Aqueous Cl Research Articles

Revealing the Molecular Origin of Anisotropy around Chloride Ions in Bulk Water.

A clear picture of the local solvation structure around halide anions in liquid water remains elusive. This discussion has been stimulated by pioneering simulation results that proposed a "hydrophobic cavity" around anions in the bulk, which is analogous to air at the air-water interface. However, there is also sound experimental and theoretical evidence that halide ions are rather symmetrically solvated in the bulk, leading to a different viewpoint. Using extensive ab initio molecular dynamics simulations of an aqueous Cl- solution, we indeed find an anisotropic arrangement of H-bonded versus interstitial water molecules. The latter are not H-bonded to the anions and thus do not couple much electronically to Cl-. The resulting purely electronic anisotropy of the local solvation environment correlates with that structural anisotropy, which however should not be understood as an empty cavity─as it would be at the air-water interface─but rather contains interstitial water molecules.

Study on the onset mechanism of bio-blister degradation of polyolefin by diatom attachment in seawater

It is essential to develop a mechanism for lowering the molecular weight of polyolefins to achieve biodegradation in seawater. In this study, a polypropylene/polylactic acid blend sample was first subjected to photodegradation pretreatment, and it was confirmed that in pure water, the acid generated promotes the polypropylene degradation (autoxidation), while in alkaline seawater, the promotion was inhibited by a neutralization reaction. In the autoxidation of polyolefins in alkaline seawater, aqueous Cl− was also the inhibitor. However, we found that autoxidation could be initiated even in seawater by lowering the pH and using dissociation of ClOH (called blister degradation). The blister degradation mechanism enabled autoxidation, even in seawater, by taking advantage of the ability of diatoms to secrete transparent exopolymer particles (TEP) to prevent direct contact between the surface layer of polyolefins and alkaline seawater. We named blister degradation in seawater with diatoms as bio-blister degradation and confirmed its manifestation using linear low-density polyethylene (LLDPE)/starch samples by SEM, IR, DSC and GPC analysis.

CsPbBr3 nanocrystals as luminescent probe for in situ detection of chloride and iodide ions in water

All-inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) Perovskite nanocrystals (PNCs) are promising new luminescent nanomaterials. However, PNCs are less stable in ambient environments. The fully encapsulated protective layer greatly improves the stability but limits direct contact with substances in the environment, leading to great challenges for luminescent probe applications. We developed a simple approach that hydrogen-bond cross-linking reinforcement to deal with the challenge. Target ACD-PNCs, which use β-CD (β- cyclodextrin) as the ligand with addition of Arginine, were prepared by adding arginine to an ethanol solution of CsPbBr3 stabilized by β-CD. The ACD-PNCs have a luminescence efficiency of 82% and show good stability in external environments including high temperature, humidity, and ethanol–water mixed solvents. It is worth noting that neither arginine nor cyclodextrin alone could have allowed PNCs to perform so well. More interestingly, the hydrogen-bond network permits the passage of chloride and iodide ions. Through the response of luminescence color upon ion exchange, the ACD-PNCs can detect aqueous Cl− and I− with good selectivity and sensitivity. Under optimum conditions, the LOD and % RSD were determined as 3.2*10−6 M and 5.7% for Cl−, 9.0*10−6 M and 6.7% for I−, respectively. To identify halide ions in samples like sweat, saliva, and kelp, conveniently prepared ACD-PNCs test strips were employed. This work provides insights into the design and development of perovskite probes capable of detection in aqueous solution, and also demonstrates the importance of rapidly forming hydrogen-bonding networks when studying such sensing systems.

Rapid detection of urine chloride enabled by ion exchange in hydrophilic lead halide perovskite nanocrystals.

The rapid and precise detection of chloride ions in biosystems is of great importance for clinical diagnosis. In this work, hydrophilic CsPbBr3 perovskite nanocrystals (PNCs) with a high photoluminescence (PL) quantum yield (QY) of 59% (0.5 g L-1) are successfully achieved through the passivation of micellar glycyrrhizic acid (GA), which enables good dispersion of PNCs in ethanol. Due to the ionic nature and halogen-dominated band edge, PNCs exhibit fast ion-exchange and halogen-dependent optical properties. As a result, colloidal GA-capped PNC ethanol solution shows a continuous PL shift once aqueous Cl- with different concentrations is added. This fluorescence sensor shows a wide linear detection range (2-200 mM) of Cl-, short response time (∼1 s), and low limit of detection (1.82 mM). Because of the encapsulation of GA, good water and pH stability, and anti-interference performance are observed for the GA-capped PNC-based fluorescence sensor. Our findings provide an insight into the biosensor applications of hydrophilic PNCs.

Over- and underpotential deposition of copper from a deep eutectic solvent: Pt(1 1 1) single crystal versus polycrystalline Pt substrates

• Deposition/dissolution of Cu on Pt from ethaline occur in one-electron reactions. • A full (1x1) monolayer of Cu adatoms is formed on Pt(111) in ethaline. • No voltammetric signals of Cu UPD were observed for Pt(poly) in ethaline. • Surface structure determines the mechanism and rate of Cu OPD at the initial stages. • Cu OPD on Pt(111) and Pt(poly) in ethaline occurs via 2D and 3D growth, respectively. Deep eutectic solvents (DESs) attract ever greater interest as nonaqueous media for the electrodeposition of metals and alloys. This work investigates the initial stages of Cu electrodeposition from DES representing a mixture of choline chloride and ethylene glycol (ChCl:EG) with a (1:2) molar ratio that contains CuCl or CuCl 2 salts. These studies were performed by means of cyclic voltammetry and scanning probe microscopy on single-crystalline Pt(111) and polycrystalline Pt(poly) electrodes. Additional experiments on Cu deposition were carried out using an aqueous Cl - -rich solution (3 M NaCl + 0.01 M CuCl). The process of Cu underpotential deposition (UPD) on the surface of Pt(111) in DES is observed for the first time. It is proposed that a complete (1x1) monolayer of Cu adatoms is formed at potentials more positive than the onset of overpotential deposition (OPD). The comparison of results for Pt(111) and Pt(poly) in ChCl:EG (1:2) and in the aqueous 3 M NaCl solution confirms that the surface morphology and (co)adsorption of solution components play an important role in the Cu UPD process. In DES, as well as in the aqueous solutions containing CuCl, Cu OPD occurs via the reduction of Cu(I) ions. The Cu(I)/Cu(II) redox transition was observed at significantly more positive potentials. We conclude on the basis of voltammetry and in situ scanning tunneling microscopy (STM) data that the mechanism of Cu electrodeposition in DES is determined by the surface structure. STM data demonstrate the layer-by-layer growth of a two-dimensional Cu deposit on Pt(111), while the resulting Cu deposit on Pt(poly) is characterized by a grain-like morphology. We also demonstrate that the mechanism of Cu OPD affects the initial deposition rate under conditions of diffusion limitations.

Synergistic effects of chloride anions and carboxylated cellulose nanocrystals on the assembly of thick three-dimensional high-performance polypyrrole-based electrodes

Porous three-dimensional (3D) structures generally improve the performance of electrodes by increasing their active surface area and the diffusion speed of electrolyte ions during charging/discharging. Three-dimensional polypyrrole (PPy) based films were created by electrodepositing PPy in the presence of varying amounts of chloride anions (Cl−) and polyanionic ribbonlike nanoparticles (carboxylated cellulose nanocrystals (CNC-COO−)) as scaffold material. The assembly mechanism of the 3D PPy electrodes combines the effect of different nucleation and growth mechanisms during electropolymerization and deposition of the formed PPy with CNC-COO− and with Cl−. The highest area capacitance of these electrode materials was 1.39 F cm−2 (150.2 F g−1) at a current density of 1 mA cm−2 (0.1 A g−1). More importantly, at a high current density of 20 mA cm−2 (2.2 A g−1), the thick (ca. 130 μm), 3D, and high mass loading (9.2 mg cm−2) Cl−:CNC-COO−/PPy films exhibited an excellent areal capacitance of 0.85 F cm−2 (70.8 F g−1), increasing about 16% over CNC-COO−/PPy films prepared without Cl− present during electrodeposition. In addition, an aqueous Cl−:CNC-COO−/PPy (with Cl−:CNC-COO− = 2.0) symmetric supercapacitor had an outstanding energy density of 41.15 μWh cm−2 (4.46 Wh kg−1) and excellent cycling stability, while even improving on its original areal capacitance (to 111.2% of its original capacitance) after cycling 3000 cycles at 8 mA cm−2, indicating their potential in energy storage devices.

Photo aging of polypropylene microplastics in estuary water and coastal seawater: Important role of chlorine ion

Photo aging of microplastics (MPs) in water environment are relevant to free radical associated polymer chain reaction, and various photo chemical reactive constitutes (i.e., Cl−, Br−, NO3−, CO32−, and natural organic matters) would affect the reaction, leading to a great difference in the photo aging mechanism of MPs between freshwater and seawater system. This study investigated light induced photo aging process of polypropylene (PP) MPs in ultrapure water, estuary water, and seawater. Results revealed that the aging rate of PP MPs was significantly decreased in estuary water and seawater compared with that in ultrapure water, leading to a longer resistance time after emission in marine environment. Besides, lower carbonyl index was found with the increased aqueous Cl− concentration, highlighting the important role of Cl− in the inhibitory effect for PP MPs aging process in seawater. This is due to the formation of Cl2•− in seawater which could react with HO2• and prevent the formation of O2•−, thus inhibit the photo aging process of PP MPs under light irradiation. The finding in this study clearly indicates the impact of the water matrices on the photo aging rate of MPs in natural water.

Transport of chloride and deuterated water in peat: The role of anion exclusion, diffusion, and anion adsorption in a dual porosity organic media

The dual-porosity structure of peat and the extremely high organic matter content give rise to a complex medium that typically generates prolonged tailing and early 50% concentration breakthrough in the breakthrough curves (BTCs) of chloride (Cl−) and other anions. Untangling whether these observations are due to rate-limited (physical) diffusion into inactive pores, (chemical) adsorption or anion exclusion remains a critical question in peat hydrogeochemistry. This study aimed to elucidate whether Cl− is truly conservative in peat, as usually assumed, and whether the prolonged tailing and early 50% concentration breakthrough of Cl− observed is due to diffusion, adsorption, anion exclusion or a combination of all three. The mobile-immobile (MiM) dual-porosity model was fit to BTCs of Cl− and deuterated water measured on undisturbed cores of the same peat soils, and equilibrium Cl− adsorption batch experiments were conducted. Adsorption of Cl− to undecomposed and decomposed peat samples in batch experiments followed Freundlich isotherms but did not exhibit any trends with the degree of peat decomposition and sorption became negligible below aqueous Cl− concentrations of ~310 mg L−1. The dispersivity determined by fitting the Cl− BTCs whether assuming adsorption or no adsorption were significantly different than determined by the deuterated water (p < .0001). However, no statistical differences in dispersivity (p = .27) or immobile water content (p = .97) was observed between deuterated water and Cl− when accounting for anion exclusion. A higher degree of decomposition significantly increased anion exclusion (p < .0001) but did not influence the diffusion of either tracer into the immobile porosity. Contrary to previous assumptions, Cl− is not truly conservative in peat due to anion exclusion, and adsorption at higher aqueous concentrations, but the overall effect of anion exclusion on transport is likely minimal.

Determination of Chlorine in Plastics via SrCl by Solid-Sampling High-Resolution Continuum Source Graphite Furnace Molecular Absorption Spectrometry

Solid sampling high resolution continuum source molecule absorption spectrometry (SS-HR-CS MAS) was applied for the determination of chlorine in plastic using the strontium monochloride (SrCl) molecule. For this purpose, 10 µL of 20 g L−1 strontium (prepared from Sr(NO3)2) solution were pipetted with aqueous Cl standards or 0.05 to 4 mg of slivered plastic samples on a platform and introduced into the furnace. Chlorine was determined with the molecular absorption of SrCl at 635.862 nm using 1100 °C and 2200 °C for the pyrolysis and vaporization temperatures, respectively. Aqueous standards were used for calibration. The accuracy of the method was evaluated using a certified polyethylene reference material. The limit of detection and characteristic mass values of the method were 2.5 ng and 0.4 ng, respectively. The chlorine concentrations in various polyethylene beverage containers were determined.

Synergistic extraction and separation of Fe(III) and Zn(II) using TBP and D2EHPA

ABSTRACTWaste chloride pickle liquors from hot-dip galvanizing plants, steel plants and flue dust contain reasonable amounts of heavy metals such as Zn, Cr, Ni, etc. Iron is invariably associated with most of these materials and comes into solution during leaching. Thus, the synergistic extraction of zinc(II) and iron(III) from leach solutions in tri-n-butyl phosphate (TBP)–di(2-ethylhexyl) phosphoric acid (D2EHPA) system diluted in kerosene was investigated. The Zn and Fe concentrations in the leach liquor used in the present study were 2 g/L. Experiments were carried out in the pH range of 0.5–4.0, temperature of 25°C, using sole D2EHPA, sole TBP and D2EHPA–TBP mixtures at different ratios. Results showed that the co-extraction of zinc(II) and iron(III) increased with increasing equilibrium pH using D2EHPA. It is demonstrated that the mixtures of TBP and D2EHPA are more efficient and selective than D2EHPA alone. At low pH values, the separation factor is low when pure D2EHPA is used as an extractant; however, using TBP as a synergist, the separation factor increases and results in a better separation of zinc from iron. Increasing TBP to D2EHPA ratios in the organic phase caused a slight shift to the right in the extraction isotherm of iron and a marked shift to the right in the extraction isotherm of zinc, and the maximum separation factor of 13.3 × 103 was achieved at a TBP to D2EHPA volume ratio of 4:1 (0.58 M TBP: 0.12 M D2EHPA). Furthermore, the effect of equilibrium pH, organic to aqueous phase ratio and Cl− concentration on the selective extraction was investigated. Using two extraction stages at the O/A ratio of 2:1 and pHe (equilibrium pH) of 3 and 1 for zinc and iron, respectively, 99% of zinc(II) and 96.25% of iron(III) were extracted.

Hydration structure of Na+, K+, F−, and Cl− in ambient and supercritical water: A quantum mechanics/molecular mechanics study

The ion solvation in aqueous solution under different temperatures and pressures governs many important biological, geological, and chemical processes. In this work, we present a theoretical study of hydration structures of several alkali metal cations and halide anions, Na+, K+, F−, and Cl−, in ambient and supercritical water through quantum mechanics/molecular mechanics (QM/MM) simulations. It is shown that our calculated first peak or minimum positions for the radial distribution functions of ion‐water pairs and hydration numbers as well as hydrogen bond numbers are in good agreements with available experimental determinations or other high‐level QM/MM simulated results. We reveal that under supercritical condition does not reduce much comparing to that under ambient condition due to the inherent local clustering effect although the bulk density decreases evidently. After the investigation of the angular distribution of oxygen‐ion‐oxygen within the first hydration sphere, it is shown that Na+ or F− in ambient water tends to be six‐fold coordinated in a octahedral‐like structure. Through the analysis of ion‐oxygen‐hydrogen angle distributions within the first hydration spheres of F− and Cl−, we also find that strong hydrogen bonds exist in ambient aqueous F− and become weakened under supercritical condition, whereas weak hydrogen bonds exist in ambient aqueous Cl− and become nearly disappeared under supercritical condition. © 2013 Wiley Periodicals, Inc.

Evaluation of 1,2-dimethyl-3-hydroxy-4-pyridinecarboxylic acid and of other 3-hydroxy-4-pyridinecarboxylic acid derivatives for possible application in iron and aluminium chelation therapy

Four new possible chelating agents for iron and aluminium, 1,2-dimethyl-3-hydroxy-4-pyridinecarboxylic acid (DT712), 3-hydroxy-1,2,6-trimethyl-4-pyridinecarboxylic acid, 2,6-dimethyl-3-hydroxy-4-pyridinecarboxylic acid, and 2-ethyl-3-hydroxy-1-methyl-4-pyridinecarboxylic acid, were synthesized, and their complex formation with Fe(III) and Al(III) was studied by potentiometry, UV–Vis, 1H NMR, and electrospray mass spectrometry (ESI-MS). Number, stoichiometry, and stability constants of metal–ligand complexes were obtained at 25°C in aqueous (Na)Cl 0.6m. DT712 is the most promising hydroxypyridinecarboxylic acid considered so far for iron chelation therapy, as it forms the strongest Fe(III) complexes. This compound was further investigated to better clarify its possible behaviour in vivo with particular respect to iron chelation therapy. UV–Vis measurements were performed to determine the kinetics by which DT712 extracts Fe(III) from transferrin. DT712 resulted to have better kinetic properties than existing iron chelators. Ternary metal/DT712/citric acid complexes were studied by ESI-MS to check the competition with a typical low molecular weight ligand in the blood. The formation of only binary Fe(III)/DT712 and Al(III)/DT712 complexes (and ternary complexes in aged solutions), suggests that DT712 effectively compete with citric acid in the metal complexation. Standard reduction potentials of Fe(III)/DT712 complexes, and the kinetic constants of complex formation, were obtained by cyclic voltammetry. Accordingly, no redox cycling is expected to occur at in vivo conditions, and Fe(III)/DT712 complex formation should not be kinetically limited. On the basis of the present results, DT712 is proposed as candidate for iron chelation therapy.

A variable ultra-short-pathlength solution cell for XAFS transmission spectroscopy of light elements

An X-ray absorption fine-structure spectroscopy (XAFS) cell that is suitable for solution-phase studies of the light elements in the series from Na(+) and Ca(2+) is described. This cell has an ultra-short pathlength that can be remotely adjusted using a miniature stepper-motor drive and thereby readily provides transmission pathlengths in the range from submicrometer to several hundred micrometers. The flexibility to vary the pathlength enables acquisition of high-quality XAFS spectra and also allows one to check for potential distortions in the spectra from thickness effects. The primary components are mostly commercially available optical parts. The performance of this device is demonstrated at the Cl K-edge (2.8 keV) for several different aqueous Cl(-) solutions.

Oxygen isotope effects associated with substitution of Al for Fe in synthetic goethite: Some experimental evidence and the criterion of oxygen yield

Measurements of the fractional abundance (m) of high temperature nonstoichiometric (HTN) hydrogen in goethite are shown to predict the reduction in O2 yield associated with removal of HTN oxygen by routine pre-treatment of a sample with BrF5 at 22°C. The predicted relationship between smaller O2 yields and m is linear and defines an “oxygen yield limit” (OYL), which is introduced for use in oxygen isotope analyses of goethite. The OYL sets lower limits for O2 yields that would be consistent with: (1) removal of all HTN oxygen during pre-treatment and (2) complete recovery of the goethite structural oxygen during subsequent reaction with BrF5 at 450°C. Measured O2 yields that are less than those predicted by the OYL are anomalously low and indicate probable partial loss of structural oxygen during pre-treatment at 22°C. After such partial loss, measured δ18O values of the residue are more negative than the actual δ18O of the total structural oxygen. Therefore, the OYL can be used to distinguish between robust and suspect δ18O analyses of goethite.This OYL criterion was applied to some newly analyzed synthetic goethites in which Al substitutes for Fe up to mole fractions (XAl) of ∼0.13. As expected, the robust δ18O values indicate that 1000ln18α (where, 18α=[18O/16Omineral]/[18O/16Owater]) increases with increasing XAl, but comparison of these results with the predictions of a published solid solution model suggests that the relationship between 1000ln18α and XAl is sensitive to very high pH and possibly to the concentration of aqueous Cl− during synthesis of goethite. The cause of the apparent sensitivity to Cl− remains unknown. The various relationships are: (A)T=42°C,pH=1.5–2.5,[Cl-]≈0.16M:1000ln18α=18±5XAl+1.8±0.3(B)low-pH model,[Cl-]=0.00M:1000ln18α=13(±2)XAl+4.1(±0.3)(C)T=22°C,pH=14,[Cl-]=0.00M:1000ln18α=5(±3)XAl+1.6(±0.3)(D)low-pH model,[Cl-]=0.00M:1000ln18α=13(±2)XAl+6.5(±0.3)However, for natural freshwater goethites, the low-pH, no-Cl, solid solution model (e.g., isothermal equations B and D) best predicts the oxygen isotope effects associated with substitution of Al for Fe. Thus, for goethites from freshwater systems with acidic to circum-neutral pH, the following expression can be used to calculate end member goethite (FeOOH) δ18O values from the measured values of δ18O and XAl:δ18OFeOOH=δ18Omeasured-13(±2)XAlBecause the slope of the preceding expression appears to be relatively insensitive to temperature, the equation should be applicable over the range of temperatures at which goethite commonly crystallizes in natural systems (0°C⩽T⩽∼70°C). However, the value of δ18OFeOOH is sensitive to temperature via the temperature dependence of 1000ln18α for pure goethite at acidic to circum-neutral pH in freshwaters as follows (T in degrees Kelvin):1000ln18α=1.66×106T2-12.6The results of this study affirm the need to correct measured δ18O values of goethite for the effects of substituent Al to obtain useful paleoenvironmental information, and they support the existing model for doing so.

The Potential Feasibility of Chlorinic Photosynthesis on Exoplanets

The modern search for life-bearing exoplanets emphasizes the potential detection of O(2) and O(3) absorption spectra in exoplanetary atmospheres as ideal signatures of biology. However, oxygenic photosynthesis may not arise ubiquitously in exoplanetary biospheres. Alternative evolutionary paths may yield planetary atmospheres tinted with the waste products of other dominant metabolisms, including potentially exotic biochemistries. This paper defines chlorinic photosynthesis (CPS) as biologically mediated photolytic oxidation of aqueous Cl(-) to form halocarbon or dihalogen products, coupled with CO(2) assimilation. This hypothetical metabolism appears to be feasible energetically, physically, and geochemically, and could potentially develop under conditions that approximate the terrestrial Archean. It is hypothesized that an exoplanetary biosphere in which chlorinic photosynthesis dominates primary production would tend to evolve a strongly oxidizing, halogen-enriched atmosphere over geologic time. It is recommended that astronomical observations of exoplanetary outgoing thermal emission spectra consider signs of halogenated chemical species as likely indicators of the presence of a chlorinic biosphere. Planets that favor the evolution of CPS would probably receive equivalent or greater surface UV flux than is produced by the Sun, which would promote stronger abiotic UV photolysis of aqueous halides than occurred during Earth's Archean era and impose stronger evolutionary selection pressures on endemic life to accommodate and utilize halogenated compounds. Ocean-bearing planets of stars with metallicities equivalent to, or greater than, the Sun should especially favor the evolution of chlorinic biospheres because of the higher relative seawater abundances of Cl, Br, and I such planets would tend to host. Directed searches for chlorinic biospheres should probably focus on G0-G2, F, and A spectral class stars that have bulk metallicities of +0.0 Dex or greater.

Structure of Hydronium (H3O+)/Chloride (Cl−) Contact Ion Pairs in Aqueous Hydrochloric Acid Solution: A Zundel-like Local Configuration

A comprehensive analysis of the H(3)O(+) and H(2)O structure in the first solvation shell about Cl(-) in aqueous HCl solutions is reported from X-ray absorption fine structure (XAFS) measurements. Results show increasing degree of contact ion pairing between Cl(-) and H(3)O(+) as the HCl concentration increases from 6.0 m, 10.0 m, and finally 16.1 m HCl (acid concentrations are expressed as molality or mole HCl/1000 g water). At the highest acid concentration there are on average, approximately 1.6 H(3)O(+) ions and 4.2 H(2)O's in the first shell about Cl(-). The structure of the Cl(-)/H(3)O(+) contact ion pair is distinctly different from that of the H(2)O structure about Cl(-). The Cl-O bond length (2.98 A) for Cl(-)/H(3)O(+) is approximately 0.16 A shorter than the Cl(-)/H(2)O bond. The bridging proton resides at an intermediate position between Cl and O at 1.60 A from the Cl(-) and approximately 1.37 A from the O of the H(3)O(+). The bridging-proton structure of this contact ion pair, (Cl-H-OH(2)), is similar to the structure of the water Zundel ion, (H(2)O-H-OH(2)(+)). In both cases there is a shortened Cl-O or O-O bond, and the intervening proton bond distances are substantially longer than for the covalent bonds of either HCl or H(2)O. A detailed structural analysis of the aqueous chloride species, Cl(-)/(H(2)O)(n), was also completed as part of this study in order to understand the relative importance of various XAFS photoelectron scattering paths. For aqueous Cl(-) the measured Cl-O and Cl-H distances of 3.14 A and 2.23 A, respectively, are in excellent agreement with earlier neutron and X-ray diffraction results. Overall, these results significantly improve our understanding of the interaction of H(3)O(+) with Cl(-). The results are of interest to fundamental physical chemistry and they have important consequences in biochemical, geochemical, and atmospheric processes.

Specific Ion Effects of Salt Solutions at the CaF2/Water Interface

Calcium fluoride is a slightly soluble compound commonly extracted from ores via flotation at elevated pH, where surfactant molecules bind with hydroxylated surface sites. The addition of F-(aq) suppresses surfactant adsorption by replacing these sites. In this paper, we look at the effects of aqueous Cl-, Br-, F-, and SO4(2-) on the water structure at the CaF2/H2O interface at a pH where surface hydroxylation has not yet occurred. Using static and time-resolved vibrational sum-frequency spectroscopy (VSFS), we find that aqueous Cl- and Br- have only electrostatic screening effects on the interface and do not perturb the interfacial water or surface structure. Sulfate, which we find to be strongly attracted to the interface, affects the interfacial water more than Cl- or Br-. This is in contrast to F- ions that directly interact with the surface and alter the water structure and bonding at the CaF2 surface in addition to screening the surface charge.

Crystal structure refinement of synthetic Ca0.43 Sr0.57 [SiO3 ]-walstromite and walstromitefluid CaSr distribution at upper-mantle conditions

(Ca,Sr)-walstromite with the mean composition Ca 0.43 Sr 0.57 [SiO 3 ] was synthesized at 4 GPa/600 °C and X Sr bulk = 0.875 in presence of a 1 molar aqueous (Ca,Sr)Cl 2 fluid together with monoclinic (Ca,Sr)-lawsonite, grossular and strontianite. Intracrystalline as well as walstromite–mineral and walstromite–fluid Ca–Sr distribution was determined by analysing the product fluid with ICP–OES for Ca and Sr concentrations, solids by electron-microprobe analysis, powder XRD-analysis with Rietveld refinement and single-crystal X-ray diffraction. Based on the single-crystal X-ray diffraction data the crystal structure of (Ca,Sr)-walstromite was solved in space group P -1 with refined lattice parameters a = 6.7580(9) A, b = 9.464(3) A, c = 6.7507(16) A, α = 83.22(2)°, β = 76.83(2)°, γ = 70.33(2)°, and V = 395.46(17) A 3 . The data indicate that (Ca,Sr)-walstromite has slightly smaller volume and A-sites than the polymorph (Ca,Sr)-wollastonite-II over the entire compositional range. Coordination numbers and mean bond lengths for the three A-sites in Ca 0.43 Sr 0.57 -walstromite are [VIII] A1–O>= 2.588 A, [VI] A2–O>= 2.369 A, and [VII] A3–O>= 2.660 A. The smaller volume suggests that (Ca,Sr)-walstromite is the high- P /low- T polymorph. The data show extreme intracrystalline fractionation of Sr within the (Ca,Sr)-walstromite solid solution series with exchange coefficients K D (Sr – Ca) site1 – site2 defined as (Sr/Ca) site1 /(Sr/Ca) site2 of K D (Sr–Ca) A3–A1 = 21, K D (Sr–Ca) A3–A2 = 2400, and K D (Sr–Ca) A1–A2 = 114. The walstromite–mineral and walstromite–fluid Ca–Sr distribution indicates notable fractionation of Sr into the coexisting phases lawsonite, strontianite and fluid compared to (Ca,Sr)-walstromite. Grossular has only very minor amounts of Sr. Exchange coefficients K D(Sr–Ca) phase1–phase2 = [(Sr/Ca) phase1 ] n /[(Sr/Ca) phase2 ] m with n and m being the stoichiometric coefficients of the respective exchange reaction are 0.00068 for walstromite–fluid, 0.000011 for walstromite–lawsonite and walstromite–strontianite, and 31.8 for walstromite–grossular.

Potentiometric Response of a Neutral-carrier-based Membrane to Aqueous Mercury in Cl−-rich Media

The unique potentiometric response of mercury sensors was investigated in aqueous Cl(-)-rich media, which are often encountered in natural, especially biological samples. The conventional neutral-carrier-based Hg(II)-ISEs are not practically useful because the Cl(-) concentrations in natural aqueous samples are normally too high for mercury to be present in the form of Hg(2+). Negative potentiometric slopes, which are the opposite behavior of the previously reported Hg(II)-ISEs, were experimentally confirmed and quantitatively reasoned based on the aqueous solution equilibrium of Hg(2+).

Perchlorate production by ozone oxidation of chloride in aqueous and dry systems

Overwhelming evidence now exists that perchlorate is produced through natural processes and can be ubiquitously found at environmentally relevant concentrations in arid and semi-arid locations. A number of potential production mechanisms have been hypothesized and ClO 4 − production by ozone oxidation of surface bound Cl − was demonstrated. However, no information concerning the impact of concentration, final reaction products distribution, impact of reaction phase, or oxidation of important oxychlorine intermediates has been reported. Using IC-MS–MS analysis and replicate oxidation experiments, we show that exposing aqueous solutions or Cl − coated sand or glass surfaces to O 3 (0.96%) generated ClO 4 − with molar yields of 0.007 and 0.01% for aqueous Cl − solutions and 0.025 and 0.42% for Cl − coated sand and glass, respectively. Aqueous solutions of Cl − produced less ClO 4 − than Cl − coated sand or glass as well as a higher ratio of ClO 3 − to ClO 4 −. Reduction of the initial Cl − mass resulted in substantially higher molar yields of ClO 4 − and ClO 3 −. In addition, alkaline absorbers that captured gaseous products contained substantial quantities of Cl −, ClO 3 −, and ClO 4 −. Solutions of possible oxychlorine intermediates (OCl − and ClO 3 −) exposed to O 3 produced only scant amounts of ClO 4 − while a ClO 2 − solution exposed to O 3 produced substantial molar yields of ClO 4 − (4% molar yield). Scanning electron microscopy coupled with energy energy-dispersive X-ray analysis demonstrated a significant loss of Cl − and an increase in oxygen on the Cl − coated silica sand exposed to O 3. While the experimental conditions are not reflective of natural conditions this work clearly demonstrates the relative potential of Cl − precursors in perchlorate production and the likely importance of dry aerosol oxidation over solution phase reactions. It also suggests that ClO 2 − may be a key intermediate while ClO 3 − and OCl − are unlikely to play a significant role.