(354b) Sustainable Synthesis of Ultrathin Non-Van Der Waals 2D Uio-66-NH? Films for High-Performance Ion Separation

Metal-organic frameworks (MOFs) with two-dimensional (2D) morphologies hold promise for molecular and ionic separations, yet their synthesis has been limited to layered structures stabilized by weak van der Waals (vdW) interactions. UiO-66, a chemically robust 3D MOF^[1], has never been realized in 2D form due to its isotropic bonding (Figure 1A). Here, we present the first synthesis of non-vdW 2D UiO-66-NH₂ films via a rapid, room-temperature aqueous method that promotes anisotropic in-plane growth^[2]. By optimizing precursor concentrations, pH, and acetic acid modulation, we achieved continuous, oriented films with thicknesses tunable from 0.5 to 2 unit cells (1.7-4.7 nm) (Figure 1B), surpassing conventional µm-thick MOF membranes. The use of water as a solvent and atomically smooth graphene substrates enabled sustainable, scalable fabrication while minimizing defects.

Characterization by AFM, XPS, and GIWAXS confirmed sub-10 nm pinhole-free films with high crystallinity and preferential orientation (Figure 1C and D). These films demonstrated exceptional monovalent/divalent ion selectivity (e.g., K⁺/Mg²+ selectivity up to 99.8) via size exclusion and electrostatic interactions, attributed to linker defects and amino-functionalized pores. Stability tests revealed over 36 days of performance in 0.1 M salt solutions, underscoring their robustness (Figure 1E). The synthesis method-free of organic solvents, high temperatures, and prolonged reaction times-aligns with green chemistry principles and offers a pathway to ultrathin MOF membranes for energy-efficient separations.

This work advances the field of non-vdW 2D materials, providing a scalable platform to engineer MOF films for applications in desalination, ion recovery, and selective molecular transport, with significant implications for sustainable chemical processes.

References

[1] A. Schaate, P. Roy, A. Godt, J. Lippke, F. Waltz, M. Wiebcke, P. Behrens, Chemistry – A European Journal 2011, 17, 6643-6651.

[2] H.-Y. Chi, S. Song, K. Zhao, K.-J. Hsu, Q. Liu, Y. Shen, A. F. Sido Belin, A. Allaire, R. Goswami, W. L. Queen, K. V. Agrawal, J. Am. Chem. Soc. 2025.