Shell Ionization Research Articles

Mathematical Model of Double-Pulse Electrolysis of Alkalines

A mathematical model of a simple two-chamber electrolyzer was formulated and substantiated for the study of possible processes occurring during electrolysis. In the calculations, the following factors were taken into the account: electrochemical reactions, electromigration of ions in the potential gradient field, diffusion through the membrane that separates the cathode and anode chambers, the change in the volume of the solution due to the water molecules compaction in the hydration shells of ions, and the change in the alkali concentration. The electrolysis mode consists of two consecutive current pulses: the first-cathodic and the next – anodic. Theoretical calculations of the system state in the two-pulse mode are the most accurate since the chemical composition of the electrolyte does not change at the moment of switching the current. However, the directions of electrode reactions, electromigration, and electroosmosis change. In the electrolysis mode with more pulses, it would be impossible to calculate the state parameters. A mathematical model was created for a comparative analysis of the influence of different electrolysis conditions on the speed ratio of various processes.

Experimental study of the effect of oil polarity on smart waterflooding in carbonate reservoirs

This study investigates the influence of oil polarity on interfacial tension (IFT), contact angle, oil recovery, and effluent pH in smart water and Low-salinity water injection. The results indicate that the interaction between the hydration shell of ions and the polar components (PCs) of oil is crucial. Increasing oil polarity enhances the potential for interaction with the hydration shell of ions, leading to reduced IFT, altered wettability, and improved oil recovery; which could be boosted by the contribution of a higher number of anions in the smart water bulk through the enhancement of their interaction with the PCs (especially acidic components) of oil. The study demonstrates that increasing the SO42− concentration in seawater increased oil recovery for oils with higher acid component content, as indicated by total acid number values of 0.87, 0.99, and 1.32 mgKOH/g, the tertiary oil recovery factors for these oils were 61.10%, 69.82%, and 87.09%, respectively. The effluent pH results align with the findings of contact angle and oil recovery, confirming the dominant influence of anions on oil recovery. The interaction between the PCs of oil and the hydration shell of ions is thus highlighted as a critical factor in the observed outcomes.

Hydration structure and dynamics of phosphoric acid and its anions-Ultrafast 2D-IR spectroscopy and abinitio molecular dynamics simulations.

The hydration shells of phosphate ions and phosphate groups of nucleotides and phospholipid membranes display markedly different structures and hydrogen-bond strengths. Understanding phosphate hydration requires insight into the spatial arrangements of water molecules around phosphates and in thermally activated structure fluctuations on ultrafast time scales. Femtosecond two-dimensional infrared spectroscopy of phosphate vibrations, particularly asymmetric stretching vibrations between 1000 and 1200cm-1, and abinitio molecular dynamics (AIMD) simulations are combined to map and characterize dynamic local hydration structures and phosphate-water interactions. Phosphoric acid H3PO4 and its anions H2PO4-, HPO42-, and PO43- are studied in aqueous environments of different pH value. The hydration shells of phosphates providing OH donor groups in hydrogen bonds with the first water layer undergo ultrafast structural fluctuations, which induce a pronounced spectral diffusion of vibrational excitations on a sub-300fs time scale. With a decreasing number of phosphate OH groups, the hydration shell becomes more ordered and rigid. The 2D-IR line shapes observed with hydrated PO43- ions display a pronounced inhomogeneous broadening, reflecting a distribution of hydration geometries without fast equilibration. The AIMD simulations allow for an in-depth characterization of the hydration geometries with different numbers of water molecules in the first hydration layer and different correlation functions of the fluctuating electric field that the water environment exerts on the vibrational phosphate oscillators.

Differential phase contrast from electrons that cause inner shell ionization

Differential Phase Contrast (DPC) imaging, in which deviations in the bright field beam are in proportion to the electric field, has been extensively studied in the context of pure elastic scattering. Here we discuss differential phase contrast formed from core-loss scattered electrons, i.e. those that have caused inner shell ionization of atoms in the specimen, using a transition potential approach for which we study the number of final states needed for a converged calculation. In the phase object approximation, we show formally that differential phase contrast formed from core-loss scattered electrons is mainly a result of preservation of elastic contrast. Through simulation we demonstrate that whether the inelastic DPC images show element selective contrast depends on the spatial range of the ionization interaction, and specifically that when the energy loss is low the delocalisation can lead to contributions to the contrast from atoms other than that ionized. We further show that inelastic DPC images remain robustly interpretable to larger thicknesses than is the case for elastic DPC images, owing to the incoherence of the inelastic wavefields, though subtleties due to channelling remain. Lastly, we show that while a very high dose will be needed for sufficient counting statistics to discern differential phase contrast from core-loss scattered electrons, there is some enhancement of the signal-to-noise ratio with thickness that makes inelastic DPC imaging more achievable for thicker samples.

Why Is Surface-Enhanced Raman Scattering Insensitive to Liquid Water?

Surface-enhanced Raman scattering (SERS) is widely recognized as a remarkably powerful analytical technique that enables trace-level detection of organic molecules on a metal surface in aqueous systems with negligible spectral interference of water. This insensitivity of SERS to liquid water is violated in a restrictive manner under specific electrochemical conditions. However, the origin of such different SERS sensitivities to liquid water remains unclear. Here, we show that hydrogen-bond networks of water play a pivotal role in losing SERS enhancement for liquid water, and SERS detection of water requires local defects in the hydrogen-bond networks, which are formed around hydration shells of solute ions or on a polarized electrode surface. This work gives a new perspective on in situ SERS investigations in aqueous systems, including electrochemical and biological reactions.

Interfacial Reconstruction Unlocks Inherent Ionic Conductivity of Li‐La‐Zr‐Ta‐O Garnet in Organic Polymer Electrolyte for Durable Room‐Temperature All‐Solid‐State Batteries

AbstractRigid‐flexible coupled composite polymer electrolytes (CPEs, e.g., polyethylene oxide/Li6.4La3Zr1.4Ta0.6O12, PEO/LLZTO) hold the promise of integrating the respective merits of organic polymer electrolyte and inorganic ceramic fillers to achieve better all‐solid‐state batteries (ASSBs), but commonly suffer from poor synergistic effect owing to the ionically/electronically resistive layer on the ceramic surface. Representatively, the Li2CO3 passivation layer‐isolated LLZTO not only contributes minimally to the Li+ conduction in PEO/LLZTO CPE, but also narrows the available electrochemical window. Herein, an interfacial reconstruction strategy is disclosed based on mild liquid‐phase chemical reaction and subsequent self‐assembly, allowing the detrimental Li2CO3 to fully react with succinic anhydride (SA), and simultaneously constructing a robust ultra‐thin lithium succinate (SALi) ionic conductor shell to eradicate its regeneration. Accordingly, the obtained PEO/LLZTO@SALi (PLS) CPE shows a high room‐temperature ionic conductivity (1.2 × 10−4 S cm−1), a wide electrochemical window (4.8 V), a notable Li+ transference number (0.37), as well as nonflammability and exceptional compatibility with Li metal in Li/Li symmetric cells (2000 h at 0.2 mA cm−2). More encouragingly, the Li/PLS CPE/LiFePO4 full ASSB maintains an ultrahigh capacity retention of 84.3% after 1400 cycles at room temperature. This work propels the design of high‐performance CPEs through the interfacial modulation of inorganic ceramic fillers.

Redox potentials in ionic liquids: Anomalous behavior?

Redox potentials depend on the nature of the solvent/electrolyte through the solvation energies of the ionic solute species. For concentrated electrolytes, ion solvation may deviate significantly from the Born model predictions due to ion pairing and correlation effects. Recently, Ghorai and Matyushov [J. Phys. Chem. B 124, 3754-3769 (2020)] predicted, on the basis of linear response theory, an anomalous trend in the solvation energies of room temperature ionic liquids, with deviations of hundreds of kJ/mol from the Born model for certain size solutes/ions. In this work, we computationally evaluate ionic solvation energies in the prototypical ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM/BF4), to further explore this behavior and benchmark several of the approximations utilized in the solvation energy predictions. For comparison, we additionally compute solvation energies within acetonitrile and molten NaCl salt to illustrate the limiting behavior of purely dipolar and ionic solvents. We find that the overscreening effect, which results from the inherent charge oscillations of the ionic liquid, is substantially reduced in magnitude due to screening from the dipoles of the molecular ions. Therefore, for the molten NaCl salt, for which the ions do not have permanent dipoles, modulation of ionic solvation energies from the overscreening effect is most significant. The conclusion is that ionic liquids do indeed exhibit unique solvation behavior due to peak(s) in the electrical susceptibility caused by the ion shell structure; redox potential shifts for BMIM/BF4 are of more modest order ∼0.1V, but may be larger for other ionic liquids that approach molten salt behavior.

Structural and transport properties of the molten salt NaCl-KCl-UCl3 using the polarizable ion model

Molecular dynamics simulations are a powerful tool for predicting the properties of molten salts at conditions sometimes challenging to achieve experimentally. Here, they are applied within the framework of the polarizable ion model (PIM) for the investigation of the NaCl-KCl-UCl3 molten salt at two different compositions and for a temperature range between 1000 and 1400 K. This allowed us to understand the impact of sodium and potassium ions on the structure of the solvation shell of uranium ions, as well as predicting their density, viscosity, self-diffusion coefficients and heat capacity at different conditions.

Characterization of the Coordination and Solvation Dynamics of Solvated Systems─Implications for the Analysis of Molecular Interactions in Solutions and Pure H2O.

The characterization of solvation shells of atoms, ions, and molecules in solution is essential to relate solvation properties to chemical phenomena such as complex formation and reactivity. Different definitions of the first-shell coordination sphere from simulation data can lead to potentially conflicting data on the structural properties and associated ligand exchange dynamics. The definition of a solvation shell is typically based on a given threshold distance determined from the respective solute-solvent pair distribution function g(r) (i.e., GC). Alternatively, a nearest neighbor (NN) assignment based on geometric properties of the coordination complex without the need for a predetermined cutoff criterion, such as the relative angular distance (RAD) or the modified Voronoi (MV) tessellation, can be applied. In this study, the effect of different NN algorithms on the coordination number and ligand exchange dynamics evaluated for a series of monatomic ions in aqueous solution, carbon dioxide in aqueous and dichloromethane solutions, and pure liquid water has been investigated. In the case of the monatomic ions, the RAD approach is superior in achieving a well separated definition of the first solvation layer. In contrast, the MV algorithm provides a better separation of the NNs from a molecular point of view, leading to better results in the case of solvated CO2. When analyzing the coordination environment in pure water, the cutoff-based GC framework was found to be the most reliable approach. By comparison of the number of ligand exchange reactions and the associated mean ligand residence times (MRTs) with the properties of the coordination number autocorrelation functions, it is shown that although the average coordination numbers are sensitive to the different definitions of the first solvation shell, highly consistent estimates for the associated MRT of the solvated system are obtained in the majority of cases.

Study of optical, structural and radiation shielding properties of (55 − x)TeO2–20ZnO–25B2O3–xEr2O3 glass matrix

Abstract Erbium doped zinc boro-tellurite (EZBT) glass samples with molar composition of (55 − x)TeO2–20ZnO–25B2O3–xEr2O3 (x = 0.0, 0.5, 1.0, 1.5 and 2.0 mol.%) were prepared by a conventional melt quenching technique. The prepared samples were characterised using X-ray diffraction, Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy techniques to investigate the structural, optical and dielectric properties. To study the radiation shielding capabilities, the parameters such as mass attenuation coefficient (μ m), half-value layer (HVL), effective atomic number (Z eff) etc., were evaluated using WinXCom software. Judd–Ofelt analysis was carried out to determine the intensity of electronic transitions and other radiative transition parameters within the 4f shell of erbium ions. The μ m values in a range of (108.5–0.03) cm2 g−1 for energy range (0.01–10) MeV were obtained for 2.0 mol.% erbium-doped tellurite glass matrix. The μ m and HVL values were also compared with conventionally used ordinary concrete and specific lead borate glass at certain energies. The detailed investigation of this current EZBT glass matrix is very useful in the specific optical and radiation shielding applications of this EZBT glass.

Enhanced separation via confined shear flow in microchannel: A novel insight into the role of confined hydrogen bonds in microfluid and its effect on competitive mass transfer of hydrated ions

Microfluidic extraction and separation have demonstrated enormous potential in the field of purification and separation, but the essence of its enhanced separation has always been a focus of debate in the academic community. This study reveals that the interaction between extractant molecules and ions in the process of microfluidic extraction exhibits some significant differences from conventional liquid–liquid two phase stirring dispersed droplet extraction. The interaction between extractant molecules and metal ions through the hydrogen bonds (H-bonds) bridged by water molecules around the hydration shell of metal ions exhibits a noticeable change in confined flow in microchannel. It was demonstrated that in our experiments that the strength difference of this interaction is subjected to the ability of different metal ions to bind water molecules. Therefore, the differences in the interaction between extractant molecules and ions through the hydrogen bonding “water-bridge” are easier to be distinguished within the confined fluid, due to the different effects from the confined environment on mass transfer of metal ions with different abilities to bind water molecules. The confined fluid environment strengthened the difference in the interaction, leading to an amplification of difference in ion diffusion rates, thereby achieving enhanced separation of target rare earth Er3+ ions from the coexisting background ions. Hydrophilic coexisting background ions can be separated by reducing the microchannel width, so that the βEr/Al increases from 2.95 to 49.78. However, the relatively hydrophobic background ions can be separated by increasing flow rates, so that the βEr/Mg increases from 75.32 to 299.06. This work provides a new insight into the essence of microfluidic enhanced separation from the perspective of confined H-bonds.

S-HGMS coupling with alkali precipitation for the scale inhibition in recirculating cooling water with high hardness: Performance, mechanism and field application

Recirculating cooling water (RCW) contains various scale-forming ions, such as Ca2+ and Mg2+, which tend to form the hard scale in the heat transfer process. In this study, a novel method via superconducting high-gradient magnetic separation (S-HGMS) coupling with alkali precipitation for scale inhibition in RCW was proposed, which could achieve efficient removal of total hardness (91.64 %). The scale inhibition mechanism of the S-HGMS coupling is attributed to the increase of ionic hydration shell thickness and the formation of hydrogen bonds, enhancing the solubility of scale-forming ions and diminishing their nucleation rate. Furthermore, this coupling induces a crystalline transformation from recalcitrant calcite to looser aragonite, contributing to the separation of scale from the pipe wall. Significantly, the proposed method was implemented in the field application by establishing a pilot-scale system with a capacity of 800–1000 L/h, which realized a stable reduction in the total hardness of the RCW from 1270 mg/L to below 127 mg/L at a magnetic flow ratio of 0.05 T·s/m. Moreover, the heat exchanger surface scaling was effectively controlled after 71 days of continuous treatment. This study helps promote the industrial application of S-HGMS technology for scale inhibition in high-hardness water.

Threading Subunits for Polymers to Predict the Equilibrium Ensemble of Solid Polymer Electrolytes.

We present a computational method for polymer growth called "threading subunits for polymers (TSP)" that can efficiently sample solid polymer electrolyte structures with extended conformations. The TSP method involves equilibrating subunit (e.g., monomer) conformations that form favorable solvation ion shells, followed by consecutively connecting the subunits and minimizing the structures. The TSP method can sample polymers with good solvent-like conformations and from near-equilibrium structures in which ions are well-dispersed, avoiding unusual ion clustering under ambient conditions. Using the TSP method, the equilibration time can be reduced significantly by effectively sampling the polymer conformations near equilibrium. We anticipate that the TSP method can be applied to simulate various polymer electrolytes.

Tailoring Gene Transfer Efficacy through the Arrangement of Cationic and Anionic Blocks in Triblock Copolymer Micelles.

The arrangement of charged segments in triblock copolymer micelles affects the gene delivery potential of polymeric micelles and can increase the level of gene expression when an anionic segment is incorporated in the outer shell. Triblock copolymers were synthesized by RAFT polymerzation with narrow molar mass distributions and assembled into micelles with a hydrophobic core from poly(n-butyl acrylate). The ionic shell contained either (i) an anionic segment followed by a cationic segment (HAC micelles) or (ii) a cationic block followed by an anionic block (HCA micelles). The pH-responsive anionic block contained 2-carboxyethyl acrylamide (CEAm), while the cationic block comprised 3-guanidinopropyl acrylamide (GPAm). Increasing the molar content of CEAm in HAC and HCA micelles from 6 to 13 mol % improved cytocompatibility and the endosomal escape property, while the HCA micelle with the highest mol % of anionic charges in the outer shell exhibited the highest gene expression. It became evident that improved membrane interaction of the best performing HCA micelle contributed to achieving high gene expression.

Structure and size of complete hydration shells of metal ions and inorganic anions in aqueous solution.

The structures of nine hydrated metal ions in aqueous solution have been redetermined by large angle X-ray scattering to obtain experimental data of better quality than those reported 40-50 years ago. Accurate M-OI and M-(OI-H)⋯OII distances and M-OI(H)⋯OII bond angles are reported for the hydrated magnesium(II), aluminium(III), manganese(II), iron(II), iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions; the subscripts I and II denote oxygen atoms in the first and second hydration sphere, respectively. Reported structures of hydrated metal ions in aqueous solution are summarized and evaluated with emphasis on a possible relationship between M-OI-OII bond angles and bonding character. Metal ions with high charge density have M-OI-OII bond angles close to 120°, indicative of a mainly electrostatic interaction with the oxygen atom in the water molecule in the first hydration shell. Metal ions forming bonds with a significant covalent contribution, as e.g. mercury(II) and tin(II), have M-OI-OII bond angles close to 109.5°. This implies that they bind to one of the free electron pairs in the water molecule. Comparison of M-O bond distances of hydrated metal ions in the solid state with one hydration shell, and in aqueous solution with in most cases at least two hydration shells, shows no significant differences. On the other hand, the X-O bond distance in hydrated oxoanions increases by ca. 0.02 Å in aqueous solution in comparison with the corresponding X-O distance in the solid state. A linear correlation is observed between volume, calculated from the van der Waals radius of the hydrated ion, and the ionic diffusion coefficient in aqueous solution. This correlation strongly indicates that monovalent metal ions, except lithium and silver(I), and singly-charged monovalent oxoanions have a single hydration shell. Divalent metal ions, bismuth(III) and the lanthanoid(III) and actinoid(III) ions have two hydration shells. Trivalent transition and tetravalent metal ions have two full hydration shells and portion of a third one. Doubly charged oxoanions have one well-defined hydration shell and an ill-defined second one.

The mechanisms underlying Li+/Mg2+ separation in ZIF-8 under an electric field from atomistic simulations.

In this study, we explore the mass transfer and separation mechanism of Li+ and Mg2+ confined within the flexible nanoporous zeolite imidazolate framework ZIF-8 under the influence of an electric field, employing molecular dynamics simulation. Our results highlight that the electric field accelerates the dehydration process of ions and underscore the critical importance of ZIF-8 framework flexibility in determining the separation selectivity of the ZIF-8 membrane. The electric field is shown to diminish ion hydration in the confined space of ZIF-8, notably disrupting the orientation of water molecules in the first hydration shells of ions, leading to an asymmetrical ionic hydration structure characterized by the uniform alignment of water dipoles. Furthermore, despite the geometrical constraints imposed by the ZIF-8 framework, the electric field significantly enhances ionic mobility. Notably, the less stable hydration shell of Li+ facilitates its rapid, dehydration-induced transit through ZIF-8 nanopores, unlike Mg2+, whose stable hydration shell impedes dehydration. Further investigation into the structural characteristics of the six-ring windows traversed by Li+ and Mg2+ ions reveals distinct mechanisms of passage: for Mg2+ ions, significant window expansion is necessary, while for Li+ ions, the mechanism involves both window expansion and partial dehydration. These findings reveal the profound impact of the electric field and framework flexibility on the separation of Li+ and Mg2+, offering critical insights for the potential application of flexible nanoporous materials in the selective extraction of Li+ from salt-lake brine.

(Invited) The Effect of Surfactants on Vanadium Electrochemistry in Porous Carbon Electrodes

We present a study of vanadium electrochemistry in porous electrodes with and without sodium dodecyl sulfate (SDS) additives present. Carbon paper and felt electrodes are compared. Carbon felt electrodes are the de facto standard in flow batteries. There are significant differences in the electronic conductivity of these media. The carbon paper has a much higher conductivity than the felt, which has an electronic conductivity similar to the ionic conductivity of the electrolytes used. The latter fact motivates an extension of available theory for polarization curve fitting to explicitly include both electronic and ionic contributions in the porous electrode. We demonstrate agreement between our model and an existing model evaluated at the limit where electrode conductivity is significantly greater than electrolyte conductivity. Our model uses the product of the electrode surface area per volume ratio and the heterogeneous electron transfer rate constant, and the Damköhler number as fitting parameters for carbon paper and felt electrodes. We discuss the effect of SDS additives on kinetics in the context of the cation hydration shell for the vanadium ions. To this point, we apply Marcus-Hush-Chidsey formalism to our porous electrode model to quantify reorganization energies obtained through polarization curve fitting. This work was supported as part of the Breakthrough Electrolytes for Energy Storage (BEES2), an Energy Frontier Research Center funded by the United States. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409.

Hybrid electrolyte with biomass-derived carbon host for high-performance aqueous Zn–S battery

The aqueous Zinc-Sulfur battery (AZSB) utilizes earth-abundant zinc anode along with sulfur cathode, making it a low-cost and safe alternative with decent energy density. In order to tackle the side reactions at the cathode and anode, a hybrid electrolyte is developed by incorporating dimethyl carbonate (DMC) as a co-solvent and iodine as an additive. Incorporating an optimal amount of dimethyl carbonate (DMC) in the aqueous electrolyte does not compromise the conductivity and non-flammability of the AZSB system, yet brings effective changes to the solvation shell of the zinc ions, reducing the free water activity and thus, limiting the water-based side reactions. In addition, the hybrid electrolyte is found to improve the wettability of the sulfur cathode which enhances the reaction kinetics at the cathode. To support the hybrid electrolyte, a low-cost porous carbon material derived from waste jackfruit peel biomass is employed as the sulfur host on the cathode. Combining hybrid electrolyte and biomass-derived porous carbon–sulfur composite allows for an exceptional performance in AZSB, i.e., a capacity of 1167 mAh gS−1 at 0.1 A gS−1, along with an energy density of 502 Wh kgS−1. Even at a high rate of 1 A gS−1, the battery is able to retain 47.6 % capacity after 200 cycles. This innovative electrolyte design, coupled with the incorporation of an inexpensive porous carbon host, significantly enhances the Zn/S electrochemistry, showcasing the immense potential of AZSB for future applications.

Tailoring the solvation shells of dual metal ions for high-performance aqueous zinc ion batteries

For a long time, the issue of dendrites in neutral/mild electrolyte-based aqueous zinc-ion batteries (AZIBs) has been a matter of concern. The dendrites resulting from this problem lead to short-circuit faults and significantly reduce the cycle life, which is quite troublesome. Here, we induce uniform Zn deposition by utilizing the enhanced electrostatic shielding effect of a hybrid additive of Na2SO4 and EDTA. The limited tip-blocking effect of Na+ is due to the higher exchange reaction rate constant (kex) of water molecules in the solvation shell. The coordination of EDTA can provide a more stable solvation shell for Na+, ensuring a stronger blocking effect on Zn deposition at the tip. This enhanced electrostatic shielding effect effectively suppresses the growth of Zn dendrites. In addition, EDTA also enters the solvation shell of Zn2+ and displaces some coordinated water molecules, allowing for more reversible Zn plating/stripping without significant side reactions occurring at the Zn anode.

Exploring the impact of ions on oxygen K-edge X-ray absorption spectroscopy in NaCl solution using the GW-Bethe-Salpeter-equation approach.

X-ray absorption spectroscopy (XAS) is a powerful experimental tool to probe the local structure in materials with the core hole excitations. Here, the oxygen K-edge XAS spectra of the NaCl solution and pure water are computed by using a recently developed GW-Bethe-Salpeter equation approach, based on configurations modeled by path-integral molecular dynamics with the deep-learning technique. The neural network is trained on abinitio data obtained with strongly constrained and appropriately normed density functional theory. The observed changes in the XAS features of the NaCl solution, compared to those of pure water, are in good agreement between experimental and theoretical results. We provided detailed explanations for these spectral changes that occur when NaCl is solvated in pure water. Specifically, the presence of solvating ion pairs leads to localization of electron-hole excitons. Our theoretical XAS results support the theory that the effects of the solvating ions on the H-bond network are mainly confined within the first hydration shell of ions, however beyond the shell the arrangement of water molecules remains to be comparable to that observed in pure water.