Tailoring ultrathin microporous polyamide films with rapid solvent transport by molecular layer-by-layer deposition

Abstract

Abstract In this work, a new molecular layer-by-layer deposition (MLD) approach was demonstrated to tailor thin-film composite (TFC) membranes with ultrathin microporous polyamide (PA) films as separation layers used for organic solvent nanofiltration (OSN). The extrinsic and intrinsic microstructures of the crosslinked PA layers were synergistically tailored by the layer-by-layer reaction between rigid tri-amine monomer 1,3,5-tris(4-aminophenyl)benzene (TAPB) with trimesoyl chloride (TMC). The thickness of defect-free PA layers, which exhibited a homogeneous cross-sectional morphology, was decreased down to 26\u202fnm by regulating the deposition cycles, which is advantageous to achieve high solvent permeability. Moreover, the generated PA layers displayed high microporosity (specific surface area up to 114\u202fm2\u202fg−1) due to the rigid polyphenyl tri-amine structure of TAPB monomer. These characteristics conferred upon the prepared TFC membranes with exceptional solvent permeabilities (5.5, 5.0, 14.6, and 39.8\u202fL\u202fm−2\u202fh−1\u202fbar−1 for ethanol, dimethyl formamide, methanol, and acetonitrile, respectively) and high rejection (93.2%) towards methyl orange (327\u202fDa of molecular weight), all of which are higher than those of the majority of state-of-the-art TFC membranes using PA or other newly porous materials (e.g., polyacrylates, polymers of intrinsic microporosity-1) as separation layers. Furthermore, the membranes showed excellent solvent and pressure resistance due to highly cross-linking network character. Given the noticeable advantages of this method, a new alternative for preparing high-performance TFC OSN membranes can be provided.