Specific Cation Research Articles

PH: A core node of interaction networks among soil organo-mineral fractions

Mineral-associated organic matter (MAOM) is the largest soil organic carbon (OC) pool with the longest turnover. MAOM is expected to have relatively little sensitivity to climate change due to mineral protection, but its persistence involves several organo-mineral fractions. The uncertainty in the response of specific organo-mineral fractions to climate change hampers the reliability of predictions of MAOM preservation in the future. Here, we applied a sequential chemical fractionation method integrated with network analysis to investigate MAOM stabilization mechanisms across five alpine ecosystems: alpine desert, alpine steppe, alpine meadow, alpine wetland, and alpine forest. Hierarchical cluster analysis revealed grouping of seven extractable OM fractions in MAOM into three OM clusters: a cluster with weak bondings consisting of water-soluble OM (WSOM) and weakly adsorbed fractions (2.1–21.3% of total OC); a cluster with metal-bound complexes comprising Ca-OM complexes and Fe/Al-OM complexes (3.8–12.2% of total OC); and a cluster with strong bonding composed of Al oxyhydroxides, carbonates and Fe oxyhydroxides (12.2–33.5% of total OC). The relative percentages of OM from soils of the five ecosystems in the three clusters exhibited distinct pH dependence patterns. With the increase in pH, the cluster with weak bondings decreased, and that with strong bondings increased, while the one with metal-bound complexes showed a maximum at weakly acidic pH. Organo-mineral fractions and metal cations in MAOM constructed a complex network with pH as the central node. Results suggest that precipitation does not only alter vegetation type and microbial biomass but also regulate soil pH, which is balanced by specific metal cations, thus resulting in particular pH preference of specific OM clusters. These findings demonstrate that soil pH plays a central role in unveiling MAOM dynamics and can serve as a good predictor of soil organo-mineral fractions across alpine ecosystems.

Physicochemical and mineral characteristics of soil materials developed naturally on two ∼ 50 years old coal combustion residue disposal sites in Croatia

Coal combustion has been one of the most dominant sources of energy for the last two centuries, generating tonnes of coal combustion residue (CCR). Rapid soil formation has been observed at old CCR disposal sites, altering the physiochemical and mineral properties of CCR, affecting contaminant release mechanisms and nutrient availability. Although ubiquitous, pedological properties of weathered CCR have been studied at only a small number of disposal sites. This study characterized two CCR landfills of similar age (∼50 years) using a range of parameters, including pH, total nitrogen and organic carbon content, major oxides (Al2O3, CaO, and SiO2), and macronutrients (Ca, K, Mg, P, and S), as well as textural and mineralogical data. In addition, specific surface area and cation exchange capacity were determined to assess particle properties, and 13C and 29Si NMR spectra were examined to characterize the organic matter and degree of polymerization of the coal ash glassy phase. Such comprehensive approach aimed to determine indicators of soil formation and to characterize the capacity of such landfills to retain water, nutrients, and contaminants. Both landfills displayed evidence of pedogenesis reflected in the pH decrease, formation of secondary minerals (such as ettringite, hydrotalcite, gypsum, and calcite), and changes in the C:N ratio. The Plaški landfill seems to have a better capacity to hold water, nutrients, and contaminants evident by higher clay content, CEC, and SSA values, possibly explaining why it developed more rapidly than Štrmac despite their similar age. The presence of montmorillonite in Plaški could be one of the main factors accelerating pedogenesis. 13C NMR spectra point to the unburned coal particles as the main origin of organic matter and 29Si NMR spectra showed higher depolymerization of a non-crystalline fraction in bare ash samples than in vegetated ash samples.

Function of TRP channels in monocytes/macrophages.

The transient receptor potential channel (TRP channel) family is a kind of non- specific cation channel widely distributed in various tissues and organs of the human body, including the respiratory system, cardiovascular system, immune system, etc. It has been reported that various TRP channels are expressed in mammalian macrophages. TRP channels may be involved in various signaling pathways in the development of various systemic diseases through changes in intracellular concentrations of cations such as calcium and magnesium. These TRP channels may also intermingle with macrophage activation signals to jointly regulate the occurrence and development of diseases. Here, we summarize recent findings on the expression and function of TRP channels in macrophages and discuss their role as modulators of macrophage activation and function. As research on TRP channels in health and disease progresses, it is anticipated that positive or negative modulators of TRP channels for treating specific diseases may be promising therapeutic options for the prevention and/or treatment of disease.

Deciphering the specific interaction of humic acid with divalent cations at the nanoscale

Humic acid (HA), a representative class of natural organic matter (NOM), can interact with a variety of divalent cations to form the metal-HA complexes, which is of vital significance in both the natural and engineered environments. To decipher the specific HA-divalent cation interaction mechanism, the intermolecular forces and adhesion energies between two HA surfaces in aqueous environment with varying divalent cations were directly quantified at the nanoscale using atomic force microscope (AFM). In the presence of Ca2+, the considerably increased HA aggregation and HA-Ca(II)-HA adhesion were detected with elevated Ca2+ concentration mainly due to the enhanced bridging effect, while the excessive amounts of Ca2+ could significantly suppress the aggregation and adhesion behavior. The adhesion energy was also found to be dependent on other aqueous conditions (e.g., pH, cation type), with the highest adhesion energy measured for Cu2+ (∼1.642 mJ m−2), approximately 2 ∼ 3-fold higher than the case of Zn2+ (∼0.950 mJ m−2), Ca2+ (∼0.829 mJ m−2) and Mg2+ (∼0.583 mJ m−2). Such robust adhesion for Cu2+ could stem from the synergistic bonding of Cu2+ with both the oxygen and amine sites of HA, which was evidently different from the single metal–oxygen bonding for Zn2+, Ca2+ and Mg2+ shown by X-ray photoelectron spectroscopy (XPS). Based on density functional theory (DFT) simulation, HA molecules could bridge with all these four types of divalent cations mainly by the deprotonated catechol and phthalic acid (PA) structures in the bidentate coordination mode, while the deprotonated aniline could only bond with Cu2+, ultimately leading to the highest Cu(II)-HA binding energy among the studied divalent cations. This work provides insights into the quantitative understanding of HA-divalent cation interaction mechanisms, shedding light on developing effective strategies to modulate the aggregation, transport and fate of NOM in aqueous environments as well as engineering applications.

Physicochemical Variation of Clay Minerals and Enrichment of Rare Earth Elements in Regolith-hosted Deposits: Exemplification from The Bankeng Deposit in South China

AbstractThe wide application of rare earth elements (REEs) in the development of a carbon–neutral society has urged resource exploration worldwide in recent years. Regolith-hosted REE deposits are a major source of global REE supply and are hosted mostly in clay minerals. Nonetheless, the ways in which changes in the physicochemical properties of clay minerals during weathering affect the concentrations of REEs in the regolith are not well known. In the current study, a world-class regolith-hosted REE deposit (Bankeng, South China) has been studied to illustrate further the effect of clay minerals on sorption and fractionation of REEs during weathering to form economic deposits. In the weathering profile, halloysite and illite are abundant in the saprolite due to weathering of feldspars and biotite from the bedrock. During weathering, halloysite and illite transform gradually to kaolinite and vermiculite. The large specific surface area, pore volume, and cation exchange capacity of the clay mineral assemblages are favorable to the sorption of REEs, probably because of the formation of vermiculite. The abundance of vermiculite could explain the enrichment of REEs in the upper part of the lower pedolith. For the saprolite-pedolith interface, halloysite is probably the main sorbent for the REEs, as indicated by the distinctive appearance of pore sizes of 2.4–2.8 nm characteristic of halloysite. The progressive transformation of halloysite to kaolinite reduces the pores and desorbs the REEs, causing REE depletion in the shallower soils. As a result, REEs were mobilized downward and re-sorbed in the lower pedolith-upper saprolite causing gradual enrichment and formation of these regolith-hosted deposits.

Influence of Mg2+ Distribution on the Stability of Folded States of the Twister Ribozyme Revealed Using Grand Canonical Monte Carlo and Generative Deep Learning Enhanced Sampling.

Metal ions, particularly magnesium ions (Mg2+), play a role in stabilizing the tertiary structures of RNA molecules. Theoretical models and experimental techniques show that metal ions can change RNA dynamics and how it transitions through different stages of folding. However, the specific ways in which metal ions contribute to the formation and stabilization of RNA's tertiary structure are not fully understood at the atomic level. Here, we combined oscillating excess chemical potential Grand Canonical Monte Carlo (GCMC) and metadynamics to bias toward the sampling of unfolded states using reaction coordinates generated by machine learning allowing for examination of Mg2+-RNA interactions that contribute to stabilizing folded states of the pseudoknot found in the Twister ribozyme. GCMC is used to sample diverse ion distributions around the RNA with deep learning applied to iteratively generate system-specific reaction coordinates to maximize conformational sampling during metadynamics simulations. Results from 6 μs simulations performed on 9 individual systems indicate that Mg2+ ions play a crucial role in stabilizing the three-dimensional (3D) structure of the RNA by stabilizing specific interactions of phosphate groups or phosphate groups and bases of neighboring nucleotides. While many phosphates are accessible to interactions with Mg2+, it is observed that multiple, specific interactions are required to sample conformations close to the folded state; coordination of Mg2+ at individual specific sites facilitates sampling of folded conformations though unfolding ultimately occurs. It is only when multiple specific interactions occur, including the presence of specific inner-shell cation interactions linking two nucleotides, that conformations close to the folded state are stable. While many of the identified Mg2+ interactions are observed in the X-ray crystal structure of Twister, the present study suggests two new Mg2+ ion sites in the Twister ribozyme that contribute to stabilization. In addition, specific interactions with Mg2+ are observed that destabilize the local RNA structure, a process that may facilitate the folding of RNA into its correct structure.

Efficient cadmium immobilization by organic loaded Na-montmorillonite in a contaminated soil

Clay minerals are effective sorbents for toxic metal immobilization in contaminated soils and waters. However, their Cd immobilization efficiency is unclear when they are loaded with organics. In this study, sodium montmorillonite (Na-M) was successfully loaded with potassium humate, chitosan, and glycine to adsorb Cd(II) in solution. Potassium humate loaded Na-M (Na-M-HA), which had the highest specific surface area and cation exchange capacity (CEC), showed the highest Cd(II) adsorption capacity (73.7 mg g−1), 22.5 % and 81.8 % higher than that of chitosan loaded Na-M (Na-M-CTS) and glycine loaded Na-M (Na-M-G), respectively. The pseudo-second-order kinetic model best described (R2 > 0.98) the adsorption kinetics of Cd(II) on the three Na-Ms, indicating that the adsorption processes were of chemisorption nature. The adsorption isotherm of Cd(II) on Na-M-HA was of the Freundlich type, suggesting multilayer adsorption. In contrast, the isothermal adsorption of Cd(II) on Na-M-CTS (R2 = 0.99) and Na-M-G (R2 = 0.89) was better described by the Langmuir model, suggesting the dominance of monolayer adsorption in the adsorption process. High temperature, high pH, low background ionic strength, and low valence competing cations favored Cd(II) adsorption on Na-M-HA. The underlying mechanisms of Cd(II) sorption on Na-M-HA were electrostatic attraction, ion exchange and complexation. Na-M-HA was applied to a Cd polluted soil planted with lettuce (Lactuca sativa L.). in a pot experiment. Compared to the control with no adsorbent application, Na-M-HA application at 2 % effectively reduced the available Cd content in soil and Cd accumulation in plant by 36.0 % and 56.8 %, respectively. This work demonstrated that Na-M-HA is a green, low-cost and excellent adsorbent for Cd stabilization, and that its application in Cd-polluted soils can efficiently reduce Cd bioavailability and thereby Cd transfer along the food chain and eventually reduce the threat of Cd pollution to human health.

1H NMR and EPR Spectroscopies Investigation of Alginate Cross-Linking by Divalent Ions

Alginate is a natural polymer widely applied in materials science, medicine, and biotechnology. Its ability to bind metal ions in order to form insoluble gels has been comprehensively used to create capsules for cell technology, drug delivery, biomedical materials, etc. To modify and predict the properties of cross-linked alginate, knowledge about the mechanism of alginate binding with metal ions and the properties of its gels is necessary. This article presents the results obtained by proton Nuclear Magnetic Resonance Spectroscopy for alginate containing calcium and strontium (alkaline earth metal diamagnetic) ions and by Electron Paramagnetic Resonance Spectroscopy for alginate with copper (Cu) and manganese (Mn) (transition metal paramagnetic) ions. It was found that in the case of calcium (Ca) and Mn ions, their concentration does not affect their distribution in the alginate structure and the cross-linking density. In the case of strontium (Sr) and Cu ions, their number affects the number of binding sites and, accordingly, the cross-linking density. Thus, the cross-linking of alginate depends mainly on the characteristics of specific cations, while the nature of the bond (ionic or coordination type) is less important.

Simulation of Triple-Cation Perovskite Solar Cells: Key Design Factors for Efficiency Promotion

Compositional engineering is considered one of the recent interesting techniques used in the field of perovskite solar cells (PSCs). In this method, more than one material was used in a specific cation in the perovskite structure. This work aims to simulate the cesium-containing triple-cation perovskite (TCP) via the SCAPS-1D simulation program with a device structure of ITO/SnO2/TCP/Spiro-OMeTAD/Au. First, we studied the effect of interface defects on the PCSs with respect to experimental results and found that when no interface defects occur, the power conversion efficiency (PCE) reaches a value of 22.16% which is higher than the reported PCE, implying that the fabricated cell suffers from the interface defects as a main effect on cell degradation. Incorporating interface defects into the simulation results in a very good match between the experimental and simulated data with a PCE of 17.92%. Further, to provide possible routes to enhance the performance of the solar cell under investigation, impacts of absorber layer thickness, conduction band offset (CBO), surface recombination velocity, and light intensity were explored. In addition, hole transport layer (HTL)-free design was investigated to alleviate the instability issues associated to the organic HTL, leading to a PCE of 18.28%, for a surface velocity of 104 cm/s, which is interestingly higher than the initial cell. The provided study reveals the critical role of interface defects and other key design factors and suggests potential solutions to alleviate the subsequent degradation mechanisms, thereby enhancing the overall cell performance.

Effect of Modified Illite on Cd Immobilization and Fertility Enhancement of Acidic Soils

Cadmium pollution in the soil induces significant hazards to agricultural growth and public health. Therefore, new routes are needed to develop low-cost soil amendments that can effectively stabilize cadmium and improve soil fertility. This study introduces modified illite (MIT) with the enhanced ability to stabilize heavy metal Cd through the mixing of illite with calcium carbonate, silicate and sulfate in specific proportions by using the well-known calcination-hydrothermal process. The characterization findings revealed that the modified MIT is predominantly composed of gehlenite and akermanite, with greatly improved specific surface area, pore structure and cation exchange capacity. The main purpose of the present study is to unravel a plausible mechanism on how MIT can stabilize Cd(II) in the soil and to investigate the effect of MIT on the fertility of the contaminated soil. Experiments on soil remediation revealed that MIT has a more profound stabilizing impact on Cd(II) compared to natural illite, resulting in a 22.84% reduction in acid-soluble Cd of the soil when MIT was dosed at 0.5%. The potential mechanism of Cd(II) immobilization by MIT involves the ionic exchange of Cd2+ with the exchangeable Ca2+ and Mg2+. In addition, the hydrolysis products of gehlenite and akermanite are prone to form silicate precipitates with free Cd, leading to soil pH increment. The pot experiments showed that MIT significantly reduces the cadmium content of soil and improves the growth of water spinach organs. Meanwhile, enhancement of the indicators in rhizosphere soil further proved that MIT effectively increases the nutrient content, improves the soil structure and promotes microorganism growth.

Cation and buffer specific effects on the DNA-lipid interaction

Knowledge of DNA - lipid layer interactions is key for the development of biosensors, synthetic nanopores, scaffolds, and gene-delivery systems. These interactions are strongly affected by the ionic composition of the solvent. We have combined quartz crystal microbalance (QCM) and ellipsometry measurements to reveal how pH, buffers and alkali metal chloride salts affect the interaction of DNA with lipid bilayers (DOTAP/DOPC 30:70 in moles). We found that the thickness of the DNA layer adsorbed onto the lipid bilayer decreased in the order citrate > phosphate > Tris > HEPES. The effect of cations on the thickness of the DNA layer decreased in the order (K+ > Na+ > Cs+ ∼ Li+). Rationalization of the experimental results requires that adsorption, due to cation specific charge screening, is driven by the simultaneous action of two mechanisms namely, the law of matching water affinities for kosmotropes (Li+) and ion dispersion forces for chaotropes (Cs+). The outcome of these two opposing mechanisms is a “bell-shaped” specific cations sequence. Moreover, a superimposed buffer specificity, which goes beyond the simple effect of pH regulation, further modulated cation specificity. In summary, DNA-lipid bilayer interactions are maximized if citrate buffer (50 mM, pH 7.4) and KCl (100 mM) are used.

Ion-Selective Assembly of Supertetrahedral Selenido Germanate Clusters for Alkali Metal Ion Capture and Separation

Supertetrahedral chalcogenido (semi)metalate cluster-based frameworks possess high selectivity for alkali metal cations, matching the specific charge density of their inner surfaces, which enables their use as ion-exchange materials. Aggregates of the supertetrahedral chalcogenido metalate cluster offer even new perspectives for metal ion capture and separation. Herein, we report on ionothermal preparation of two corresponding model compounds, (C2C1Im)7[Cs@GeII4(GeIV4Se10)4] (1) and (C2C1Im)10[Na5(CN)6@Cu6(Ge4Se10)4(Cu)] (2). Their formation is reliant on one specific cation type each, Cs+ for 1 and Na+ for 2, thus providing promising separation potential during crystallization. Compound 1 is based on the largest discrete binary selenido germanate cluster reported to date and the first mixed-valent chalcogenido germanate(II/IV) supertetrahedron. Moreover, it adds to the few examples of chalcogenides capable of capturing Cs+ ions. Its high selectivity for Cs+ compared to that of Li+, Na+, K+, and Rb+ was confirmed by single-crystal X-ray diffraction, energy-dispersive X-ray spectroscopy, and electrospray ionization mass spectrometry. Quantum chemical studies indicate that smaller ions, K+ and Rb+, could also be embedded in an isolated cluster assembly, but as the cluster aggregate slightly distorts for crystallization, the selectivity for Cs+ becomes exclusive in the salt. The anionic substructure of compound 2 is based on a two-dimensional network of supramolecular assemblies and exhibits an exclusive preference for Na+. This work thus provides the first comprehensive insight into the selective incorporation of specific alkali metal ions into supramolecular aggregates of supertetrahedral chalcogenide clusters, as a promising basis for new ion trapping techniques─especially for heavy alkali metal ions that pose environmental challenges.

Shallow traps-induced ultra-long lifetime of metal halide perovskites probed with light-biased time-resolved microwave conductivity

Metal halide perovskites have emerged as promising candidates for next-generation optoelectronics. However, the present understanding of their recombination processes and trap states within the devices are still limited, which is also inevitable in the state-of-the-art perovskite solar cells with multiple passivation strategies and various additives involved. Recent works have also demonstrated that metal cations incorporated perovskites could potentially reduce the non-radiative losses and improve the device performance to some extent. However, the underlying “doping” mechanism is not clear. In this work, we systematically investigated the trap-induced ultra-long carrier lifetime of the metal cation incorporated perovskites and found that some specific cations could extend the carrier lifetime up to ∼100 μs, which could be correlated with the formation of shallow trap states. In addition, such shallow trap-mediated charge dynamics could be effectively probed with light-biased time-resolved microwave conductivity technique, which provides additional information to conventional time-resolved photoluminescence.

Enhancing Titania-Tantala Amorphous Materials as High-Index Layers in Bragg Reflectors of Gravitational-Wave Detectors

Amorphous mixed titania-tantala coatings are key components of Bragg reflectors in gravitational-wave detectors (GWDs). Attaining the lowest possible values of optical absorption and mechanical losses in coatings is of paramount importance for GWDs, and this requires a complex optimization of the coating deposition and postdeposition annealing. We present here a systematic investigation of the optical properties and internal friction of amorphous mixed titania-tantala coatings grown by ion beam sputtering. We consider coatings with six different cation mixing ratios─defined as Ti/(Ti + Ta)─and we study them both in the as-deposited and annealed states. All coatings have been subject to the same annealing of 500 °C for 10 h in air, which is the postdeposition treatment adopted so far for Bragg reflectors in GWD applications. By exploiting spectroscopic ellipsometry data and modeling, along with ancillary techniques, we retrieved the dielectric function of the coatings in a wide spectral range. When varying the mixing ratio and performing the annealing, we find monotonic─in some cases, almost linear─trends for most of the aforementioned properties. Remakably, the postannealing Urbach energy displays a definite minimum for a mixing ratio around 20%, very close to the composition of the coatings showing the lowest optical absorption for GWD applications. We suggest that the observed minimum in the Urbach energy depends not only on the mixing ratio but also on the annealing parameters. On the other hand, the minimum coating loss angle was found to be weakly dependent on the considered measurement frequency and to lie within a rather broad range of Ti content (cation ratios of 21 and 44%), suggesting that the search for an absolute minimum following postdeposition annealing should be rather sought in the study of the best annealing parameters for each specific cation ratio considered. This work constitutes a reference for the optical properties of the amorphous mixed titania-tantala coatings and highlights the relevance of the Urbach energy as an additional parameter to guide the optimization process of materials for high-performing Bragg reflectors.

A novel 2,6-bis(benzoxazolyl)phenol macrocyclic chemosensor with enhanced fluorophore properties by photoinduced intramolecular proton transfer.

Macrocyclic ligand L, in which a 2,6-bis(2-benzoxazolyl)phenol (bis-HBO) group is incorporated in triethylenetetramine, was designed and synthesized with the aim of creating a chemosensor with high selectivity and specificity for metal cations in an aqueous environment. The availability of several proton acceptors and donors, and amine and phenol hydroxy groups, respectively, affects the keto-enol equilibrium in both the ground and excited states, and the ligand properties show dependence on the pH of the solution. L is fluorescent in the visible range, through an excited-state intramolecular proton transfer (ESIPT) mechanism. The results of an exhaustive characterization of L by spectroscopic techniques and DFT calculations, as well as of its Zn(II), Cd(II) and Pb(II) complexes, show promising properties of L as a ratiometric metal cation chemosensor, since metal coordination prevents the ESIPT and gives rise to a peculiar displacement of the fluorescence emission from green to blue with Zn(II) and Cd(II), while with Pb(II) the fluorescence is quenched.

Unlimiting ionic conduction: manipulating hydration dynamics through vibrational strong coupling of water.

The energy states of molecules and the vacuum electromagnetic field can be hybridized to form a strong coupling state. In particular, it has been demonstrated that vibrational strong coupling can be used to modify the chemical dynamics of molecules. Here, we propose that ion dynamics can be altered through modifications of the dynamic hydration structure in a cavity vacuum field. We investigated the effect of different electrolyte species on ionic conductivity. Infrared spectroscopy of aqueous electrolyte solutions within the cavity confirmed the formation of vibrational ultrastrong coupling of water molecules, even in the presence of electrolytes. Interestingly, we observed significant enhancements in ionic conductivity, for specific alkali cations, particularly those classified as structure-breaking cations. These enhancements cannot be explained within the current theoretical framework for liquid electrolytes. Our analysis suggests that the vibrational strong coupling modifies the local dielectric friction experienced by hydrated ions. In addition, we propose the enthalpic and entropic modification of ionic conductivity through the systematic investigation of the hydration properties of different electrolytes. This study unveils the potential role of polaritons for exploring uncharted spaces in the design of materials with enhanced ionic conduction. Harnessing the unique properties of strong coupling and its influence on hydration dynamics could lead to the development of novel electrolytes and advancements in the field of ionic conduction.

Stable and Uniform Extraframework Cations in Faujasite Zeolites.

Extraframework transition metal ions (TMIs) in zeolites can serve as active sites for adsorption and catalysis. However, due to the complexity and mobility of extraframework cation sites, their applications are significantly limited and the structure-performance relationship is poorly understood. In this Perspective, stable and uniform TMIs in zeolites are exemplified and their characteristics are discussed. A series of TMIs can be introduced to specific cation sites of faujasite via a ligand-protected in situ synthesis route to construct uniform TMIs in the zeolite matrix, namely, TMI@FAU (TMI= Co, Ni, Cu, Rh, and Pt). Coordinatively unsaturated TMIs within faujasite are active for small-molecule adsorption and activation, and therefore, TMI@FAU zeolites show unique properties in adsorption and catalysis. TMI@FAU zeolites appear to be ideal model systems, and the well-defined structure of TMI@FAU greatly facilitates the mechanism studies by spectroscopic investigations and theoretical simulations.

Characterization of bentonite, vermiculite and soil as potential materials to compose the natural barriers in a near-surface repository

The use of nuclear technology is growing in Brazil, where it is possible to carry out the entire nuclear fuel cycle. This technology generates radioactive waste that must be treated before being released into the environment or stored in suitable facilities. Then, the first national repository - CENTENA - will be implemented, where all low and intermediate level radioactive waste generated in Brazilian territory will be safely stored. One of the barriers that will compose the repository will be composed of natural materials such as soils and clays, the latter for having a high adsorption and cation exchange capacities and swelling potential. The purpose of the article is to show the research carried out in Centro de Desenvolvimento da Tecnologia Nuclear (CDTN) with natural materials aiming their use in natural barriers. Four materials were characterized: CDTN soil, this soil with bentonite, expanded vermiculite and bentonite, using the clay characterization protocol. Primary mineralogical, physical and chemical analyzes were performed, such as X-ray diffraction, scanning electron microscopy, particle size distribution, specific surface area and cation exchange capacity. The results showed that these clays are potentially candidates for composing CENTENA's natural barriers.

The Unexpected Role of Cations in the Self-Assembly of Positively Charged Amphiphiles at Liquid/Liquid Interfaces.

Conventional wisdom suggests that cations play a minimal role in the assembly of cationic amphiphiles. Here, we show that at liquid/liquid (L/L) interfaces, specific cation effects can modulate the assemblies of hydrophobic tails in an oil phase despite being attached to cationic headgroups in the aqueous phase. We used oligo-dimethylsiloxane (ODMS) methyl imidazolium amphiphiles to identify these specific interactions at hexadecane/aqueous interfaces. Small cations, such as Li+, bind to the O atoms in the ODMS tail and pin it to the interface, thereby imposing a kinked conformation─as evidenced by vibrational sum frequency generation spectroscopy and molecular dynamics simulations. While larger Cs+ ions more readily partition to the interface, they do not form analogous complexes. Our data not only point to ways for controlling amphiphile structure at L/L interfaces but also suggest a means for the separation of Li+, or related applications, in soft-matter electronics.

Reaction Mechanism of CO2 with Choline-Amino Acid Ionic Liquids: A Computational Study.

Carbon capture and sequestration are the major applied techniques for mitigating CO2 emission. The marked affinity of carbon dioxide to react with amino groups is well known, and the amine scrubbing process is the most widespread technology. Among various compounds and solutions containing amine groups, in biodegradability and biocompatibility perspectives, amino acid ionic liquids (AAILs) are a very promising class of materials having good CO2 absorption capacity. The reaction of amines with CO2 follows a multi-step mechanism where the initial pathway is the formation of the C-N bond between the NH2 group and CO2. The added product has a zwitterionic character and can rearrange to give a carbamic derivative. These steps of the mechanism have been investigated in the present study by quantum mechanical methods by considering three ILs where amino acid anions are coupled with choline cations. Glycinate, L-phenylalanilate and L-prolinate anions have been compared with the aim of examining if different local structural properties of the amine group can affect some fundamental steps of the CO2 absorption mechanism. All reaction pathways have been studied by DFT methods considering, first, isolated anions in a vacuum as well as in a liquid continuum environment. Subsequently, the role of specific interactions of the anion with a choline cation has been investigated, analyzing the mechanism of the amine-CO2 reaction, including different coupling anion-cation structures. The overall reaction is exothermic for the three anions in all models adopted; however, the presence of the solvent, described by a continuum medium as well as by models, including specific cation- -anion interactions, modifies the values of the reaction energies of each step. In particular, both reaction steps, the addition of CO2 to form the zwitterionic complex and its subsequent rearrangement, are affected by the presence of the solvent. The reaction enthalpies for the three systems are indeed found comparable in the models, including solvent effects.