(42b) Designing Iron Oxide-Metal Organic Framework Superstructures By Ligand-Mediated Self-Assembly

Exploring the impact of surface ligands on self-assembly indicates the potential of a delicate controlled structures, which favors the various relevant applications through collective properties of assembled independent NPs. We demonstrate for the first time a co-assembly of Metal Organic Framework (MOF) and Iron Oxide (Fe₃O₄)nanoparticles, which is mediated by surface ligands on Fe₃O₄ nanoparticles. In the co-assembly process by adding a mixture solution of Fe₃O₄ and MOF NPs onto a liquid-air interface, the oleic acid capped Fe₃O₄ NPs initially formed a superlattice template which enhanced a single layered MOF film co-assemble on its top, resulting a 2D double-layered superstructure. When the surface ligands of Fe₃O₄ NPs were exchanged to polystyrene (PS), Fe₃O₄ and MOF NPs randomly assembled into single-layered structure. STEM/EDX and three-dimensional tomography reconstruction images have confirmed the different hierarchical structures formed by co-assembly of Fe₃O₄ NPs and MOF NPs with different capping ligands. By varying the experimental conditions, we found that the different self-assembly processes could be mediated by the surface ligands of Fe₃O₄ NPs. First principle calculations and Monte Carlo (MC) simulations were used to understand the different self-assembly behaviors, which further confirmed our hypothesis on ligand-mediated self-assembly. This study opens a new avenue for co-assembly of MOF NPs with inorganic NPs for functional materials, and provides deep kinetic understanding on self-assembly.