Scalable Art-Inspired Tessellated Covalent Organic Framework Membranes Enable Highly Selective Ion Separation

Covalent organic frameworks (COFs), distinguished by their periodic and tunable network structures, exhibit great potential for molecular and ionic separation. Nevertheless, fabricating COF membranes with angstrom-scale pores faces challenges in precisely controlling channel dimensions and achieving seamless integration of frameworks. Here, we report the synthesis of a substoichiometric aminal-linked COF with a pore size of ∼5 Å and develop a covalent tessellation strategy inspired by Escher's art and derived from interfacial polymerization, that successfully fabricates defect-free tessellated COF (tCOF) membranes. The resulting tCOF membrane exhibits ultra-microporous structures, achieving high water permeance of 10.2 L m^-2 h^-1 bar^-1, nearly perfect Na₂SO₄ rejection of 99.4%, and exceptional Cl^-/SO₄ ^2- selectivity of 1,090. The tCOF membranes can be continuously scaled up to roll-to-roll format with a width of 30 cm and an unlimited length. The potential applications in resource recovery are proved with a two-stage nanofiltration process, which produces NaCl with a high purity of >99% from NaCl/Na₂SO₄ mixtures. Therefore, the innovative covalent tessellation methodology reported in this work provides a new avenue for the development of scalable COF membranes with angstrom-scale pores for highly selective separation.