Oxide Radical Ion Research Articles

Biomolecule assisted morphology-controllable synthesis of Zinc Sulphide nanomaterials for efficient photocatalytic activity under solar irradiation

Tuning the optical and morphological properties of Zinc Sulphide (ZnS) nanomaterials (NMs) may be executed based on its synthetic approaches with experimental parameters that may improve the photocatalytic degradation efficiency as compared to bulk ZnS. A bio-molecule (Citrus limetta juice) assisted synthetic method was employed with the variation of precursors and stabilizer ratio for manipulating the morphology of as-synthesized ZnS NMs. Field emission scanning electron microscopic analysis confirmed the structure of nanospheres/nanoflowers/nanotubes of ZnS NMs, corresponding to different sulphur ratios and amount of Citrus limetta juice-extract. Chemical composition of the ZnS NMs was substantiated by X-ray photoelectron spectroscopy. The photocatalytic degradation ability of the ZnS NMs toward major water pollutants: Rhodamine B and Methyl orange, indicated the correlation between morphological and photocatalytic properties. Highest defect emission due to Sulphur interstices and lowest band edge emission due to less electron-hole pair recombination, as-observed through Photoluminescence spectroscopy, accounted for maximum degradation of dyes by ZnS nanospheres as compared to nanoflowers/nanotubes, which may be attributed to the high separation efficiency of electron-hole pairs and high surface-to-volume ratio. Electrochemical impedance spectroscopy established the highest electrical conductivity of ZnS nanospheres. 85% degradation of RhB and 82% degradation of MO under sunlight were achieved with ZnS nanospheres. Reusability and radical scavenging studies revealed reduction of ∼10% degradation efficiency after 3rd cycle and super oxide radical ions as the prominent reactive species during degradation processes, respectively.

Facile fabrication of visible light-driven CeO2/PMMA thin film photocatalyst for degradation of CR and MO dyes

CeO2/PMMA NCTF was successfully fabricated by a facile, room-temperature, inexpensive, and simple solution casting method. Ultra-violet, Fourier-transform infrared spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy techniques have been used to scrutinize the structure and properties of CeO2/PMMA NCTF. It has been found that the CeO2 nanocubes are constantly dispersed into the PMMA matrix thus forming a thin film. Due to its unique structure, the CeO2/PMMA NCTF has enhanced activity and selectivity towards the visible light-driven degradation of various organic pollutants. The photocatalytic degradation efficiency of the catalyst was tested against Congo red and methyl orange, selected as model organic contaminants. The synergistic effect of the catalyst reduces the electron–hole recombination rate and thus enhances the photocatalytic activity. Hydroxyl radical and super oxide radical ion species induce the photocatalysis which can be determined by trapping experiments. The synthesized CeO2/PMMA NCTF can be reused several times without loss of activity, and a plausible mechanism was also proposed. It is hoped that our present effort may inspire further studies in new, efficient, recyclable photocatalysts and the degradation of organic contaminants driven by visible light.

Oxidation Reactions of 1- and 2-Naphthols: An Experimental and Theoretical Study

The transients formed during the reactions of oxidizing radicals with 1-naphthol (1) and 2-naphthol (2) in aqueous medium have been investigated by pulse radiolysis with detection by absorption spectroscopy and density functional theory (DFT) calculations. The transient spectra formed on hydroxyl radical ((•)OH) reactions of 1 and 2 exhibited λ(max) at 340 and 350 nm at neutral pH. The rate constants of the (•)OH reactions of 1 (2) were determined from build-up kinetics at λ(max) of the transients as (9.63 ± 0.04) × 10(9) M(-1) s(-1) ((7.31 ± 0.11) × 10(9) M(-1) s(-1)). DFT calculations using the B3LYP/6-31+G(d,p) method have been performed to locate favorable reaction sites in both 1 and 2 and identification of the pertinent transients responsible for experimental results. Calculations demonstrated that (•)OH additions can occur mostly at C1 and C4 positions of 1, and at C1 and C8 positions of 2. Among several isomeric (•)OH adducts possible, the C1 adduct was found to be energetically most stable both in 1 and 2. Time-dependent density functional theory (TDDFT) calculations in the solution phase has shown that the experimental spectrum of 1 was mainly attributed by 1a4 (kinetically driven (•)OH-adduct) formed via the addition of (•)OH at the C4 position which was 0.73 kcal/mol endergonic compared to 1a1 (thermodynamic (•)OH adduct), whereas 2a1 (thermodynamic/kinetic (•)OH-adduct) was mainly responsible for the experimental spectrum of 2. Naphthoxyl radicals of 1 and 2 have been predicted as the transient formed in the reaction of (•)OH at basic pH. In addition, the same transient species resulted from the reactions of oxide radical ion (O(•-)) at pH ≈ 13 and azide radical (N3(•)) at pH 7 with 1 and 2. Further, UV photolysis of aqueous solutions of 1 and 2 containing H2O2 (UV/H2O2) were used for the (•)OH induced oxidation product formations up on 60% degradations of 1 and 2; profiling of the oxidation products were performed by using an ultraperformance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) method. According to the UPLC-Q-TOF-MS analyses, the preliminary oxidation products are limited to dihydroxy naphthalenes and naphthoquinones with N2-saturation, while some additional products (mainly isomeric monohydroxy-naphthoquinones) have been observed in the degradations of 1 and 2 in the presence of O2. We postulate that dihydroxy naphthalenes are derived explicitly from the most favorable (•)OH-adducts speculated (preference is in terms of the kinetic/thermodynamic dominancy of transients) by using theoretical calculations which in turn substantiate the proposed reaction mechanisms. The observations of (•)OH-adducts for an aromatic phenol (herein for both 1 and 2 at pH 7) rather than phenoxyl type radical in the pulse radiolysis experiments is a distinct and unique illustration. The present study provides a meaningful basis for the early stages associated with the (•)OH initiated advanced oxidation processes of 1- and 2-naphthols.

Time-resolved study on the reactions of organic selenides with hydroxyl and oxide radicals, hydrated electrons, and H-atoms in aqueous solution, and DFT calculations of transients in comparison with sulfur analogues

A complementary experimental and quantum chemical study has been undertaken on the reactivity, formation and properties of transients generated in the reaction of selected organic selenides with hydroxyl radicals, oxide radical ions, hydrated electrons and hydrogen atoms in aqueous solution. A detailed study of the OH and O (-) reactions with Me(2)Se revealed the formation of the respective adduct-radicals as precursors of (Me(2)Se thereforeSeMe(2))(+) radical cations. In case of the neutral adduct radical Me(2)Se (OH) the conversion into the three-electron bonded dimer species proceeds, in part, via the molecular (Me(2)Se thereforeOH(2))(+) radical cation. Absolute rate constants have been determined for all the underlying processes. The respective reactions with hydrated electrons and hydrogen atoms indicate that selenides exhibit a higher reactivity towards redox-active species than sulfides. A most interesting finding is that the reaction of Me(2)Se with H atoms is faster (k = 4.1 x 10(9) M(-1) s(-1)) than the reduction by hydrated electrons (k = 2.1 x 10(8) M(-1) s(-1)), precluding an electron transfer as mechanistic background. The rationale is rather an effective dissociative attack of the hydrogen atom on the selenium. Both, the e(aq)(-)- and H -induced reductions of Me(2)Se and Me(2)S lead, under cleavage of CH(3) radicals, to the direct formation of selenol and thiol, respectively. Complementary quantum chemical studies, performed with Density Functional Theory (DFT) BHandHLYP methods, confirm this mechanism. They also reveal a generally higher thermodynamic stability of the Se-centered radicals relative to the S-centered ones, e.g., for the molecular radical anions (Me(2)Se) (-) (DeltaH-27 kJ mol(-1)) and (Me(2)S) (-) (DeltaH-16 kJ mol(-1)). Despite of these stabilization energies the calculations indicate an instantaneous Se/S-CH(3) bond lengthening in the respective molecular radical anions. The same applies for the reaction of Me(2)S and Me(2)Se with H atoms. Here the calculations indicate, in fact, no thermodynamic stability of a tentative H-adduct which, therefore, is only a fictional transition state in the H -induced CH(3)-displacement process.

Anomalous reaction of oxide radical ion with 5-azacytosines: An experimental and theoretical study

The reactions of oxide radical ion ( O - ) with 5-azacytosine ( 5AC) and 5-azacytidine ( 5ACyd) in aqueous medium were studied using the pulse radiolysis technique and quantum chemical calculation using density functional theory (DFT). It is demonstrated that the major reaction pathway is the addition of O - to the ring nitrogen of 5AC, followed by a fast protonation of adducts by water. Only a minor percentage (<18%) undergoes an electron transfer reaction. The similarity in the reaction mechanism of O - (addition to azacytosine) and OH (which generally participates in an addition reaction) is an interesting observation and is quite unusual in the case of heterocyclic compounds.

UV absorption spectrum, formation and disappearance of the oxide radical ion O [rad]− in aqueous solution: A pulse radiolysis study

The formation and disappearance of O − in oxygen-free aqueous solution at pH 13 has been studied and its spectrum has been re-determined utilizing pulse radiolysis optical measurements in the UV region. The rate constant for the reaction H + OH − is determined to be 2.5 × 10 7 dm 3 mol −1 s −1. A determination of the rate constants for the equilibrium OH + OH - ⇔ O - was not possible; the p K value for this equilibrium was determined to be 11.9. The rate constant for the demerisation O − + O − was measured at 325 nm to be 2 k = 2 × 10 9 dm 3 mol −1 s −1. The absorption spectrum of O − differs significantly from that in the literature below 250 nm.

Reactions of oxide radical ion (O [rad]− ) with pyrimidine nucleosides

The reaction of oxide radical ions (O − ) with nucleosides 1– 5 at pH 13.7 has been investigated by the pulse radiolysis technique. Rate constants for the reaction of the O − radical with the various nucleosides are in the range of (0.7–1.3)×10 9 M −1 s −1. The intermediate derived from uridine ( 1) disappeared by second-order kinetics, whereas the initial transient species derived from 2′-deoxyribonucleosides ( 2– 5) undergo unimolecular transformations with rate constant in the range of (0.6–1.0)×10 4 s −1 followed by a second slower unimolecular process with rate constant in the range of 30–50 s −1. The observed differences suggest two distinct mechanistic paths. In the uridine case, hydrogen abstraction preferentially occurs at the C2′ position, whereas in the 2′-deoxynucleosides favored hydrogen abstraction occurs at the C5′ position. Both attacks lead to release of the base as shown by γ-radiolysis experiments associated with product studies.

Reaction of oxide radical ion (O.–) with substituted pyrimidines

Pulse radiolysis technique has been used to investigate the reaction of oxide radical ion (O.–) with 4,6-dihydroxy-2-methyl pyrimidine (DHMP), 2,4-dimethyl-6-hydroxy pyrimidine (DMHP), 5,6-dimethyl uracil (DMU) and 6-methyl uracil (MU) in strongly alkaline medium. The second-order rate constants for the reaction of O.– with these compounds are in the range 2-5 × 108 dm3 mol–1 s–1. The transient absorption spectra obtained with DHMP have two maxima at 290 and 370 nm and with DMHP have maxima at 310 and 470 nm. The transient spectrum from DMU is characterized by its absorption maxima at 310 and 520 nm and that of MU by its single maximum at 425 nm. The intermediate species were found to react with N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) with high G(TMPD.+) values ranged between 3.9 × 10–7 molJ–1 and 4.8 × 10–7 molJ–1. These radicals undergo decay by second-order kinetics (2k/∈ = 1.0-1.7 × 106 s–1). The reaction of O.– with the selected pyrimidines is proposed to proceed through a hydrogen abstraction from the methyl group forming allyl type radicals. These are mainly oxidizing radicals and hence readily undergo electron transfer reactions with TMPD.

Addition of Oxide Radical Ions (O-) to Nitrite and Oxide Ions (O2-) to Nitrogen Dioxide

Addition of Oxide Radical Ions (O^-) to Nitrite and Oxide Ions (O²^-) to Nitrogen Dioxide

Primary cathodic steps of electrogenerated chemiluminescence of lanthanide(III) chelates at oxide-covered aluminum electrodes in aqueous solution

The primary processes occurring at cathodically polarized oxide-covered aluminum electrode are discussed in detail. It is pointed out that more energetic cathodic processes can be induced in aqueous media at thin insulating film-coated electrodes than at any semiconductor or active metal electrode. It is proposed that tunnel emission of hot electrons with energies well above the level of the conduction band edge of water occur, and the thermalization and solvation of the emitted electrons can result in generation of hydrated electrons. The cathodically pulse-polarized oxide-covered aluminum also generates a strong oxidant (or oxidants) at the oxide/electrolyte interface, and it is proposed that this species is the hydroxyl radical which is generated either by cathodic high field-induced ejection of self-trapped holes as oxygen dianions (i.e. oxide radical ions) into the electrolyte solution, or by the action of anion vacancies and/or F +-centers as the primary oxidants capable of oxidizing hydroxide ions or the hydroxyl groups of the hydroxylated surface on the oxide film. These radicals, hydrated electrons/hydroxyl radicals, can act as mediating reductants/oxidants in reduction/oxidation of solutes. The formation of the primary species is monitored by electrochemiluminophores which cannot be cathodically excited at active metal electrodes in fully aqueous solutions, but which can be chemically excited in aqueous media in the simultaneous presence of highly reducing and highly oxidizing radicals.

Reactions of Oxide Radical Ion (·O-) with Pyrimidine and Purine Derivatives

The reaction of oxide radical ion (·O-) with a variety of pyrimidine and purine derivatives, in strong alkaline aqueous solution (pH 13.7), has been investigated by means of the pulse radiolysis technique. Rate constants for the reaction of ·O- species with various substrates are in the range of (2.8−7.8) × 108 M-1 s-1. Absorption spectra of the transients and information on their decay reactions have also been obtained. For comparison, the one-electron oxidation of the same substrates with Br2•- have also been carried out at the same pH when it was necessary. With uracil, cytosine, adenine, and guanine, the oxide radical ion effects a one-electron oxidation, whereas in the presence of extractable hydrogens (e.g., with methyl-substituted derivatives) it abstracts a hydrogen atom from the methyl group. The transient species derived from uracil and adenine decay by first-order kinetics (kdecay = 1.0 × 104 s-1), whereas the transient species derived from cytosine and guanine as well as those obtained after h...

Activation energies for the reactions oxide + hydrogen and oxide + deuterium in aqueous solution

The reaction between molecular hydrogen and oxide radical ion in aqueous solution has been studied by pulse radiolysis in the temperature range 15-90{degree}C. At room temperature, k(O{sup {minus}} + H{sub 2}) = (1.1 {plus minus} 0.2) {times} 10{sup 8} mol{sup {minus}1} L s{sup {minus}1}, and the activation energy of the reaction is 13.8 {plus minus} 2 kJ/mol. The isotope effect on the reaction rate has been determined in H{sub 2}O. At 20{degree}C, k(O{sup {minus}} + D{sub 2}) = (2.5 {plus minus} 0.5) {times} 10{sup 7} mol{sup {minus}1} L s{sup {minus}1}, and the activation energy in the temperature range 20-80{degree}C is 20.8 {plus minus} 3 kJ/mol. Steady-state irradiation of H{sub 2}, D{sub 2}, and N{sub 2}O in alkaline solutions gives rise to a chain reaction. The chain is initiated and propagated by the hydrated electron and the oxide radical ion. The net result is an oxidation of H{sub 2} and D{sub 2} by N{sub 2}O with an important enrichment of the heavier isotope in the remaining hydrogen. The mechanism of the reaction O{sup {minus}} + H{sub 2} and the possibility that the primary step is not a hydrogen abstraction are discussed.

Catalytic oxidation by oxide radical ions. 1. One-step hydroxylation of benzene to phenol over Group 5 and 6 oxides supported on silica gel

ADVERTISEMENT RETURN TO ISSUEArticleNEXTCatalytic oxidation by oxide radical ions. 1. One-step hydroxylation of benzene to phenol over Group 5 and 6 oxides supported on silica gelMasakazu Iwamoto, Junichiro Hirata, Kazuto Matsukami, and Shuichi KagawaCite this: J. Phys. Chem. 1983, 87, 6, 903–905Publication Date (Print):March 1, 1983Publication History Published online1 May 2002Published inissue 1 March 1983https://doi.org/10.1021/j100229a001RIGHTS & PERMISSIONSArticle Views871Altmetric-Citations136LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (353 KB) Get e-Alerts

ChemInform Abstract: PULSE RADIOLYSIS OF AQUEOUS SOLUTIONS OF BENZYLTRIALKYLAMMONIUM CATIONS. REACTIONS WITH THE PRIMARY TRANSIENTS FROM WATER RADIOLYSIS

The primary reactions of hydrogen atoms, hydrated electrons, hydroxyl radicals, and oxide radical ions with benzyltrimethylammonium cations in aqueous solutions have been studied by the technique of pulse radiolysis. Hydrogen atoms react with the rate constant (2.0 +- 0.1) x 10/sup 9/ M/sup -1/ s/sup -1/. The cyclohexadienyl-type radical decayed in a second-order process with a rate constant 2k = (4.8 +- 0.2) x 10/sup 9/ M/sup -1/ s/sup -1/. Hydrated electrons react with a rate constant (4.3 +- 0.2) x 10/sup 9/ M/sup -1/ s/sup -1/ to form benzyl radical. It has been concluded that irradation of benzyltrimethylammonium cations results in deamination brought about by hydrated electrons. Hydroxyl radicals react with benzyltrimethylammonium cation with a rate constant (5.0 +- 0.6) x 10/sup 9/ M/sup -1/ s/sup -1/ to form the cyclohexadienyl-type radical HOC/sub 6/H/sub 5/CH/sub 2/N/sup +/(CH/sub 3/)/sub 3/ (approx. 65%) and C/sub 6/H/sub 5/CHN/sup +/(CH/sub 3/)/sub 3/ (approx. 35%) radicals. The cyclohexadienyl radical has a broad absorption maximum at 325 nm (epsilon approx. = 3300 M/sup -1/ cm/sup -1/). Oxide radical ions react with the rate constant (5.9 +- 0.5) x 10/sup 8/ M/sup -1/ s/sup -1/ to form C/sub 6/H/sub 5/CHN/sup +/(CH/sub 3/)/sub 3/ with absorption maximamore » at 260 and 305 nm. With the increasing chain length of the alkyl substituent (as in the benzyltri-n-butylammonium cation) the reaction of hydrogen abstraction from the alkyl groups becomes more important.« less

Pulse radiolysis study on tetra-alkylammonium hydroxides in alkaline solutions containing O 2 and N 2O

The reactivity of the oxide radical ion, O −, and the decay kinetics of the ozonide ion, O 3 −, have been investigated in aqueous solutions at pH 12·8, in the presence of tetramethyl-, tetraethyl-, tetrapropyl- and tetrabutylammonium ions, O 2 and N 2O. Using pulse radiolysis to follow the O 3 − kinetics gives information on the competition of O 2 and R 4N + for O −. Absolute rate constants for these reactions are: 3·0 × 10 8 dm 3 mol −1 s −1 for O − + (CH 3) 4N +, 1·0 × 10 9 dm 3 mol −1 s −1 for O − + (C 2H 5) 4N +, 1·3 × 10 9 dm 3 mol −1 s −1 for O − + (C 3H 7) 4N + and 2·2 × 10 9 dm 3 mol −1 s −1 for O − + (C 4H 9) 4N +. The decay of O 3 − occurs through the thermal dissociation reaction, O 3 ⇌ O 2 + O −, for which the absolute rate constant at 22°C was found to be 6·2 ± 1·2 × 10 3 s −1.

Gas-phase reactions of oxide radical ion and hydroxide ion with simple olefins and of carbanions with oxygen

Gas-phase reactions of oxide radical ion and hydroxide ion with simple olefins and of carbanions with oxygen

Absolute reactivity of the oxide radical ion with methanol and ethanol in water

Absolute reactivity of the oxide radical ion with methanol and ethanol in water