NANOMETER-SIZED BI PARTICLES IN AQUEOUS-SOLUTION - ABSORPTION-SPECTRUM AND SOME CHEMICAL-PROPERTIES

Nanometer-sized particles of bismuth are formed by the radiolytic redu ction of aqueous solutions of bismuth perchlorate, the size and shape of the particles depending on the nature of the stabilizer. Well-facet ted particle shapes (mean diameter: 20 nm) are observed with 2 x 10(-4 ) M polyethyleneimine or 1 x 10(-3) M polyacrylamide-10 (10% carboxyl groups) as stabilizer, whereas particles of less regular shape (mean d iameter: 8 nm) are obtained with 1 x 10(-3) M polyacrylamide-70 (70% c arboxyl groups). The reduction of Bi(III) by 1-hydroxy ethyl methyl ra dicals, (CH3)(2)COH, is accompanied by H-2 production, the bismuth par ticles formed serving as a catalyst. The absorption spectrum of colloi dal bismuth has a weak maximum at 253 nm, which is not rendered by the spectrum calculated from the (rather scarce) dielectric data of Bi. R adiolysis experiments for the preparation of composite metal particles are also reported. The reduction of Cd2+ ions by organic radicals is catalyzed by Bi particles and leads to a cadmium shell. Reduction of B i(III) in the presence of colloidal silver leads to a blue-shift of th e silver plasmon absorption band, which is explained by a deposition o f bismuth on the silver particles.