(248b) Towards the Rational Design of Metal-Organic Frameworks: Using Molecular Simulations to Understand Adsorption Phenomena in Mofs

Porous metal-organic frameworks (MOFs) have recently gained much attention as promising materials for gas adsorption. These materials are generated in a directed-assembly process under mild synthesis conditions and feature metal vertices interconnected by organic linker molecules to form three-dimensional, nanoporous crystalline materials. As a result of the building block approach, a multitude of materials with different pore shapes, pore sizes, and framework topologies exist. Furthermore, these materials offer the possibility to tune host / guest interactions by functionalisation of the linker molecules and therefore to tailor them rationally for a given adsorption separation or storage task. Because of the predictability of the synthetic routes to MOFs and the nearly infinite number of variations possible, molecular modelling is an attractive tool for screening new structures before they are synthesised. They also allow predictions to be made about the adsorption potential once enough of a material has been synthesised to determine the structure thus enabling to judge whether to scale up the synthesis. Additionally, the molecular level details provided by the simulations give valuable information about the relationship between material properties and adsorption performance.

Atomistic models and grand canonical Monte Carlo simulations were used to predict single-component and binary adsorption of alkanes and hydrogen in MOFs with different pore sizes, shapes and framework topologies. Simulation results were compared to experimental adsorption isotherms and heat of adsorption data where available and in general showed good quantitative agreement. The materials were carefully characterised using Monte Carlo methods to get e.g. pore size distributions, surface areas, and pore volumes. Comparing these characteristics with the performance of the adsorbents in terms of uptake or selectivities allows conclusions about the most promising pore shapes and framework topologies for a given application, which is an important step towards developing a design strategy for MOFs.