The separation of Li⁺ from Mg²⁺ in salt-lake brines using nanofiltration (NF) has become the most popular solution to meet the rising demand for lithium, particularly driven by the extensive use of lithium-ion batteries. This study presents the fabrication of a uniquely designed polyamide (PA) thin-film nanocomposite (TFN) membranes with ultrahigh Li⁺/Mg²⁺ selectivity and enhanced water flux by covalently incorporating mixed ligands functionalized silica nanoparticles (F-SiO₂NPs) into the selective PA layer and covalently bonding them to the membrane surface. In this strategy, bare silica nanoparticles (SiO₂NPs) were functionalized with mixed superhydrophilic ligands, including primary amine and quaternary ammonium groups, resulting in a highly positive surface charge primarily from the quaternary ammonium groups and enabling covalent conjugation via amine groups. Among the F-SiO₂NP-incorporated membranes, M500 containing 500 ppm of F-SiO₂NPs exhibited the best performance. In a solution with 2000 ppm salt concentration (Li⁺/Mg²⁺ ratio of 1:20), the M500 membrane showed an improved Li⁺/Mg²⁺ selectivity of 7.41 compared to the nonmodified TFC membrane, which had a selectivity of 5.05. Further surface conjugation of the M500 sample with 1500 ppm of F-SiO₂NPs resulted in the C1500 membrane, demonstrating the best performance among all of the surface-modified membranes. C1500 showed an outstanding Li⁺/Mg²⁺ selectivity of 37.95, with a Mg²⁺ rejection of 95.7% and a Li⁺ rejection of −63.2%, and a water flux of 56.0 L m^–2 h^–1 at 70 psi. Notably, a 7.5-fold improvement in Li⁺/Mg²⁺ selectivity over the TFC membrane was achieved without compromising the water flux. This is evident from the nearly identical water flux values of the TFC, M500, and C1500 membranes, which were 57.1, 54.8, and 56.0 L m^–2 h^–1, respectively. Considering key factors for large-scale applications, such as cost-effectiveness, environmental impact, the abundance of synthetic precursors, and the maturity of synthesis and tailoring technologies, SiO₂NP-based modifications outperform all other reported approaches to date.

中文翻译：

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使用带正电荷的二氧化硅纳米颗粒改性的聚酰胺薄膜纳米复合材料 （TFN） 膜从水中高效回收锂


使用纳滤 （NF） 分离盐湖盐水中 Li⁺ 和 Mg²⁺ 已成为满足不断增长的锂需求的最流行的解决方案，尤其是在锂离子电池的广泛使用推动下。本研究通过将混合配体功能化二氧化硅纳米颗粒 （F-SiO₂NPs） 共价掺入选择性 PA 层并将它们共价键合到膜表面，制备了一种独特设计的聚酰胺 （PA） 薄膜纳米复合 （TFN） 膜，该膜具有超高的 Li⁺/Mg²⁺ 选择性和增强的水通量。在这种策略中，裸二氧化硅纳米颗粒 （SiO₂NPs） 用混合的超亲水配体（包括伯胺和季铵基团）进行功能化，导致主要来自季铵基团的高度正表面电荷，并能够通过胺基进行共价偶联。在 F-SiO₂NP 掺入膜中，含有 500 ppm F-SiO₂NPs 的 M500 表现出最佳性能。在盐浓度为 2000 ppm（Li⁺/Mg²⁺ 比率为 1：20）的溶液中，M500 膜的 Li⁺/Mg²⁺ 选择性提高至 7.41，而未改性的 TFC 膜的选择性为 5.05。M500 样品与 1500 ppm 的 F-SiO₂NP 进一步表面偶联，得到 C1500 膜，在所有表面改性膜中表现出最佳性能。C1500 显示出出色的 Li⁺/Mg²⁺ 选择性，为 37.95，Mg²⁺ 截留率为 95.7%，Li⁺ 截留率为 -63.2%，水通量为 56。0 L m^–2 h^–1 在 70 psi 下。值得注意的是，与 TFC 膜相比，Li⁺/Mg²⁺ 选择性提高了 7.5 倍，而不会影响水通量。TFC、M500 和 C1500 膜的水通量值几乎相同，分别为 57.1、54.8 和 56.0 L m^–2 h^–1，这可以从中明显看出。考虑到大规模应用的关键因素，例如成本效益、环境影响、合成前体的丰度以及合成和定制技术的成熟度，基于 SiO₂NP 的修饰优于迄今为止报道的所有其他方法。