Adsorption and Dynamics in Hierarchical Metal Organic Frameworks

F. Villemot, A. Galarneau, B. Coasne
Institut Charles Gerhardt, FR

Keywords: hierarchical, metal-organic frameworks, adsorption, transport

Summary:

Metal organic frameworks (MOF) are nanoporous solids made of metallic clusters linked by organic ligands. However, diffusion and transport of molecules inside these MOFs are hindered by their small pore sizes, which limit their efficiency toward specific applications. To overcome these diffusion issues, an approach is to connect the microporous framework to a secondary pore network with wider pores. In this presentation, we investigate hierarchical porous MOFs by means of molecular simulation. The models of hierarchical porous solids are obtained by carving mesopores of different diameters out of a crystal of Cu-BTC or by inserting a microporous particle of Cu-BTC in an amorphous silica mesopore. We show that the adsorption isotherms at 77K for the hierarchical solids can be described as a linear combination of reference adsorption isotherms for pure microporous and mesoporous solids, as long as there is no spatial overlap between the different porosity scales. We also perform molecular simulations under a pressure gradient in order to obtain the transport coefficients of the adsorbate. These coefficients are then used as input parameters for a novel bottom-up multiscale model which rigorously accounts for adsorption in each porosity scale.