Synthesis And Characteriation Of Nanosized Tin Oxide Powder

Because of its unique electrical and catalytic properties, tin oxide has been widely used for various electrochemical and catalytic applications, such as gas sensors for environmental monitoring and catalysts. As an n-type semiconductor, tin oxide shows very high sensitivity to many reducing gases such as H₂, CO, hydrocarbon, and alcohol. It is shown that the sensitivity can be improved by increasing the sensor surface area so as to increase the number of oxygen sites on the surfaces in these reducing gas atmospheres. With the decrease of the crystal size and the increase of specific area, homogeneity and highly reactive surfaces of the nanocrystalline particles and other good properties have attracted much attention.Several chemical methods are available for preparation of this material including sol-gel, chemical vapor deposition, annealing precursor powders, and thermal evaporation method. One prominent feature of these processes is employing thermal treatment to improve the stability and purity of these materials. Pang calcined SnO₂ nanocrystals at 600℃. Liu have prepared SnO₂ on quartz substrates via a simple vapor deposition process at 1150℃. However, thermal treatments lead to an increase of the average particle size, spreading of the grain size distribution, decreasing of specific surface area, and changes in the phase composition with increasing annealing temperature. Hitherto, hydrothermal process is one of the most promising solutions of chemical method for preparing nanocrystals in relatively low temperature without subsequent thermal treatments. The particle's size and their distribution, phase homogeneity, and morphology could be well controlled.Hydrothermal method has been used to synthesize TiO₂, BaTiO₃, Al₂O₃, MgAl₂O₄, and Fe₃O₄ powders. However, no descriptions concerning the preparation of tin oxide powders for gas sensors using RPB reactor and then by the use of hydrothermal method have appeared. Especially, it is a challenging task to synthesize SnO₂ with controlled particle size. Herein, we describe a simple approach to synthesize uniform tin oxide nanoparticles with controlled size based on tin tetrachloride and ammonia. The advantage of this process is no need of protective reagents and other thermal treatments. In this paper, we mainly discuss three routines in which well SnO₂ particles were prepared. High gravity technology had successfully been used to produce nanosized SnO₂ powder. The technique in the form of a rotating packed bed (RPB) on the earth has been used to intensify mass transfer and micro mixing. Under these optimum conditions, smallness and well-dispersed SnO₂ nanoparticles was obtained. SnO₂ nanocrystal was prepared by high-gravity precipitation followed by hydrothermal synthesis using SnCl₄-5H₂O and ammonia as the starting materials. The structure and particle size of SnO₂ were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM) and so on. The influences of the thermal hydrolysis temperature, reactant concentration and hydrothermal time on crystal structure, the morphology and particle size were discussed. The experimental results indicated that SnO₂ powder exhibit well crystallinity with size of 2-6 nm, high specific surface area (90-170 m²/g) and good dispersibility. The optimized conditions are thermal hydrolysis temperature 240-280℃, reactant concentration (SnC14) 0.05 mol/L and hydrothermal time 3-8 h.