Graphene Quantum Dots-Doped Thin Film Nanocomposite Polyimide Membranes with Enhanced Solvent Resistance for Solvent-Resistant Nanofiltration

The core of the organic solvent nanofiltration (OSN) technology is solvent-resistant nanofiltration (SRNF) membranes. Till now, relative poor performance of solvent resistance is still the bottleneck of industrial application of SRNF membranes. This work reports a novel polyimide (PI) based thin-film nanocomposite (TFN) membrane which was embedded with graphene quantum dots (GQDs) and showed an improved solvent resistance for OSN application. This kind of SRNF membrane, termed (PI-GQDs/PI)(XA), was synthesized via serial processes of interfacial polymerization (IP), imidization, cross-linking, and solvent activation. The IP process was performed between an aqueous m-phenylenediamine solution doped with GQDs, having an average size of 1.9 nm, and an 1,2,4,5-benzenetetracarboxylic acyl chloride n-hexane solution on the PI substrate surface. The prepared (PI-GQDs-50/PI)(X) SRNF membranes without organic solvent activation achieved an ethanol permeance of nearly 50% higher than those of the GQD-free membranes under the same preparation conditions, while no compromise of the dye rejection was observed. Further, after the solvent activation using N,N-dimethylformamide (DMF) at 80 degrees C for 30 min, the ethanol permeance achieved about an 8-folds increment, from 2.84 to 22.6 L m(-2) h(-1) MPa-1. Interestingly, the rejection of rhodamine B also increased from 97.8 to 98.6%. A long-term permeation test of more than 100 h using rose bengal (RB, 1017 Da)/DMF solution at room temperature demonstrated that the synthesized (PI-GQDs-50/PI)(XA) membranes could maintain the DMF permeance and the RB rejection as high as 18.3 L m(-2) h(-1) MPa-1 and 99.9%, respectively. Moreover, the immersion test of the prepared (PI-GQDs-50/PI)(XA) SRNF membranes in both DMF and ethanol at room temperature for about one year also demonstrated the long-term organic solvent stability, indicating their good potential for OSN application.