LAUSR

An in situ FTIR combined with online LCR method was used to study the sensing mechanism of the prepared sensors at room temperature. Our study revealed that the sensing mechanism for the sensors that were responsive was a total decomposition of the analytes, ethanol and methanol, through a total oxidation process. Carbon nanoparticles (CNPs; candle soot), manganese dioxide and polyvinylpyrrolidone (PVP) were used as sensing materials to fabricate five various sensors for the detection of ethanol and methanol vapor in a closed chamber. Different sensors were prepared by mixing variable ratio of the sensing materials. Sensor A was prepared by mixing all three sensing materials; CNPs:MnO2:PVP (1:1:3 mass ratio) in dichloromethane (as a solvent), while sensor B, C, D and E were prepared by mixing two of the materials; CNPs:MnO2 (1:1 mass ratio), MnO2:PVP (1:3 mass ratio), CNPs:PVP (1:3 mass ratio) and MnO2 (only), respectively. The sensing materials were characterized using Brunauer–Emmett–Teller, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The sensing experiments were carried out at room temperature, for both ethanol and methanol vapor and the concentrations were varied from 345 to 4146 and 498 to 5983 ppm, respectively. Sensor C was the most sensitive sensor to ethanol with the sensitivity of 0.195 Ω ppm−1 and sensor D was the most sensitive for methanol with a sensitivity of 0.389 Ω ppm−1.