AGGREGATION OF SILVER HYDROSOLS PREPARED IN AIR

The chemistry involved in the preparation and activation of silver hyd rosols was monitored by pH, potential, and surface charge measurements , by absorption spectra in the visible region, and by surface-enhanced Raman spectroscopy (SERS). The activation, displayed by a red-shift o f the colloid absorption at 392 nm, corresponds to a partial aggregati on of elementary silver particles as displayed by transmission electro n micrographs. The participation of carbonate species in the chemistry of hydrosols handled in air was made obvious by titration with strong acids. The colloid destabilization was performed either with protons, by adding strong non-complexing acids (HNO3, HClO4), or with low conc entrations of Cu2+. In contrast, HCl determined a stabilization of hyd rosols related to the complexing affinity of Cl- toward silver. The su ccessive addition of Cu(NO3)(2) and HCl allowed a balance between all the chemical reactions and a very efficient activation process. Wherea s the chemical reactants used are nominally inorganic, at total concen trations lower than 10(-3) M, the activated hydrosols display anomalou s SER spectra which were previously assigned to organic molecules. (C) 1998 Academic Press.