Construction And Properties Of Coaxial Nanofibers Based On Polyoxometalates/TiO₂ By Electrospinning

TiO₂is an important photocatalytic and gas-sensitive material with its advantages of non-toxicity,durability and low cost.However,the electrons of TiO₂are easily combined with holes,which greatly shortens the carrier lifetime and seriously hinders the photocatalytic ability and gas response intensity.At present,the main method to solve this problem is to compound TiO₂with other semiconductors to form heterojunction,so that the electron holes can be transferred to different spaces to achieve the purpose of separation.Polyoxometalates（POMs）are a class of structurally diverse metal-oxygen cluster compounds with excellent electron acceptor and good redox properties.The semiconductor-like band structure of polyoxometalates can form a heterojunction with TiO₂,making it an ideal material for modifying TiO₂.In this thesis,one-dimensional coaxial nanofibers based on Polyoxometalates/TiO₂were constructed by electrospinning.The promotion of gas sensing and photocatalytic properties is studied by using the electron acceptor effect of polyoxometalates,and the promotion mechanisms are analyzed.The research contents are as follows:1.SnO₂@PW₁₂@TiO₂ coaxial nanofibers with three-layer core-shell structure was prepared by coaxial electrospinning,and their photocatalytic and gas sensing properties were investigated.When the mass fraction of PW₁₂is 1%,its photocatalytic activity reaches the best value.Compare with pure TiO₂photocatalyst,the degradation efficiency of tetracycline hydrochloride（TCH）and rhodamine B（Rh B）are increased by 33.8%and54.7%,respectively.In addition,the nanofiber was used in gas sensor,which shows a response value of 8.2 to 100 ppm acetone and shows anti-interference to other gases.The target samples were analyzed by UV-visible diffuse reflectance spectroscopy,Mott-Schottky test and free radical capture experiments.It is proved that PW₁₂form a double Z-type heterojunction with TiO₂and SnO₂,which effectively realize carrier separation under the premise of retaining redox strength,so that more carriers participate in the reaction,thereby enhancing its performance.2.（TiO₂/Fe₂TiO₅）@PW₁₂ coaxial nanofibers were prepared by coaxial electrospinning.Compar with pure TiO₂,the heterogeneous material formed by TiO₂and Fe₂TiO₅exhibits obvious gas sensing performance and lower operating temperature.The shallow electron trap effect of polyoxometalates is used to promote electron migration and further improve the performance of the material.The results show that the response value of the best sample（TiO₂/Fe₂TiO₅）@3%PW₁₂to 100 ppm acetone is 6.4,which is 0.35 times higher than that of TiO₂/Fe₂TiO₅heterogeneous material without Polyoxometalates.3.Multi-material（TiO₂/Fe₂TiO₅/ZnFe₂O₄）@PW₁₂coaxial nanofibers were synthesized by coaxial electrospinning in one step.The four components exert a synergistic effect and achieve effective carrier migration to a greater extent.Moreover,the appropriate band position promotes the migration of electrons to the shell PW₁₂,shortens the path of electron migration to the surface of the material,and reduces the recombination rate of electrons and holes in the migration process.When the mass fraction of PW₁₂is 5%,the response value to acetone can reach 12.8,which is 3.2 times that of pure TiO₂.In this thesis,coaxial nanofibers based on Polyoxometalates/TiO₂were prepared by coaxial electrospinning technology,which provide reference information for polyoxometalates to promote the performance of photocatalysts and gas sensors with TiO₂as the core material.