Breakthrough Technology for Ultra-Precise Control of Pore Sizes in MOFs

Abstract
Efficient separation of hydrogen isotopes, especially deuterium (D2), is pivotal for advancing industries such as nuclear fusion, semiconductor processing, and metabolic imaging. Current technologies, including cryogenic distillation and Girdler sulfide processes, suffer from significant limitations in selectivity and cost-effectiveness. Herein, we introduce a novel approach utilizing an imidazolium-based Metal–Organic Framework (MOF), JCM-1, designed to enhance D2/H2 separation through temperature-dependent gate-opening controlled by ion exchange. By substituting NO3− ions in JCM-1(NO3−) with Cl− ions to form JCM-1(Cl−), we precisely modulate the gate-opening threshold, achieving a significant enhancement in isotope selectivity. JCM-1(NO3−) exhibited a D2/H2 selectivity (SD2/H2) of 14.4 at 30 K and 1 bar, while JCM-1(Cl−) achieved an exceptional selectivity of 27.7 at 50 K and 1 mbar. This heightened performance is attributed to the reduced pore aperture and higher gate-opening temperature resulting from the Cl− exchange, which optimizes the selective adsorption of D2. Our findings reveal that JCM-1 frameworks, with their finely tunable gate-opening properties, offer a highly efficient and adaptable platform for hydrogen isotope separation. This work not only advances the understanding of ion-exchanged MOFs but also opens new pathways for targeted applications in isotope separation and other gas separation processes.

A research team, jointly led by Professor Hyunchul Oh in the Department of Chemistry at UNIST and Professor Eunsung Lee at Seoul National University, has introduced a novel approach, capable of adjusting the pore size of porous materials in increments of 0.01 nm (10-9 m).

This innovative technology efficiently separates deuterium, an isotope of hydrogen that constitutes only 0.015% of the total hydrogen found in nature and shares similar properties with ordinary hydrogen. Deuterium is a crucial resource for applications in nuclear fusion power generation and semiconductor manufacturing, making its efficient separation highly valuable.

The research team demonstrated that the pore sizes of metal-organic frameworks (MOFs) can be fine-tuned through ion exchange, achieving unprecedented control and significantly enhancing the separation efficiency of deuterium in these materials.

To optimize separation efficiency, the researchers illustrated that deuterium and hydrogen can effectively be separated using the precisely adjusted pores of a newly developed MOF. It is essential to finely calibrate the pore size, which acts as a molecular sieve. Given that both hydrogen and deuterium are approximately 0.3 nm in size, achieving precise modifications at the 0.01 nm scale is critical.

Figure 1. A schematic diagram representing the summary of the study. Gate-opening control via anion exchange in JCM-1 enables enhanced hydrogen isotope separation through precise tuning of pore aperture and diffusion barriers. The dynamic interplay between structural flexibility and adsorption energetics maximizes D2/H2 selectivity, establishing a robust platform for cryogenic gas separation applications.

The researchers successfully reduced the pore inlet size of the JCM-1 MOF from about 0.39 nanometers to 0.36 nanometers by replacing nitrate ions (NO₃⁻) with chloride ions (Cl⁻). Their analysis revealed that Cl⁻ induces a stronger inward pull on the outer framework connected to the pore, resulting in a smaller pore size.

As a result of this modification, the selectivity for deuterium separation in JCM-1 (Cl⁻) increased significantly from 14.4 to 27.7, effectively doubling the efficiency compared to JCM-1 (NO₃⁻). Notably, JCM-1 (NO₃⁻) exhibited selectivity nine times greater than the conventional cryogenic distillation method at 24K (-249.15°C), while JCM-1 (Cl⁻) demonstrated over 18 times higher selectivity than that method.

Professor Oh, the lead investigator, stated, “This achievement offers a novel approach to precisely controlling the nanopore sizes of porous materials, with potential applications not only in isotope separation but also in various gas separation processes.”

Their findings have been published in Angewandte Chemie International Edition (Impact Factor: 16.1) on February 12, 2025. This research was funded by the National Research Foundation of Korea (NRF) and the Ministry of Science and ICT (MSIT).

Journal Reference
Hyunlim Kim, Younggyu Seo, Jaewoo Park, et al., “A Gate-Opening Control Strategy via Nitrate–Chloride Anion Exchange for Enhanced Hydrogen Isotope Separation in Metal–Organic Frameworks,” Angew. Chem. Int. Ed., (2025).