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

Abstract

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 AHPs. 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.

Atomistic insight in the flexibility and heat transport properties of the stimuli-responsive metal–organic framework MIL-53(Al) for water-adsorption applications using molecular simulations

“…The influence of guest molecules on the thermal conductivity of MOFs is still a topic of debate, but lies beyond the scope of the current study. 26,32,109,110 Some studies have suggested that guest molecules improve the heat transfer (i.e. the thermal conductivity increases with the loading), while others have reported the opposite.…”

“…For practical MOF applications, the required amount of material will play an important role and is expected to remain constant throughout the operation of the device. Therefore, it is instructive to determine the absolute thermal conductivity κ abs , which is an extensive property (with units W/K): 30,110 with A the cross-sectional area perpendicular to the path of the heat flow (i-direction), d the thickness along the path of the heat flow, and κ the thermal conductivity along the path of the heat flow ( Figure S5). This quantity can be used to compare the heat transfer characteristics of the lp and the np phases for the same amount of matter, correcting for their different physical dimensions.…”

“…[112][113][114] For ZIF-8, Zhang and Jiang demonstrated that there is little overlap between the atomic VDOS of the main energy carriers (Zn and N) in the framework. 30,110 For MIL-53(Al), we quantified the overlap in VDOS along all atomic bonds using a similarity index: 97…”

Abnormal Effect of Phase Transition on Thermal Transport in Soft Porous Crystals

“…To data, only the thermal conductivity of some conventional SPCs such as MOF-5, [23][24][25][26] ZIF-8, [27][28][29][30][31][32] and HKUST-1 21,33,34 has been investigated in detail by experimental or computational approaches, while the thermal transport properties of the aforementioned DUT series remain unknown. In addition, the existing studies mainly focus on the influence of gas and water adsorption, 29,34 framework architecture, 24,28,[35][36][37] defects, 33 and physical environment including pressure 18 and temperature 20 on the thermal conductivity of SPCs, little attention has been paid to the evolution of the thermal transport properties of SPCs during their dynamic process, i.e., the phase transition. To the best of our knowledge, there are only two studies regarding the effect of phase transition on the thermal transport in SPCs using MD simulations.…”

Effect of Phase Transition on the Thermal Transport in Isoreticular DUT Materials

“…However, compared with the gas adsorption property, the study of thermal transport in SPCs is still in its very early stage. To data, only the thermal conductivity of some conventional SPCs such as MOF-5, 23-26 ZIF-8, [27][28][29][30][31][32] and HKUST-1 21, 33,34 has been investigated in detail by experimental or computational approaches, while the thermal transport properties of the aforementioned DUT series still remain unknown. In addition, the existing studies mainly focus on the influence of gas and water adsorption, 29,34 framework architecture, 24,28,[35][36][37][38] defects, 33 and physical environment including pressure 18 and temperature 20 on the thermal conductivity of SPCs, little attention has been paid to the evolution of the thermal transport properties of SPCs during their dynamic process, i.e., the phase transition.…”