Isomeric Nonpolar Amino Acid–Derived Metal–Organic Frameworks for Xenon/Krypton Separation

Abstract

ABSTRACT Efficient xenon/krypton separation remains challenging due to their similar physicochemical properties. Herein, we demonstrate that ligand isomerism can be leveraged as an effective structural handle for constructing new metal–organic frameworks from readily available, low‐cost amino acids. Using leucine and isoleucine—two constitutional regioisomers among proteinogenic amino acids that possess the largest nonpolar alkyl side chains—we construct a pair of zinc‐based metal–organic frameworks, Zn‐LEU and Zn‐ILE, which share identical connectivity yet differ subtly in side‐chain branching. Zn‐ILE retains a more robust framework under a range of conditions, whereas Zn‐LEU undergoes a pronounced phase transformation under relatively mild conditions. This structural integrity, combined with a precisely tailored nonpolar pore environment (∼4.4 Å), enables Zn‐ILE to exhibit a ∼40% increase in Xe uptake and superior Xe/Kr selectivity over its isomer. Dynamic breakthrough experiments further validate the Xe/Kr separation performance under representative operating conditions, including humid streams and ultradilute xenon concentrations (400 ppm). We further formalize a cost‐normalized figure of merit that quantifies dynamic xenon capture per unit synthetic input, under which Zn‐ILE exhibits cost‐normalized Xe productivity of 2.21 × 10 −3  mmol USD − 1 , ranking among the most cost‐efficient MOF‐based xenon sorbents reported to date.