One-dimensional Oxide Material: Electrospinning Fabrication And Their Optical And Gas Sensing Properties

Due to the unique, fascinating properties and actual value, one-dimensional (1D) functional materials have gained wide attention all over the world. Currently, the studies on 1D nanostructure are in an unprecedented and prosperous period and have been developed to a hot area that being filled of new opportunities and freshness. Among various methods used to fabricate 1D structure, electrospinning is a very flexible technique. It can control the morphology, structure, composition and even macroscopic appearance of 1D material from different ways. With the development of human society and the scientific level, people are no longer satisfied with only studing on the classical electrospinning materials, they further develop the 1D structure, and hope to find some new properties. Ongoing studies have demonstrated that after addition of some rare earth (RE) component into 1D materials, in the form of surface additives or dopants, their physical properties could be improved in many cases. These enhanced properties are not limited to optical area, but also can be extended to sensing field. However, there are many rare earth elements and they have similar but different nature. Therefore, systematic study on the influence of RE to the morphology, structure and function of 1D materials is important both for understanding the basic properties and development of new materials with new-applications.In this thesis, electrospinning 1D structure and RE modified functional materials are the two main paths throughout the entire article. On one hand, we used electrospinning to fabricate different nanowires (NWs) and nanotubes (NTs) materials. Herein, we mainly focused on NTs structure and systematically studied on the factors affecting NTs formation and the formation mechanism of NTs. On the other hand, we systematically studied the photoluminescenct properties or gas sensing performance of various RE doped ID nanomaterials. The results are as follows:(1) We fabricated europium doped lanthanum phosphate NWs and NTs with uniform diameters by electrospinning method for the first time and their crystalline structure, morphology and luminescence properties were carefully studied. By changing the ratio of inorganic to PVP in the precursors, ultralong, uniform, and size-controllable NTs and NWs were obtained, ranging of 60-300 nm. The average wall thicknesses of the nanotubes were-20 nm. The structure research results indicate that as the ratio of the inorganic to PVP decreased, a phase transition from LaPO4 to La3PO4 gradually occurred and the formation mechanism of the different lanthanide phosphate nanowires and nanotubes is also discussed carefully. The studies on photoluminescence indicated that the emission intensity, lifetime and the intensity ratio of 3Do-7F2 to 5Do-7F1 all depended strongly on the structure of the electrospinnig products.(2) Porous In2O3 NTs and NWs in cubic phase were fabricated via electrospinning. The NTs yield an average outer diameter of-80 nm and wall thickness of-15 nm, while the NWs yield a diameter of-120 nm. The gas sensing properties of the prepared NTs/NWs were measured for H2S. The results demonstrate that the sensors had optimum and high responses to H2S at room temperature in dilute 1-100 ppm concentration range. They also display excellent selectivity, anti-interference and stability. The gas sensing mechanism at room temperature was attributed to the sulfuration of In2O3. The present electrospun In2O3 NTs/NWs have demonstrated potential applied for H2S gas detection under room temperature.(3) We successfully fabricated porous In2O3:RE (RE= Gd, Tb. Dy, Ho, Er, Tm, Yb) NTs samples and the room temperature gas sensing properties of In2O3;RE NTs were also studied. The structure analysis results demonstrated that with the increase of doped RE atom order, the band gap energies and the resistances in air of cubic In2O3.RE gradually increased, the lattice constants also had the decreased trend. As a consequence, it was exciting to observe that the doping of RE gradually and significantly improved the gas sensing properties of In2O3:RE NTs to H2S gas as RE varied from Gd to Yb in order. In contrast to undoped In2O3 NTs, the room-temperature response sensitivity of the In2O3:Yb NTs sensors to 20 ppm H2S increased about seven times and reached as high as 1241, while the response time of the In2O3:Yb NTs sensors was shortened four times and reached～49s.(4) The porous binary In2O3-CeO2 oxides NTs in cubic phase were first fabricated by electrospinning. By adjusting the In2O3 and CeO2 molar ratio, the out diameters and wall thicknesses of the final composites were tuned ranging of 90-180 nm and 15-9 nm, respectively. The band gap of the binary oxides gradually decreases, and the ratio of Ce3+ to Ce4+ increases with the increase of CeO2 implying that surface oxygen vacancies gradually increase. The gas sensing test reveals that when the content of CeO2 is appropriate, the as fabricated In2O3-CeO2 NTs could be bi-functional gas sensors to detect H2S at low temperature(25-110℃) while acetone at relative high temperature (300℃). The In75Ce25 NTs sensor is an optimum one. which exhibits the highest response of 498 to H2S at 80℃and the highest response of 30 to acetone at 300℃. In contrast to the pure In2O3 sensor. the response and recovery times as well as the sensing reaction barrier height for In75Ce25 both degrade considerably.