Range Of Solution Compositions Research Articles

Using voltammetry augmented with physics-based modeling and Bayesian hypothesis testing to identify analytes in electrolyte solutions

Voltammetry is a foundational electrochemical technique that can qualitatively and quantitatively probe electroactive species in solutions and as such has been used in numerous fields of study. Recently, automation has been introduced to extend the capabilities of voltammetric analysis through approaches such as Bayesian parameter estimation and compound identification. However, opportunities exist to enable more versatile methods across a wider range of solution compositions and experimental conditions. Here, we present a protocol that uses experimental voltammetry, physics-driven models, binary hypothesis testing, and Bayesian inference to enable robust labeling of analytes in multicomponent solutions across multiple techniques. We first describe the development of this protocol, and we subsequently validate the methodology in a case study involving five N-functionalized phenothiazine derivatives. In this analysis, the protocol correctly labels solutions each containing 10H-phenothiazine and 10-methylphenothiazine from both cyclic voltammograms and cyclic square wave voltammograms, demonstrating the ability to identify redox-active constituents of a multicomponent solution. Finally, we identify areas of further improvement—such as achieving greater detection accuracy—and future applications to potentially enhance in situ or operando diagnostic workflows.

Nonpolar solute cononsolvency in ethanol/water mixtures – Connections to solvent structure

We present a molecular simulation study of argon cononsolvency in ethanol/water mixtures over the full range of solution compositions. First, we evaluate the solubility of argon in ethanol/water mixtures using particle insertion techniques to evaluate solute excess chemical potentials. Our simulations are in good agreement with available experimental results, importantly exhibiting a solubility minimum (excess chemical potential maximum) at intermediate ethanol concentrations at the lowest temperatures examined. Breaking the solvation free energies down into is entropic, enthalpic, and heat capacity contributions we find a distinct break between water-like and ethanol-like solvation thermodynamics at an ethanol concentration of 20 mol%. This break is accompanied with distinct changes in the solution structure suggesting argon partitions into ethanol-rich domains away from water with increasing ethanol composition. In addition, the boundary between water-like and ethanol-like solvation thermodynamics is found to lie within a concentration range in which the mixture forms bicontinuous water and ethanol clusters that span the simulation box at a nearly 50/50 vol fraction of the solvent components. We conclude with a study of the impact of cononsolvency on the association thermodynamics of argon pairs in the mixture. We find a break between water-like and ethanol-like argon interaction thermodynamics occurring at an ethanol composition of 25 mol%, similar to our solvation study. Examining the solvation shells of the two interacting argons as a function of separation, the shell is found to become progressively enriched in ethanol as the argon's come into contact. This solvation shell enrichment could subsequently provide a driving force for cononsolvency driven association/assembly.

Thorium oxide dissolution in HNO3-HF mixture: kinetics and mechanism

Abstract This paper is an attempt to find out thorium oxide dissolution mechanism in HNO3-HF mixture. In a previous paper, several parameters effects on thorium oxide dissolution have been described, with specific focus on hydrofluoric acid effect, which can lead to an increase of the dissolution rate if present in small amount, but precipitates as ThF4 at higher content. Based on this previous study, experimental data were fitted using several dissolution models in order to find out the best one. Finally, a revisited model based on literature and considering the ThF4 formation was proposed. It describes the main steps of dissolution and is able to fit the experimental data for a wide range of solution compositions. This point is crucial since it allows considering an extrapolation of the established model to not-yet-studied conditions.

Ion Transport and Competition Effects on NaTi2(PO4)3 and Na4Mn9O18 Selective Insertion Electrode Performance.

We evaluate the efficiency and capacity of electrochemically reversible insertion electrodes for use in targeted ion removal applications in aqueous solutions. The relative attributes of insertion material chemistry are evaluated by comparing the performance of two different sodium insertion materials, NaTi2(PO4)3 and Na4Mn9O18, in different electrolyte environments. We performed experiments over a range of solution compositions containing both sodium and other non-inserting ions, and we then developed mechanistic insight into the effects of solution concentration and composition on overpotential losses and round trip Coulombic efficiency. In dilute aqueous streams, performance was limited by the rate of ion transport from the bulk electrolyte region to the electrode interface. This leads to slow rates of ion removal, large overpotentials for ion insertion, parasitic charge loss due to water electrolysis, and lower round trip Coulombic efficiencies. This effect is particularly large for insertion electrodes with redox potentials exceeding the water stability window. In solutions with high background concentrations of non-inserting ions, the accumulation of non-inserting ions at the electrode interface limits inserting ion flux and leads to low ion removal capacity and round trip Coulombic efficiency.

Factors influencing the stability of AFm and AFt in the Ca-Al-S-O-H system at 25 °C.

The stabilities of Al2O3-Fe2O3-mono (AFm) and -tri (AFt) phases in the Ca-Al-S-O-H system at 25 °C are examined using Gibbs energy minimization as implemented by GEM-Selektor software coupled with the Nagra/PSI thermodynamic database. Equilibrium phase diagrams are constructed and compared to those reported in previous studies. The sensitivity of the calculations to the assumed solid solubility products, highlighted by the example of hydrogarnet, is likely the reason why some studies, including this one, predict a stable SO4-rich AFm phase while others do not. The majority of the effort is given to calculating the influences on AFm and AFt stability of alkali and carbonate components, both of which are typically present in cementitious binders. Higher alkali content shifts the equilibria of both AFt and AFm to lower Ca but higher Al and S concentrations in solution. More importantly, higher alkali content significantly expands the range of solution compositions in equilibrium with AFm relative to AFt phases. The introduction of carbonates alters not only the stable AFm solid solution compositions, as expected, but also influences the range of solution pH over which SO4-rich and OH-rich AFm phases are dominant. Some experimental tests are suggested that could provide validation of these calculations, which are all the more important because of the implications for resistance of portland cement binders to external sulfate attack.

Structure and adsorption properties of microporous glassy-carbon materials

Products of the calcination of polymer based on furan resin modified by surface-active agent and diluter are studied. Microporous glassy-carbon materials with specific areas of up to 1350 m2/g are obtained. The materials are studied by means of electron microscopy, and their specific surface areas are compared to their structures. The range of solution compositions in which bicontinual structures are formed as three-dimensional networks from polymer drops is determined; the drop size varies from 0.3 to 1.5 μm.

Kinetics of Ferric Ion Reduction on Chalcopyrite and its Influence on Leaching up to 150 °C

The reduction kinetics of ferric ion on chalcopyrite in the quaternary H2SO4-Fe2(SO4)3-FeSO4-H2O system were systematically studied by cathodic potentiodynamic polarization (0.5mV/s) through a wide range of solution compositions and temperatures (25–150°C). Results reveal that all of the pseudo-polarization plots exhibit reproducible well-defined linear Tafel regions and thus the temperature dependence of various kinetic parameters, such as the exchange current density, transfer coefficient and rate constant, has been determined. The exchange current densities of the Fe3+/Fe2+ couple obtained by extrapolating the cathodic linear Tafel line to the reversible potential are on the order of 10−7-10−5 A/cm2 in the range of 25–150°C, substantially less than that on platinum due to the formation of a passive film. In general, at the same nominal Fe3+/Fe2+ ratio, increasing the temperature from 25 to 150°C was observed to give rise to an increase in i0, especially when a larger amount of free ferrous existed in the solution. Based on the obtained exchange current densities, the rate constants for ferric ion reduction were calculated, and further analysis indicates that the rate constants can be well described by the Arrhenius equation. Experimental evidence clearly shows an anomalous independent variation of Tafel slope with temperature and a corresponding unexpected increased linear variation of transfer coefficient with respect to temperature (rather than being constant throughout the investigated temperature range). Analysis by mixed potential theory indicates that in the acidic iron sulfate leaching system the control scenario highly depends on both the solution composition and temperature. The importance of the cathodic ferric ion reduction reaction on the overall leaching process is progressively increased when increasing the nominal Fe3+/Fe2+ ratio and temperature. The leaching reaction is under anodic control when the nominal Fe3+/Fe2+ ratio is around 1:1, whereas at higher nominal Fe3+/Fe2+ ratios and temperatures the reaction is under mixed control, by both anodic oxidation and cathodic reduction reactions.

Speciation of the H2SO4–Fe2(SO4)3–FeSO4–H2O system and development of an expression to predict the redox potential of the Fe3 +/Fe2 + couple up to 150 °C

A thermodynamic model is developed and shown to reliably simulate the speciation of the quaternary H2SO4–Fe2(SO4)3–FeSO4–H2O system through a wide range of solution compositions and temperatures (25°C–150°C). The main species involved (including H+, Fe2+, Fe3+, SO42−, HSO4−, FeHSO4+, FeSO4°, FeHSO42+, Fe(SO4)2−, FeSO4+, Fe2O3 and H2O) were investigated, and their thermodynamic data were collected and critically assessed to evaluate their activity coefficients and equilibrium constants. Results show that the species distribution depends highly on the initial total amount of iron, acidity, nominal Fe3+/Fe2+ ratio and temperature. Modeling results also reveal that most of the Fe(III) is distributed as complexes or precipitates and the free Fe3+ accounts for only a minor percentage, whereas a large amount of Fe(II) exists in the form of free Fe2+, with the rest dissolved as complexes. Moreover, based on the model results, the temperature dependence of the real Fe3+/Fe2+ ratios and their activity coefficient ratios was subsequently obtained and employed to systematically study the redox potential of the Fe3+/Fe2+ couple. The redox potentials predicted by the model increase with the nominal Fe3+/Fe2+ ratio and temperature when the nominal Fe3+/Fe2+ ratios are 10:1, 100:1 and 1000:1, with its values in the range of 736–956mV (all potentials in the present study are quoted with respect to the Standard Hydrogen Electrode at 25°C) from 25°C to 150°C in the studied acidic iron sulfate solutions. At a nominal Fe3+/Fe2+ ratio of 1:1, the predicted potentials are relatively stable with respect to temperature, typically between 671mV and 679mV, because the real Fe3+/Fe2+ ratio in solution is much lower for such a condition. The speciation model explains the change of redox potential with temperature for all nominal Fe3+/Fe2+ ratios. An expression is also developed to calculate the redox potential and is supported by experimental results from the literature. It appears that the redox potential can be easily and accurately determined only based on the variables of temperature and nominal Fe3+/Fe2+ ratio, independent of the nominal concentrations of H2SO4 and Fe3+. Moreover, this expression is probably applicable to more general cases at or around room temperature. The proposed model was validated by reliable prediction of measured redox potential from 25°C to 150°C. Comparison of previously published results of ferric solubility, together with an analysis of the calculated pH and ionic strength, provides additional justification for the model developed herein. These findings contribute to the research on aqueous speciation of acid iron sulfate solutions, the reduction kinetics of the Fe3+/Fe2+ couple, as well as the mechanistic analysis in industrial leaching processes of chalcopyrite and other sulfide minerals.

A new material for the icy Galilean moons: The structure of sulfuric acid hexahydrate

AbstractThis study presents a newly identified water‐rich crystalline form of sulfuric acid hydrate, H2SO4•6H2O, a hexahydrate. The method of formation of this material suggests that sulfuric acid hexahydrate (SAHx) could be an abundant material on the surface of Jupiter's Galilean ice moons, Europa, Ganymede, and Callisto. The structure of SAHx was determined by the combined use of synchrotron X‐ray and neutron powder diffraction data. The structural arrangement of SAHx exhibits the same water layer topology that has been determined for sulfuric acid octahydrate (SAO), but differs in the stacking of this water layer and the interlayer species. SAHx is observed to form over a large range of solution compositions and displays stability over the temperature range 80 to 190 K.

Crossed mixture–process design approach to model nanofiltration rejection for non-dilute multi-ionic solutions in a given range of solution compositions

The goal of the present work is to illustrate the applicability of crossed mixture–process design to predict the rejection of the nanofiltration membranes when treating non-dilute solutions. The method used in this work is based on the use of mixture factors derived from the fractions of equivalents of the major ions present in solution combined with the total concentration as a process variable. In this way, polynomial models for permselectivity properties can be obtained. Model accuracy is improved by using pseudo-components to restrict the range of the composition variables to that expected for the feed water compositions. The experimental plan uses the D-optimal criterion. As an application example, the procedure was used to model the performance of the nanofiltration membrane NF270 (Dow-Filmtec) with ionic mixtures containing chloride, nitrate, sulfate, sodium and calcium. The experiments were carried out in a pilot plant with solutions of total concentration ranging from 2480 to 4050mg/L. The obtained polynomial models could satisfactorily describe individual ion rejection despite the solutions not being dilute. The polynomial models can be useful for design and operation purposes as an alternative to physical-based nanofiltration models.

Fluorescence and absorbance spectroscopy of the uranyl ion in nitric acid for process monitoring applications

Near real time process monitoring of the ura- nium content in an aqueous fuel recycling plant is a desired component of an advanced safeguards suite; Ultraviolet- Visible spectroscopy and Time Resolved Laser induced Fluorescence Spectroscopy can contribute to this technol- ogy gap. This work presents the observation of the spec- troscopic parameters (molar absorptivities, fluorescent response) of the uranyl ion across the range of conditions expected in reprocessing chemistry. From this data, a monitor using the ratio of the absorbance of the uranyl ion at 403 and 426 nm has been developed. This technique can determine the nitrate solution concentration and can be coupled with a condition appropriate molar absorptivity to determine the uranyl concentration. This method provides a reliable technique for online, real time process monitoring of the uranyl and nitrate concentration under a wide range of solution compositions.

Number of Solution States of Bradykinin from Ion Mobility and Mass Spectrometry Measurements

Ion mobility and mass spectrometry measurements have been used to examine the populations of different solution structures of the nonapeptide bradykinin. Over the range of solution compositions studied, from 0:100 to 100:0 methanol:water and 0:100 to 90:10 dioxane:water, evidence for 10 independent populations of bradykinin structures in solution is found. In some solutions as many as eight structures may coexist. The solution populations are substantially different than the gas-phase equilibrium distribution of ions, which exhibits only three distinct states. Such a large number of coexisting structures explains the inability of traditional methods of characterization such as nuclear magnetic resonance spectroscopy and crystallography to determine detailed structural features for some regions of this peptide.

Effect of complexation of poly(acrylic acid) with Cu2+ ions on the size of copper nanoparticles prepared via reduction in aqueous solutions

Sols of zero-valence copper are prepared via the chemical reduction of Cu(II) ions by hydrazine borane in aqueous solutions of high-molecular-mass poly(acrylic acid), which forms stable complexes with copper ions at 20°C in a wide pH range. The study of the composition of coordination centers, the ligand surrounding of metal ions, and the character of distribution of copper ions over poly(acrylic acid) coils in a wide range of solution compositions and pH values shows that the size of copper nanoparticles in the sols can be controlled by varying the ratio between ligand groups (carboxylate anions in poly(acrylic acid)) and copper ions in the reaction system during the synthesis of sols. This effect can be accomplished either by variation in the initial composition of solution or change in pH (the degree of ionization of the initial poly(acrylic acid) in the presence of copper ions).

Surface and Solution Properties of Anionic/Nonionic Surfactant Mixtures of Alkylbenzene Sulfonate and Triethyleneglycol Decyl Ether

The surface adsorption behavior and the solution microstructure of mixtures of the C(6) isomer of anionic surfactant sodium para-dodecyl benzene sulfonate, ABS, with nonionic surfactant monodecyl triethyleneglycol ether, C(10)E(3,) have been investigated using a combination of neutron reflectivity, NR, and small-angle neutron scattering, SANS. In solution, the mixing of C(10)E(3) and ABS results in the formation of small globular micelles over most of the composition range (100:0 to 20:80 ABS/C(10)E(3)). Planar aggregates (lamellar or unilamellar vesicles, ULV) are observed for solution compositions rich in the nonionic surfactant (>80 mol % nonionic). Prior to the transition to planar aggregates, the micelle aggregation number increases with increasing nonionic composition. The lamellar-phase region is preceded by a narrow range of composition over which mixtures of micelles and small unilamellar vesicles coexist. The variation in surface absorption behavior with solution composition shows a strong surface partitioning of the more surface-active component, C(10)E(3). This pronounced departure from ideal mixing is not readily explained by existing surfactant mixing theories. In the presence of Ca(2+) ions, a more complex evolution of solution phase behavior with solution composition is observed. The lamellar-phase region occurs over a broader range of solution compositions at the expense of the small-vesicle phase. The phase boundaries are shifted to lower nonionic compositions, and the extent to which the solution-phase diagrams are modified increases with increasing calcium ion concentration. The SANS data for the large planar aggregates are consistent with large polydisperse flexible unilamellar vesicles. In the presence of Ca(2+) ions, the surface adsorption patterns become more consistent with ideal mixing in the nonionic-rich region of the surface-phase diagram. However, in the ABS-rich regions the surface behavior is more complex because of the spontaneous formation of more complex surface microstructures (bilayers to multilayers). Both in water and in the presence of Ca(2+) ions the variations in the surface adsorption behavior and in the solution mesophase structure do not appear to be closely correlated.

Electrochemical formation and investigation of a self-assembled [60]fullerene monolayer

The formation and characterisation of a C(60) monolayer at the electrode|electrolyte interface has been studied by cyclic voltammetry, potential step chronoamperometry and ac voltammetry. The presence of the monolayer is evidenced by the presence of a very sharp peak P in the voltammogram, attributed to the faradaic phase formation of an ordered monolayer, and of a reduction post peak Q associated with the reduction of adsorbed species. The chronoamperograms exhibit a well-defined maximum, characteristic of a nucleation and growth mechanism. By comparison with existing models of phase transitions, a progressive polynucleation and growth mechanism is demonstrated. The monolayer is proposed to consist of a 2D fulleride salt. It is suggested that the formation of the monolayer can take place for a broad range of solution compositions, but requires an atomically smooth substrate such as mercury.

Challenges in Fabrication of Mesoporous Carbon Films with Ordered Cylindrical Pores via Phenolic Oligomer Self-Assembly with Triblock Copolymers

Mesoporous phenol formaldehyde (PF) polymer resin and carbon films are prepared by a solution self-assembly of PF oligomers with amphiphilic triblock copolymers. After thermopolymerization of the PF to cross-link the network, the films show an ordered morphology as determined by X-ray diffraction and grazing incidence small-angle X-ray scattering (GISAXS). Our results show that the amphiphilic triblock copolymer template greatly influences the stability of the final porous mesostructures. The pyrolysis of the two-dimensional (2-D) hexagonal films with p6mm symmetry templated by Pluronic F127 yields a disordered porous structure following the template removal. Conversely, films templated by Pluronic P123 can exhibit well-ordered cylindrical pores after the template removal, but the solution composition range to yield ordered cylindrical mesopores is significantly reduced (nearly 70%) for thin films in comparison to bulk powders. We propose two dominant difficulties in fabricating well-ordered cylindrical mesopores in films: first, the stress from contraction during the pyrolysis can lead to a collapse of the mesostructure if the wall thickness is insufficient, and second, the surface wetting behavior in thin films leads to a small compositional range.

Complexation in the Cu(II)–LiCl–H 2O system at temperatures to 423 K by UV-Visible spectroscopy

Thermodynamic data for the solubility and formation of copper(I)and copper(II) species are required to model innovative designs of the electrolysis cells used in the thermochemical copper-chloride hydrogen production process. Cumulative formation constants of Cu 2+(aq) complexes with Cl −(aq) were determined by Principal Component Analysis of UV-spectra, obtained over a very wide range of solution compositions and temperature, coupled with an appropriate model for activity coefficients of the solution species. Shortcomings in the existing database and future work to extend these studies to higher temperatures and much higher copper concentrations are discussed.

Brackish water reverse osmosis (BWRO) operation in feed flow reversal mode using an ex situ scale observation detector (EXSOD)

The feasibility of operating brackish water reverse osmosis (BWRO) desalination in a feed flow reversal (FFR) mode so as to mitigate mineral scaling was evaluated with feed solutions containing calcium, sodium, sulfate and chloride ions. The premise of the FFR approach is to enable dissolution of surface mineral crystals, that form first at the BWRO plant tail elements, by periodic exposure to the undersaturated feed solution. Automatic triggering of FFR was accomplished by integrating an Ex-situ scale observation detector (EXSOD) with the BWRO plant controller. The EXSOD system consisted of a small high pressure plate-and-frame RO cell, with its membrane surface digitally imaged in real-time, to monitor the onset and development of membrane mineral scaling. During normal feed flow (NFF) operation, the EXSOD monitored a concentrate side-stream from the BWRO plant tail element, signaling the BWRO plant controller to initiate FFR when the specified scaling threshold was reached. Once the plant feed flow was reversed, the EXSOD feed stream was switched from the BWRO plant concentrate to the plant's permeate in order to dissolve mineral crystals formed on the EXSOD membrane during NFF operation. Successful operation of automated FFR, whereby scale formation was prevented, required adjustment of the EXSOD operating conditions such that the saturation index in the EXSOD RO cell was at a level that would not result in scale detection significantly before or after scaling would occur in the RO plant. Although the onset of mineral scaling was detected at the level of appearance of the first observable mineral crystal, the results suggest that it would be more practical to trigger FFR based on a threshold that considers both the mineral crystal number density and fractional surface scale coverage. Current work is continuing to demonstrate the broad applicability of FFR mode of RO mineral scale-free operation (with reduced or no antiscalant addition) over a wide range of solution compositions and operating conditions.

Structure and composition of binary monolayers self-assembled from sodium 2-mercaptoetanosulfonate and mercaptoundecanol mixed solutions on silver and gold supports

Voltammetric reductive desorption, scanning tunneling microscopy (STM) and surface-enhanced Raman scattering (SERS) were used to determine the composition and structure of mixed, two-component monolayers of sodium 2-mercaptoetanosulfonate (MES) and mercaptoundecanol (MUL) on silver and gold supports. Monolayers were prepared by self assembling from ethanolic solutions of varying composition. Preferred adsorption of MUL was found in the electrochemical experiments on Au(111). The presence of two well-separated reductive desorption peaks in the voltammograms of the mixed monolayers on Au(111) indicated the existence of MES-rich and MUL-rich phases in a wide range of solution compositions. STM imaging confirmed formation of a few-nanometer-wide thiol domains for xMES greater than 0.5 in the solution used for SAMs preparation. On the contrary, SERS experiments pointed at dominant adsorption of MES on rough Ag and Au substrates. Nearly exclusive adsorption of the MES for xMES greater than 0.5 was observed on the rough Ag surface.

Solvent induced shifts of fundamental vibrational frequency and first overtone of CO + Ar solution. Monte-Carlo simulation

CO/Ar solutions in composition range from 0.044 to 0.188 mol fraction of carbon monoxide have been simulated by Monte-Carlo calculation within NPT ensemble. The simulations have been carried out at different values of temperature and pressure. The intermolecular pair potentials depend on the CO vibrational quantum number v, which is vital for the solvent induced frequency shift calculations. The results of these calculations were compared with a few available data of spectroscopic measurements. An analysis of the contributions of different intermolecular interaction types to internal energy and CO vibrational red and blueshift is made. As it follows from simulation results there is a possibility to change the solvent induced shift from red to blue by solution composition variation.