO₃ solution was added and Fe³⁺was introduced.Fe³⁺formed a coordination with the amino group at the edge of g-C₃N₄,which changed the electronic structure of the catalyst and formed a photocatalytic and self-Fenton collaborative system,which effectively improved the photocatalytic activity of the catalyst.At the same time,silver nanoparticles（Ag NPs）were introduced as cocatalyst,and the surface plasmon resonance（SPR）effect was used to further enhance the light absorption efficiency and charge separation ability of the Fe-g-C₃N₄ hybrid system.By optimizing the doping content of Fe³⁺and the loading of Ag NPs,the catalyst 3%Ag/Fe-g-C₃N₄ showed efficient degradation of amaranth.Under visible light irradiation,the degradation efficiency of3%Ag/Fe-g-C₃N₄ was up to 98.7%within 40min,which was 1.8 times（54.7%）that of unmodified g-C₃N₄.After 5 cycles,the degradation efficiency can still reach more than 80%.The valence band and conduction band positions of 3%Ag/Fe-g-C₃N₄ were calculated by Mortschottky curve,and·O₂^-was found to be the main active substance by combining with sacrificial agent experiments.