Microwave Dielectric Spectroscopy Study of MOF Clathrates in Volatile Organic Compounds Detection

Abstract

Metal-organic frameworks (MOFs) are porous defective crystalline compounds that can form clathrates. In principle, the defects in these materials behave like the defects in other metal oxides such as ZnO, which are used as metal-oxide semiconductor gas sensors. Traditional chemical resistivity based MOS gas sensors require electrical contact to the sensing materials. These contacts are imperfect and will subsequently introduce errors into the measurements. In this paper, we will demonstrate the feasibility of using contactless broadband dielectric spectroscopy (BDS)-based metrology in gas monitoring that avoids distortions in the reported resistivity values due to probe use, and parasitic errors (i.e., tool-measurand interactions). Specifically, we will show how radio frequency (RF) propagation characteristics can be applied to study discrete processes involved in HKUST-1 SURMOF (Surface Anchored Metal-Organic Framework) sensing and detection of gases and volatile organic compounds (VOCs). HKUST-1 MOF films, also known as Cu3(BTC)2 (BTC: benzenetricarboxylicacid), consist of metal ions connected by organic ligands, forming highly ordered porous structures and are commonly grown by a layer-by-layer (LBL) liquid phase epitaxy (LPE) technique. We intend to use BDS to investigate the initial oxidization of MOF gas sensing material in air and nitrogen at temperatures below 200 °C, and to show that the technique yields new mechanistic insights that are unobtainable with the conventional resistance-based measurements.