Structure Of Ions Research Articles

Surface Electric Dipole Moment Engineering of All‐Inorganic Transparent Solid Matrix for Information Encryption and X‐Ray Imaging

AbstractPerovskite nanocrystals (PNCs) show excellent optoelectronic performance and controlled synthesis of PNCs is arising as research hot spot recently. Transparent all‐inorganic glass matrix has been proved perfect protector of PNCs from aggregation. However, the precise precipitation of PNCs in glass with high photoluminescence quantum yield (PLQY) through a facile routing is still challenge. Here, site‐specifically crystallization of PNCs are rationally designed in all‐inorganic transparent solid matrix through surface electric dipole moment engineering, achieving exceptional PLQY (89.9%). Modifying the orientation of the surface electric dipole moment reduces the water‐induced nucleation barrier and promotes the crystallization of PNCs at the selected sites. In addition, the inherent ionic structure and low formation energy of CsPbBr3 PNCs allow the luminescent structure to be erased by annealing and then recovered by water‐inducing. Combining the intense luminescence, high stability and completely reversable crystallization, the applications of PNCs‐glass in information encryption and reusable X‐ray dosimeter and imaging are demonstrated. The PNCs‐glass scintillation screen achieves the X‐ray imaging resolution of 17.5 lp mm−1, which is the highest among all the PNCs based scintillation screen.

Correlating Ionic Conductivity to Structure and Dynamics of Li-Ion Battery Electrolyte Systems: Raman Spectroscopy, Dielectric Relaxation Measurements, and Streak Camera Solvation Data Analysis.

A correlation between ionic conductivity and electrolyte solution structure and dynamics was explored by performing electrolyte concentration- and temperature-dependent measurements of conductivity, viscosity, and dielectric relaxation (DR) in solutions of lithium bis(trifluoromethane)sulfonimide (LiTFSI) in triethylene glycol dimethyl ether (also known as triglyme, G3). In addition, an electrolyte concentration-dependent Raman spectroscopic study and ultrafast dynamic fluorescence Stokes shift measurements of solvation of a dissolved solute by employing a streak camera detection technique were carried out. Measured conductivities (σ) and the average DR times (⟨τDR⟩) were found to be partially decoupled from the solution viscosities (η) and obeyed the relation, σ or ⟨τDR⟩-1 ∝(η/T)-p, with p = 0.6-0.75 for σ and p = 0.2-0.45 for ⟨τDR⟩-1. Raman data indicated the formation of ion pairs and ionic aggregates in these solutions, while the measured glass transition temperature increased with LiTFSI concentration. Conductivities (σ) showed a nonlinear concentration dependence but increased linearly with the solution static dielectric constants (εs). The latter may be explained by considering the temperature effects on complex electrolyte species and the subsequent solution dielectric behavior. Interestingly, an inverse power-law dependence of σ on the measured DR or solvation time scales, σ ∝ (τx)-m, with m = 1.2-1.9, was observed. This dependence may be explained by considering that the same environmental friction regulates both the ion diffusion and the medium polarization relaxation. The control of a slow process (ion translation) by relatively faster medium dynamics (dipolar rotation), although quite fascinating for the present system, warrants further experimental scrutiny for other electrolyte systems relevant to battery applications.

Polarized Bimetallic Site Synergy in Ionic Structures of Cu(II), Fe(III), and Mn(III) Porphyrins: Electrochemistry and Catalytic Hydrogenation of Nitroaromatics.

Binuclear catalytic sites attained in a controlled way with complementary and cooperative metal ion centers are highly relevant in the development of new or enhanced catalytic processes. Herein, binuclear sites carrying Fe(III), Cu(II), or Mn(III) metal ions with a polarized structure have been prepared using the ionic self-assembly of oppositely charged metalloporphyrins. Binary porphyrin structures (BIPOS) have been prepared based on metalloporphyrin cations carrying pyridinium or methylpyridinium groups in conjugation with metalloporphyrin anions carrying sulfonatophenyl groups. BIPOS carrying [cation/anion] tecton pairs of [Cu/Fe], [Fe/Cu], [Cu/Cu], [Fe/Fe], [Mn/Fe], [Fe/Mn], and [Mn/Mn] have been compared. Electrochemical interaction and enhanced catalytic behavior are noticeable for BIPOS [Fe/Cu], [Fe/Fe], and [Mn/Fe] carrying a Fe center and [less electronegative/more electronegative] metal ion centers in the [cation/anion] porphyrin ionic pairs. For high-performance BIPOS, cyclic voltammograms showed a greater separation of the cathodic and anodic peaks, within ΔEp = 0.095-0.125 V, and the rate constants for the catalytic reduction of 4-nitrophenol were within k = 0.380-0.535 min-1/mg of catalyst, significantly superior to the related individual metalloporphyrins. Inverse heterobimetallic [Cu/Fe] and [Fe/Mn] and the homometallic BIPOS [Cu/Cu] and [Mn/Mn] were significantly less active or inefficient. A [Fe/Cu] material could be reused in at least 5 catalytic cycles, maintaining catalytic activity; the best catalysts were also active in the reduction of nitrobenzene to aniline in mild conditions (visible light, 30 °C, 0.5 mol % catalyst), and an [Fe/Fe] catalyst showed 100% aniline yield after 2 h.

Mechanically Reinforced Pseudosolid Polyelectrolyte Membranes via Layer‐by‐Layer Assembly for High‐Performing Lithium‐Metal Batteries

AbstractIonogels are emerging as high‐potential pseudosolid electrolytes for lithium‐metal batteries (LMBs), leveraging their intrinsic high ionic conductivity from entrapped ionic liquid (IL) electrolytes. However, their practical application is hindered by poor mechanical strength stemming from the confinement of ILs within a polymer matrix. To address this challenge, the formation of conformal polyion coatings with functional groups is reported to be relevant to LMBs’ application on ionogels, utilizing a layer‐by‐layer (LbL) assembly strategy. This approach significantly enhances the mechanical strength (Young's modulus and tensile strength) and electrochemical performance of ionogels, owing to the tailored interface modifications introduced by functional groups’ specific conformal polyion coatings. The core of this methodology leverages the inherent ionic structure of ionogels to enable facile interface modification through Coulombic interactions between polyanions and polycations. These conformally coated interface functionalized membranes show improved electrochemical performance when integrated with cathode materials such as LiFePO4 (LFP) and LiNi0.8Mn0.1Co0.1O2 (NMC811) in an LMB configuration, underscoring their potential for robust, high‐conductivity, pseudosolid membranes for LMB applications. These innovative pseudosolid membranes offer improved mechanical and electrochemical properties, leading to higher battery efficiency and safety, making them promising candidates for next‐generation LMB technology.

Investigation of short-term chemical changes in stable ruthenium added to soil by using X-ray absorption fine-structure analysis.

Radioactive ruthenium may be accidentally released from spent nuclear fuel reprocessing plants to the surrounding environment. However, research on the chemical behavior of radioactive Ru in the environment is limited, and the complex chemical properties of this element complicate the application of extraction methods for the analyses of its chemical forms. To obtain basic information regarding the outcome of radioactive Ru in the environment, we investigated the changes in the form of stable Ru added to soil through X-ray absorption fine-structure (XAFS) analysis. This study uses ruthenium tetroxide (RuO4), ruthenium dioxide (RuO2), ruthenium nitrosyl nitrate (Ru(NO)(NO3)3) and ruthenium chloride (RuCl3) as test sources. These are added to ultrapure water, soil solution or fresh soil samples, which are analyzed using XAFS immediately or 5 days after Ru addition. The Ru K-edge X-ray absorption near edge structure spectra acquired immediately after Ru addition differed with respect to the source. The XAFS results suggest that RuO4 immediately changes to tetravalent form after deposition from air to soil. For RuCl3, the ionic structure in the vicinity of Ru is affected by the soil even if the valence does not change immediately. By contrast, RuO2 and Ru(NO)(NO3)3 are highly stable in soil. The results show that the chemical forms of RuO2 and Ru(NO)(NO3)3 added to the soil solution and soil are retained for 5 days, whereas those of RuCl3 and RuO4 are affected by the soil solution and soil within a short period. These results emphasize the need to focus on the chemical form of Ru deposits and the form change after Ru addition when investigating the environmental fate of radioactive Ru.

Inelastic scattering effects on the inhomogeneous transverse conductivity of liquid metals and plasmas

Abstract On the basis of the quantum Wigner density operator formalism for multicomponent charged particle systems, the wavenumber (k)- and frequency (ω)- dependent transverse conductivity σ^T (k,ω) of simple liquid metals is presented for homogeneous (k = 0) and inhomogeneous (k≠0) electric fields separately. The theory takes into account correlated density fluctuations of electrons and ions, with their mutual inelastic scattering being described by the ionic dynamic structure factors. Since homogeneous and inhomogeneous fields perturb the diagonal and off-diagonal elements of the density matrix, respectively, the corresponding transport equations exhibit a dissimilarity in their collision terms. In both cases, approximate solutions to the transport equations yield a conductivity of generalized Drude form characterized by the k- and ω-dependent complex relaxation time. It is shown that the k→0 limit of the inhomogeneous conductivity, σ^T (k→0,ω), coincides with the homogeneous one in classical ion regime such that βℏω_i≪1, where β is the inverse temperature and ω_i is a characteristic frequency of ionic density fluctuation; this condition may be satisfied for metals well above melting. At lower temperatures, it is suggested that the (homogeneous) DC conductivity σ(0) can exceed the (inhomogeneous) optical conductivity extrapolated to zero frequency, σ^T (k→0,0). This trend is qualitatively consistent with earlier observations for liquid polyvalent metals.

Application of novel Dy0.06Gd0.02Er0.02Bi1.9O3 oxide ion electrolyte for intermediate-temperature reversible solid oxide cells

Bismuth-based oxides are promising electrolyte materials for Reversible Solid Oxide Cells (RSOCs) due to their high ion conductivity and rapid surface oxygen exchange kinetics. In this work we propose a multi-element doping strategy to obtain a novel Dy0.06Gd0.02Er0.02Bi1.9O3 (DGESB) quaternary oxide bismuth material whose ionic conductivities and crystal structure are characterized by AC impedance and X-ray diffraction technique in the temperature range from 600 to 700 °C. Along with promising structure stability and durability, our novel DGESB showed a remarkable ionic conductivity that is 65 times higher than the commercial yttria-stabilized zirconia (YSZ) electrolyte at 700 °C. With composite electrode of DGESB + LCN (LaCo0.6Ni0.4O3) and DGESB/YSZ bilayer electrolyte consisting of RSOC symmetric cell, which achieves a high peak power density (PPD) of 1.62 W/cm2 in fuel cell mode which is 2.7 times higher than that of YSZ single-layer electrolyte, while the electrolysis current density is as high as 1.66 A/cm2 at 1.3 V under H2/H2O:50/50 in electrolysis mode at the same operation temperature of 700 °C. The electrochemical performance measurements revealed a certain stable operation for 200 h in fuel cell mode. The performance degradation can be attributed to the microstructure evolution at the interface between electrolyte and electrodes. The high ionic conductive DGESB proves to be an excellent intermediate electrolyte layer for improving cell performance in RSOCs

Exploring the Influence of Ionic Liquid Anion Structure on Gas-Ionic Liquid Partition Coefficients of Organic Solutes Using Machine Learning.

This article presents an in-depth investigation into the influence of anionic structures of ionic liquids (ILs) on gas-ionic liquid partition coefficients (log K) of organic solutes in three ILs. While the primary objective was to examine whether there is a relationship between the molecular structure of the IL anion component and log K, additionally it was looked at whether the molecular descriptors of the anion in the relationships encode possible molecular interactions during the miscibility and partitioning in the IL. The research involves the compilation of data series of experimental log K values, where the cation component is constant. Such representative data series were obtained for three solutes─benzene, cyclohexane, and methanol─in three ILs with a uniform cationic component of methylimidazoliums. Using multiple linear regression models enhanced with machine learning techniques, the relationship between anionic structures and log K values was successfully quantified and modeled. Systematically selected molecular descriptors describing the anion structure show that in the case of methanol log K is strongly dependent on hydrogen bonds and Coulomb-dipolar interactions with the anion component, while in the case of benzene and cyclohexane the dispersion forces of the anion component are dominant. The outlier analysis and data interpretation highlight the need for extensive experimental data. The results confirm the initial hypothesis and provide valuable information on the role of the structure of the anionic component in determining the partitioning behavior of organic solutes. This knowledge is important for the design and optimization of ILs for specific applications, particularly as solvents in various industrial processes. The research also provides useful information about molecular interactions taking place in the interfaces of IL and organic additives in complex liquid media such as multicomponent electrolyte solutions, for example in energy storage applications.

Ionic channel structure in perfluorinated membranes studied by small angle X-ray scattering, optical and Mössbauer spectroscopy

Ionic channel structure in perfluorinated membranes studied by small angle X-ray scattering, optical and Mössbauer spectroscopy

Solvent-Free in Situ Synthesis of a CsPbBr3 Nanocrystal/ZrO2 Hybrid Phosphor with Excellent Thermal Stability for White Light-Emitting Diodes.

All-inorganic cesium lead halide perovskite CsPbX3 (X = Cl, Br, I, or mixed) nanocrystals (NCs) are emerging as promising candidates in light-emitting diodes (LEDs) owing to their excellent luminescent properties. However, CsPbX3 NCs are extremely susceptible to the elevated temperature associated with prolonged LED operation due to their low formation energy and soft ionic crystal structure. Here, CsPbBr3 NCs hybridized with ZrO2 were in situ synthesized by a rapid solvent-free method under an ambient environment for the first time, which was also suitable for large-scale production. The as-prepared CsPbBr3/ZrO2 hybrid phosphor not only presented enhanced photoluminescence (PL) properties but also exhibited improved thermal stability. For example, the PL intensity of the CsPbBr3/ZrO2 hybrid phosphor could retain 70% of the initial value at 130 °C, obviously higher than that of 34% for pure CsPbBr3. The exceptional thermal stability of the CsPbBr3/ZrO2 hybrid phosphor could be attributed to the introduction of ZrO2, which effectively preserved the initial perovskite structure of CsPbBr3 during heat treatment, as confirmed by XRD results. The as-prepared CsPbBr3/ZrO2 hybrid phosphor had great practical applications verified by the construction of white LEDs (WLEDs) with a luminance degradation of only 9% after continuous operation for 24 h at the initial luminance of 2000 cd m-2, which was significantly better than that of 63% for control WLEDs. The proposed thermally stable hybrid phosphor is expected to greatly contribute to the industrialization process of perovskites.

Widening the Stimuli-Responsiveness of Aqueous Biphasic Systems by Changing the Ionic Liquid Cation Basicity.

Herein we demonstrate the formation of new stimuli-responsive aqueous biphasic systems (ABS), able to respond simultaneously to temperature and pH, or just to one stimulus, therefore allowing the design of more sustainable separation processes. This dual behavior is achieved with ABS formed by mono- or dicationic protic ionic liquids as phase-forming components, being defined by the ionic liquid cation chemical structure or its basicity. While ABS comprising monocationic ionic liquids only respond to the effect of temperature, systems comprising dicationic ionic liquids are simultaneously affected by both temperature and pH variations. Dicationic ionic liquids are here identified as the key to unlock a double response to stimuli, which is due to the presence of two pKa values afforded by the cation. The reported findings contribute to increase the customizability of double stimuli-responsive ABS based on ionic liquids, whose development was up to date limited to ionic liquids bearing pH-responsive anions, opening the door towards the development of more sustainable separation processes.

Stability of inorganic ionic structures: the uniformity approach.

The crystal structure uniformity is numerically estimated as the standard deviation of the crystal space quantizer 〈G3〉. This criterion has been applied to explore the uniformity of ionic sublattices in 21465 crystal structures of inorganic ionic compounds. In most cases, at least one kind of sublattice (whole ionic lattice, cationic or anionic sublattice) was found to be highly uniform with a small 〈G3〉 value. Non-uniform structures appeared to be either erroneous or essentially non-ionic. As a result, a set of uniformity criteria is proposed for the estimation of the stability of ionic crystal structures.

Calcium titanate corrosion inhibitor enabling carbon as inert anode for oxygen evolution in molten chlorides

The corrosion inhibition efficacy of titanate (CaTiO3) for carbon anodes in molten salts was investigated through various analytical techniques, including linear sweep voltammetry, X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The results demonstrate that the addition of CaTiO3 corrosion inhibitor efficiently passivates the carbon anode and leads to the formation of a dense CaTiO3 layer during the electrolysis process in molten CaCl2−CaO. Subsequently, the passivated carbon anode effectively undergoes the oxygen evolution reaction, with an optimal current density for passivation identified at 400 mA/cm2. Comprehensive investigations, including CaTiO3 solubility tests in molten CaCl2−CaO and numerical modeling of the stability of complex ionic structures, provide compelling evidence supporting “complexation−precipitation” passivation mechanism. This mechanism involves the initial formation of a complex containing TiO2·nCaO by CaTiO3 and CaO, which subsequently decomposes to yield CaTiO3, firmly coating the surface of the carbon anode. In practical applications, the integration of CaTiO3 corrosion inhibitor with the carbon anode leads to the successful preparation of the FeCoNiCrMn high-entropy alloy without carbon contamination in the molten CaCl2−CaO.

Development of transition metal oxide platforms for aptasensing of PSA in cell cultures.

In this study, a novel aptasensor based on a transition metal oxide-modified pencil graphite electrode (PGE) was developed for the diagnosis of early-stage prostate cancer (PCa) via monitoring the prostate-specific antigen (PSA), which is the main biomarker for PCa. Single-use PGEs modified with pulsed deposited manganese oxide (MnOx) film were used to attach the amino-terminated aptamer specific to the PSA via carbodiimide chemistry. The designed aptasensor was placed in an electrochemical cell containing ferri/ferrocyanide ions as a redox probe to measure the charge transfer resistances (Rct) of the electrode surface by electrochemical impedance spectroscopy (EIS) to follow the response of each modification step. The effect of the medium pH on the ionic structure of the aptamer molecule according to its pI value and, thus, the reversing of the direction of the response (ΔRct) by the pH change was also discussed. The level of PSA secreted from PCa cells was investigated using impedimetric transduction. The specificity of the aptasensor was validated through selectivity studies against non-specific tumor markers like VEGF and different cancer cell lines including breast cancer and androgen-insensitive prostate cancer. The developed system showcases a label-free, fast, specific, and cost-effective approach for PSA detection, highlighting the importance of medium pH and the electrostatic environment on the aptamer's response. Our work emphasizes the potential for such aptasensors in clinical diagnostics and paves the way for further exploration into using transition metal oxides in biosensing applications.

Highly Deformable and Robust Ionic Structure for Multi‐Tissue Adaptive Hemostatic Sponges

AbstractAccidental trauma is always accompanied by tissue defects with noncompressible hemorrhages. Deformable and tough biomaterials are desirable for self‐compressible hemostasis, although their preparation is challenging. Here, a critical‐size calcium phosphate (C–CaP) with polymer‐like high deformability and mineral‐like high bending strength is prepared, which is hybridized with silk fibroin (SF) to fabricate a hemostatic sponge (SF‐C). C–CaP endows SF‐C with an ultrahigh elastic modulus (36.0 kPa) among analogous materials, leading to an ultrafast water absorption rate (1.2 g cm−3 s−1) and space‐filling rate (200.0%/s). The deformability of the SF‐C sponge further enables self‐adaptability to defects with micrometre‐scale precision. Consequently, SF‐C achieves rapid hemostasis in both damaged soft tissues and hard tissues in rats, resulting in less blood loss and a shorter hemostatic time than those of clinical materials. This study provides a promising hemostatic material for the treatment of hemorrhages in defective tissues and expands the current knowledge by revealing the critical‐sized ionic structure and unique mechanics of C–CaP.

Phase transition and ionic conductivity of pyrrolidinium-based ionic plastic crystals with magnesium salts

Abstract Despite being safe for use in secondary Mg batteries, solid electrolytes exhibit lower ionic conductivities than those of traditional liquid electrolytes. Organic ionic plastic crystals—soft crystals with excellent thermal and electrochemical stabilities and ionic conductivities—are promising solid electrolytes. Herein, we investigated the effects of various anion species and Mg salt concentrations on the properties of pyrrolidinium-based organic ionic plastic crystals (N,N-diethylpyrrolidinium bis(fluorosulfonyl)amide [[C2epyr][FSA]] and N,N-diethylpyrrolidinium bis(trifluoromethylsulfonyl)amide [[C2epyr][TFSA]]) upon Mg(TFSA)2 addition. The Mg-ion transference number (tMg2+) was measured using the Vincent–Bruce method; ionic conductivity via impedance measurements; and phase transition via differential scanning calorimetry. The phase transition behavior, dissociation state of the Mg salt, and electrochemical properties varied with the organic ionic plastic crystal anionic structure. The FSA system became liquid when the Mg salt concentration exceeded 15 mol%. The ionic conductivity of the pyrrolidinium-based organic ionic plastic crystals increased substantially with the Mg salt concentration. In the solid state, [C2epyr][FSA]/Mg(TFSA)2 (5 mol%) (FT5) showed the highest ionic conductivity (2.9 × 10−4 S cm−1 at 25 °C). The tMg2+ of FT5 at 60 °C was 0.29. Mg exhibited redox behavior in FT5 but not in [C2epyr][TFSA]/Mg(TFSA)2 (5 mol%). The FSA− structure is suitable for Mg electrochemistry and will aid in developing high-performance secondary Mg batteries.

Modeling solvation dynamics of transition metal redox ion through on-the-fly multi-objective Bayesian-optimized force field.

Modeling solvation dynamics and properties is crucial for developing electrolytes for electrochemical energy storage and conversion devices. This work reports an on-the-fly multi-objective Bayesian optimization (OTF-MOBO) method to parameterize force fields for modeling ionic solvation structures, thermodynamics, and transport properties using molecular dynamics simulations. By leveraging solvation-free energy and solvation radii as training data, we employ the data-driven OTF-MOBO algorithm to actively optimize the force field parameters. The modeling accuracy was evaluated in molecular dynamics simulations until the Pareto front in the parameter space was reached through minimized prediction errors in both solvation-free energy and solvation radii. Using transition metal redox ions (Fe3+/Fe2+, Cr3+/Cr2+, and Cu2+/Cu+) in aqueous solution as examples, we demonstrate that simple force fields combining the Lenard-Jones potential and Coulombic potential can achieve relative error below 2% in both solvation free energy and solvation radii. The optimized force fields can be further extrapolated to predict solvation entropy and diffusivities with relative error below 10% compared with experiments.

Quantum Chemical Calculation on ScCl3-NaCl-KCl Molten Salt System

Background: The study of the ionic structure of the ScCl3-NaCl-KCl molten salt system is of guiding significance for the production of metal Sc and Sc alloy by molten salt electrolysis using ScCl3-NaCl-KCl molten salt system as electrolyte. However, limited research has been conducted on the structural analysis of molten salt within this system using Raman spectroscopy. Methods: The Gaussian and GaussView programs are used to simulate Sc-Cl ionic groups that may exist in the ScCl3-NaCl-KCl molten salt system based on density functional theory (DFT) and calculate their theoretical Raman spectra. Then, the wave function analysis of these Sc-Cl ionic groups is carried out using the Multiwfn program. Results: When the ScCl3-NaCl-KCl system is used as the electrolyte, it is considered that the 8 Sc atom in ScCl74− ionic groups is most easily reduced by electrochemistry at the cathode when the concentrations of eight Sc-Cl ionic groups are the same. In Sc2Cl7− Sc2Cl82− and Sc2Cl93− ionic groups, the sites that are most likely to attract electrophiles to attack and react are 1Cl and 7Cl, respectively, and the two Sc atoms located in the "chlorine bridge" structure contribute the most to LUMO orbitals, and nucleophiles will preferentially attack the Sc atoms located in the "chlorine bridge" structure. For Sc2Cl7−、Sc2Cl82− and Sc2Cl93− ionic groups, which have two Sc atoms, the bonds formed between Sc and Cl in the "chlorine bridge" structure have the smallest bond order, so the bonds formed by Sc and Cl in the "chlorine bridge" structure break first during the reaction, and then the bond formed by Sc and Cl located at both ends of the whole structure breaks Conclusion: The key information, such as bond length, point group structure, and theoretical Raman spectral characteristic peak after optimization, are obtained by the Gaussian and GaussView programs. The net atomic charge in each ionic group, the direction of electron migration during the formation of the ionic groups, the sites where electrophilic and nucleophilic reactions are most likely to occur in each ionic group, and the order of bond breaking during chemical reactions are obtained by the Multiwfn program.

Solvent Effect on Dative and Ionic Bond Strengths: A Unified Theory from Potential Analysis and Valence-Bond Computations.

Solvent molecules interact with a solute through various intermolecular forces. Here we employed a potential energy surface (PES) analysis to interpret the solvent-induced variations in the strengths of dative (Me3NBH3) and ionic (LiCl) bonds, which possess both ionic and covalent (neutral) characteristics. The change of a bond is driven by the gradient (force) of the solvent-solute interaction energy with respect to the focused bond length. Positive force shortens the bond length and increases the bond force constant, leading to a blue-shift of the bond stretching vibrational frequency upon solvation. Conversely, negative force elongates the bond, resulting in a reduced bond force constant and red-shift of the stretching vibrational frequency. The different responses of Me3NBH3 and LiCl to solvation are studied with valence bond (VB) theory, as Me3NBH3 and LiCl are dominated by the neutral covalent VB structure and the ionic VB structure, respectively. The dipole moment of an ionic VB structure increases along the increasing bond distance, while the dipole moment of a neutral covalent VB structure increases with the decreasing bond distance. The roles of the dominating VB structures are further examined by the geometry optimizations and frequency calculations with the block-localized wavefunction (BLW) method.

Dissolution process and mechanism of montmorillonite in oxalic acid and sulfuric acid media at various pH levels

The dissolution of silicate minerals plays a crucial role in many natural geological processes. In order to better comprehend the reaction mechanisms and dissolution characteristics of montmorillonite in different acidic systems, the effects of interfacial reactions of montmorillonite with oxalic and sulfuric acid solutions at various pH levels on the ionic dissolution, crystal structure, and micro-morphology were studied, and the morphology of aluminum and saturation index of secondary mineral were simulated. It was shown that the dissolution amounts of Mg2+, Al3+ and Si4+ in montmorillonite structure decreased with the increase of pH value, which reflected the dependence of montmorillonite dissolution on the pH value of solution. The dissolution percentages of Mg2+, Al3+ and Si4+ after the reaction of montmorillonite with oxalic acid solution were greater than those in sulfuric acid solution, and the highest dissolution rate of Al3+, indicated that both ligands and protons attacked the surface sites of montmorillonite and accelerated the dissolution of ions. Moreover, oxalate ligands exerted specific binding effects on Al3+ ions. While reacting with oxalate and sulfate, the tetrahedral, octahedral and interlayer cations of montmorillonite exhibited the non-stoichiometric and inconsistent dissolution. The oxalate ligands have a strong complexation effect on Al3+, so that Al3+ in oxalate solution exists in the form of aluminum oxalate complex, which reduces the effective concentration of Al3+ in solution and promotes the dissolution of Al3+ in montmorillonite structure. The Mg2+ ions settled at octahedral substitution sites possessed weak stability, while those from the interlayer featured strong interlayer interchangeability, demonstrating the dissolution percentage up to 10.85 % and 8.62 % even in oxalic and sulfuric acid solutions at pH of 6.5. All secondary mineral phases in the solution were undersaturated, making the montmorillonite dissolution difficult to balance. Montmorillonite has a high cation exchange capacity, which makes it have a strong buffer capacity to exogenous acids. This study helps to explain the dissolution process of montmorillonite in inorganic and organic acid solutions at different pH value.