Guozhong Wu

Hydrated electron in subcritical and supercritical water: a pulse radiolysis study

Temperature dependences of the eaq− spectrum and Gemax were investigated by the pulse radiolysis method over a temperature range of 25–400°C including the supercritical condition and the eaq− formation in supercritical water (D2O) was confirmed. With increasing temperature, the absorption peak (λmax) of eaq− shifts significantly to longer wavelength. The value of Gemax in supercritical water is considerably smaller than in liquid water at room temperature. The behavior of eaq− revealed here is helpful for an extensive understanding of water radiolysis and for the study of eaq− involving radical reactions in supercritical water.

Temperature dependence of radiation effects in polyethylene: Cross-linking and gas evolution

High-density polyethylene (HDPE) and low-density polyethylene (LDPE) were irradiated in vacuo at 30–220 and 30–360°C, respectively, with γ-rays at doses of 10–400 kGy. Temperature dependence of cross-linking and gas evolution was investigated. It was found that cross-linking was the predominant process up to 300°C and the gel point decreased smoothly with temperature. The increase of G(x) with temperature was likely attributed to the temperature effect on addition of radicals to the double bonds present in the polymer. Above 300°C, the gel fraction at a given dose decreased remarkably with temperature and turned to zero at 360°C. The molecular weight variation determined with gel permeation chromatography (GPC) indicated the enhanced degradation at 360°C by radiation. G-values of H2 increased with temperature and varied with dose. The compositions of the C1–C4 hydrocarbons evolved depended on the structures of side branches. Raising the temperature favored the formation of unsaturated hydrocarbons, and the yield of unsaturated relative to saturated hydrocarbons decreased with dose.

Pulse radiolysis of high temperature and supercritical water: experimental setup and eaq− observation

Abstract This paper describes the setup of a high-temperature cell for water pulse radiolysis and the preliminary result of e aq - observation. The experiment was performed using D 2 O at 25–400°C including supercritical conditions. The e aq - formation in supercritical water was confirmed. Temperature dependences of e aq - spectrum and Ge max were investigated. With increasing temperature, it was found that absorption peak shifts significantly to lower energy (red shifting) and Ge max decreases.

Temperature dependence of ketyl radical in aqueous benzophenone solutions up to 400 °C: A pulse radiolysis study

Pulse radiolysis studies with aqueous benzophenone solutions were performed over the range 25–400 °C, including conditions beyond the critical point of water. The addition of eaq− to benzophenone forms either ketyl anion in alkaline solutions or neutral ketyl radical in acidic/neutral solutions. Although both have an intense and sharp absorption band in the UV region and a weak but broad band in the visible region, their spectra are clearly different. The peak of the visible band is at 545 nm for the neutral ketyl radical and 610 nm for the anion at room temperature. With increasing temperature, the absorption peak of the ketyl radical shifts to a shorter wavelength while that of the anion shifts to a substantially longer wavelength. The decay of the ketyl radical is not monotonically temperature-dependent: its rate constant (2k/e) increases with temperature up to 100 °C and then decreases at higher temperatures. The rate constant for the addition of eaq− to benzophenone can be considered to be diffusion controlled and the Arrhenius plot can be fitted with a curved line. The temperature dependence of the rate constant for the reaction of eaq− with proton was determined up to 400 °C by the competition method using benzophenone as the reference solute. It was also found that the addition of OH˙ radical to benzophenone forms a transient species with a strong absorption band centered at 380 nm and the peak seems to be slightly blue-shifted with temperature. The decay of this species increases rapidly with temperature, indicating the enhanced conversion to stable products at high temperatures.

Photolytic and radiolytic studies of SO4•− in neat organic solvents

A study of SO4•− in neat organic solvents by laser photolytic and pulse radiolytic methods has been described for the first time. The sulfate radical was produced in neat CH3CN and CHCl3 by laser photolysis of (CTA)2S2O8 (CTA = cetyltrimethylammonium), or in CH3CN ia reduction of (CTA)2S2O8 with a reducing species produced from pulse radiolysis. The quantum yield of SO4•− in CH3CN was 30% higher than in water, based on our experimental results. The SO4•− reacts slowly with CH3CN, but rapidly with CHCl3 to form •CCl3 which is further converted into CCl3O2• in the presence of oxygen. Rate constants for hydrogen abstraction from alkanols by SO4•− were lower by 1–2 orders of magnitude in CH3CN than in aqueous solutions.

Observation of hydrated electron, (SCN)2.- and CO3.- radical in high temperature and supercritical water

Transient radicals (hydrated electron, (SCN)2.- and CO3.-) formed in supercritical water have been observed by the pulse radiolysis technique. The change of spectra of these radicals with temperature has been measured. It was found that the spectra and absorption coefficients of the radicals, e-aq and (SCN)2.-, are strongly dependent on the temperature of the water. Since it was found that the absorption spectrum and molar absorption coefficient of CO3.- radical seem to be almost independent of temperature, G-values of OH and e-aq could be derived. Then, the absolute values of the absorption coefficients for the radicals could be calculated. The G-values of the radical products in water radiolysis tend to increase with increasing temperature up to 400°C. Based on the above observation, radiolysis of supercritical water is discussed.

A pulse radiolysis study of oil/water microemulsions

Abstract Absorption spectrum and the yield of e aq − determined in quaternary benzene/water and dodecane/water microemulsions were found to be identical with those in pure water. This indicates that the excess electrons produced in the oil droplets cross the oil/water interface and appear in the aqueous phase as hydrated electrons. On the contrary, it was found that the OH radical yield measured by converting into (SCN) 2 .− was directly proportional to the water content and there was no contribution from the oil phase. The e aq − decay in aerated microemulsion showed that the [O 2 ] in the aqueous phase was decreasing with continuous pulse irradiation and the estimated G (–O 2 ) in the oil was higher than in water. However, peroxides were predominantly formed in the aqueous phase and almost not in the oil. Rate constants for the addition of e aq − and OH to benzene in the benzene/water microemulsion and the following bimolecular decay of cyclohexadienyl and hydroxycyclohexadienyl radicals agree well with those reported in aqueous solutions.

H2 evolution in hexadecane irradiated at high temperatures

Abstract H 2 yields of n -hexadecane irradiated at 330–400°C were determined and compared with that at room temperature. The temperature dependence of G(H 2 ) was found to be insignificant up to 330°C. High G(H 2 ) values above 330°C indicated the enhanced dehydrogenation of hydrocarbons. Compared to alkane, irradiation of alkene at high temperature produces higher H 2 yields as shown from the correlation between G(H 2 ) and the fraction of alkene.