Preparation Of SrBi₄Ti₄O₁₅ And Study Of Their Performance In Photocatalytic CO₂ Reduction

Photocatalytic CO₂ reduction is a green and clean CO₂ conversion technology,which not only realizes the effective conversion and storage of solar energy to chemical energy,but also realizes the recycling of carbon.In the reactions,the development of stable,efficient and cheap photocatalysts is considered to be the crucial in the wide application of photocatalytic CO₂ reduction.Layered structure[Bi₂O₂]²⁺semiconductors have received extensive attention in the field of energy and environment due to their unique layered structure,optical and electronic properties.However,the low charge separation efficiency driven by rapid recombination and the slow interfacial mass transfer process are limited the large-scale develop of bismuth-based materials.In this work,Sr Bi₄Ti₄O₁₅ is taken as the research object with excellent advantages of structural,which is the intersection of the traditional ferroelectric layered bismuth-based semiconductor and the perovskite structure crystal.However,the performance and selectivity in photocatalytic CO₂ reduction process of Sr Bi₄Ti₄O₁₅needs to be improved because of the photocatalyst is a single component,which has shortcomings such as insufficient active sites.Herein,the microstructure of Sr Bi₄Ti₄O₁₅was regulated by means of structural modification,heterostructure construction and metal ion doping to improve the absorption performance of light,enhance the separation efficiency of photogenerated charge,increase the number of active sites,and finally achieve high efficiency and high selectivity of CO₂ photocatalytic conversion.The main research contents are as follows:（1）Sr Bi₄Ti₄O₁₅ photocatalyst with Bi₂O₃ quantum dots was successfully synthesized by one-step hydrothermal method using hexadecyl trimethyl ammonium bromide（CTAB）as assistant.XRD and TEM tests show that the composite photocatalyst forms an ultra-thin sheet structure and is uniformly loaded with a large number of Bi₂O₃ quantum dots.Meanwhile,BET shows that the composite photocatalyst has a larger specific surface area,which greatly shortens the electron diffusion distance within the photocatalyst,increases more active sites on the surface of the photocatalyst,and enhances the separation efficiency of photogenerated carriers.With full-spectrum light irradiation,the photocatalytic CO₂ reduction activity of Sr Bi₄Ti₄O₁₅ with 0.08 g CTAB（8SBTO-1）displays the highest CO production rate of73.0μmolg^-1,which is about three times that of pure SBTO(27.2μmolg^-1).And the yield of CH₄ is 30.2μmolg^-1,which is 30 times of pure SBTO.Electrochemical test results revealed the electron transfer process in the catalyst.In addition,CO₂ was labeled by isotope labeling method,and the final product was analyzed by gas chromatography,which proved that the product in the photocatalytic reaction process came from the transformation of CO₂ rather than the decomposition of photocatalyst.The intermediate products in the reaction process were analyzed by in situ infrared test,which further speculated the mechanism of photocatalytic reduction of CO₂.（2）In order to further improve the activity and selectivity of Bi₂O₃/Sr Bi₄Ti₄O₁₅,and improve the separation efficiency of photogenerated electrons and holes.In this work,Bi₂O₃/Sr Bi₄Ti₄O₁₅ composite photocatalyst doped with different Co ions content was successfully prepared by hydrothermal method.Among them,the photocatalyst5SBTO-2 with Co doping content of 5%possessed the best photocatalytic performance for CO₂ reduction,which the final products were CO,CH₄and CH₃OH,with yields of14.1,62.3 and 54.1μmolg^-1,respectively.It is worth noting that,compared with the photocatalyst before metal ion doping,the material doped with Co ions has improved selectivity to CO₂ reduction products,while the yield of CO decreases and the yield of CH₃OH increases.XRD,TEM and XPS fully proved that Co ions were successfully doped into Bi₂O₃/Sr Bi₄Ti₄O₁₅ composite photocatalyst,and DRS indicated that the photocatalyst doped with Co ions has a wider range of light response.PL and electrochemical tests proved that the doped composite photocatalyst reduced its band conductance potential and the band gap width of the photocatalyst,and widened the response range of the composite photocatalyst to light.Finally,it can further promote the separation of photogenerated electrons and holes on the surface of the catalyst,so that more electrons can participate in the reaction.BET test results showed that the specific surface area of the composite photocatalyst increased after doping Co ions,providing more active sites for adsorbing CO₂.The results show that 5SBTO-2photocatalyst has high stability through cyclic experiment and XRD and XPS analysis before and after reaction.The mechanism of photocatalytic CO₂ reduction process was deduced by analyzing the reaction intermediates through in situ infrared.In this work,two bismuth-based photocatalysts were prepared by hydrothermal method,which showed high efficiency,stability and other characteristics in the photocatalytic CO₂ reduction process,providing some new insights for the design of bismuth-based photocatalysts that can significantly capture CO₂ and effectively reduce CO₂.