International Journal of Scientific Engineering and Technology (ISSN : 2277-1581) Volume No.4 Issue No.4, pp: 268-272 01 April. 2015 IJSET@2015 Page 268 Fabrication of Sno2/Reduced Graphene Oxide Nanocomposite Films for Sensing No2 Gas at Room-Temperature Pi-Guey Su*, Ching-Hsuan Wei and Wei-Luen Shiu Department of Chemistry, Chinese Culture University, Taipei 11114, Taiwan *Corresponding Author: spg@faculty.pccu.edu.tw Abstract : One-pot polyol process was combined with metal organic decomposition (MOD) method to fabricate a room-temperature NO2 gas sensor based on tin dioxide and reduced graphene oxide (SO2/RGO) nanocomposite films. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were used to analyze the structure and morphology of the fabricated films. The electrical and NO2 gas-sensing properties of SnO2 to which various amounts of RGO were added were measured in detail as a function of concentration of NO2 gas at room temperature, to elucidate the contribution of RGO to the NO2 gas-sensing capacity. The sensor that was based on a nanocomposite film of SnO2/RGO exhibited a strong response to low concentrations of NO2 gas at room temperature, satisfactory linearity and favorable long-term stability. Keyword: Tin dioxide (SnO2); reduced graphene oxide (RGO); nanocomposite film; room-temperature NO2 sensor. 1. Introduction NO 2 generated by combustion facilities and automobiles are known to be extremely harmful to the human body and the environment, so highly sensitive detection is needed for monitoring NO 2 gas. Metal oxides are well known to be effective in detecting various gases with enough sensitivity. Tin dioxide (SnO2), as oxygen-deficient n-type semiconductor with a wide bandgap (Eg = 3.6 eV), much effort has been made to elucidate their ability to detect various toxic and flammable gases [1-3]. According to reports, the SnO 2 sensors operate only at high temperatures, such as 200~500C. Accordingly, the development of SnO 2 sensors that can operate at lower temperatures, with high sensitivity and low production cost has attracted much attention [4,5]. Graphene consists of a two-dimensional (2D) array of carbon atoms that are covalently connected via sp2 bonds to form a honeycomb sheet [6]. Graphene oxide (GO) sheets have recently become attractive as possible intermediates in the manufacture of grapheme [7]. GO can be chemically or thermally reduced to conductive reduced GO (RGO) [8]. Many methods have been used to prepare metal oxide/graphene composite materials, including the hydro/solvothermal method, solution mixing method, the in-situ growth method and the photoreduction method, all of which have their own advantages and particular conditions of application [9-11]. Among these methods, hydro/solvothermal method is the most widely used to prepare metal oxide/graphene composite because chemical bonds form between metal oxides and graphene, which can improve the electric properties of the composite over those of the same metal oxides or graphene alone. Recently, composite films that are based on SnO 2 nanopowders and graphene have been reported to be as new gas-sensitive materials to reduce further the operating temperature and to improve the sensitivity of sensors based on these materials [12,13]. Neri et al. fabricated SnO 2 /graphene nanocomposites using the one-pot microwave-assisted non-aqueous sol–gel method for sensing NO 2 [12]. Zhang et al. fabricated a more rapidly responding NO 2 gas sensor based on SnO 2 nanoparticles/graphene nanocomposites that were made by the hydrothermal treatment of aqueous dispersion of GO in the presence of Sn salts [13]. The sensing characteristics of these SnO 2 /graphene-based NO 2 gas sensors depend on their microstructure, which are determined by their fabrication process. Most NO 2 gas sensors have been fabricated by synthesizing graphene that is decorated with SnO 2 nanomaterial and drop-coating it on a substrate. In this work, SnO 2 /RGO nanocomposite films were fabricated by combining the one-pot process with the metal organic decomposition (MOD) method. These films have the advantages of being highly effective, inexpensive and suitable for industrial for mass production. The structural characteristics of the SnO 2 /RGO nanocomposite films were investigated by X-ray diffraction (XRD). The surface characteristics of the SnO 2 /RGO nanocomposite films were observed using scanning electron microscopy (SEM). The NO 2 sensing performance of SnO 2 /RGO nanocomposite films with various amounts of the RGO loaded into the SnO 2 matrix was studied as a function of concentration of NO 2 gas at room temperatuer. Differences in the composition and microstructure were adopted to explain the effect of adding RGO on the sensing mechanism of the SnO 2 /RGO nanocomposite films. 2. Experimental 2.1 Preparation of RGO in glycerol solution GO was prepared from natural graphite by a modified Hummers method [14]. Briefly, 0.5 g graphite powder was reacted with a mixture of 2 g NaNO 3 , 12 mL concentrated H 2 SO 4 and 3 g KMnO 4 ; then 40 mL deionized water (DIW) and 10 mL H 2 O 2 (30%) were added. The resultant mixture was filtered and washed with DIW by centrifuging until the solution attained a pH of 6, and was then sonicated to form a stable suspension of GO in aqueous media. The resulting aqueous GO solution had a concentration of 0.85 mg/mL. The GO was reduced to form RGO in glycerol solution that was prepared as follows: the required amounts of GO were added to 10 g of glycerol and the resultant solution was heated to 190C for 1 h with vigorous magnetic stirring. The solution was continuously stirred until a stable suspension was obtained.