Simultaneous regulation of pore size and surface charge of nanofiltration membrane using carbon quantum dots for improved selective separation

Designing nanofiltration (NF) membranes with tunable pore sizes and surface charges is highly desirable to meet the growing demand for precise separation. In this study, carbon quantum dots generated through lysine pyrolysis (l-CQDs) were utilized as monomers to fabricate NF membranes via interfacial polymerization (IP). Intriguingly, the surface charge (from negative to positive) and effective pore size (from loose to dense structure) of the resultant NF membranes could be simultaneously modulated by simply adjusting the diffusion of l-CQDs during the IP process, which endowed the obtained l-CQD-based NF membrane with a tunable separation performance. The negative and loose NF membranes (l-CQD; 0.1 wt%) achieved excellent dye/salt fractionation performance even at high NaCl concentrations (20 g/L). The recovered NaCl from the highly saline dyeing effluent could be directly reused in cotton fabric dyeing, indicating potential application prospects in the treatment of saline textile effluents. A dense and positive NF membrane was obtained when l-CQD concentration increased to 1.0 wt%; this membrane showed exceptional desalination performance with high rejection of MgCl2, CuCl2, and CaCl2 (98.77 %, 99.06 %, and 99.0 %, respectively), demonstrating the ability to remove metal ions from water. This work provides an approach for preparing NF membranes with tailorable pore size and surface charge and highlights the potential of l-CQD-based NF membranes for the practical separation toward various charged components.