Highly Effective H2/D2 Separation within the Stable Cu(I)Cu(II)-BTC: The Effect of Cu(I) Structure on Quantum Sieving

Unveiling the Hydrogen Isotope Separation Potential of under Elevated Temperatures

The separation of hydrogen isotopes under moderate conditions remains a significant challenge, primarily due to their nearly identical physicochemical properties. Among emerging approaches, the chemical affinity quantum sieving (CAQS) effect in porous materials has shown promise for achieving selective adsorption at elevated temperatures. Herein, we evaluate the isotope separation performance of MIL-101 (Cr), a hydrothermally stable metal-organic framework featuring supertetrahedral cages and open metal sites. The synergistic interaction between these structural motifs imparts a high adsorption enthalpy, promoting strong isotope-framework interactions. In combination with its large pore size and high porosity, which enhance molecular exchange, MIL-101 (Cr) exhibits effective hydrogen isotope separation, as confirmed by dynamic breakthrough experiments conducted up to 100 K.

A Gate-Opening Control Strategy via Nitrate-Chloride Anion Exchange for Enhanced Hydrogen Isotope Separation in Metal-Organic Frameworks

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.

Mixed-valence metal-organic frameworks: concepts, opportunities, and prospects

Owing to increasing global demand for the development of multifunctional advanced materials with various practical applications, great attention has been paid to metal-organic frameworks due to their unique properties, such as structural, chemical, and functional diversity. Several strategies have been developed to promote the applicability of these materials in practical fields. The induction of mixed-valency is a promising strategy, contributing to exceptional features in these porous materials such as enhanced charge delocalization, conductivity, magnetism, etc. The current review provides a detailed study of mixed-valence MOFs, including their fundamental properties, synthesis challenges, and characterization methods. The outstanding applicability of these materials in diverse fields such as energy storage, catalysis, sensing, gas sorption, separation, etc. is also discussed, providing a roadmap for future design strategies to exploit mixed valency in advanced materials. Interestingly, mixed-valence MOFs have demonstrated fascinating features in practical fields compared to their homo-valence MOFs, resulting from an enhanced synergy between mixed-valence states within the framework.

Metal-Organic Framework with Open Metal Sites for D2/H2 Separation

The separation of hydrogen isotopes remains a significant challenge due to their nearly identical physicochemical properties. Recently, metal-organic frameworks employing the chemical affinity quantum sieving effect have garnered increasing attention for hydrogen isotope separation. In this study, Cu-BTT with open metal sites was synthesized and demonstrated high hydrogen isotope adsorption capacities of 266 cm3/g for H2 and 288 cm3/g for D2. Dynamic breakthrough experiments revealed a selectivity of 1.58 at 77 K, highlighting the potential of Cu-BTT as a promising candidate for hydrogen isotope separation.

Comprehensive Design and Experimental Protocol for Scalable and Temperature-Controllable Cryogenic Hydrogen Isotope Separation

Hydrogen isotope separation is a complex task due to the nearly identical physical and thermodynamic properties of isotopes, such as deuterium and protium. Traditional methods, including cryogenic distillation, exhibit limitations such as low selectivity and high energy consumption. Recent advancements utilizing the quantum sieving effect in crystalline porous materials have shown promise under cryogenic conditions, but experimental approaches using larger, more practical sample sizes remain scarce. This study introduces a novel cryogenic breakthrough apparatus designed for hydrogen isotope separation using gram-scale adsorbents. The apparatus supports both refrigerant-based and contact-cooling temperature control methods, with precooling employed to enhance separation efficiency. Results showed that precooling significantly improved deuterium selectivity over hydrogen, and the contact-cooling method demonstrated superior thermal stability and reliability during extended experiments. This system offers a scalable and practical solution for hydrogen isotope separation, addressing current limitations in experimental methodologies and providing valuable insights for both scientific research and industrial applications.

A Mini Review of Advances in Porous Materials Designing for Hydrogen Isotope Separation

The separation of mixtures of hydrogen isotopes is one of the greatest challenges of modern separation technology. A newly proposed separation mechanism, the quantum sieving (QS) effect, is expected to achieve high separation factors, the main desired properties for hydrogen isotope separation (HIS). Metal-organic frameworks (MOFs) and zeolites are excellent candidates to study these quantum effects because of their well-defined and tunable pore structure and the potential to introduce strong adsorption sites directly into the framework structure. This paper briefly discusses the fundamentals of QS of hydrogen isotopes in nanoporous materials, mainly including kinetic quantum sieving (KQS) and chemical affinity quantum sieving (CAQS). Recent experimental advances in the separation of hydrogen isotopes from MOFs and zeolites are highlighted.

Redox Concomitant Formation Method for Fabrication of Cu(I)-MOF/Polymer Composites with Antifouling Properties

Marine biofouling, which is one of the technical challenges hindering the growth of the marine economy, has been controlled using cuprous oxide (Cu2O) nanoparticles due to the exceptional antifouling properties of Cu(I) ions. However, Cu2O nanoparticles have encountered bottlenecks due to explosive releases of Cu+ ions, high toxicity at elevated doses, and long-term instability. Here, we present a novel method called Redox Concomitant Formation (RCF) for fabricating a hierarchical Cu(I) metal-organic framework polypyrrole (Cu(I)-MOF/PPy) composite. This method enables in situ phase transition via successive redox reactions that change the chemical valence state and coordination mode of Cu(II)-MOF, resulting in a new structure of Cu(I)-MOF while creating a PPy layer surrounded by the hierarchical structure. Owing to the steady release of Cu+ ions from the Cu(I) sites and photothermal properties of PPy, Cu(I)-MOF/PPy exhibits superior and broad-spectrum resistance to marine bacteria, algae, and surface-adhered biofilms in complex biological environments, as well as long-term stability, resulting in 100 % eradication efficiency under solar-driven heating. Mechanistic insights into successive structural redox reactions and formation using the RCF method are provided in detail, enabling the fabrication of novel MOFs with the desired composition and structure for a wide range of potential applications.

Pd-doped HKUST-1 MOFs for enhanced hydrogen storage: effect of hydrogen spillover

Extensive research has been devoted to developing metal nanoparticle (NP) doped porous materials with large hydrogen storage capacity and high hydrogen release pressure at ambient temperature. The ultra-sound assisted double-solvent approach (DSA) was applied for sample synthesis. In this study, tiny Pd NPs are confined into the pore space of HKUST-1, affording Pd@HKUST-1-DS with minimizing the aggregation of Pd NPs and subsequently the formation of Pd NPs on the external surface of HKUST-1. The experimental data reveal that the obtained Pd NP doped Pd@HKUST-1-DS possessed an outstanding hydrogen storage capacity of 3.68 wt% (and 1.63 wt%) at 77 K and 0.2 MPa H₂ (and 298 K and 18 MPa H₂), in comparison with pristine HKUST-1 and impregnated Pd/HKUST-1-IM. It is found that the storage capacity variation is not only ascribed to the different textural properties of materials but is also illustrated by the hydrogen spillover induced by different electron transport from Pd to the pores of MOFs (Pd@HKUST-1-DS > Pd/HKUST-1-IM), based on X-ray photoelectron spectroscopy and temperature desorption spectra. Pd@HKUST-1-DS, featuring high specific surface area, uniform Pd NP dispersion and strong interaction of Pd with hydrogen in the confined pore spaces of the support, displays the high hydrogen storage capacity. This work highlights the influence of spillover caused by Pd electron transport on the hydrogen storage capacity of metal NPs/MOFs, which is governed by both physical and chemical adsorption.