Electrostatically Tuned Graphene Oxide–Covalent Organic Framework Membranes for High-Flux Rejection of Low Molecular Weight Organic Compounds

Achieving high water flux without compromising the rejection of low-molecular-weight organic compounds (LMWOCs) remains a key challenge in two-dimensional laminar membrane design. Here, we report a structurally tunable graphene oxide (GO)-covalent organic framework (COF) hybrid membrane assembled from sulfonated COF nanosheets and GO layers via vacuum-assisted self-assembly. The integration of ionic COF nanosheets expands the GO interlayer spacing from 0.78 to 1.58 nm while simultaneously introducing fixed negative charges and intrinsic microporosity. This dual-functionality enables enhanced water permeability (193.5 L·m^-2·h^-1·bar^-1) and exceptional rejection (>99%) of methylene blue (MB), a small cationic dye often used as a model LMWOC. Beyond performance metrics, this study provides a comprehensive analysis of the separation mechanism. A synergistic interplay of Donnan exclusion, size sieving, and transient interlayer restructuring was observed. Electrostatic repulsion governs the partial rejection of methyl orange (MO), while MB triggers charge compensation and interlayer compaction upon accumulation, narrowing the channels and reinforcing steric exclusion. This adaptive structural behavior accounts for the flux-rejection dynamics and antifouling resistance of the membrane under various filtration conditions. Our findings establish a mechanistic framework for understanding dye transport in 2D membranes and demonstrate a scalable, charge-guided strategy for designing high-performance membranes. This work bridges material design and transport physics, offering insights applicable to emerging separation technologies targeting persistent organic micropollutants.