| Silver nanoparticles can be readily generated in micellar environments by ketyl radicals formed from the photoreduction of benzophenone in the presence of a suitable hydrogen donor. The yield of these ketyl radicals can be increased by extending the lifetime of the triplet radical pair through Zeeman splitting of the triplet sublevels in an externally applied magnetic field. This provides control over the rate of photogeneration of nanoparticles under very mild conditions. The rate of photogeneration can be monitored by the distinctive surface plasmon resonance absorption around 420 nm. In this work, micelles of sodium dodecyl sulphate (SDS) were employed, and 1,4-cyclohexadiene (1,4-CHD), an excellent hydrogen donor, was used to promote the generation of ketyl radicals. When benzophenone and a silver salt are added to this system and it is irradiated in the presence of a magnetic field, the rate of appearance of the plasmon band is enhanced. In addition to serving as a hydrogen donor, 1,4-CHD also has a stabilising influence on the nanoparticles, adsorbing onto the surface and preventing aggregation. 1,4-CHD added to a solution of nanoparticles synthesised without the diene present will even break up existing aggregates. |
