Fluorinated ultramicroporous metal–organic framework for efficient Ne/He separation at liquid nitrogen temperature zone

Deep removal of trace Ne from He feedstocks at liquid nitrogen temperature (77 K) is an important and challenging problem due to their similar molecular dimensions and weak polarizability difference. Herein, the Ne/He separation performance in fluorinated ultramicroporous metal-organic framework, KAUST-7, was systematically investigated at 77 K. KAUST-7 features narrow 3.5 Å channels lined with highly electronegative fluorine atoms, generating a localized negative electrostatic field in the confined pores. Static adsorption measurements revealed a Ne uptake of 2.95 mmol·g⁻¹ at 77 K versus only 0.0227 mmol·g⁻¹ for He in KAUST-7. IAST calculations predicted an exceptional Ne/He selectivity of 3.6 × 10³ for a 0.1/99.9 feed, remaining 262 at 87 K. Kinetic tests demonstrated rapid Ne capture in KAUST-7, which can reach 67% of equilibrium uptake within 10 s at an initial rate of 0.198 mmol·g⁻¹·s⁻¹, with a kinetic selectivity of 216.05. DFT calculations yielded Ne and He binding energies in KAUST-7 was −9.92 and − 0.22 kJ·mol⁻¹, respectively, confirming fluorine-induced polarization as the origin of selective Ne capture. Breakthrough experiments tests confirmed excellent dynamic separation performance at 77 K. This work highlights the synergistic effect of ultramicroporous confinement and fluorine-functionalized pore chemistry for ultrahigh-selectivity Ne/He separation.