Organic mixture fractionation enabled by carbon nanotube/graphene nanoribbon organic solvent nanofiltration membrane

We developed a hybrid membrane composed of carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) by controlling the degree of unzipping in multi-walled CNTs through oxidation. The CNT/GNR hybrid hydrogel was applied onto a porous polymer filter by large-scale coating using slot-die coating, which was then subjected to hot-pressing at 150 °C and 20 bar. The resulting CNT/GNR hybrid membrane exhibited outstanding performance in organic solvent nano-filtration (OSN), with ultrafast permeance of 60–200 LMH/bar for alcohol solvents and a molecular weight cut-off of 961 Da, surpassing the upper bound of polymer-based OSN membranes. The rapid solvent permeance can be attributed to the increased interlayer spacing due to CNT intercalation and the elimination of oxygen functionalities through an additional reduction process. Meanwhile, the stacked nanoribbon structure effectively separated organic molecules based on interlayer spacing size. Notably, this membrane demonstrated exceptional stability under practical separation conditions, with consistent performance even after 1315 h of cross-flow operation. This operational lifespan is a record for graphene-based membranes and can be attributed to the enhanced adhesion between the polymer substrate and the carbon layer as a result of the welding effect. Finally, the membrane was used to separate a concentrated binary dye mixture solution made of nanometer-sized components, showing precise separation ability with a separation factor of 740 and nearly 100 % purity of permeate and retentate solution after the filtration-based separation process. The membrane has the potential for a wide range of applications in the separation and purification of organic compounds dissolved in organic solvents.