Metal‐organic nanosheet gels: Hierarchically porous materials for selective loading and differential release

Metal-organic nanosheets (MONs) are intrinsically porous 2D materials with a high surface area and tunable chemistry, which have been widely used in suspensions or on surfaces for a variety of applications. Here, this work demonstrates that MONs can be used to form gels through a simple centrifugation process, and their hierarchically porous structures used to enable the selective loading and differential release of small molecules based on their size and charge. Centrifugation of a suspension of monolayer Zr-BTB MONs (BTB = 1,3,5-benzenetribenzoate) formed gels in a range of solvents with a concentration of ≈1.5 wt.%. The gels displayed rapid self-healing behavior, can be extruded through a syringe needle into different shapes, and freeze-dried to form self-supporting aerogels. Rapid and selective loading of the gels with a range of small molecules can be achieved by centrifugation of suspensions of nanosheets containing different cargo solutions. Small neutral molecules are found to diffuse out of the gel significantly faster than larger molecules, which is attributed to the nanosheets acting as “fishing nets” that allow small molecules to pass through the pores, whilst larger molecules have to take a tortuous path through the hierarchically porous structure. Charged molecules are released slower than the neutral ones, which is attributed to electrostatic interactions with the nanosheets. It is anticipated that hierarchically porous MON-based gels will open up a variety of interesting new applications, including sensing, separation, controlled release, drug loading, and drug delivery.