The rapid growth of renewable energy technologies has driven a surge in global lithium demand, intensifying the need for efficient and scalable lithium extraction technologies. Specifically, low-quality brines, which are abundant and widely distributed, remain largely untapped despite their promising potential. Separating Li+ from these brines is intrinsically difficult due to the comparable hydrated sizes of Li⁺ and Mg²⁺ ions, combined with the high Mg2+ concentration and high Mg2+/Li+ ratios.
A research team led by Yang Su from Tsinghua University has addressed this challenge by developing a polyelectrolyte-intercalated graphene oxide membrane with a uniform and controllable interlayer spacing. Through mild thermal treatment, the membrane undergoes in situ crosslinking, which stabilizes the structure and enables precise tuning of the interlayer nanochannels. The resulting positively charged two-dimensional channels facilitate selective ion transport dominated by size-exclusion effects.
The findings were published in Nano Research on August 7, 2026.
The study demonstrates efficient Mg²⁺ rejection and effective Mg²⁺/Li⁺ separation under conditions of high Mg²⁺ concentration and high Mg²⁺/Li⁺ ratio, highlighting its applicability to realistic low-quality brine systems. The researchers also demonstrated the practical application of this membrane by simulating a multi-stage nanofiltration process on low-quality brines with high Mg2+ concentration and Mg2+/Li+ ratio. After three-stage filtration, the membrane rejected 99.53% of Mg2+, effectively upgrading the brine to a high-quality lithium source.
This work also reveals a "counter-ion controlled" ionic sieving mechanism. The team found that halide counter-ions, such as chloride (Cl-), adsorb onto the charged channel walls, narrowing the effective interlayer gallery width and enabling size-exclusion-based separation. These findings are supported by both experimental observations and theoretical simulations. Furthermore, at high ionic concentrations, the team proposed a counter-ion exchange mechanism, in which Cl⁻ ions within the hydration shell of Mg²⁺ partially exchange with those adsorbed on the channel walls. This process reduces the effective hydrated size of Mg²⁺, allowing limited permeation and thereby explaining the moderate decline in ion rejection observed at high concentrations
Overall, this study provides new insights into the regulation of the mass transport channels through the ionic environment of the solutions and advances the understanding of ionic transport behaviors under nanoconfinement. Furthermore, it offers a new strategy and technical foundation for sustainable Li+/Mg2+ separation and resource recovery from low-quality brines using membrane-based processes.
Contributors of this research include Xinyu Gong, Dingxin Xu, Miaofei Huang, Yuxin Li, Hanlu Jiang, Kuang Yu, Zhen Chen and Yang Su from the Institute of Materials Research, Tsinghua Shenzhen International Graduate School, Tsinghua University, China.
DOI Link:
https://doi.org/10.26599/NR.2026.94908964
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 8,000 articles. In 2025 InCites Journal Citation Reports, its 2025 IF is 9.4 (8.3, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.
