Thin-Film Nanocomposite Membrane with the Minimum Amount of MOF by the Langmuir-Schaefer Technique for Nanofiltration

An innovative procedure for positioning a monolayer of hydrophilic metal organic framework (MOP) MIL-101(Cr) (MIL, Materials of Institute Lavoisier) nano- particles (NPs) in thin-film nanocomposite (TFN) membranes has been implemented by transferring a Langmuir-Schaefer (LS) film of the MOF in between the polyamide thin layer at the top and the cross-linked asymmetric polyimide (P84) support at the bottom. The presence and layout of the LS-MIL-101(Cr) monolayer in the TFN membrane was confirmed by scanning transmission electron microscopy imaging with a high-angle annular dark-field detector images and X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy, and atomic force microscopy analyses. This methodology requires the smallest amount of MOF reported to date,3.8 mu g cm(-2), and promotes the formation of a defect-free ultrathin MOF film. Although conventional TFN membranes tend to show MOF agglomerates that could contribute to the formation of unselective defects, LS-TFN membranes, characterized by a homogeneous and continuous MOF coating, exhibit an optimal membrane performance, without a significant decrease in selectivity. Outstanding methanol permeances, one of the best results reported to date, of 10.1 +/- 0.5 L m(-2) h(-1) bar(-1) when filtering sunset yellow and of 9.5 +/- 2.1 L m(-2)h(-1) bar(-1) when filtering rose bengal have been achieved in LS-TFN membranes with a rejection higher than 90% in all cases. Methanol permeates through the polyamide and the LS-MIL-101(Cr) monolayer, greatly enhanced by the MOF pore system, in comparison to thin-film composite and conventional TFN membranes (7.5 +/- 0.7 and 7.7 +/- 1.1 L m(-2) h(-1) bar(-1) when filtering sunset yellow), respectively, in which polyamide areas free of MOF NPs are present.