Structurally anisotropic COF membranes with tilted skeletons for high-efficiency desalination

Abstract

Addressing the global water crisis requires breakthroughs in membrane design that fundamentally alter water and ion transport mechanisms. Here, we demonstrate that the structurally anisotropic 1,3,5-HPB-COF membranes with tilted skeletons redefine desalination at the molecular level. These skeletons, oriented perpendicularly to the COF plane, form directional interconnected pores that enhance membrane porosity and effectively suppress lateral water diffusion, thereby channeling molecules through vertical transmembrane pathways. In addition to geometric confinement, the inherent anisotropic electrostatic environment generates pronounced energy barrier differentiation—4.3 kJ mol⁻¹ for H₂O, compared to 19.4 kJ mol⁻¹ for Na⁺ and 15.7 kJ mol⁻¹ for Cl⁻, enabling precise molecular sieving and robust ion exclusion. These synergistic mechanisms, including directional confinement, energy barrier selectivity, and electrostatic exclusion, collectively yield exceptional desalination performance. Molecular dynamics simulations reveal that a trilayer 1,3,5-HPB-COF membrane (∼2 nm thick) achieves a water permeance of 3485 L m⁻² h⁻¹ bar⁻¹ and a salt rejection of 97.3%. Our findings provide theoretical insight into tilted-skeleton frameworks as a promising direction for membrane design, illustrating how precise structural control at the molecular level can overcome the permeability–selectivity trade-off and inform the development of next-generation high-efficiency desalination membranes.