Reticulating Supramolecular Anion Receptors to Engineer Water Channels in Metal–Organic Framework/Polymer Membranes

To combine the advantages of the crystalline microenvironment ensured by reticular chemistry and the specific recognition ability of supramolecular anion receptors, a metal–organic framework (MOF), Zn(BPCz) (aka. ROD-66, H2BPCz = 3,6-bis(1H-pyrazol-4-yl)carbazole), is designed and synthesized, which contains helical rod-like metal chains pillaring carbazole N–H hydrogen-bond-donor-based anion receptors. The gourd-shaped nanochannels equipped with tetramers of anion recognition sites play a critical role in resolving the captured HgCl3– anionic species through N–H···Cl interaction, as well as a surrounding (H2O)n network, featuring an unusually abrupt disorder-to-order transition due to guest-induced host symmetry change. Such a bifunctional microenvironment endows both high anion capture capacity and high hydrophilicity, establishing water channels in the MOF/polymer membranes to break the trade-off between ion rejection and water permeance. The achieved high removal efficiency (>95%) and high-water flux (>1000 L/m2·h) simultaneously outperform various metal oxide/sulfide/phosphate-, carbon-, and MOF-based hybrid water purification membranes. This work sheds light on leveraging the advantages of supramolecular chemistry and MOF materials to engineer synthetically designed nanochannels in advanced membrane materials, reminiscent of biological water channel aquaporin.