Low-level detection of ethanol and H 2S with temperature-modulated WO 3 nanoparticle gas sensors

Abstract

Low-level detection of ethanol and H 2S was achieved with thermally modulated WO 3 nanoparticle gas sensors. Nanoparticle WO 3 films, with a mean grain size of ∼5 nm and a thickness of ∼20 μm, were produced by advanced reactive gas evaporation onto alumina substrates. The working temperature of the sensor was periodically modulated between 150 and 250 °C, and the response was analysed by fast Fourier transform (FFT) and discrete wavelet transform (DWT) methods in order to extract characteristic parameters from the sensors’ response transients. After calibration of the sensor for low concentrations of ethanol and H 2S, it was possible to detect as little as 200 ppb of ethanol and 20 ppb of H 2S (both of them dry gases) with good accuracy. Long-term sensor behaviour was assessed. Unsupervised and supervised linear pattern recognition methods, specifically principal component analysis (PCA) and discriminant factor analysis (DFA), were successfully applied to distinguish the investigated gases.