Structure Of Cs Research Articles

Convolutional Two-Stream Generative Adversarial Network-Based Hyperspectral Feature Extraction

Hyperspectral image processing is faced with difficulties considering its redundant features and complex information. Studies on hyperspectral feature extraction in the deep learning domain have become increasingly popular. The mainstream techniques fully consider the spatial information in local neighborhoods when extracting spectral features by constructing deep neural networks. Deep generative models simulate the intrinsic structure of samples by adequately training, showing their potential values for signal processing. In this article, a convolutional two-stream network (cs <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> GAN-FE) based on the improved Wasserstein generative adversarial network (WGAN) is proposed for unsupervised hyperspectral spatial–spectral feature extraction. The improved WGAN is composed of one generator and one discriminator; the former perceives real data distributions, and the latter determines the attribution of generated data. The designed two-stream strategy is not a simple extension of a one-stream strategy and considers both the static spectral–spatial information and the dynamic spectral reflectance variation in multiple bands. Intrinsic spatial–spectral features are extracted by the trained discriminator considering sample distributions and feature relationships. The loss function is also improved for the unique structure of cs <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> GAN-FE. Various state-of-the-art techniques are chosen for comparison. Experimental results show the feasibility and potential of this network. Besides, experiments with the random split and the disjointed split both show that the proposed method can outperform other comparison techniques.

Effect of Initial CoII Salts on the Composition and Structure of Cs–CoII Dimethylmalonates

Effect of Initial CoII Salts on the Composition and Structure of Cs–CoII Dimethylmalonates

Novel chitosan-hydroxyapatite macroporous composites for biomedical applications

Composites made of natural and/or naturally-derived polymers intended for biomedical applications are expected to exhibit structures analogous to the natural ones, as well as valuable properties as biologic compatibility and activity, and the ability to allow new, biologically recognizable interactions/signals with the host tissue. Under these circumstances, novel chitosan-hydroxyapatite (Cs-HAp) macroporous composites were prepared through a simple procedure and subsequently characterized by the means of Fourier transformed infrared spectrometry (FTIR), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and mechanical tests. Experimental data confirmed the materials have high porosity, originating in the structure of Cs, and good mechanical properties, due to the presence of HAp, which enables them to be further employed in various biomedical applications, but only when low to moderate loads were used.

Cs ADSORPTION ON GaAS(001) As-RICH β2 (2×4) AND Ga-RICH (4×2) RECONSTRUCTION PHASES: A FIRST-PRINCIPLES RESEARCH

Using plane-wave ultrasoft pseudopotential method based on first-principles density functional theory (DFT), the adsorption of Cs atom on As-rich GaAs(001)[Formula: see text]([Formula: see text]) reconstruction phase and Ga-rich GaAs(001)([Formula: see text]) reconstruction phase are investigated. The adsorption energy, work function, dipole moment, ionicity, band structure and density of state (DOS) of Cs adsorbed GaAs [Formula: see text]([Formula: see text]) and ([Formula: see text]) models are calculated. The stability and electronic structure of Cs adsorbed GaAs [Formula: see text]([Formula: see text]) and ([Formula: see text]) models are compared. Result shows that [Formula: see text]([Formula: see text]) phase is stable than the ([Formula: see text]) phase and after that Cs adsorption [Formula: see text]([Formula: see text]) phase is more beneficial for photoemission.

Die unerwartete Kristallstruktur des Cäsium-Dodekahydro-Monocarba-closo-Dodekaborats Cs[CB11H12

Abstract The cesium dodecahydro-monocarba-closo-dodecaborate Cs[CB11H12] crystallizes with an unexpected trigonal crystal structure having the lattice parameters a = 2094.73(3) and c = 1324.56(2) pm (c/a = 0.632) for Z = 18. The non-centrosymmetric space group R3 allows an ordering of the unsymmetric [CB11H12]– anions in a way that the least electronegative vertices of the pseudo-icosahedral cages avoid close proximity to the Cs+ cations. Hence there are channels at [0 0 z], [1/3 2/3 z] and [2/3 1/3 z], into which the C–H bonds of the [CB11H12]– units are pointing. There are two crystallographically independent Cs+ cations and [CB11H12]– anions present with unsurprising interatomic distances (d(C–B) = 166–181 pm, d(B–B) = 170–183 pm, d(B–H) = d(C–H) ≈ 110 pm) for the latter. Both Cs+ cations have contact to 18 hydrogen atoms (d(Cs–H) = 296–427 pm) stemming from six unevenly face-grafting [CB11H12]– anions, where only B–H bonds are involved. This fact is nicely reflected by IR and Raman spectroscopy. According to a 6/6 motif of the ions with highly distorted mutual octahedral coordination spheres of their centres of gravity, the crystal structure of Cs[CB11H12] follows roughly a rock salt-like arrangement. This becomes even more evident, when order-disorder transitions starting at T = 60 °C lead to more highly symmetrical structures with orientationally disordered [CB11H12]– anions.

Cs(Be2Li)Al2Si6O18, a cesium-stuffed host-guest structure, and its structure-property variations with temperature and pressure

The solid-state structure of (Cs,Na)[(Be2Li)Al2Si6O18], a beryl-type material, was studied in-situ on single crystal and powder samples at hydrostatic high pressure conditions (P ​≤ ​9.8 ​GPa) as well as under temperature variation (83 ​≤ ​T ​≤ ​1173 ​K) by means of Raman spectroscopy, X-ray and synchrotron diffraction. The investigations show an inconspicuous, easily overlooked transformation from R3¯c to non-centrosymmetric R3c space-group symmetry on increasing pressure (Pc ​~ ​4 ​GPa) and decreasing temperature (Tc ​= ​312 ​± ​5 ​K), as revealed by Raman band splitting as well as discontinuities in the evolution of Raman spectra, thermal expansivity coefficients and anomalous compression behavior. Distortions to acentric symmetry originate from the Cs and Na guest atoms inside the channels parallel the c-axis. The occurrence of diffuse scattering planes in all measured data sets indicates substitutional defects inside the channels following an approximate ~4.6 ​Å periodicity, without any remarkable ordering between adjacent channels. The determined thermal expansivity follows an inverse behavior compared to other beryl-type structures for the R3c phase. The bulk moduli for the two polymorphs compare, together with the observed compressional anisotropy, to other complex beryl-type framework structures. However, the symmetry reduction at high pressure leads to independent displacements of the framework oxygen positions, and as a consequence, to the increase of the coordination number from [6 ​+ ​6] to [6 ​+ ​9] for one of the Cs sites.

Density functional theoretical tailoring of electronic effect through various substituents on calix[4]arene‐crown‐6 for efficient Cs+ ion encapsulation and extraction

AbstractThe structure, energetic, and quantum chemical descriptors of Cs+ complexes of calix[4]arene‐crown‐6 (C4C6) and substituted C4C6, that is, 1,3 alternate‐diethoxy C4C6, are reported here based on the analysis of results obtained using density functional theory (DFT). Substitution of benzo group in both C4C6 and 1,3 alternate‐diethoxy C4C6 resulted in a reduction of binding energy (BE). Further substitution of the benzo group with methyl, methoxy, and amino groups leads to an increase in BE, and nitro substitution leads to decrease in BE for C4C6, whereas in the case of 1,3 alternate‐diethoxy calix[4]arenebenzocrown‐6, methoxy substitution leads to the highest BE compared to other complexes. The calculated Gibbs free energy, ΔGgas also followed the same order as BE in the case of 1,3 alternate‐diethoxy C4C6 and their substituted ligands. Furthermore, the ΔG of complexation was computed using a thermodynamic cycle with conductor‐like screening model in different solvents: toluene, chloroform, octanol, and nitrobenzene. The values of ΔGext are found to be increased with an increase in the dielectric constant of the solvent and were found to be highest in the nitrobenzene. The atoms in molecule analysis reveals partial ionic character in the CsO bond. Among all the studied complexes, 1,3 alternate‐diethoxy calix[4]arene 3′‐methoxy benzo crown‐6 displays highest ΔGext in nitrobenzene. The calculated value of ∆∆Gext (∆∆G = ∆GCs+ − ∆GNa+) is found to be −41.82 kcal/mol with 1,3 alternate‐diethoxy calix[4]arene 3′‐methoxy benzocrown‐6, which is higher than that obtained with calix [4] bis‐crown‐6 (−5.24 kcal/mol). The newly designed ligand might be suitable for the selective extraction of Cs+ over Na+ in the reprocessing of nuclear waste and thus invites experimentalists to test this DFT finding in the laboratory.

Beware, commercial chondroitinases vary in activity and substrate specificity.

Chondroitin sulfate (CS)and dermatan sulfate (DS) are negatively charged polysaccharides found abundantly in animal tissue and have been extensively described to play key roles in health and disease. The most common method to analyze their structure is by digestion into disaccharides with bacterial chondroitinases, followed by chromatography and/or mass spectrometry. While studying the structure of oncofetal CS, we noted a large variation in the activity and specificity of commercially available chondroitinases. Here studied the kinetics of the enzymes and used high-performance liquid chromatography-mass spectrometry to determine the di- and oligosaccharide products resulting from the digestion of commercially available bovine CS A, shark CS C and porcine DS, focusing on chondroitinases ABC, AC and B from different vendors. Application of a standardized assay setup demonstrated large variations in the enzyme-specific activity compared to the values provided by vendors, large variation in enzyme specific activity of similar enzymes from different vendors and differences in the extent of cleavage of the substrates and the generated products. The high variability of different chondroitinases highlights the importance of testing enzyme activity and monitoring product formation in assessing the content and composition of chondroitin and DSs in cells and tissues.

DFT: B3LYP/ LANL2DZ Study for the Removal of Fe, Ni, Cu, As, Cd and Pb with Chitosan

Human activities are responsible for the existence of heavy metals in the environment. The accumulation of these metals in the environment causes several risks, such as toxicological, mutagenic, and carcinogenic effects. Chitosan (Cs) based materials have been explored its competitive efficacy in heavy metals removal from contaminated water. In this study, an attempt is presented to develop a natural, reliable, and cost-effective biopolymer structure of Cs with a high ability to entrap some heavy metals, which can be found in polluted water. The correlation between Cs-heavy metals and its stability was studied by density functional theory (DFT) using B3LYP together with the basis set LANL2DZ. The observed results revealed that the bandgap energy values for Cs, Cs- Fe, Cs-Ni, Cs-Cu, Cs-As, Cs-Cd and Cs-Pb were 2.571, 0.6147, 0.7176, 0.3396, 0.6648, 1.5007 and 0.4128 eV, respectively. The later showed that Cs structure has high selectivity and binding affinity to Cu and Pb hydrated metals, respectively rather than Fe, Ni, As and Cd. The examined correlation between Cu and Pb with Cs revealed that Cs could be applied for sensing and removing of Cu and Pb from wastewater.

Structural features, anti-coagulant and anti-adhesive potentials of blue crab (Portunus segnis) chitosan derivatives: Study of the effects of acetylation degree and molecular weight

The present study was undertaken to establish a distinct relationship between blue crab chitosan (Cs) acetylation degree (AD) and molecular weight (Mw) and its structural features, thermal properties and bioactivity. Therefore, chitosans with different AD were prepared and Cellulase was used to produce Cs derivatives with decreasing Mw. Results clearly display a decrease of the ordered structure of Cs, with the increase of AD and the decrease of Mw. Thermal stability/degradation screening disclose a greater thermal resistance for Cs with lower AD and higher Mw. The anti-adhesive potential of Cs was, additionally, studied, as function of AD and Mw. The effectiveness of Cs in preventing biofilm adhesion was strongly influenced by its AD and Mw, with the lowest inhibition values for higher AD and lower Mw. Interestingly, the effectiveness of Cs in disrupting pre-formed biofilms increased with decreasing Mw. Moreover, Cs derivatives were found to be advantageously efficient in prolonging human blood clotting times, based on data of activated partial thromboplastin time, Quick time and thrombin time assays, typically for the intrinsic coagulation pathway. Accordingly, depending on the predicted application of Cs, either in food, biomedical and pharmaceutical industries, AD and Mw are critical traits to be inevitably reflected on.

Bio-inspired hierarchical assembly of Au/ZnO decorated carbonized spinach leaves with enhanced photocatalysis performance

Inspired by the characteristics that plant leaves are beneficial for solar light absorption, we have prepared a bio-inspired hierarchical assembly of carbonized spinach leaves@Au/ZnO (CS@Au/ZnO) for solar energy utilization. CS@Au/ZnO shows a low light reflectance of 5% and a high specific surface area of 311.41 m2/g. CS@Au/ZnO demonstrates higher photocatalytic degradation efficiency: more than 97% of Rhodamine B (RhB) and 61% of ciprofloxacin (CIP) could be degraded in 180 min under the visible light irradiation. In addition, we also tested the photocatalytic H2 production performance of CS@Au/ZnO and the H2 evolution rate is 2.384 mmol g−1 h−1 under simulated solar light. CS@Au/ZnO shows a high cycling stability in recyclable photocatalytic degradation and photocatalytic water splitting. Moreover, CS@Au/ZnO shows a swift and steady photocurrent of about 63.6 μA/cm2, illustrating a high sensitivity to solar light. The enhanced photocatalysis performance of CS@Au/ZnO could be ascribed to the naturally optimized macroporous structure of CS with high conductivity, which could enhance the light harvesting and carrier transport, simultaneously. Moreover, modification of AuNPs can broaden the light response range of ZnONRs and reduce the probability of electron-hole recombination. Due to the wide availability of plant leaves, CS@Au/ZnO assembly has broad application prospects in photocatalytic degradation of organic pollutions, photovoltaic devices, and photocatalytic H2 evolution.

Evolutions of structural and optical properties of lead-free double perovskite Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; under high pressure

In recent years, organic-inorganic hybrid perovskite materials have been widely used in solar cells, photodetectors, and light-emitting diodes due to their advantages such as high light absorption coefficient, good carrier mobility, and long carrier diffusion length. However, the high toxicity of lead and poor stability still restrict the application and promotion of such materials. The lead-free double perovskite material derived from the concept of “heterovalent substitution”, while maintaining the high symmetrical structure of perovskite, avoids using the toxic lead elements, which has the advantages of environmental friendly, stable structure, and suitable band gap. At present, the limited research on lead-free double perovskite materials still leaves a big room to researchers, and such a limited research seriously restricts the development and promotion of such materials. Therefore, the relationship between the structure and performance of lead-free double perovskite materials needs further exploring in order to provide theoretical basis for the practical application of such materials. Here in this work, the lead-free double perovskite material Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; is prepared by the solution method. The crystal structure and optical properties of the lead-free double perovskite Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; under high pressure are investigated by using diamond anvil cell combined with &lt;i&gt;in-situ&lt;/i&gt; high-pressure angle-dispersive X-ray diffraction and ultraviolet-visible absorption technology. The results show that the crystal structure of Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; is not changed within the experimental pressure range of 0－50.0 GPa, and the structural symmetry of &lt;i&gt;Fm-&lt;/i&gt;3&lt;i&gt;m&lt;/i&gt; is still maintained, indicating the sample has good stability. The lattice constant and volume of Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; gradually decrease within the pressure range of 0－50.0 GPa. The volume and pressure of Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; are fitted using the third-order Birch-Mumaghan equation of state, the bulk elastic modulus is obtained to be &lt;i&gt;B&lt;/i&gt;&lt;sub&gt;0&lt;/sub&gt; = (18.77 ± 2.88) GPa. The smaller bulk elastic modulus indicates that the lead-free double perovskite material Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; has higher compressibility. The optical band gap of Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; is 2.68(3) eV at 1 atm and its optical band gap gradually decreases with the increase of pressure, which is related to the shrinkage of octahedral [TeCl&lt;sub&gt;6&lt;/sub&gt;]&lt;sup&gt;2–&lt;/sup&gt; under high pressure. The calculation results show that the Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; possesses an indirect band gap, the valence band maximum is mainly composed of Cl 3p orbits, and the conduction band minimum is mainly composed of Te 5p and Cl 3p orbits. After the pressure is completely relieved, Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt; returns to the initial state. The above conclusions further deepen the understanding of the crystal structure and optical properties of lead-free double perovskite Cs&lt;sub&gt;2&lt;/sub&gt;TeCl&lt;sub&gt;6&lt;/sub&gt;, and provide a theoretical basis for designing and optimizing the lead-free double perovskite materials.

Systematic investigation of the magneto-electronic structure and optical properties of new halide double perovskites Cs2NaMCl6 (M = Mn, Co and Ni) by spin polarized calculations.

A cohesive study using density functional theory simulations is performed to reveal and understand the structural stability, optoelectronic and magnetic properties of Cs2NaMCl6 (M = Mn, Co and Ni) halide double perovskites. The exchange-correlation potential, which is the only unknown parameter in the state-of-the-art formulism is determined through the well-known generalized gradient approximation and integration of the mBJ potential to it. The structural optimization, mechanical stability criteria and tolerance factor confirmed the stability of the double perovskites in a cubic structure with Fm3̄m symmetry. The elastic constants endorsed the mechanical stability and justify the brittle character of these double perovskites. The spin polarized electronic band profile and behaviour of the dielectric constant and absorption coefficient in the spin up and down channels revealed the presence of half-metallic nature in these materials. Moreover, herein, we have discussed the origin of the half-metallic gap and magnetism. The unpaired electrons in the crystal field splitted d-orbitals of the M-sited constituents are responsible for the half-metallic and magnetic character. The total magnetic moment was determined to be 4μB, 4μB and 1μB for the Mn-, Co- and Ni-based double perovskites, respectively, with main contributions solely coming from the transition metal atoms. The perfect spin polarization at the Fermi level suggests the application of double perovskites in spintronic technology.

Structure and dynamics of Cs+ in kaolinite: Insights from molecular dynamics simulations

In the present study, the adsorption and diffusion behaviors of Cs+ in kaolinite are investigated by classical molecular dynamics (MD) simulations with the effects of concentration, temperature, and competing cations. The obtained results turn out that Cs+ adsorbs preferentially on siloxane surface in the form of inner- and outer-sphere surface complexes. The adsorption percent of Cs+ diminishes with increasing concentration. Elevating temperature facilitates the adsorption of Cs+, while introduction of foreign cations weakens the interaction between siloxane surface and Cs+. It is indicated that the diffusion coefficient of Cs+ increases remarkably as the temperature rises. Nevertheless, varying concentration and competing cations have only slight effects on diffusion coefficient of Cs+. The results presented here can provide valuable insights into the interaction mechanism between Cs+ and kaolinite basal surfaces.

An injectable and self‐healing novel chitosan hydrogel with low adamantane substitution degree

AbstractChitosan (CS) is a semi‐natural polymer with supreme biological function, while the strong interchain hydrogen bonds cause poor water solubility and limit its broader use. To break the semi‐rigid structure of CS, a kind of CS modified by adamantane (AD‐CS) was successfully synthesized by amidation reaction with 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride as catalyst. The chemical structure of AD‐CS was characterized by Fourier transform infrared spectroscopy and 1H NMR. The AD substitution degree of CS is around 2%, calculated by 1H NMR. A soft and transparent hydrogel composed of hydrogen bonds was obtained directly by simply adding a certain amount of water under mild conditions. Rheological measurements were carried out to research the mechanism of hydrogel formation by measuring the influence of different additives and conditions on the AD‐CS hydrogel. Reinforced hydrogels were prepared by freezing and thawing. The mechanical strength and self‐healing property of reinforced and pristine hydrogels were assessed with an oscillatory rheometer. The modulus of the reinforced hydrogel was obviously enhanced without much loss of self‐healing property. Other properties such as adhesion, injectability and temperature response were also studied. These injectable and self‐healing hydrogels show potential value in medical care. Additionally, this is a new method to design CS hydrogels with their original interchain hydrogen bonds. © 2019 Society of Chemical Industry

Experimental and theoretical investigations of Cs+ adsorption on crown ethers modified magnetic adsorbent.

Carboxyl Fe3O4 nanoparticles (Fe3O4@R-COOH) modified with 18-Crown-6 ether functional groups have been prepared via an amidation reaction and used as bifunctional adsorbent for Cs+. The adsorbent has a superparamagnetic property, allowing an easy recycling, and a high capacity of Cs+ adsorption on the crown ether. The adsorption isotherms and kinetic behaviors agree well with the Langmuir and the pseudo-second-order models. The material exhibits a high selectivity for Cs+ in the solution with co-existing cations (NH4+, Rb+, K+, Na+ and Li+). A theoretical calculation according to density functional theory (DFT) is used to estimate the structure of Cs+ adsorption on crown ether, demonstrating an exothermic process and showing a good agreement with the experimental observations. The adsorption behavior is affected not only by the size of macrocyclic crown ethers, but also by the chelating symmetry and the binding energy. The newly developed adsorbent has a potential application for removing cesium out of wastewater and salt lakes.

Impurity induced cross luminescence in KMgCl3: an ab initio study

Density functional theory calculations have been carried out to calculate the electronic structure and optical properties of host and Cs doped KMgCl3. All the calculations were performed by using the Tran and Blaha modified Becke–Johnson potential (TB-mBJ) in order to accurately predict the band gap and the optical spectra. The investigated compound is found to be an insulator with direct band gap of 4.7, 6.9 eV using generalized gradient approximation (GGA), and TB-mBJ functionals respectively. The calculated refractive index shows the optical isotropy of this compound in the low energy region, though the structure is anisotropic. From our theoretical calculations we predict KMgCl3 doped with Cs to be a better cross luminescence material compared to host compound, where additional Cs states are present below the valence band of the compound. Detailed discussion is presented in the manuscript.

Many-Body Effects Determine the Local Hydration Structure of Cs+ in Solution.

A systematic analysis of the hydration structure of Cs+ ions in solution is derived from simulations carried out using a series of molecular models built upon a hierarchy of approximate representations of many-body effects in ion-water interactions. It is found that a pairwise-additive model, commonly used in biomolecular simulations, provides poor agreement with experimental X-ray spectra, indicating an incorrect description of the underlying hydration structure. Although the agreement with experiment improves in simulations with a polarizable model, the predicted hydration structure is found to lack the correct sequence of water shells. Progressive inclusion of explicit many-body effects in the representation of Cs+-water interactions as well as accounting for nuclear quantum effects is shown to be necessary for quantitatively reproducing the experimental X-ray spectra. Besides emphasizing the importance of many-body effects, these results suggest that molecular models rigorously derived from many-body expansions hold promise for realistic simulations of aqueous solutions.

The Stable Phase Equilibria of the Ternary Systems Na2SO4 + Rb2SO4 (Cs2SO4) + H2O at 298.2 K

To understand the crystallographic forms of salts in sulfate systems containing sodium and rubidium (cesium), the stable phase equilibria of ternary systems Na2SO4 + Rb2SO4 + H2O and Na2SO4 + Cs2SO4 + H2O at 298.2 K were studied with the isothermal dissolution method. The composition and crystallographic forms of the equilibrated solid phase was verified by Schreinemaker’s wet residue method combined with X-ray diffraction. Experimental results show that there is no double salt or solid solution formed. The stable phase diagram of Na2SO4 + Rb2SO4 + H2O at 298.2 K is characterized by one invariant point (H), two univariant curves, and two crystallographic forms (corresponding to Na2SO4·10H2O and Rb2SO4). The ternary system Na2SO4 + Cs2SO4 + H2O is of the hydrate type II, there are two invariant points (E1, E2), three univariant curves, and three crystallographic forms (corresponding to salts Na2SO4·10H2O, Na2SO4 and Cs2SO4). Affected by the unique structure of Cs+, both salt Na2SO4·10H2O and Na2SO4 have be...

Adsorption mechanisms of cesium at calcium-silicate-hydrate surfaces using molecular dynamics simulations

Understanding the mechanisms of interactions and immobilization of radionuclides in cement systems at the molecular level is key to developing safe and novel solutions for the long-term storage of nuclear wastes. The molecular level adsorption mechanisms of cesium (Cs+) ions onto tobermorite 9 Å, tobermorite 14 Å, and jennite – three crystalline structural analogues for calcium-silicate-hydrates, the main components in cement-based materials, were investigated using molecular dynamics (MD) simulations. Convergence monitoring of the simulations, using the root mean square displacement with average correlation analysis, indicated that MD trajectories of 10–15 ns were needed given the size of the selected computational cell to properly capture the dynamic process of adsorption. Cs+ ions adsorbed as inner-sphere complexes at the tobermorite surfaces, while they showed lower affinity for jennite. The charge and structure of the surface layer strongly influenced the adsorption mechanisms of Cs+ ions. Strong association with the hexagonal cavities of the silica sites were seen at the tetrahedral SiO4 surface of the tobermorite structures. Cs+ ion adsorption was attributed to co-ion adsorption at the octahedral CaO6 surface of tobermorite 9 Å, cation exchange at that of tobermorite 14 Å, and electrostatic interaction with the surface hydroxyl groups for jennite. Distribution coefficients of Cs+ ions onto cement pastes derived from molecular dynamics by taking the surface structure and dynamics of Cs+ ions directly into account showed a range of overlap with experimental results.