Study On Preparation,Properties And Photocatalytic Mechanism Of Bi-Based Photocatalyst

Semiconductor photocatalytic technology has been widely studied by researchers because of its potential applications in energy conversion and environmental remediation.In recent years,Bi-based semiconductor photocatalysts have become the hot research materials due to their non-toxic properties,adjustable band gap and unique physical and chemical properties.However,Bi-based photocatalytic materials also have some disadvantages,such as weak photocatalytic activity and poor stability.In order to improve these shortcomings and further enhance their photocatalytic activities.In this work,several typical Bi-based semiconductor materials were selected as the research objects.The influences of the modified microstructure of the composite materials on their macroscopic photocatalytic performances were discussed by through the construction of composites.The synergistic photocatalytic mechanism was also analyzed.It mainly includes the following sections:（1）Study on preparation,properties and photocatalytic mechanism of Bi₂SiO₅/Bi VO₄composite photocatalyst.Bi₂SiO₅/Bi VO₄composite photocatalyst was obtained by in-situ hydrothermal growth of Bi VO₄on Bi₂SiO₅nanosheets.The photocatalytic activity of the as-prepared composite photocatalyst with different molar ratio of raw materials was discussed.The microstructure,morphology and optical properties of the composite photocatalyst were characterized by XRD,TEM,UV-vis DRS,XPS and electrochemical tests.Moreover,with increasing the amount of Bi₂SiO₅,the photocatalytic degradation efficiency of the composite photocatalyst towards tetracycline（TC）and levofloxacin（LEV）takes on a trend of first increasing and then decreasing under visible light illumination.When the theoretical molar ratio of Bi₂SiO₅to Bi VO₄reaches 2:3,the photocatalytic efficiency of the as-prepared composites is the highest,that is 72.2%for TC and 80.3%for LEV solution in 120min.Compared with pure Bi₂SiO₅and Bi VO₄samples,the degradation efficiency of the as-prepared composite photocatalyst is increased by 28.7%and 5%towards TC,and 72.7%and 10.6%towards LEX,respectively.After five cycles experiment,the degradation efficiency of the samples towards TC and LEV is 72.0%and 73.0%,respectively.In addition,h⁺is the major active species during the process the photocatalytic degradation for LEV,while·O₂^-and·OH are the secondary and tertiary active species.The improvement of photocatalytic performance may be ascribed to the formation of n-n heterojunction between Bi₂SiO₅and Bi VO₄in the as-obtained composite photocatalyst,which improves the separation and migration efficiency of photogenerated electron hole pairs.（2）Study on preparation,properties and photocatalytic mechanism of Bi₂SiO₅/Ag₆Si₂O₇composite photocatalyst.Bi₂SiO₅/Ag₆Si₂O₇composite photocata-lyst was obtained by in-situ growth of Ag₆Si₂O₇on Bi₂SiO₅nanosheets via a physical stirring method.The photocatalytic activity of the composite photocatalyst prepared with different ratio of raw materials was discussed.The microstructure,morphology and optical properties of the composite photocatalyst were characterized by XRD,TEM,UV-vis DRS,XPS and electrochemical tests.The experimental results show that with increasing the amount of Bi₂SiO₅,the photocatalytic degradation efficiency of the as-prepared composite photocatalyst towards TC takes on a trend of first increasing and then decreasing under visible light irradiation.When the theoretical molar ratio of Bi₂SiO₅to Ag₆Si₂O₇is 2:1,the photocatalytic efficiency of the as-prepared composite reaches the highest,and the oxidation degradation of 72.8%TC solution can be achieved within 120 min under visible light illumination.Compared with pure samples of Bi₂SiO₅and Ag₆Si₂O₇,the degradation efficiency increases by 34.8%and 44.9%,respectively.In addition,h⁺and·O₂^-are the main active species in the photocatalytic degradation of TC,and·OH is the secondary active species.The improvement of photocatalytic performance may be ascribed to the formation of heterojunction between Bi₂SiO₅and Ag₆Si₂O₇in the as-synthesized composite photocatalyst,which reduces the interfacial charge transfer impedance and improves the separation and migration efficiency of photogenerated electron hole pairs.（3）Study on preparation,properties and photocatalytic mechanism of Bi/Bi₂O₃composite photocatalyst.Based on Bi nanoparticles,Bi/Bi₂O₃composite photocatalyst was prepared via an in-situ calcination oxidation method.The photocatalytic activity of the as-obtained composite photocatalyst,which were prepared in different calcination time,was discussed.The microstructure,morphology and optical properties of the composite photocatalyst were also characterized by XRD,TEM,UV-Vis DRS,XPS,EPR and electrochemical tests.The analytic results show that when the calcination time is 15 min,the as-synthesized composite photocatalyst has the highest photocatalytic efficiency,and can achieve the oxidation degradation of about 86%TC solution within 120 min under visible light.Moreover,the as-prepared composite sample still has 61.5%degradation efficiency for TC after 5 photocatalytic cycle experiments.In addition,h⁺is the most active species during the photocatalytic degradation of TC,and·O₂^-is the secondary active species.The reason of the improved photocatalytic performance may be that the synergistic effect of surface plasma effect（SPR）and oxygen vacancy can improve the light absorption and enhance the separation and migration efficiency of photogenerated electron hole pairs.