Aqueous Perchlorate Research Articles

Rate and extent of aqueous perchlorate removal by iron surfaces.

The rate and extent of perchlorate reduction on several types of iron metal was studied in batch and column reactors. Mass balances performed on the batch experiments indicate that perchlorate is initially sorbed to the iron surface, followed by a reduction to chloride. Perchlorate removal was proportional to the iron dosage in the batch reactors, with up to 66% removal in 336 h in the highest dosage system (1.25 g mL(-1)). Surface-normalized reaction rates among three commercial sources of iron filings were similar for acid-washed samples. The most significant perchlorate removal occurred in solutions with slightly acidic or near-neutral initial pH values. Surface mediation of the reaction is supported by the absence of reduction in batch experiments with soluble Fe2+ and also by the similarity in specific reaction rate constants (kSA) determined for three different iron types. Elevated soluble chloride concentrations significantly inhibited perchlorate reduction, and lower removal rates were observed for iron samples with higher amounts of background chloride contamination. Perchlorate reduction was not observed on electrolytic sources of iron or on a mixed-phase oxide (Fe3O4), suggesting that the reactive iron phase is neither pure zerovalent iron nor the mixed oxide alone. A mixed valence iron hydr(oxide) coating or a sorbed Fe2+ surface complex represent the most likely sites for the reaction. The observed reaction rates are too slow for immediate use in remediation system design, but the findings may provide a basis for future development of cost-effective abiotic perchlorate removal techniques.

Kinetics and mechanism of oxidation of Chitosan Polysaccharide by Permanganate Ion in Aqueous Perchlorate Solutions

The kinetics of oxidation of chitosan as polysaccharide by permanganate in aqueous perchlorate media at a constant ionic strength was found to have second-order overall kinetics and to be first-order in the concentration of both reactants, the results obtained showed that the reaction is acid catalysed.

Kinetics and mechanism of oxidation of chitosan polysaccharide by permanganate ion in aqueous perchlorate solutions

Kinetics and mechanism of oxidation of chitosan polysaccharide by permanganate ion in aqueous perchlorate solutions

Modification of Electronic Structure of Mesoscopic Perchlorate-Doped Polypyrrole Films by Ion Irradiation

The effects of low-energy (1−3 keV) argon ion irradiation on a 100 nm thick polypyrrole film deposited potentiostatically in an aqueous perchlorate solution have been studied by X-ray photoelectron spectroscopy (XPS). Dramatic spectral changes in the valence band structure and Cl 2p region with increasing ion impact energy and total ion dose have been observed for the perchlorate-doped conductive polymer surface. Higher impact energy (3 keV) is found to be more effective in modifying the polymer backbone, particularly in the breakage and formation of terminal bonding units, while higher ion flux (for impact energy above 1 keV) appears to produce complete dissociation of the perchlorate counterions, leaving behind only Cl atoms. These observations are also consistent with the spectral changes in the C 1s, N 1s, and O 1s regions observed under different ion irradiation conditions.

Determination of recent antidepressant citalopram in human plasma by liquid chromatography—Fluorescence detection

A reliable and sensitive high-performance liquid chromatographic method for the determination of the recent antidepressant citalopram and two metabolites in human plasma has been developed. Fluorescence detection at 300 nm was used, exciting at 238 nm. Separation was obtained using a reversed-phase column (C18, 250 × 3.0 mm i.d., 5 μm) and a mobile phase. 40% acetonitrile: 60% aqueous tetramethylammonium perchlorate (pH 1.9). Calibration curves were linear over a working range: 5–300 ng mL−1 for citalopram, 2.5–150.0 ng mL−1 for desmethylcitalopram and 2.5–50.0 ng mL−1 for didesmethylcitalopram. The limits of quantitation (LOQ) were 1.5 ng mL−1 for citalopram and desmethylcitalopram and 2.0 ng mL−1 for didesmethylcitalopram. Precision data, as well as accuracy, were satisfactory and no interference from different psychotropic drugs was found. The method was therefore suitable for therapeutic drug monitoring of citalopram and its active metabolites in plasma of depressed patients.

Outer-sphere electron transfer reactions of aqua(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato) nickel(II) and (III).

The outer-sphere oxidation of the nickel(II) complex of the deprotonated pendant-arm macrocycle, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetate, [NiL1(OH2)]+ by bis-(1,4,7-triazacyclononane)nickel(III), [Ni(tacn)2]3+ has been studied in aqueous perchlorate media. The reaction displays reversible second-order behaviour and the kinetic study reveals the forward and reverse rate constants for the reaction: [Formula: see text] The kinetics show the forward reaction to be acid dependent, a feature that is attributed to protonation of the acetato group of the nickel(II) complex. Using Marcus theory, the self-exchange rate for the [NiL1(OH2)]+/2+ couple has been calculated. The nickel(II/III) electron transfer is a reversible one electron process with E° = 1.04 V (vs. S.H.E.). The formation of the authentic nickel(III) product has been confirmed by esr spectroscopy. The kinetics of reduction of the [NiL1(OH2)]2+ species by Fe2+(aq) exhibits a second-order rate law, the reaction being independent of acid. Using the calculated self-exchange rate for the nickel complex, its reaction with Fe2+(aq) has been examined in terms of an inner- versus outer-sphere mechanism. Key words: nickel(III), pendant-arm macrocycles, hexaaquairon(II), outer sphere, kinetics, Marcus theory.

Solvent Extraction of Heavy Lanthanides(III) with 5,7‐Dibromo‐8‐hydroxyquinoline from Aqueous Perchlorate Solution

The extraction of Tb(III), Dy(III), Ho(III), Er(III), Tm(III), and Yb(III) with 5,7‐dibromo‐8‐hydroxyquinoline (Hdbq or HA) in chloroform from aqueous perchlorate solutions was investigated. The formation of the LnA3 species (where Ln = Tb, Dy, Ho, Er, Tm, and Yb) in the organic phase was supported by the data. The parameters of the extraction processes were determined, and the separation factors between two adjacent lanthanides(III) were calculated.

Dependence of the mobility of tracer ions in aqueous perchlorate solutions on the hydrogen ion concentration

The dependence of the absolute individual ion mobility (AIIM) of the carrier-free radioactive ions [137Cs]Cs+, [201Tl]Tl+ and [57Co]Co2+ on the hydrogen ion concentration in aqueous perchlorate electrolyte mixtures was studied by means of the electromigration technique. The AIIM of the radioactive ions was found to decrease as the hydrogen ion concentration of the electrolyte mixture increases. Above pH > 4 there is a fairly good agreement between experimental and calculated values. Below pH 4 the experimentally observed decrease of the AIIM is not explained by the extended Debye–Huckel–Onsager limiting law. The effect can possibly be explained by a change of the dynamical properties of electrolyte bulk water due to the increasing presence of an excess of hydrated protons in the bulk solution. From the variation of the rotational reorientation time of bulk water molecules in HClO4 electrolytes with the proton concentration, a value of 0.69 ps−1 is derived for the rate constant for proton transfer between the hydronium ions and the acceptor water molecules. For the proton hopping length a value of 2.46 A was found. These two values are in good agreement with the literature values. Finally, we propose a relation for mobility of tracer ions in HClO4 electrolytes involving the proton hopping time and length.

Preparation of alumina stabilized aqueous Pd colloid by reduction using gamma-radiolysis, UV-photolysis and H2

The techniques of gamma-radiolysis, UV photolysis and hydrogen-induced reduction of aqueous palladium perchlorate to ultrafine particles of Pd, in the presence of alumina sol, have been studied. As compared to H2-induced reduction, both UV photolytic and gamma-radiolytic reduction methods lead to a very stable, brown colored Pd colloid with relatively less absorption in the higher wavelength region and possessing much smaller volume average particle size (62 and 61 nm, respectively). Higher concentration of alumina sol and increase in pH from 1.8 to 7.2, favour the formation of smaller sized particles as determined by the dynamic light scattering technique.

Perchlorate retention and mobility in soils.

Adsorption and release of perchlorate in a variety of soils, minerals, and other media were studied when the solid media were exposed to low and high aqueous solutions of perchlorate salts. Low level ClO4- exposure was investigated by subjecting triplicate 5.0 g portions of a solid medium (38 different soils, minerals, or dusts) to 25 mL of an aqueous ammonium perchlorate (NH4ClO4) solution containing 670 ng mL(-1) (6.8 microM) perchlorate. This corresponds to a perchlorate-to-soil ratio of 3.4 microg g(-1) (34 nmol g(-1)). At this level of exposure, more than 90% of the perchlorate was recovered in the aqueous phase, as determined by ion chromatography. In some cases, more than 99% of the perchlorate remained in the aqueous phase. In some cases, the apparent loss of aqueous perchlorate was not clearly distinguishable from the variation due to experimental error. The forced perchlorate anion exchange capacities (PAECs) were studied by soaking triplicate 5.0 g portions of the solid media in 250 mL of 0.20 M sodium perchlorate (NaClO4) followed by repeated deionized water rinses (overnight soaks with mixing) until perchlorate concentrations fell below 20 ng mL(-1) in the rinse solutions. The dried residua were leached with 15.0 mL of 0.10 M sodium hydroxide. The leachates were analyzed by ion chromatography and the perchlorate concentrations thus found were subsequently used to calculate the PAECs. The measurable PAECs of the insoluble and settleable residua ranged from 4 to 150 nmol g(-1) (micromol kg(-1)), with most in the 20-50 nmol g(-1) range. In some soils or minerals, no sorption was detectable. The mineral bentonite was problematic, however. Overall, the findings support the widely accepted idea that perchlorate does not appreciably sorb to soils and that its mobility and fate are largely influenced by hydrologic and biologic factors. They also generally support the idea that intrasoil perchlorate content is depositional rather than sorptive. On the other hand, sorption (anion replacement) of perchlorate appears to occur in some soils. Therefore, the measurement of perchlorate in soils requires accounting for ion exchange phenomena; leaching with water alone may give inaccurate results. If perchlorate anion exchange is confirmed to be negligible, then leaching procedures may be simplified accordingly.

Pulse Radiolysis Study on Reactions of a Hydrated Electron with Europium(III)−Aminopolycarboxylate Complexes in Aqueous Perchlorate Media

Pulse radiolysis of 1:1 complexes of europium(III)-aminopolycarboxylates was studied in aqueous perchlorate solutions to understand relations of the reduction rate of Eu(III) with hydration state and stability of the complex. The rate constant for the reaction of a hydrated electron (e aq - ) with the complex was determined in the temperature range of 278.15 to 333.15 K and the ionic strength range of 0.05 to 1.0 mol kg -1 . The rate constant was linearly related not only with the residual hydration number of the complex representing the hydration state but also with the stability constant and redox potential as equilibrium constants. The reaction of eaq - with the complex was described by diffusive encounter and successive electron-transfer processes between eaq - and the complex. Gibbs free energy, enthalpy, and entropy of activation for the reaction were obtained from the effect of temperature on the rate constant, and the entropy term was found to be a dominant factor for the electron-transfer process after the diffusion process. These indicated that the entropy term, reflecting ionic interaction of Eu(III) -carboxylate groups and dehydration of aquo Eu(III) ion on the complexation, caused the difference in the rate constant between the complexes, and linear correlation between the rate constant and hydration number. The effect of ionic strength on the rate constant was examined by

Solid–solute phase equilibria in aqueous solution. XVI. Thermodynamic properties of malachite and azurite—predominance diagrams for the system Cu 2 + – H2 O– CO 2

The thermodynamic properties of the copper carbonates malachite, Cu 2(OH)2 CO 3, and azurite, Cu 3(OH) 2(CO 3)2, have been obtained from solubility measurements as a function of temperature as well as ionic strength of aqueous perchlorate media. First, solubility constants have been determined from T= 288.15 K toT= 338.15 K at constant ionic strength, I= 1.00 mol · kg−1NaClO 4. Second, solubility experiments have been carried out fromI= 1.00 mol · kg−1toI= 3.00 mol · kg−1NaClO 4at constant temperature, T= 298.15 K. All experimental data have been evaluated by application of the optimization routine of ChemSage, yielding an internally consistent set of thermodynamic properties for malachite (T= 298.15 K):log★Kps00 (mal.) = (6.34 ± 0.10),ΔfGmo {Cu2(OH)2CO3 } = (− 903.3 ± 1.2)kJ · mol−1,ΔfHmo {Cu2(OH)2CO3 } = (− 1067.1 ± 3.4)kJ · mol−1,Smo { Cu2(OH)2CO3} = (166.3 ± 2.5)J · mol−1· K−1; and azurite (T= 298.15 K):log★Kps00 (azu.) = (6.30 ± 0.10),ΔfGmo {Cu3(OH)2(CO3)2 } = (−1434.2 ± 1.8)kJ · mol−1,ΔfHmo {Cu3(OH)2(CO3)2 } = (−1675.1 ± 5.1)kJ · mol−1,Smo {Cu3(OH)2(CO3)2 } = (254.4 ± 3.8)J · mol−1· K−1. Whereas these results confirm the literature data for the standard molar entropies, new values for the standard molar enthalpy of formation of malachite and azurite are recommended. Moreover, the phase relations in the ternary system Cu 2+– H 2O– CO 2are discussed by the construction of two-dimensional as well as three-dimensional predominance diagrams.

Measurement of adsorption rates of anions on Au(111) electrodes by impedance spectroscopy

We have measured impedance spectra on Au(111) electrode in aqueous perchlorate solutions containing specifically adsorbing anions (SO 4 2−, Cl −, Br − and I −) of about 10 −4 M concentrations at potentials where the dominant electrode process is the adsorption of the above anions. Accordingly, the impedance spectra have been analyzed in terms of the Frumkin–Melik-Gaykazyan adsorption impedance theory. With SO 4 2−, Cl − we found the adsorption rates to be immeasurably high; with Br − and I − the apparent rate coefficients could be determined. For the halide anions this quantity increases in the order of Cl −>Br −>I −; and rapidly decreases with increasing electrode potential and coverage. We attribute this change to the decrease of the occupancy related hindrance factor overcompensates the increase of the rate coefficient.

Substitution reactions of [Pt(dien)Cl]+, [Pt(dien)(GSMe)]2+, cis-[PtCl2(NH3)2] and cis-[Pt(NH3)2(GSMe)2]2+ (GSMe =S-methylglutathione) with some sulfur-bonding chemoprotective agents

Sulfur-containing compounds are used as rescue agents to protect normal tissue from the toxic side effects of cis-[PtCl2(NH3)2] (cisplatin) without affecting its anti-tumour activity. Reactions of the model complexes [Pt(dien)Cl]+ (1) and [Pt(dien)(GSMe)]2+ (2) (GSMe = S-methylglutathione) with the rescue agents glutathione (GSH), thiourea, thiosulfate, and diethyldithiocarbamate (DDTC) have been studied in a 1.0 mol dm−3 aqueous perchlorate medium at 37 °C and pH 7.30 using stopped-flow and conventional UV/VIS spectrophotometry. The reactions of 1 with 2-mercaptoethanesulfonate (mesna) and 2-mercaptoethylamine (cysteamine), which is the parent compound of 2-(3-aminopropylamino)ethylphosphorothioic acid (WR2721), and of cis-[Pt(NH3)2(GSMe)2]2+ with thiosulfate have also been studied. The reactions between cisplatin and DDTC, thiourea and thiosulfate were investigated in an unbuffered 0.10–0.05 mol dm−3 chloride medium at 37 °C. All reactions follow the rate law: −d[complex]/dt = k2[Pt(II)][Nu] where k2 denotes a second-order rate constant and [Nu] is the total concentration of nucleophile. The rate law indicates that the reactions proceed via a direct nucleophilic substitution pathway. The rescue agents display a relatively narrow range of reactivity towards 1, mesna < Hcysteamine < GSH < thiourea < thiosulfate < DDTC with rate constants k2 of 0.156 ± 0.001, 0.22 ± 0.01, 0.237 ± 0.003, 1.17 ± 0.01, 5.57 ± 0.04, and 8.0 ± 0.1 mol−1 dm3 s−1, respectively. The sequence is consistent with the report that DDTC is the most effective rescue agent discovered so far when administered after cisplatin. The activation parameters ΔH≠ and ΔS≠ have been determined and the products of the reaction of 1 with the rescue agents have been characterised.

Do Perchlorate and Triflate Anions Bind to the Uranyl Cation in an Acidic Aqueous Medium? A Combined EXAFS and Quantum Mechanical Investigation

Structural properties of uranyl cations in acidic aqueous perchlorate and triflate solutions were investigated using uranium LIII -edge extended X-ray absorption fine-structure spectroscopy (EXAFS) in conjunction with quantum mechanical calculations of gas-phase model complexes. EXAFS spectra were measured in aqueous solutions of up to 10 M triflic and 11.5 M perchloric acid, as well as mixtures of perchloric acid and sodium perchlorate. In no case is the perchlorate anion coordinated to UO2(2+). The number of equatorial water molecules bound to UO2(2+) is always about five. In the case of the 10 M CF3SO3H solution, an inner-sphere complexation of the triflate is observed with a U-S radial distance of 3.62 Å. These results are in qualitative agreement with quantum mechanical calculations of model uranyl complexes, according to which the interaction energies of anions follow the order perchlorate<triflate<<nitrate.

Double layer capacitance of Pt(111) single crystal electrodes

In order to determine the double layer capacitance of the Pt(111) electrode, impedance and capacitance measurements were carried out in neutral and acidic aqueous perchlorate solutions. Separation of the double layer and adsorption contributions of the interfacial capacitance were based on the adsorption impedance theory. The double layer capacitance versus potential plot exhibits a peak at about 0.12 V versus SCE in the 1.5–7 pH range; from here towards cathodic potentials the capacitance attains a value of about 20 μF/cm 2. The peak may be related to the potential of zero free charge of the Pt(111) electrode.

Electron self-exchange in the solid-state: cocrystals of hydroquinone and bipyridyl triazole.

Solid-state voltammetry, spectroscopy, and microscopy studies have been used to probe the proton and electron conductivity within a self-assembled cocrystal, HQBpt. This crystallographically defined material contains 3,5-bis(pyridin-2-yl)-1,2,4-triazole, HBpt, dimers that are pi-stacked and hydrogen bonded to 1,4-hydroquinone, H(2)Q, in a herringbone arrangement. When deposited onto platinum microelectrodes, the cocrystal exhibits a well-defined voltammetric response corresponding to oxidation of H(2)Q to the quinone, Q, across a wide range of voltammetric time scales, electrolyte compositions, and pH values. Scanning electron microscopy reveals that redox cycling in aqueous perchlorate solutions in which the pH is systematically varied from 1 to 7 triggers electrocrystallization and the extensive formation of rodlike crystals. Fast scan rate voltammetry reveals that the homogeneous charge transport diffusion coefficient, D(app), is independent of the perchlorate concentration for 0.1 < [ClO(4)(-)] < 1.0 M (pH 6.6) at 3.14 +/- 0.11 x 10(-)(9) cm(2) s(-)(1). Moreover, D(app) is independent of the perchloric acid concentration for concentrations greater than approximately 2.0 M, maintaining a value of 4.81 +/- 0.07 x 10(-)(8) cm(2) s(-)(1). The observation that D(app) is independent of the supporting electrolyte suggests that the rate-determining step for homogeneous charge transport is not the availability of charge-compensating counterions or protons, but the dynamics of electron self-exchange between H(2)Q and Q. We have used the Dahms-Ruff formalism to determine electron self-exchange rate constants which are 2.84 +/- 0.22 x 10(9) and 9.69 +/- 0.73 x 10(10) M(-)(1) s(-)(1) for pH values greater than approximately 2.0 and less than -0.3, respectively. Significantly, these values are more than 2 orders of magnitude larger that those found for benzoquinone self-exchange reactions in aqueous solution. These results indicate that hydrogen bonds play an important role in supporting rapid electron transfer. The increase in D(app) between pH 1.0 and -0.3 is associated with protonation of the HBpt moieties, which triggers a reversible change in the material's structure.

Extraction of cadmium and iodocadmat species by di(2-ethylhexyl) phosphoric acid from perchloric and phosphoric media

We have investigated the extraction of cadmium with di(2-ethylhexyl) phosphoric acid (HDEHP) in various solvents from perchloric and phosphoric solutions. The distribution coefficient D obtained is not very dependent on the nature and the polarity of the diluent used. The extraction of Cd(II) by HDEHP dissolved in benzene, from sulfophosphoric solutions shows the absence of sulfuric or mixed sulfophosphoric complexes of the metal. However, the presence of iodide anions in aqueous perchloric or phosphoric media results in enhanced extraction coefficient of cadmium with HDEHP (HX) in benzene. The extracted species were found to be CdIX,3(HX) 2 and CdI 2,3(HX) 2 and their formation constants are 0.033 and 0.036, respectively. The recovery of cadmium from phosphoric medium by tributylphosphate (TBP), trioctyl phosphine oxide (TOPO), triphenyl phosphine oxide (TPPO), diphenylamine or their mixtures with HDEHP is lesser than with HDEHP alone.

Dynamics of [Os(bpy)2(p3p)2]2+ Adsorption and Desorption on Platinum and Gold Microelectrodes

The mechanism for the formation of monolayers of on gold and platinum microelectrodes has been investigated by monitoring the time evolution of the surface coverage. The monolayers were formed in 2:1 solution containing between 10 and 100 μM of the complex. The voltammetric response of these films corresponding to the redox reaction is nearly ideal. Cyclic voltammetry was used to determine the surface coverage vs. time profile following transfer of the modified electrode into aqueous perchlorate electrolyte. Monolayer formation occurs on the tens of minutes time scale and follows a second order rate law for both gold and platinum electrodes. For gold, the rate constant is for bulk concentrations between 10 and 100 μM. In contrast, more complex behavior is observed on platinum with multilayers being formed where exceeds approximately 20 μM. The apparent rate constants for binding to platinum are at least a factor of 2 smaller than for gold. For both electrode materials, desorption follows first order rate kinetics indicating that the adsorbates do not interact strongly with one another. The time constants for desorption are comparable with those found for adsorption. The first order desorption rate constants are and for modified gold and platinum electrodes, respectively. © 2000 The Electrochemical Society. All rights reserved.

Solvation of the bismuth(III) ion by water, dimethyl sulfoxide, N,N'-dimethylpropyleneurea, and N,N-dimethylthioformamide. An EXAFS, large-angle X-ray scattering, and crystallographic structural study.

The structure of the solvated bismuth(III) ion in aqueous, dimethyl sulfoxide, N,N'-dimethylpropyleneurea, and N,N-dimethylthioformamide solution has been studied by means of EXAFS and large-angle X-ray scattering (LAXS). The crystal structures of the solid compounds octakis(dimethyl sulfoxide)bismuth(III) perchlorate, [Bi(OS(CH3)2)8](ClO4)3, hexakis(N,N'-dimethylpropyleneurea)bismuth(III) perchlorate, [Bi(OCN2(CH2)3(CH3)2)6](ClO4)3, and nonaaquabismuth(III) trifluoromethanesulfonate, [Bi(H2O)9](CF3SO3)3 (redetermination), have been determined. The aqueous solutions must be strongly acidic, since the hydrated bismuth(III) ion starts to hydrolyze into Bi6O4(OH)4(6+) complexes already at an excess of strong acid at 1.0 mol.dm-3. For very acidic aqueous perchlorate solutions, the LAXS and EXAFS data gave a satisfactory fit for eight-coordination of the bismuth(III) ion, with a mean Bi-O bond distance of 2.41(1) A. The crystal structure of octakis(dimethyl sulfoxide)bismuth(III) perchlorate shows that the bismuth(III) ion coordinates eight dimethyl sulfoxide molecules via the oxygen atoms in a distorted square antiprismatic configuration. The mean Bi-O bond distance is 2.43 A and the mean Bi...S distance 3.56 A. For the dimethyl sulfoxide solution, the corresponding mean distances were found to be 2.411(6) and 3.535(12) A. The N,N'-dimethylpropyleneurea-solvated bismuth(III) ion is octahedrally coordinated in both solid state and solution with the Bi-O bond distances of 2.324(5) and 2.322(3) A, respectively. The bismuth(III) ion is six-coordinated in the sulfur donor solvent N,N-dimethylthioformamide with a mean Bi-S bond distance of 2.794(8) A. A comparison with the structure of the solvated lanthanum(III) ion shows that the bismuth(III) ion is smaller for all coordination numbers. New effective ionic radii for the bismuth(III) ion in different coordination numbers are proposed, based on results in this study and in the literature.