Efficient dye nanofiltration of a graphene oxide membrane via combination with a covalent organic framework by hot pressing

Although graphene oxide (GO) membranes show great potential for nanofiltration, there is always a trade-off between the permeation flux and rejection rate. In this study, a covalent organic framework (COF-TpPa) was incorporated into a GO membrane for efficient dye separation. The good bonding interactions between two species was facilitated via a facile hot-pressing (HP) method, mitigating the issue of the solubility of GO in water and preventing the interface void. The as-prepared composite membrane (HP-COF-TpPa/GO) exhibited greatly enhanced stability in universal pH conditions with good retention of its original morphology. The COF-TpPa provided additional water passage in the membrane, leading to the water permeance of 166.8 L m(-2) h(-1) bar(-1), which was much higher than that of most membranes. Furthermore, owing to the molecular sieving, electrostatic repulsion and improved adhesion brought by introducing the COF-TpPa with HP step, the HP-COF-TpPa/GO exhibited a more efficient dye rejection rate (97.05%) of methylene blue as compared to the pristine GO membrane (91.87%) and COF-TpPa/GO without the HP process (68.57%). This study can provide an alternative approach of fabricating high-performance COF/GO membranes for nanofiltration and extend the application of COF materials in the separation field.