Impacts of Ethanol and Water Adsorptions on Thermal Conductivity of ZIF-8

Metal-organic frameworks are promising nanoporous materials for adsorption heat pumps (AHPs) using water and alcohols as working fluids due to their ultrahigh surface area. The heat transfer in porous crystals containing adsorbed gases is vital for their performance in adsorbed natural gas storage or AFIPs. However, limited attention has been paid to their thermal properties. In this study, equilibrium molecular dynamics simulations were performed to investigate the impacts of ethanol/water adsorption on the thermal conductivity of zeolitic imidazolate framework-8 (ZIF-8). The results demonstrated that the thermal conductivity of ZIF-8 increased from 0.165 to 0.319 W m(-1) K-1 with the increased number of adsorbed ethanol molecules. On the contrary, the thermal conductivity of ZIF-8 upon water adsorption is approximately 0.190 W m(-1) K-1, which is not significantly affected by the number of adsorbed water molecules. Such a different tendency may be ascribed to the different interaction strengths between ZIF-8 and gas molecules. In addition, the larger overlap energy in the vibrational density of state of ZIF-8/ethanol than that of ZIF-8/water also correlates with the higher thermal conductivity of the ZIF-8/ethanol system. This work provides molecular insights into the effects of ethanol/water adsorption on the thermal conductivity of ZIF-8, which may inspire further exploration of novel techniques to improve the heat transfer performance of practical applications.