Photochemical Generation of Ag, Pd, and Pt Particles in Octane

Metal crystallites formed upon UV irradiation of benzophenone (BP) solutions in octane containing oleoyl sarcosine as a particle stabilizer and Ag neodecanoate (AgOOR), as well as the complexes Pd(acac) 2 and Pt(acac) 2, with acac = acetylacetonate anion. Initial quantum yields of metal formation for Pd(acac) 2 and Pt(acac) 2 were 7 × 10 –3 and 4.5 × 10 –3, respectively, which are about 7 times higher than those for analogous reactions conducted in the absence of the BP photosensitizer. Direct irradiation of AgOOR, on the other hand, resulted in no reaction, but silver particles were formed with a quantum yield of 1.2 in the presence of BP. Whereas the Pd colloids decay within 1 week of preparation, the Ag and Pt particles have remained stable, thus far, in octane for more than 4 months. The resulting octane colloids were evaluated for enhancements in thermal conductivity using the thermal hot disk method. Enhancements of up to 10% were observed for the Ag and Pt systems at metal concentrations of 5 mM, which are far larger than what Maxwell’s theory predicts for a colloid of low volume fraction (∼5 × 10 –5 vol %).