Study On Synthesis And Properties Of Bi₄nbo₈cl Photocatalytic Material

Recently,Bi₄NbO₈Cl has been demonstrated to be a stable and efficient visible-light driven photocatalyst for water splitting,and with a relatively special energy band.In theory,it can split water to H₂ and O₂ under the visible-light irradiation.However,due to the unsuitable conduction band,the efficiency of photogenerated charge separation is low,which seriously restricts its photocatalytic activity.So,through construction of Z-scheme heterojunction,surface modification and metal ion doping,Bi4NbO8Cl with different structure was prepared,which improved the charge separation and migration efficiency of photogenerated charge and improved the activity of photocatalytic water splitting.In this study,the Z-scheme heterojunction g-C3N4/Bi4NbO8Cl fabricated between g-C₃N₄ derived from thermal polymerization and Bi₄NbO₈Cl obtained by high temperature solid state method by a facile high-energy ball milling method.Bi4NbO8Cl was optimized by molten salt method with different melt salt ratio,and different urea and NaOH solutions with different pH values modified the surface of Bi₄NbO₈Cl.The four elements V,Ta,Sr,and La were selected to dope during the preparation of Bi₄NbO₈Cl by the molten salt method and successfully obtained.Bi₄NbO₈Cl doped with four ions,respectively.The above strategies have effectively improved the photogenerated charge separation,migration efficiency and light absorption performance of Bi₄NbO₈Cl,and enhanced its activity of photocatalytic water splitting under visible-light irradiation.Among them,the Z-scheme heterojunction of g-C₃N₄/Bi₄NbO₈Cl exhibits an enormously promoted photocatalytic activity for H₂production with visible light illumination（λ>420 nm）,and the H₂ evolution rate is 6.9and 67.2 times higher than that of bare g-C₃N₄ and Bi₄NbO₈Cl,respectively.The morphology of Bi₄NbO₈Cl prepared by the molten salt method with different molten salt ratios is regular and the surface and edges are smooth.The NaOH solution with pH=9.5 is used to modify the surface of the Bi₄NbO₈Cl prepared with the best molten salt ratio.The hydrogen production rate of the modified sample was 10.6 times that of unmodified Bi₄NbO₈Cl.Among the Bi₄NbO₈Cl samples doped with metal ions,only the V-doped samples have improved oxygen production performance,which is 1.3times that of the Bi4NbO8Cl samples.The main factors for improving the photocatalytic water splitting performance of Bi₄NbO₈Cl by the three methods are to promote the separation and migration of their photogenerated charges.