AOCOF-intercalated GO nanofiltration membranes with tailored hybrid nanochannels for high-performance dye separation

To overcome the trade-off between permeability and selectivity in nanofiltration processes, this paper designs a novel membrane structure (GAM) with 1D/2D hybrid nanochannels by intercalating amidoxime-functionalized covalent organic framework (AOCOF) nanosheets into graphene oxide (GO) layers. Driven by electrostatic interactions and π-π stacking, the robust intercalation of AOCOF effectively expands the interlayer spacing of GO from 0.86 nm to 0.90 nm. This structural expansion, combined with the intrinsic strong hydrophobicity of the 1D AOCOF channels, significantly reduces mass transfer resistance, thereby achieving an excellent pure water permeability of 92 L m^-2 h^-1 bar^-1. Furthermore, polyethylene glycol (PEG) tests reveal a molecular weight cut-off (MWCO) of approximately 399.4 Da for the membrane. The rejection mechanism involves the combined effects of size sieving, charge repulsion, and adsorption of dye molecules by GAM, among which physical size exclusion plays a dominant role in rejecting large dye molecules. Meanwhile, as confirmed by density functional theory (DFT) and molecular dynamics (MD) simulations, strong electrostatic repulsion and adsorption dominate the rejection of small dye molecules, with their synergistic effect ensuring a rejection rate exceeding 90% for all types of dyes. Notably, the membrane exhibits excellent practical reliability, maintaining a rejection rate above 75% during 100 h of continuous filtration of real printing and dyeing wastewater. This work breaks through the permeability-selectivity trade-off effect to a certain extent and provides a new structural strategy for the design of advanced dye separation membranes.