Evidence of Gate-Opening on Xenon Adsorption on ZIF-8: An Adsorption and Computer Simulation Study

Abstract

We report on experimental (thermodynamics and kinetics) and computer simulation results for Xe sorption in ZIF-8. At temperatures below ∼145 K, there are two substeps present in adsorption isotherms (before saturation is reached). The substep that occurs at higher loadings was identified as corresponding to ZIF-8’s gate-opening transition. Above 145 K, this higher-loading substep is no longer resolvable. We determined the isosteric heat of adsorption for this system and obtained a value of 244 meV for sorption on the more strongly binding sites in the ZIF-8. We found that there is a peak in the isosteric heat of adsorption, as a function of sorbent loading, associated with the gate-opening transition. We estimated the heat of transition for gate-opening to have an upper bound of ∼30 meV. Our results for the isotherms and the isosteric heats are compared with those from our Monte Carlo computer simulations, obtained using both the structure of ZIF-8 before and after the gate-opening transition and a new set of mixed Lennard-Jones parameters. We conducted measurements for the sorption kinetics for this system. We found that, while the sorption occurs faster as the loading increases before the gate-opening transition, the equilibration times increase with loading in the gate-opening region, resulting in an unusual nonmonotonic behavior for the variation of this quantity as a function of sorbent loading.

The impact of crystal size and temperature on the adsorption-induced flexibility of the Zr-based metal-organic framework DUT-98

“…In a recent report, we demonstrated the suppression of adsorption-induced contraction in DUT-49 (DUT-Dresden University of Technology) upon downsizing of the crystals below 1 µm 9 and loss of flexibility upon downsizing of DUT-8 crystals 17,18 . In a similar fashion suppression of gate opening in ZIF-8 upon crystal downsizing was reported [10][11][12][13] and Kitagawa and co-worker reported on a shape-memory effect of gate opening transitions upon crystal downsizing in a pillared-layer MOF. 19 Although these reports demonstrate the influence of crystal size on the structural behavior of flexible MOFs, the materials for which this phenomena were reported differ in terms of topology, the nature of the structural transitions and the resulting adsorption behavior.…”

“…An increasing number of the so-called flexible MOFs are being reported and their use in the areas of storage 4 , separation 5 and sensing 6 of gases are being evaluated and their structural flexibility and adsorption behavior can be manipulated by applying chemical functionalization to the ligand 7 and metal cluster 8 . However, recent examples progressively illustrate the manipulation of adsorption properties of switching adsorbents by variation of size [9][10][11][12][13] and morphology 14 of the crystals, without changing the composition of the MOF. Reports on MIL-53 indicate an impact of crystal morphology and size on the structural contraction upon solvent removal 15,16 .…”

Reversible control of triplet dynamics in metal-organic framework-entrapped organic emitters via external gases

“…Because, the ZIF-8 pores can adsorb Xe molecules 44 , this result can be attributed to an external heavy-atom effect induced by Xe. The yellow phosphorescence with peaks of 487, 509, 527, 539, 563, and 608 nm in Ar changes into green phosphorescence with peaks of 517, 525, 529, 563, 594, and 609 nm in Xe.…”

“…These results clearly indicate that the strength of the external heavy-atom effect can be tuned with the concentration of the external gas. Even though the atomic size (4.4 Å) of Xe is slightly larger than the window size of ZIF-8 (3.4 Å), Xe atoms can pass through the windows of ZIF-8 and interact with the coronene-d 12 because the window size can be expanded by the rotation of the imidazole linkers 44 . Since there is no strong encapsulation effect between the Xe atoms and the pores of ZIF-8, Xe atoms can be removed by exposing the film to a different gas or placing the film under vacuum.…”

Solvent‐Dependent Adsorption‐Driven Mechanism for MOFs‐Based Yolk–Shell Nanostructures

“…To our knowledge,the gate-opening behavior of ZIF-8 can be triggered by the adsorption of gas or even solvent molecules, which is at opological transition due to the partial reorientation of imidazolyl-linked ligands. [31][32][33][34] Thus,t he mechanism for the formation of yolk-shell structures may be attributed to selective or competitive adsorption of CH 3 OH and H 2 Oo n the hydrophobic backbone of ZIF-8 and microporous compounds,aswell as nanoscale Ostwald ripening.…”