Separation of Xe from Kr with Record Selectivity and Productivity in Anion‐Pillared Ultramicroporous Materials by Inverse Size‐Sieving

The separation of xenon/krypton (Xe/Kr) mixture is of great importance to industry, but the available porous materials allow the adsorption of both, Xe and Kr only with limited selectivity. Herein we report an anion‐pillared ultramicroporous material NbOFFIVE‐2‐Cu‐i (ZU‐62) with finely tuned pore aperture size and structure flexibility, which for the first time enables an inverse size‐sieving effect in separation along with record Xe/Kr selectivity and ultrahigh Xe capacity. Evidenced by single‐crystal X‐ray diffraction, the rotation of anions and pyridine rings upon contact of larger‐size Xe atoms adapts cavities to the shape/size of Xe and allows strong host‐Xe interaction, while the smaller‐size Kr is excluded. Breakthrough experiments confirmed that ZU‐62 has a real practical potential for producing high‐purity Kr and Xe from air‐separation byproducts, showing record Kr productivity (206 mL g^?1) and Xe productivity (42 mL g^?1, in desorption) as well as good recyclability.     

A Microporous Hydrogen-Bonded Organic Framework Based on Hydrogen-Bonding Tetramers for Efficient Xe/Kr Separation

Hydrogen-bonded organic frameworks (HOFs) have been emerging as a new type of very promising microporous materials for gas separation and purification, but few HOFs structures constructed through hydrogen-bonding tetramers have been explored in this field. Herein, we report the first microporous HOF (termed as HOF-FJU-46) afforded by hydrogen-bonding tetramers with 4-fold interpenetrated diamond networks, which shows excellent chemical and thermal stability. What's more, activated HOF-FJU-46 exhibits the highest xenon (Xe) uptake of 2.51 mmol g⁻¹ and xenon/krypton (Kr) selectivity of 19.9 at the ambient condition among the reported HOFs up to date. Dynamic breakthrough tests confirmed the excellent Xe/Kr separation of HOF-FJU-46a, showing high Kr productivity (110 mL g⁻¹) and Xe uptake (1.29 mmol g⁻¹), as well as good recyclability. The single crystal X-ray diffraction and the molecular simulations revealed that the abundant accessible aromatic and pyrazole rings in the pore channels of HOF-FJU-46a can provide the multiple strong C−H⋅⋅⋅Xe interactions with Xe atoms.     

Dynamic separation of Xe and Kr by metal-organic framework and covalent-organic materials: a comparison with activated charcoal

We systematically investigate dynamic separation of Xe and Kr at room temperature using four representative porous materials (Cu-BTC, ZIF-8, COP-4 and activated carbon (AC)). Results indicate that among the four materials, Cu-BTC not only shows the highest retention volume per gram (V_g=788 mL g^-1, which is 1.8 times of activated carbon (436 mL g^-1)) under flowing condition, but also can separate 350 ppm Xe from 35 ppm Kr mixture in air with a high Xe/Kr selectivity of 8.6 at room temperature and 200 kPa, due to its suitable pore morphology, open metal sites, small side pockets in the framework. Moreover, the Cu-BTC also performs well on individual separation of Xe, Kr, CO₂ from five-component gas mixture (Xe:Kr:CO₂:Ar:N₂=1:1:1:1:0.5, V/V) and has the longest retention time for Xe (20 min) in gas chromatographic separation, suggesting that it is a good candidate for potential applications as polymeric sieves.     

Hydrogen-Bonding Assembly Meets Anion Coordination Chemistry: Framework Shaping and Polarity Tuning for Xenon/Krypton Separation

Hybrid hydrogen-bonded (H-bonded) frameworks built from charged components or metallotectons offer diverse guest-framework interactions for target-specific separations. We present here a study to systematically explore the coordination chemistry of monovalent halide anions, i.e., F⁻, Cl⁻, Br⁻, and I⁻, with the aim to develop hybrid H-bond synthons that enable the controllable construction of microporous H-bonded frameworks exhibiting fine-tunable surface polarity within the adaptive cavities for realistic xenon/krypton (Xe/Kr) separation. The spherical halide anions, especially Cl⁻, Br⁻, and I⁻, are found to readily participate in the charge-assisted H-bonding assembly with well-defined coordination behaviors, resulting in robust frameworks bearing open halide anions within the distinctive 1D pore channels. The activated frameworks show preferential binding towards Xe (IAST Xe/Kr selectivity ca. 10.5) because of the enhanced polarizability and the pore confinement effect. Specifically, dynamic column Xe/Kr separation with a record-high separation factor (SF=7.0) among H-bonded frameworks was achieved, facilitating an efficient Xe/Kr separation in dilute, CO₂-containing gas streams exactly mimicking the off-gas of spent nuclear fuel (SNF) reprocessing.     

Hybrid Ultra‐Microporous Materials for Selective Xenon Adsorption and Separation

The demand for Xe/Kr separation continues to grow due to the industrial significance of high‐purity Xe gas. Current separation processes rely on energy intensive cryogenic distillation. Therefore, less energy intensive alternatives, such as physisorptive separation, using porous materials, are required. Herein we show that an underexplored class of porous materials called hybrid ultra‐microporous materials (HUMs) affords new benchmark selectivity for Xe separation from Xe/Kr mixtures. The isostructural materials, CROFOUR‐1‐Ni and CROFOUR‐2‐Ni, are coordination networks that have coordinatively saturated metal centers and two distinct types of micropores, one of which is lined by CrO₄^2? (CROFOUR) anions and the other is decorated by the functionalized organic linker. These nets offer unprecedented selectivity towards Xe. Modelling indicates that the selectivity of these nets is tailored by synergy between the pore size and the strong electrostatics afforded by the CrO₄^2? anions.     

Employing an Unsaturated Th4+ Site in a Porous Thorium–Organic Framework for Kr/Xe Uptake and Separation

Actinide based metal–organic frameworks (MOFs) are unique not only because compared to the transition‐metal and lanthanide systems they are substantially less explored, but also owing to the uniqueness of actinide ions in bonding and coordination. Now a 3D thorium–organic framework ( SCU‐11 ) contains a series of cages with an effective size of ca. 21×24 Å. Th⁴⁺ in SCU‐11 is 10‐coordinate with a bicapped square prism coordination geometry, which has never been documented for any metal cation complexes. The bicapped position is occupied by two coordinated water molecules that can be removed to afford a very unique open Th⁴⁺ site, confirmed by X‐ray diffraction, color change, thermogravimetry, and spectroscopy. The degassed phase ( SCU‐11‐A ) exhibits a Brunauer–Emmett–Teller surface area of 1272 m² g^?1, one of the highest values among reported actinide materials, enabling it to sufficiently retain water vapor, Kr, and Xe with uptake capacities of 234 cm³ g^?1, 0.77 mmol g^?1, 3.17 mmol g^?1, respectively, and a Xe/Kr selectivity of 5.7.     

Determination of low level85Kr and133Xe concentrations in the environment

This study was performed under the joint TRMC/INER program for the determination of low level⁸⁵Kr and¹³³Xe concentrations in the environmental air samples. Based on cryogenic adsorption of krypton and xenon on charcoal followed by chromatographic separation from other gases, the⁸⁵Kr and¹³³Xe recovered from 200 liters of atmospheric air can be determined by either on-line gas flow proportional counter or liquid scintillation counting. The recovery yields of krypton and xenon examined by using⁸⁵Kr and¹³³Xe tracers were nearly 100%. The minimum detectable activity of⁸⁵Kr and¹³³Xe by gas flow proportional counting is about 7.40 Bq. The method is satisfactory for environmental monitoring applications under abnormal conditions of nuclear facilities. However, for lower level environmental⁸⁵Kr and¹³³Xe measurements, the liquid scintillation counting method can be applied due to their extremely low detection limits (i.e. 0.107 Bq and 0.093 Bq for⁸⁵Kr and¹³³Xe, respectively). Using this method, the measurable limits of concentrations are 0.535 Bq/m³ and 0.466 Bq/m³ for⁸⁵Kr and¹³³Xe, respectively.     

Tailoring Pore Structure and Morphologies in Covalent Organic Frameworks for Xe/Kr Capture and Separation

As a rising star among porous solid materials, covalent organic frameworks(COFs) with excellent properties including but not limit to facilely controllable structure, high porosity, and multi-chemical functionality represent significant potential for efficient ¹²⁷Xe/⁸⁵Kr capture and separation. In this study, through tuning the length of the organic ligands, two-dimensional(2D) COF mate-rials with identical connection group but different pore properties, denoted as ATFG-COF and TpPa-COF with AA-stacking model and TpBD-COF with AB-stacking model were synthesized and tested for Kr and Xe adsorption for the first time. Adsorption measurements indicate that the narrower pore apertures and higher porosity are conducive for COF materials to capture Xe and Kr. Furthermore, the Henry's constant, isosteric heat of adsorption(Q_st), and ideal adsorbed solution theory(IAST) selectivity of ATFG-COF, the pore size of which is closest to the kinetic diameter of the Xe atom(0.41 nm) among 2D COF materials, were carried out based on the single component sorption isotherms. The results illustrate that the high isosteric heat values of Xe/Kr adsorption on ATFG-COF are 25 and 16 kJ/mol at room temperature, respectively. Henry's law predicts that the selectivity factor of Xe to Kr is 6.07, consistent with the adsorption selectivity(ca. 6) calculated based on the IAST.     

An improved apparatus for the determination of krypton-85 and xenon-133 in an emergency situation

A simple and portable apparatus was developed for measurements of⁸⁵Kr and¹³³Xe that would be released into the atmosphere in an emergency situation of nuclear facilities. The method is based on cryogenic adsorption of these gases on charcoal followed by chromatographic separation from other gases. The⁸⁵Kr and¹³³Xe recovered from atmospheric air are determined separately by liquid scintillation counting. It takes about 1 hour for the stepwise determination of⁸⁵Kr and¹³³Xe. The atmospheric concentration of 3·10^–3 Ci per m³ air (1.1·10² Bq/m³ air) is measurable for both nuclides with 20% counting error.     

Synergistic Nitrogen Binding Sites in a Metal-Organic Framework for Efficient N2/O2 Separation

Porous materials with d₃ electronic configuration open metal sites have been proved to be effective adsorbents for N₂ capture and N₂/O₂ separation. However, the reported materials remain challenging to address the trade-off between adsorption capacity and selectivity. Herein, we report a robust MOF, MIL-102Cr, that features two binding sites, can synergistically afford strong interactions for N₂ capture. The synergistic adsorption site exhibits a benchmark Q_st of 45.0 kJ mol⁻¹ for N₂ among the Cr-based MOFs, a record-high volumetric N₂ uptake (31.38 cm³ cm⁻³), and highest N₂/O₂ selectivity (13.11) at 298 K and 1.0 bar. Breakthrough experiments reveal that MIL-102Cr can efficiently capture N₂ from a 79/21 N₂/O₂ mixture, providing a record 99.99 % pure O₂ productivity of 0.75 mmol g⁻¹. In situ infrared spectroscopy and computational modelling studies revealed that a synergistic adsorption effect by open Cr(III) and fluorine sites was accountable for the strong interactions between the MOF and N₂.     

Determination of 131mXe and 133mXe in the presence of 133gXe via combined beta-spectroscopy and delayed coincidence

The International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty will include measurements of Xe fission products. Pacific Northwest National Laboratory has developed an automated system for separating Xe from air which detects Xe fission products using a beta-gamma counting system for ^131mXe, ^133mXe, ^133gXe, and ^135gXe. Betas and conversion electrons are detected in a plastic scintillation cell containing the Xe sample. Gamma and X-rays are detected in a NaI(Tl) scintillation detector which surrounds the plastic scintillator sample cell. Two-dimensional pulse-height spectra of gamma-energy versus beta-energy are obtained. The plastic scintillator spectrum in coincidence with the 31-keV X-rays from ^131mXe. ^133mXe, and ^133gXe is a complex mixture of conversion electrons and betas. A new technique to simultaneously measure the delayed coincidence (T _1/2 = 6.27 ns) between beta-particles from ^133gXe and conversion electrons depopulating the 81-keV state in 133 Cs is being developed. This technique allows separation of the ^133gXe beta spectrum from the conversion electrons due to ^131mXe and ^133mXe and uniquely quantifies all three nuclides.     

Quantitative and isotopic analysis of released and retained krypton and xenon fission gases from irradiated metallic fuels

We quantitatively measured the amounts and isotopic distributions of the released and retained fission gases (Kr and Xe) from two irradiated metallic fuels (U–10Zr and U–10Zr–5Ce) at approximately 2.9 at.% burnup, using a gas chromatography and a quadrupole mass spectrometer. The obtained Xe/Kr ratios indicate that the released and retained fission gases from the irradiated metallic fuels came primarily from the fission of ²³⁵U, instead of that of heavy isotopes such as ²³⁹Pu and ²⁴¹Pu. The calculated (⁸³Kr + ⁸⁴Kr)/⁸⁶Kr and (¹³¹Xe + ¹³²Xe)/¹³⁴Xe ratios suggest that no fuel rods became defective during the irradiation process.     

Switching Kr/Xe selectivity with temperature in a metal-organic framework

Krypton (Kr) and xenon (Xe) adsorption on two partially fluorinated metal-organic frameworks (FMOFCu and FMOFZn) with different cavity size and topologies are reported. FMOFCu shows an inversion in sorption selectivity toward Kr at temperatures below 0 °C while FMOFZn does not. The 1D microtubes packed along the (101) direction connected through small bottleneck windows in FMOFCu appear to be the reason for this peculiar behavior. The FMOFCu shows an estimated Kr/Xe selectivity of 36 at 0.1 bar and 203 K.     

An Ultra-Microporous Metal–Organic Framework with Exceptional Xe Capacity

Molecular confinement plays a significant effect on trapped gas and solvent molecules. A fundamental understanding of gas adsorption within the porous confinement provides information necessary to design a material with improved selectivity. In this regard, metal–organic framework (MOF) adsorbents are ideal candidate materials to study confinement effects for weakly interacting gas molecules, such as noble gases. Among the noble gases, xenon (Xe) has practical applications in the medical, automotive and aerospace industries. In this Communication, we report an ultra-microporous nickel-isonicotinate MOF with exceptional Xe uptake and selectivity compared to all benchmark MOF and porous organic cage materials. The selectivity arises because of the near perfect fit of the atomic Xe inside the porous confinement. Notably, at low partial pressure, the Ni–MOF interacts very strongly with Xe compared to the closely related Krypton gas (Kr) and more polarizable CO₂. Further ¹²⁹Xe NMR suggests a broad isotropic chemical shift due to the reduced motion as a result of confinement.     

Influence of ionic liquid counterions on activity and selectivity of ethylene trimerization using chromium-based catalysts in biphasic media

In recent years ionic liquids (ILs) have attracted much interest because of their widespread use in various fields. Several trimerization and oligomerization catalysts have been evaluated in ILs with different organic–inorganic hybrid structures. High catalytic activity and selectivity, easy product separation, and recycling of the catalyst are the advantages of a biphasic catalyst system compared to the homogeneous catalysts. In this study, the influence of IL counter-anions on activity and selectivity of the ethylene trimerization catalysts based on Cr-SNS-R was investigated. All synthesized materials were characterized using Fourier-transform infrared spectroscopy, ¹H NMR, ¹³C NMR, UV–Vis. spectroscopy, thin-layer chromatography, and elemental analysis (CHNS). In ethylene trimerization reaction, the dodecyl substituent in the SNS ligand exhibited better activity and selectivity than the butyl substituent. The results revealed that the presence of BF₄⁻ as a counter-anion in the IL led to an increase in activity and selectivity compared to Br⁻ and I⁻ counter-anions. It was found that the BF₄⁻ counter-anion plays a conclusive role in the development of 1-hexene activity and selectivity to a maximum amount of 71,132 g_1-C6/(g_Cr × h) and more than 99%, respectively. Finally, the catalyst was reused thrice without losing its 1-hexene selectivity.     

Metal-Organic Frameworks for Breakthrough Separation of 2-Butene Isomers with High Dynamic Selectivity and Capacity

Developing porous sorbents represents a potential energy-efficient way for industrial gas separation. However, a bottleneck for reducing the energy penalty is the trade-off between dynamic adsorption capacity and selectivity. Herein, we showed this problem can be overcome by modulating the kinetic and thermodynamic separation behaviours in metal–organic frameworks for sieving 2-butene geometric isomers, which are desired for upgrading the raffinates to higher value-added end products. We found that the iron-triazolate framework can realize the selective shape screening of 2-butene isomers assisted by electrostatic interactions at the pore apertures. Further introducing uncoordinated N binding sites by ligand substitution lowered the gas diffusion barrier and greatly boosted the dynamic separation performance. In breakthrough tests under ambient conditions, trans-2-C₄H₈ can be efficiently separated from cis-2-C₄H₈ with a record capacity of 2.10 mmol g⁻¹ with high dynamic selectivity of 2.39.     

Sulfone-Modified Covalent Organic Frameworks Enabling Efficient Photocatalytic Hydrogen Peroxide Generation via One-Step Two-Electron O2 Reduction

Photocatalytic oxygen reduction reaction (ORR) offers a promising hydrogen peroxide (H₂O₂) synthetic strategy, especially the one-step two-electron (2e⁻) ORR route holds great potential in achieving highly efficient and selectivity. However, efficient one-step 2e⁻ ORR is rarely harvested and the underlying mechanism for regulating the ORR pathways remains greatly obscure. Here, by loading sulfone units into covalent organic frameworks (FS-COFs), we present an efficient photocatalyst for H₂O₂ generation via one-step 2e⁻ ORR from pure water and air. Under visible light irradiation, FS-COFs exert a superb H₂O₂ yield of 3904.2 μmol h⁻¹ g⁻¹, outperforming most reported metal-free catalysts under similar conditions. Experimental and theoretical investigation reveals that the sulfone units accelerate the separation of photoinduced electron-hole (e⁻-h⁺) pairs, enhance the protonation of COFs, and promote O₂ adsorption in the Yeager-type, which jointly alters the reaction process from two-step 2e⁻ ORR to the one-step one, thereby achieving efficient H₂O₂ generation with high selectivity.     

Neuraminidase Based Electro-Nano Diagnostic Platforms: Development of Model Systems for Cancer Diagnosis

An electrochemical biosensor that monitored neuraminidase (NEU3), activity was developed. The analysis platform included a graphene-platinum hybrid modified gold screen printed electrode as a transducer. The detection protocol was based on observation of NEU3 activity which was used to remove sialic acid from the GD3 ganglioside. Examination of analytical characteristics resulted with two linear ranges of 10⁻⁸ U/mL–10⁻¹ and 10⁻¹ U/mL–2.53 U/mL with limit of detection values of 10⁻⁸ U/mL and 10⁻¹ U/mL, respectively. The selectivity of the developed NEU3 activity based electrochemical biosensor was tested with HeLa, VERO and A549 cell lines.     

De-Linker-Enabled Exceptional Volumetric Acetylene Storage Capacity and Benchmark C2H2/C2H4 and C2H2/CO2 Separations in Metal–Organic Frameworks

An ideal adsorbent for separation requires optimizing both storage capacity and selectivity, but maximizing both or achieving a desired balance remain challenging. Herein, a de-linker strategy is proposed to address this issue for metal–organic frameworks (MOFs). Broadly speaking, the de-linker idea targets a class of materials that may be viewed as being intermediate between zeolites and MOFs. Its feasibility is shown here by a series of ultra-microporous MOFs (SNNU-98-M, M=Mn, Co, Ni, Zn). SNNU-98 exhibit high volumetric C₂H₂ uptake capacity under low and ambient pressures (175.3 cm³ cm⁻³ @ 0.1 bar, 222.9 cm³ cm⁻³ @ 1 bar, 298 K), as well as extraordinary selectivity (2405.7 for C₂H₂/C₂H₄, 22.7 for C₂H₂/CO₂). Remarkably, SNNU-98-Mn can efficiently separate C₂H₂ from C₂H₂/CO₂ and C₂H₂/C₂H₄ mixtures with a benchmark C₂H₂/C₂H₄ (1/99) breakthrough time of 2325 min g⁻¹, and produce 99.9999 % C₂H₄ with a productivity up to 64.6 mmol g⁻¹, surpassing values of reported MOF adsorbents.