Preparation And Gas Sensing Performance Of WO₃ Nanocrystral And WO₃ Composites

In recent decades,toxic gas such as N02,have caused serious environmental problems,such as photochemical smog and acid rain with the rapid development of economy and industrialization.Thus the detection of NO2 has attracted many attentions for its poisonousness and destructiveness.Thus,there is a great demand to investigate sensitive,reliable,low detect limitation and low-power NO2 sensors.Among metal oxide semiconductors,WO3 is considered to be one of promising sensing materials for detection of NO2.In this work,we prepared WO3 nanoparticles and three metal(Sb,Cd and Ce)doped WO3 samples as NO2 sensing materials by a chemical method,and carefully investigated the corresponding sensors' performance as well as the improved NO2 sensing mechanism.The obtained results demonstrate that the 2 wt%Sb-doped WO3 sample is suitable as a room-temperature N02 sensor.In addition,we have successfully prepared the mesoporous WO3 via hydrothermal method using KIT-6 template and prepared a series of composites loaded with different wt%ZnO.The novel composite of mWO3/5%ZnO is a promising sensing material for fabrication of high performance NO2 sensor.The specific works are summarized as follows:1.WO3 nanoparticles doped with Sb,Cd and Ce were synthesized by a chemical method to enhance the sensing performance of WO3 to NO2 at room temperature.The doping of Sb element can significantly enhance the NO2-sensing properties of WO3.Upon exposure to 10 ppm of NO2,particularly,the 2 wt%Sb-doped WO3 sample exhibits a 6.8 times higher response and an improved selectivity at room temperature compared with undoped WO3.The enhanced NO2 sensing mechanism of WO3 by doping was discussed in detail,which is mainly due to the increase of oxygen vacancies in the doped WO3 samples as confirmed by Raman,PL and XPS spectra.Besides,the narrower band gap is also responsible for the enhancement of response as observed from the corresponding UV-Vis spectra.2.Ordered mesoporous WO3 nanocrystals have been successfully synthesized by a hydrothermal method with mesoporous silica of KIT-6 as a template and phosphotungstic acid as a precursor of WO3.The structure,morphology,and specific surface of WO3 nanocrystals were systematically characterized by SAXS,TEM and BET.To further improve the sensing properties of WO3 to NO2,a series of different wt%ZnO were loaded on the mesoporous WO3 to construct nanocomposites with n-n isotype heterojunction and fabricate sensors.The sensing behaviors show that the 5 wt%ZnO/mWO3 composite based sensor not only exhibits the high response at 150 ? of operating temperature,but also has good selectivity and stability to 1 ppm of NO2,which can be ascribed to the large specific surface and porous channels for gas adsorption and diffusion provided by the ordered mesoporous composite,and the n-n heterojunction formation at interface between both oxides.