Tuning Intercrystal Interactions between Metal-Organic Frameworks through Water Adsorption

Naturally powdered metal-organic frameworks (MOFs) usually require packing for practical applications, where intercrystal interactions play pivotal roles. Herein, using an atomic force microscope with a MOF HKUST-1 crystallite-tipped probe, we directly find that the intercrystal adhesion energy of as-synthesized HKUST-1 with adsorbed water molecules is quadruple that of its activated counterpart. A similar large enhancement in the intercrystal adhesion energy of HKUST-1 due to water adsorption is also observed in molecular dynamics simulations, which is ascribed to the formation of strongly interacting hydrogen-bond networks, driven by copper paddlewheels massively exposed on HKUST-1 surfaces and intercalated water molecules adsorbed in surface cavities. Our discrete-element-method simulations further illustrate that the broad tunability of intercrystal interactions of HKUST-1 via water adsorption provides a new avenue to manipulate its packing properties. This work not only expands the understanding of intercrystal surface properties of MOFs but also offers a novel strategy to tune their intercrystal interactions.