Assembly of ZIF-67 Metal-Organic Framework over Tin Oxide Nanoparticles for Synergistic Chemiresistive CO2 Gas Sensing

Metal-organic frameworks (MOFs) are widely known for their record storage capacities of small gas molecules (H-2, CO2, and CH4). Assembly of such porous materials onto well-known chemiresistive gas sensing elements such as SnO2 could be an attractive prospect to achieve novel sensing properties as this affects the surface chemistry of SnO2. Cobalt-imidazole based ZIF-67 MOF was grown onto preformed SnO2 nanoparticles to realize core-shell like architecture and explored for greenhouse gas CO2 sensing. CO2 sensing over SnO2 is a challenge because its interaction with SnO2 surface is minimal. The ZIF-67 coating over SnO2 improved the response of SnO2 up to 12-fold (for 50% CO2). The SnO2@ZIF-67 also showed a response of 16.5 +/- 2.1% for 5000ppm CO2 (threshold limit value (TLV)) at 205 degrees C, one of the best values reported for a SnO2-based sensor. The observed novel CO2 sensing characteristics are assigned to electronic structure changes at the interface of ZIF-67 and SnO2.