A wide range of metal-organic frameworks (MOFs) have been synthesized through isoreticular synthesis using organic linkers and metal ions or metal clusters, to create a new class of porous materials with large surface area for more efficient gas storage, catalysis, separation, and gas sensing.
However, MOFs are typically formed as crystalline powders making them difficult to handle, manipulate and position for desired application. One way to address this constraint is to integrate or couple MOFs onto fibrous scaffolds. Our previous work has demonstrated atomic layer deposition (ALD) can impart uniform and conformal MOF nucleation sites onto the fiber mats, thus leading to nucleation and growth of highly absorbent MOFs that are covalently attached to the mats. We previously attained high mass loading (up to 300 wt.%) for Cu(BTC) MOFs on fibers, but mass loading for UiO-66-NH2 is typically smaller (30 wt.%).
Here we report a novel synthesis route to assemble UiO-66-NH2 onto polymeric fibrous scaffolds to achieve additional MOF mass loading and mesoporosity in the MOF-fiber structures. Especially UiO-66-NH2 has been well known to reveal high thermal stability over 400 °C, decent chemical stability to atmospheric moisture, and photocatalytic effect in visible range at high efficiency. Using solvothermal synthesis at 85 °C, we prepared a UiO-66-NH2 seed layer on ALD-coated polypropylene fiber mats. Subsequently, we assembled UiO-66-NH2 onto the seeded fiber surface using cetyltrimethylammonium bromide (CTAB) and β-cyclodextrin (β-CD). Owing to host-guest interaction, we were able to obtain a supramolecular complex, thereby further increasing the mass loading of UiO-66-NH2. X-ray diffraction confirms good crystallinity of the UiO-66-NH2 coating. Furthermore, SEM images show UiO-66-NH2 agglomerates fill the void space inside the MOF-seeded fiber mesh. Moreover, N2 adsorption analysis shows the creation of extra mesoporosity and reveals the Brunauer-Emmett-Teller (BET) surface area of the MOF-functionalized fiber mats, exceeding 90 m2/gMOF+Fiber. We will discuss how synthesis conditions affect the assembly of UiO-66-NH2 and show how robust these MOF coatings are on the fiber substrates. Similar assembly strategy can also be applied to other MOFs such as CuBTC, and is promising for new MOF-based composites for a wide variety of applications.