Hierarchical Graphene/Metal–Organic Framework Composites with Tailored Wettability for Separation of Immiscible Liquids

Membrane filtration is a promising technology for the separation of organic immiscible liquids. Surface topography has a direct impact on the wettability of membranes, and it remains largely unexplored. Here, we introduce on-demand liquid separation by coating porous graphene/metal-organic framework (MOF) composites with tunable wettability on porous substrates. Our results have shown that polydopamine (PDA) coating mediates the controlled growth of MOF nanostructures and subsequent fluorination on the porous graphene framework. Surface topography of the graphene frameworks strongly depends on the loading content of MOF nanostructures. The concurrent control of surface coverage of MOF and surface chemistry allows tailoring of the trapped air fraction underneath the porous graphene frameworks in the range of 0.97 to 0.8. As a result, the surface energy of the graphene/MOF coatings can be programmed to afford the change in surface properties from superamphiphobicity to lyophobicity and the selective penetration of low-surface-energy (SE) liquids and the interception of high-SE liquids were achieved. The tailored wettability of graphene/MOF coatings allows for the separation of liquid mixtures of different ranges of SE, making it a general strategy for complex liquid treatment and chemical purification.