A humidity tolerance and room temperature carbon soot@ZIF-71 sensor for toluene vapour detection

Abstract

The Solid-state chemiresistive gas sensing devices are the desirable recruit to detect toxic gases and volatile organic compounds; however, the growth of real-life applications of these sensors is poor due to their drawbacks, including high working temperature, showing poor responses during moderate to high humidity, and poor selectivity towards the gas of interest. In this work, we synthesised zeolitic imidazolate framework (ZIF-71), carbon soot (CNPs) and CNPs@ZIF-71 composite and were successfully characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The ZIF-71, CNPs and CNPs@ZIF-71 composites are used to fabricate the sensors to detect toluene, ethanol, mesitylene, diethyl ether and acetonitrile vapours at room temperature. The ZIF-71 did not respond to any of the tested VOCs at room temperature; however, the CNPs sensor showed some little response to the tested VOCs. However, the linear response was not observed as the analyte concentration increased. However, the CNPs@ZIF-71 showed excellent response and sensitivity towards the toluene vapour and less sensitivity towards mesitylene, diethyl ether, acetonitrile and ethanol vapours. ZIF-71 synergistically improves CNPs sensing performances on toluene vapour detection. The CNPs@ZIF-71 sensor was found to be highly resistive during the detection of toluene vapour. The calculated limit for the detection of toluene vapour on the CNPs@ZIF-71 composite sensor was 518 ppb. In situ, FTIR coupled with LCR meter online analysis was done to study the sensing mechanism, and it was found that toluene vapour detection on sensor 3 undergoes total deep oxidation to form H₂O and CO₂ as by-products.