Sorption-Induced Structural Transition of Zeolitic Imidazolate Framework-8: A Hybrid Molecular Simulation Study

Abstract

A new force field and a hybrid Monte Carlo/molecular dynamics simulation method are developed to investigate the structural transition of zeolitic imidazolate framework-8 (ZIF-8) induced by N2 sorption. At a high loading (approximately 50 N2 molecules per unit cell), ZIF-8 shifts from low-loading (LL) to high-loading (HL) structure. A stepped sorption isotherm is predicted with three distinct regions, which agrees well with experimental data. The orientation of imidazolate rings and the motion of framework atoms exhibit sharp changes upon structural transition. Furthermore, pronounced changes are observed in various contributions to potential energies (including stretching, bending, torsional, van der Waals, and coulombic). The analysis of radial distribution functions between N2 and framework atoms suggests N2 interacts strongly with the imidazolate rings in ZIF-8. The simulation reveals that the structural transition of ZIF-8 is largely related to the reorientation of imidazolate rings, as attributed to the enhanced van der Waals interaction between N2 and imidazolate rings as well as the reduced torsional interaction of framework in the HL structure. This is the first molecular simulation study to describe the continuous structural transition of ZIF-8 and, it provides microscopic insight into the underlying mechanism.

Methane in zeolitic imidazolate framework ZIF-90: Adsorption and diffusion by molecular dynamics and Gibbs ensemble Monte Carlo

“…The results showed a significant effect between rigid and flexible framework in the self-diffusion coefficient (D s ) and the flexible model using GAFF gives better results compared with the experiment. This influence of the flexibility on D s can also be found in other ZIFs [13][14][15] and MOFs [16] while the adsorption isotherm seems to be much less sensitive with respect to the lattice flexibility [17,18] as long as no structural phase transition like the so called gate opening [19][20][21] takes place. On the other hand, Zhang et al.…”

Characteristic features of molecular transport in MOF ZIF-8 as revealed by IR microimaging

“…The first separating ZIF membranes were synthesized with ZIF-8 [23]. The experimental studies were accompanied by a variety of molecular simulations to provide insight into the underlying mechanism on the atomistic scale [16,[24][25][26][27][28][29][30][31].…”

Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

“…The force field used to describe intra-and intermolecular interactions of the ZIF structures, as well as the ZIF/CH 4 intermolecular interactions, was taken from the very recent work of Zhang et al 28 This force field is derived from the very generic AMBER forcefield, where some of the terms involving Zn atoms were reoptimized to better reproduce the ZIF-8 structure and possible overall rotations of the imidazolate linker. Since ZIF-8 contains 2-methylimidazolate as a linker, we adapted it slightly by replacing the methyl group with a hydrogen atom, taking its parameters from the original AMBER parametrization for consistency.…”