Molding of Core–Shell Pellets of Flexible Metal–Organic Frameworks to Prevent Slacking of Gate Adsorption Behavior

Abstract

Flexible metal–organic frameworks (MOFs) exhibit stepwise adsorption behavior, so-called gate adsorption, and are expected to bring dramatic advances in adsorption separation processes. Since flexible MOFs are obtained in powder form, molding is required for their use in industrial applications. However, the gate adsorption is accompanied by non-negligible volume expansion, which makes it difficult to balance durability and adsorption performance in the molded form: pellets are crushed with low binder content, while the gate adsorption is smeared with high binder content. In this study, core-shell-like pellets of elastic layer-structured MOF-11 (ELM-11) were formed by a newly developed method mimicking the artificial caviar production process. The obtained pellets achieved both the robustness and sharpness of gate adsorption, which resulted from a rational design of the pellets that the shell ensured the durability of the pellet, while in the core part, ELM-11 particles were not tightly bound to allow the structural deformation.