Novel aminated graphene quantum dots (GQDs-NH2)-engineered nanofiltration membrane with high Mg2+/Li+ separation efficiency

To achieve both high Mg2+/Li+ separation ability and permeability of the nanofiltration (NF) membrane, we developed a novel NF membrane by incorporating nano-sized aminated graphene quantum dots (GQDs-NH2). The effect of GQDs-NH2 dosage on the structure and properties of the NF membrane was systematically investigated by several characterization methods. Membrane NF-0.03 with a GQDs-NH2 incorporation value of 0.03 wt% performed best during Mg2+/Li+ separation. Membrane NF-0.03 with higher positive chargeability had a lower separation factor SF of 0.0359 and a higher difference of up to 77% between Mg2+ and Li+ rejection, suggesting its excellent Mg2+/Li+ separation capability. Importantly, membrane NF-0.03 had a high permeation flux of 11.94 L/m2hbar, which was 137.8% more than that of pure NF-0 membrane. Furthermore, the (GQDs-NH2)-optimized morphology structure and hydrophilicity led to strong anti-fouling and stability of membrane NF-0.03. In summary, the incorporation of GQDs-NH2 is an effective way to improve the lithium enrichment efficiency of NF membrane.