MWCNTs-COOK-assisted high positively charged composite membrane: Accelerating Li+ enrichment and Mg2+ removal

Abstract In this work, we successfully synthesized a new functional nano-additive called potassium carboxylate functionalized multi-wall carbon nanotubes (MWCNTs-COOK) and introduced it into the interfacial polymerization system to fine-tune the structure and properties of the nanofiltration (NF) membrane. The embedded MWCNTs-COOK (150 ppm) tightened the network-crosslink structure of the selective layer and contributed to a dense hydrophilic membrane surface with high positive chargeability. In addition, MWCNTs-COOK nano-additives in membrane created some intrinsic fast transport channels for water molecules. The MWCNTs-COOK(150 ppm)-assisted NF membrane exhibited a remarkable high flux of 12.23 L/m2hbar, a high separation factor SLi,Mg of 58, and a high difference in Li+ and Mg2+ rejections around 77%, indicating an excellent Li+ enrichment and Mg2+ removal capabilities, and breaking through the trad-off limit of permeate flux. Simultaneously, the comprehensive performance of the NF membrane can be maintained stably even in long-term utilization. This work opens a simple and effective pathway for accelerating Li+ enrichment and Mg2+ removal, which has great potential for lithium extraction application.