Printed Capacitive Sensors Based on Ionic Liquid/Metal-Organic Framework Composites for Volatile Organic Compounds Detection

In this paper, the potential of 2D printing technologies to create thin film gas sensors from ionic liquid (IL)/metal–organic framework (MOF) composites is evaluated. To accomplish this, the MOF is synthesized solvothermally, and impregnated with the IL. The structure and basic properties of the IL/MOF composites are characterized using thermal, spectroscopic, and X-ray diffraction techniques, and the resultant sensing capacity of the bulk material is evaluated by impedance spectroscopy. The IL/MOF systems are then integrated into a 2D printed silver capacitive circuit by spray and tested on a custom-made gas flow apparatus. Exposure of the IL/MOF based sensors to water, acetone, and ethanol induces a repetitive variation of the capacitance (from 0.05 to 7 pF) that is dependent on the nature of the gas. IL/MOF based sensors can detect changes in concentrations in the range of 10k–100k ppm in less than a second. The conclusions of this work are the first steps towards the development of 2D printed sensors based on IL/MOF materials. Such materials offer countless possibilities to tailor the porosity, chemistry, selectivity, and electrical response to make the sensor suitable to detect the desired analyte.