The Thermal Properties of Pristine and Loaded HKUST-1 Thin Films Under Different Environmental Conditions

Abstract

Metal Organic Frameworks (MOFs) may prove as useful materials for the improvement of the efficiency of thermoelectrics. An improved Figure of Merit could be realized by taking advantage of the intrinsically low thermal conductivity of their porous organic makeup and improving the electrical conductivity by infiltrating the pores with selective host molecules. This study experimentally examines the thermal properties of HKUST-1 Metal Organic Framework (MOF) thin films using Time Domain Thermoreflectance (TDTR). The time scale associated with TDTR allows for a valid representation of thermal transport within the solid network of the porous composite. The MOF thicknesses vary from 200-350 nm and are constructed from Cu++ dimers and benzene-tricarboxylate (BTC) units which form a crystalline, 3-D porous structure with a pore diameter of 1.2 nm. The available pores allow the loading or storage of guest molecules, such as tertracyanoquin odimethane (TCNQ). We find evidence of no size effects on the thermal conductivity of the thin MOF films with thicknesses ranging from 200 – 350 nm. Additionally, the introduction of TCNQ host molecules within the infiltrated MOF does not significantly alter the thermal conductivity compared to the pristine samples. Exposure to ambient atmosphere causes an increase in the thermal conductivity of both the pristine and infiltrated MOFs, indicating that water adsorption may be occurring and altering the thermal properties of these materials. Activation of the pristine MOF recovers the thermal conductivity of the ideal state (before exposure to an ambient air environment) showing further application of these materials as a thermal switch.