Xenon Adsorption Research Articles

A N-heterocyclics induced π-π interaction strategy to synthesis hyper-crosslinked polymers with enhanced porosity for xenon adsorption

Hyper-crosslinked polymers (HCPs) with large specific surface areas play an important role in gas adsorption and separation. However, the method to enhance the specific surface area of HCPs and gas adsorption performance without changing the polyaromatic hydrocarbons (PAHs) monomer structure and reaction condition is still missing. Here, we present a general and facile N-heterocyclics induced π-π interaction strategy to increase the specific surface area of HCPs by simply adding N-heterocyclics during the Friedel-Crafts alkylation reaction. The specific surface areas of HCP (tetraphenylmethane based HCPs, TPMBPy-TCM) increased up to 7.78 times compared to the one without adding N-heterocyclics. The crosslinking and stacking of PAHs was influenced by the π-π stacking between the N-heterocyclic complexes and PAHs. More importantly, N-heterocyclics coordinated with Lewis acids have lower electron density and do not react with PAHs in the Friedel-Crafts alkylation reaction, which can be removed easily from HCPs. The HCPs obtained shown good xenon adsorption performance with Xe uptake of 3.63 mmol/g, which is the highest value for organic adsorbents reported in literature. This work provides new insight into the preparation of high-performance HCPs.

Suitable Pore Confinement with Multiple Interactions in a Low-Cost Zeolitic Imidazolate Framework for Efficient Xe Capture and Separation

The increasing industrial demand for the noble gases xenon (Xe) and krypton (Kr), along with growing environmental concerns on their radionuclides, has made the efficient separation and purification of Xe and Kr a critical issue. Leveraging advanced porous materials to achieve highly efficient adsorptive Xe/Kr separation has been recognized as an energy-saving and economical alternative to the widely used cryogenic distillation technology. Herein, we present a stable, low-cost, and easily scalable zeolitic imidazolate framework (ZIF) material, ZIF-4, for effective xenon adsorption and separation. ZIF-4 possesses uniformly distributed pore cavities with ideally matched pore size (4.3 Å) with that of Xe atom (4.047 Å), providing appropriate pore confinement for Xe binding. Sorption isotherms of ZIF-4 demonstrate the remarkably high Xe uptake (1.64 mmol/g at 0.2 bar and 298 K) and excellent Xe/Kr separation selectivity (16.2 for IAST selectivity of 20/80 Xe/Kr gas mixtures). Breakthrough experiments further validate the efficient separation performance of ZIF-4 in both binary Xe/Kr (20/80) gas mixtures and under dilute conditions. Single-crystal X-ray diffraction studies of activated and Xe-loaded ZIF-4 crystals reveal that the flexible pore cavities of ZIF-4 can self-adaptively adsorb and accommodate Xe atoms through the rotation of imidazolate rings, forming multiple Xe···H and Xe···π interactions to create strong binding sites for Xe capture and discrimination. The stability, economic feasibility, and scalability of ZIF-4 underscore its significant potential for industrial Xe/Kr separation.

Understanding and Predicting the Spatially Resolved Adsorption Properties of Nanoporous Materials.

Using knowledge from statistical thermodynamics and crystallography, we develop an image-image translation model, called SorbIIT, that uses three-dimensional grids of adsorbate-adsorbent interaction energies as input to predict the spatially resolved loading surface of nanoporous materials over a broad range of temperatures and pressures. SorbIIT consists of a closed-form differential model for loading-surface prediction and a U-Net to generate spatial differential distributions from the energy grids. SorbIIT is trained using the energy grids and adsorbate distributions (obtained from high-throughput simulations) of 50 synthesized and 70 hypothetical zeolites and applied for predicting the adsorption of carbon dioxide, hydrogen sulfide, n-butane, 2-methylpropane, krypton, and xenon in other zeolites from 256 to 400 K. Employing a quadratic isotherm model for the local differentiation, SorbIIT yields mean R2 values of 0.998 for total adsorption and 0.6904 for local adsorption with a resolution of 0.2 Å, and a value of 0.721 for the structural similarity of the local loading distribution.

Adsorption of Xenon, Krypton, and Their Mixture on the Flexible Metal–Organic Framework DUT-8(Ni)

Adsorption of Xenon, Krypton, and Their Mixture on the Flexible Metal–Organic Framework DUT-8(Ni)

Effect of ligands regulation on Al-based metal organic frameworks for selective adsorption of xenon from spent fuel

Effective separation of inert gas such as Xe and Kr from used nuclear fuel is significant for maintaining ecological environment safety and recycling nuclear fuel. In this study, Al-CDC and Al-BDC with similar linear ligands were synthesized to reveal the influence of ligand regulation on Xe separation under different pressure conditions. The results displayed that the adsorption capacity of Al-BDC for Xe could reach 2.66 mmol g-1 under normal pressure, which is 1.11 times higher than that of Al-CDC, depending on its higher specific surface area and bigger pore volume. On the contrary, the Xe adsorption capacity of Al-CDC with the feature of narrow micropore structure and saturated C-H or oxygen-containing functional groups reached 1.44 mmol g−1 at 0.1 bar, which was 2.82 times higher than that of Al-BDC, resulting in a remarkable difference in Xe working capacity between Al-CDC (0.43 mmol g−1) and Al-BDC (0.073 mmol g−1) through dynamic breakthrough experiments. Meanwhile, the Henry’s selectivity of Al-CDC for Xe/Kr and Xe/N2 was up to 13.97 and 110.31, Compared with most porous adsorbents in previous reports, Al-CDC exhibits both high adsorption capacity and high selectivity. Innovatively, we analyzed the advantage in capacity and selectivity by the perspective of ligands, and the calculation results of the complete cell also proved that the saturated C-H group and benzene ring center on cyclohexane are the main adsorption sites of Al-CDC and Al-BDC for Xe, respectively. Therefore, a higher polar ligand in Al-CDC could lead to strong static binding energy and single cell binding energy which attribute to a high selective Xe adsorption. These results revealed the key structural characteristics for selective Xe adsorption under different pressure conditions, providing valuable suggestions for the design of separation materials from spent fuel.

High yield, large-scale synthesis of calcium-based microporous metal-organic framework and examination of the long-term stability for xenon adsorption applications

Scale-up synthesis of calcium-based microporous metal-organic framework (SBMOF-1) up to ∼400 g in a batch with a yield of >90 % was achieved by a solvothermal reaction of sulfonyldibenzoic acid (SDB) with an excess of calcium chloride. Here, we observed that recrystallization of unreacted SDB at a solvothermal condition caused a moderate reaction yield (40–50 %) at the reference condition of CCaCl2/ CSDB = 1 and CSDB/ CSDB(ref) = 1. Simply adding more reagents to the reactor did not increase the mass of product formed per unit volume due to a more pronounced loss of the yield at those conditions. By simultaneously changing the molar ratio of CaCl2 to SDB, CCaCl2/ CSDB, and the molar concentration of the SDB reagent, CSDB/ CSDB(ref), we explored %yield of the reaction. Interestingly, a linear improvement in the yield was observed from 21 % (at CCaCl2/ CSDB = 0.5) up to 78 % (at CCaCl2/ CSDB = 6) at a fixed ratio of CSDB/ CSDB(ref) = 2 and the yield leveled off after further addition. Unlike those at CCaCl2/ CSDB = 1, the yields at a high CaCl2 excess continued to improve with increasing the CSDB/ CSDB(ref). When a large pressure vessel (2500 mL EtOH, CCaCl2/ CSDB = 6, CSDB/ CSDB(ref) = 8) was used, about 415 g of SBMOF-1 with a yield of 92.3 % was produced, indicating 16 × the space yield improvement. The ability to synthesize SBMOF-1 on a large scale allowed us to examine the long-term stability of SBMOF-1 for almost 200 days in the presence of varying levels of relative humidity.

Toward Optimal Xenon Adsorption Capacity at Low Pressure on Silver-Exchanged Zeolites

Toward Optimal Xenon Adsorption Capacity at Low Pressure on Silver-Exchanged Zeolites

Thermally Tunable Adsorption of Xenon in Crystalline Molecular Sorbent.

The thermostability of encapsulated xenon is investigated in a series of isostructural crystalline sorbents. These sorbents consist of metal-organic capsules, with the general formula of [ConFe4-nL6]4- (n = 1, 2, 3 and 4), where L2- is an organic linker with two sulfonate groups. In the crystalline sorbent, guanidinium cations form H-bond networks with the peripheral sulfonate groups in the solid state and trap xenon in the molecular cavities, which are at least 2.7 times the volume of xenon. When heated, the sorbent retains xenon up to 561 K, i.e., 396 K higher than the boiling point of xenon. Furthermore, the thermostability of trapped xenon can be modulated by varying the ratio of Co:Fe in the crystalline sorbent. Elemental analysis on a single crystal by energy dispersive X-ray spectroscopy confirms the homogeneous distribution of Co and Fe in the sorbent. Structural analyses reveal that the expansion of capsule cavity is proportional to the Co:Fe ratio, with increases of 0.049(1) Å and 6.4(8) Å3 in metal-metal distance and cavity volume, per substitution of Fe by Co center. Steric repulsion between peripheral sulfonate groups is found to render a hypothetical face-centered cubic structure of (C(NH2)3)4[Fe4L6] not accessible, which would have trapped xenon with exceptional thermostability. The stable and tunable trapping of xenon in crystalline sorbents by over-sized molecular cavities suggests a new strategy for separation and storage of xenon, through introduction of kinetic barriers, such as H-bond networks.

Desilicated ZSM-5 zeolites for optimized xenon adsorption at very low pressure

Selective Xe adsorption on regenerable porous materials such as activated carbons, MOFs and zeolites has been found to be promising and economically attractive. The beneficial effect of silver doping of zeolites on Xe adsorption and Xe/Kr separation has been studied for numerous zeolites such as Ag-ZSM-5, Ag-mordenite and Ag-chabazite. Among them, we had shown that Ag-exchanged ZSM-5 is the most effective material for atmospheric Xe capture and selective separation at very low pressure (ppm level). A linear tendency was observed with a ratio of 2 mol of Ag for 1 mol of strong adsorption sites. Based on this observed tendency, we hypothesize that increasing the number of exchangeable sites by lowering the Si/Al ratio could be an approach to improve silver loading and selective xenon adsorption.The aim of this study is to evaluate the impact of desilication of ZSM-5 zeolites on decreasing their Si/Al ratio and increasing the concentration of sodium-exchanged sites and, possibly, strong silver-based adsorption sites. We have shown here that light desilication of this parent ZSM-5 makes it possible to significantly increase xenon uptake at very low pressure. The desilication creates a larger concentration of Al in the zeolite and thus enables a larger concentration of silver to be loaded. Yet we found that for severe desilication, decreased xenon uptake is observed, likely due to the facilitated formation of silver particles in which the core atoms are not accessible for xenon uptake. It appears that a concentration of 0.5 mmol g−1 of strong adsorption sites is a maximum achievable value for the Ag-ZSM-5 system. Surprisingly, we found that the parent ZSM-5 zeolite prepared by organic templating yields Ag-ZSM-5 with a similar concentration of strong adsorption sites but at higher silver loading. We could hypothesize that silanol defects present in commercial zeolites may be responsible for the stabilization of silver clusters.

Electron-Beam Source with a Superconducting Niobium Tip

Electron-beam sources are foundational in high-resolution electron microscopy and spectroscopy, but applications have been limited due to their relatively large energy spread. The authors fabricate a monocrystalline niobium nanotip electron field emitter and characterize it in superconducting and normal-conducting regimes. This bright, stable, coherent electron beam source features an exceptionally narrow energy spread. The authors also study the role of xenon adsorption and two-electron correlations. This work may improve aberration-corrected microscopy and electron energy-loss spectroscopy and enable high-resolution vibrational spectroscopy or quantum electron microscopy.

Boosting xenon adsorption with record capacity in microporous carbon molecular sieves

Boosting xenon adsorption with record capacity in microporous carbon molecular sieves

Adsorption of Xenon and Krypton onto Microporous Carbon Adsorbents from a Depleted Gas–Air Mixture

Adsorption of Xenon and Krypton onto Microporous Carbon Adsorbents from a Depleted Gas–Air Mixture

Adsorption-Induced Expansion of Graphene Oxide Frameworks with Covalently Bonded Benzene-1,4-diboronic Acid: Numerical Studies.

Graphene oxide frameworks (GOFs) are interesting adsorbent materials with well-defined slit-shaped pores of almost monodisperse separation of ∼1 nm between graphene-like layers; however, the exact nature of the structure has remained undetermined. Recently, GOFs were observed to swell monotonically upon the adsorption of methane and xenon under supercritical conditions. Here, we present the results of molecular dynamics simulations of the adsorption of methane and xenon for various proposed GOF structures based upon force fields based on ab initio B3LYP density functional theory calculations. The simulations reproduce well both the adsorption isotherms and the expansion of the interlayer spacing for methane and xenon for a model of GOFs formed by covalently bonded benzene-1,4-diboronic acid oriented at quasirandom angles with respect to the graphene layers.

Extrusion-Spheronization of UiO-66 and UiO-66_NH2 into Robust-Shaped Solids and Their Use for Gaseous Molecular Iodine, Xenon, and Krypton Adsorption.

The use of an extrusion-spheronization process was investigated to prepare robust and highly porous extrudates and granules starting from UiO-66 and UiO-66_NH2 metal-organic framework powders. As-produced materials were applied to the capture of gaseous iodine and the adsorption of xenon and krypton. In this study, biosourced chitosan and hydroxyethyl cellulose (HEC) are used as binders, added in low amounts (less than 5 wt % of the dried solids), as well as a colloidal silica as a co-binder when required. Characterizations of the final shaped materials reveal that most physicochemical properties are retained, except the textural properties, which are impacted by the process and the proportion of binders (BET surface area reduction from 5 to 33%). On the other hand, the mechanical resistance of the shaped materials toward compression is greatly improved by the presence of binders and their respective contents, from 0.5 N for binderless UiO-66 granules to 17 N for UiO-66@HEC granules. UiO-66_NH2-based granules demonstrated consequent iodine capture after 48 h, up to 527 mg/g, in line with the pristine UiO-66_NH2 powder (565 mg/g) and proportionally to the retaining BET surface area (-5% after shaping). Analogously, the shaped materials presented xenon and krypton sorption isotherms correlated to their BET surface area and high predicted xenon/krypton selectivity, from 7.1 to 9.0. Therefore, binder-aided extrusion-spheronization is an adapted method to produce shaped solids with adequate mechanical resistance and retained functional properties.

Argon, krypton and xenon adsorption coefficients on various activated carbons under dynamic conditions

Argon, krypton and xenon adsorption coefficients on various activated carbons under dynamic conditions

Digitization of Adsorption Isotherms from "The Thermodynamics and Hysteresis of Adsorption".

Sorption isotherms collected from tables in the seminal dissertation, “The Thermodynamics and Hysteresis of Adsorption” by A. J. Brown, have been digitized and made publicly available, along with supporting software scripts that facilitates usage of the data. The isotherms include laboratory measurements of xenon, krypton, and carbon dioxide adsorption (and, when possible, desorption) isotherms on a single sample of Vycor glass1, at various temperatures including subcritical conditions for xenon and krypton. The highlight of this dataset is the collection of “scanning” isotherms for xenon on Vycor at 131 K. The scanning isotherms examine numerous trajectories through the adsorption-desorption hysteresis region, such as primary adsorption and desorption scanning isotherms that terminate at the hysteresis boundary, secondary scanning isotherms made by selective reversals that return to the boundary, and closed scanning loops. This dataset was originally used to test the independent domain theory of adsorption and continues to support successor theories of adsorption/desorption scanning hysteresis including more recent theories based on percolation models. Through digital preservation and release of the tables from Brown’s dissertation, these data are now more easily accessible and can continue to find use in developing models of adsorption for fundamental and practical applications.

Tuning surface inductive electric field in microporous organic polymers for Xe/Kr separation

Understanding how the local polar sites in porous adsorbent surface affect their adsorption performance remains a challenge in molecular related separation process. We present an in-depth study of silver (Ag), cobalt (Co), iron (Fe) and nickel (Ni) ions on hyper cross-linked microporous organic polymer (HCP) in which all metal ions act as polar sites for xenon (Xe) and krypton (Kr) adsorption. Surface electrostatic potential analysis revealed that Xe adsorption strength at metal sites differs from that of Kr. Charge density difference analysis proved that the precise charge transfer between metal ions and Xe. These effects could strengthen the inductive energy caused by surface electric field for Xe adsorption in metal ions decorated HCP (HCP-M). Adsorption kinetics experiments showed that the adsorption rates of Xe on HCP-M (20.45–47.19 cm3/(cm3·s)) are much higher than that of Kr (9.45–17.38 cm3/(cm3·s)). The HCP-Ni can adsorb 90 ml Xe per volume with 16.20 Xe/Kr selectivity in Xe, Kr and N2 ternary gas mixture, which was among the well performing porous organic polymers reported. The Xe/Kr adsorptive separation performance of HCP-M stemmed mainly from the optimized inductive energy and the small-pore confinement effect of HCP-M, which could significantly facilitate preferential selective adsorption of Xe over Kr.

Peculiarities of Thermodynamic Behaviors of Xenon Adsorption on the Activated Carbon Prepared from Silicon Carbide.

An activated carbon prepared from silicon carbide by thermochemical synthesis and designated as SiC-AC was studied as an adsorbent for xenon. The examination of textural properties of the SiC-AC adsorbent by nitrogen vapor adsorption measurements at 77 K, powder X-ray diffraction, and scanning electron microscopy revealed a relatively homogeneous microporous structure, a low content of heteroatoms, and an absence of evident transport macropores. The study of xenon adsorption and adsorption-induced deformation of the Si-AC adsorbent over the temperature range of 178 to 393 K and pressures up to 6 MPa disclosed the contraction of the material up to −0.01%, followed by its expansion up to 0.49%. The data on temperature-induced deformation of Si-AC measured within the 260 to 575 K range was approximated by a linear function with a thermal expansion factor of (3 ± 0.15) × 10−6 K−1. These findings of the SiC-AC non-inertness taken together with the non-ideality of an equilibrium xenon gaseous phase allowed us to make accurate calculations of the differential isosteric heats of adsorption, entropy, enthalpy, and heat capacity of the Xe/SiC-AC adsorption system from the experimental adsorption data over the temperature range from 178 to 393 K and pressures up to 6 MPa. The variations in the thermodynamic state functions of the Xe/SiC-AC adsorption system with temperature and amount of adsorbed Xe were attributed to the transitions in the state of the adsorbate in the micropores of SiC-AC from the bound state near the high-energy adsorption sites to the molecular associates.

Describing adsorption of benzene, thiophene, and xenon on coinage metals by using the Zaremba-Kohn theory-based model.

Semilocal (SL) density functional approximations (DFAs) are widely applied but have limitations due to their inability to incorporate long-range van der Waals (vdW) interaction. Non-local functionals (vdW-DF, VV10, and rVV10) or empirical methods (DFT+D, DFT+vdW, and DFT+MBD) are used with SL-DFAs to account for such missing interaction. The physisorption of a molecule on the surface of the coinage metals (Cu, Ag, and Au) is a typical example of systems where vdW interaction is significant. However, it is difficult to find a general method that reasonably describes both adsorption energy and geometry of even the simple prototypes of cyclic and heterocyclic aromatic molecules such as benzene (C6H6) and thiophene (C4H4S), respectively, with reasonable accuracy. In this work, we present an alternative scheme based on Zaremba-Kohn theory, called DFT+vdW-dZK. We show that unlike other popular methods, DFT+vdW-dZK and particularly SCAN+vdW-dZK give an accurate description of the physisorption of a rare-gas atom (xenon) and two small albeit diverse prototype organic molecules on the (111) surfaces of the coinage metals.

Docking of CuI and AgI in Metal–Organic Frameworks for Adsorption and Separation of Xenon

AbstractWe present a metal docking strategy utilizing the precise spatial arrangement of organic struts as metal chelating sites in a MOF. Pairs of uncoordinated N atoms on adjacent pyrazole dicarboxylate linkers distributed along the rod‐shaped Al–O secondary building units in MOF‐303 [Al(OH)(C5H2O4N2)] were used to chelate CuI and AgI with atomic precision and yield the metalated Cu‐ and Ag‐MOF‐303 compounds [(CuCl)0.50Al(OH)(C5H2O4N2) and (AgNO3)0.49Al(OH)(C5H2O4N2)]. The coordination geometries of CuI and AgI were examined using 3D electron diffraction and extended X‐ray absorption fine structure spectroscopy techniques. The resulting metalated MOFs showed pore sizes matching the size of Xe, thus allowing for binding of Xe from Xe/Kr mixtures with high capacity and selectivity. In particular, Ag‐MOF‐303 exhibited Xe uptake of 59 cm3 cm−3 at 298 K and 0.2 bar with a selectivity of 10.4, placing it among the highest performing MOFs.