Conformal and highly adsorptive metal–organic framework thin films via layer-by-layer growth on ALD-coated fiber mats

Abstract

Integration of metal–organic frameworks (MOFs) on textiles shows promise for enabling facile deployment and expanding MOF applications. While MOFs deposited on flat substrates can show relatively smooth surface texture, most previous reports of MOFs integrated on fibers show poor conformality with many individual crystal domains. Here we report a new low-temperature (<70 °C) method to deposit uniform and smooth MOF thin films on fiber surfaces using an energy enhanced layer-by-layer (LbL) method with an ALD Al₂O₃ nucleation layer. Cross-sectional TEM images show a well-defined core@shell structure of the MOF-functionalized fiber, and SEM shows a flat MOF surface texture. We analyze the thickness and mass increase data of LbL HKUST-1 MOF thin films on ALD-coated polypropylene fibers and find the growth rate to be 288–290 ng cm⁻² per LbL cycle. Unlike planar LbL MOF embodiments where adsorption capacities are difficult to quantify, the large volume quantity on a typical fiber mat enables accurate surface area measurement of these unique MOF morphologies. After 40 LbL cycles the MOFs on fibers exhibit N₂ adsorption BET surface areas of up to 93.6 m² g_MOF+fiber⁻¹ (∼535 m² g_MOF⁻¹) and breakthrough test results reveal high dynamic loadings for NH₃ (1.37 mol_NH3 kg_MOF+fiber⁻¹) and H₂S (1.49 mol_H2S kg_MOF+fiber⁻¹). This synthesis route is applicable to many polymer fibers, and the fiber@ALD@MOF structure is promising for gas filtration, membrane separation, catalysis, chemical sensing and other applications.