The Study Of Piezoelectric Catalysis And Photocatalytic Properties Of Layered Bismuth Strontium Titanate Ferroelectric Materials

In recent years,2 D bismuth-layered ferroelectric material SrBi₄Ti₄O₁₅nanosheets（SBTO NSs）has attracted extensive attention in photocatalytic and piezoelectric catalytic due to its unique bismuth-layered structure and spontaneous polarization.On the one hand,2D layered structure can provide large specific surface area,light irradiation area,and stress-strain ability for catalytic reactions.On the other hand,the built-in electric field induced by spontaneous polarization（spontaneous polarization electric field and piezoelectric electric field）can drive the separation of internal electron-hole pairs.Therefore,this thesis systematically investigated the effects of different synthesis pathways on the performance of SBTO photo-and piezoelectric-catalytic water splitting.On this basis,the catalytic performance of SBTO-precious metal composites was further explored.Details of the study are as follows:（1）Firstly,this thesis investigates the effect of different synthesis methods on the photocatalytic and piezoelectric catalytic water splitting performance of SBTO to determine the best synthesis method for SBTO.The experimental results show that the catalytic performance of SBTO prepared by the hydrothermal method is much better than the other synthesis method,whether photocatalytic or piezoelectric catalytic.On this basis,to remove the impurity phase Bi₂Ti₂O₇,we investigated different hydrothermal conditions on the crystallinity of SBTO by regulating the mineralizer concentration and the hydrothermal temperature.The results showed that the crystallinity of the SBTO NSs was directly affected by the mineralizer concentration,and the optimum mineralizer concentration was 3 M.The crystallinity of the SBTO NSs became better as the hydrothermal temperature increased.In addition,the experimental results of photo-and piezoelectric catalytic water splitting showed that the optimal hydrothermal temperatures of SBTO were 220°C and 240°C,respectively.（2）Secondly,to further enhance the surface activity and light absorption range of SBTO,SBTO-Pt composites were prepared by photo-reduction and different Pt loadings on the photocatalytic performance of SBTO-Pt composites was investigated.The SBTO-Pt-6%composites exhibited a higher photocatalytic hydrogen evolution rate,about 3707.7μmol g^-1h^-1.The effects of different external conditions（light intensity,light source distance,sacrificial agent,and p H）on the photocatalytic performance were investigated to determine the optimum external conditions.The photocatalytic mechanism of SBTO-Pt composites was also proposed by calculating the H adsorption Gibbs free energy（G_H）and comparing the photocatalytic water splitting performance under simulated sunlight and visible light.（3）Finally,to further enhance the deformation ability and surface activity of SBTO and clarify the piezoelectric catalytic mechanism of SBTO,the effects of morphology and different loading exposure surfaces of Ag nanoparticles on the piezoelectric catalytic performance of SBTO were studied,respectively.The experimental results show that,SBTO single-nanosheet has the best piezoelectric catalytic performance compared with SBTO nano-cross-plate,and its piezoelectric catalytic performance for water splitting to hydrogen evolution is 4126μmol g^-1h^-1.Based on the above research,the influence of ultrasonic power on the piezoelectric catalytic performance of SBTO nanosheets was studied with methanol as sacrificial agent to determine the best piezoelectric catalytic conditions.In addition,SBTO-Ag-（001）and SBTO-Ag-（010）composites were prepared by photo-reduction and piezoelectric reduction methods,and the H adsorption Gibbs free energy and piezoelectric catalytic performance of SBTO composites with different load exposure surfaces were studied.Theoretical calculation shows that the surface activity of SBTO-Ag-（010）composite（-0.31 e V）is better than that of SBTO-Ag-（001）composite（-0.65 e V）.Piezoelectric catalysis experiments show that the hydrogen evolution rate of SBTO-Ag-（001）composite(8572μmol g^-1h^-1)is much higher than that of SBTO-Ag-（010）composite(5963μmol g^-1h^-1).Finally,combined with theoretical calculation and experimental results,the mechanism of piezoelectric catalytic water splitting and hydrogen evolution of SBTO-Ag composites is proposed.