A. Henglein et C. Brancewicz, ABSORPTION-SPECTRA AND REACTIONS OF COLLOIDAL BIMETALLIC NANOPARTICLES CONTAINING MERCURY, Chemistry of materials, 9(10), 1997, pp. 2164-2167
Silver and mercury ions are reduced in a common solution by sodium bor
ohydride in the presence of poly(ethyleneimine). Colloidal alloy parti
cles are formed, whose plasmon absorption band is blue-shifted with in
creasing mercury-to-silver ratio. The reduction mechanism is rather co
mplex: large mercury ''drops'' are first formed, although silver ions
are reduced simultaneously. This effect is explained by an interaction
of the two metal redox systems, as silver clusters are reoxidized by
mercury ions. The final particles are formed in a reaction of the merc
ury drops with reduced silver clusters, yielding amalgam particles sma
ller than the mercury drops. These processes are followed by spectroph
otometric and light-scattering measurements. The alloy colloids are st
able up to a mercury to silver molar ratio of 2. Upon exposure to air,
part of the mercury in the alloy particles is oxidized.