Quantum Effects on H2 Diffusion in Zeolite RHO: Inverse Kinetic Isotope Effect for Sieving

Room-Temperature Deuterium Separation in van Der Waals Gap Engineered Vermiculite Quantum Sieves

As the demand for nuclear energy grows, enriching deuterium from hydrogen mixtures has become more important. However, traditional methods are either very energy-intensive because they require extremely cold temperatures, or they don't separate deuterium (D2) from regular hydrogen (H2) very well, with a D2/H2 selectivity of ≈0.71. To achieve efficient deuterium separation at room temperature, materials with very tiny spaces, on an atomic scale are needed. For the first time, a material with spaces just ≈2.1 Å (angstroms) wide is successfully created, which is similar in size to the wavelength of hydrogen isotopes at room temperature. This allows for efficient deuterium separation, with a much higher D2/H2 selectivity of ≈2.20, meaning the material can separate deuterium from hydrogen much more effectively at room temperature. The smaller deuterium molecules are more likely to pass through these tiny spaces, showing that quantum effects play a key role in this process. In contrast, a material like graphene oxide, with larger spaces (≈4.0 Å), only shows a lower D2/H2 selectivity of ≈1.17, indicating weaker quantum effects. This discovery suggests that materials with very small, atomic-scale spaces can be key to efficient separation of hydrogen isotopes at room temperature.

Construction of an Indium-Based Coordination Polymer with Redox Non-Innocent Ligand for High-Efficient Electrochemical CO2 Reduction

Developing high-activity and long-term stable electrocatalysts for electrochemical CO2 reduction reaction (eCO2RR) to valuable products is still a challenge. An in-depth understanding of reaction mechanisms and the structure-function relationship is required for the development of an advanced catalytic eCO2RR system. Herein, a coordination polymer of indium(III) and benzenehexathiol (BHT) was developed as an electrocatalyst (In-BHT) for eCO2RR to HCOO-, which displayed an outstanding catalytic performance over the entire pH range. However, experimental results revealed significantly different catalytic pathways in the acid and neutral/alkaline solutions, which are attributed to the influence of redox non-innocent ligands on the rate-determining step (RDS). In the acid solution, the RDS is the formation of *OCOH intermediate through the proton transfer that originates from H2O in the solution, leading to relatively sluggish kinetics. But in the neutral or alkaline solution, the thiolate groups could be protonated during the catalytic process, and such proton can attack on carbon of absorbed CO2 via an intramolecular proton transfer, promoting the formation of *OCHO intermediate, resulting in faster kinetics. Our findings revealed the pivotal roles of the redox non-innocent ligands of metal active sites for eCO2RR, providing a new idea for designing highly efficient electrocatalysts.

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.

Recent Progress in Functional Nanomaterials towards the Storage, Separation, and Removal of Tritium

Tritium is a sustainable next-generation prime fuel for generating nuclear energy through fusion reactions to fulfill the increasing global energy demand. Owing to the scarcity-high demand tradeoff, tritium must be bred inside a fusion reactor to ensure sustainability and must therefore be separated from its isotopes (protium and deuterium) in pure form, stored safely, and supplied on demand. Existing multistage isotope separation technologies exhibit low separation efficiency and require intensive energy inputs and large capital investments. Furthermore, tritium-contaminated heavy water constitutes a major fraction of nuclear waste, and accidents like the one at Fukushima Daiichi leave behind thousands of tons of diluted tritiated water, whose removal is beneficial from an environmental point of view. In this review, the recent progress and main research trends in hydrogen isotope storage and separation by focusing on the use of metal hydride (e.g., intermetallic, and high-entropy alloys), porous (e.g., zeolites and metal organic frameworks (MOFs)), and 2-D layered (e.g., graphene, hexagonal boron nitride (h-BN), and MXenes) materials to separate and store tritium based on their diverse functionalities are discussed. Finally, the challenges and future directions for implementing tritium storage and separation are summarized in the reviewed materials.

Molecular hydrogen isotope separation by a graphdiyne membrane: a quantum-mechanical study

Graphdiyne (GDY) has emerged as a very promising two-dimensional (2D) membrane for gas separation technologies. One of the most challenging goals is the separation of deuterium (D₂) and tritium (T₂) from a mixture with the most abundant hydrogen isotope, H₂, an achievement that would be of great value for a number of industrial and scientific applications. In this work we study the separation of hydrogen isotopes in their transport through a GDY membrane due to mass-dependent quantum effects that are enhanced by the confinement provided by its intrinsic sub-nanometric pores. A reliable improved Lennard-Jones force field, optimized on accurate ab initio calculations, has been built to describe the molecule-membrane interaction, where the molecule is treated as a pseudoatom. The quantum dynamics of the molecules impacting on the membrane along a complete set of incidence directions have been rigorously addressed by means of wave packet calculations in the 3D space, which have allowed us to obtain transmission probabilities and, in turn, permeances, as the thermal average of the molecular flux per unit pressure. The effect of the different incidence directions on the probabilities is analyzed in detail and it is concluded that restricting the simulations to a perpendicular incidence leads to reasonable results. Moreover, it is found that a simple 1D model-using a zero-point energy-corrected interaction potential-provides an excellent agreement with the 3D probailities for perpendicular incidence conditions. Finally, D₂/H₂ and T₂/H₂ selectivities are found to reach maximum values of about 6 and 21 at ≈50 and 45 K, respectively, a feature due to a balance between zero-point energy and tunneling effects in the transport dynamics. Permeances at these temperatures are below recommended values for practical applications, however, at slightly higher temperatures (77 K) they become acceptable while the selectivities preserve promising values, particularly for the separation of tritium.

Dynamic metal-organic frameworks for the separation of hydrogen isotopes

Reversible structural transformation upon exposure to external stimuli can lead to breathing effect or gate-opening phenomena for dynamic metal-organic frameworks (MOFs), which endow them with excellent gas separation performance. The separation of hydrogen isotopes remains a huge challenge due to their nearly identical physical and chemical properties. The unique feature of dynamic MOFs, especially structural transition triggered by isotopes or by temperature, maximally enhances kinetic quantum sieving and contributes to the highly selective separation of hydrogen isotopes. Herein, we present some examples for the separation of hydrogen isotopes based on dynamic frameworks, and we expect to attract increasing attention to this research field.

DFT and MD simulation supplemented experiments for isotopic fractionation of zinc compounds using a macrocyclic crown ether appended polymeric resin

Isotope effect is a quantum mechanical phenomenon and thus poses a challenge for the separation of isotopes of an element of interest, especially for heavy elements. Isotopic fractionation of zinc is also quite difficult and challenging but is necessitated due to various applications of its isotopes ranging from nuclear medicine to nuclear power reactors. Here, we developed the dibenzo-18-crown-6 (DB18C6) ether-functionalized poly(methacrylic acid) (PMA) resin by exploiting the ion and isotope recognition ability of the crown ether using DFT/MD simulations followed by experiments for isotopic fractionation of zinc. The PMADB18C6 adsorbent was prepared and suitably characterized. Both computational and experimental findings demonstrate that the adsorption and isotope separation of zinc with PMADB18C6 are due to the molecular recognition effect of the "O" dipole of the crown ether. Furthermore, both MD simulations and experiments suggest Langmuir type adsorption isotherms. The adsorption of Zn2+ ions on the PMA resin is predicted to be endothermic, whereas it is exothermic on the PMADB18C6 resin, as revealed from the experimentally observed enthalpy change. A small scale fixed bed column study was demonstrated to test the scale-up application. The values of the experimental separation factors: 1.0013 for 66/64 and 1.0027 for 68/64 confirm the computationally predicted results of 1.00088 and 1.0010, respectively, thus establishing the combined strength of the theory and experiments for the identification of efficient fractionating agents for a complex quantum isotope effect which eventually helps in planning further experiments in view of medicinal and technological applications of zinc isotopes.