β-Ketoenamine Porous Organic Cage Membranes Through Hydrogel-Induced Shielding for Efficient Ion Sieving

Porous organic cages (POCs) with intrinsic and extrinsic microporosity offer a promising platform for efficient ion sieving. However, assembling these cages into a continuous POC nanofilm with well-defined pore architecture remains a challenge. Here we propose a hydrogel-induced interfacial shielding strategy to fabricate continuous cage membranes via interfacial polymerization between (1R,2R)-1,2-cyclohexanediamine (CHDA) and 1,3,5-triformylphloroglucinol (Tp). Kevlar hydrogel capable of storing high-concentration CHDA is utilized for rapid formation of an initial film barrier, preventing the diffusion of hydrophilic Tp-based intermediates into the aqueous phase. This shielding effect enables the confinement of Tp-based compounds within the organic phase and thereby intensifies molecular cage assembly at the hydrogel-organic interface. Manipulation of high-concentration diamine leads to accelerated formation of continuous nanofilms, which intensifies the shielding effect and thus yields crystalline cage films and POC nanoparticles in the organic phase. The resultant cage membranes exhibit an impressive water permeability of 22.8 L m^-2 h^-1 bar^-1 and high cation removal efficacy. Further insights from molecular dynamics simulations reveal that the ordered assembly of POC molecules within the membrane is critical to enable the rapid and selective transport of ions. Our interfacial shielding strategy sheds light on developing crystalline cage membranes for efficient ion separations.