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1.
Diffusion-kinetic calculations [1-3] have been analysed to determine the isotopic effect in the radiolysis of water with ionising radiation of linear energy transfer characteristics (LET) from 0.2 to 60 eV/nm and at temperatures up to 300°C. This analysis shows that, for low LET radiation, the spur decay of e- aq is slower in D2O and results in a higher yield of e- aq, g(e- aq), at 10-7 -10-6s after the ionisation event. In low LET radiolysis, g(OD) ≈ g(OH) over the whole range of temperature but in high LET radiolysis g(OD) is clearly lower than g(OH). The isotopic effect on the yields of the radical products is enhanced by increasing LET but diminished by increasing temperature. The yields of the molecular products show the opposite isotopic effect to their radical precursors, namely g(D2) is 10-20% lower than g(H2) and g(D2O2) > g(H2O2). A particularly significant difference between g(D2O2) and g(H2O2) has been found at LET = 20 eV/nm. The isotopic dependence of the g-values estimated for fast neutron radiolysis is also presented. 相似文献
2.
《Radiation Physics and Chemistry》2004,69(5):379-386
Pulse radiolysis of aqueous diphenyloxide (DPO) has been performed under various experimental conditions. The OH radicals react with DPO on various positions of the molecule with a rate constant, k=2.1×1010 l mol−1 s−1. The major reaction step appears to be a cleavage of the C–O bond of DPO resulting into C6H4OH (λ=285 nm) and C6H5O(λ=325 nm) radicals in addition to DPO–OH adducts. They disappear according to a second-order reaction. In the presence of air or in a gas mixture of N2O:O2=4:1 the DPO–OH adducts are scavenged by oxygen, resulting into peroxyl radicals, which are long-lived species. For the reaction of eaq− with DPO a rate constant, k=2×1010 l mol−1 s−1 was found. 相似文献
3.
《Radiation Physics and Chemistry》2008,77(2):162-168
H radicals react with chlorobenzoic acids and chlorobenzene (k(H+substrates)=(0.7–1.5)×109 dm3 mol−1 s−1) by addition to the benzene ring forming H adducts with characteristic absorption bands in the range of 310–360 nm. The rate constants for their second-order decay are 2k=(3.5–6)×108 dm3 mol−1 s−1. By reduction with eaq− fragmentation and chloride release was established for 2- and 4-chlorobenzoic acid, for 3-chlorobenzoic acid the addition of electrons to the carboxylate group was observed by pulse radiolysis. By gamma radiolysis could be proved that these radical anions undergo intramolecular electron transfer and quantitave dechlorination. The efficiency in degradation was 4-chlorobenzoic acid>3-chlorobenzoic acid>2-chlorobenzoic acid. Benzoic acid was found as final product for all substrates. 相似文献
4.
《Radiation Physics and Chemistry》2006,75(1):70-77
Pulse radiolysis technique has been employed to study the reaction of different oxidizing and reducing radicals with mangiferin. The reaction of OH radical showed the formation of transient species absorbing in 380–390 and 470–480 nm region. The reaction with specific one-electron oxidants (N3, CCl3O2) also showed the formation of similar transient absorption bands and is assigned to phenoxyl radicals. The pKa values of the transient species have been determined to be 6.3 and 11.9. One-electron oxidation potential of mangiferin at pH 9 has been found to be 0.62 V vs. NHE. The reaction of eaq− showed the formation of transient species with λmax at 340 nm, which is assigned to the ketyl anion radical formed on addition of eaq− at carbonyl site. Reactions of one-electron oxidised mangiferin radicals with ascorbic acid have also been studied. 相似文献
5.
《Radiation Physics and Chemistry》2009,78(2):77-80
ZnO nanostructures have been synthesized by radiolytic methods. A Cobalt-60 γ-source and a 7 MeV linear electron accelerator (LINAC) was used for the radiolysis experiments. Reducing agent like hydrated electron (eaq−), which is produced in radiolysis of water, was used to synthesize ZnO nanostructure materials from zinc salt. 1 M tert-butanol was used to quench the primary oxidizing radical like hydroxyl radical (OH) radiolytic water solution. Doses of about 80–130 kGy were used to perform radiolysis experiments in the present investigation. Time-resolved pulse radiolysis has been used to monitor the transient species involved in the formation of ZnO nanostructures by monitoring at different wavelengths. A scheme for the formation of the ZnO nanostructured materials by the radiolytic method has been described. The formation of ZnO nanostructures was confirmed by X-ray diffraction (XRD) measurements. Dynamic light scattering (DLS) measurements indicated that the size of the nanostructures is in the range of 6–8 nm, which is in agreement with that obtained from XRD. It is interesting to note that ZnO nanostructured materials, as prepared by the radiolytic method, exhibit strong room-temperature fluorescence. 相似文献
6.
《The Journal of chemical thermodynamics》2007,39(3):488-492
The Freundlich and Langmuir isotherms were used to describe the biosorption of Cu(II), Pb(II), and Zn(II) onto the saltbush leaves biomass at 297 K and pH 5.0. The correlation coefficients (R2) obtained from the Freundlich model were 0.9798, 0.9575, and 0.9963 for Cu, Pb, and Zn, respectively, while for the Langmuir model the R2 values for the same metals were 0.0001, 0.1380, and 0.0088, respectively. This suggests that saltbush leaves biomass sorbed the three metals following the Freundlich model (R2 > 0.9575). The KF values obtained from the Freundlich model (175.5 · 10−2, 10.5 · 10−2, and 6.32 · 10−2 mol · g−1 for Pb, Zn, and Cu, respectively), suggest that the metal binding affinity was in the order Pb > Zn > Cu. The experimental values of the maximal adsorption capacities of saltbush leaves biomass were 0.13 · 10−2, 0.05 · 10−2, and 0.107 · 10−2 mol · g−1 for Pb, Zn, and Cu, respectively. The negative ΔG∘ values for Pb and the positive values for Cu and Zn indicate that the Pb biosorption by saltbush biomass was a spontaneous process. 相似文献
7.
《Radiation Physics and Chemistry》2004,69(3):211-216
The temperature dependence of the rate constant for the reactions of HO2 with OH, H, Fe2+ and Cu2+ has been determined using pulse radiolysis technique. The following rate constants, k (dm3 mol−1 s−1) at 20°C and activation energies, Ea (kJ mol−1) have been found. The reaction with OH was studied in the temperature range 20–296°C (k=7.0×109, Ea=7.4) and the reaction with H in the temperature range 5–149°C (k=8.5×109, Ea=17.5). The reaction with Fe2+ was studied in the temperature range 16–118°C (k=7.9×105, Ea=36.8) and the reaction with Cu2+ in the temperature range 17–211°C (k=1.1×108, Ea=14.9). 相似文献
8.
The radiation induced degradation of 4-nitrophenol (4-NP) has been studied by gamma irradiation, while the reactivity and spectral features of the short lived transients formed by reaction with primary transient radicals at different pHs has been investigated by pulse radiolysis technique. In steady state radiolysis a dose of 4.4 k Gy is able to degrade 98% of 1×10−4 mol dm−3 4-NP. 4-NP has pKa at 7.1, above which it is present in the anionic form. At pH 5.2, •OH and N3• radicals were found to react with 4-NP with rate constants of 4.1×109 dm3 mol−1 s−1 and 2.8×108 dm3 mol−1 s−1, respectively. Differences in the absorption spectra of species formed in the reactions of 4-NP with •OH and N3• radicals suggested that •OH radicals add to the aromatic ring of 4-NP along with electron transfer reaction, whereas N3• radicals undergo only electron transfer reaction. At pH 9.2, rate constants for the reaction of •OH radicals with 4-NP was found to be higher by a factor of 2 compared to that at pH 5.2. This has been assigned to the deprotonation of 4-NP at pH 9.2. 相似文献
9.
《The Journal of chemical thermodynamics》2002,34(3):409-412
Heat capacity of platinic acid, hydrogen hexahydroxyplatinate(IV)H2Pt(OH)6 , was measured from T = 7 K toT = 310 K by means of adiabatic calorimetry. The standard entropy and the standard Gibbs energy of formation of platinic acid in the crystalline state were determined to be 176.5 ± 3.6 J · K − 1· mol − 1and − 988.8 ± 3.8 kJ · mol − 1, respectively. 相似文献
10.
《The Journal of chemical thermodynamics》2001,33(7):803-819
The thermodynamic properties ofZn5(OH)6(CO3)2 , hydrozincite, have been determined by performing solubility and d.s.c. measurements. The solubility constant in aqueous NaClO4media has been measured at temperatures ranging from 288.15 K to 338.15 K at constant ionic strength (I = 1.00 mol · kg − 1). Additionally, the dependence of the solubility constant on the ionic strength has been investigated up to I = 3.00 mol · kg − 1NaClO4at T = 298.15 K. The standard molar heat capacity Cp, mofunction fromT = 318.15 K to T = 418.15 K, as well as the heat of decomposition of hydrozincite, have been obtained from d.s.c. measurements. All experimental results have been simultaneously evaluated by means of the optimization routine of ChemSage yielding an internally consistent set of thermodynamic data (T = 298.15 K): solubility constant log * Kps 00 = (9.0 ± 0.1), standard molar Gibbs energy of formationΔfGmo {Zn5(OH)6(CO3)2 } = ( − 3164.6 ± 3.0)kJ · mol − 1, standard molar enthalpy of formation ΔfHmo{Zn5(OH)6(CO3)2 } = ( − 3584 ± 15)kJ · mol − 1, standard molar entropy Smo{Zn5(OH)6(CO3)2 } = (436 ± 50)J · mol − 1· K − 1and Cp,mo / (J · mol − 1· K − 1) = (119 ± 11) + (0.834 ± 0.033)T / K. A three-dimensional predominance diagram is introduced which allows a comprehensive thermodynamic interpretation of phase relations in(Zn2 + + H2O + CO2) . The axes of this phase diagram correspond to the potential quantities: temperature, partial pressure of carbon dioxide and pH of the aqueous solution. Moreover, it is shown how the stoichiometric composition{n(CO3) / n(Zn)} of the solid compoundsZnCO3 and Zn5(OH)6(CO3)2can be checked by thermodynamically analysing the measured solubility data. 相似文献
11.
The samples of dibarium magnesium orthoborate Ba2Mg(BO3)2 were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba2Mg(BO3)2 were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba2Mg(BO3)2 polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5Eu + 4A2u + 5Eg + 4A1g + 1A2g + 1A1u, of which 5Eg + 4A1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba2Mg(BO3)2 were assigned as Eg (42 cm−1), A1g (85 cm−1), Eg (156 cm−1), Eg (237 cm−1), A1g (286 cm−1), Eg (564 cm−1), A1g (761 cm−1), A1g (909 cm−1), Eg (1165 cm−1). The strongest band at 928 cm−1 in the experimental spectrum is assigned to totally symmetric stretching mode of the BO3 units. 相似文献
12.
《Radiation Physics and Chemistry》2009,78(3):191-194
In a recent paper (Radiation Physics and Chemistry, 2005, vol. 74, pp. 210) it was suggested that the anomalous increase of molecular hydrogen radiolysis yields observed in high-temperature water is explained by a high activation energy for the reaction H+H2O→H2+OH. In this comment we present thermodynamic arguments to demonstrate that this reaction cannot be as fast as suggested. A best estimate for the rate constant is 2.2×103 M−1 s−1 at 300 °C. Central to this argument is an estimate of the OH radical hydration free energy vs. temperature, ΔGhyd(OH)=0.0278t−18.4 kJ/mole (t in °C, equidensity standard states), which is based on analogy with the hydration free energy of water and of hydrogen peroxide. 相似文献
13.
《The Journal of chemical thermodynamics》2004,36(5):359-375
The molar heat capacities of GeCo2O4 and GeNi2O4, two geometrically frustrated spinels, have been measured in the temperature range from T=(0.5 to 400) K. Anomalies associated with magnetic ordering occur in the heat capacities of both compounds. The transition in GeCo2O4 occurs at T=20.6 K while two peaks are found in the heat capacity of GeNi2O4, both within the narrow temperature range between 11.4<(T/K)<12.2. Thermodynamic functions have been generated from smoothed fits of the experimental results. At T=298.15 K the standard molar heat capacities are (143.44 ± 0.14) J · K−1 · mol−1 for GeCo2O4 and (130.76 ± 0.13) J · K−1 · mol−1 for GeNi2O4. The standard molar entropies at T=298.15 K for GeCo2O4 and GeNi2O4 are (149.20 ± 0.60) J · K−1 · mol−1 and (131.80 ± 0.53) J · K−1 · mol−1 respectively. Above 100 K, the heat capacity of the cobalt compound is significantly higher than that of the nickel compound. The excess heat capacity can be reasonably modeled by the assumption of a Schottky contribution arising from the thermal excitation of electronic states associated with the CO2+ ion in a cubic crystal field. The splittings obtained, 230 cm−1 for the four-fold-degenerate first excited state and 610 cm−1 for the six-fold degenerate second excited state, are significantly lower than those observed in pure CoO. 相似文献
14.
In reply to “Comment on the possible role of reaction H+H2O→H2+OH in the radiolysis of water at high temperatures” (Bartels, 2009 Comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) we present an alternative thermodynamic estimation of the reaction rate constant k. Based on the non-symmetric standard state convention we have calculated that the Gibbs energy of reaction ΔrG=57.26 kJ mol?1 and the reaction rate constant k=7.23×10?5 M?1 s?1 at ambient temperature. Re-analysis of the thermodynamic estimation (Bartels, 2009 Comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) showed that the upper limit for the rate constant at 573 K is k=1.75×104 M?1 s?1 compared to the value predicted by the diffusion-kinetic modelling (3.18±1.25)×104 M?1 s?1 (Swiatla-Wojcik, D., Buxton, G.V., 2005. On the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 74(3–4), 210–219). The presented thermodynamic evaluation of k(573) is based on the assumption that k can be calculated from ΔrG and the rate constant of the reverse reaction which, as discussed, are both uncertain at high temperatures. 相似文献
15.
16.
《The Journal of chemical thermodynamics》2001,33(5):471-484
Heat capacities of 2,2-dimethyl-1,3-propanediol(CH3)2C(CH2OH)2 were measured in the temperature range between T = 13 K and T = 350 K using an adiabatic calorimeter. The compound underwent a first-order phase transition at T = (314.5 ± 0.1) K. The enthalpy and the entropy of transition were (12.52 ± 0.02)kJ · mol − 1and (39.81 ± 0.08)J · K − 1· mol − 1, respectively. Measurement of the fusion peak by d.s.c. showed that the purity of the sample was 0.9999 mass fraction and the entropy of fusion was 9.9 J · K − 1· mol − 1. Another first-order phase transition was observed at T = (60.4 ± 0.1) K with the associated entropy change of (2.93 ± 0.05)J · K − 1· mol − 1. Heat capacities of two deuterated samples,(CH3)2C(CH2OD)2 and(CD3)2C(CD2OD)2 , were also measured and the results were compared with those on the natural compound. Possible mechanisms of the transition have been discussed from the isotope effects on the thermodynamic quantities associated with the transition. Standard thermodynamic functions of the compounds are tabulated. 相似文献
17.
《The Journal of chemical thermodynamics》2007,39(3):455-461
Three members of the lead (II) n-alkanoates (from etanoate to n-butanoate) have been synthesized, purified and studied by d.s.c., X-ray diffraction, and FTIR spectroscopy. Lead (II) acetate, propanoate, and butanoate present only a melting transition at T = (452.6, 398.2, and 346.5) K, with ΔfH = (16.0, 13.1, and 15.6) kJ · mol−1, and ΔfS = (35.3, 32.8, and 45.1) J · mol−1 · K−1, respectively. These temperature data correct to a great extent the historical values reported in the literature. These three members readily quench into a glass state. Their corresponding Tg values are (314.4, 289.0, and 274.9) K, respectively, measured by d.s.c. at a heating rate of 5 K · min−1. 相似文献
18.
《The Journal of chemical thermodynamics》2007,39(11):1413-1417
A visible spectrophotometric method has been developed for the reaction kinetics of o-phenylenediamine in the presence of gold (III). The method is based on the measurement of the absorbance of the reaction o-phenylenediamine and gold (III). Optimum conditions for the reaction were established as pH 6 at λ = 466 nm.When the reaction kinetic of o-phenylenediamine by gold (III) was investigated, it was observed that the following rate formula was found as ln (A/A0) = −kt, according to absorbance measurements. The activation energy Ea and Arrhenius constant A were calculated from the Arrhenius equation as 1.009 kJ · mol−1 and 3.46 · 10−2 s−1, respectively. Other activation thermodynamic parameters, entropy, ΔS (J · mol−1 · K−1), enthalpy, ΔH (kJ · mol−1), Gibbs free energy, ΔG (kJ · mol−1) and equilibrium constant, Ke were calculated at T = (283.2, 303.2, 323.2, and 343.2) K. The study was exothermic due to the decrease of entropy and was a non-spontaneous process during activation. 相似文献
19.
《Electrochemistry communications》2008,10(7):1035-1037
Nanostructured amorphous RuO2 · xH2O/C composite materials are prepared via a modified sol–gel process using glycolic acid. The glycolate anion, which dissociates from glycolic acid at pH 7, behaves as a stabilizer by adsorbing onto the RuO2 · xH2O surface, thus resulting in particles with a size of about 2 nm. As evidenced by zeta potential measurements, the surface charge of RuO2 · xH2O becomes more electronegative as the amount of glycolic acid increases. After heat treatment at 160 oC to remove the stabilizer, RuO2 · xH2O/C is found to exhibit an amorphous structure. The specific capacitance of RuO2 · xH2O/C particles (40 wt% Ru) prepared in the presence of glycolic acid (0.3 g L−1) is 462 F g−1, which is 30% higher than that of the material prepared in the absence of glycolic acid. Both the nanosized particles and the amorphous structure mainly contribute to this increase in the specific capacitance. 相似文献
20.
《The Journal of chemical thermodynamics》2002,34(11):1777-1785
The molar enthalpies of reaction of metallic barium with 0.047 mol·dm−3 HClO4 as well as the molar enthalpies of dissolution of BaCl2 in 1.01 mol·dm−3 HCl and in water have been measured at T=298.15 K in a sealed swinging calorimeter with an isothermal jacket. From these results the standard molar enthalpy of formation of the barium ion in an aqueous solution at infinite dilution, as well as the enthalpies of formation of barium chloride and barium perchlorate, are calculated to be: ΔfH0m(Ba2+,aq)=−(535.83±1.25) kJ · mol−1; ΔfH0m(BaCl2,cr)=−(855.66±1.28) kJ · mol−1; and ΔfH0m(BaClO4,cr)=−(796.26±1.35) kJ · mol−1. The results obtained are discussed and compared with previous experimental values. 相似文献