Sensors and Actuators B 135 (2008) 1–6 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Sn/In/Ti nanocomposite sensor for CH 4 detection Bai Shouli a , Chen Liangyuan b , Yang Pengcheng a , Luo Ruixian a , Chen Aifan a,∗ , Chung Chiun Liu b a State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China b Department of Chemical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA article info Article history: Received 22 December 2007 Received in revised form 18 June 2008 Accepted 18 June 2008 Available online 9 July 2008 Keywords: CH4 sensor Sn–In–Ti Nanocomposite Sensing properties abstract Novel CH 4 gas sensors made of the nanocomposites of Sn/In/Ti oxides were investigated. The nano- sized crystalline oxides and their composites were successfully prepared by a sol–gel and controlled precipitation method, respectively, through manipulating the salts concentration, precipitation pH value, aging time and composition of composites. The derived precursors exhibited superior ther- mal stability. To ensure sufficient crystallinity and insignificant grain growth of the materials, the appropriate calcination temperatures were 600 ◦ C for 4h and 700 ◦ C for 2 h for the precursors of oxides and composites, respectively. The performance and structure of the composites were charac- terized by EDX, TEM, BET, TG–DTA and XRD. The sensing tests showed that these nanocomposites exhibited high response and selectivity for the detection of CH 4 at operating temperatures between 200 ◦ C and 250 ◦ C and the response depended on the composition of composites, calcination temper- ature, operating temperature and gas concentration in air. The gas sensing mechanism of the sensor s was also discussed by X-ray photoelectron spectroscopic (XPS) and temperature-programmed desorp- tion (TPD) studies. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Tin oxide is an important semiconductor gas sensing material due to its good chemical stability and high sensitivity at lower operating temperature, compared to other oxides for detection of reducing and oxidizing gases [1]. With a decrease in crystal- lite size, a large interfacial area, homogeneity and highly reactive surface of the nanocrystalline particles have attracted much atten- tion for electronic, catalytic and optical applications. The grain size reduction is one of the main factors enhancing the sensitivity of semiconductor sensors. Xu et al. [2] suggested a model concern- ing the grain size (D) and the thickness of space charge layer (L) to explain the effect of particle size on the response of a sensor. The model has widely been accepted to explain the sensing mech- anism of semiconductor oxide gas sensors. Unfortunately, sensor fabrication process requires higher calcination temperature, even when nanocrystalline SnO 2 is used as the starting sensing material. This would result in significant grain growth after sensor fabrica- tion, greatly compromising the sensitivity of the resulting device. In order to enhance the thermal stability and response towards a specific gas, nanocomposites have been considered as sensing ∗ Corresponding author. E-mail address: chenaf@mail.buct.edu.cn (C. Aifan). materials. de Lacy Costello et al. [3] studied a highly sensitive mixed oxide sensor for detection of ethanol; the proportion for the most sensitive response was 25%SnO 2 –75%ZnO. Serra et al. [4] reported the sensing properties of a new sensor for NO gas; the sensing mate- rial was made of a composite of In–Se oxide crystallites which were obtained by thermal evaporation of polycrystalline In–Se and sub- sequent thermal annealing in an oxygen flow. Ishihara et al. [5] examined mixed oxides of Al 2 O 3 –V 2 O 5 as sensing materials for detection of NO and NO 2 gases. Chen and coworkers [6] synthesized SnO 2 –ZnO nanocomposites which exhibited superior thermal sta- bility, and achieved superb response to CO and NO 2 gases through introduction of metal (Cd) or Al 2 O 3 coating. This paper aims at enhancing the CH 4 response through intro- ducing TiO 2 into binary composites of SnO 2 and In 2 O 3 . The structural symmetry and high temperature firing nature of CH 4 molecules determine its low reactivity and response. The cross- sensing between CH 4 and CO is still one of major problems for CH 4 sensors because of the same reducing characteristics of both gases. To further improve the response and selectivity and also to decrease the optimal operating temperature of the present CH 4 sen- sor, a small amount of Pd or Pt or a MgO coating was employed as a dopant or a surface modifier. The design of a CH 4 sensor possessing good response and selectivity is very important for the safe detec- tion in household and coal mines as well as for industrial process control of natural gas combustion. 0925-4005/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2008.06.051