Developing membranes that show selective molecular transport properties is of great importance for fundamental research and practical applications (Refs: Nat. Rev. Mater., 2021, 6, 294; Science, 2017, 356, eaab0530). However, it remains challenging to precisely control the nanostructure and porosity in membranes to separate molecules or ions with angstrom-level size differences. Here, we present ultrathin and ordered 2D conjugated-polymer-framework (CPF) films with thicknesses down to 1 nm via surface-confined chemical vapor deposition (CVD), recently published in Nature Materials 2022, 21, 1183. The CPF membranes inherently have regular rhombic sub-nanometer (10.3 × 3.7 Å) channels for achieving a superior separation ability, unlike the membranes made of carbon nanotube or graphene, whose separation performance depends on the alignment or stacking of materials. The optimized membrane stably exhibited a high water/NaCl selectivity of ~6900, water permeance of ~112 mol m-2 h-1 bar-1 for more than 200 hours, and salt rejection greater than 99.5% in the high-salinity mixed-ion separation. Molecular dynamics simulations revealed that water molecules quickly and collectively pass through the membrane by forming a continuous three-dimensional network within the hydrophobic channels. In addition, our work revealed that the porosity and surface charge of CPF membranes could be finely tuned by controlling the CVD growth conditions, which were further engineered for ion sieving and osmotic energy harvesting with an output power density of ~2.3 W m-2. We envisage that through the rational molecular design of monomers, our strategy will allow facile synthesis of other types of CPF materials, which are promising for many potential applications, including carbon capture, energy-efficient separation, ion batteries, and organic solar cells.

Ultrathin and ordered conjugated-polymer-framework membranes

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