The tripartite role of 2D covalent organic frameworks in graphene-based organic solvent nanofiltration membranes

Two-dimensional covalent organic frameworks (2D-COFs) have well-defined porosity and stability. Herein, we demonstrate that 2D-COFs can have three roles in nanolaminated graphene membranes for organic solvent nanofiltration (OSN). The optimized hybrid nanolaminate, assembled from 2D-COFs and reduced graphene oxide (rGO), shows a 162% enhancement in methanol permeance without sacrificing selectivity. When dry, intercalated 2D-COFs serve as a nanospacer to prevent the restacking of rGO. However, when wetted, 2D-COFs assume the additional roles of a stabilizer and a porous filler material. 2D-COFs alleviate rGO swelling in solvents because of a solvation-driven charge redistribution at the COF/rGO interface, which induces an attractive stabilizing force between COF and rGO nanosheets. Further, 2D-COFs can reduce transport pathway length by 15.5% and deliver "shortcuts" for solvent permeance. This work unravels the tripartite role of 2D-COFs as nanospacers/stabilizers/porous fillers, offering new insights into shaping the development of hybrid nanolaminated membranes for OSN.