Cation Association with Sodium Dodecyl Sulfate Micelles As Seen by Lanthanide Luminescence

The interaction of trivalent lanthanides with sodium dodecyl sulfate micelles (SDS) in aqueous solution has been studied by a variety of experimental techniques. Potentiometric measurements with a sodium selective electrode, steady-state fluorescence spectra of Ce(III), emission lifetime measurements of Ce(III), Tb(III), and Eu(III), and electronic paramagnetic resonance spectra (EPR) of Gd(III) all show that the lanthanide ions bind to the micellar surface. From analysis of the Tb(III) lifetime measurements in water and D2O solutions, it is found that the lanthanide ions lose one hydration water on binding to SDS. However, the EPR measurements suggest that the lanthanide ions still have considerable freedom of movement. Energy transfer between Ce(III) and Tb(III) has been used to obtain further information on multiple lanthanide ion binding. From steady-state fluorescence measurements in aqueous solution in the absence of SDS no energy transfer is observed, although there is quenching of Tb(III) emission by Ce(III), which is found to follow good Stern-Volmer kinetics. In the presence of SDS micelles, very different behavior is observed and energy transfer occurs from excited Ce(III) to Tb(III). This is only possible when the two ions are on the same micelle. The energy transfer phenomena is highly dependent on micelle concentration and has been analyzed theoretically via a Monte Carlo simulation. This shows that the lanthanide ions bind close to the micelle surface, and are consistent with the loss of a water molecule. Also, assuming a Dexter-type model in which the energy transfer intensity is proportional to the inverse of the square root of the average distance between cerium and the closest terbium it is possible to reproduce qualitatively the experimental cerium(III)-sensitized Tb(III) luminescence intensity data

Photodegradation of atrazine and ametryn with visible light using water soluble porphyrins as sensitizers

Abstract The photodegradation of the herbicides atrazine and ametryn with visible light in aerated neutral aqueous solutions and 5, 10, 15, 20-tetrakis (2,6-dichloro-3-sulfophenyl) porphyrin or 5, 10, 15, 20-tetrakis (4-sulfophenyl) porphyrin as sensitizers are reported for the first time. Our findings show that the degradation percentage reached 30% for atrazine and 63% for ametryn. The final photoproducts were characterized as dealkylated s-triazines. Photolysis of the pesticides in the presence of a singlet oxygen quencher showed only a minor contribution of this type of mechanism, while a bimolecular quenching reaction between the triplet state of the sensitizer and the pesticides is excluded by flash photolysis studies. It is proposed that the mechanism may involve the formation of a superoxide radical anion from the triplet state of the sensitizer and molecular oxygen, followed by a radical decomposition pathway

Deactivation processes of the lowest excited state of [UO2(H2O)5]2+ in aqueous solution

A detailed analysis of the photophysical behaviour of uranyl ion in aqueous solutions at room temperature is given using literature data, together with results of new experimental and theoretical studies to see whether the decay mechanism of the lowest excited state involves physical deactivation by energy transfer or a chemical process through hydrogen atom abstraction. Comparison of the radiative lifetimes determined from quantum yield and lifetime data with that obtained from the Einstein relationship strongly suggests that the emitting state is identical to that observed in the lowest energy absorption band. From study of the experimental rate and that calculated theoretically, from deuterium isotope effects and the activation energy for decay support is given to a deactivation mechanism of hydrogen abstraction involving water clusters to give uranium(V) and hydroxyl radicals. Support for hydroxyl radical formation comes from electron spin resonance spectra observed in the presence of the spin traps 5,5-dimethyl-1-pyrroline N-oxide and tert-butyl-N-phenylnitrone and from literature results on photoinduced uranyl oxygen exchange and photoconductivity. It has previously been suggested that the uranyl emission above pH 1.5 may involve an exciplex between excited uranyl ion and uranium(V). Evidence against this mechanism is given on the basis of quenching of uranyl luminescence by uranium(V), together with other kinetic reasoning. No overall photochemical reaction is observed on excitation of aqueous uranyl solutions, and it is suggested that this is mainly due to reoxidation of UO2+ by hydroxyl radicals in a radical pair. An alternative process involving oxidation by molecular oxygen is analysed experimentally and theoretically, and is suggested to be too slow to be a major reoxidation pathway