Aqueous Hydroxyl Research Articles

The Electron Attachment Energy of the Aqueous Hydroxyl Radical Predicted from the Detachment Energy of the Aqueous Hydroxide Anion

Combining photoemission and electrochemical data from the literature we argue that the difference between the vertical and adiabatic ionization energy of the aqueous hydroxide anion is 2.9 eV. We then use density functional theory based molecular dynamics to show that the solvent response to ionization is nonlinear. Adding this to the experimental data we predict a 4.1 eV difference between the energy for vertical attachment of an electron to the aqueous hydroxyl radical and the corresponding adiabatic electron affinity. This places the state accepting the electron only 2.2 eV below vacuum or 7.7 eV above the edge of the valence band of water.

Thermochemistry of aqueous hydroxyl radical from advances in photoacoustic calorimetry and ab initio continuum solvation theory.

Photoacoustic signals from dilute ( approximately 30 mM) solutions of H2O2 were measured over the temperature range from 10 to 45 degrees C to obtain the reaction enthalpy and volume change for H2O2(aq) --> 2 OH(aq) from which we ultimately determined DeltafG degrees , DeltafH degrees and partial molal volume, v degrees , of OH (aq). We find DeltarH = 46.8 +/- 1.4 kcal/mol, which is 4 kcal/mol smaller than the gas-phase bond energy, and DeltaVr = 6.5 +/- 0.4 mL/mol. The v degrees for OH in water is 14.4 +/- 0.4 mL/ml: smaller than the v degrees of water. Using ab intio continuum theory, the hydration free energy is calculated to be -3.9 +/- 0.3 kcal/mol (for standard states in number density concentration units) by a novel approach devised to capture in the definition of the solute cavity the strength and specific interactions of the solute with a water solvent molecule. The shape of the cavity is defined by "rolling" a three-dimensional electron density isocontour of water on the ab initio water-OH minimum interaction surface. The value of the contour is selected to reproduce the volume of OH in water. We obtain for OH(aq): DeltafH degrees = -0.2 +/- 1.4 and DeltafG degrees = 5.8 +/- 0.4 kcal/mol that are in agreement with literature values. The results provide confidence in the pulsed PAC technique for measuring aqueous thermochemistry of radicals and open the way to obtaining thermochemistry for most radicals that can be formed by reaction of OH with aqueous substrates while advancing the field of continuum solvation theory toward ab initio-defined solute cavities.

Determination of the metal complexation capacity of natural waters by ligand titration in the presence of complexing resins

The complexation properties of some drinking waters for U(VI), Al(III) and Cu(II) are determined by ligand titration (LT) with the metal ions, using a new method for monitoring, i.e. the sorpion of metal ion on complexing resins. The concentration of the free metal ion in solution is evaluated from the concentration of sorbed metal ion and from the quantity K * , which is the ratio of the concentration of the metal ion sorbed on the resin to the concentration of free metal ion in solution, and can be independently evaluated. The concentration of the ligands in solution (c I ) and the conditional stability constant (K M(I) ) are obtained by the Ruzic linearization. Different resins, i.e. the iminodiacetic resin Chelex 100, the carboxylic resin Amberlite CG 50 and the anion exchange resin AG1X8 were used for monitoring the titration, since they have different sorbing properties, and in principle they allow the detection of different ligands. Ligands at low concentration and with very high complexation constants were detected in the considered samples. Particularly in the case of U(VI), they are able to complex the metal ion much more strongly than the ligands that are usually considered in aqueous solution, i.e. carbonate and hydroxyl.

Heavy metal ion removal by amidoximated bagasse

AbstractAmidoximated bagasse (Am‐B) was prepared by treating sugarcane bagasse fibers with acrylonitrile in the presence of sodium hydroxide followed by aqueous hydroxyl amine. Adsorption of some heavy metal ions, namely, Cu(II), Hg(II), Ni(II), Cr(III), and Pb(II) on the prepared Am‐B at different metal ion concentration, intervals, and temperatures was studied. Also, the selectivity of the prepared Am‐B toward adsorption of the aforementioned metal ions in an equimolar mixture was studied. The effect of regeneration of Am‐B using ethylenediamine tetraacetic acid disodium salt (EDTA), up to five times, on its adsorption capacity of the aforementioned metal ions was investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 666–670, 2003

Hydrolysis of the Nafion® precursor studied by X-ray scattering and in-situ atomic force microscopy

AbstractThe hydrolysis of Nafion® † precursor material to a perfluorosulfonate ion exchange membrane has been studied in situ at the surface of a sample using atomic force microscopy (AFM), and in the bulk using a combination of small and wide-angle X-ray scattering. The AFM results show that there is a rapid and significant change in the surface morphology of the sample during the first 12 min after the introduction of aqueous hydroxyl ions, provided that an appropriate swelling agent is used. After this point there is little change in surface morphology, although bulk swelling of the sample continues. The wide-angle X-ray scattering results indicate a significant drop in the degree of crystallinity of fluorocarbon matrix from 14±1% to 7±1% on hydrolysis, as a result of the bulk structural reordering necessary to accommodate the formation of ionic clusters. Ionic clustering is confirmed by the appearance of a characteristic small-angle X-ray peak. However, the peak forms towards the end of the hydrolysis process, and subsequently coarsens, suggesting that the formation of ionic clusters is a slow process compared to the rate of hydrolysis. It is confirmed that an appropriate water/solvent mixture is necessary to achieve an efficient conversion of precursor to membrane. AFM images of the precursor surface, when water alone is used, show no signs of structural change.

Field Evaluation of High Voltage Electron Beam Technology for Treating VOC-Contaminated Groundwater. Part II: Acute Toxicity Changes and By-Product Formation

AbstractAs part of the Superfund Innovative Technology Evaluation program, the U.S. Environmental Protection Agency evaluated the High Voltage jEnvironmental Applications, Inc. (HVEA), electron beam (E-beam) technology at the U.S. Department of Energy Savannah River Site (SRS) in Aiken, South Carolina. This technology irradiates water with a beam of high-energy electrons, causing the formation of three primary transient reactive species: aqueous electrons, hydroxyl radicals, and hydrogen radicals. Target organic compounds are either mineralized or broken down into low molecular weight organic compounds, primarily by these species. The E-beam system used for the evaluation is housed in an 8- by 48-foot trailer and is rated for a maximum flow rate of 50 gpm. During two different periods totaling 3 weeks in September and November 1994, about 70,000 gallons of SRS M-area groundwater contaminated with volatile organic compounds (VOCs) was treated with the E-beam system. E-beam treatment increased groundwater acute toxicity for fathead minnows but not for water fleas. Although several VOCs were removed, lack of decrease in toxicity appears to be due to formation of toxic by-products, including haloacetic acids and aldehydes, during E-beam treatment of groundwater. An increase in inorganic carbon and chloride concentrations was observed, in the treated groundwater indicating that some VOCs were mineralized during E-beam treatment. Formation of CO

Field Evaluation of High Voltage Electron Beam Technology for Treating VOC-Contaminated Groundwater. Part I: VOC Removals and Treatment Costs

AbstractAs part of the Superfund Innovative Technology Evaluation program, the U.S. Environmental Protection Agency evaluated the High Voltage Environmental Applications, Inc. (HVEA), electron beam (E-beam) technology at the U.S. Department of Energy Savannah River Site (SRS) in Aiken, South Carolina. This technology irradiates water with a beam of high-energy electrons, causing the formation of three primary transient reactive species: aqueous electrons, hydroxyl radicals, and hydrogen radicals. Target organic compounds are either mineralized or broken down into low molecular weight organic compounds, primarily by these species. The E-beam system used for the evaluation is housed in an 8- by 48-foot trailer and is rated for a maximum flow rate of 50 gpm. During two different periods totaling 3 weeks in September and November 1994, about 70,000 gallons of SRS M-area groundwater contaminated with volatile organic compounds (VOCs) was treated with the E-beam system. The highest removal efficiencies (REs) observed for unsaturated chlorinated VOCs in groundwater - trichloroethene (TCE), tetrachloroethene (PCE), and cis-1,2-dichloroethene (1,2-DCE) - were >99, 99, and > 91%, respectively. REs ranged from 68 to > 98% for 1,1,1-trichloroethane (1,1,1-TCA), 1,2-dichloroethane (1,2-DCA), chloroform, and carbon tetrachloride (CCl

Mechanisms of copper- and iron-dependent oxidative modification of human low density lipoprotein

Oxidative modification of low density lipoprotein (LDL) has been suggested as a causal step in atherosclerosis, and both redox-active transition metal ions and superoxide (O2.-) have been implicated in this process. In order to determine the mechanisms of metal ion-dependent oxidation of LDL in the presence of O2.-, LDL was exposed to hypoxanthine (HX) and purified xanthine oxidase (XO) without and with added CuCl2 or Fe(3+)-citrate. Production of O2.- and hydrogen peroxide (H2O2) at pH 7.4 by the HX/XO system in the absence of metal ions was not sufficient to oxidize LDL. Preincubation of LDL with Cu2+ or Fe(3+)-citrate with subsequent removal of metal ions not tightly bound to the lipoprotein did not enable the HX/XO system to oxidize LDL. However, incubation of LDL with HX/XO and Cu2+ resulted in extensive modification of LDL. Exposure of LDL to Cu2+ alone also led to extensive modification, although the LDL was initially free of detectable amounts of lipid hydroperoxides (LOOH), i.e., < 0.005 molecules of LOOH per LDL particle. Although HX/XO and Cu2+ did not produce detectable amounts of O2.- or aqueous hydroxyl radicals (HO.), oxidation of LDL under these conditions was partially inhibited by superoxide dismutase, and completely inhibited by the HO. scavenger thiourea. In contrast to Cu(2+)-mediated oxidation of LDL, oxidation mediated by Fe(3+)-citrate was strictly dependent upon O2.-, as it was abolished by omission of the HX/XO system or by addition of superoxide dismutase to this system.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid measurement of aqueous hydroxyl radical concentrations in steady-state HO· flux systems

The spin-trap compound a-(4-pyridyl-1-oxide)-N-tert-butyl-nitrone (4-POBN) is utilized for the detection and quantitation of the hydroxyl radical (HO·) in aqueous solution. Capillary electrophoresis enables rapid analysis of the probe compound. The thermally unstable HO· radical adduct of 4-POBN can be unequivocally identified by gas chromatography/mass spectrometry analysis of it's pentafluorobenzyl ether. The minimum steady-state flux of HO· is determined in several “advanced oxidation systems” including photo-Fenton, ozone, and titanium dioxide based radical generators.

Phases and thermal decomposition characteristics of hydro-sodalites Na 6+x,[AlSiO 4] 6,(OH) x· nH 2O

Reinvestigation of the hydro-sodalite system does not verify the solid solution character of the series in respect to a steady variation in properties of the samples. Thermoanalyses of carefully prepared pure phases reveal an antagonistic volume/concentration effect of hydrate water in the two end-member series Na 8[AlSiO 4] 6(OH) 2· nH 2O. 0 ⩽ n ⩽ 4 (“basic series”) and Na 6[AlSiO 4] 6· nH 2O, 0 < n ⩽ 8 (“non-basic series”), however. Thermogravimetry and X-ray diffraction heating experiments confirm partial collapse of the sodalite framework upon dehydration of phases of the basic hydro-sodalites which is the common behaviour of framework compounds in decomposition or ion exchange experiments. In contrast, phases of the non-basic sodalite hydrate series Na 6[AlSiO 4] 6· nH 2O show significant expansion of the alumino-silicate framework, when H 2O (0 < n ⩽ 8) is released at temperatures of 350–450 K under open system conditions. This antagonistic effect on the sodalite type host lattice is discussed in terms of hydrogen bonding, which has been verified by supplementary neutron diffraction analyses for the non-basic hydro-sodalites, distinctively. From IR and X-ray diffraction heating experiments strong evidence is given for the dynamic nature of interactions between all the non-framework constituents with increasing activation barriers for the hydrogen, oxygen and sodium atoms, respectively. The truncated octahedral geometry of the sodalite cage in the given 1:1 alumino-silicate matrix controls the corresponding interactions, which result in some new stereochemical features of the aqueous hydroxyl groupings [O n H 2 n−1 ] − in the basic hydro-sodalite phases with different hydrate water contents. Samples of partially leached samples with intermediate concentrations of NaOH, 0 < x < 2, show decomposition into mixed phase samples of the basic ( x = 2) and of the non-basic ( x = 0) type of hydro-sodalite, respectively. The data on the givenβ-cage chemistry are discussed in terms of some corresponding findings with zeolites A and Y.

The aqueous oxidation of SO 2 by OH radicals

The reaction of aqueous hydroxyl radicals with bisulphite ion has been proposed as a significant and in some cases a primary pathway by which SO 2 is oxidized to sulphate in tropospheric cloud. It is shown that many uncertainties still remain with regard to the kinetics and mechanism of this oxidation process. Illustrative computations indicate that reaction schemes taking account of the aqueous oxidation of SO 2 by OH in existing models of cloud chemistry are inconsistent with the mechanisms on which they are based and yield a wide range of oxidation rates. Calculations are presented which suggest that the reaction of the SO 5 − radical with bisulphite ion is rate determining, although the rate constant remains uncertain. The products of this reaction must be identified before the mechanism of sulphate production can be elucidated and the relevance of this process to tropospheric SO 2 oxidation reliably assessed.

Uniformity of vegetable composition

The volatility of secondary organic aerosol (SOA) formed through cloud processing (aqueous hydroxyl radical (OH) oxidation and droplet evaporation) of methylglyoxal (MGly) was studied. Effective vapor pressure and effective enthalpy of vaporization (ΔHvap,eff) were determined using 1) droplets containing MGly and its oxidation products, 2) a Vibrating Orifice Aerosol Generator (VOAG) system, and 3) Temperature Programmed Desorption Aerosol-Chemical Ionization Mass Spectrometry (TPD Aerosol-CIMS). Simulated in-cloud MGly oxidation (for 10–30 min) produces an organic mixture of higher and lower volatility components with an overall effective vapor pressure of (4 ± 7) × 10−7 atm at pH 3. The effective vapor pressure decreases by a factor of 2 with addition of ammonium hydroxide (pH 7). The fraction of organic material remaining in the particle-phase after drying was smaller than for similar experiments with glycolaldehyde and glyoxal SOA. The ΔHvap,eff of pyruvic acid and oxalic acid + methylglyoxal in the mixture (from TPD Aerosol-CIMS) were smaller than the theoretical enthalpies of the pure compounds and smaller than that estimated for the entire precursor/product mix after droplet evaporation. After 10–30 min of aqueous oxidation (one cloud cycle) the majority of the MGly + OH precursor/product mix (even neutralized) will volatilize during droplet evaporation; neutralization and at least 80 min of oxidation at 10−12 M OH (or >12 h at 10−14 M) is needed before low volatility ammonium oxalate exceeds pyruvate.