This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The effect of ozone oxidation on the second order reaction rate constant between effluent organic... more The effect of ozone oxidation on the second order reaction rate constant between effluent organic matter (EfOM) and hydroxyl radical (
The β-lactam antibiotics are some of the most persistent anthropogenic pharmaceutical contaminant... more The β-lactam antibiotics are some of the most persistent anthropogenic pharmaceutical contaminants, and consequently are currently being detected in many aquatic environments. The presence of any level of antibiotics in water may contribute to the emergence of antibiotic-resistant bacterial strains, and therefore the active removal of these pharmaceuticals by additional water treatments such as advanced oxidation and reduction processes may be required. In this study, we report on our efficiency measurements for the hydroxylradical- based degradation of three β-lactam antibiotics obtained using steady-state
Proceedings of the Water Environment Federation, 2007
ABSTRACT Increasing demand for reclaimed water from wastewater treatment facilities has revolutio... more ABSTRACT Increasing demand for reclaimed water from wastewater treatment facilities has revolutionized the need for awareness of effluent quality and its properties. Wastewater can be made suitable for many reuse applications. Many of these applications for reclaimed water in industry, agriculture, and other beneficial uses have required stricter controls on the effluent quality from wastewater plants. These controls may apply to microbial pathogens, disinfection-by-products, or endocrine disruptors. In 1956, a paper to the Virginia Section meeting of the American Waterworks Association titled Destruction of Microorganisms in Water, Sewage, Sewage Sludge by Ionizing Radiation, Lowe, Lacy, Surkiewicz, and Jager concluded that it was possible to kill or inactivate pathogenic microorganisms in water by60Co gamma irradiation. Disinfectants such as chlorine, chloramines and ozone, react with natural organic matter to form disinfection-by-products (DBPs), many of which are regulated. Endocrine disruptors represent an emerging concern for their impact to the environment and fate within the ecosystem. Advanced oxidation processes using free radical chemistry represent a reasonably viable alternative to chemical additives such as chlorine or ozone for removal or elimination of objectionable contaminants from water. The process for production of free radicals has been well established. This paper explores the efficacy for use of advance oxidation processes using free radical chemistry for the elimination of objectionable contaminants from wastewater effluent and for reuse applications. Central to the focus of this paper will be the application of reuse water to the paper mill industry and agriculture. Relevant data and information on the needed reuse water quality criteria required for various processes are addressed and the criteria for treatment for removal of unwanted or objectionable contaminants will be identified.
The techniques of electron pulse radiolysis and absorption spectroscopy have been used to directl... more The techniques of electron pulse radiolysis and absorption spectroscopy have been used to directly measure rate constants for the hydrated electron reaction with CH3I, C2H5I, 1-C3H7I and 2-C3H7I. At 25°C, specific values of (1.78 +/- 0.05) × 1010, (1.57 +/- 0.07) × 1010, (1.05 +/- 0.06) × 1010 and (1.05 +/- 0.03) × 1010 dm3 mol-1 s-1 were determined for these compounds respectively, with corresponding overall activation energies of 16.9 +/- 1.3 (3.2-35.5°C), 19.5 +/- 1.1 (3.3-51.6°C), 16.60 +/- 0.65 (2.5-85.1°C) and 12.94 +/- 0.44 (2.5-84.5°C) kJ mol-1. The slight curvature observed in the Arrhenius plots for the three larger iodoalkanes suggests that these rate constants are influenced by both diffusion and chemical processes. By fitting the measured temperature-dependent rate constants to the general equation 1/kobs = 1/kdiff + 1/kreact, where kobs is the measured rate constant,kdiff is the encounter rate constant of the two reacting species and kreact is the rate constant that would be measured if diffusion of the species was not rate influencing, specific Arrhenius parameters for only the chemical component have also been determined.
ABSTRACT The ultrasonically induced oxidation of arsenite, As(III), in aqueous media is effective... more ABSTRACT The ultrasonically induced oxidation of arsenite, As(III), in aqueous media is effective over a range of concentrations and may be applicable as a pretreatment step for the removal of arsenic from water. We have conducted detailed studies on the conversion of arsenite in aqueous media by ultrasonic irradiation, focusing on the roles of ·OH, O2-· and H2O2 formed during the irradiation. The rate of the H2O2 induced transformation of As(III) is much slower than under hydroxyl radical generating ultrasonic conditions. The addition of superoxide dismutase does not change the rate of disappearance of As(III) under ultrasonic irradiation. The conversion of As(III) is very slow under selective generation of superoxide anion radical and its protonated form using gamma radiolysis, indicating that superoxide anion radical does not play a significant role in the conversion of As(III). In summary, hydroxyl radical plays the key role in the conversion of As(III), while hydrogen peroxide plays a minor role and superoxide anion radical has little or no role in the conversion of arsenite during ultrasonic irradiation.
The formation of KrF* and XeF* has been studied in electron-beam irradiated Kr/ Xe/SF6 gas mixtur... more The formation of KrF* and XeF* has been studied in electron-beam irradiated Kr/ Xe/SF6 gas mixtures. An electron-beam-energy dependent process has been observed, and confirmed to be due to ion recombination processes between rare gas cations and halide anions. The anions are formed by thermal electron capture by SF6 and the cations either being directly formed in the electron pulse (Kr +), or by subsequent charge transfer (Xe +).
Radical-based mineralization of aqueous halonitromethane disinfection byproducts. c Constructed k... more Radical-based mineralization of aqueous halonitromethane disinfection byproducts. c Constructed kinetic computer model for tri-halogenated halonitromethane removal. c Model predicted that superoxide reaction is unimportant for halonitromethanes. c Measured superoxide reaction with chloropicrin was negligibly slow, o 2 Â 10 4 M À 1 s À 1 .
Journal of the Chemical Society, Faraday Transactions, 1994
The reactions of primary water radiolysis radicals with IO–3 have been re-investigated using elec... more The reactions of primary water radiolysis radicals with IO–3 have been re-investigated using electron pulse radiolysis and absorption spectroscopy. Rate constants for iodate reaction with e–(aq)[(5.45 ± 0.45)× 109 dm3 mol–1 s–1], O˙–[(1.82 ± 0.04)× 109 dm3 mol–1 s–1] and ˙OH (< 105 dm3 mol–1 s–1) have been measured and compared with previously determined values. The observed iodate concentration dependence of the two transient absorptions produced by its reaction with the hydrated electron and the oxide radical were found to be due only to spur scavenging effects, and thus the dimerization equilibria proposed by previous workers is not necessary. The previously reported rate constants for the reaction of iodate with hydroxyl radicals have been shown to be due to just iodate reaction with the small concentration of O˙– present in equilibrium with the hydroxyl radical.
The efficient detection, decontamination, and destruction of chemical warfare (CW) agents remain ... more The efficient detection, decontamination, and destruction of chemical warfare (CW) agents remain an active area of scientific research. Rate constants for the reaction of substituted diethyl phosphates and phosphonates with the hydroxyl radical and hydrated electron have been measured in water to elucidate the primary destruction pathway for the CW agents Tabun (GA), Sarin (GB), Soman (GD), and VX with these two species. The measured kinetics for simulants with leaving groups that more closely mimic these actual CW agents predict that reductive destruction will be the most efficient mechanism, and that nontoxic simulants such as alkyl phosphonates undergo different redox chemistry.
Lactic acid is a major component of the TALSPEAK process planned for use in the separation of tri... more Lactic acid is a major component of the TALSPEAK process planned for use in the separation of trivalent lanthanide and actinide elements. This acid acts both as a buffer and to protect the actinide complexant from radiolytic damage. However, there is little kinetic information on the reaction of water radiolysis species with lactic acid, particularly under the anticipated process conditions of aerated aqueous solution at pH ∼ 3, where oxidizing reactions are expected to dominate. Here we have determined temperature-dependent reaction rate constants for the reactions of the hydroxyl radical with lactic acid and the lactate ion. For lactic acid this rate constant is given by the following equation: ln k 1) (23.85 (0.19)-(1120 (54)/T, corresponding to an activation energy of 9.31 (0.45 kJ mol-1 and a room temperature reaction rate constant of (5.24 (0.35) × 10 8 M-1 s-1 (24.0°C). For the lactate ion, the temperature-dependent rate constant is given by ln k 2) (24.83 (0.14)-(1295 (42)/T, for an activation energy of 10.76 (0.35 kJ mol-1 and a room temperature value of (7.77 (0.50) × 10 8 M-1 s-1 (22.2°C). These kinetic data have been combined with autotitration measurements to determine the temperature-dependent behavior of the lactic acid pK a value, allowing thermodynamic parameters for the acid dissociation to be calculated as ∆H°)-10.75 (1.77 kJ mol-1 , ∆S°)-103.9 (6.0 J K-1 mol-1 and ∆G°) 20.24 (2.52 kJ mol-1 at low ionic strength.
Arrhenius parameters for the reaction of hydrogen atoms with azide and thiocyanate in aqueous sol... more Arrhenius parameters for the reaction of hydrogen atoms with azide and thiocyanate in aqueous solution have been determined using electron pulse radiolysis and electron paramagnetic resonance free induction decay attenuation measurements. Absolute values for SCN-, N 3-, and HN 3 were well-described over the temperature range of 9-81°C by the equations log k 5) (12.03 (0.12)-[(21.05 (0.66 kJ mol-1)/2.303RT], log k 10) (12.75 (0.21)-[(18.43 (1.22 kJ mol-1)/2.303RT], and log k 15) (11.59 (0.12)-[(21.44 (0.69 kJ mol-1)/2.303RT], corresponding to room temperature (22°C) rate constants of (2.07 (0.03) × 10 8 , (3.15 (0.08) × 10 9 , and (6.31 (0.05) × 10 7 M-1 s-1 and activation energies for these chemicals of 21.05 (0.66, 18.4 (1.2, and 21.44 (0.69 kJ mol-1 , respectively. The similarity of these three measured activation energies, taken together with the available information on reaction products, suggests a similar reaction mechanism, which is proposed to be an initial hydrogen atom adduct formation in these molecules, followed by single bond breakage.
A pulsed, two-beam, thermal lensing experiment was performed to determine the concentration of aq... more A pulsed, two-beam, thermal lensing experiment was performed to determine the concentration of aqueous solutes above the critical point of water. Despite a very significant mirage effect due to thermal gradients in the cell and absorption by water itself, the thermal lensing signal strength for aqueous benzoic acid in supercritical water was found to be linear with concentration in the sub-millimolar range. Although thermal lensing experiments in aqueous media are notoriously insensitive, the sharp density gradient near the critical point considerably improves the signal intensity. In this study a short-pulse pump 266 nm YAG laser and continuous low-power probe Ar ion beam were both focused into a supercritical water cell, giving a lensing signal whose strength could be maximized by changing the overlap of the two beams.
The beta-lactam antibiotics are some of the most prevalent pharmaceutical contaminants currently ... more The beta-lactam antibiotics are some of the most prevalent pharmaceutical contaminants currently being detected in aquatic environments. Because the presence of any trace level of antibiotic in water may adversely affect aquatic ecosystems and contribute to the production of antibiotic-resistant bacteria, active removal by additional water treatments, such as using advanced oxidation and reduction processes (AO/RPs), may be required. However, to ensure that any AOP treatment process occurs efficiently and quantitatively, a full understanding of the kinetics and mechanisms of all of the chemical reactions involved under the conditions of use is necessary. In this study, we report on our kinetic measurements for the hydroxyl-radical-induced oxidation of 11 beta-lactam antibiotics obtained using electron pulse radiolysis techniques. For the 5-member ring species, an average reaction rate constant of (7.9 +/- 0.8) x 10(9) M(-1) s(-1) was obtained, slightly faster than for the analogous 6-member ring containing antibiotics, (6.6 +/- 1.2) x 10(9) M(-1) s(-1). The consistency of these rate constants for each group infers a common reaction mechanism, consisting of the partitioning of the hydroxyl radical between addition to peripheral aromatic rings and reaction with the central double-ring core of these antibiotics.
Direct infusion electrospray ionization mass spectrometry (ESI-MS) approaches were developed for ... more Direct infusion electrospray ionization mass spectrometry (ESI-MS) approaches were developed for rapid identification of impurity compounds formed from octylphenyl-(N,N-(diisobutyl)carbamoylmethyl) phosphine oxide (CMPO) during alpha and gamma irradiation experiments of this compound in dodecane. CMPO is an aggressive Lewis base, and produces extremely abundant metal complex ions in the ESI-MS analysis that make identification of low abundance compounds that are less nucleophilic challenging. Radiolysis products were identified using several approaches including restricting ion trapping so as to exclude the abundant natiated CMPO ions, extraction of acidic products using aqueous NaOH, and extraction of basic products using HNO 3. These approaches generated protonated, natiated and deprotonated species derived from CMPO degradation products formed via radiolytic cleavages of several different bonds. Cleavages of the amide and methylene-phosphoryl bonds appear to be favored by both alpha and gamma irradiation, while alpha irradiation also appears to induce cleavage of the methylene-carbonyl bond. The degradation products observed are formed from recombination of the initially formed radicals with hydrogen, methyl, isopropyl and hydroxyl radicals that are derived either from CMPO, contacted aqueous nitric acid, or the dodecane solvent.
ABSTRACT Octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in dodecane wa... more ABSTRACT Octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in dodecane was subjected to α-irradiation using a He-ion beam, 244 Cm isotopic α-rays, and He and Li ions created by the n,α reaction of 10B in a nuclear reactor. Post-irradiation samples were analyzed for the radiolytically-induced decrease in CMPO concentration, the appearance of degradation products, and their Am solvent extraction distribution ratios. The –G CMPO-value for the radiolytic degradation of CMPO was found to be very low compared to values previously reported for γ-irradiation. Additionally, isotopic irradiation to absorbed α-doses as high as 600 kGy in aerated solution had no effect on Am solvent extraction or stripping. The main CMPO radiolysis products identified in He-ion beam irradiated samples by ESI-MS include amides, an acidic amide, and amines produced by bond rupture on either side of the CMPO carbonyl group. Deaerated samples irradiated using the reactor in the absence of an aqueous phase, or with a dilute nitric acid aqueous phase showed small but measurable decreases in CMPO concentration with increasing absorbed doses. Higher concentrations of nitric acid resulted in lower decomposition rates for the CMPO. The radio-protection by dissolved oxygen and nitric acid previously found for γ-irradiated CMPO also occurs for α-irradiation. This suggests that similar free-radical mechanisms operate in the high-LET system, but with lower degradation yields due to the lower overall radical concentrations produced.
The partitioning of the long‐lived α‐emitters and the high‐yield fission products from dissolved ... more The partitioning of the long‐lived α‐emitters and the high‐yield fission products from dissolved nuclear fuel is a key component of processes envisioned for the safe recycling of nuclear fuel and the disposition of high‐level waste. These future processes will likely be based on aqueous solvent‐extraction technologies for light‐water reactor fuel and consist of four main components for the separation of uranium, fission products, and group trivalent actinides and lanthanides and separation of trivalent actinides from lanthanides. Since the solvent systems will be in contact with highly radioactive solutions, they must be robust toward radiolytic degradation in an irradiated, mixed organic and aqueous acidic environment. Therefore, an understanding of their radiation chemistry is important to the design of a practical system. In a previous paper, we reviewed the radiation chemistry of irradiated aqueous nitric acid and the tributyl phosphate ligand used for uranium extraction in the first step of the series of four extractions. In this paper, we review the radiation chemistry of the ligands proposed for use in the second extraction of cesium and strontium fission products. This includes not only the crown ethers and calixarenes but also cobalt dicarbollide and polyethylene glycol. Since many disparate units have been applied for measuring absorbed radiation dose in the literature, we also present a discussion of that topic and provide conversion factors.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The effect of ozone oxidation on the second order reaction rate constant between effluent organic... more The effect of ozone oxidation on the second order reaction rate constant between effluent organic matter (EfOM) and hydroxyl radical (
The β-lactam antibiotics are some of the most persistent anthropogenic pharmaceutical contaminant... more The β-lactam antibiotics are some of the most persistent anthropogenic pharmaceutical contaminants, and consequently are currently being detected in many aquatic environments. The presence of any level of antibiotics in water may contribute to the emergence of antibiotic-resistant bacterial strains, and therefore the active removal of these pharmaceuticals by additional water treatments such as advanced oxidation and reduction processes may be required. In this study, we report on our efficiency measurements for the hydroxylradical- based degradation of three β-lactam antibiotics obtained using steady-state
Proceedings of the Water Environment Federation, 2007
ABSTRACT Increasing demand for reclaimed water from wastewater treatment facilities has revolutio... more ABSTRACT Increasing demand for reclaimed water from wastewater treatment facilities has revolutionized the need for awareness of effluent quality and its properties. Wastewater can be made suitable for many reuse applications. Many of these applications for reclaimed water in industry, agriculture, and other beneficial uses have required stricter controls on the effluent quality from wastewater plants. These controls may apply to microbial pathogens, disinfection-by-products, or endocrine disruptors. In 1956, a paper to the Virginia Section meeting of the American Waterworks Association titled Destruction of Microorganisms in Water, Sewage, Sewage Sludge by Ionizing Radiation, Lowe, Lacy, Surkiewicz, and Jager concluded that it was possible to kill or inactivate pathogenic microorganisms in water by60Co gamma irradiation. Disinfectants such as chlorine, chloramines and ozone, react with natural organic matter to form disinfection-by-products (DBPs), many of which are regulated. Endocrine disruptors represent an emerging concern for their impact to the environment and fate within the ecosystem. Advanced oxidation processes using free radical chemistry represent a reasonably viable alternative to chemical additives such as chlorine or ozone for removal or elimination of objectionable contaminants from water. The process for production of free radicals has been well established. This paper explores the efficacy for use of advance oxidation processes using free radical chemistry for the elimination of objectionable contaminants from wastewater effluent and for reuse applications. Central to the focus of this paper will be the application of reuse water to the paper mill industry and agriculture. Relevant data and information on the needed reuse water quality criteria required for various processes are addressed and the criteria for treatment for removal of unwanted or objectionable contaminants will be identified.
The techniques of electron pulse radiolysis and absorption spectroscopy have been used to directl... more The techniques of electron pulse radiolysis and absorption spectroscopy have been used to directly measure rate constants for the hydrated electron reaction with CH3I, C2H5I, 1-C3H7I and 2-C3H7I. At 25°C, specific values of (1.78 +/- 0.05) × 1010, (1.57 +/- 0.07) × 1010, (1.05 +/- 0.06) × 1010 and (1.05 +/- 0.03) × 1010 dm3 mol-1 s-1 were determined for these compounds respectively, with corresponding overall activation energies of 16.9 +/- 1.3 (3.2-35.5°C), 19.5 +/- 1.1 (3.3-51.6°C), 16.60 +/- 0.65 (2.5-85.1°C) and 12.94 +/- 0.44 (2.5-84.5°C) kJ mol-1. The slight curvature observed in the Arrhenius plots for the three larger iodoalkanes suggests that these rate constants are influenced by both diffusion and chemical processes. By fitting the measured temperature-dependent rate constants to the general equation 1/kobs = 1/kdiff + 1/kreact, where kobs is the measured rate constant,kdiff is the encounter rate constant of the two reacting species and kreact is the rate constant that would be measured if diffusion of the species was not rate influencing, specific Arrhenius parameters for only the chemical component have also been determined.
ABSTRACT The ultrasonically induced oxidation of arsenite, As(III), in aqueous media is effective... more ABSTRACT The ultrasonically induced oxidation of arsenite, As(III), in aqueous media is effective over a range of concentrations and may be applicable as a pretreatment step for the removal of arsenic from water. We have conducted detailed studies on the conversion of arsenite in aqueous media by ultrasonic irradiation, focusing on the roles of ·OH, O2-· and H2O2 formed during the irradiation. The rate of the H2O2 induced transformation of As(III) is much slower than under hydroxyl radical generating ultrasonic conditions. The addition of superoxide dismutase does not change the rate of disappearance of As(III) under ultrasonic irradiation. The conversion of As(III) is very slow under selective generation of superoxide anion radical and its protonated form using gamma radiolysis, indicating that superoxide anion radical does not play a significant role in the conversion of As(III). In summary, hydroxyl radical plays the key role in the conversion of As(III), while hydrogen peroxide plays a minor role and superoxide anion radical has little or no role in the conversion of arsenite during ultrasonic irradiation.
The formation of KrF* and XeF* has been studied in electron-beam irradiated Kr/ Xe/SF6 gas mixtur... more The formation of KrF* and XeF* has been studied in electron-beam irradiated Kr/ Xe/SF6 gas mixtures. An electron-beam-energy dependent process has been observed, and confirmed to be due to ion recombination processes between rare gas cations and halide anions. The anions are formed by thermal electron capture by SF6 and the cations either being directly formed in the electron pulse (Kr +), or by subsequent charge transfer (Xe +).
Radical-based mineralization of aqueous halonitromethane disinfection byproducts. c Constructed k... more Radical-based mineralization of aqueous halonitromethane disinfection byproducts. c Constructed kinetic computer model for tri-halogenated halonitromethane removal. c Model predicted that superoxide reaction is unimportant for halonitromethanes. c Measured superoxide reaction with chloropicrin was negligibly slow, o 2 Â 10 4 M À 1 s À 1 .
Journal of the Chemical Society, Faraday Transactions, 1994
The reactions of primary water radiolysis radicals with IO–3 have been re-investigated using elec... more The reactions of primary water radiolysis radicals with IO–3 have been re-investigated using electron pulse radiolysis and absorption spectroscopy. Rate constants for iodate reaction with e–(aq)[(5.45 ± 0.45)× 109 dm3 mol–1 s–1], O˙–[(1.82 ± 0.04)× 109 dm3 mol–1 s–1] and ˙OH (< 105 dm3 mol–1 s–1) have been measured and compared with previously determined values. The observed iodate concentration dependence of the two transient absorptions produced by its reaction with the hydrated electron and the oxide radical were found to be due only to spur scavenging effects, and thus the dimerization equilibria proposed by previous workers is not necessary. The previously reported rate constants for the reaction of iodate with hydroxyl radicals have been shown to be due to just iodate reaction with the small concentration of O˙– present in equilibrium with the hydroxyl radical.
The efficient detection, decontamination, and destruction of chemical warfare (CW) agents remain ... more The efficient detection, decontamination, and destruction of chemical warfare (CW) agents remain an active area of scientific research. Rate constants for the reaction of substituted diethyl phosphates and phosphonates with the hydroxyl radical and hydrated electron have been measured in water to elucidate the primary destruction pathway for the CW agents Tabun (GA), Sarin (GB), Soman (GD), and VX with these two species. The measured kinetics for simulants with leaving groups that more closely mimic these actual CW agents predict that reductive destruction will be the most efficient mechanism, and that nontoxic simulants such as alkyl phosphonates undergo different redox chemistry.
Lactic acid is a major component of the TALSPEAK process planned for use in the separation of tri... more Lactic acid is a major component of the TALSPEAK process planned for use in the separation of trivalent lanthanide and actinide elements. This acid acts both as a buffer and to protect the actinide complexant from radiolytic damage. However, there is little kinetic information on the reaction of water radiolysis species with lactic acid, particularly under the anticipated process conditions of aerated aqueous solution at pH ∼ 3, where oxidizing reactions are expected to dominate. Here we have determined temperature-dependent reaction rate constants for the reactions of the hydroxyl radical with lactic acid and the lactate ion. For lactic acid this rate constant is given by the following equation: ln k 1) (23.85 (0.19)-(1120 (54)/T, corresponding to an activation energy of 9.31 (0.45 kJ mol-1 and a room temperature reaction rate constant of (5.24 (0.35) × 10 8 M-1 s-1 (24.0°C). For the lactate ion, the temperature-dependent rate constant is given by ln k 2) (24.83 (0.14)-(1295 (42)/T, for an activation energy of 10.76 (0.35 kJ mol-1 and a room temperature value of (7.77 (0.50) × 10 8 M-1 s-1 (22.2°C). These kinetic data have been combined with autotitration measurements to determine the temperature-dependent behavior of the lactic acid pK a value, allowing thermodynamic parameters for the acid dissociation to be calculated as ∆H°)-10.75 (1.77 kJ mol-1 , ∆S°)-103.9 (6.0 J K-1 mol-1 and ∆G°) 20.24 (2.52 kJ mol-1 at low ionic strength.
Arrhenius parameters for the reaction of hydrogen atoms with azide and thiocyanate in aqueous sol... more Arrhenius parameters for the reaction of hydrogen atoms with azide and thiocyanate in aqueous solution have been determined using electron pulse radiolysis and electron paramagnetic resonance free induction decay attenuation measurements. Absolute values for SCN-, N 3-, and HN 3 were well-described over the temperature range of 9-81°C by the equations log k 5) (12.03 (0.12)-[(21.05 (0.66 kJ mol-1)/2.303RT], log k 10) (12.75 (0.21)-[(18.43 (1.22 kJ mol-1)/2.303RT], and log k 15) (11.59 (0.12)-[(21.44 (0.69 kJ mol-1)/2.303RT], corresponding to room temperature (22°C) rate constants of (2.07 (0.03) × 10 8 , (3.15 (0.08) × 10 9 , and (6.31 (0.05) × 10 7 M-1 s-1 and activation energies for these chemicals of 21.05 (0.66, 18.4 (1.2, and 21.44 (0.69 kJ mol-1 , respectively. The similarity of these three measured activation energies, taken together with the available information on reaction products, suggests a similar reaction mechanism, which is proposed to be an initial hydrogen atom adduct formation in these molecules, followed by single bond breakage.
A pulsed, two-beam, thermal lensing experiment was performed to determine the concentration of aq... more A pulsed, two-beam, thermal lensing experiment was performed to determine the concentration of aqueous solutes above the critical point of water. Despite a very significant mirage effect due to thermal gradients in the cell and absorption by water itself, the thermal lensing signal strength for aqueous benzoic acid in supercritical water was found to be linear with concentration in the sub-millimolar range. Although thermal lensing experiments in aqueous media are notoriously insensitive, the sharp density gradient near the critical point considerably improves the signal intensity. In this study a short-pulse pump 266 nm YAG laser and continuous low-power probe Ar ion beam were both focused into a supercritical water cell, giving a lensing signal whose strength could be maximized by changing the overlap of the two beams.
The beta-lactam antibiotics are some of the most prevalent pharmaceutical contaminants currently ... more The beta-lactam antibiotics are some of the most prevalent pharmaceutical contaminants currently being detected in aquatic environments. Because the presence of any trace level of antibiotic in water may adversely affect aquatic ecosystems and contribute to the production of antibiotic-resistant bacteria, active removal by additional water treatments, such as using advanced oxidation and reduction processes (AO/RPs), may be required. However, to ensure that any AOP treatment process occurs efficiently and quantitatively, a full understanding of the kinetics and mechanisms of all of the chemical reactions involved under the conditions of use is necessary. In this study, we report on our kinetic measurements for the hydroxyl-radical-induced oxidation of 11 beta-lactam antibiotics obtained using electron pulse radiolysis techniques. For the 5-member ring species, an average reaction rate constant of (7.9 +/- 0.8) x 10(9) M(-1) s(-1) was obtained, slightly faster than for the analogous 6-member ring containing antibiotics, (6.6 +/- 1.2) x 10(9) M(-1) s(-1). The consistency of these rate constants for each group infers a common reaction mechanism, consisting of the partitioning of the hydroxyl radical between addition to peripheral aromatic rings and reaction with the central double-ring core of these antibiotics.
Direct infusion electrospray ionization mass spectrometry (ESI-MS) approaches were developed for ... more Direct infusion electrospray ionization mass spectrometry (ESI-MS) approaches were developed for rapid identification of impurity compounds formed from octylphenyl-(N,N-(diisobutyl)carbamoylmethyl) phosphine oxide (CMPO) during alpha and gamma irradiation experiments of this compound in dodecane. CMPO is an aggressive Lewis base, and produces extremely abundant metal complex ions in the ESI-MS analysis that make identification of low abundance compounds that are less nucleophilic challenging. Radiolysis products were identified using several approaches including restricting ion trapping so as to exclude the abundant natiated CMPO ions, extraction of acidic products using aqueous NaOH, and extraction of basic products using HNO 3. These approaches generated protonated, natiated and deprotonated species derived from CMPO degradation products formed via radiolytic cleavages of several different bonds. Cleavages of the amide and methylene-phosphoryl bonds appear to be favored by both alpha and gamma irradiation, while alpha irradiation also appears to induce cleavage of the methylene-carbonyl bond. The degradation products observed are formed from recombination of the initially formed radicals with hydrogen, methyl, isopropyl and hydroxyl radicals that are derived either from CMPO, contacted aqueous nitric acid, or the dodecane solvent.
ABSTRACT Octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in dodecane wa... more ABSTRACT Octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in dodecane was subjected to α-irradiation using a He-ion beam, 244 Cm isotopic α-rays, and He and Li ions created by the n,α reaction of 10B in a nuclear reactor. Post-irradiation samples were analyzed for the radiolytically-induced decrease in CMPO concentration, the appearance of degradation products, and their Am solvent extraction distribution ratios. The –G CMPO-value for the radiolytic degradation of CMPO was found to be very low compared to values previously reported for γ-irradiation. Additionally, isotopic irradiation to absorbed α-doses as high as 600 kGy in aerated solution had no effect on Am solvent extraction or stripping. The main CMPO radiolysis products identified in He-ion beam irradiated samples by ESI-MS include amides, an acidic amide, and amines produced by bond rupture on either side of the CMPO carbonyl group. Deaerated samples irradiated using the reactor in the absence of an aqueous phase, or with a dilute nitric acid aqueous phase showed small but measurable decreases in CMPO concentration with increasing absorbed doses. Higher concentrations of nitric acid resulted in lower decomposition rates for the CMPO. The radio-protection by dissolved oxygen and nitric acid previously found for γ-irradiated CMPO also occurs for α-irradiation. This suggests that similar free-radical mechanisms operate in the high-LET system, but with lower degradation yields due to the lower overall radical concentrations produced.
The partitioning of the long‐lived α‐emitters and the high‐yield fission products from dissolved ... more The partitioning of the long‐lived α‐emitters and the high‐yield fission products from dissolved nuclear fuel is a key component of processes envisioned for the safe recycling of nuclear fuel and the disposition of high‐level waste. These future processes will likely be based on aqueous solvent‐extraction technologies for light‐water reactor fuel and consist of four main components for the separation of uranium, fission products, and group trivalent actinides and lanthanides and separation of trivalent actinides from lanthanides. Since the solvent systems will be in contact with highly radioactive solutions, they must be robust toward radiolytic degradation in an irradiated, mixed organic and aqueous acidic environment. Therefore, an understanding of their radiation chemistry is important to the design of a practical system. In a previous paper, we reviewed the radiation chemistry of irradiated aqueous nitric acid and the tributyl phosphate ligand used for uranium extraction in the first step of the series of four extractions. In this paper, we review the radiation chemistry of the ligands proposed for use in the second extraction of cesium and strontium fission products. This includes not only the crown ethers and calixarenes but also cobalt dicarbollide and polyethylene glycol. Since many disparate units have been applied for measuring absorbed radiation dose in the literature, we also present a discussion of that topic and provide conversion factors.
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Papers by Stephen Mezyk