The Preparation Of Titanium Dioxide Composite Nanofibers And Their Gas-sensing Performance

With the development of industrialization and human society, the poisonous and harmful gases such as NO2, NH3 have become one of the sources of dangers in our production and life. Therefore, it is important to research and development of highly sensitive gas sensor for detection, monitoring and alarm the poisonous and harmful gas.Titanium dioxide is an important transitional metal oxides, which has excellent physical and chemical properties, and is applied in the field of gas sensor. In this thesis, based on controlling the morphology or modified metallic oxide/noble metal, a series of titanium dioxide composite nanofibers were designed and already prepared by electrospinning.All the prepared gas sensing materials possess high activity and sensitivity and great potential of room temperature gas sensing materials. The main research contents are as following.(1)The p-type mesoporous TiO2 nanorods were synthesized via electrospinning process and heat treatment method by using block polymer P123 as soft templates. And the mesoporous TiO2 nanorods was obtained after optimal aging of precursor solution for 6 h. XRD and HRTEM show that mesoporous TiO2 nanorods is composed of rutile titanium dioxide and anatase titanium dioxide, and approved that the mesoporous TiO2 nanorods is p- type semiconductor by MS curves. The nanorods materials have high sensitivity, repeatability and selective at room temperature, when the concentration of NO2 gas is 100 ppm. The sensitivity to 100 ppm NO2 is 76.6%, and the response time and recovery time are within 0.7 s.(2) The p-type In2O3-TiO2 composite nonafibers were fabricated via the electrosponning process, followed by heating to remove PVP, and converted solid composite nanofibers into loose, mesoporous p-type In2O3-TiO2 composited nanofibers,the morphology of the nanofibers consisted of fine grain size TiO2 nanoparticles.The ITCN2(14.3 at% of In2O3) thin film sensor displayed an excellent sensing performance toward NO2, such as low detection limit of 97 ppb and short response time of 3 s to 97 ppm NO2. The enhanced gas sensing could be ascribed to two aspects. On the one hand, the loose and mesoporous structure with 4~6 nm pores and small TiO2nanoparticles(7~12 nm) provided high surface-to-volume ratio than bulks. On the other hand, oxygen defects/vacancies which the indium ions created acted as catalytic centers for gas sensing, causing the faster response of gas sensing towards NO2 at RT.(3) The Porous In2TiO5-TiO2 composite nanotubes were synthesized using electrospinning followed by two-step calcination and were proven to be advantageous for detection of NO2 gas. Porous In2TiO5-TiO2 composite nanotubes sensors demonstrated better sensitivity behavior, especially the sensor fabricated by porous composite nanotubes with 12.5 at% In2TiO5, which has a stable response of 4.04 to 100 ppm, equal to 20 times as high as pure In2TiO5 sensors under the same conditions, with excellent selectivity over other gas species(CO, H2, NH3, H2 S and CH4) at room temperature.The performance enhancement of porous In2TiO5-TiO2 composite nanotubes is thus attributed to the synergistic effect of In2TiO5 with rutile of more vacancies on(110)crystal plane, heterojunction of single-crystal, and nanotubular structure, which favors the mobility of charge carriers and elevates the activity of composite. Hence, the porous In2TiO5-TiO2 composite nanotubes sensor has a potential use for fabricating novel gas sensors at room temperature.(4) The Pd/TiO2 composite nanorods were synthesized with different contents of H2PdCl4 in precursor solution via electrospinning followed by calcination under the mixed atmosphere of N2 and air and reduction. Compared with Pure TiO2 materials, the Pd/TiO2 composite nanorods were proven to be advantageous for detection of NH3 gas.Especially the composite nanorods with 2 wt% Pd, which has a highest response of 6.97 to 100 ppm NH3.At the same time, the surface statuses of the Pure TiO2 and the Pd/TiO2 composite nanorods before and after exposure to the NH3 gas were investigated by XPS spectra and FT-IR spectra at room temperature. The analysis results show that the introduction of metal Pd not only improves the electron exchange rate on the surface of the sensor due to generation of electronic sensitization and chemical sensitization, but also increase the activity sites between ammonia and composite materials owing to inducing the production of lewis acid and brown centers. In addition, synergistic effects with Pd andthe remaining element of C and N could play vital roles in improving the sensitivity of the sensor.