Adsorption Of Noble Gases Research Articles

Anomalous thermal conductivity in 2D silica nanocages of immobilizing noble gas atom

Noble gas atoms such as Kr and Xe are byproducts of nuclear fission in nuclear plants. How to trap and confine these volatile even radioactive gases is particularly challenging. Recent studies have shown that they can be trapped in nanocages of ultrathin silica. Here, we exhibit with self-consistent phonon theory and four-phonon (4ph) scattering where the adsorption of noble gases results in an anomalous increase in lattice thermal conductivity (κL), while the presence of Cu atoms doping leads to a reduction in κL. We trace this behavior in host–guest 2D silica to an interplay of tensile strain, rattling phonon modes, and redistribution of electrons. We also find that 4ph scatterings play indispensable roles in κL of 2D silica. Our work illustrates the microscopic heat transfer mechanism in 2D silica nanocages with the immobilization of noble gas atoms and inspires further exploring materials with the kagome and glasslike κL.

Exploring the energy landscape of graphynes for noble gas adsorption using swarm intelligence

Gas adsorption on one-atom-thick membranes is a growing technology for separation applications owing to its excellent energy efficiency. Herein, we investigate the adsorption of the noble gases, Ne, Ar and Kr on graphynes (GYs), a novel class of one-atom-thick carbon membranes using a swarm intelligence technique, namely particle swarm optimization (PSO). Modeling the adsorption of noble gas clusters on two-dimensional substrates requires a thorough examination of the energy landscape. The high dimensionality of the problem makes it tricky to employ ab initio methods for such studies, necessitating the use of a metaheuristic global optimization technique such as PSO. We explored the adsorption of 1–30 atoms of Ne, Ar and Kr on α-, β-, γ- and rhombic-GYs to predict the most suitable form of GY for the adsorption of each of the gases. Employing the dispersion-corrected density functional theory (DFT-D) data for the adsorption of single gas atoms as the reference data, we parametrized two empirical pairwise potentials, namely, Lennard-Jones (LJ) and improved Lennard-Jones (ILJ) potentials. We then analyzed the growth pattern as well as the energetics of adsorption using the parametrized potentials, in combination with the PSO technique, which enabled us to predict the best possible membrane for the adsorption of the noble gases: α-GY for Ne and γ-GY for Ar and Kr. The accuracy of our modeling approach is further validated against DFT-D computations thereby establishing that PSO, when combined with the ILJ potential, can serve as a computationally feasible approach for modeling gas adsorption on GYs.

Molecular Dynamics Simulation of Pore-Size Effects on Gas Adsorption Kinetics in Zeolites

AbstractStrong gas-mineral interactions or slow adsorption kinetics require a molecular-level understanding of both adsorption and diffusion for these interactions to be properly described in transport models. In this combined molecular simulation and experimental study, noble gas adsorption and mobility is investigated in two naturally abundant zeolites whose pores are similar in size (clinoptilolite) and greater than (mordenite) the gas diameters. Simulated adsorption isotherms obtained from grand canonical Monte Carlo simulations indicate that both zeolites can accommodate even the largest gas (Rn). However, gas mobility in clinoptilolite is significantly hindered at pore-limiting window sites, as seen from molecular dynamics simulations in both bulk and slab zeolite models. Experimental gas adsorption isotherms for clinoptilolite confirm the presence of a kinetic barrier to Xe uptake, resulting in the unusual property of reverse Kr/Xe selectivity. Finally, a kinetic model is used to fit the simulated gas loading profiles, allowing a comparison of trends in gas diffusivity in the zeolite pores.

On the nature of noble gas - metal bond in silver aggregates.

The aim of this paper is to extend the study of the nature of the bond between noble gas to nano- and sub nanoscale silver aggregates. In the framework of DFT-PAW calculations implemented in the abinit package, we carried out a thorough investigation on the nature of the bond between the six noble gases NG (He, Ne, Ar, Kr, Xe and Rn) and numerous neutral silver aggregates Agn from the single atom Ag1 to the nanoparticle Ag147 using atoms-in-molecules (AIM) dual functional analysis,. We evaluated the impact of the silver aggregate size, the adsorption site and of the noble gas on the Ag-NG bond. Our study concluded on the favored adsorption of heavier noble gases (Kr, Xe and Rn) over that of lighter noble gases (He, Ne and Ar) on any aggregate size due to an enhanced chemical contribution in the bond. For these heavier noble gases, in accordance with studies carried out on surfaces, we noted their preferential adsorption on on-top sites rather than on hollow sites, which further evidences the chemical contribution to the bond. Moreover, the slight positive Bader charge on these heavier noble gases implies an electron transfer from the noble gas to the silver atom. Noble gas adsorption is favored on smaller, few-atom, two-dimensional clusters rather than on larger three-dimensional nanoparticles. Finally, we identified a universal power law with a unique exponent linking bond length and electronic density at the bond critical point for all aggregate sizes, noble gases and adsorption sites.

Comparison of Adsorption Coefficients of Argon, Krypton, and Xenon on Various Activated Charcoal Grades in Static Conditions

Coefficients of adsorption (Henry’s constants) of noble gases (argon, krypton, xenon) on activated charcoal grades AG-3, VSK-5, SKT-3, NWC 12x40 in the temperature range of 15 °C to 80 °C were determined. Temperature dependence parameters of Henry’s constants were determined with a calculation of isosteric adsorption heat values. The experimental data were used to calculate stationary operating conditions of a radiochromatographic column in NPP’s noble gas delay system. Out of all the studied charcoals, the results show that coconut charcoals VSK-5 and NWC 12x40 have the highest decontamination factor to airflow purification from radioactive noble gases. They far outweigh sulfur–potassium activated peat charcoal SKT-3 used presently at most Russian nuclear power plants. Activated charcoal AG-3 does not ensure the decontamination level required. The results also show that the overall decontamination factor depends heavily on temperature. Precooling gas flow at the adsorber’s input can considerably increase air decontamination factor from radioactive noble gases.

Aluminum-based microporous metal–organic framework for noble gas separation

Obtaining pure Xe from Xe/Kr mixture arising from various sources (nuclear accidents, advanced reactors, reprocessing of used nuclear fuel, air etc) is of environmental and industrial importance. We evaluated the Xe/Kr separation performance of aluminum-based MOF (Al-SDB) constructed with a V-shaped organic linker. The Al-SDB has a high Xe capacity of 1.6 mmol/g at 100 kPa and 298 K, while exhibiting a low affinity for Kr. In addition, it shows a high working capacity (0.6 mmol/g) compared to other metal based SDB MOFs, confirming its potential for PSA process and role of metal nodes in noble gas adsorption. The Al-SDB also exhibited an IAST Xe/Kr selectivity of 14.2, which is a relatively high Xe/Kr selectivity compared to reported MOFs under similar conditions. To further evaluate the utility of Al-SDB for Xe/Kr separation from gas mixture under flow conditions, the breakthrough experiment was carried out using Al-SDB-filled column under dynamic flow condition. Remarkably, the breakthrough curves of Al-SDB shows that Xe/Kr mixture can be separated efficiently. These results indicated that Al-SDB can be regarded as a potential adsorbent to replace cryogenic distillation for the separation of Xe/Kr mixtures.

Computation-informed optimization of Ni(PyC)2 functionalization for noble gas separations

Our objective is to tune a “lead” metal-organic framework, Ni(PyC) 2 (pyridine-4-carboxylate [PyC]), by functionalizing its PyC ligands to maximize its adsorptive selectivity for xenon over krypton at room temperature. To guide experiments, we (1) construct a library of Ni(PyC-X) 2 (X = functional group) crystal structure models then (2) use molecular simulations to predict their noble gas adsorption and selectivity at room temperature. Motivated by our virtual screening, we synthesize Ni(PyC- m -NH 2 ) 2 , determine its crystal structure by X-ray powder diffraction, measure its Xe, Kr, and Ar adsorption isotherms (298 K), and indeed find that its dilute Xe/Kr selectivity at 298 K (20) exceeds that of its parent Ni(PyC) 2 (17). Corroborated by molecular models, in situ X-ray diffraction shows that Ni(PyC- m -NH 2 ) 2 organizes well-defined, Xe-tailored binding pockets along its one-dimensional channels. Our study illustrates the computation-informed optimization of a “lead” metal-organic framework. • Virtual screening of Ni(PyC-X) 2 MOFs for Xe/Kr separations at room temperature • Synthesize, determine structure of, and measure Xe, Kr, Ar adsorption in Ni(PyC- m -NH 2 ) 2 • Ni(PyC- m -NH 2 ) 2 exhibits a dilute Xe/Kr selectivity (298 K) higher than Ni(PyC) 2 • The channels of Ni(PyC- m -NH 2 ) 2 present well-defined Xe binding pockets Gantzler et al. find that virtual screening of functionalized Ni(PyC) 2 analogs for Xe/Kr separations at room temperature highlights Ni(PyC- m -NH 2 ) 2 . They synthesize Ni(PyC- m -NH 2 ) 2 , determine its structure, and measure its noble gas adsorption isotherms, confirming that Ni(PyC- m -NH 2 ) 2 exhibits a higher Xe/Kr selectivity than Ni(PyC) 2.

Elucidation of Noble Gas Cluster Configurations Bound on Graphdiyne: A Metaheuristic Approach.

Graphynes are a class of all-carbon two-dimensional membranes that have been intensely researched for various membrane-based technologies on account of their unique pore architectures. Herein, we report an investigation of the mechanism and energetics of adsorption of noble gases (He, Ne and Ar) on graphdiyne (GDY), the most popular form of graphynes. Two global optimization techniques, namely particle swarm optimization (PSO) and differential evolution are employed to predict the putative global minima configurations of rare gas clusters in the size range 1-30 when adsorbed on GDY. We use the 12-6 Lennard-Jones potential to represent the pairwise non-covalent interactions between various interacting atoms. Initially, the gas atoms adsorb as monolayers on GDY at the centers of the triangular pores until all the triangular pores are filled. This is followed by a second layer formation on top of the hexagonal pore centers or on top of the C-C bonds. The findings from the empirical approach are further validated by performing density functional theory calculations on the predicted adsorbed cluster configurations. We have also looked into the adsorption of noble gas clusters on bilayer GDY systems and have found that the intercalation of gas atoms within the bilayers is feasible. Our study suggests that the stochastic nature of the swarm intelligence technique, PSO can assist in an effective search of the potential energy surfaces for the global minima, eventually enabling large-scale simulations.

The Use of Noble Gases to Constrain Subsurface Fluid Dynamics in the Hydrocarbon Systems

Geochemical techniques have been widely applied to study the generation and migration of hydrocarbons in sedimentary basins over the last several decades. Diagnostic biomarkers and stable carbon and hydrogen isotopes (such as δ13C and D) are generally used to identify the sources and thermal maturity of hydrocarbons and to reveal the accumulation process and mechanism of oil and gas reservoirs. However, some questions, such as secondary migration processes and pathways of oil and gas, and the relationship between groundwater flow and hydrocarbon transport, remain unclear and challenging. The low abundance and chemical inertness properties allow noble gases to serve as robust tools for tracing subsurface fluid flow. Additionally, they can be used for identifying and quantifying the role of the concomitant groundwater related to the generation and migration of hydrocarbons. This paper reviews the previous modeling work on using noble gases to study the fluid flow, flow paths, and gas/oil-water interactions in hydrocarbon systems. Noble gases from various sources can be readily identified due to their distinct isotopic and elemental signatures. Atmosphere-derived noble gases can be used to evaluate the amount of involved aquifer water associated with the hydrocarbon system and determine the groundwater migration paths and flow rates. Radiogenic noble gases accumulate over time, providing information about the subsurface fluid residence time. Questions concerning the specific trapping sites and mechanisms that affect heavy noble gas adsorption into organic sediments are still unresolved. Investigating the hydrocarbon generation, migration, and subsurface crustal fluid interactions in the hydrocarbon reservoirs can improve our understanding of noble gases as useful tracers in the subsurface environment and provide valuable geological evidence for the exploration and production of petroleum sources.

Adsorption of Noble Gases on Hydrogenated Group IV Monolayers: Stability and Electronic Properties

Adsorption of Noble Gases on Hydrogenated Group IV Monolayers: Stability and Electronic Properties

A unified method for measuring noble gas isotope ratios in air, water, and volcanic gases via dynamic mass spectrometry

We describe a new method for the purification, transfer, and analysis of heavy noble gas isotope ratios in water, air, or volcanic gas samples using a dynamic dual-inlet isotope-ratio mass spectrometer (IRMS). IRMS noble gas analysis offers the potential for orders-of-magnitude higher precision than traditional (static) noble gas mass spectrometry. However, due to both inherent IRMS requirements and challenges associated with sample collection and purification, measuring noble gases via IRMS has typically been limited to samples with an air-like elemental composition. Our new method allows for highly accurate and precise measurements of Ar, Kr, and Xe isotope ratios via IRMS, independent of sample composition, thereby opening the door to air, water, or volcanic gas analyses all made with the same technique. This approach exploits the fact that purified heavy noble gas samples are dominated by 40Ar, such that matching 40Ar ion beams between sample and reference gas streams results in pressure balancing. We further introduce new techniques for precisely quantifying and correcting for (i) Kr and Xe isotope non-linearity and matrix effects, (ii) interference of the low energy 40Ar tail on 36Ar and 38Ar ion beams, and (iii) the impact of short-term background fluctuations on trace Xe isotope measurements. We also present results from adsorption-desorption experiments with multiple adsorbent materials across a range of temperatures. For adsorption on silica gel, we find small equilibrium isotopic fractionation of Kr (εeq = −0.37 ± 0.04‰ amu−1, ±2 SE) and Xe (εeq = −0.06 ± 0.02‰ amu−1, ±2 SE) that may be relevant to studies of terrestrial Xe isotope signatures. We demonstrate that adsorption and desorption of heavy noble gases on silica gel at 77 K and 303 K, respectively, is highly reproducible and thus constitutes a viable and efficient method for transferring gases without reliance on cryostats or liquid helium.

Noble gas adsorption to tuff

A method was developed to measure trace noble gas element adsorption to the surfaces of geologic materials in the presence of a background gas that could potentially compete for surface adsorption sites. Adsorption of four noble gas elements (Ne, Ar, Kr, and Xe) at a concentration of 100 ppm in helium and nitrogen were measured on a sample of crushed tuff at 0, 15, 30, and 45 °C. In addition, Ne, Ar, Kr, and Xe at 250 ppm and 500 ppm in nitrogen at 15 °C were measured. Noble gas adsorption was found to increase with increasing atomic mass and decreasing temperature. It was also observed that the relative increase in noble gas element adsorption with decreasing temperature tends to increase with increasing atomic mass. As the noble gas concentrations in nitrogen increased, adsorption increased in a slightly non-linear fashion which could be modeled using a Freundlich isotherm. For noble gas concentrations that were ≤100 ppm Henry's Law constant were calculated.

An anisotropic dressed pairwise potential model for the adsorption of noble gases on boron nitride sheets.

Development of empirical potentials with accurate parameterization is indispensable while modeling large-scale systems. Herein, we report accurate parameterization of an anisotropic dressed pairwise potential model (PPM) for probing the adsorption of noble gases, He, Ne, Ar and Kr on boron nitride sheets. For the noble gas binding on B48N48H24, we carried out a least-squares fit analysis of the dispersion and dispersionless contributions of the interaction potential separately. The transferability of the parameters for a range of molecular model systems of boron nitride is further established. The dressed PPM is then used in conjunction with a global optimization technique, namely particle swarm optimization (PSO) to assess the possibility of performing large-scale simulations with the PPM-PSO methodology. The results obtained for the adsorption of 2-5 noble gases on BN sheets establish the proof-of-concept, encouraging the pursuit of large-scale simulations using the PPM-PSO approach.

Advancement of radioactive material removal system by silver zeolite (Quantitative evaluation of noble gas adsorption characteristics by XeA and construction of noble gas adsorption system)

Advancement of radioactive material removal system by silver zeolite (Quantitative evaluation of noble gas adsorption characteristics by XeA and construction of noble gas adsorption system)

Understanding the Adsorption of Noble Gases in Metal–Organic Frameworks Using Diffuse Reflectance Infrared Fourier Transform Spectroscopy

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to study noble gas (i.e., He, Kr, and Xe) adsorption in metal-oxide frameworks (MOFs). To study the adsorption of infra...

Unprecedented saturation limit achieved by inorganic polycationic cluster (Sb7Te8)5+ for light noble gases (He & Ne)

Among noble gases, Helium and Neon have smaller size, high ionization potential and low polarizability due to which these two gases exhibit weak binding affinities toward any surface. Bartlet’s discovery and subsequent similar successful discoveries of stable complexes of noble gases opened new avenues for the storage of noble gases particularly on the new surfaces and their interactions for the storage of these gases. Here, we report the adsorption of light noble gases on polycationic clusters. Our current work not only investigates the interaction behavior of He and Ne with (Sb7Te8)5+ cluster but also explores the saturation limit of the cluster for He and Ne. Stability of various complexes of He and Ne with cationic surfaces is determined by the calculation of their interaction energies which reveal that the adsorption of single and multiple atoms of noble gases at faces of double cubic cluster is comparatively more favorable than at the bond lengths. Electronic properties such as HOMO-LUMO gaps show that complexes of He and Ne are more stable electronically than that of pure cluster, because HOMO-LUMO gap of complexes are higher than the bare polycationic cluster. NCI analysis of iso-surfaces and RDG maps confirms the presence of van der Waals forces between light noble gases and polycationic clusters. Saturation studies reveal that cluster can adsorb eleven He and/or ten Ne atoms with no or minimum distortion in the geometry of cluster. The results showed that Ne has greater tendency to interact with polycationic clusters due to the large electronic cloud and polarizability value than He.

Kinetic Barriers and Microscopic Mechanisms of Noble Gas Adsorption by Nanoporous γ‐Mg(BH4)2 Obtained by Means of Sub‐Second X‐Ray Diffraction

AbstractGas adsorption by porous frameworks sometimes results in structure “breathing”, “pores opening/closing”, “negative gas adsorption”, and other phenomena. Time‐dependent diffraction can address both kinetics of the guest uptake and structural response of the host framework. Using sub‐second in situ powder X‐ray diffraction, three intracrystalline diffusion scenarios have been evaluated from the isothermal kinetics of Ar, Kr, and Xe adsorption by nanoporous γ‐Mg(BH4)2. These scenarios are dictated by two possible simultaneous transport mechanisms: diffusion through the intra‐ (i) and interchannel apertures (ii) of γ‐Mg(BH4)2 crystal structure. The contribution of (i) and (ii) changes depending on the kinetic diameter of the noble gas molecule and temperature regime. The lowest single activation barrier for the smallest Ar suggests equal diffusion of the atoms trough both pathways. Contrary, for the medium sized Kr we resolve the contributions of two parallel transport mechanisms, which tentatively can be attributed to the smaller barrier of the migration paths via the channel like pores and the higher barrier for the diffusion via narrow aperture between these channels. The largest Xe atoms diffuse only along 1D channels and show the highest single activation barrier.

Kinetic Barriers and Microscopic Mechanisms of Noble Gas Adsorption by Nanoporous γ-Mg(BH4 )2 Obtained by Means of Sub-Second X-Ray Diffraction.

Gas adsorption by porous frameworks sometimes results in structure "breathing", "pores opening/closing", "negative gas adsorption", and other phenomena. Time-dependent diffraction can address both kinetics of the guest uptake and structural response of the host framework. Using sub-second in situ powder X-ray diffraction, three intracrystalline diffusion scenarios have been evaluated from the isothermal kinetics of Ar, Kr, and Xe adsorption by nanoporous γ-Mg(BH4 )2 . These scenarios are dictated by two possible simultaneous transport mechanisms: diffusion through the intra- (i) and interchannel apertures (ii) of γ-Mg(BH4 )2 crystal structure. The contribution of (i) and (ii) changes depending on the kinetic diameter of the noble gas molecule and temperature regime. The lowest single activation barrier for the smallest Ar suggests equal diffusion of the atoms trough both pathways. Contrary, for the medium sized Kr we resolve the contributions of two parallel transport mechanisms, which tentatively can be attributed to the smaller barrier of the migration paths via the channel like pores and the higher barrier for the diffusion via narrow aperture between these channels. The largest Xe atoms diffuse only along 1D channels and show the highest single activation barrier.

Effects of natural zeolites on field-scale geologic noble gas transport

Improving predictive models for noble gas transport through natural materials at the field-scale is an essential component of improving US nuclear monitoring capabilities. Several field-scale experiments with a gas transport component have been conducted at the Nevada National Security Site (Non-Proliferation Experiment, Underground Nuclear Explosion Signatures Experiment). However, the models associated with these experiments have not treated zeolite minerals as gas adsorbing phases. This is significant as zeolites are a common alteration mineral with a high abundance at these field sites and are shown here to significantly fractionate noble gases during field-scale transport. This fractionation and associated retardation can complicate gas transport predictions by reducing the signal-to-noise ratio to the detector (e.g. mass spectrometers or radiation detectors) enough to mask the signal or make the data difficult to interpret. Omitting adsorption-related retardation data of noble gases in predictive gas transport models therefore results in systematic errors in model predictions where zeolites are present.Herein is presented noble gas adsorption data collected on zeolitized and non-zeolitized tuff. Experimental results were obtained using a unique piezometric adsorption system designed and built for this study. Data collected were then related to pure-phase mineral analyses conducted on clinoptilolite, mordenite, and quartz. These results quantify the adsorption capacity of materials present in field-scale systems, enabling the modeling of low-permeability rocks as significant sorption reservoirs vital to bulk transport predictions.

The effect of doping on adsorption of Xe and Kr on graphyne and graphdiyne

Sequestration of radioactive noble gases xenon (Xe) and krypton (Kr) from off-gas streams of nuclear reactors and spent nuclear fuel reprocessing plants are essential. The Generally employed cryogenic distillation process for Xe/Kr separation is expensive and adsorption based techniques using porous materials are viable alternative. Recently, carbon allotropes such as graphynes (Gyn) and graphdiynes (Gdyn) attained importance due to their significance in many applications similar to graphene. In both graphyne and graphdiyne, the carbon atoms are sp-sp2 hybridized where benzene rings are linked through acetylenic and diacetylenic linkages respectively. They are good candidates for gas adsorption/separation due to their chemical stability and large surface area. In this regard, we have investigated the noble gas adsorption properties of doped/undoped graphyne and graphdiyne materials using density functional theory calculations. The graphyne and graphdiyne display enhanced adsorption affinity for Xe and Kr when doped with selective heteroatoms.