Flexible MOF–aminoclay nanocomposites showing tunable stepwise/gated sorption for C₂H₂, CO₂ and separation for CO₂/N₂ and CO₂/CH₄

Abstract

Miniaturization of flexible metal–organic frameworks (F-MOFs) to nanoscale is expected to show interesting structural dynamics and serve numerous applications from separation and drug delivery to sensing. However, nanoscale F-MOFs or their composites have remained largely unexplored to date. Here, we present a new and facile method to stabilize F-MOF nanocrystals on an aminoclay (AC) template and study their tunable, enhanced gas adsorption and separation properties. We demonstrate miniaturization of two different 2D F-MOFs, {[Cu(pyrdc)(bpp)](5H₂O)}_n (F-MOF1) with a pillared-bilayer structure and {[Cu(dhbc)₂(4,4′-bpy)]·H₂O} (F-MOF2) with an interdigitated network, on AC that acts as a functional template to grow and stabilize MOF nanocrystals. Different F-MOF1@AC composites were synthesized where the gate/step pressure for specific adsorbate molecules (CO₂/C₂H₂) could be tuned by varying the AC content. Enhanced guest adsorption with stepwise behaviour has also been realized in a certain composite. Breakthrough column experiments with the F-MOF2@AC composite show its capability to separate CO₂/N₂ and CO₂/CH₄ gas mixtures under ambient conditions.