FORMATION OF COLLOIDAL SILVER BY PUSH-PULL REDUCTION OF AG+

A radiolytic ''push-pull'' reduction method for the preparation of reasonably monodisperse silver particles (7.0 nm in diameter) in aqueous solution is described. Slow particle growth is achieved in this method by simultaneously reducing Ag+ ions and partially oxidizing Ag(n) particles. The absorption spectrum of the particles contains a particularly narrow surface plasmon band at 382 nm (epsilon(max) = 2.9 x 10(4) M-1 cm-1). A comparison with particles in a glass matrix shows that the plasmon oscillation in ''aqueous' particles is less damped. The absorption band is as strongly damped by chemisorbed iodide as for particles prepared by other methods which have a broader absorption band. It is concluded that the narrow band of the particles grown by ''push-pull'' reduction is due to a particularly perfect lattice structure of the colloidal particles and that there is only weak interaction of the particles with the aqueous solvent. It seems that the absorption band is even narrower than for particles in glassy matrices, a result which is in variance with previous experiences.