Formation of Copper Nanoparticles in Sol-Gel Glass by the Photoinduced Electron Transfer of Riboflavin.

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Copper nanoparticles were formed by photoirradiation of sol-gel silica doped with Cu²⁺ ions, ethylenediaminetetraacetic acid, and riboflavin. The formation of copper nanoparticles was identified by the plasmon peak around 580 nm. The mechanism and the parameters of the preparation conditions were examined. A decrease in the fluorescence intensity of riboflavin and an increase in that of lumichrome were found during photoirradiation. The plasmon peak appeared during the formation of lumichrome. Copper nanopartices were also formed in sol-gel silica doped with Cu²⁺ ions, ethylenediaminetetraacetic acid, and lumichrome. These results indicate that riboflavin molecules are photochemically decomposed to lumichrome and the copper nanoparticles are formed by the photoinduced electron transfer of riboflavin and lumichrome.