Tailoring nanofiltration membrane via low temperature-assisted layer-by-layer interfacial polymerization for highly...

To address the growing lithium resource shortage, the development of nanofiltration (NF) membranes with enhanced ion-ion selectivity is crucial for advancing lithium extraction from brine solutions and recovering lithium from industrial wastewater. However, engineering NF membranes with uniform pore size distribution to facilitate precise ion-ion selective separation through steric hindrance poses a substantial challenge. Herein, we propose an innovative approach utilizing low-temperature (LT) assisted layer-by-layer (LBL) interfacial polymerization (IP) to fabricate a thin and defect-free bi-polyamide (PA) layer NF membrane, which exhibited uniformly distributed pore size and enhanced selectivity of mono- and di-valent cations. The experiments and molecular dynamics simulations indicate that the LT can reduce the diffusion rate of piperazine and regulate IP reaction rate. Meanwhile, the presence of first PA layer was conductive to the uniform distribution of piperazine during the second IP process. The synergistic effects of LT-regulation and LBL IP facilitated the fabrication of tightly adhered thinner PA layers with smooth surface and narrow pore size distribution. The optimal membrane exhibited a molecular weight cut-off (MWCO) of 160 Da, enabling a Li⁺/Mg²⁺ selectivity of up to 26.7 even in a 100:1 mixed-salt solution through size exclusion. Additionally, it achieved lithium recovery rates of 71.4 % (purity 99.5 %) and 59.5 % (purity 88.0 %) from simulated salt lake brine and spent lithium-ion batteries discharge wastewater, respectively. This strategy offers an easy-to-operate and facile method to improve the ion-sieving capability of PA NF membranes.