Preparation And Performance Research For Bi₄NbO₈Cl-based Nanocomposite Photocatalysts

In this thesis,the pure phase Bi₄NbO₈Cl was prepared by solid-phase method,and then combined with different materials to form heterojunction improving their photocatalytic performance.The as-prepared photocatalysts are used in organic contaminants degradation in water.The main researches in this thesis are as follows:1.In-situ synthesis of Bi₂S₃ quantum dots to improve Bi₄Nb O₈Cl photocatalytic activities:Based on the Bi₄Nb O₈Cl prepared by solid-phase method,through a one-step hydrothermal method,Bi₂S₃ quantum dots were successfully introduced on Bi₄Nb O₈Cl by in-situ synthesis,which were characterized by powder X-ray Diffraction（XRD）,X-ray Photoelectron Spectroscopy（XPS）,Fourier Transform Infrared Spectroscopy（FT-IR）,Liquid Chromatography（LC）and Transmission Electron Microscopy（TEM）.The Bi₂S₃ possesses a strong light absorption ability,which can act as a sensitizer to improve the absorption capacity of composites,meanwhile,the interface effects caused by the formation of composites effectively separate the photo-induced electron-hole pairs and suppress their recombination.Besides,DFT calculation further explained the formation and interfacial properties of Bi₂S₃/Bi₄Nb O₈Cl.2.Construction of 0D/2D Bi₂O₃/Bi₄Nb O₈Cl heterojunction with enhanced photo-degradation performance for organic pollutants:In this section,a two-step method was used to synthesis the 0D/2D Bi₂O₃/Bi₄Nb O₈Cl heterojunction,which combines them through a hydrothermal method and heat-treatment.Bi₂O₃ quantum dots were prepared successfully with a uniform distribution on the Bi₄Nb O₈Cl surface,oxygen vacancies were also introduced,which was demonstrated by a series of characterizations.Compared to bare Bi₄Nb O₈Cl,the photocatalytic activity of 0.5Bi₂O₃/Bi₄Nb O₈Cl increases by 2.6 times in the degradation of Rhodamine B since the formation of heterojunctions,and superoxide radicals and holes are active species in the process of photodegradation,in which holes play a major role.The properties of carriers were investigated by EIS and photocurrent.Besides,the mechanism of photocatalytic degradation was also discussed,which photo-induced electrons and holes were separated in different semiconductors,suppressing the recombination of them and oxygen vacancies existed as active electron trap sites.3.Constructing heterojunction of Bi OCl/Bi₄Nb O₈Cl to enhance photocatalytic activity for organic degradation:In the basis of the Bi₄Nb O₈Cl prepared by solid-phase method,the 2D/2D Bi OCl/Bi₄Nb O₈Cl heterojunction was synthesized by solvothermal method,which was proved by phase analysis and surface state analysis.The photocatalytic performances in the degradation of Rhodamine B（Rh B）,Methyl Orange（MO）,Ciprofloxacin（CIP）and Tetracycline（TC）were better than that of pristine Bi₄Nb O₈Cl.In the same experimental conditions,a series of Bi OCl/Bi₄Nb O₈Cl-x were synthesized,and the Bi OCl/Bi₄Nb O₈Cl-3 possesses the best performance,whose rate constant in Rh B degradation is 9 times higher than that of pristine Bi₄Nb O₈Cl.The reasons why Bi OCl/Bi₄Nb O₈Cl showes an excellent performance was investigated by diffuse reflectance spectra（DRS）,photocurrent（PC）,electrochemical impedance spectroscopy（EIS）and photoluminescence spectroscopy（PL）,briefly,the separation efficiencies of photo-induced carriers were improved due to the formation of heterojunction and the appropriate energy band potentials are beneficial to the redox reactions during photocatalysis.