Nanosize silver particles are formed in aqueous surfactant systems and
have been found to be very reactive toward oxygen in the presence of
borohydride. Purging of air (O-2) or simple shaking leads to complete
dissolution of silver particles, which is further regenerated on stand
ing. Thus an oscillation between a yellow silver plasmon band and colo
rless solution is observed on periodic shaking. This oscillation conti
nues as long as excess borohydride is present. Investigation shows tha
t borohydride, which is a strong nucleophile, adsorbs on the surface o
f the silver particle and decreases the reduction potential of the sil
ver particle so that it reacts rapidly with oxygen. Surfactant plays a
n extra role over particle stabilization. It removes the oxidized silv
er from the particle surface to the bulk and also retards the rate of
reduction of Ag-I to Ag-0.