Research On Synthesis And Their Gas Sensing Property To No₂ Of SnO₂ Based Gas Sensing Material

The stannic oxide is known to be a cubic system material with the characteristics of rutile phases and n-type semiconductor.Due to its ideal physical and chemistry stability,great mechanical properties and easy preparing process,SnO₂ have drew abroad attentions from the researchers through the years,playing a core role in the area of metal oxide semiconductor gas sensing materials.However,there are obvious limitations for the application of the traditional SnO₂ sensing materials:First of all,the low selectivity may not be able to guarantee the accuracy of detecting signal for pollutants from the disturbing of other gases,making the test lack of convincible.Besides,the short service life of traditional SnO₂ limits the reliability of the results and the long-term application.In addition,the high operating temperature that the SnO₂ sensing materials require in the test process also greatly raises the cost of application.To solve these problems,porous SnO₂ sphere with large specific surface areas were synthesized and modified to improve the response and reduce the operating temperafture.In this thesis,the SnO₂ porous nanocomposites have been successfully synthesized through a facile hydrothermal method followed by a modifying process with Sb₂O₅ nanoparticles to form p-n conjunctions.The gas sensing properties and mechanism have been studied.The main contents of research in this thesis are shown as follows:1.By controlling the mass ratio,reacting temperature and time,the porous SnO₂ sphere was synthesized through a one-step facile hydrothermal method.Stannic chloride hydrated was used as Sn source while absolute methanol was used as solvent and polyvinylpyrrolidone?PVP?as surfactant.Based on the X-ray diffraction?XRD?patterns of SnO₂ porous sphere,the refinement results matched well with the pure peaks of rutile phases without other impurity.The SEM and TEM pictures reveal that the SnO₂ porous sphere has a diameter of 0.5-1 ?m,consisting of a large number of nanoparticles with diameter of 5-20 mn.The measured BET surface area of the SnO₂ porous sphere is 39.3 m2g-1.2.The SnO₂ porous sphere as synthesized were prepared as gas sensor and tested the gas sensing properties to NO2.The results show that the best operating temperature is 260 °C.Compared with reported traditional amorphous SnO₂,the porous SnO₂ sphere shows a better response and a shorter response time.The better sensing properties of the porous structure may attribute to the larger specific surface area which would be able to provide more active exposed surface.3.Based on the as-prepared SnO₂ sphere with porous structure,the Sb₂O₅ modified SnO₂ porous sphere was conducted by a precipitation method with SbCl3 as source of Sb.The SEM,TEM and EDX element mappings results reveal that Sb₂O₅modifier are shown as thick sheets with the average size under 10 nm,uniformly distributing on the surface and inner of the porous SnO₂.Compared with pure SnO₂ porous sphere,the measured BET surface area of the Sb₂O₅ modified SnO₂ porous sphere reduced to 37.2 m2g-1.Through the analysis of XPS,the composite is observed to be pure and the valence state of Sb in the product is +5?4.The Sb₂O₅ modified SnO₂ porous sphere as synthesized were prepared as gas sensor and tested the gas sensing properties to NO2.The results showed that the best operating temperature reduced to 260 ? and the response value increased triple as the value of unmodified SnO₂ under the same concentration of NO2.And the Sb₂O₅ modified SnO₂ porous sphere nanocomposites also displayed superior selectivity to NO2 gas comparing with other test gases.The excellent improvement of sensing properties may be attributed to the great number of p-n conjunctions formed by the contacting between the p-type modifier Sb₂O₅ and the n-type semiconductor SnO₂.The conjunctions may provide a new barrier during the transportation of the electrics and reduce the reacting activation energy and then improve the sensing properties of the Sb₂O₅ modified SnO₂ porous sphere nanocomposites.In summary,SnO₂ porous sphere was successfully synthesized and modified with Sb₂O₅ nanoparticles.Gas sensing test results showed that the response to the NO2 had been greatly improved and the optimum operating temperature had reduced by means of modifying porous SnO₂ with Sb₂O₅.Due to the facile synthesis processand superior gas sensing properties,the Sb₂O₅ modified SnO₂ porous sphere nanocomposites would be greatly potential in gas sensing application.