TIN DIOXIDE NANOPARTICLES PREPARED BY SOL-GEL METHOD FOR AN IMPROVED HYDROGEN SULFIDE SENSOR S.V. Manorama, C.V. Gopal Reddy and V.J. Rao Materials Science Group, Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad-500 007 India (Received February 12, 1999) (Accepted June 26, 1999) Abstract—Semiconducting tin dioxide incorporated with specific additives has been prepared by the technique of sol-gel to achieve particle sizes in the range of nanometers. This reduced size has been shown to significantly improve the gas sensing characteristics of the sensor elements. Sensitivity of tin dioxide doped with CuO prepared by this method shows an increase in sensitivity over the same composition obtained by conventional hydrolysis method. The results clearly brings out the influence of the crystallite size on the gas sensing characteristics of sensors based on these semiconducting materials. ©1999 Acta Metallurgica Inc. Keywords: Sol-gel synthesis; Nano-particles; Tindioxide; Hydrogen sulfide sensor 1. Introduction Enormous efforts are being directed towards the development of nanometer sized materials in studies related on one hand to their fundamental mechanisms such as the size effect and the quantum effect, and on the other hand towards applications of these materials. Tin dioxide is a versatile material with a wide variety of applications. It has been used for example, as a catalyst for the oxidation of organics (1,2), as solid state sensors for reducing gases (3,4), to make indium tin dioxide (ITO) transparent conductive thin film coatings (5) etc. The success in many of these applications relies on the ability in obtaining nano-sized particles, pore or grain structure. The preparation of ultra-fine tin dioxide has attracted much attention recently, since it shows outstanding properties when used as a gas sensing material and also as a catalyst support. Such microstructures in general can be achieved by the sol-gel method as demonstrated in other ceramic materials (6). A number of methods have been developed to synthesize ultra-fine particles of tin oxide. In recent years because of its simplicity, low cost and uniformity in product composition, the sol-gel process has been considered an effective one. Another added advan- tage of this technique is the convenience of bulk preparation of the material by this method with better dispersion of the component species. Activation energies and thus the temperatures necessary to get crystalline phases usually are much lower when the ceramic material is formed from an (amorphous) gel with a high dispersion of the individual components. There are also some earlier reports on the preparation of SnO 2 by the hydrolysis of tin chloride and the peptization of the precipitates with ammonium hydroxide (7). There are some other similar methods where the gel formation takes place only after the NH 4 + and Cl - ions were eliminated by washing in bi-distilled water for a period of 30 days (8). Either alkoxides or inorganic salts particularly tin tetrachloride are suitable starting reagents for the sol-gel processing. Nevertheless, Pergamon NanoStructured Materials, Vol. 11, No. 5, pp. 643– 649, 1999 Elsevier Science Ltd Copyright © 1999 Acta Metallurgica Inc. Printed in the USA. All rights reserved. 0965-9773/99/$–see front matter PII S0965-9773(99)00352-9 643