Preparation Of G-C₃N₄ Composite Photocatalytic Materialand Its Photocatalytic Performance

In recent years,in order to solve the problems of deteriorating environmental pollution and energy shortage,semiconductor photocatalytic technology has become one of the most promising technologies.Among many photocatalysts,g-C₃N₄ has attracted wide attention due to its unique characteristics and excellent photocatalytic activity under visible light.However,the rapid recombination of photocarriers has greatly negatively affected its photocatalytic performance.This thesis mainly introduces the research progress and modification of g-C₃N₄photocatalyst.Using melamine as a precursor,g-C₃N₄ powder was synthesized by thermal condensation polymerization method,and two parts of research work were carried out to study its photocatalytic efficiency by the composite modification method.The details are as follows:?1?Using zinc acetate,hexamethylenetetramine,and urea as precursors,and water as a solvent,a flower-like microband ZnO was synthesized by a hydrothermal method.Then a normal temperature and pressure solvent synthesis method is used to synthesize the composite of g-C₃N₄ and ZnO by stirring.Three kinds of ZnO/g-C₃N₄ composite photocatalysts were prepared by changing the mass of g-C₃N₄.X-ray diffraction?XRD?and scanning electron microscope?SEM?were used to characterize the structure,composition and morphology of the samples.The photocatalytic activity of the obtained samples was evaluated by photocatalytic degradation of rhodamine B solution.The results show that when the mass ratio of ZnO to g-C₃N₄ is 1:5,the synthesized composite possess the best photocatalytic activity.Under visible light irradiation,the degradation of rhodamine B reached 93%within 70 minutes.Moreover,after 4 cycles,the photocatalytic activity of ZnO/g-C₃N₄?1:5?composite did not show significant attenuation.This may be due to the band structure of ZnO/g-C₃N₄,which is helpful to promote the separation and rapid transfer of photo-generated electrons and holes,preventing the recombination of photocarriers,and improve the photocatalytic efficiency.?2?With Zn?NO₃?₃·6H₂O as the zinc source,2-methylimidazole as the organic ligand,and methanol as the solvent,the compounding of two kinds of semiconductors,ZIF-8 and g-C₃N₄,was achieved by simple solvent synthesis at normal temperature and pressure with stirring.X-ray diffraction?XRD?and scanning electron microscope?SEM?were used to characterize the structure,composition and microstructure of the samples.The results show that ZIF-8 particles grow uniformly on the surface of g-C₃N₄,and a heterojunction interface is formed between ZIF-8 and g-C₃N₄.The photocatalytic activity of the obtained samples was evaluated by photocatalytic degradation of rhodamine B solution.The experimental results show that under visible light irradiation,the ZIF-8/g-C₃N₄ composite material degraded 97.3%of rhodamine B in 50 minutes,which showed much higher photocatalytic activity than pure g-C₃N₄ and pure ZIF-8.At the same time,the ZIF-8/g-C₃N₄ composite material maintained high photocatalytic activity after 4 cycles experiments,and showed good photocatalytic stability.This is because the small ZIF-8 particles on the surface of g-C₃N₄ can provide more active sites in the photocatalytic process,and the heterojunction interface formed between g-C₃N₄and ZIF-8 semiconductors can effectively promote the separation and transfer of photo-enerated electron-hole pairs,so its greatly enhance the photocatalytic activity.