|Budget Amount *help
¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1997 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1996 : ¥1,800,000 (Direct Cost : ¥1,800,000)
"Photo-acetone method" has been known as a tractable method to prepare finely dispersed colloidal metals (Ag, Au, Pt and Cu). In this study, aromatic ketone was used instead of acetone in order to investigate the role of the ketyl radical during the reaction. Aqueous silver percholate solutions were photolyzed with near-UV light in the presence of sodium dodecylsulfate (SDS) micelle and aromatic ketone, such as benzophenone and acetophenone. The formation of finely dispersed colloidal silver and the photobleach of aromatic ketone were caused by irradiation with near-UV light, which was absorbed solely by aromatic ketone (sensitized photoreduction). Gross features of the sensitized photoreduction of silver ion and the photobleach of aromatic ketone were interpreted in term of a simple reaction scheme entailing suitable combinations of the kinetics parameters. Namely, the excitation of aromatic ketone by near-UV light yields an aromatic ketone triplet, which abstracts an H atom from SDS micelle, giving rise to a ketyl radical. Some ketyl radical reduces silver ion and silver ion cluster and goes back to aromatic ketone. Other ketyl radical changes into certain byproducts such as the corresponding pinacol, hydrol and coupling compound with SDS.It was noticed that an extinction coefficient of colloidal silver formed during the early stage was smaller than the usual value because of the size effect of the particles. The existence of the ketyl radical of benzophenone in the reaction mixture was confirmed by laser photolvsis, It was tried to compare the lifetime of the ketyl radical under various reaction conditions. Taking advantage of the unique reaction process of the photo-acetone method, the composite noble metal colloid, whose structure and spectroscopic properties were different from alloy colloid, has been successfully prepared.