Heterostructured two-dimensional covalent organic framework membranes for enhanced ion separation.

A heterostructured covalent organic framework (COF) membrane is synthesized via in situ linker exchange. Narrowed pores can be formed at the interface between two types of COFs by adjusting the linker exchange duration. The resultant COF membrane demonstrates a high rejection rate toward Na 2 SO 4 of up to 97%.