Fabrication of Chemiresistive Gas Sensors from Triphenylene-Based MOFs for Greenhouse Gas Monitoring

Current monitoring systems of Greenhouse Gases (GHGs) are bulky and energetically expensive, thus being restricted to a few fixed locations. However, the need arises to develop gas sensing devices that could be placed in large numbers and many locations. For instance, by introducing gas sensors in autonomous data collection and transmission systems, data on specific target gas levels would be acquired, allowing the development of more precise climate change models via the Internet of things (IoT). To fulfil that purpose, the sensing devices must be designed to fit the following criteria: miniaturized, cost-effective, energy efficient and selective. Within the wide arrange of sensor types, room temperature chemiresistive devices stand out due to their low-energy consumption and miniaturized characteristics.<br/><br/>Metal-organic Frameworks (MOFs) show great promise as active materials for gas sensing devices. Their nanostructured, high surface area and high-porosity nature make them a fitting choice for gas related applications, and a subfamily of the MOFs present room-temperature conductivity values ideal for chemiresistive studies. There are various types of conductive MOFs depending on their conduction mechanisms. In this work, we focus on 2D MOFs with extended conjugation and though-plane conduction mechanisms. Our work ranges from triphenylene derivative MOFs, such as 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7,10,11-hexaaminotriphenylene (HITP) MOFs, to new MOFs based on highly-conjugated ligands containing N heterocycles and imine groups. We synthesized highly crystalline layers of the beforementioned 2D MOFs, aiming to improve their conductive and gas sensing properties and also carrying out a comprehensive study of their crystallographic structures to elucidate the conduction and gas sensing mechanisms. The conductive MOFs are deposited onto interdigitated electrodes (IDE) to fabricate the gas sensing devices. We compare IDEs of different designs, as well as the ligand and metal of choice of each MOF that yield the most suitable chemiresistive responses for the GHGs sensing devices.<br/><br/>In this presentation, we will present and discuss the findings regarding the full characterization of the crystallinity and morphology of the 2D MOFs and the deposited layers, bringing new insights on the underlying conduction and gas sensing mechanisms. We will also present the gas sensing performance of these chemiresistive devices towards the most relevant GHG, namely CO₂, CH₄ and N₂O.