Abstract
This paper is aimed at selectivity investigation of gas sensors, based on chemically modified nanocrystalline tin dioxide in the detection of CO and ammonia mixtures in air. Sol-gel prepared tin dioxide was modified by palladium and ruthenium oxides clusters via an impregnation technique. Sensing behavior to CO, NH3 and their mixtures in air was studied by in situ resistance measurements. Using the appropriate match of operating temperatures, it was shown that the reducing gases mixed in a ppm-level with air could be discriminated by the noble metal oxide-modified SnO2. Introducing palladium oxide provided high CO-sensitivity at 25–50 °C. Tin dioxide modified by ruthenium oxide demonstrated increased sensor signals to ammonia at 150–200 °C, and selectivity to NH3 in presence of higher CO concentrations.
Highlights
Lack of selectivity is a major drawback of semiconductor metal oxide gas sensors
We demonstrated that nanocrystalline tin dioxide modification by palladium oxide increased sensor responses to CO at as low temperature as room temperature [23]; while introducing ruthenium oxide provided high responses to NH3 at a raised temperature [24]
Using X-ray photoelectron spectroscopy (XPS), XANES, EXAFS, and electron paramagnetic resonance (EPR), the modifiers were shown to exist in the form of mixed-valence noble metal oxides, which could be formalized as
Summary
Lack of selectivity is a major drawback of semiconductor metal oxide gas sensors. Nanocrystalline tin dioxide is one of the most utilized materials for such devices due to a combination of appropriate structural, adsorptive, and electrophysical properties [1]. The material, possessing several advantages, such as large active surface area and surface-to-volume ratio, result in high gas sensitivity, stability in Chemosensors 2015, 3 air, and low cost, makes it challenging to improve selectivity [2]. The problem of selectivity is complicated by the fact that most toxic gases (CO, NH3, H2S, volatile organic compounds) are the reducing ones. The sensor response to these gases is determined by the molecules oxidation on the material surface. There are several tools to improve the sensitivity and selectivity of the detection of reducing gases
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