Investigation On The Preparation And Properties Of SnO₂Porous Nanosolid

In this dissertation, the solvothermal hot-press (SHP) method was used to prepare SnO2porous nanosolid (PNS), in which the nanoparticles connected to each other and channels for carrier migration formed. For further improving the carrier mobility of SnO2PNS, it was calcined in high-pressure oxygen to reduce the oxygen vacancies and improve the interfacial crystallinity of SnO2nanoparticles. Furthermore, the SnO2PNS gas sensor was fabricated, and it was calcined in different atmospheres to analyse the relationship between the gas-sensing performance and carrier mobility. Finally, the sol-gel method was combined with the SHP one to prepare SnO2PNS with uniform pore size and high specific surface area. Besides, the SnO2PNS thus prepared exhibited rather good gas-sensing performance. The major results are listed below:(1) SnO2PNS was prepared by SHP method by using commercial SnO2nanoparticles as the starting material. The influences of the key parameters, including solvent volume, hot-press temperature, pressure and calcining temperature, on the pore structure and electric performance of SnO2PNS were explored. The results suggest that large amount of pores/channels have formed after SHP process. Moreover, it is proved that all the pore diameter distribution, pore volume and specific surface area of SnO2PNS can be modulated by optimizing the experimental parameters. As a result, the carrier concentration and mobility also changed accordingly. For3g SnO2nanoparticles used in the experiments, the SnO2PNS possesses optimumal pore structure and electric properties when the solvent volume, hot-press temperature, pressure and calcining temperature were5ml,200℃,60MPa and500℃, respectively.(2) In order to improve the carrier mobility of SnO2PNS, they were calcined both in different atomospheric-pressure atmospheres and high-pressure oxygen. The Hall effect measurement and the complex impedance spectra are used to analyze the changes of electric properties and related mechanism. The results suggest that during the calcining process, the experimental parameters greatly affected the electric properties of SnO2PNS:calcining at500℃in oxygen can facilitate the annihilation of oxygen vacancies within the interfacial region of SnO2nanoparticles, thus the carrier mobility greatly improved. In comparison, when being calcined at500℃in N2, the existing oxygen vacancies in SnO2cannot be effectively eliminated, contrarily, more new oxygen vacancies must have formed in SnO2nanoparticles. This phenomenon made the carrier concentration increased while the mobility decreased. However, calcining in high-pressure oxygen obviously increased the rate of oxygen vacancy annihilation, resulting in the increase of carrier mobility. When being heated at350℃in high-pressure oxygen, three processes may have happened within SnO2PNS:the re-distribution of oxygen vacancies, the annihilation of oxygen vacancies and oxygen molecule chemisorption. The last process competes with the former two processes, and they reached an equilibrium at a specific oxygen pressure, for example,4MPa in our sample, the highest carrier mobility of SnO2PNS reached35cm2/(V·s).(3) After being calcined in different atmoshperes, the SnO2PNS sensors were fabricated and their gas-sensing response to1000ppm CO was tested. The results demonstrated that when being calcined in N2, the oxygen vacancies in SnO2PNS cannot be effectively repaired. Contrarily, more oxygen vacancies may have formed, thus SnO2PNS sensor exhibits much higher response to CO. On comparison, considerable amount of oxygen vacancies in SnO2must have disappeared when it was calcined in O2, resulting in the poor gas-sensing performance of SnO2PNS sensor. This result reveals that the concentration of oxygen vacancy played a dominant role in gas-sensing performance. Due to the competition between the effects of oxygen vacancies and carrier mobility, calcining SnO2PNS in oxygen of ever-increasing pressure resulted in the degradation of gas-sensing performance at first, followed by a monotonic improvement above4.0MPa. On comparison, because of introduction of N-containing species, the response of SnO2PNS sensors was severely harmed after calcining them in high-pressure nitrogen.(4) In order to further improve the pore size uniformity of SnO2PNS, and increase its specific surface area, we combined the sol-gel method and SHP route to prepare SnO2PNS for the first time. The results show that the SnO2PNS samples thus prepared possesses much smaller nanoparticle size, more uniform pore diameter, larger pore volume and higher specific surface area, but its carrier mobility becomes lower. The influences of the key parameters, including hot-press temperature and pressure, on the pore structure and electric performance of SnO2PNS were investigated. Besides, the gas-sensing response of this kind of SnO2PNS to CO is much higher than that of the SnO2PNS prepared from the commercial SnO2nanoparticles.