Structural Regulation And Property Of Porous And Flexible TiO₂-SiO₂ Nanofibrous Mats

The structure regulation and mechanical property improvement of inorganic oxide nanofibers are the hot and difficult topic in current researches.Considering the internal structure of nanofibers has a critical impact on its material properties,inorganic oxide nanofibers with porous internal structures have been prepared,such as hollow fibers and"lotus root-like"fibers.Nanofibers with porous internal structure possess larger specific surface area,more active sites,rich internal space,and more heterogeneous interface,these characteristics are of great significance to the physical and chemical properties of the materials.Porous inorganic oxides have been widely used in electrode materials for lithium-ion batteries,photoanodes for solar cells,photocatalyst,sensors,drug release and tissue engineering,and so on.At present,the methods for preparing hollow and"lotus root-like"inorganic oxide nanofibers mainly include coaxial electrospinning?multifluidic electrospinning?,hard-template method,the method of controlling heating process,and the method of microemulsion electrospinning.Among many methods,coaxial electrospinning?multifluidic electrospinning?requires intricate spinning nozzles;moreover,the solvent choice of the core layer and the parameter control during the spinning process are difficult,the structure of the fibers is unstable,so it is not universally applicable.The process of the hard-template method is complicated and energy-consuming.The method of controlling heating process is not common and is not suitable for the preparation of composite inorganic oxide fibers.Compared with these methods,microemulsion electrospinning is a single needle electrospinning without the requirement for special structure spinneret.It is simple,easy to use,universal and efficient,and can be used to prepare nanofibers with a length of several centimeters after calcination,so it has attracted wide attention.TiO₂ is outstanding among various inorganic oxides because of its abundant reserves,low price,non-toxicity,environmental friendliness,good chemical and photo-corrosion resistance,and strong oxidation activity.SiO₂ has also received widespread attention due to its good thermal conductivity,higher strength,larger specific surface area,excellent thermal stability and chemical resistance.However,the brittleness of the inorganic oxide nanofibrous membranes is a fatal defect.Improving the mechanical property of the inorganic oxide nanofibrous membranes is significant and profound for expanding its application range and improving its application performance.In this paper,TiO₂ and SiO₂ nanofibers with hollow and"lotus root-like"structures were prepared by microemulsion electrospinning.The inner structure of the fibers was regulated by changing precursor solution compositions.The regulation mechanism of microemulsion electrospinning on the internal structure of inorganic oxide nanofibers was discussed in depth.The nanofibers were applied in different fields,investigating whether the rich internal structure significantly improved the application performance of the materials.On this basis,the brittleness of the fibrous membranes was improved,and flexible inorganic oxide nanofibrous membranes were prepared to improve theirs application performance.The specific research is as follows:?1?"Lotus root-like"TiO₂ nanofibers were prepared by microemulsion electrospinning combined with calcination,and the interior structure was regulated by changing the ratio of continuous phase TBT to dispersed phase paraffin oil in the precursor solution.TiO₂ nanofibers were used as the anode materials of lithium-ion batteries,and the influence of the internal structure changes of the fibers on the electrochemical performance of lithium-ion batteries was investigated.The results showed that the pores inside the fibers were channel structure distributed along the fiber axis.As the ratio of TBT to paraffin oil increases,the number of channels inside the fiber gradually increases,resulting in the specific surface area gradually increases.Compared with solid TiO₂ nanofibers,the electrochemical performance was obviously improved,which showed great potential as the anode materials for lithium-ion batteries.?2?In order to further regulate the internal structure of TiO₂ nanofibers,determine whether hollow nanofibers can be prepared by microemulsion electrospinning,hollow TiO₂ nanofibers were prepared by the method of microemulsion electrospinning and calcination,and the nanofibers were calcined at different temperature including 500,700,900�C,thus TiO₂nanofibers with different crystal forms were prepared.The properties for photocatalytic degradation of methylene blue were investigated.The results indicated that TiO₂ nanofibers not only showed hollow structure,but also possessed abundant mesoporous structure on the wall of TiO₂ nanofiber.The photocatalytic performance was significantly improved compared to solid TiO₂ nanofibers,mainly because the larger specific surface area can provide more active sites,and is beneficial for improving the electron-holes separation efficiency.?3?In order to investigate whether the microemulsion electrospinning is universal and the regulation rule is consistent,�lotus root-like�SiO₂ nanofiber were prepared by microemulsion electrospinning method,and the internal structure of SiO₂ nanofibers was regulated by changing the ratio of the continuous phase TEOs to dispersive phase paraffin oil in the precursor solution.SiO₂ nanofibrous mats were used as the supporting material of phase change materials,which adsorbed quinary fatty acids to obtain form-stable phase change materials?FSPCMs?.The results showed that the microemulsion electrospinning has universal applicability,and as the ratio of TEOs to paraffin oil decreased,the number of internal channels of SiO₂ fibers gradually decreased,which was consistent with that of TiO₂ nanofibers.Thus the specific surface area of SiO₂ nanofibers gradually decreased,and the enthalpy of the FSPCMs decreased.?4?The above-prepared SiO₂ nanofibrous membranes had poor mechanical properties and obvious brittleness,which limited its wide applications.It is urgent to prepare the soft SiO₂nanofibrous membranes.Therefore,the method of microemulsion electrospinning was applied to prepare SiO₂ nanofibers with certain softness and hollow structure.SiO₂ nanofibers were used as the supporting materials of phase change material to adsorb quinry fatty acid so as to obtain the FSPCMs.The results indicated that the prepared nanofibrous mats had a certain degree of flexibility,there was no obvious crease on the mats after a series of folding,and the enthalpy values of the FSPCMs was slightly increased compared with the above-prepared SiO₂fibrous membranes.?5?Mechanical properties of TiO₂ nanofibrous mats prepared in the first two chapters are poor.Improving the mechanical properties of TiO₂ nanofibrous membranes by SiO₂ doped TiO₂has been proven to be an effective method.Therefore,in this paper,flexible TiO₂/SiO₂composite nanofibrous membranes with mesoporous,"lotus root-like"and hollow structure were prepared by microemulsion electrospinning.The proportion of the continuous phase to the dispersed phase was adjusted by changing the amount of paraffin oil added,and the internal structure of the fiber was also regulated.It is applied to dye adsorption.The results showed that with the increase of the content of paraffin oil,the interior of the fiber underwent a change from mesoporous,"lotus root-like"to hollow structure,and its specific surface area was above 500m²�g^-1,showing excellent adsorption performances.Besides,TiO₂/SiO₂ nanofibrous membranes showed good flexibility.