Defect-induced tuning of polarity-dependent adsorption in hydrophobic–hydrophilic UiO-66

Abstract

Structural defects in metal–organic frameworks can be exploited to tune material properties. In the case of UiO-66 material, they may change its nature from hydrophobic to hydrophilic and therefore affect the mechanism of adsorption of polar and non-polar molecules. In this work, we focused on understanding this mechanism during adsorption of molecules with different dipole moments, using the standard volumetric adsorption measurements, IR spectroscopy, DFT + D calculations, and Monte Carlo calculations. Average occupation profiles showed that polar and nonpolar molecules change their preferences for adsorption sites. Hence, defects in the structure can be used to tune the adsorption properties of the MOF as well as to control the position of the adsorbates within the micropores of UiO-66.

Efficient Generation of Large Collections of Metal–Organic Framework Structures Containing Well-Defined Point Defects

“…For each molecule, the defect concentration has only a small impact on the adsorbed loading at low loadings, but at higher loadings, the presence of defects leads to substantial changes in the adsorbed amount. The trend of CO 2 adsorption isotherm from our study agrees with the previous studies of Wu et al and Jajko et al Further discussion of the data for UiO-66 can be found in the SI. The simulated adsorption isotherms of ethane, ethene, CO 2 , and H 2 S for HKUST-1, IRMOF-1, and ZIF-8 are shown in Figures S6–S8.…”

“…Tan et al reported experimental evidence that COO – and H 2 O are the capping agent in some treatments of UiO-66 . Our capping choice is chemically similar and has also been used in multiple previous studies. ,, …”

“…31 Our capping choice is chemically similar and has also been used in multiple previous studies. 20,27,32 Once it is straightforward to generate defective structures with varying concentrations of defects, it is interesting to ask what concentrations of defects are consistent with the structural information routinely available experimentally. To this end, we define a MOF's maximum possible defect concentration (MPDC) as the largest defect concentration that does not cause significant changes in the crystallinity or surface area relative to the pristine material.…”

The Boost of Toluene Capture in UiO-66 Triggered by Structural Defects or Air Humidity

“…Therefore, the presence of defects is of great effect on adsorption properties. In previous studies, we demonstrated the effect of the presence of defects on the adsorption of water, 24 polar and nonpolar molecules, 29 and carbon dioxide capture. 23 Based on the refined force field for toluene adsorption in ideal UiO-66, adsorption isotherms in defective materials were also calculated.…”

“…The UiO-66 material is known to contain structural defects, the concentration of which can be controlled by the synthesis temperature. Experimental studies (TG, EA, adsorption experiments) made it possible to determine the type of defects so formed. , It was shown that they are vacancies of linkers–bulky fragments, significantly increasing the available void fraction. Therefore, the presence of defects is of great effect on adsorption properties.…”