Pan Yuanhui, Saha Suman, Burigana Matthew, Singh Vivek, Yaghi Omar M, Paesani Francesco
Department of Chemistry and Biochemistry, University of California San Diego La Jolla California 92093 USA.
Department of Chemistry, University of California Berkeley California 94720 USA.
Chem Sci. 2025 Jun 2;16(26):12129-12138. doi: 10.1039/d5sc01596k. eCollection 2025 Jul 2.
The growing global demand for critical metals has intensified the search for sustainable and efficient extraction methods. Passive uptake from seawater using advanced sorbent materials has emerged as a promising alternative, offering a renewable and environmentally responsible resource. Metal-organic frameworks (MOFs), with their high surface area and tunable pore structures, offer great potential for selective ion uptake; however, a molecular-level understanding of ion uptake from dilute aqueous solutions remains incomplete. In this study, we employ free-energy calculations and enhanced sampling simulations to investigate alkali metal ion uptake in MOF-808, a prototypical hydrothermally stable MOF. Our results reveal that large pores provide a similarly stable environment for all studied ions, indicating a lack of intrinsic selectivity, whereas small pores exhibit distinct thermodynamic and kinetic preferences that govern ion uptake. Dehydrated alkali metal ions are stable within small pores, and free-energy profiles reveal that their transfer from large to small pores occurs with lower energy barriers than that of water molecules. Among these ions, Li faces the highest barrier due to its strong hydration shell, whereas K exhibits the greatest thermodynamic preference for uptake in its dehydrated state. However, within hydrated small pores, Li is the most stable, underscoring the interplay between hydration structure and confinement effects. These findings provide fundamental insights into ion uptake in MOFs and offer guidance for designing next-generation MOFs with enhanced selectivity for metal ion extraction from dilute solutions. Future efforts should explore pore functionalization and tailored confinement strategies to optimize MOFs for efficient and selective metal recovery.
全球对关键金属不断增长的需求加剧了对可持续和高效提取方法的探索。使用先进吸附剂材料从海水中被动摄取已成为一种有前途的替代方法，提供了一种可再生且对环境负责的资源。金属有机框架（MOF）具有高比表面积和可调节的孔结构，在选择性离子摄取方面具有巨大潜力；然而，对于从稀水溶液中摄取离子的分子水平理解仍不完整。在本研究中，我们采用自由能计算和增强采样模拟来研究MOF-808（一种典型的水热稳定MOF）中碱金属离子的摄取。我们的结果表明，大孔为所有研究离子提供了类似稳定的环境，表明缺乏内在选择性，而小孔则表现出控制离子摄取的独特热力学和动力学偏好。脱水的碱金属离子在小孔内稳定，自由能分布表明它们从大孔转移到小孔时的能垒低于水分子。在这些离子中，Li由于其强大水合壳而面临最高能垒，而K在脱水状态下对摄取表现出最大的热力学偏好。然而，在水合小孔内，Li最稳定，突出了水合结构和限制效应之间的相互作用。这些发现为MOF中离子摄取提供了基本见解，并为设计对稀溶液中金属离子提取具有更高选择性的下一代MOF提供了指导。未来的工作应探索孔功能化和定制限制策略，以优化MOF实现高效和选择性金属回收。
