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We report the successful detection of ethanol among a variety of volatile organic compounds (VOCs), including isopropanol, toluene, and acetone at room temperature (RT) via a thermally reduced graphene oxide (T-RGO) based sensor. T-RGO material was prepared by thermal reduction of graphene oxide (GO) at 250°C for 20 min. The properties of as-synthesized T-RGO were elucidated by X-ray diffraction, Raman spectroscopy, FT-IR spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and Brunauer-Emmett-Teller (BET) techniques. The BET analysis of T-RGO revealed a mesoporous structure with specific surface area of 86.21 m2/g. The proposed T-RGO sensor was exposed to various ethanol concentrations ranging from 5 to 100 ppm and the sensor exhibited maximum response (15%) toward 100 ppm of ethanol at RT. The high sensitivity, fast response (3s)/recovery time (6s), and excellent repeatability of ethanol suggest good selectivity over other tested VOCs. The optimum operating temperature of the sensor was found to be RT (28°C). Upon exposure to different relative humidity (RH) levels, the ethanol sensing response was found to vary by 1.5% from 33% to 83% RH, indicating low dependence of humidity on the sensor performance. In addition, the sensor displayed efficient long-term stability towards ethanol at RT.

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Functioning of hydrothermally synthesized WO3 nanoplates was investigated for humidity sensing and respiration monitoring under different breathing conditions. The monoclinic phase was identified by X-ray diffraction. The average crystallite size was calculated by Williamson-Hall (W-H) plot (27 nm) and modified Scherrer equation (24 nm). The optical band gap was calculated as 2.7 eV using UV-Visible spectroscopy. The field emission electron microscopy and high resolution transmission electron microscopy micrographs of readied WO3 have confirmed the formation of microstructured nanoplates having an average diameter of 216 nm. Fluorine-doped tin oxide substrate was used for the deposition of film and also used as an electrode. The investigation of humidity was carried out at different relative humidity (RH)-11%, 33%, 44%, 54%, 74%, and 95%. The fabricated humidity sensor has shown excellent reversibility, stability and very small humidity hysteresis (<2%) at room temperature. The maximum response was observed as 41.95% at 95% RH with response and recovery time as 2 and 134 seconds, respectively. During the 30 days of observation, only a 0.4% decrease in response was observed. The fabricated WO3-based humidity sensor was investigated for human respiration having respiration rates of 2.51, 3.09, and 3.74 min-1.

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