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. 2020 Aug 3;11(32):8433-8437.
doi: 10.1039/d0sc03318a.

Free-standing metal-organic framework (MOF) monolayers by self-assembly of polymer-grafted nanoparticles

Kyle Barcus  1 , Seth M Cohen  1
Affiliations

Free-standing metal-organic framework (MOF) monolayers by self-assembly of polymer-grafted nanoparticles

Kyle Barcus et al. Chem Sci. .

Abstract

We report a general method for the synthesis of free-standing, self-assembled MOF monolayers (SAMMs) at an air-water interface using polymer-brush coated MOF nanoparticles. UiO-66, UiO-66-NH2, and MIL-88B-NH2 were functionalized with a catechol-bound chain-transfer agent (CTA) to graft poly(methyl methacrylate) (PMMA) from the surface of the MOF using reversible addition-fragmentation chain transfer polymerization (RAFT). The polymer-coated MOFs were self-assembled at the air-water interface into monolayer films ∼250 nm thick and capable of self-supporting at a total area of 40 mm2. Mixed-particle films were prepared through the assembly of MOF mixtures, while multilayer films were achieved through sequential transfer of the monolayers to a glass slide substrate. This method offers a modular and generalizable route to fabricate thin-films with inherent porosity and sub-micron thickness composed of a variety of MOF particles and functionalities.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Scheme 1
Scheme 1. Surface functionalization procedure for coordinating cat-CTA to MOF. MOF particles (UiO-66) are depicted by polyhedron with aqueous and organic solvents represented by the blue and yellow layers, respectively. Mixed (vortexed) solutions represented by green color.
Fig. 1
Fig. 1. Free-standing monolayer of self-assembled UiO-66(Zr)-PMMA. (a) Images of the monolayer taken at different angles to show both clarity and iridescence. (b) SEM image of the monolayer surface showing tightly packed UiO-66(Zr)-PMMA particles. Scale bar is 2 μm. (c) SEM image of film from the side, illustrating the continuous monolayer. Scale bar is 5 μm.
Fig. 2
Fig. 2. Effect of polymer brush molecular weight on order and packing of UiO-66(Zr) particles. (a) 30 minutes, Mn = 6.3 kg mol−1Đ = 2.15. (b) 1 hour, Mn = 8.3 k Đ = 1.8. (c) 2 hours, Mn = 59 kg mol−1Đ = 1.49. (d) 4 hours, Mn = 138 kg mol−1Đ = 1.16. All scale bars are 3 μm.
Fig. 3
Fig. 3. Monolayer, multilayers, and mixed monolayers of MOFs. (a) Monolayer of MIL-88B(Fe)-NH2-PMMA. (b) Bilayer of UiO-66(Zr)-PMMA (bottom) and MIL-88B(Fe)-NH2-PMMA (top). (c) Multilayer of UiO-66(Zr)-PMMA (bottom) and MIL-88B(Fe)-NH2-PMMA (middle) and UiO-66(Zr)-NH2-PMMA (top). (d) Mixed monolayer comprised of UiO-66(Zr)-PMMA (larger particles) and UiO-66(Zr)-NH2-PMMA (smaller particles). All scale bars are 1 μm.
See this image and copyright information in PMC

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