Assembling two-dimensional (2D) materials by polyelectrolyte often suffers from inhomogeneous microstructures due to the conventional mixing-and-simultaneous-complexation procedure (“mix-and-complex”) in aqueous solution. Herein a “mix-then-on-demand-complex” concept via on-demand in-situ cascade anionization and ionic complexation of 2D materials with poly(ionic liquid) is raised that drastically improves structural order in 2D assemblies, as exemplified by classical graphene oxide (GO)-based ultrathin membranes.[1] Specifically, in dimethyl sulfoxide the carboxylic acid-functionalized GO sheets (COOH-GOs) were mixed evenly with a cationic poly(ionic liquid) (PIL), and upon filtration formed a well-ordered layered composite membrane with homogenous distribution of PIL chains in it; next whenever needed, it was alkali-treated to convert COOH-GO in situ into its anionized state COO--GO that immediately complexed ionically with the surrounding cationic PIL chains. This “mix-then-on-demand-complex” concept separates the ionic complexation of GO and polyelectrolytes, from their mixing step. By synergistically combining the PIL-induced hydrophobic confinement effect and supramolecular interactions, the as-fabricated nanofiltration membranes carry interface transport nanochannels between GO and PIL, reaching a high water permeability of 96.38 L m-2 h-1 bar-1 at a maintained excellent dye rejection 99.79% for 150 h, exceeding the state-of-the-art GO-based hybrid membranes. The molecular dynamics simulations support the experimental data, confirming the interface spacing between GO and PIL as the water transport channels.

On-demand complexation of poly(ionic liquid) with graphene oxide for high-performance nanofiltration membranes

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