Assembly of Two-Dimensional Metal Organic Framework Superstructures via Solvent-Mediated Oriented Attachment

Due to their high anisotropy and tunable chemical composition, two-dimensional metal organic frameworks (2D MOFs) have great potential as building blocks for next-generation materials in a diverse range of applications—from electrochemical catalysis to membrane separation. However, the controllable synthesis is complicated by the environment–surface interactions that arise from the high anisotropy, thinness, and functionally diverse surfaces of 2D MOFs. Liquid cell transmission electron microscopy (LCTEM) offers a unique opportunity to study these interactions in situ. In this work, we analyzed the effects of different solvent environments on the structure and aggregation dynamics of copper benzene dicarboxylic acid (CuBDC) nanosheets, which were synthesized using a high shear annular microreactor. LCTEM revealed that 2D MOF nanosheets undergo oriented attachment and that the rate and direction of oriented attachment is controlled by solvent–surface interactions. We investigated the nature of these solvent interactions using density functional theory calculations, which suggest that the binding energy of solvents to different MOF surfaces is likely responsible for this behavior. The CuBDC nanosheets were then applied as adsorbents in organic solvents, in which we showed how solvent-mediated oriented attachment could significantly affect adsorption properties.