Abstract
Nanocrystalline cobalt oxide Co3O4 has been prepared by precipitation and subsequent thermal decomposition of a carbonate precursor, and has been characterized in detail using XRD, transmission electron microscopy, and FTIR spectroscopy. The sensory characteristics of the material towards carbon monoxide in the concentration range 6.7–20 ppm have been examined in both dry and humid air. A sensor signal is achieved in dry air at sufficiently low temperatures T = 80–120 °C, but the increase in relative humidity results in the disappearance of sensor signal in this temperature range. At temperatures above 200 °C the inversion of the sensor signal in dry air was observed. In the temperature interval 180–200 °C the sensor signal toward CO is nearly the same at 0, 20 and 60% r.h. The obtained results are discussed in relation with the specific features of the adsorption of CO, oxygen, and water molecules on the surface of Co3O4. The independence of the sensor signal from the air humidity combined with a sufficiently short response time at a moderate operating temperature makes Co3O4 a very promising material for CO detection in conditions of variable humidity.
Highlights
Resistive semiconductor gas sensors are widely used to control the quality of atmospheric air in industrial plants and in residential areas
The calcination temperature of precipitate was determined by thermogravimetric analysis–mass spectrometry (TG-MS) with heating rate 10 ◦ C/min in an air atmosphere using a STA 409 PC Luxx thermal analyzer (Netzsch-Gerätebau GmbH, Selb, Germany) equipped with a QMS 403 C Aëolos quadrupole mass spectrometer (Netzsch-Gerätebau GmbH, Selb, Germany)
The obtained cobalt oxide was characterized by X-ray diffraction (XRD) analysis on a DRON-4-07 diffractometer (Burevestnik, Moscow, Russia, CuKα radiation, λ = 1.5406 Å), the crystallite size was calculated using the Scherrer formula
Summary
Resistive semiconductor gas sensors are widely used to control the quality of atmospheric air in industrial plants and in residential areas They have many advantages: high sensitivity, small size, fast response, and low cost in mass production. Is mainly due to their high electrical resistance and lower sensitivity to gases in dry air in comparison with n-type oxides [11]. They are characterized by a higher concentration of chemisorbed oxygen [12], and exhibit high catalytic activity in oxidation reactions [13], which makes them promising materials for detecting gases in humid air.
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