Nanocomposites in Gas Sensors: Promising Approach to Gas Sensor Optimization
Present short chapter gives general view on the prospects of nanocomposites applications in gas sensor design. Chapter includes 1 figures, 1 Tables and 24 references.
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Nanocomposites in Gas Sensors: Promising Approach to Gas Sensor Optimization
Nanocomposites provide another promising direction in the development of materials for gas sensors (Ferroni et al. 1999; Gas’kov and Rumyantseva 2001; Comini et al. 2002; Galatsis et al. 2002; Sadek et al. 2006; Rumyantseva et al. 2006; Yang 2011). Nanocomposite materials have recently attracted increasing interest because of the possibility of synthesizing materials with unique physical–chemical properties (Gas’kov and Rumyantseva 2001; Zhang et al. 2003a, b). It was established that highly sophisticated surface-related factors important for gas sensor applications such as optical, electronic, catalytic, mechanical, and chemical properties can be obtained by advanced nanocomposites synthesized from various materials. Recently, various nanocomposite films consisting of either metal–metal oxide, mixed metal oxides, polymers mixed with metals or metal oxides, or carbon nanotubes mixed with polymers, metals, or metal oxides have been synthesized and investigated for their application as active materials for gas sensors. For example, it was established that metallic and metal-oxide nanoparticles incorporated in various matrixes are capable of increasing the activities for many chemical reactions due to the high ratio of surface atoms with free valences to the cluster of total atoms. As a result, we can obtain an ideal platform for gas sensor design. In particular, we should note that most of the chemiresistors are devices based on metal oxide–noble metal nanocomposites. Nanoclusters of noble metals such as Pd, Pt, Au, Rh, and Ag incorporated in a metal-oxide matrix increase catalytic activity of gas-sensing materials, change adsorption/desorption parameters, and promote the reducing operation temperature, increasing sensor response, enhancing the response rate, and improving sensor selectivity. More detailed reviews of the effects of doping on metal oxide gas sensors are available elsewhere (Kohl 1990; Korotcenkov 2005, 2007; Miller et al. 2006). It was found that transition to nanocomposites could also improve mechanical properties and promote stabilization of the basic material’s parameters (Konig 1987). For example, it was established that in CNTs–polymer composites, the presence of carbon nanotubes inside the polymeric matrix can provide a mechanical support to the polymeric chain’s conformational rearrangement. CNTs are hollow nanopipes, and therefore the incorporation of CNTs in a metal oxide matrix can provide better gas permeability for sensing materials and thus enhance gas diffusion into the bulk film. Thus, combination of CNTs with metal oxide (see Fig. 12.1) can lead to development of gas sensors with improved rate of response. Nanocomposites also provide more possibilities for control of the catalytic activity of the sensing matrix. For example, it has been shown that the introduction of TiO2 nanoparticles into the polymer matrix of poly(p-phenylenevinylene) (PPV) changes the adsorption properties of the matrix. Adsorption of oxy
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