Physical and Chemical Dual Confinement Promotes Controllable Synthesis of Loose-Structured Azine-Linked Nanofilms for Fast Molecular Separation

Thin-film composite (TFC) membranes, featuring nanoscale film thickness and customizable pore structures, hold promise for solute-solute separations. However, achieving on-demand molecular sieving requires fine control over the membrane microstructure. Here, the concept of physical and chemical dual confinement (PCDC) is introduced to fabricate loose-structured TFC membranes via confined interfacial polymerization (IP). This concept leverages the synergistic effects of physically restricted monomer diffusion and a chemically inhibited reaction to achieve controlled nanofilm growth. Dorsal addition of the aqueous phase to the hydrogel reduces the diamine diffusion via electrostatic and H-bonding interactions within its nanopores. The prepassivation of hydrazine using acid protonation effectively weakens its ability for nucleophilic reactivity. This confined IP between twisted TFPA and short-chain hydrazine yielded loosely structured azine-linked nanofilms, which displayed a high permeability of 53.4 LMH bar^-1 and effective differentiation of binary mixtures. This PCDC concept offers a useful guideline to finely tailor polymeric nanofilms for precise separations.