The Synthesis And Properties Research Of The Bi₄NbO₈Cl/C₃N₄ Heterojunction Photocatalyst

The global energy crisis and environmental pollution have become the two major challenges for human society in the 21st century.Photocatalytic technology which can use solar energy to produce renewable energy and eliminate pollutants is considered to be an effective solution for these problems.Because of wide band gap for the traditional photocatalyst TiO₂,researchers develop a series of new visible light-responsive photocatalysts such as Bi₄NbO₈Cl and C₃N₄.However,the novel visible light-responsive photocatalysts Bi₄NbO₈Cl and C₃N₄ still have the disadvantage of weak photocatalytic hydrogen production performance.This paper takes Bi₄NbO₈Cl and C₃N₄as research objects.Firstly,the pure phase Bi₄NbO₈Cl is prepared by molten salt method.Then the effect of different synthesis method to complex Bi₄NbO₈Cl and C₃N₄ was discussed.The product samples were analyzed and verified by the related characterization test.The performance and the photogenerated charge transfer mechanism of Bi₄NbO₈Cl/C₃N₄ composite for improving photocatalytic hydrogen production has been verified.The Bi₄NbO₈Cl photocatalyst was synthesized by the molten salt method.The influence of process parameters such as synthesis temperature,synthesis time and molten salt ratio for the performance and structure of Bi₄NbO₈Cl photocatalyst was determined.The Bi₄NbO₈Cl photocatalyst synthesized with best process parameters when the synthesis temperature was 700℃,the synthesis time was 2 h,and the molten salt ratio was 1:5 has better morphology and performance than the Bi₄NbO₈Cl obtained by solid phase method.Although Bi₄NbO₈Cl photocatalyst prepared by the molten salt method was good at photocatalytic degradation,its photocatalytic hydrogen production performance was weak.Bi₄NbO₈Cl synthesized by molten salt method and C₃N₄ were combined by different synthesis method,and the phase composition,microstructure and photocatalytic properties of the composited product samples were investigated by XRD,SEM and photocatalytic hydrogen production test.Determining whether the Bi₄NbO₈Cl/C₃N₄ composite with improved photocatalytic performance has been synthesized.The study found that Bi₄NbO₈Cl and C₃N₄ may lead to side reaction when prepared by molten salt method and hydrothermal method using water as solvent.However,solvothermal method with ethylene glycol as solvent can directly combine Bi₄NbO₈Cl and C₃N₄ to obtain Bi₄NbO₈Cl/C₃N₄ composite,and 3%BNCN sample（the mass fraction of Bi₄NbO₈Cl in the sample is 3%）has optimal photocatalytic hydrogen production rate of 574.69μmol?g^-1?h^-1among them.At the same time,the band structure of 3%BNCN sample was confirmed by XPS valence band spectrum and UV-visible diffuse reflectance spectra,and TEM,PL,XPS and·O₂^-capture experiments were carried out for 3%BNCN sample to analyze the migration direction of the photogenerated electrons and holes.It was found that the 3%BNCN sample improved the photocatalytic performance because of the direct Z-scheme heterojunction.In this paper,Bi₄NbO₈Cl/C₃N₄ heterojunction photocatalyst with strong photocatalytic hydrogen production performance has been successfully prepared through the study of Bi₄NbO₈Cl and C₃N₄,which provides ideas for the design of photocatalysts and reference for future photocatalytic research.