Impact of Flushing Agents in Broadband Dielectric Spectroscopy (BDS) Study of Ethanol Detection By HKUST-1 Metal-Organic Frameworks

Abstract

Traditional volatile organic compounds (VOC) detection with metal semiconductor oxide (MOS) sensing elements depends on chemical resistivity measurements which require electrical contact to the sensing materials [1]. These measurement contacts / probes are inadequate because they tend to introduce parasitic electrical errors which result in misleading reported resistivity values [2]. On the other hand, contactless broadband dielectric spectroscopy (BDS) is a potential alternative metrology [3]. In this paper, we will demonstrate that by using contactless broadband dielectric spectroscopy (BDS)-based metrology, in combination with a metal-organic framework (HKUST-1 SMOF) sensing element, we can avoid distortions in the reported resistivity values in gas monitoring, as well as develop new and unique mechanistic insights into the VOC detection. Specifically, we show that the experimental ambient influences the detection mechanism. The microwave insertion loss data (S21) shows that we lose resolution when N2 was used as the flushing agent, as compared to air, during the measurements. This suggests a possible competition between the ethanol and the N2 for the unsaturated copper centers inside the MOF. Therefore, we opted to use air as a flushing agent in the subsequent experiments. Additionally, the use of BDS enables stable VOC sensing in air at temperatures below 100 °C, which are well below the 200-300C normally used for VOC detection [1, 2].1) Huaping Wang et al 2021 J. Phys.: Condens. Matter 33 3030012) Chem. Soc. Rev., 2020,49, 6364-6401, https://doi.org/10.1039/C9CS00778D3) Papa K Amoah et al 2021 J. Phys. D: Appl. Phys. 54 135104