Ionic liquid modified COF nanosheet interlayered polyamide membranes for elevated nanofiltration performance

Abstract

Presently, advanced Thin-film nanocomposite (TFN) nanofiltration membranes fabricated using microporous materials displayed distinctly enhanced separation performance. Herein, tetrakis(hydroxymethyl) phosphonium chloride (THPC)-modified COF nanosheets (termed as IL@COF-367 NSs) were designed as the intermediate layer to construct a high-hydrophilic membrane support, with the purpose of regulating interfacial polymerization (IP) to optimize the physicochemical characters of polyamide films. Due to the high hydrophilicity and favored dispersion of IL@COF-367 NSs in aqueous phase, the as-fabricated COF nanosheet interlayer not only promotes uniform distribution of amine monomers, but also slows down their diffusion toward the organic interface. Compared pristine thin-film composite (TFC) membranes, the IC-TFN membranes yield a nodular polyamide film with a higher surface roughness (from 14.5 to 54.5 nm) and a lower film thickness (from 95 to 30 nm). Introducing IL@COF-367 NSs additionally improves the pore size (from 0.31 to 0.47 nm) of the functionalized TFN membrane revealed by the MWCO measurement. Consequently, IL@COF-367 NSs-interlayer polyamide (IC-TFN) membrane manifests a high permeability of 36.5 L m−2 h−1 bar−1 and satisfactory Na2SO4 rejection of 98.5 %. The usage of 2D hydrophilic COF nanosheet as an interlayer to optimize the polyamide membranes offers a guideline for the design of high-performance TFN membrane.