Hydrated Electrons in a Quaternary Microemulsion System: A Pulse Radiolysis Study

Observation of Nanoconfinement Effect on the Kinetics of Hydrated Electron in the Nanoscale Water Pools of Water-AOT-Cyclohexane Microemulsions by Picosecond Pulse Radiolysis

The decay kinetics of the hydrated electron (eaq-) in aerosol OT (AOT)-based ternary microemulsions with pool sizes ranging from 0.34 to 4.85 nm were studied using picosecond pulse radiolysis coupled with transient absorption UV-vis spectroscopy. Electron transfer from oil to water and the subsequent solvation occurred within a time resolution of 7 ps. The decay kinetics of eaq- were accurately modeled using a double-exponential decay model, revealing the occurrence of two types of reactions, i.e., the recombination reaction at the water-oil interface and the radical-radical reactions in the water pools. The apparent lifetimes of both types of decays decreased significantly as the size of water pools decreased, indicating the influence of nanoconfinement effects. Moreover, the importance of the water-oil interface increased with decreasing water content, regardless of the presence or absence of NO3- as an electron scavenger in the water pools. Our findings provide a comprehensive understanding on the kinetics of the radiation reaction in AOT-based microemulsions.

Radiolytic syntheses of nanoparticles in supramolecular assemblies

Ionizing radiation is a powerful method in the syntheses of nanoparticles (NPs). The application of ionizing radiation in supramolecular assemblies can afford us more unique conditions to control the composition and morphology of the NPs. So far, most work focused on water-in-oil (W/O) microemulsions or reversed micelles. In this supramolecular organization, it has been proved that the effects of many conditions on the yield of e(aq)(-) play a key role, remarkably different from the mechanism in routine chemical method. Besides, some supramolecular assemblies of cyclodextrins and ionic liquids have been used in the syntheses of NPs by ionizing radiation, and many novel and interesting phenomena appeared. This review is intended to underline the three significant aspects of the radiolytic syntheses of NPs in supramolecular assemblies.

Formation of solid and hollow cuprous oxide nanocubes in water-in-oil microemulsions controlled by the yield of hydrated electrons

A local ordered structure constructed from solid Cu(2)O nanocubes was obtained by the radiolytic reduction of Cu(NO(3))(2) in a water-in-oil (W/O) microemulsion composed of Triton X-100, n-hexanol, cyclohexane, and water in the presence of ethylene glycol (EG). However, when Triton X-100 was replaced with Brij 56 in the microemulsion, hollow Cu(2)O nanocubes were synthesized. The addition of toluene into the Brij 56 system could decrease the ratio of hollow nanocubes. It was suggested that the balance between the reduction rate of Cu(2+) depending on the yield of hydrated electrons (e(aq)(-)) and the escape rate of the mixed solvent determined their final morphologies. The presence of EG influenced the rigidity of the interface of the microemulsion and thus the above balance, which resulted in the different morphologies of Cu(2)O nanoparticles in the Brij 56-based microemulsion.

Formation of nanoparticles in water-in-oil microemulsions controlled by the yield of hydrated electron: The controlled reduction of Cu2+

In the water-in-oil (W/O) microemulsions based on nonionic surfactants, i.e., Brij 30, Brij 56, or Triton X-100, the omega value (molar ratio of water to surfactant), anion, and surfactant could remarkably affect the radiolytic reduction of Cu2+ and the morphologies of the reduction products simultaneously. The addition of toluene or naphthalene could transform the reduction products from copper to cuprous oxide in the Brij 56-based microemulsion, and the efficiency of naphthalene was obviously higher than that of toluene. After the effects of pH value and cosurfactant were excluded, it could be concluded that the effects of the omega value, the anion, and the structure of the surfactant on the yield of hydrated electrons (eaq-) play a key role in the radiolytic reduction of Cu2+. It was also suggested that the morphology of the reduction product may be controlled by the yield of eaq-.

Pulse radiolytic oxidation of beta-carotene with halogenated alkylperoxyl radicals in a quaternary microemulsion: formation of retinol

Pulse radiolytically generated halogenated alkylperoxyl radicals, namely CCl3OO*, CBr3OO*, CHCl2OO*, CHBr2OO*, etc. have been employed for a study of the oxidation of beta-carotene in a quaternary microemulsion. All these halogenated alkylperoxyl radicals produce a radical cation (absorption maximum at 840 nm), either via the initial formation of an adduct (absorption maximum at 740 nm), or by direct reaction. There was a considerable blue shift of both absorption peaks in the present system as compared to those earlier reported in non-polar as well as in micellar media. An additional intense absorption peak at approximately 345 nm was noted at a longer time scale and was stable up to 5 ms. On irradiation with a large number of electron pulses, a stable product with an absorption maximum at 315 nm appeared. On excitation at 315 nm, this product gave a fluorescence spectrum with an emission maximum at 525 nm. The absorption and fluorescence spectra of the stable product compared with those of retinol; this was further confirmed by HPLC analysis. A suitable mechanism has been proposed.