Controllable synthesis of a chemically stable molecular sieving nanofilm for highly efficient organic solvent nanofiltration

Abstract

Membranes with versatile separation capacity and strong chemical resistance are necessary for organic solvent nanofiltration (OSN). Here, a molecular sieving nanofilm with Janus pore structures was synthesized by introducing alkyl (–CH₂–) moieties into the hydrophilic cross-linked polyamide network. In situ interfacial polymerization between m-xylylenediamine (m-XDA) and trimesoyl chloride (TMC) monomers was manipulated on a solvent-resistant nanofibrous hydrogel substrate. By varying monomer concentrations, thin film composite (TFC) OSN membranes were achieved with tuneable nanofilm thickness and hydrophobicity. Janus pathways in the m-XDA/TMC molecular sieving nanofilm contribute to a high solvent permeability for both polar and non-polar solvents; for example, for acetone the permeability is 8.2–54.5 L m⁻² h⁻¹ bar⁻¹, for n-hexane 0.6–2.6 L m⁻² h⁻¹ bar⁻¹, and for toluene 4.2 L m⁻² h⁻¹ bar⁻¹. The composite membrane revealed a molecular weight cut-off of 242–327 g mol⁻¹ in both acetone and methanol. Moreover, the membrane exhibited chemical and structural stability after immersing it in both strongly acidic or strongly basic environments for 15 days. This outstanding chemical stability, combined with the excellent permeability and selectivity, makes the m-XDA/TMC composite membrane a promising candidate for versatile OSN applications in polar and non-polar solvents as well as under extreme conditions.