Understanding of the Graphene Oxide/Metal-Organic Framework Interface at the Atomistic Scale

An atomistic model of the metal-organic framework (MOF) ZIF-8/graphene oxide (GO) interface has been constructed using a combination of density functional theory calculations and force-field-based molecular dynamics simulations. Two microscopic models of GO were constructed integrating basal plane and both basal and edge plane functional groups, called GO-OH and GO-CO₂H, respectively. Analysis of the MOF/GO site-to-site interactions, surface coverage, and GO conformation/stiffness and a full characterization of the interfacial region is provided with a special emphasis on the influence of the chemical composition of GO. It was evidenced that the structure of the GO/ZIF-8 composite at the interface is stabilized by a relatively homogeneous set of interactions between the hydrogen atoms of the -NH and -OH terminal functions of ZIF-8 and the oxygen atoms of the epoxy, hydroxyl, and carboxylic groups of GO, leading to an optimal coverage of the MOF surface by GO. Such a scenario implies a significant distortion of the first GO layer brought into contact with the MOF surface, leading to an interfacial region with a relatively small width. This computational exploration strongly suggests that a very good compatibility between these two components would lead, in turn, to the preparation of defect-free ZIF-8/GO films. These predictions are correlated with an experimental effort that consists of successfully prepared homogeneous MOF/GO films that were further characterized by transmission electron microscopy and mechanical testing.