Sensing selectivity of SnO2-Mn3O4 nanocomposite sensors for the detection of H2 and CO gases

Abstract

Metal oxide semiconductor sensor have a drawback of similar gas sensing response to homogeneous gases. Taking H2 and CO with similar properties (reducing gases), these sensors cannot detect the concentrations of both gases, because the MOS sensors have cross-sensitive behavior to H2 and CO. In this paper, SnO2-Mn3O4 nanocomposites are prepared by sol-gel method. XRD, HRTEM, and XPS are used to characterize the crystal structure, surface morphology, chemical composition, and surface physico-chemical state of the material, respectively. The gas sensitive composites show n-type response to H2 and CO for the molar ratio of Sn to Mn greater than 1:2.33, whereas the composites shows p-type response to H2 and CO for the molar ratio of Sn to Mn smaller than 1:2.33. Interestingly, when the Sn to Mn ratio is 1:2.33, the S1M2.33 presents n-type and p-type behavior to CO and H2, respectively. The mechanism of this inverse sensing behavior to H2 and CO is presented based on the series of the characterizations performed. This paper indicates that modulation the concentrations of p-type or n-type MOS sensor is an ideal strategy to overcome the poor selectivity of such sensors.