Large and Dense Block-like ZIF Aggregates with High Bulk Density for Enhancing Volumetric Adsorption Capacity

The bulk density and volumetric capacity are crucial indicators of an adsorbent in fixed-bed adsorption and separation operations. Herein, two types of CHA-ZIFs aggregates (CHA-ZIFs-H and CHA-ZIFs-L) with completely different morphologies were prepared by controlling the molar ratio of the mIm:RbIm (R = -Br/-Cl/-CH3) mixed ligand in the synthesis solution. All large and dense block-like CHA-ZIFs-H exhibit higher bulk density than small rodlike or disc-shaped CHA-ZIFs-L. The experimental and molecular simulation results demonstrate that the difference in bulk density of CHA-ZIFs is closely related to the stacked void volume caused by their aggregate morphology (size and shape) rather than being related to the difference in their limited mixed-linker composition, pore structure, and skeletal density. All CHA-ZIFs-H exhibit enhanced volumetric CO2 capacity compared to CHA-ZIFs-L. The CHA-ZIFs with a unique large-sized block morphology represent a new dimension of control over high bulk density and volumetric capacity.