Abstract
Multilayers consisting of graphene oxide (GO) and α-Fe2O3 thin layers were deposited on the ceramic substrates by the spray LbL (layer by layer) coating technique. Graphene oxide was prepared from graphite using the modified Hummers method. Obtained GO flakes reached up to 6 nanometers in thickness and 10 micrometers in lateral size. Iron oxide Fe2O3 was obtained by the wet chemical method from FeCl3 and NH4OH solution. Manufactured samples were deposited as 3 LbL (GO and Fe2O3 layers deposited sequentially) and 6 LbL structures with GO as a bottom layer. Electrical measurements show the decrease of multilayer resistance after the introduction of the oxidizing NO2 gas to the ambient air atmosphere. The concentration of NO2 was changed from 1 ppm to 20 ppm. The samples changed their resistance even at temperatures close to room temperature, however, the sensitivity increased with temperature. Fe2O3 is known as an n-type semiconductor, but the rGO/Fe2O3 hybrid structure behaved similarly to rGO, which is p-type. Both chemisorbed O2 and NO2 act as electron traps decreasing the concentration of electrons and increasing the effective multilayer conductivity. An explanation of the observed variations of multilayer structure resistance also the possibility of heterojunctions formation was taken into account.
Highlights
Nitrogen dioxide is a typical air pollutant, being a component of motor vehicle exhaust gas and is generated in the house and industrial combustion processes
The early applications of NOx detectors for diesel engine exhausts utilized dense zirconia-based electrolytes. It is shown in more recent investigations of nitrogen oxide sensors that good results can be obtained by integrating the sensor with NOx trap materials [1] or by the use of LaSrMnO3 type perovskite electrodes [2]
Good sensitivity of GO to acetone at room temperature was obtained recently by using a microwave-based gas sensor realized as a coupled-line section covered with a graphene oxide film [26]
Summary
Nitrogen dioxide is a typical air pollutant, being a component of motor vehicle exhaust gas and is generated in the house and industrial combustion processes. Good sensitivity of GO to acetone at room temperature was obtained recently by using a microwave-based gas sensor realized as a coupled-line section covered with a graphene oxide film [26]. Another gas-sensitive oxide, α-Fe2 O3 (hematite), is recently investigated as a NO2 sensor [27] but more frequently in the form of a nanocomposite with rGO [28,29,30]. Good sensitivity to NO2 was obtained at temperatures close to RT but with quite high response and recovery times
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