Jacqueline Belloni

Radiation-induced copper aggregates and oligomers

Abstract γ radiolysis of CuSO 4 solutions containing surfactants (polyvinyl alcohol, polyacrylic acid) induces the formation of copper nanoaggregates which dissolve readily when brought into contact with oxygen. The pink copper clusters and the intermediate Cu I are studied spectrophotometrically under various conditions: pH, Cu 2+ concentration, radiolytic dose. The reactivity of the aggregates in redox reactions is used to determine, notwithstanding the presence of excess copper ions, the metal atom content and the radiolytic yield. The optical absorption band at 570 nm has thus been calibrated to be ϵ(Cu n ) 570 nm = 1950 ± 50 l mol −1 cm −1 at pH 6.2 and 2400 ± 100 at pH 2.6. Oligomers of lower nuclearity stabilized by polyacrylate ions are shown to absorb at 292, 350 and 455 nm.

Optical limitation induced by gold clusters: Mechanism and efficiency

The optical limiting effect induced by gold clusters was measured as a function of excitation wavelength. The limiting effect is most efficient below 530 nm, and decreases towards the red. Two different behaviors are seen in the time-resolved signals in the nanosecond and picosecond ranges. These behaviors have different time delays for the amplitude maxima and for the fluence thresholds where nonlinear effects are observed. This suggests that two types of scattering centers are responsible for the optical limitation. The fast mechanism, which reaches a maximum amplitude in less than 1 ns, occurs at relatively high fluence and for short pulses and is assigned to the vaporization of metal particles. It is more pronounced for large clusters where the absorbed light energy is primarily highly confined. The slow mechanism, which develops in a few nanoseconds, is assigned to the energy transfer from the gold particles to the surrounding solvent and to the formation of solvent bubbles. nAt lower fluence and for smaller size clusters, only the second mechanism is observed in the nanosecond range, because the efficient dissipation of energy from the small clusters to the solvent, which produces bubbles, precludes metal-particle vaporization.

Mechanism of trivalent gold reduction and reactivity of transient divalent and monovalent gold ions studied by gamma and pulse radiolysis.

The detailed kinetics of the multistep mechanism of the Au(III) ion reduction into gold clusters have been investigated by radiation chemistry methods in 2-propanol. In particular, a discussion on the steady state radiolysis dose-dependence of the yields concludes to a comproportionation reaction of nascent gold atoms Au(0) with excess Au(III) ions into Au(II) and Au(I). This reaction should be achieved through Au(III) consumption before the coalescence of atoms Au(0) into gold clusters may occur. Then gold clusters catalyze the reduction of Au(I) by 2-propanol. It was also found that a long-lived Au(II) dimer, (Au(II))(2), was transiently formed according to the quantitative analysis of time-resolved absorbance signals obtained by pulse radiolysis. Then the disproportionation of Au(II) is intramolecular in the dimer instead of intermolecular, as usually reported. The yields, reaction rate constants, time-resolved spectra, and molar extinction coefficients are reported for the successive one-electron reduction steps, involving especially the transient species, such as Au(II), (Au(II))(2), and Au(I). The processes are discussed in comparison with other solvents and other metal ions.

Radiation-induced reduction of mixed silver and rhodium ionic aqueous solution

Silver and rhodium metal nanoparticles were synthesized by electron beam and g-radiolysis of mixed solutions containing (Rh II acetate) dimer and Ag + sulfate in variable proportions. From the observation of the optical absorption spectra, transmission electron microscopic images and local X-ray analysis at increasing doses, it is concluded that the metals are segregated into two populations, which are randomly distributed according to the mixture content, one of 1.5–2 nm pure rhodium clusters, and the other of 15–20 nm pure silver clusters. At complete reduction of both metals, the Ag nanoparticles are systematically surrounded by the small rhodium clusters. r 2002 Elsevier Science Ltd. All rights reserved.

Radiolytic Yield of UIV Oxidation into UVI: A New Mechanism for UV Reactivity in Acidic Solution

The yields of the radiolytic oxidation of U(IV) and of the U(VI) formation, measured by spectrophotometry, are found to be the same (G(-U(IV))(N2O) = G(U(VI))(N2O) = 8.4 x 10(-7) mol J(-1)) and almost double the H(2) formation yield (G(H(2)) = 4.4 x 10(-7) mol J(-1)) in the (60)Co gamma radiolysis of N(2)O-aqueous solutions in the presence of 2 mol L(-1) Cl(-) at pH = 0 (HCl). According to the mechanism of U(IV) radiolytic oxidation, we show that under the conditions of our experiments the U(V) ions do not disproportionate, but undergo a stoichiometric oxidation into U(VI) by H(+) with forming H(2).