A DFT investigation of the adsorption of iodine compounds and water in H-, Na-, Ag-, and Cu- mordenite

Ketene Conversion Chemistry within Mordenite Zeolite: Pore-Size-Dependent Reaction Mechanism, Product Selectivity, and Catalytic Activity

The oxide-zeolite bifunctional catalyst for ketene-bridged syngas conversion has gained great attention for addressing the selectivity challenge in light olefin production, where zeolite dominates the ketene conversion selectivity. However, the atomic-level mechanism underlying ketene-to-light olefin conversion within zeolite remains unclear. Herein, we focus on mordenite (MOR) zeolite and perform systematic first-principles calculations combined with microkinetic simulations to elucidate pore-type-dependent reaction networks for ketene-to-light olefin conversion. Our microkinetic results reveal that ketene conversion within MOR follows an autocatalytic process initiated by the Brønsted acid site, involving the generation and subsequent catalysis of reactive intermediates. Time-dependent dynamic evolution simulation shows that within the 12-membered-ring (12MR) pore, a thermodynamically stable five-membered-ring carbocation (FMR-CH3+) self-evolves and acts as the active center to convert CH2CO to multihydrocarbons. Instead, in the 8-membered-ring side pocket (8MR), direct CH3+ formation occurs via acetyl carbocation (CH3CO+) decarbonylation, inducing CH2CO conversion with exclusive ethylene selectivity. The distinct reaction mechanisms and product selectivities are attributed to the thermodynamic and kinetic constraints of cyclic/long-chain intermediate formation imposed by the smaller 8MR pore. Despite its higher free energy barrier, 8MR is identified as the key active site for light olefin formation due to its lower dependence on ketene pressure. We also highlight the critical factors influencing both the selectivity and activity of light olefin formation, offering valuable insights for the optimization of MOR catalysts. This study provides a quantitative mechanistic understanding of ketene conversion, emphasizing the role of pore structure in shaping catalytic activity and product selectivity, which may facilitate the design of efficient zeolite-based catalysts.

Exploration on the mechanism of crystal morphology transformation in mordenite

Mordenite is extensively utilized in the domains of adsorption and catalysis owing to its excellent selectivity, stability, and renewability. In this work, the effects of crystal seeds, the ratio of SiO2/Al2O3, crystallization temperature, silicon source, and structure directing agents on the morphologies of mordenite are investigated by utilizing hexamethyleneimine (HMI) as the OSDA. Results indicate that the transformation of rod-like and flake-like mordenites is mainly related to the increasing ratio of SiO2/Al2O3, and the formation of flake-like morphology is related to various conditions. On a macro level, the rod-like and flake-like zeolites are formed by transforming amorphous precursors into small crystals and growing them epitaxially. On a micro level, HMIH+ progressively displaces Na+ to balance the framework charge with the increasing ratio of SiO2/Al2O3. DFT calculation and nuclear magnetic resonance results confirm the specific guidance of HMI on the T2 and T4 sites of the rod-like and flake-like mordenites. The conclusion can serve as a reference for regulating the morphology and active sites of mordenite.

Synthesis and Characterization of Silver-Modified Nanoporous Silica Materials for Enhanced Iodine Removal

In aquatic environments, the presence of iodine species, including radioactive isotopes like 129I and I2, poses significant environmental and health concerns. Iodine can enter water resources from various sources, including nuclear accidents, medical procedures, and natural occurrences. To address this issue, the use of natural occurring nanoporous minerals, such as zeolitic materials, for iodine removal will be explored. This study focuses on the adsorption of iodine by silver-modified zeolites (13X-Ag, 5A-Ag, Chabazite-Ag, and Clinoptilolite-Ag) and evaluates their performance under different conditions. All materials were characterized using scanning electron microscopey (SEM), energy-dispersive X-ray spectroscopy (EDS), powdered X-ray diffraction (P-XRD), Fourier-transform infrared spectrometry (FTIR), and nitrogen adsorption studies. The results indicate that Chabazite-Ag exhibited the highest iodine adsorption capacity, with an impressive 769 mg/g, making it a viable option for iodine removal applications. 13X-Ag and 5A-Ag also demonstrated substantial adsorption capacities of 714 mg/g and 556 mg/g, respectively, though their behavior varied according to different models. In contrast, Clinoptilolite-Ag exhibited strong pH-dependent behavior, rendering it less suitable for neutral to slightly acidic conditions. Furthermore, this study explored the impact of ionic strength on iodine adsorption, revealing that Chabazite-Ag is efficient in low-salinity environments with an iodine adsorption capacity of 51.80 mg/g but less effective in saline conditions. 5A-Ag proved to be a versatile option for various water treatments, maintaining its iodine adsorption capacity across different salinity levels. In contrast, Clinoptilolite-Ag exhibited high sensitivity to ionic competition, virtually losing its iodine adsorption ability at a NaCl concentration of 0.1 M. Kinetic studies indicated that the pseudo-second-order model best describes the adsorption process, suggesting chemisorption mechanisms dominate iodine removal. Chabazite-Ag exhibited the highest initial adsorption rate with a k2 value of 0.002 mg g-1 h-1, emphasizing its superior adsorption capabilities. Chabazite and Clinoptilolite, naturally occurring minerals, provide eco-friendly solutions for iodine adsorption. Chabazite superior iodine removal highlights its value in critical applications and its potential for addressing pressing environmental challenges.

Ab Initio Screening of Divalent Cations for CH4, CO2, H2, and N2 Separations in Chabazite Zeolite

The efficient separation and adsorption of critical gases are, more than ever, a major focus point in important energy processes, such as CH4 enrichment of biogas or natural gas, CO2 separation and capture, and H2 purification and storage. Thanks to its physicochemical properties, cation-exchanged chabazite is a potent zeolite for such applications. Previous computational screening investigations have mostly examined chabazites exchanged with monovalent cations. Therefore, in this contribution, periodic density functional theory (DFT) calculations in combination with dispersion corrections have been used for a systematic screening of divalent cation exchanged chabazite zeolites. The work focuses on cheap and readily available divalent cations, Ca(II), Mg(II), and Zn(II), Fe(II), Sn(II), and Cu(II) and investigates the effect of the cation nature and location within the framework on the adsorption selectivity of chabazite for specific gas separations, namely, CO2/CH4, N2/CH4, and N2/H2. All the cationic adsorption sites were explored to describe the diversity of sites in a typical experimental chabazite with a Si/Al ratio close to 2 or 3. The results revealed that Mg-CHA is the most promising cation for the selective adsorption of CO2. These predictions were further supported by ab initio molecular dynamics simulations performed at 300 K, which demonstrated that the presence of CH4 has a negligible impact on the adsorption of CO2 on Mg-CHA. Ca(II) was found to be the most favorable cation for the selective adsorption of H2 and CO2. Finally, none of the investigated cations were suitable for the preferential capture of N2 and H2 in the purification of CH4 rich mixtures. These findings provide valuable insights into the factors influencing the adsorption behavior of N2, H2, CH4, and CO2 and highlight the crucial role played by theoretical calculations and simulations for the optimal design of efficient adsorbents.

Potential of nanostructured carbon materials for iodine detection in realistic environments revealed by first-principles calculations

In the context of effective detection of iodine species (I2, CH3I) formed in nuclear power plants and nuclear fuel reprocessing facilities, we perform a comparative study of the potential sensing performance of four expectedly promising 2D materials (8-Pmmn borophene, BC3, C3N, and BC6N) towards the iodine-containing gases and, with the view of checking selectivity, towards common inhibiting gases in the containment atmosphere (H2O and CO), applying methods of dispersion-corrected density functional theory with periodic boundary conditions. A covalent bond is formed between the CO molecule and boron in BC3 or in 8-Pmmn borophene, compromising the anticipated applicability of these materials for iodine detection. The presence of nitrogen atoms in BC6N-2 prevents the formation of a covalent bond with CO; however, the closeness of adsorption energies for all the four gases studied does not distinguish this material as specifically sensitive to iodine species. Finally, the energies of adsorption on C3N yield a significant and promising discrimination between the adsorption energies of (I2, CH3I) vs. (CO, H2O), revealing possibilities for this material's use as an iodine sensor. The conclusions are supported by simulations at finite temperature; underlying electronic structures are also discussed.

Five Porous Complexes Constructed from a Racemic Ligand: Synthesis, Chiral Self-Assembly, Iodine Adsorption, and Desorption Properties

Herein, a chiral bispyridyl ligand (L) was designed and synthesized using a Schiff base condensation reaction, followed by a 1,3-H shift. Five complexes, [Zn₂L₂(OAc)₄] (1), {[CdLCl₂(DMF)]·4H₂O}_n (2), [Cd₂L₂I₄]·4H₂O (3), {[CdL₂(H₂O)₂](NO₃)₂·2CH₃OH}_n (4), and [Hg₂L₂Cl₄]·2DMF (5), were synthesized and characterized upon its reaction with Zn(II), Cd(II), or Hg(II) ions, respectively. X-ray crystallography shows that the organic compound exists as a racemic ligand with equal amounts of its R- and S-isomers, and all of the synthesized complexes exhibit heterochiral self-assembly via a chiral self-discrimination process. Complexes 1, 3, and 5 exist as centrosymmetric binuclear metallamacrocycles, while complexes 2 and 4 exist as 1D looped-chain coordination polymers. Inspired by the assembled structures of the five complexes, I₂ adsorption/desorption measurements for the complexes were carried out. The results show that complexes 1 and 5 exhibit good adsorption capacities toward I₂ in n-hexane and in water, respectively.

Interplay between alkali-metal cations and silanol sites in nanosized CHA zeolite and implications for CO2 adsorption

Silanols are key players in the application performance of zeolites, yet, their localization and hydrogen bonding strength need more studies. The effects of post-synthetic ion exchange on nanosized chabazite (CHA), focusing on the formation of silanols, were studied. The significant alteration of the silanols of the chabazite nanozeolite upon ion exchange and their effect on the CO2 adsorption capacity was revealed by solid-state nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR) spectroscopy, and periodic density functional theory (DFT) calculations. Both theoretical and experimental results revealed changing the ratio of extra-framework cations in CHA zeolites changes the population of silanols; decreasing the Cs+/K+ ratio creates more silanols. Upon adsorption of CO2, the distribution and strength of the silanols also changed with increased hydrogen bonding, thus revealing an interaction of silanols with CO2 molecules. To the best of our knowledge, this is the first evidence of the interplay between alkali-metal cations and silanols in nanosized CHA.

Theoretical Study for Adsorption-Diffusion on H-MOR and Pyridine Pre-adsorbed H-MOR of Dimethyl Ether Carbonylation

For dimethyl ether (DME) carbonylation, pyridine pre-adsorbed hydrogen mordenite (H-MOR) is beneficial to prolonging the catalyst life. The adsorption and diffusion behaviors on periodic models H-AlMOR and H-AlMOR-Py were simulated. The simulation was based on Monte Carlo and molecular dynamics. The following conclusions were drawn from the simulation results. The adsorption stability of CO in 8-MR is increased, and the adsorption density of CO in 8-MR is more concentrated on H-AlMOR-Py. 8-MR is the main active site for DME carbonylation, so the introduction of pyridine would be beneficial for the main reaction. The adsorption distributions of methyl acetate (MA) (in 12-MR) and H₂O on H-AlMOR-Py are significantly decreased. It means the product MA and the byproduct H₂O are more easily desorbed on H-AlMOR-Py. For the mixed feed of DME carbonylation, the feed ratio (P_CO/P_DME) must reach 50:1 on H-AlMOR so that the reaction molar ratio can reach the theoretical value (N_CO/N_DME ≈ 1:1), while the feed ratio on H-AlMOR-Py is only up to 10:1. Thus, the feed ratio can be adjusted, and raw materials can reduce consumption. In conclusion, H-AlMOR-Py can improve the adsorption equilibrium of reactants CO and DME and increase the concentration of CO in 8-MR.

Removal of iodine by dry adsorbents in filtered containment venting system after 10 years of Fukushima accident

Radioactive iodine is a hazardous fission product and a major concern for public health. Special attention is paid to iodine out of 80 fission products because of its short half-life of 8.02 days, high activity, and potential health hazards like its irreversible accumulation in thyroid gland and ability to cause thyroid cancer locally. Radioactive iodine can get released in the form of aerosols (cesium iodide), elemental iodine, and organic iodide after a nuclear accident and can cause off-site and on-site contamination. Filtered containment venting system (FCVS) is a safety system whose main objective is mitigation of severe accidents via controlled venting and removal of different forms of iodine to ensure safety of people and environment. After nuclear accidents like Fukushima, extensive research has been done on the removal of iodine by using dry scrubbers. This review paper presents research status of iodine removal by dry adsorbents especially after 10 years of Fukushima to assess the progress, research gap, and challenges that require more attention. A good adsorbent should be cost-effective; it should have high selective adsorption towards iodine, high thermal and chemical stability, and good loading capacity; and its adsorption should remain unaffected by aging and the presence of inhibitors like CO, NO₂, CH₃Cl, H₂O, and Cl₂ and radiation. Research on different dry adsorbents was discussed, and their capability as a potential filter for FCVS was reviewed on the basis of all the above-mentioned features. Metal fiber filters have been widely used for removal of aerosols especially micro- and nanoscale aerosols. For designing a metal fiber filter, optimal size or combination of sizes of fibers, number of layers, and loading capacity of filter should be decided according to feasibility and requirement. Balance between flow resistance and removal efficiency is also very important. Sand bed filters were successful in retention of aerosols, but they showed low trapping of iodine and no trapping of methyl iodide at all. For iodine and methyl iodide removal, many adsorbents like activated carbon, zeolites, metal organic frameworks (MOFs), porous organic frameworks (POPs), silica, aerogels, titanosilicates, etc. have been used. Impregnated activated carbon showed good results but low auto-ignition temperature and decline in adsorption due to aging and inhibitors like NO_x made them less suitable. Silver zeolites have been very successful in methyl iodide and iodine removal, but they are expensive and affected by presence of CO. Titanosilicates, macroreticular resins, and chalcogels were also studied and they showed good adsorption capacities, but their thermal stability was low. Other adsorbents like silica, MOFs, aerogels, and POPs also showed promising results for iodine adsorption and good thermal stability, but very limited or no research is available on their performance in severe accident conditions. This review will be very helpful for researchers to understand the merits and demerits of different types of dry adsorbents, the important operating parameters that need optimization for designing an efficient scrubber, margin of research, and foreseeable challenges in removal of different forms of iodine.

New Hg(II) coordination polymers based on a thioimidazole ligand with good performance to detoxify Hg(II) and reversibly capture iodine

In the current paper, we have successfully synthesized three new mercury coordination polymers with fascinating structures and properties via a flexible sulfur donor ligand, namely, {[Hg(μ₂-Cl)(μ₂-Ls)]}_n[BF₄]_n(1), {[Hg(μ₂-Cl)(μ₂-Ls)]}_n[ClO₄]_n(2), and [Hg(SCN)₂(μ₂-Ls)]_n(3) [Ls = 1,1-bis(3-methyl-4-imidazoline-2-thione)methane]. These complexes have been characterized by means of different techniques such as single crystal X-ray crystallography, FT-IR, elemental analysis (CHNS), UV-Vis, PXRD, BET, and TGA. Suitable single crystals of all complexes were obtained using the branch tube method with a very high yield and good stability due to the high affinity of mercury to bind to the thione groups. The cationic moieties of polymers 1 and 2 were isostructural, with a HgCl₂S₂ coordination core structure. The voids of the quasi-hexagonal packing of the columnar chains were occupied by unbonded tetrahedral BF₄^- ions in 1 and perchlorate anions in polymer 2. Polymer 3 has a less distorted tetrahedral geometry than 1 and 2, with a HgS₄ core structure. By considering the thiophilicity of mercury, a thioamide-based Ls ligand was used to detoxify Hg(II) into insoluble polymers 1-3. The results of an MTT assay for (HepG2) liver cells confirmed the excellent cytoprotective effect of this ligand against mercury. Based on IC₅₀ calculations, their toxicity was in order of polymer 1 > polymer 2 > polymer 3. These polymers were also considered as adsorbents for the reversible removal of iodine from solution and the kinetics of the process has been studied in detail. Interestingly, all of them showed an excellent stability and high capacity, in order of 763.53 mg g^-1, 877.10 mg g^-1, and 905.31 mg g^-1 for polymers 1-3, respectively.

Adsorption of NO, NO2 and H2O in divalent cation faujasite type zeolites: a density functional theory screening approach

Emissions of diesel exhaust gas in confined work environments are a major health and safety concern, because of exposition to nitrogen oxides (NO_x). Removal of these pollutants from exhaust gas calls for engineering of an optimum sorbent for the selective trapping of NO and NO₂ in the presence of water. To this end, periodic density functional theory calculations along with a recent dispersion correction scheme, namely the Tkatchenko-Scheffler scheme coupled with iterative Hirshfeld partitioning TS/HI, were performed to investigate the interactions between NO, NO₂, H₂O and a series of divalent cation (Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Fe²⁺, Cu²⁺, Zn²⁺, Pd²⁺, and Pt²⁺) faujasites. This enabled the identification of the optimum zeolites to selectively capture NO_x in the presence of H₂O, with respect to two important criteria, such as thermodynamic affinity and regeneration. Our results revealed that Pt²⁺ and Pd²⁺ containing faujasites are the best candidates for effective capture of both NO and NO₂ molecules, which paves the way towards the use of these sorbents to address this challenging application.

Crystalline structures of L-cysteine and L-cystine: a combined theoretical and experimental characterization

It is assumed that genetic diseases affecting the metabolism of cysteine and the kidney function lead to two different kinds of pathologies, namely cystinuria and cystinosis whereby generate L-cystine crystals. Recently, the presence of L-cysteine crystal has been underlined in the case of cystinosis. Interestingly, it can be strikingly seen that cystine ([-S-CH₂-CH-(NH₂)-COOH]₂) consists of two cysteine (C₃H₇NO₂S) molecules connected by a disulfide (S-S) bond. Therefore, the study of cystine and cysteine is important for providing a better understanding of cystinuria and cystinosis. In this paper, we elucidate the discrepancy between L-cystine and L-cysteine by investigating the theoretical and experimental infrared spectra (IR), X-ray diffraction (XRD) as well as Raman spectra aiming to obtain a better characterization of abnormal deposits related to these two genetic pathologies.

Assessing the Accuracy of Machine Learning Thermodynamic Perturbation Theory: Density Functional Theory and Beyond

Machine learning thermodynamic perturbation theory (MLPT) is a promising approach to compute finite temperature properties when the goal is to compare several different levels of ab initio theory and/or to apply highly expensive computational methods. Indeed, starting from a production molecular dynamics trajectory, this method can estimate properties at one or more target levels of theory from only a small number of additional fixed-geometry calculations, which are used to train a machine learning model. However, as MLPT is based on thermodynamic perturbation theory (TPT), inaccuracies might arise when the starting point trajectory samples a configurational space which has a small overlap with that of the target approximations of interest. By considering case studies of molecules adsorbed in zeolites and several different density functional theory approximations, in this work we assess the accuracy of MLPT for ensemble total energies and enthalpies of adsorption. It is shown that problematic cases can be detected even without knowing reference results and that even in these situations it is possible to recover target level results within chemical accuracy by applying a machine-learning-based Monte Carlo (MLMC) resampling. Finally, on the basis of the ideas developed in this work, we assess and confirm the accuracy of recently published MLPT-based enthalpies of adsorption at the random phase approximation level, whose high computational cost would completely hinder a direct molecular dynamics simulation.

Ab initio molecular dynamics investigation of the co-adsorption of iodine species with CO and H2O in silver-exchanged chabazite

In the field of nuclear energy, there is particular interest for the trapping of harmful iodine species (I2 and CH3I) that could be released during a nuclear accident, due to their dangereous impact on the human metabolic processes and on nature.

Theoretical insights into volatile iodine adsorption onto COF-DL229

COF-DL229 is one of the promising sorbents for the capture of volatile radioiodine due to its large adsorption capacity. However, the interaction mechanism between them remains unclear. In the present work, the adsorption of volatile iodine onto COF-DL229 was systematically investigated using periodic density functional theory and crystal orbital Hamilton population calculations. The "soft" characters of COF-DL229 have been theoretically demonstrated. Furthermore, the adsorption energies are extremely large (-8.38 to -9.26 eV), which mainly originate from the framework deformation energies, accounting for 90% at least. The I₂ interacts with the skeleton mainly through the N atoms of the imine linkers or the C atoms of the phenyl rings. And, the I-N bond is the strongest bond among all the potential secondary bonds formed between the skeleton and I₂. The electrons could be transferred from the skeletons to the iodine atoms and from the near iodine atom to the far one. It is also found that the energy gap becomes narrow after iodine adsorption and the skeletons mainly interact with the bonding orbital σ_p of I₂. The present work could provide reasonable theoretical explanations to the corresponding experimental investigations and contribute to the design and screening of better sorbents for the capture of volatile radioiodine.

Adsorption of Toluene and Water over Cationic-Exchanged Y Zeolites: A DFT Exploration

In this study, density functional theory (DFT) calculations have been performed to investigate the adsorption mechanisms of toluene and water onto various cationic forms of Y zeolite (LiY, NaY, KY, CsY, CuY and AgY). Our computational investigation revealed that toluene is mainly adsorbed via π-interactions on alkalis exchanged Y zeolites, where the adsorbed toluene moiety interacts with a single cation for all cases with the exception of CsY, where two cations can simultaneously contribute to the adsorption of the toluene, hence leading to the highest interaction observed among the series. Furthermore, we find that the interaction energies of toluene increase while moving down in the alkaline series where interaction energies are 87.8, 105.5, 97.8, and 114.4 kJ/mol for LiY, NaY, KY and CsY, respectively. For zeolites based on transition metals (CuY and AgY), our calculations reveal a different adsorption mode where only one cation interacts with toluene through two carbon atoms of the aromatic ring with interaction energies of 147.0 and 131.5 kJ/mol for CuY and AgY, respectively. More importantly, we show that water presents no inhibitory effect on the adsorption of toluene, where interaction energies of this latter were 10 kJ/mol (LiY) to 47 kJ/mol (CsY) higher than those of water. Our results point out that LiY would be less efficient for the toluene/water separation while CuY, AgY and CsY would be the ideal candidates for this application.

Capture of iodine in solution and vapor phases by newly synthesized and characterized encapsulated Cu2O nanoparticles into the TMU-17-NH2 MOF

The efficient capture and storage of radioactive iodine (¹²⁹I or ¹³¹I) formed during the extensive use of nuclear energy is of paramount importance. Therefore, it is a great deal to design new adsorbents for effectively disposing of iodine from nuclear waste. In this work, a new Cu₂O/TMU-17-NH₂ composite has been prepared by a simple encapsulation of Cu₂O nanoparticles (NPs) into the metal organic framework (MOF) TMU-17-NH₂ for the first time. The as-synthesized Cu₂O/TMU-17-NH₂ was fully characterized in details and the iodine sorption/release capability of the Cu₂O/TMU-17-NH₂ composite has been investigated both in solution and in the vapor phase. According to the FE-SEM images, the Cu₂O/TMU-17-NH₂ was obtained with same morphology to that of the pristine TMU-17-NH₂. The I₂ sorption/release experiments were examined by UV-vis spectroscopy. The optimal iodine sorption was obtained by almost complete removal of iodine with a sorption capacity of about 567 mg/g. Detailed experimental evidence demonstrating that the iodine was captured by chemisorption process. Furthermore, photoluminescence (PL) properties of Cu₂O/TMU-17-NH₂ have also been investigated in which indicate that the Cu₂O/TMU-17-NH₂ composite exhibits stronger emission than the pristine TMU-17-NH₂.

A first principle evaluation of the adsorption mechanism and stability of volatile organic compounds into NaY zeolite

Removal of volatile organic compounds (VOCs) from indoor or outdoor environments is an urgent challenge for the protection of human populations. Inorganic sorbents such as zeolites are a promising solution to tackle this issue. Using dispersion corrected periodic DFT calculations, we have studied the interaction between sodium-exchanged faujasite zeolite and a large set of VOCs including aromatics, oxygenates and chlorinated compounds. The computed interaction energies range from about −25 (methane) to −130 kJ/mol (styrene). Methane is by far the less interacting specie with the NaY zeolite. All other VOCs present interaction energies higher in absolute value than 69 kJ/mol. Most of them show a similar adsorption strength, between −70 and −100 kJ/mol. While the electrostatic interactions are important in the case of oxygenates and acrylonitrile, van der Waals interactions predominate in hydrocarbons and chlorides. By monitoring the variation of molecular bond lengths of the different VOCs before and after adsorption, we have then evaluated the tendency of adsorbate to react and form by-products, since a significant stretching would evidently lead to the activation of the bond. While hydrocarbons, tetrachloroethylene and acrylonitrile seem to be not activated upon adsorption, all oxygenates and 1,1,2-trichloroethane could possibly react once adsorbed.

Dibenzyl Disulfide Adsorption on Cationic Exchanged Faujasites: A DFT Study

Although dibenzyl disulfide (DBDS) is used as a mineral oil stabilizer, its presence in electrical transformer oil is associated as one of the major causes of copper corrosion and subsequent formation of copper sulfide. In order to prevent these undesirable processes, MY zeolites (with M = Li, Na, K, Cs, Cu or Ag) are proposed to adsorb molecularly DBDS. In this study, different MY zeolites are investigated at the DFT+D level in order to assess their ability in DBDS adsorption. It was found that CsY, AgY and CuY exhibit the best compromise between high interaction energies and limited S-S bond activation, thus emerging as optimal adsorbents for DBDS.

Benchmarking the performance of approximate van der Waals methods for the structural and energetic properties of SiO2 and AlPO4 frameworks

Density functional theory (DFT) calculations using sixteen different approaches, fourteen of which were designed to include dispersion interactions [DFT + D and van der Waals (vdW)-DF methods], were performed for a set of sixteen framework compounds with either SiO₂ or AlPO₄ composition. The compounds include four dense structures (α-quartz, α-cristobalite, and their AlPO₄ analogues), eight all-silica zeolites, and four aluminophosphate zeotypes (AlPOs). We analyzed the performance in reproducing the equilibrium structure for all systems, and computed bulk moduli and relative stabilities were compared to experiments for those compounds where experimental data are available. We found that the results obtained with functionals that take into account dispersive interactions are closer to experiments than those obtained with a bare generalized gradient functional. However, the variation among individual methods is considerable, and functionals that perform well for one quantity may give rather large deviations for another. Taking together the whole body of results, it appears that the Perdew-Burke-Ernzerhof functional including a many-body dispersion correction and the rev-vdW-DF2 methods present the best performance for the description of SiO₂ and AlPO₄ materials.

Research Works on Iodine and Ruthenium Behavior in Severe Accident Conditions

This paper deals with near past, ongoing, and planned R&D works on fission products (FPs) behavior in reactor cooling system (RCS), containment building and in filtered containment venting systems (FCVS) for severe accident (SA) conditions. All the researches are collaborative works; the overall objective is to develop confident models to be implemented in simulation software. After being initiated in 2004, researches on iodine transport through the RCS are still ongoing and for containment, the last advances are linked to the source term (ST) evaluation and mitigation (STEM) OECD/NEA project. The objective is to improve the evaluation of ST for a SA on a nuclear power plant and to reduce uncertainties on specific phenomena dealing with the chemistry of two major FPs: iodine and ruthenium. For ruthenium attention has been paid to study the amount and nature (gas/aerosol partition) of ruthenium species along the RCS. A follow-up, called STEM2, has started to reduce some remaining issues and be closer to reactor conditions. For FCVS works, the efficiencies for trapping iodine covering scrubbers and dry filters are examined to get a clear view of their abilities in SA conditions. Another part is focused on specific porous materials able to trap volatile iodine. Influence of zeolite materials parameters (nature of the counter-ions, structure, Si/Al ratio…) are tested as well as new kind of porous materials constituted by Metal organic Frameworks will also be looked at.

Porous sorbents for the capture of radioactive iodine compounds: a review

The number of studies on the capture of radioactive iodine compounds by porous sorbents has regained major importance in the last few years. In fact, nuclear energy is facing major issues related to operational safety and the treatment and safe disposal of generated radioactive waste. In particular during nuclear accidents, such as that in 2011 at Fukushima, gaseous radionuclides have been released in the off-gas stream. Among these, radionuclides that are highly volatile and harmful to health such as long-lived ¹²⁹I, short-lived ¹³¹I and organic compounds such as methyl iodide (CH₃I) have been released. Immediate and effective means of capturing and storing these radionuclides are needed. In the present review, we focus on porous sorbents for the capture and storage of radioactive iodine compounds. Concerns with, and limitations of, the existing sorbents with respect to operating conditions and their capacities for iodine capture are discussed and compared.

In the capture of radioactive iodine compounds by porous sorbents, concerns with, and limitations of, the existing sorbents with respect to operating conditions and their capacities for iodine capture are discussed and compared.

A DFT study of RuO4 interactions with porous materials: metal–organic frameworks (MOFs) and zeolites

The potential use of zeolite and MOF materials for the capture of RuO₄ has been investigated for the first time. A hydrated form of HKUST-1 could be a promising sorbent due to its ability to form multiple hydrogen bonds.

Performance of CuII -, PbII -, and HgII -Exchanged Mordenite in the Adsorption of I2 , ICH3 , H2 O, CO, ClCH3 , and Cl2 : A Density Functional Study

Periodic dispersion-corrected DFT is used to investigate the adsorption of I₂ and ICH₃ , which may be released during a severe nuclear accident, for three divalent cation (Cu²⁺ , Pb²⁺ and Hg²⁺ )-exchanged mordenites with an Si/Al ratio of 23. Gases such as H₂ O, CO, ClCH₃ , and Cl₂ present in the containment atmosphere can inhibit the selective adsorption of iodine species. To identify the most promising adsorbents, a systematic study is performed in which all the possible cationic sites in the main channel of the mordenite structure are considered. For the energetically most stable sites, the divalent cation is located in the small rings (five- or six-membered) containing two Al atoms, while in the energetically less stable configurations, the two Al atoms are far apart (>7 Å) and the cation is close to only one Al atom. Upon adsorption of the various molecules, the coordination number of the cation decreases with increasing interaction energy, as the molecules can attract the divalent cations from the framework. Finally, the computed interaction energies show that Hg-mordenite (MOR) could be a suitable material for selective adsorption of volatile iodine species, contrary to Cu-MOR and Pb-MOR.

Dissociative iodomethane adsorption on Ag-MOR and the formation of AgI clusters: an ab initio molecular dynamics study

Using ab initio MD simulations, a full transformation path of iodomethane in Ag-MOR is explored: from adsorption to formation of AgI clusters.

Impact of the Si/Al ratio on the selective capture of iodine compounds in silver-mordenite: a periodic DFT study

Decreasing the Si/Al ratio in silver exchanged mordenite drastically limits the potential inhibiting effect of H₂O and CO on the adsorption of I₂ and ICH₃, and allows a spontaneous dissociation of I₂ leading to the formation of AgI complexes.