Improving the performance of the QCM sensor in detecting IPA using chitosan and MOF-199 [EMBARGOED]

Abstract

Excessive exposure to volatile organic compounds (VOC) gas may lead to detrimental effects on humans, change in global climate, and damage the ecosystem as a whole. The conventional analytical instruments such as gas-chromatography mass-spectroscopy (GCMS) have its own limitations as they are not portable, and requires expertise. Hence, there is an urgent need for the development of the gas sensor for VOC detection. Quartz crystal microbalance (QCM) sensor based on piezoelectric effect offers potential alternative solution. Many efforts on designing sensing materials such as polymer and carbon-based material overlaying on QCM sensor have been reported. However, the reported sensing materials are prone to frequency change misinterpretation due to the variation in mass density of the sorbate and adsorbate. In this thesis, two types of QCM-based sensing materials: chitosan biopolymer and metal-organic framework (MOF) have been studied for VOC gas sensing namely isopropyl alcohol (IPA), acetone and toluene. The sensing materials were synthesized and characterized through X-Ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Field Effect Scanning Electron Microscopy (FESEM) to verify the material properties. Static, dynamic, and continuous measurements were conducted to analyze the sensor's performance in terms of sensitivity, selectivity and limit of detection (LOD). Finite element and adsorption isotherm modelling were also performed for further analysis. For chitosan biopolymer, the effect of different acetic acid solution concentrations (1.0% to 2.5% v/v) in chitosan was investigated. For MOF, two alcohol solutions used in MOF dispersion were tested (ethanol and mixture of methanol with water). Chitosan dissolved in 2.0% v/v acetic acid and MOF-199 powder dispersion in a methanol-water mixture demonstrated the highest response and frequency shift, respectively, when exposed to IPA analyte gas. Both chitosan and MOF-199 significantly improved the sensitivity of the QCM sensor in detecting IPA, with values of 26.1972 Hz/ppm and 79.0032 Hz/ppm, respectively. The LOD (0.1137 ppm) and response-rescovery time values (80 to 159 seconds) are comparable to prior research. Selectivity test shows that chitosan and MOF-199 are highly selective to IPA compared to acetone and toluene because of the presence of hydroxyl bond in IPA gas molecule. Chitosan demonstrated a good fit with Freundlich adsorption while MOF-199 showed an excellent fit with Freundlich adsorption regardless of the solvent used. The model was validated and observed to be in good agreement with the experimental data. These findings hold promise for improving sensor’s performance and achieving highly sensitive VOC detection.