The detection of volatile organic compounds using a CNPs/polypyrrole-based Solid-State sensor operating at room temperature

In this work, we report the use of carbon nanoparticles (CNPs), commonly as carbon soot, as they are prepared from the pyrolysis of lighthouse candle, polypyrrole (PPy) and carbon nanoparticles@polypyrrole (CNPs@PPy) composite sensors to detect volatile organic compounds at room temperature. Five sensors were fabricated wherein the first sensor was made up of PPy only was named sensor 1, sensor 2 was made up of CNPs only; sensor 3 was made up of a 1:1 mass ratio of CNPs@PPy, sensor 4 was made up of a 2:1 mass ratio of CNPs@PPy, and sensor 5 was fabricated using a 3:1 mass ratio of CNPs@PPy respectively. The sensors were tested dynamically using acetone, 2-propanol, ethanol, and mesitylene vapours. Among all the tested sensors, sensor 5 showed improved sensitivity towards the analytes as compared to sensors; sensor 5 showed higher sensitivity towards acetone vapour than 2-propanol, ethanol, and mesitylene vapours because of a changed amount of CNPs within the composite. The response and recovery times of sensor 5 towards acetone vapour were 72 and 110 s, respectively and a limit of detection (LOD) of 1.212 ppm. Sensor 5 showed a slight increase in acetone vapour as humidity increased. The gas sensing mechanism on sensor 5 was studied using an in situ Fourier Transform infrared spectroscopy (FTIR) combined with an LCR meter; basically, the acetone vapour interacts with the solid-state gas sensor supplied with 0.5 V at 25 kHz. The setup confirmed that the acetone completely decomposes into carbon dioxide (CO₂). It was also confirmed that the CO₂ band intensity increases as the exposure time between the acetone vapour and the sensor increases.