N2O-saturated Solutions Research Articles

One-step synthesis of tin oxide nanoparticles in aqueous solution induced by free radicals

Tin oxide nanoparticles of uniform size with around 5 nm distribution were synthesized in the aqueous solution of stannous chloride under an oxidizing environment. The syntheses were carried out with Cobalt-60 gamma radiation in N2O saturated solution, photoirradiation using 300 nm UV lamps as well as normal chemical route in the presence of H2O2 at room temperature under ambient laboratory conditions. The nanoparticles were characterized by XRD, FTIR and Raman spectroscopy, SEM and HRTEM measurements. The synthesis mechanism was investigated through the electron pulse radiolysis studies. It was established that the formation of tin oxide nanoparticles takes place only through the reactions of oxidizing free radicals like OH• or Cl2•- with Sn2+ ions in aqueous solution. The formation of tin oxide was found follow similar pathways in all the three cases, except that it took a longer time in the case of normal chemical route as compared to the other two routes. The size and shapes of the nanoparticles were found to be identical in all these three cases.

Diversity-oriented synthesis through gamma radiolysis: Preparation of unusual ecdysteroid derivatives activating Akt and AMPK in skeletal muscle cells

Gamma-ray radiation is a unique way to induce chemical transformations of bioactive compounds. In the present study, we pursued this approach to the diversity-oriented synthesis of analogs of 20-hydroxyecdysone (20E), an abundant ecdysteroid with a range of beneficial, non-hormonal bioactivities in mammals including humans. Gamma irradiations of aqueous solutions of 20E were conducted either in N2- or N2O-saturated solutions. Centrifugal partition chromatography was used to fractionate crude resulting irradiated materials using a biphasic solvent system composed of tert-butyl alcohol - ethyl acetate - water (0.45:0.9:1, v/v/v) in ascending mode. Subsequently, the products were purified by RP-HPLC. Fourteen ecdysteroids, including five new compounds, were isolated, and their structure were elucidated by 1D and 2D NMR and HRMS. Compounds 2–4, 7, 9, 12 and 15 were tested for their capacity to increase the Akt- and AMPK-phosphorylation of C2C12 murine skeletal myotubes in vitro. The compounds were similarly active on Akt as their parent compound. Stachysterone B (7) and a new ring-rearranged compound (12) were more potent than 20E in activating AMPK, indicating a stronger cytoprotective effect. Our results demonstrate the use of gamma irradiation in expanding the chemical diversity of ecdysteroids to obtain new, unusual bioactive metabolites.

Radiolysis induced degradation of 1,3-dichlorobenzene and 4-chlorophenol in aqueous solution

1,3-dichlorobenzene (1,3-DClB) degradation was studied to obtain radiolytic product yields (Gtotal = 0.546 μmol/J) and degradation in aerated or oxygen-free aqueous solutions, saturated with either N2O or N2O containing K3Fe(CN)6. In the four environments, several peaks were observed in the chromatograms, corresponding to byproducts, with more oxidized products produced in N2O saturated solutions. The absorbed dose necessary for the removal of 1,3-DClB increased with increasing solute concentrations in aerated solution. Further, 4-chlorophenol (4-ClP) degradation was investigated in a 0.3 mmol/dm3 solution by gamma radiolysis in the presence and absence of oxygen. The results showed that 4-ClP degrades more rapidly in a N2O environment, demonstrated by quantification of product concentrations in different doses, the value of Chemical oxygen demand, and a kinetics study. Hydroquinone, a radiolytic product, is very resistant to degradation. The dose necessary for the complete degradation of a 4-ClP solution containing air reached 9 kGy; however, in N2O saturated solution only 4.5 kGy were necessary for that purpose. The kinetics have a similar behavior in the two compounds, being pseudo-first-order. Importantly, the number of chlorine atoms in the molecule determined the chemical oxygen demand, as this determination was easy in 4-ClP but not possible in 1,3-DClB.

Radiolytic degradation of chlorobenzene in aerated and deoxygenated aqueous solutions.

Radiation-induced degradation of chlorobenzene was conducted at 0.1, 0.4, 0.5, 0.7, and 1.0mmol/dm3 concentrations in aerated environment and at 1.0mmol/dm3 in oxygen-free and N2O-saturated solutions. The results demonstrated that the elimination of chloride is important when the solution is oxygen free, because the [Formula: see text] attacks at the ipso position of the chloro group produces hydrochloric acid. The degradation was affected to a large extent by the concentration and to a lesser extent by the presence or absence of oxygen in the solutions which were irradiated. Thereby, the degradation occurred faster in the solutions with air and without oxygen and more slowly in the saturated solution with N2O. Some by-products were identified using an HPLC-UV-mass system. In addition, it was found that there is a linear correlation between the ln C/C0 and the dose, indicating that the radiolytic degradation followed pseudo-first-order reaction kinetics. The radiolytic oxidation was followed by the chemical oxygen demand (COD) test. The COD decreases when the solute concentration increases. The COD results were for a 0.47mmol/dm3 of 5.94mg O2 dm-3kGy-1 and for 0.09mmol/dm3 of 7.45mg O2 dm-3kGy-1.

Assessing potential impacts of phosphate precipitation on nitrous oxide emissions and the carbon footprint of wastewater treatment plants

ABSTRACTMetal salts are widely used for the precipitation of phosphorus during wastewater treatment transforming soluble orthophosphate to an insoluble salt. In practice, more complex reactions are taking place including a reduction of the chemical solubility of dissolved greenhouse gases, such as nitrous oxide, present in the wastewater stream. In this respect, it was postulated that phosphorous precipitation will lead to artificial N2O stripping and hence to an increased carbon footprint of wastewater treatment plants. From lab-scale experiments utilizing N2O-saturated synthetic sewage solutions, it was evidenced that metal salt addition leads to N2O stripping with 20.8 g N2O per liter for a FeCl2-based precipitant to 26.4 g N2O per liter for a Aln(OH)mCl3n-m-based precipitant. Taking this maximum potential stripping effect into account for a carbon footprint analysis, a potential contribution of 16.11 kg CO2,eq·PE−1·a−1 was calculated in a case study, where FeCl3 was considered. With respect to the defined system boundary conditions, the overall on-site and off-site CO2 emissions were raised by 34% from 46.87 kg CO2,eq·PE−1·a−1 to 62.97 kg CO2,eq·PE−1·a−1 through CO2,eq coming from phosphorous precipitation.

Radiation induced environmental remediation of Cr(VI) heavy metal in aerated neutral solution under simulated industrial effluent

Abstract Cr(VI) compounds are major water contaminants in most industrial effluents, due to their carcinogenicity, while Cr(III) is an important element for human metabolism. In a previous work, we showed that Cr(VI) was radiolytically reduced to Cr(III) by the CO2ˉ• radical at pH 3 N2O-saturated solution in the presence of formate. Here in the present work, this removal was investigated by steady state irradiation and pulse radiolysis in aerated solution at neutral pH, which is close to natural conditions in most wastewaters, where the reducing agent is the superoxide radical anion O2ˉ•. The degradation of Cr(VI) increased linearly with the absorbed dose and was significantly enhanced by the added formate but not by the radiolitically produced hydrogen peroxide at this pH. The rate constant for this reduction was found to be 1.28×108 M−1 s−1 and the absorption spectrum of Cr(V) transient species was obtained. A partial recovery of Cr(VI) is observed over a period of ca. 5 ms following a second order kinetics with a rate constant 8.0×106 M−1 s−1. These outcomes suggest that gamma-irradiation of Cr(VI)-contaminated wastewaters and industrial effluents in presence of formate can be simple, effective and economical means for the remediation of this major contaminant.

The degradation and mineralization of acephate by ionization irradiation

The degradation and mineralization of acephate in aqueous solutions by 60Co-γ irradiation were investigated. The acephate was dissolved in different pH buffer solutions and purged for 30 min using anticipate gas. It was found that the degradation ratio of acephate increased gradually with the absorbed dose, and the inorganic ions, , , and , were generated in the irradiated solutions. For the solutions without oxygen, the degradation ratio of acephate in N2-saturated solutions containing t-BuOH was the highest, and that in N2-saturated solutions was higher than that in N2O-saturated solutions. However, the total concentration of inorganic ions in N2O-saturated solutions was higher than that in the other solutions. Moreover, the concentration of in N2-saturated solutions containing t-BuOH was larger than that of and , whereas in or N2O− saturated solutions, the concentrations of inorganic ions were in the order of > > . In the air-saturated and O2-saturated solutions, it was found that the concentration of inorganic ions generated was in the order of > > . The degradation degree of acephate and the concentrations of inorganic ions in O2-saturated solutions were higher than those in the air-saturated solutions. The result showed that both of the oxidative and reductive radicals could degrade the acephate, and the oxidative could improve the mineralization of acephate. It was further concluded that it was easier for the reductive radicals to attack the bonds around N than other bonds around S and P, and the SC and PS bond are easily attacked by oxidative radicals. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 324–332, 2015

The Influence of Sodium Dodecyl Sulfate on the Photoionization of the Ruthenium(tris)bipyridine Dication

Abstract Using single-pulse and two-pulse two-colour laser flash photolysis (308 nm and 355 nm), we have quantitatively studied the effect of sodium dodecyl sulfate (SDS), at concentrations above and below the critical micellar concentration (cmc), on the cyclic photoionization of the ruthenium(tris)bipyridine dication in aqueous medium. In contrast to reports in the literature (Chem. Phys. Lett. 315 (1999) 416) about a superincrease of the electron yield by SDS concentrations in the range between 3.0 · 10 –4 M and 4.5 · 10 –4 M we found that the observed absorption increases are entirely due to background signals in the vicinity of an insolubility range, as can be proved by difference experiments (argon-saturated vs. N2O-saturated solutions); SDS has no appreciable effect on the reaction below the cmc, and causes a moderately increased electron yield above the cmc. By varying the excitation intensities and analyzing the intensity dependences, we have shown that that increase is not due to a facilitation of the photoionization proper by the micelles but to a more efficient photoreduction of the oxidized complex by SDS in that cyclic mechanism.

Role of radiolytically generated species in polymerization of [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETC) in aqueous medium: Steady state and pulse radiolysis study

Radiation induced polymerization of [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETC) in aqueous solution has been studied by steady state and pulse radiolysis techniques. The effect of absorbed dose, dose rate, monomer concentration and ambient conditions were investigated by measuring the relative viscosity of monomer solution. AETC has been found to react with OH and e−aq with bimolecular rate constants of 7.6×109M−1s−1 and 3.7×1010M−1s−1, respectively. The bimolecular rate constants for the reaction of AETC− and AETC-OH with the monomer molecule AETC have been found to be 1.7×107M−1s−1 and 2.2×106M−1s−1, respectively. Further, AETC− and AETC-OH have been found to react with oxygen with k=3.2×109M−1s−1 and 2.2×109M−1s−1, respectively. The monomer underwent polymerization upto an absorbed dose of 0.14 and 0.42kGy in N2O and N2 saturated solutions and later the radiolytic degradation of the polymer was predominant. The reaction of AETC transients with oxygen was also established by decrease in polymerization extent in aerated and oxygenated solution.

Radiation-induced decomposition of cyclotrimethylenetrinitramine in aqueous solutions

Radiation-induced decomposition of cyclotrimethylenetrinitramine, a representative of heterocyclic nitramines, in dilute aqueous solutions saturated with argon, air, and N2O has been investigated. Dose dependence curves have been obtained, and the initial yields of formation of nitrite ions and hydrogen peroxide have been measured, making up 0.122 and 0.049 in deaerated solutions, 0.050 and 0.065 in aerated solutions, and 0 and 0.074 μmol/J in N2O-saturated solutions, respectively. The main radiolysis initial steps involve the reaction of dissociative electron capture with nitro-group elimination in the form of nitrite ion and the reaction of hydrogen atom abstraction from the methylene group by hydroxyl radicals and atomic hydrogen.

Application of ionizing radiation to environmental protection: removal of toxic Cr(VI) metal ion in industrial wastewater: preliminary study

Hexavalent chromium, a major contaminant in most wastewater sites, is a potential health threat inducing cancer to humans while trivalent chromium is an essential element for the metabolism of sugar. The radiation-induced reduction of Cr(VI) metal ion to Cr(III) by the perhydroxyl radical (HO2 • ) and carboxyl radical anion (CO2 -• ) pro- duced by continuous radiolysis of water was investigated by steady state radiolysis of O2, Ar and N2O-saturated pH 3 solutions in the presence of formate. In all cases the removed Cr(VI) was a linear function of the absorbed dose. The added formate was favorable for removing Cr(VI). Its presence protects the solution from reverse radiolytic oxi- dation of Cr(III) to Cr(VI). The measured and calculated yield of removal of Cr(VI) do agree quite well at low formate concentration but at high formate concentration the measured yield was higher than the expected. When all formate is exhausted no recovery of Cr(VI) from Cr(III) was observed in case of O2- and Ar-saturated solutions whilst in the case of N2O-saturated solutions Cr(VI) recovers. The results obtained in this study highlight the potential of this technology for industrial wastewater treatment.

Iodide-Mediated Photooxidation of Arsenite under 254 nm Irradiation

The preoxidation of As(III) to As(V) is a desirable process to increase the removal efficiency of arsenic in water treatment In this work, the photooxidation of As(III) under 254 nm irradiation was investigated in the concentration range of 1-1000 microM in the presence of potassium iodide (typically 100 microM). Although the direct photooxidation of As(III) in water was negligible, the presence of iodide dramatically enhanced the oxidation rate. The quantitative conversion of As(III) to As(V) was achieved. The quantum yields of As(III) photooxidation ranged from 0.08 to 0.6, depending on the concentration of iodide and As(III). The excitation of iodides under 254 nm irradiation led to the generation of iodine atoms and triiodides, which seem to be involved in the oxidation process of As(III). Because the efficiency of iodine atom generation is highly dependent on the presence of suitable electron acceptors,the photooxidation of As(III) was efficient in an air- or N2O-saturated solution but markedly reduced in the N2-saturated solution. The production of H2O2 was also accompanied by the generation of As(V). The addition of excess methanol (OH radical scavenger) did not reduce the photooxidation rate at all, which ruled out the possibility of hydroxyl radical involvement. It was found that the in situ photogenerated triiodides oxidize As(III) with regenerating iodides by completing a cycle. The proposed UV254/KI/As(III) process is essentially an iodide-mediated photocatalysis.

Oxygen-Copper (II) Interplay in the Repair of Semi-Oxidized Urate by Quercetin Bound to Human Serum Albumin

The 1:1 complex of copper (II) and human serum albumin (HSA) slowly reacts with radiolytically generated •O2- radical-anion at a rate constant of 6.1×106 M-1 s-1. Absorbance and fluorescence spectroscopies demonstrate that addition of an equimolar portion of quercetin (QH2) to the solution of the copper (II)-HSA complex induces a relocalization of the copper resulting in a ternary copper (II)-QH2-HSA complex. This form of quercetin slowly oxidizes in air-saturated solutions. A 10-fold excess urate, a plasma antioxidant, cannot displace copper (II) bound to HSA. In N2O-saturated solutions the ternary complex form of QH2 can repair the urate radical with a rate constant of 2.7×106 M-1 s-1 by an electron transfer reaction similar to that observed in the absence of copper (II). In O2-saturated solutions and in the absence of copper, HSA-bound QH2 fails to repair the urate radical because of the fast competitive reaction of •O2- with urate radicals. However, addition of equimolar copper (II) restores the electron transfer from QH2 to the urate radical. These contrasting results are tentatively explained either by an enhanced reactivity of copper (II) with •O- in the ternary complex or by direct production of quercetin radicals via a copper-catalyzed reduction of the •O- radicals by QH2.

Gamma-radiation induced agglomeration of chicken muscle myosin and actine

Radiolytic behaviour of themajor vertebrate muscle proteins: fibrillarmyosin (molar mass, Mm = 520,000 g/mol) and filament forming actin (Mm = 42,050 g/mol) was studied using a SDS-polyacrylamide gel electrophoresis and quantified by high precision laser-densitometry. In order to study the OH radical contribution to the radiation damage, purified chicken myosin and actin (4 ?M) were prepared in N2O saturated solution and irradiated with 1?3 kGy at 60Co gamma source. With respect to changes in the molecular mass, the only observed myosin and actin damage was dose dependent agglomeration of proteins. The corresponding radiation chemical yields of 5 x?10-8 mol J-1 and 6.3 x?10-8 mol J-1 were obtained for myosin and actin, respectively. This result confirmed that only the radiation-induced agglomeration is initiated with the reaction of the OH radical even in the situation where the OH radical concentration produced exceeds the protein concentration 500 times thus enabling the multi-radical attack to occur.

Demethoxylation and hydroxylation of methoxy- and hydroxybenzoic acids by OH-radicals. Processes of potential importance for food irradiation

The hydroxylation process for methoxy- and hydroxy-benzoic acids (MBA, HBA) induced by γ-radiation is compared. 2-, 3-, and 4-methoxybenzoic acid as well as 3-hydroxybenzoic acid have been irradiated in N2O and aerated solutions up to 1.5 kGy. The products were analyzed by HPLC. The results for 2- and 4-HBA have been taken from literature data. The OH·-adduct distribution is generally the same for the hydroxy- as well as for the methoxy-benzoic acid isomers. With both 4-HBA and 4-MBA more than 65% C3-adducts and about 15% C4-adducts are formed, which could be proved by their reactions with K3Fe(CN)6. Oxidation of the nonipso-adducts of 3-HBA and 3-MBA results in 84 and 87% of the corresponding phenols. Whereas in N2O-saturated solutions only part of the OH·-radicals leads to substrate decomposition, in the presence of air, the degradation of both kinds of compounds is equivalent to [OH·]. The nonipso OH·-adducts of the HBAs are converted into 68–77% hydroxylation products. With the MBAs, the hydroxylation process is [Formula: see text] 10%. This is attributed to different decay pathways of the peroxyl radicals, intermediates formed by O2 addition to the OH·-adducts. The hydroxyperoxycyclohexadienyl radicals of the HBAs decay mainly by HO2· elimination to the corresponding phenols, those of the MBAs decay predominantly by fragmentation of the benzene ring, yielding to nonidentified aliphatic products. The replacement of -OCH3 by -OH is practically not influenced by the presence of oxygen, it increases in the sequence 3-MBA < 4-MBA < 2-MBA. For 2-MBA, yields of more than 15% are obtained. Both processes, hydroxylation as well as demethoxylation, might be of importance for the recognition of radiolytical changes in foodstuff.Key words: γ-radiolysis, methoxybenzoic acids, hydroxybenzoic acids, phenolic acids, food components, reaction mechanisms, product analysis, HPLC analysis.

OH Radical Reaction of 5-Substituted Uracils: Pulse Radiolysis and Product Studies of a Common Redox-Ambivalent Radical Produced by Elimination of the 5-Substituents

Using a redox titration method in the pulse radiolysis of N2O-saturated phosphate buffer solution, the redox properties of the intermediate radicals derived from OH radical reactions of 5-substituted uracils 1c−h (R = F, Cl, Br, NO2, NH2, OH) have been characterized. While the primary intermediates were oxidizing C(5) radicals 2c−h and reducing C(6) radicals 3c−h of the respective OH adducts, a common allyl-type radical of “redox ambivalence” with limiting mesomeric forms of reducing carbon-centered 5-oxo-5,6-dihydrouracil-6-yl radical (4) and oxidizing oxygen-centered uracil-5-oxyl radical (5) was secondarily formed via elimination of 5-substituents from 3c−h. The rate of 5-substituent elimination decreased with varying structures of the 5-substituents in the order halo > amino, nitro > hydroxy groups. The common radical 4/5 showed weaker reducing/oxidizing abilities than the typical pyrimidine C(6) and C(5) radicals. The product study demonstrated that the one-electron reduction of 5-oxyl radical 5 by N,N,N‘,N‘-tetramethyl-p-phenylenediamine ((2.0 ± 0.1) × 108 dm3 mol-1 s-1) increased the yield of isobarbituric acid (1h), while the one-electron oxidation of 5-oxo C(6) radical 4 by tetranitromethane increased the yield of isodialuric acid (6).

OH-Radical-induced oxidation of methanesulfinic acid. The reactions of the methanesulfonyl radical in the absence and presence of dioxygen

Hydroxyl radicals were generated radiolytically in N2O-saturated solutions. As shown by pulse radiolysis, methanesulfinic acid reacts with ˙OH (k = 5.3 × 109 dm3 mol−1 s−1) and N3˙ giving rise to an intermediate which has an absorption maximum at 330 nm (Ge ≈ 5.2 × 10−5 m2 mol−1). This is attributed to the methanesulfonyl radical, CH3S(O)O˙. Pulse radiolysis with conductometric detection indicates that CH3S(O)O˙ is formed in only ∼80% yield. This is confirmed by scavenging experiments with Fe(CN)64−, ascorbate and sulfite, which are oxidised by CH3S(O)O˙ with rate constants of ∼2 × 109 dm3 mol−1 s−1. Steady-state radiolysis of methanesulfinic acid shows that methanesulfonic acid is the major product (G = 2.1 × 10−7 mol J−1). Further products are sulfate (0.7 × 10−7 mol J−1), methane (0.3 × 10−7 mol J−1), ethane (0.08 × 10−7 mol J−1) and dimethyl sulfone (not quantified). It is suggested that an OH-adduct is formed initially which mainly eliminates OH−, but also decomposes yielding ˙CH3 and bisulfite. The formation of methanesulfonic acid can be explained by a disproportionation of the methanesulfonyl radicals via recombination and subsequent hydrolysis. In the presence of dioxygen, a chain reaction occurs whereby 2 mol methanesulfonic acid are formed per 1 mol dioxygen consumed. G(methanesulfonic acid) ≈ 250 × 10−7 mol J−1 was found to be independent of dose rate (0.011–0.165 Gy s−1), methanesulfinic acid concentration [(0.1–4) × 10−3 mol dm−3] and dioxygen concentration. An efficient chain process was also observed upon electron beam irradiation [G(methanesulfonic acid) ≈ 200 × 10−7 mol J−1 at 0.8 Gy per pulse and 75 × 10−7 mol J−1 at 9 Gy per pulse (pulse duration 2 μs)]. It is proposed that the oxidation of the substrate by the methylsulfonylperoxyl radical, CH3S(O2)OO˙, to give the strongly oxidising CH3S(O2)O˙ radical, initiates the chain reaction, with the latter propagating the chain by reacting with a substrate molecule to give methanesulfonic acid and the methanesulfonyl radical. Branching and partial removal of the chain-carrying CH3S(O2)O˙ radicals by H-abstraction from the substrate is suggested as the likely path leading to chain termination. Oxidation of methanesulfinate by ozone (k = 2 × 106 dm3 mol−1 s−1) occurs only by O-atom transfer, and an electron transfer that would start a chain reaction was not observed.

OH-Radical-induced chain scission of chitosan in the absence and presence of dioxygen

Hydroxyl radicals (and 15% H-atoms) were generated radiolytically in N2O-containing aqueous solutions of protonated chitosan (Mw = 4.0 × 105 Da, degree of deacetylation 90.5%, pH ≈ 3). The rate constant of H-abstraction from chitosan by OH radicals is k = 6.4 × 108 dm3 mol−1 s−1, as measured by pulse radiolysis using thymine as competitor. With SCN− as competitor the apparent rate constant is found to be too high, because of a condensation of SCN− around the positively charged macromolecule. The radiation-chemical yields of chain scission are G = 3.4 × 10−7 mol J−1 in N2O-saturated and G = 2.1 × 10−7 mol J−1 in N2O–O2-saturated solutions. The kinetics have been followed by pulse radiolysis with conductometric detection. For each chain break, ≈3.1 counterions (ClO4−) are released, on average, from the condensation zone into the bulk solution. In N2O-saturated solution the kinetics of chain scission are independent of dose rate, although more than one first-order process contributes (overall: k ≈ 95 s−1 at pH 3.3). In the presence of dioxygen, the kinetics of chain scission depend on the dose rate, i.e. second-order processes play also a significant role.

Radiolysis of Aqueous Solutions with Pulsed Helium Ion Beams. 3. Yields of OH Radicals and the Sum of eaq- and H Atom Yields Determined in Methyl Viologen Solutions Containing Formate

The production of methyl viologen radical cation (MV•+) in the radiolysis of aqueous solutions of 0.5 mM methyl viologen (MV2+) containing formate and tertiary butanol (t-BuOH) was studied using fast electron (integral yields) and 21 MeV 4He ion beam pulses (track segment yields). The formate concentration was varied in the range of 10-3−2 M. It was confirmed that MV•+ is formed within microseconds and that it is stable in the measured time regions if the solution contains neither t-BuOH nor oxygen. Tertiary butanol radical formed through the scavenging of OH radical or H atom by t-BuOH reacts with MV•+, and this rate constant was determined as (8 ± 2) × 108 M-1 s-1. The effect of formate concentration on the yield of methyl viologen radical cation was measured in deaerated or N2O-saturated solutions. The radical yields in deaerated solutions agreed well with those measured by continuous ion beam radiolysis, which confirmed that this system can be used as a chemical dosimeter for ion beam pulse radiolysis. The yields of OH radicals were derived from the yields of G(MV•+) in the presence and the absence of t-BuOH. In the radiolysis with low linear energy transfer (LET) radiations, the calculated OH radical yields agree well with the values determined by other OH radical scavengers, formate and formic acid, except at high scavenging capacity. In 4He ion beam radiolysis, the yields have a discrepancy in the measured scavenging capacity range. The sum of the contributions of eaq- and H atoms to form MV•+ was also determined. This value was lower than the yields estimated from other studies with 4He ion beams. Yields are highly dependent on the nature of the solutes and combination of solutes because of intratrack reactions of the products.

Mechanisms of Ionizing Radiation-Induced Destruction of 2,6-Dichlorobiphenyl in Aqueous Solutions

Polychlorinated biphenyls (PCBs) appear as environmental pollutants in various phases. Aqueous media polluted with such compounds may potentially be detoxified by electron beam irradiation. In the present study, we discuss the possible mechanisms of radiolytic detoxification under various conditions, and we study 2,6-dichlorobiphenyl (DCB) as a model compound for PCBs. Electron beam and γ-irradiation of DCB in aqueous methanol solutions lead to degradation of this compound and formation of Cl- ions, but high doses are required. Solutions of 1 mmol L-1 DCB require a dose of 30 kGy to produce 1 equiv of Cl- (G = 0.03 μmol J-1) to form the less toxic monochlorobiphenyl (MCB), but 600 kGy is required to achieve full dechlorination. This low yield is due to the concomitant formation of acid, which competes with DCB for the solvated electrons, the main reducing species in this system. The radiolytic yields are improved dramatically by the addition of carbonate; only 20 kGy are required for practically quantitative dechlorination of DCB. For the oxidation process, the dechlorination of DCB by •OH radicals was measured in N2O-saturated solutions and found to be much less effective than the reduction process.