Fabrication and deployment of nanodisc ZnO@ZIF-8, ZnO@NA and ZnO@INA core–shell MOFs: enhanced NH3 and HCHO gas sensing

Three nanodisc ZnO@MOFs, ZnO@ZIF-8 (1), ZnO@NA (2) and ZnO@INA (3) with structural building units 2-methylimidazole, nicotinic acid and isotonic acid are synthesized. These are fabricated and deployed as an advanced chemical capacitive sensors to detect formaldehyde and ammonia (NH3) at room temperature. These composite materials are characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD) spectra, scanning electron microscope (SEM) analysis, energy-dispersive X-ray spectroscopy (EDS), differential thermal analysis (DTA) and Brunauer–Emmett–Teller (BET) analysis. TGA studies suggest that these MOFs are stable up to 400 to 450 °C temperature. ZnO@ZIF-8 detected ammonia, formaldehyde, acetone and ethanol, while ZnO@NA and ZnO@INA detected ammonia and formaldehyde gases from 5 to 100 ppm range. ZnO@ZIF-8 showed microporous behaviour, while ZnO@NA and ZnO@INA showed mesoporous behaviours. Sensing performances were carried out at 5, 10, 25, 50 and 100 ppm concentrations of ammonia, acetone, formaldehyde, toluene, xylene and ethanol.