Metal-Organic Frameworks with a Bioinspired Porous Polymer Coating for Sieving Separation

Polymer/metal-organicframework (MOF) composites have beenwidely studied for their favorable combination of polymer flexibilityand MOF crystallinity. While traditional polymer-coated MOFs maximizethe polymer properties at the surface, the dramatic loss of MOF porositydue to blockage by the nonporous polymeric coating remains a problem.Herein, we introduce intrinsically microporous synthetic allomelanin(AM) as a porous coating on the zirconium-based MOF (Zr-MOF) UiO-66via an in situ surface-constrained oxidative polymerization of theAM precursor, 1,8-dihydroxynaphthalene (1,8-DHN). Transmission electronmicroscopy images verify the formation of well-defined nanoparticleswith a core-shell morphology (AM@UiO-66), and nitrogen sorptionisotherms indicate the porosity of the UiO-66 core remains constantand is not disturbed by the AM coating. Notably, such a strategy couldbe adapted to MOFs with larger pores, such as MOF-808 by generatingporous AM polymer coatings from bulkier DHN oligomers, highlightingthe versatility of this method. Finally, we showed that by tuningthe AM coating thickness on UiO-66, the hierarchically porous structuresof these AM@UiO-66 composites engender excellent hexane isomer separationselectivity and storage capacity.

Automated summary

In this study, micro-porous synthetic allomelanin (AM) was used as a porous coating on the surface of the MOF material UiO-66. The core-shell structured AM@UiO-66 nanoparticles were successfully prepared through in situ surface-constrained oxidative polymerization. Nitrogen sorption isotherms confirmed that the AM coating did not affect the pore size and porosity of UiO-66. It was demonstrated that by tuning the thickness of the AM coating, the AM@UiO-66 composites exhibited excellent hexane isomer separation selectivity and storage capacity.