A highly sensitive and fully flexible Fe-Co metal-organic framework hydrogel based gas sensor for ppb level detection of acetone

Abstract

Most nanomaterials based gas sensors are established on rigid substrates which require operation at elevated temperature and involve long recovery times, thus, limiting their practical applications. Addressing these issues, we demonstrate a fully flexible Fe/Co metal organic framework hydrogel (Fe/Co MOF HG) based gas sensor that detects ultra-low concentrations of acetone at room temperature. This hydrogel is synthesized using optimized concentration (3:1 M ratio) of Co:Fe with benzene dicarboxylic acid (BDC) in Fe/Co MOF via solvothermal method followed by lyophilization. Detailed morphological evaluation reveals 3-dimentional porous structure with multiple voids which largely enhances the specific surface area. Upon exposure to acetone, the Fe/Co MOF HG with Cu metal contacts based sensor exhibits a sensing response (S%) of 12.28 % to 500 ppb of acetone with a wide dynamic range of 200 ppb to 4 ppm. This remarkable sensitivity can be attributed to the abundance of water-adsorbed oxygen (Oc% = 24.58 %) in hydrogel as confirmed by XPS technique, which helps in the increase of the adsorption of a large proportion of acetone molecules on the surface of hydrogel. The limit of detection (LOD = 3σ/s) is found to be 103 ppb which is significantly lower than the other reported MOF-based acetone sensors. Further, the sensor demonstrates excellent selectivity against other common VOCs such as ammonia, benzene, toluene, and formaldehyde. Finally, the sensor’s outstanding stability (upto one-month), mechanical robustness when subjected to 230 cycles of bending and resilience to changes in humidity opens up new possibilities for the use of MOF-based hydrogels as gas sensors in several wearable device domains, such as health care and environmental monitoring.