We started by synthesizing MOFs and studying their properties. Then, we designed substrates for gas sensing and transferred MOFs onto it. Next, we checked if the MOFs connected well with the substrates. Finally, we tested how well they detect GHGs. We disseminated our findings through conference presentations and research papers. An overview of these actions is provided below:
1) Synthesis/characterization of MOFs: Different MOFs were successfully synthesized by a chemical approach in a well-equipped chemistry lab at the University of Barcelona. In particular, a variety of known ligands, including triphenylene (TP), porphyrin, and imidazole, were used to design MOF structures. For example, MOFs based on TP and different metal sources (Cu/Ni/Zn) were synthesized and labelled as Cu-MOF, Ni-MOF, and Zn-MOF, respectively. Similarly, other MOFs based on imidazole and porphyrin were synthesized with optimized conditions to ensure consistent results. These MOF materials were characterized using a range of analytical techniques (XRD/FTIR/SEM/TEM/XPS/BET) to confirm their size, shape, structure, composition, and surface area.
2) Design of substrates/chamber and transfer of MOFs: Two types of chips were designed on glass substrates by standard photolithography and sputtering techniques: one with Cr/Pt electrodes and another with Ti/Au electrodes (see schematic view). These chips have electrodes arranged in a comb-like structure with varying gap dimensions. These substrates/chips, when paired with MOF samples, worked well for electrical sensing measurements. We also developed a gas chamber (see schematic view) for sensing studies that allowed us to study electrical behaviours of MOFs in various conditions, with/without external light. Following that, we calibrated and aligned the chamber with labs existing gas lines. Later, we tried 2 methods to transfer MOFs on substrates: direct synthesis and a paste transfer. The direct synthesis failed due to solubility issues of organic ligands. Ultimately, we found success with a drop-casting method that involved mixing MOF powder with DI water.
3) Gas sensing tests: For sensing tests, we started by acquiring gas cylinders that contained different gases (CH4, CO2, CO, C2H5OH, NH3), all of which were air-balanced and their flow into the chamber was controlled by mass flow controllers. We focused on understanding how the electrical resistances of our MOF-based sensors vary when exposed to different gases. We began conducting sensing tests on TP-based (Cu/Ni/Zn) sensors towards target gases at room temperature, which showed that they are effective in detecting these gases. TP-based sensors, when exposed to CH4, exhibit a significant increase in resistance compared to other gases, indicating their effective detection ability, notably detecting CH4 levels of 1.2 ppm at room temperature. This achievement is significant because it surpasses the atmospheric concentration of CH4 that was reported in 2023 at 1.92 ppm. Thus, our electrical approach has been successful in achieving our objective of detecting CH4 level below those found in the atmosphere. Besides, it is important to highlight that our TP-based MOF sensors are significant for their ability to detect CO2 levels as well. Even though the atmospheric CO2 is at a high 420 ppm, our TP-based MOF sensors can detect concentrations as low as 152 ppm.
4) Dissemination and exploitation activities: The project outputs were effectively disseminated through following presentations at various conferences and publications.
Publications:
i) S. Navale, I.F. Grandas, Y. Mendoza, M. Moreno, P. Pellegrino, A.R. Rodriguez, D. Sainz, A.V. Ferran, Chemiresistive Methane Gas Sensing Properties of Triphenylene-based Metal-organic Frameworks, SMSI 2023: Sensor and Measurement Science International, pages 108-109, DOI: 10.5162/SMSI2023/B4.1.
ii) S.T. Navale, I.F. Grandas, M. Moreno, D. Sainz, A.V. Ferran, A.R. Rodriguez, Hexahydroxytriphenylene Based MOFs as a Chemiresistive Sensing Platform for Room Temperature CH4 Detection (Under preparation).
Conferences:
i) S. Navale, I.F. Grandas, Y. Mendoza, P. Pellegrino, M. Moreno, A.R. Rodriguez, D. Sainz, A.V. Ferran, Zn-Based Triphenylene Metal-organic Frameworks as a Chemiresistive Platform for Methane Detection, EUROSENSORS XXXV CONFERENCE, 10-13 Sept. 2023, Lecce, Italy.
ii) S.T. Navale, I.F. Grandas, Y. Mendoza, P. Pellegrino, M. Moreno, D. Sainz, A.V. Ferran, A.R. Rodriguez, A Chemiresistive Methane Gas Sensing Properties of Nanorods of Hexahydroxytriphenylene-based Metal-organic Frameworks, E-MRS 2023 SPRING MEETING, Strasbourg, France (May 29 to June 2, 2023).
iii) S. Navale, I.F. Grandas, Y. Mendoza, M. Moreno, P. Pellegrino, A.R. Rodriguez, D. Sainz, A. Vidal-Ferran, Chemiresistive Methane Gas Sensing Properties of Triphenylene-based Metal-organic Frameworks, Sensor and Measurement Science International, 8-11 May 2023, Nuremberg, Germany.
