Abstract
The unique properties of microporous zeolites, including ion-exchange properties, adsorption, molecular sieving, catalysis, conductivity have been exploited in improving the performance of gas sensors. Zeolites have been employed as physical and chemical filters to improve the sensitivity and selectivity of gas sensors. In addition, direct interaction of gas molecules with the extraframework cations in the nanoconfined space of zeolites has been explored as a basis for developing new impedance-type gas/vapor sensors. In this review, we summarize how these properties of zeolites have been used to develop new sensing paradigms. There is a considerable breadth of transduction processes that have been used for zeolite incorporated sensors, including frequency measurements, optical and the entire gamut of electrochemical measurements. It is clear from the published literature that zeolites provide a route to enhance sensor performance, and it is expected that commercial manifestation of some of the approaches discussed here will take place. The future of zeolite-based sensors will continue to exploit its unique properties and use of other microporous frameworks, including metal organic frameworks. Zeolite composites with electronic materials, including metals will lead to new paradigms in sensing. Use of nano-sized zeolite crystals and zeolite membranes will enhance sensor properties and make possible new routes of miniaturized sensors.
Highlights
Zeolites are crystalline aluminosilicates with pores and channels of molecular dimensions [1,2,3,4,5,6].Zeolites can be synthesized with different chemical compositions and distinct framework topologies, and about 170 of such topologies have been reported
Zeolite films were grown on piezoelectric sensor devices via seeding of nanocrystals followed by secondary growth
This study showed that the oxidative burst within the macrophage can be tracked by measuring the emission from the dye inside the zeolite held in the cell
Summary
Zeolites are crystalline aluminosilicates with pores and channels of molecular dimensions [1,2,3,4,5,6]. Due to their ion-exchange properties, as well as adsorption and reactions of molecules within its cages, zeolites have found use in numerous applications in catalysis and separations. The negative aluminosilicate framework of zeolites necessitates the presence of neutralizing ion-exchangeable cations within the framework These cations can influence adsorption, diffusion and catalytic properties of zeolites, and thereby influence sensing behavior. Interaction of the molecule with the cation is manifested in the change in impedance/capacitance as measured by the frequency dependent impedance spectra With this introduction, we address specific applications, focusing on how the above-described physical and chemical properties of zeolites have informed sensing paradigms
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