Low ppm range ethanol sensor at room temperature: improving the optical response by using mesoporous silica foam

Sápi, András (2016) Low ppm range ethanol sensor at room temperature: improving the optical response by using mesoporous silica foam. SENSORS AND ACTUATORS B-CHEMICAL. pp. 1-13. ISSN 0925-4005 (Submitted)

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Abstract

In this paper a low ppm range ethanol sensor - operating at room temperature - is presented. The three types of zinc peroxide (ZnO2) based hybrid thin films as sensor surfaces consist of the semiconductor nanoparticles, polyelectrolyte [poly(acrylic acid), PAA] and/or mesoporous silica (MPS). The silica foam (SF) and the two-dimensional (2D) hexagonally ordered SBA-15 samples were characterized by transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and BET analysis. The TEM and SAXS studies clearly showed the fractal-like mesostructure of the silica samples, as well as, the specific surface area (as) obtained from SAXS and BET analyses are in good agreement: the as values of the samples are in the range of 6-800 m2/g. The thin films were prepared by Layer-by-Layer (LbL) self-assembly method and were subjected to reflectometric interference measurements for testing sensorial application. The sensor tests showed that the detection limit of the thin films is in the sub-ppm range (< 500 ppb). Applying mesoporous silica as surface coating or interlayers in the sandwich-structured thin film (ZnO2/SF) improved the optical response, but the sensitivity showed non-linear characteristic. The thin film with mixed structure (ZnO2/PAA/ZnO2/SF) showed linear response in the 0.4-12 ppm range with 0.6 nm/ppm sensitivity and acceptable selectivity. Testing the sensor in extended (0.4-40 ppm) concentration range showed a slight (quadratic) deviation from linear behavior with R2=0.9987.

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