Foldable-Ligand-Induced Zigzag Pore Contraction in Ni-MOFs toward High-Purity O2 Production

High-purity oxygen (O 2 ) is vital for advanced applications in medicine, aerospace, and electronics, yet its sustainable production remains challenging. Pressure-swing adsorption (PSA) offers an energy-efficient alternative to cryogenic distillation, aligning with carbon-neutral objectives. However, achieving O 2 purity above 99.99% is hampered by the removal of trace argon (Ar), whose kinetic diameter and polarizability are nearly identical to those of O 2 . Herein, we introduce a Ligand-Folding Modulation Strategy to tailor contractible ultra-micropores in Ni(II)-based metal-organic frameworks (MOFs), enabling precise Ar/O 2 discrimination. Replacing rigid dicarboxylate linkers with a flexible, foldable analogue (trans-1,4-cyclohexanedicarboxylic acid, H 2 CDC) induces a zigzag pore contraction, narrowing the aperture from 7.5 Å to 5.0 Å. The resulting framework, Ni-TED-CDC (TED = 1,4-diazabicyclo[2.2.2]octane), exhibits an Ar uptake of 8.45 cm 3 /g at 298 K and 1 bar—49% higher than its large-pore analogue—and an Ar/O 2 selectivity of 1.47, placing it at the forefront of O 2 purification adsorbents. Breakthrough experiments confirm its capability to deliver ultra-high-purity O 2 (>99.99%), highlighting its practical potential for PSA applications. Molecular simulations reveal that ligand foldability drives a confined, square-shaped pore geometry that optimally complements spherical Ar atoms, enhancing van der Waals interactions while excluding linear O 2 molecules. This work establishes ligand-folding modulation as a versatile pore-engineering strategy for constructing responsive adsorption environments, providing a general design principle for inert-gas recognition and paving the way toward low-carbon, high-efficiency O 2 purification technologies.