Molecular layer deposition of conjugated microporous polymers (CMPs) thin films for fast molecular sieving

Conjugated microporous polymers (CMPs) have great potential in membrane separation for their intrinsic microporosity and outstanding stability. Unfortunately, most CMPs are insoluble and infusible, thus it is very challenging to prepare CMPs membranes through conventional strategies. Herein, we report the molecular layer deposition (MLD) strategy to synthesize CMP thin films and their outstanding molecular sieving performances as nanofiltration membranes. Thanks to the gas-phase self-limiting reactions between volatile monomers during MLD, defect-free and large-area CMP thin films are deposited on porous substrates. The thickness of the CMP films is precisely tuned by the repeating MLD cycle numbers, and 100 MLD cycles result in a CMP thin film with the thickness of ∼ 70 nm. The as-prepared composite membranes with the deposited MLD thin films as the selective layers exhibit superior molecular sieving properties with a permeance up to 134 L m^-2h⁻¹ bar⁻¹, outperforming other CMP membranes. In addition, the perm-selectivity of CMP membranes can be easily tuned by changing MLD cycle numbers. We further demonstrate that, by optimizing the deposition process including selecting proper precursors, CMP thin films can be successfully MLD-deposited onto temperature-sensitive polymeric substrates with the size as large as 10 cm × 10 cm. This work shows the feasibility and great potential of MLD synthesis of CMP thin films, which opens new avenues not only for the synthesis of CMPs with highly controllable thickness, but also for the preparation of advanced membranes for diverse applications.