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    Molecular layer deposition for the fabrication of desalination membranes with tunable metrics

    Year: 2021

    Journal: Desalination, Volume 520, DEC 15

    Authors: Welch, Brian C.; McIntee, Olivia M.; Myers, Tyler J.; Greenberg, Alan R.; Bright, Victor M.; George, Steven M.

    Organizations: National Science Foundation (NSF) through the Membrane Science, Engineering and Technology Center [NSF IUCRC Award] at the University of Colorado, Boulder [IIP 1624602]

    Keywords: Molecular layer deposition (MLD); Thin-film composite (TFC); Surface modification; RO polyamide membrane; m-Phenylenediamine and trimesoyl chloride

    The recent advancement of semiconductor devices to the near-atomic scale necessitated the development of atomic layer processing methods, including molecular layer deposition (MLD). This gas-phase deposition technique creates semipermeable polymer films with precise control of composition and thickness. Herein, MLD was used to produce thin-film composite reverse osmosis membranes. Aromatic polyamide films as thin as 0.5 nm were applied to NF270 nanofiltration membranes using m-phenylenediamine and trimesoyl chloride. Within two molecular layers, desalination performance was affected. As film thickness increased to 15 nm (48 MLD cycles), performance progressed from nanofiltration to reverse osmosis metrics in terms of salt rejection and water permeance. With film thickness > 5 nm, rejection values exceeded a small sampling of commercial membranes. In all cases, a tradeoff between rejection and permeance was observed. Atomic force microscopy measurements indicate that MLD enhancement led to removal of small-scale roughness features and resulted in a root mean square roughness difference of <0.1 nm from the substrate. These initial MLD studies represent a novel processing approach that offers a potential pathway for the fabrication of membranes with finely tailored properties.
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