Issue 32, 2014

Force field for ZIF-8 flexible frameworks: atomistic simulation of adsorption, diffusion of pure gases as CH4, H2, CO2 and N2

Abstract

A full set of flexible force field parameters for ZIF-8 is presented, based on the AMBER, UFF parameters and the partial charges computed by the density-derived electrostatic and chemical charge method (DDEC). The parameters for the 2-methyl imidazole (MeIM) ring are adopted from the AMBER force field, while the van der Waals (VDW) parameters for organic linkers and metal centers were determined by rescaling the UFF parameters as ε = 0.635εUFF and σ = 1.0σUFF to fit the CH4 adsorption isotherms obtained by Grand Canonical Monte Carlo (GCMC) simulations with the force field parameters to the experimental ones. The CH4 adsorption isotherms on four different structures of ZIF-8 at 298 K obtained by GCMC simulations are compared with the experimental data. The results show that the simulated CH4 adsorption isotherms on the ZIF-8 structure reported from the Cambridge Crystallographic Data Centre (CCDC) are closest to the ones on the ZIF-8 structure from the report of Moggach et al. To test our model, adsorption isotherms of CH4, H2, CO2 and N2 at different temperatures were computed using GCMC simulations, and the results were found to be in a good agreement with the experimental data. In the case of H2, the equilibrium configurations obtained by GCMC simulations were statistically analyzed with ad hoc code to get probability density distribution profiles. These profiles were transformed to visual slice images, which indicate that the preferential adsorption sites of H2 molecules in ZIF-8 are located close to the MeIM rings, where the host–guest VDW or electrostatic interactions are maximal, as revealed by the potential energy surfaces (PES). In addition, these force field parameters were confirmed to well reproduce the ZIF-8 structural properties including lattice constants, bond lengths and angles over a wide range of temperatures. The self-diffusivities at the specific loadings of adsorbed gases (CH4, H2 and CO2) in ZIF-8 were calculated by the mean squared displacement (MSD) method. It was found that our self-diffusivities of H2 are slightly higher than the ones in the literature, and our self-diffusivity of CO2 is as about three times as the one in the literature, due to the different partial charges and the effect of different force field parameters on framework shape and flexibility in our simulations.

Graphical abstract: Force field for ZIF-8 flexible frameworks: atomistic simulation of adsorption, diffusion of pure gases as CH4, H2, CO2 and N2

Supplementary files

Article information

Article type
Paper
Submitted
23 Jan 2014
Accepted
12 Feb 2014
First published
18 Feb 2014

RSC Adv., 2014,4, 16503-16511

Author version available

Force field for ZIF-8 flexible frameworks: atomistic simulation of adsorption, diffusion of pure gases as CH4, H2, CO2 and N2

X. Wu, J. Huang, W. Cai and M. Jaroniec, RSC Adv., 2014, 4, 16503 DOI: 10.1039/C4RA00664J

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements