Polyelectrolyte intercalated two-dimensional covalent organic framework membranes for efficient desalination

Abstract

Two-dimensional covalent organic frameworks (2D COFs) have been proven to be ideal membrane materials for highly efficient separation. However, synergistic manipulation of the in-plane pores and interlayer channel structures of 2D COF membranes (COFMs) to acquire both high permeability and selectivity has rarely been reported. In this work, we synthesized TbTG COF nanosheets with intrinsic sub-nanometer pores, which were assembled with polyelectrolytes to form intercalated 2D COFMs. The sub-nanometer in-plane pores of the COF nanosheets endowed the COFM with size sieving capacity toward hydrated multivalent ions. The polyelectrolyte introduces numerous charged groups to the interlayer channels, enhancing the Donnan effect for desalination and also enlarging the interlayer distance to facilitate permeability. Accordingly, the in-plane pores and interlayer channels of the 2D COFM were synergistically engineered to simultaneously enhance the selectivity and permeability of COFMs. By adjusting the polyelectrolytes with different charged groups, the intercalated COFMs exhibited a high Na2SO4 rejection of 97.5 % and MgCl2 rejection of 99.4 %, respectively, as well as about a fourfold increase in permeability. Compared with the pure COFM. This work highlights the significance of interlayer channel structure of 2D COFMs for precise separations, providing new guidelines on the design and construction of advanced COFMs.