Preparation Of Heterogeneous Bismuth Silicate Composite Photocatalyst And Study On Its Photocatalytic Performance

Bismuth silicate includes Bi12SiO20,Bi2SiO5 and Bi4Si3O12.And their applications in photocatalysis have received widespread attention in recent years.Among them,Bi12SiO20 has photocatalytic activity under visible light,and Bi2SiO5 has a good photocatalytic activity only under ultraviolet light irradiation.At present,the development of new photocatalysts based on the characteristics of heterojunctions for improving their application has become a new research direction in the field of photocatalysis.Heterojunction composite photocatalysts can promote the separation of electron-hole pairs,thereby improve the photocatalytic efficiency of materials.However,there are few studies on the preparation and performance of heterogeneous composite photocatalytic materials in bismuth silicate system.Through the preparation of bismuth silicate composite photocatalyst,the use of heterojunctions formed between semiconductors to improve its photocatalytic performance.In this dissertation,heterogeneous bismuth silicate powders were prepared by sol-gel method using bismuth nitrate as the source of bismuth and ethyl orthosilicate as the source of silicon.Bi12SiO20-Bi2O2SiO3 powders were prepared by controlling the molar ratio of bismuth and silicon(nBi:nSi)in the precursor.Ag-Bi12SiO20-Bi2O2SiO3 ternary composite powders were synthesized by photoreduction method.The modified composite powders were prepared by introducing polystyrene balls into the precursor and loaded on its surface Ag particles.Meanwhile,the Bi12SiO20-Bi2O2SiO3-BiOBr double heterojunction composite powders were synthesized by introducing NaBr.The phase composition,micro-morphology and photoelectric properties of the prepared powder were characterized and analyzed.At the same time,rhodamine B(Rh B)was used as the target degradant to characterize the photocatalytic performance of the sample and analyze its degradation mechanism.The effects of heat treatment temperature,heat treatment time and nBi:nSi on the photocatalytic performance of heterogeneous bismuth silicate were studied.The effects of different Ag loading contents and concentrations on the photocatalytic performance of different Bi12SiO20-Bi2O2SiO3 systems were analyzed.The influences of the content of Polystyrene spheres(PS)and heat treatment process on the morphology and property of bismuth silicate powders were investigated.The effects of pH and the concentration of NaBr on the morphology and properties of the obtained Bi12SiO20-Bi2O2SiO3 composite powders were studied.Moreover,the photocatalytic mechanism of different systems was explored.The main results are as follows:(1)Bi12SiO20-Bi2O2SiO3 powders were successfully prepared by the sol-gel method.When nBi:nsi is 6:1,the phase of the powders is mainly Bi12SiO20,and there is little Bi2O2SiO3 phase.The shape of the sample is irregular.Moreover,the powders have the minimum forbidden band width(2.58 eV).And the sample shows good photocatalytic activity on Rh B under visible light irradiation,whose degradation rate can reach 95.37%for 150 min.(2)Ag-Bi12SiO20-Bi2O2SiO3 composite powders were successfully prepared by photo-reduction.When the concentration of silver nitrate is 2 mg/mL and the volume is 5 mL,the photocatalytic performance is best,and the degradation rate of Rh B under visible light irradiation for 75 min can reach 97.66%.The excellent photocatalytic performance is attributed to the heterogeneous interface formed between Ag and Bi12SiO20-Bi2O2SiO3 after Ag loading,which can effectively improve the separation of electron-hole pairs.The synergy between the heterojunction and the hetero interface makes it have better photocatalytic activity.At the same time,the presence of Ag particles can receive photogenerated electrons,promotes the separation of electron-hole pairs,and transfers the electrons generated by light excitation to the surface of the catalyst under the action of surface plasmon resonance to combine with the adsorbed O2 to produce ·O2-with strong oxidation ability,reacts with Rh B to form CO2 and H2O.(3)Bi12SiO20-Bi2O2SiO3 powders were prepared by mixing PS colloidal spheres with the precursors.The effects of PS colloidal spheres on bismuth silicate powders under different conditions were studied.When the PS spheres of 4 mL PS solution were added into the precursor,the powders calcined at 500℃ for 3 h and then at 630℃ for 5 h have the best photocatalytic performance,and the degradation rate of Rh B under visible light irradiation for 60 min can reach 95.60%.And then the Ag-Bi12SiO20-Bi2O2SiO3 composite powders were synthesized by locating Ag.The results show that when the concentration of the silver nitrate solution is 2 mg/mL and the dosage is 5 mL,the obtained Ag-Bi12SiO2O-Bi2O2SiO3 powders has the best photocatalytic performance,and the degradation rate of Rh B reached 97.01%under visible light irradiation for 45 minutes.The addition of PS spheres changes the micro-morphology of heterogeneous bismuth silicate,reduces the particle size of the sample and provides more active sites for the photocatalytic reaction process,so the photocatalytic performance is greatly improved.(4)Bi12SiO20-Bi2O2SiO3-BiOBr powders were successfully prepared by partial ion exchange method.When the pH value is 1 and the concentration of sodium bromide is 1.30 mol/L,the composite powders exhibit a synergistic effect of adsorption-photocatalysis on Rh B under visible light irradiation.The adsorption rate of Rh B in the dark reaction process for 30 min is 79.42%,and the total degradation rate of Rh B after 20 minutes under visible light reaches 97.19%.In the system,the double heterojunction can accelerate the separation of electron-hole pairs,thereby greatly improve its photocatalytic performance.In addition,the synergistic effect of adsorption and photocatalysis can effectively improve the degradation rate of Rh B by bismuth silicate system.