Presence Of OH Scavengers Research Articles

Experimental and Theoretical Studies of Trans-2-Pentenal Atmospheric Ozonolysis

We investigated the kinetics, mechanism and secondary organic aerosols formation of the ozonolysis of trans-2-pentenal (T2P) using four different reactors with Fourier Transform InfraRed (FTIR) spectroscopy and Gas Chromatography (GC) techniques at T = 298 ± 2 K and 760 Torr in dry conditions. The rate coefficients and branching ratios were also evaluated using the canonical variational transition (CVT) state theory coupled with small curvature tunneling (CVT/SCT) in the range 278–350 K. The experimental rate coefficient at 298 K was (1.46 ± 0.17) × 10−18 cm3 molecule−1 s−1, in good agreement with the theoretical rate. The two primary carbonyls formation yields, glyoxal and propanal, were 57 ± 10% and 42 ± 12%, respectively, with OH scavenger compared to 38 ± 8% for glyoxal and 26 ± 5% for propanal without OH scavenger. Acetaldehyde and 2-hydroxypropanal were also identified and quantified with yields of 9 ± 3% and 5 ± 2%, respectively, in the presence of OH scavenger. For the OH production, an upper limit of 24% was estimated using mesitylene as OH tracer. Combining experimental and theoretical findings enabled the establishment of a chemical mechanism. Finally, the SOA formation was observed with mass yields of about 1.5%. This work provides additional information on the effect of the aldehyde functional group on the fragmentation of the primary ozonide.

Sun-light driven rapid photocatalytic degradation of methylene blue by poly(methyl methacrylate)/metal oxide nanocomposites

Discharge of dyes (major industrial coloring agents ∼700,000 tonnes) in environment is of concern due to their high perseverance, toxicity and carcinogenicity. Thus, effective elimination of organic dye (methylene blue) was carried out by poly(methyl methacrylate) (PMMA) incorporated metal oxide nanocomposites. Spherical and semi crystalline Fe3O4-PMMA, ZnO-PMMA, CuO-PMMA and Ni2O3-PMMA were self-assembled via green route employing Sapindus mukkorossi (Plant extract). At optimised conditions (dye conc: 2 mg L−1; catalyst: 80 mg: neutral pH) MO-PMMA showed maximum degradation efficiency (90–99%; t1/2 = 5.1–5.6 h) than that of individual MO (74–80%; t1/2 = 5.8–6.8 h) credited to improved thermal stability and surface area via incorporation of MO into PMMA matrix. Like MO, highest degradation with ZnO-PMMA (99%; Xm = 0.135 mg/g) followed by Ni2O3-PMMA (98%), CuO-PMMA (93%) and Fe3O4-PMMA (90%) could be attributed to its high surface area (85.32 m2 g−1) and least zeta potential (-22.5 eV). Adsorption of MB over catalyst was statistically significant with Langmuir isotherms (R2: 0.99 and p value: 0.0005) and first order kinetics with greatly reduced half-life. Comparatively higher degradation in sunlight than dark, and involving hydroxylation, oxidation and ring opening clearly reinforced boosted oxidation of MB by OH. Moreover, reduction in degradation (50-40%) in presence of OH scavengers supported the photocatalytic activity of nanocomposites. MB was degraded into minor non-toxic by-products such as (Z)-hexa-3,5-dien-1-ol and (Z)-buta-1,3-dien-1-ol and benzoquinone. Overall, by virtue of greater active sites, high surface activity and semiconducting nature, the as-synthesized MO-PMMA photocatalyst is a promising, recyclable (n = 10) and eco-friendly panorama in the treatment of organic- pollutants in water and wastewater-treatment.

Use of selected scavengers for the determination of NF-TiO2 reactive oxygen species during the degradation of microcystin-LR under visible light irradiation

Although UV-induced TiO2 photocatalysis involves the generation of several reactive oxygen species (ROS), the formation of hydroxyl radicals is generally associated with the degradation of persistent organic contaminants in water. In this study, a variety of radical scavengers were employed to discriminate the roles of different ROS during visible light-activated (VLA) photocatalysis using nitrogen and fluorine doped TiO2 (NF-TiO2) in the degradation of the hepatotoxin, microcystin-LR (MC-LR) in water. The addition of hydroxyl radical scavengers, methanol and tert-butyl alcohol to the reaction mixture resulted in negligible inhibition of NF-TiO2 photocatalytic degradation of MC-LR at pH 3.0 and only partial inhibition at pH 5.7 under visible light. While hydroxyl radicals (OH) generally play the primary role in UV-TiO2 photocatalysis, the minimal influence of MeOH and t-BuOH on the degradation process under these experimental conditions indicates that OH are not crucial in VLA NF-TiO2 photocatalysis. However, strong inhibition was observed in VLA NF-TiO2 photocatalytic degradation of MC-LR in the presence of superoxide dismutase, benzoquinone and catalase at pH 3.0 and 5.7 indicating that O2− and H2O2 play critical roles in the degradation process. Similar degradation rates were observed in the presence of deuterium oxide, which enhances singlet oxygen mediated processes further suggesting singlet oxygen is not a key species in the degradation of MC-LR. Formic acid and cupric nitrate were added to probe the roles of the valence band holes and conduction band electrons, respectively. Under UV–vis light irradiation, almost complete inhibition of MC-LR removal is observed with NF-TiO2 in the presence of OH scavengers at pH 5.7. These results demonstrate that the solution pH plays a major role in the formation and reactivity of ROS during VLA NF-TiO2 photocatalysis. The adsorption strength of scavengers and MC-LR onto NF-TiO2 as well as the speciation of ROS as a function of pH needs to be carefully considered since they also play a major role in the efficiency of the process. These results indicate that the reduction of molecular oxygen by photo-generated electrons rather than hydroxyl radicals produced by oxidative reactions of photo-generated holes is the key factor in the VLA NF-TiO2 photocatalytic degradation of MC-LR.

Photocatalytic oxidation mechanism of arsenite on tungsten trioxide under visible light

Abstract The oxidation of arsenite (As(III)) to arsenate (As(V)) and the involved oxidants on tungsten trioxide (WO 3 ) under visible light were mechanically investigated. Three oxidant species, valence-band hole (h vb + ), hydrogen peroxide (H 2 O 2 ), and hydroxyl radical ( OH), can be generated on WO 3 under visible light. However, As(III) was not oxidized to As(V) in the presence of H 2 O 2 . In addition, the oxidation rate of As(III) to As(V) was not reduced in the presence of OH scavenger. These results indicate that the oxidation of As(III) to As(V) is primarily initiated by hole, but both OH and H 2 O 2 are little involved in As(III) oxidation to As(V). This hole-mediated oxidation of As(III) to As(V) on WO 3 was further confirmed by X-ray photoelectron spectroscopy (XPS) analysis (i.e., the adsorption of As(III) on WO 3 ) and photoelectrochemical measurement (i.e., the enhanced photocurrent by As(III) addition). Although OH is little involved in As(III) oxidation to As(V), the production of OH was reduced in the presence of As(III). This behavior implies that As(III) on WO 3 acts as an external charge recombination center, where the oxidation of As(III) to intermediate As(IV) species by hole or OH is immediately followed by the reduction of As(IV) to As(III) by conduction-band electron (e cb – ). Therefore, the direct oxidation of As(III) to As(V) by two-hole transfer can be proposed as the primary oxidation pathway of As(III) to As(V) on WO 3 under visible light.

Removal of iopromide and degradation characteristics in electron beam irradiation process

The aim of this study is to evaluate the removal efficiency of iopromide using electron beam (E-beam) irradiation technology, and its degradation characteristics with hydroxyl radical (OH) and hydrated electron (eaq−). Studies are conducted with different initial concentrations of iopromide in pure water and in the presence of hydrogen peroxide, bicarbonate ion, or sulfite ion. E-beam absorbed dose of 19.6kGy was required to achieve 90% degradation of 100μM iopromide and the E-beam/H2O2 system increased the removal efficiency by an amount of OH generation. In the presence of OH scavengers (10mM sulfite ion), the required dose for 90% removal of 100μM iopromide was only 0.9kGy. This greatly enhanced removal was achieved in the presence of OH scavengers, which was rather unexpected and unlike the results obtained from most advanced oxidation process (AOP) experiments. The reasons for this enhancement can be explained by a kinetic study using the bimolecular rate constants of each reaction species. To explore the reaction scheme of iopromide with OH or eaq− and the percent of mineralization for the two reaction paths, the total organic carbon (TOC), released iodide, and intermediates were analyzed.

Inactivation of Escherichia coli in Na 2SO 4 electrolyte using boron-doped diamond anode

Electrochemical disinfection in chloride-free electrolyte has attracted more and more attention due to advantages of no production of disinfection byproducts (DBPs), and boron-doped diamond (BDD) anode with several unique properties has shown great potential in this field. In this study, inactivation of Escherichia coli ( E. coli) was investigated in Na 2SO 4 electrolyte using BDD anode. Firstly, disinfection tests were carried on at different current density. The inactivation rate of E. coli and also the concentration of hydroxyl radical ( OH) increased with the current density, which indicated the major role of OH in the disinfection process. At 20 mA cm −2 the energy consumption was the lowest to reach an equal inactivation. Moreover, it was found that inactivation rate of E. coli rose with the increasing Na 2SO 4 concentration and they were inactivated more faster in Na 2SO 4 than in NaH 2PO 4 or NaNO 3 electrolyte even in the presence of OH scavenger, which could be attributed to the oxidants produced in the electrolysis of SO 4 2−, such as peroxodisulfate (S 2O 8 2−). And the role of S 2O 8 2− was proved in the disinfection experiments. These results demonstrated that, besides hydroxyl radical and its consecutive products, oxidants produced in SO 4 2− electrolysis at BDD anode played a role in electrochemical disinfection in Na 2SO 4 electrolyte.

Evidence of the water-cage effect on the photolysis of [formula omitted] and FeOH 2+. Implications of this effect and of H 2O 2 surface accumulation on photochemistry at the air–water interface of atmospheric droplets

Experiments are conducted to determine the effect of a cage of water molecules on the photolysis quantum yields of nitrate, FeOH 2+, and H 2O 2. Results suggest that the quantum yields of nitrate and FeOH 2+ are decreased by the recombination of photo-fragments ( OH + NO 2 and Fe 2+ + OH, respectively) before they leave the surrounding cage of water molecules. However, no evidence is found for an enhanced quantum yield for H 2O 2. Therefore, the photolysis of nitrate and FeOH 2+ could be enhanced if the cage of the solvent molecules is incomplete, as is the case at the air–water interface of atmospheric droplets. The photolysis rate constant distribution within nitrate, FeOH 2+, and H 2O 2 aerosols is calculated by combining the expected quantum yield data in the bulk and at the interface with Mie theory calculations of light intensity. The photolysis rate constant of nitrate and FeOH 2+ would be significantly higher at the surface than in the bulk if quantum yields are enhanced at the surface. In the case of H 2O 2, the photolysis rate constant would be enhanced by surface accumulation. The results concerning the expected rates of photolysis of these photoactive species are applied to the assessment of the reaction between benzene and OH in the presence of OH scavengers in an atmospherically relevant scenario. For a droplet of 1 μm radius, a large fraction of the total OH-benzene reaction (15% for H 2O 2, 20% for nitrate, and 35% for FeOH 2+) would occur in the surface layer, which accounts for just 0.15% of the droplet volume.

Hydroxyl radical detection with a salicylate probe using modified CUPRAC spectrophotometry and HPLC

Reactive oxygen species (ROS) may attack biological macromolecules giving rise to oxidative stress-originated diseases, so it is important to establish efficient methods to screen hydroxyl radical scavengers for antioxidant therapy. Since OH is very short-lived, secondary products resulting from OH attack to various probes are measured. As a low-cost measurement technique, we used a salicylate probe for detecting hydroxyl radicals generated from an equivalent mixture of Fe(II) + EDTA with hydrogen peroxide. The produced hydroxyl radicals attacked both the probe and the water-soluble antioxidants in 37 °C-incubated solutions for 2 h. The CUPRAC (cupric ion reducing antioxidant capacity) assay absorbance of the ethylacetate extract due to the reduction of Cu(II)–neocuproine reagent by the hydroxylated probe decreased in the presence of OH scavengers, the difference being proportional to the scavenging ability of the tested compound. Attack by OH radicals upon salicylate produced 2,3-dihydroxybenzoate, 2,4-dihydroxybenzoate, and 2,5-dihydroxybenzoate as major products. HPLC separation combined with CUPRAC spectrophotometry was used to identify and quantify hydroxylated salicylate derivatives in the presence of synthetic water-soluble antioxidants and green tea infusion. The developed spectrophotometric method for OH detection was validated with HPLC, i.e., the concentrations of dihydroxybenzoates produced by radical attack from the probe were determined by HPLC, and the sum of (concentration × absorptivity) products of these components approximately agreed with the experimentally found CUPRAC absorbances, confirming the validity of Beer's law for the selected system. Statistical comparison of the results found with the proposed methodology and HPLC was made with two-way ANOVA (analysis of variance) test. Under optimal conditions, about 53% of the probe (salicylate) was converted into dihydroxybenzoate isomers in the absence of OH scavengers, and these isomers were more specific markers of hydroxyl radicals than the non-specific malondialdehyde end-product of the TBARS test. Thus, the more costly and less speedy HPLC method could advantageously be substituted with the proposed spectrophotometric assay of OH detection, which was also of much higher yield than the TBARS colorimetric assay.

Effects of reactive oxygen species on cellular wall disassembly of banana fruit during ripening

Fruit softening is generally attributed to cell wall disassembly. Experiments were conducted to investigate effects of various reactive oxygen species (ROS) on in vitro cellular wall disassembly of harvested banana fruit. The alcohol-extracted insoluble residue (AEIR) was obtained from the pulp tissues of banana fruit at various ripening stages and then used to examine the disassembly of cellular wall polysaccharides in the presence of superoxide anion (O2-), hydrogen peroxide (H2O2) or hydroxyl radical (OH) and their scavengers. The presence of OH accelerated significantly disassembly of cellular wall polysaccharides in terms of the increase in contents of total sugars released and uronic acid, and the decrease in molecular mass of soluble polysaccharides, using gel permeation chromatography. However, the treatment with H2O2 or O2- showed no significant effect on the disassembly of cellular wall polysaccharides. Furthermore, the degradation of the de-esterified AEIR was more susceptible to OH attack than the esterified AEIR. In addition, the effect of OH could be inhibited in the presence of OH scavenger. This study suggests that disassembly of cellular wall polysaccharides could be initiated by OH as the solublisation of the polysaccharides increased, which, in turn, accelerated fruit softening.

Novel hydroxyl radical scavenging antioxidant activity assay for water-soluble antioxidants using a modified CUPRAC method

Reactive oxygen species (ROS) such as superoxide anion, hydroxyl ( OH), peroxyl, and alkoxyl radicals may attack biological macromolecules giving rise to oxidative stress-originated diseases. Since OH is very short-lived, secondary products resulting from OH attack to various probes are measured. Although the measurement of aromatic hydroxylation with HPLC/electrochemical detection is more specific than the low-yield TBARS test, it requires sophisticated instrumentation. As a more convenient and less costly alternative, we used p-aminobenzoate, 2,4- and 3,5-dimethoxybenzoate probes for detecting hydroxyl radicals generated from an equivalent mixture of Fe(II) + EDTA with hydrogen peroxide. The produced hydroxyl radicals attacked both the probe and the water-soluble antioxidants in 37 °C-incubated solutions for 2 h. The CUPRAC (i.e., our original method for total antioxidant capacity assay) absorbance of the ethylacetate extract due to the reduction of Cu(II)-neocuproine reagent by the hydroxylated probe decreased in the presence of OH scavengers, the difference being proportional to the scavenging ability of the tested compound. A rate constant for the reaction of the scavenger with hydroxyl radical can be deduced from the inhibition of color formation. The second-order rate constants of the scavengers were determined with competition kinetics by means of a linear plot of A 0/ A as a function of C scavenger/ C probe, where A 0 and A are the CUPRAC absorbances of the system in the absence and presence of scavenger, respectively, and C is the molar concentration of relevant species. The 2,4- and 3,5-dimethoxybenzoates were the best probes in terms of linearity and sensitivity. Iodide, metabisulfite, hexacyanoferrate(II), thiourea, formate, and dimethyl sulfoxide were shown by the modified CUPRAC assay to be more effective scavengers than mannitol, glucose, lysine, and simple alcohols, as in the TBARS assay. The developed method is less lengthy, more specific, and of a higher yield than the classical TBARS assay. The hydroxyl radical scavenging rate constants of ascorbic acid, formate, and hexacyanoferrate(II) that caused interference in other assays could be easily found with the proposed procedure.

Laboratory studies on secondary organic aerosol formation from terpenes

The formation of secondary organic aerosol (SOA) following the ozonolysis of terpene has been investigated intensively in recent years. The enhancement of SOA yields from the acid catalysed reactions of organics on aerosol surfaces or in the bulk particle phase has been receiving great attention. Recent studies show that the presence of acidic seed particles increases the SOA yield significantly (M. S. Jang and R. M. Kamens, Environ. Sci. Technol., 2001, 35, 4758, ref. 1; M. S. Jang, N. M. Czoschke, S. Lee and R. M. Kamens, Science, 2002, 298, 814, ref. 2; N. M. Czoschke, M. Jang and R. M. Kamens, Atmos. Environ., 2003, 37, 4287, ref. 3; M. S. Jang, B. Carroll, B. Chandramouli and R. M. Kamens, Environ. Sci. Technol., 2003, 37, 3828, ref. 4; Y. Iinuma, O. Böge, T. Gnauk and H. Herrmann, Atmos. Environ., 2004, 38, 761, ref. 5; S. Gao, M. Keywood, N. L. Ng, J. Surratt, V. Varutbangkul, R. Bahreini, R. C. Flagan and J. H. Seinfeld, J. Phys. Chem. A, 2004, 108, 10147, ref. 6). More detailed studies report the formation of higher molecular weight products in SOA (refs. 5 and 6; M. P. Tolocka, M. Jang, J. M. Ginter, F. J. Cox, R. M. Kamens and M. V. Johnston, Environ. Sci. Technol., 2004, 38, 1428, ref. 7; S. Gao, N. L. Ng, M. Keywood, V. Varutbangkul, R. Bahreini, A. Nenes, J. He, K. Y. Yoo, J. L. Beauchamp, R. P. Hodyss, R. C. Flagan and J. H. Seinfeld, Environ. Sci. Technol., 2004, 38, 6582, ref. 8) which could result in a non-reversible uptake of organics into the particle phase. Most of the past studies concentrated on the characterisation of the yields of enhanced SOA and its composition from ozonolysis of terpenes in the presence or absence of acidic and neutral seed particles. Recent findings from cyclohexene ozonolysis show that the presence of OH scavengers can also significantly influence the SOA yield. Our new results from the IfT chemistry department aerosol chamber on terpene ozonolysis in the presence of OH scavengers show that the presence of hydroxyl radical scavengers clearly reduces the amount of formed SOA. The OH scavenger strongly depletes the formation of oligomeric compounds in the particle phase in contrast to previous findings (M. D. Keywood, J. H. Kroll, V. Varatbangkul, R. Bahreini, R. C. Flagan and J. H. Seinfeld, Environ. Sci. Technol., 2004, 38, 3343, ref. 9). This result indicates that hydroxyl radicals play an important role in the formation of precursor compounds (e.g., hydroxy pinonaldehyde) for the particle phase heterogeneous acid catalysed reactions leading to the higher molecular weight compounds and thus the enhancement of SOA yields. Better understanding of the role of hydroxyl radicals in the formation of SOA is necessary to distinguish between the contribution of ozonolysis and hydroxyl radicals to the SOA yield. If the recent findings are a ubiquitous phenomenon in the atmosphere, current atmospheric and climate models might underestimate SOA formation yields, particle phase OC contents and its impact on the atmospheric radiation budget.

Temperature dependence of hydroxyl radical formation in the hv/Fe 3+/H 2O 2 and Fe 3+/H 2O 2 systems

The thermal enhancement of the formation of OH by the hv/Fe(III)/H 2O 2 system (including the Fe(III)/H 2O 2 system) was quantitatively investigated with reaction temperatures ranging from 25 to 50 °C. A temperature dependent kinetic model for the hv/Fe(III)/H 2O 2 system, incorporating 12 major reactions with no fitted rate constants or activation energies, was developed, and successfully explained the experimental measurements. Particularly, the thermal enhancement of Fe(OH) 2+ photolysis which is the most significant step in the hv/Fe(III)/H 2O 2 system was effectively explained by two factors; (1) the variation of the Fe(OH) 2+ concentration with temperature, and (2) the temperature dependence of the quantum yield for Fe(OH) 2+ photolysis (measured activation energy=11.4 kJ mol −1). Although in both the hv/Fe(III)/H 2O 2 and Fe(III)/H 2O 2 systems, elevated temperatures enhanced the formation of OH, the thermal enhancement was much higher in the dark Fe(III)/H 2O 2 system than the hv/Fe(III)/H 2O 2 system. Furthermore, it was found that the relative thermal enhancement of the formation of OH in the presence of OH scavengers ( tert-butyl alcohol) was magnified in the Fe(III)/H 2O 2 system but was not in the hv/Fe(III)/H 2O 2 system.

Application of polyoxotungstates as environmental catalysts: wet air oxidation of acid dye Orange II

The catalytic effect of two Keggin-type polyoxotungstates, namely H 4SiW 12O 40 and Na 2HPW 12O 40, on the wet air oxidation of azo dye Acid Orange 7 (AO7; C dye=248 μM) at varying reaction temperatures ( T=160–290 °C at P H 2O= 0.6–3.0 MPa, respectively) was examined. Arrhenius parameters for catalytic and non-catalytic wet air oxidation were obtained in terms of temperature dependent AO7 and TOC abatement kinetics. To get a further insight into the dominant reaction pathway of the catalytic and non-catalytic wet air oxidation processes, isopropyl alcohol and bromide (300 μM) were added as OH scavengers. Obtained results revealed an important homogenous contribution for WAO of AO7 (Arrhenius parameters E a=84 kJ mol −1 and A=5.6×10 7 min −1). However, mineralization (TOC removal) was noticeably influenced by the investigated polyoxotungstates ( C catalyst=140 μM) and the activation energy decreased from 40 kJ mol −1 in the absence of catalyst to only 28 kJ mol −1 (PW 12 3−) and 22 kJ mol −1 (SiW 12 4−). The catalytic processes were appreciably less sensitive to the presence of OH scavengers than uncatalyzed wet air oxidation implying that polyoxotungstate-catalyzed wet air oxidation did not solely depend upon a free radical type reaction mechanism. The obtained results tend to support the free radical chain mechanism to account for Orange dye degradation only for uncatalyzed wet air oxidation.

H4SiW12O40-catalyzed oxidation of nitrobenzene in supercritical water: kinetic and mechanistic aspects

The catalytic effect of a heteropolyacid, H4SiW12O40, on nitrobenzene (20 and 30μM) oxidation in supercritical water was investigated. A capillary flow-through reactor was operated at varying temperatures (T=400–500°C; P=30.7MPa) and H4SiW12O40 concentrations (3.5–34.8μM) in an attempt to establish global power-law rate expressions for homogenous H4SiW12O40-catalyzed and uncatalyzed supercritical water oxidation. Oxidation pathways and reaction mechanisms were further examined via primary oxidation product identification and the addition of various hydroxyl radical scavengers (2-propanol, acetone, acetone-d6, bromide and iodide) to the reaction medium. Under our experimental conditions, nitrobenzene degradation rates were significantly enhanced in the presence of H4SiW12O40. The major differences in temperature dependence observed between catalyzed and uncatalyzed nitrobenzene oxidation kinetics strongly suggest that the reaction path of H4SiW12O40-catalyzed supercritical water oxidation (average activation Ea=218kJ/mol; k=0.015–0.806s−1 energy for T=440–500°C; Ea=134kJ/mol for the temperature range T=470–490°C) apparently differs from that of uncatalyzed supercritical water oxidation (Ea=212kJ/mol; k=0.37–6.6μMs−1). Similar primary oxidation products (i.e. phenol and 2-, 3-, and 4-nitrophenol) were identified for both treatment systems. H4SiW12O40-catalyzed homogenous nitrobenzene oxidation kinetics was not sensitive to the presence of OH scavengers.

A radiolysis study of the role of superoxide ion in the oxidation of sulfite by oxygen

Some apparent contradictions about the role of O ⨪ 2 in the chain oxidation of sulfites by O 2 are explained. O ⨪ 2 may indeed initiate the chain. On the other hand, if, in the presence of OH scavengers, O ⨪ 2 has a leading part in the chain termination, in the absence of OH scavengers, its role is inhibited by a chain reaction which replaces O ⨪ 2 by OH radicals.

Reaction of the solvated electron with organic halides

Studies of the competition for hydrated electrons between N 2 O and on organic halide, X, Rperformed by measuring the N 2 yields from the ultra-violet illumination of KI solutions containing these two solutes, lead to values of the relative rate constant in complete disagreement with the ratio of the absolute rate constants obtained by pulse radiolysis. This disagreement is found to persist when methanol is used as solvent, when (in aqueous solution) the hydrated electrons are generated by γ-radiolysis, and when N 2 O is replaced by H +. It is thus deduced that there is some mechanistic complication in the reactions and it is demonstrated that the data are more consistent with the scheme previously postulated by us than with one analogous to that suggested by other workers as operative in some gas-phase systems. In the radiation chemical studies, high yields of X − ion are found from all solutes, RX. The mechanism postulated by Teplý in regard to CHCl 3 does not appear adequate to explain the high yield of X − from various RX and in the presence of OH scavengers. Their occurrence means that, mechanistic complications apart, relative rate constants cannot properly be deduced from halide yields in systems containing another solute.

Radiation-induced Reduction of Nitrate Ions in Ammonia Systems

With nitrate ions the polarons of water radiolysis undergo reaction to an intermediate of the tetravalent state of nitrogen. In presence of OH scavengers (ethanol, J−) nitrite is formed by a consequent reaction. But low yields due to back reactions were observed in pure solutions of nitrates [1, 2]. In 1 M sodium nitrate the nitrite yield was raised to = 6·5 molecules per 100 eV by addition of 0·15 M ammonia after Sharpaty et al. The effect was interpreted as oxidation of ammonia to nitrite and water [3]. We compared the yields of nitrite in deaerated solutions of potassium nitrate in presence of 0·2 M ammonia, 0·2 M methanol, or both after irradiation with 60Co-γ-rays. In 10−2 M solution nearly equals the polaron yield if ammonia was added.