Synthesis Of SnO₂ By Flame Spray Pyrolysis: Structures Design And The Gas Sensing Properties

Flame Spray Pyrolysis(FSP) is an important method for preparing nanoparticles. Since the process is simple, rapid and scalable, great amount of functional nanoparticles have been prepared by FSP. However, due to the formation of nanoparticles in the flame involves complex physical and chemical reactions, the particle formation mechanism have not yet been truly understood, which limits the development of FSP method somewhat. So to fully understand the particle formation mechanism and develop general method for the the structure design of the product in the FSP prcocess is a research focus in the field of nano-materials preparation. SnO2 is an important semiconductor which is widely used in gas sensors, lithium ion batteries and solar cells. In this paper, by controlling the droplet and gas phase reaction in FSP we successfully prepared SnO2 with different structures including nanopaticles, nanorods, hollow spheres, nano-flowers and nano-urchins and investigated their gas sensing properties toward ethanol and other organic gases. The main results in this paper are displayed as follows:(1) SnO2 nanoparticles with different diameters were prepared through the Flame Spray Pyrolysis by changing the feed rate. The gas sensing test show that the sensitivity toward ethanol is increasing with the decreasing of diameter.(2) In the high-temperature gas phase reaction, the surface energy and growth direction of SnO2 crystal were changed by the doping of Fe which resulted in the formation of SnO2 nanorods. Chemical sensors constructed with those SnO2 nanorods exhibit better sensitivity and selectivity, as well as shorter response and recovery times toward ethanol gas than that of the SnO2 nanoparticle with the similar diameter.(3) Three-dimensional SnO2 hollow spheres were prepared through Flame Spray Pyrolysis by using SnSO4 as tin source and polyethylene glycol as auxiliary component. The as-prepared SnO2 hollow spheres are porous, and assembled by small SnO2 nanocrystals. The presence of polyethylene glycol keeps the shell of SnSO4 from being destroyed in the flames, which provides preconditions for the formation of hollow spheres The gas sensing test show that the SnO2 hollow spheres exhibit higher sensitivity (80ppm,35.2) and selectivity to ethanol, and shorter response and recovery times (80ppm,6s,9s) than SnO2 nanoparticles.(4) By combining the droplet and gas phase reaction, three-dimensional flower-like and urchin-like SnO2 were synthesized by using SnCl4·5H2O as tin source and TEOS as the silica source with the adding of certain percentage of water to the precursor. The silica formed through the droplet reaction provides nuclei for SnO2 gas when condensating and promotes the growth of SnO2 on the surface into nanorods. After HF etching SnO2 nano-flowers and nano-urchins with hollow cores were obtained which show higher sensitivity (100ppm,55.6, 65.6) and selectivity towards ethanol with faster response and recovery speed than that of SnO2 nanorods reported.