Investigation of Fundamental Gas Sensing Mechanism of Conductive Metal-Organic Frameworks By in-Situ/Operando Spectroscopy Analysis
Authors: Choi Seon-Jin 
Published: December 2024

Detection of various gases is important for environmental monitoring and healthcare applications. For example, volatile organic compounds (VOCs) such as toluene and xylene are harmful to human health causing headache, dizziness, and nausea, which is known as the sick-building syndrome. In addition, hydrogen sulfide (H2S) is a biomarker gas for the diagnosis of halitosis by exhaled breath analysis. The development of gas-sensing materials with high surface area and large porosity is important for the accurate detection of target molecules. Among the various types of materials, conductive metal-organic frameworks (MOFs) are attractive for the development of chemiresistive-type gas sensors, transducing chemical interaction into an electrical signal.[1]
Chemiresistive gas sensors have gained much attention considering their simple operation principle, potential for miniaturization, and capability of real-time detection. In our previous works, various nanostructures such as 1D nanofibers, 2D nanosheets, and 3D hierarchical composites were synthesized and highly sensitive gas sensing properties were demonstrated.[2-5] Conductive metal-organic frameworks exhibited characteristic sensing properties mainly resulting from the catalytic surface reaction of metal nodes. However, the fundamental sensing mechanism is largely unknown due to the difficulty of real-time surface chemical analysis during the gas sensing measurement.
In this presentation, we propose a novel in-situ/operando spectroscopy analysis to investigate fundamental sensing mechanisms of conductive metal-organic frameworks toward H2S and VOCs. We synthesized conductive 2D copper-2,3,6,7,10,11-hexahydroxytriphenylene (Cu3(HHTP)2) as a gas sensing layer. In terms of the H2S sensing mechanism, we observed surface-adsorbed polysulfide generating a characteristic peak in the in-situ Raman spectroscopy analysis. In addition, we observed oxidation of toluene (i.e., benzaldehyde) after the surface reaction between Cu3(HHTP)2 and toluene, which is confirmed by in-situ GC-MS analysis. Our unique approaches utilizing the in-situ/operando spectroscopy analysis technique pave a new way for investigating fundamental gas sensing mechanisms of emerging gas sensing materials, which will rationalize high-performance gas sensors.

Reference

[1] Jeon, M.; Kim, M.; Lee, J. S.; Kim, H.; Choi, S. J.; Moon, H. R.; Kim, J., Computational Prediction of Stacking Mode in Conductive Two-Dimensional Metal-Organic Frameworks: An Exploration of Chemical and Electrical Property Changes. Acs Sensors
2023.
[2] Kim, S. J.; Choi, S. J.; Jang, J. S.; Cho, H. J.; Kima, I. D., Innovative Nanosensor for Disease Diagnosis. Accounts Chem Res
2017, 50, (7), 1587-1596.
[3] Choi, S. H.; Lee, J. S.; Choi, W. J.; Seo, J. W.; Choi, S. J., Nanomaterials for IoT Sensing Platforms and Point-of-Care Applications in South Korea. Sensors-Basel
2022, 22, (2).
[4] Choi, S. J.; Kim, I. D., Recent Developments in 2D Nanomaterials for Chemiresistive-Type Gas Sensors. Electron Mater Lett
2018, 14, (3), 221-260.
[5] Choi, S. J.; Persano, L.; Camposeo, A.; Jang, J. S.; Koo, W. T.; Kim, S. J.; Cho, H. J.; Kim, I. D.; Pisignano, D., Electrospun Nanostructures for High Performance Chemiresistive and Optical Sensors. Macromol Mater Eng
2017, 302, (8).