| Because of the unique physical and chemical properties of TiO2, it has been widely used as photocatalysis, photovoltage, sensors, micro- or nano-electronic, paints, etc. And new contents have been inserted to the research on basic theory and application of TiO2 by the rise of nanoscience since 1990s. The quantum size effects and surface effect of nanomaterials make great differences between the structure and properties of nanosized TiO2 and regular TiO2, which demonstrated better performance and more broad application prospects. Emergence of electrospinning technique provides a new world for research on TiO2. At present, a large number of researches on TiO2 have been extended to the field of electrospinning; however only a few of study has been carried on the control and effect of the structure of electrospun TiO2 nanofibers. Detailed and accurate analysis on the effect of crystal structure of TiO2 nanofibers on its performance, will directly determine its application.In this thesis, electrospinning technical has been used to prepare a series of TiO2 nanofibers with different structures and functions combined with heat treatment, liquid phase reaction, metal doping, hydrothermal reaction, pore-forming and other methods. Moreover these nanomaterials were studied as gas sensors, humidity sensors, photocatalysis or field-effect transistors, and the effects on the performance of their structures have also been discussed. Specific research results are shown as follows:1. TiO2 nanofibers with different polymorphs were prepared via electrospinning and sintering method. The fiber structures TiO2 were formed by the accumulation of nanoparticles, and their diameters did not change with the sintering temperature; while the size of nanoparticles constituted the fiber structures grown with the increasing of sintering temperature. XRD tests shown that with the increase of sintering temperature, TiO2 gradually transited from anatase to rutile phase. The as-prepared TiO2 nanofibers have excellent gas sensing performance toward acetone. The optimal operating temperature of the sensing devices is 320℃. Different polymorphs of TiO2 gas sensor performed different sensitive characteristics toward acetone at the optimal temperature, TiO2 nanofibers prepared under 500℃shows the most outstanding sensitivity:highest sensitivity, a detection limit of only 1.4 ppm; response time of 4 s and recovery time of 3 s. In addition, the device also showed extremely high selectivity and stability. By adjusting the crystal structure of TiO2 can effectively regulate the gas sensitive properties of materials.2. Li+ or Mg2+/Na+-doped TiO2 composite nanofibers were prepared via electro-spinning, and their morphology, structure and humidity characteristics were also studied. Metal ions can cause thinning of nanofibers' diameter; while the phase transition of TiO2 will also be influenced:Li+ would promote the phase transition, while the right amount of Mg2+/Na+ will also promote the phase transition, but the excess Mg2+ inhibited phase changes occur. After the introduction of metal ions, humidity sensing properties of TiO2 nanofibers have increased dramatically. The content of metal ions and sintering temperature will directly influence the humidity sensing properties. Hysteresis, response and recovery rate, and stability, etc. have shown very good performance. The detection of the real world samples was carried out with as-prepared sensors, and the results demonstrated the usefulness of as-prepared sensor in actual environment. The humidity performance of the samples will be significantly worse after UV irradiation; however the performance will gradually restore when the samples were put into dark conditions for a period of rest. Moreover the samples will exhibit a super-hydrophilic surface after UV irradiation. Those results endow our product with the applications in anti-fogged and self-cleaning exterior tiles.3. TiO2 nanofibers with different contents of anatase/rutile phase were prepared by controlling the sintering temperature. The results of XRD, visible Raman and UV Raman show that, the phase transformation rate of TiO2 nanofiber surface is faster than its inner layer, which causing the differences in the crystal distribution between surface and inner layer. TiO2 nanofibers with different crystal contents show different photocatalytic activity. The sample prepared under 575℃exhibited the best photo- catalytic activity, which is contributed by the synergistic effect due to the interface between rutile and anatase crystallites. Subsequently, two different anatase-rutile core-shell TiO2 nanostructures were prepared. XRD results showed that the two core-shell fibers were mixed crystallites. The layered structures were confirmed by visible Raman and UV Raman results. The photocatalytic activities of the core-shell TiO2 nanostructures are similar with that of pure phases corresponding to their shell layers. These facts show that the photocatalytic activity of TiO2 nanofiber mainly controlled by their surface structure.4. Arranged TIO2 nanofibers were prepared using a parallel plate via electro-spinning and were made into top-gate field-effect transistor devices. The transistor properties of crystalline structure, mesoporous structure and core-shell structure TiO2 nanofibers were studied. Pure crystal phase (anatase or rutile) TiO2 nanofibers did not show transistor device characteristics, but the mixture-phase of TiO2 nanofiber has demonstrated a certain transistor characteristic. Mesoporous TiO2 nanofibers were obtained using P123 as pore-forming agent. Surface area of nanofibers increases with the increasing of P123, which demonstrate the existence of channels. XRD and visible Raman results show that phase transition of TiO2 will be suppressed with the increasing of pore contents. Appropriate pore structures can effectively enhance the FET properties of TiO2 nanofibers, but the FET properties will be decline with too much pores. Quasi-one dimensional anatase-rutile TiO2 heterojunction structure were prepared by hydrothermal and electrospinning methods. The growth of nanorods on the nanofibers surface was characterized by SEM, TEM, XRD, Raman and other tests. The FET characteristics improved significantly and the saturation emerges gradually. The threshold voltage of the device is -52 V, while the saturated electronic mobility is 10.1 cm2V-1s-1. In addition, the device also exhibit extremely excellent stability toward the humidity and time. The excellent performance allows the core-shell structure material has great application prospects in the field of micro- or nano-electronics.
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