Homointerface covalent organic framework membranes for efficient desalination

Abstract

Covalent organic frameworks (COFs) are an emergent class of crystalline porous polymers featuring a long-range regular pore structure, high porosity and excellent chemical stability. Bilayer COF membranes with tunable interfaces hold great promise in ionic and molecular separations. Herein, we designed a series of bilayer COF membranes with homointerface and heterointerface, which achieved efficient desalination performance through manipulating the interface confinement effect. COF membranes were prepared on a porous support through successively regulating the growth of imine-based 2D COF layers by in situ growth and counter-diffusion approach at ambient temperature. Narrowed sub-nanometer interlaced channels were created at the interface of the two adjacent COF layers. The rejection rate of homointerface COF membrane toward Na₂SO₄ was higher than that of heterointerface COF membranes, which was due to the synergistic enhancement of interface-confined size sieving and Donnan effect. The homointerface TpPa–SO₃H/TpPa–SO₃H/MPAN membrane exhibits a rejection rate of 98.3% for Na₂SO₄ and water flux of 13.1 L m⁻² h⁻¹ bar⁻¹, which is the highest performance among COF desalination membranes ever reported.