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Covalent and Selective Grafting of Polyethylene Glycol Brushes at the Surface of ZIF‑8 for the Processing of Membranes for Pervaporation

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journal contribution
posted on 05.03.2019, 00:00 by Marvin Benzaqui, Rocio Semino, Florent Carn, Sergio Rodrigues Tavares, Nicolas Menguy, Mónica Giménez-Marqués, Elena Bellido, Patricia Horcajada, Thomas Berthelot, Anna I. Kuzminova, Maria E. Dmitrenko, Anastasia V. Penkova, Denis Roizard, Christian Serre, Guillaume Maurin, Nathalie Steunou
The so-called Graftfast reaction in water and at room temperature (RT) was applied to graft polyethylene glycol (PEG) at the surface of the microporous zeolitic imidazolate framework ZIF-8 nanoparticles (NPs) using acrylPEG of different chain lengths (480 Da and 5 kDa). In comparison to nonmodified ZIF-8 NPs, both chemical and colloidal stabilities of PEGylated ZIF-8 NPs are significantly enhanced in water. A series of colloidal complex fluids by mixing PEG grafted ZIF-8 (i.e., PEG-g-ZIF-8) NPs with different amounts of poly­(vinyl alcohol) (PVA) was prepared and characterized by advanced characterization tools such as dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) thereby showing their long-term colloidal stability. Finally, dense and supported mixed matrix membranes were cast from PEG-g-ZIF-8/PVA solutions and have shown high performance in isopropanol (IPA) dehydration by pervaporation. The permeation flux of the supported MMM (i.e., 0.091 kg/(m2·h)) is 11 times higher than that of the pure PVA membrane and these MMMs present a high separation factor (i.e., 7326). These transport properties are presumably due to the molecular sieving effects induced by ZIF-8 and the good interfacial properties of the membrane. The computational exploration of the ZIF-8/PVA and PEG/PVA interfaces provides a microscopic scale explanation for the enhanced compatibility of PVA with the PEGylated MOF when compared to that for the composite based on the bare ZIF-8 as a filler.