Abstract
Air humidity is one of the main factors affecting the characteristics of semiconductor gas sensors, especially at low measurement temperatures. In this work we analyzed the influence of relative humidity on sensor properties of the hybrid materials based on the nanocrystalline SnO2 and In2O3 and Ru (II) heterocyclic complex and verified the possibility of using such materials for NO (0.25–4.0 ppm) and NO2 (0.05–1.0 ppm) detection in high humidity conditions (relative humidity (RH) = 20%, 40%, 65%, 90%) at room temperature during periodic blue (λmax = 470 nm) illumination. To reveal the reasons for the different influence of humidity on the sensors’ sensitivity when detecting NO and NO2, electron paramagnetic resonance (EPR) spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) investigations were undertaken. It was established that the substitution of adsorbed oxygen by water molecules causes the decrease in sensor response to NO in humid air. The influence of humidity on the interaction of sensitive materials with NO2 is determined by the following factors: the increase in charge carrier’s concentration, the decrease in the number of active sites capable of interacting with gases, and possible substitution of chemisorbed oxygen with NO2− groups.
Highlights
Nitric oxide (NO) and nitrogen dioxide (NO2) gases produced by fuel combustion, electric power plant boilers and industrial plants [1,2] pose a serious problem for both the environment and human health [3,4]
The composition and microstructure of the materials obtained were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) measurements; the optical properties and thermal stability were studied via ultraviolet/visible (UV/Vis) absorption spectroscopy and thermogravimetric analysis (TGA), respectively, and were discussed in detail previously [14]
The samples were illuminated with a blue LED in pulsed mode during 2 hours under dry air or in humid air before the first measurement to reach a stable resistance value, and irradiation was kept during the whole experiment in gas phase
Summary
Nitric oxide (NO) and nitrogen dioxide (NO2) gases produced by fuel combustion, electric power plant boilers and industrial plants [1,2] pose a serious problem for both the environment and human health [3,4]. Several investigations showed that nitric oxide in exhaled samples of breath condensate can indicate lung diseases and respiratory tract inflammation [5,6,7,8]. The most reliable method for quantitative analysis of NO is based on the reaction between NO and ozone O3, accompanied by chemiluminescence, the intensity of which is proportional to the NO content in the sample. Chemiluminescence occurs in the infrared (IR) range when excited electrons in the NO2 molecule pass to lower energy levels
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