STABILIZATION, GROWTH AND REACTIVITY OF SILVER AGGREGATES PRODUCED BYRADIOLYSIS IN THE PRESENCE OF EDTA

At pH greater-than-or-equal-to 6 in the presence of excess Ag+ ions, E DTA, (ethylenediaminetetraacetic acid) is able to stabilize silver agg regates of a few nanometers in size due to complexation between the CO O- groups of EDTA and some Ag+ ions at the surface of the aggregates. EDTA cannot stabilize silver oligomers. The complexation of Ag+ ions i n solution causes a negative shift in the redox potential of silver ag gregates which induces a pH-dependent behavior of the particles toward s reduction (by EDTA) as well as oxidation (air-induced corrosion) at the particle surface. At pH greater-than-or-equal-to 6, a very slow el ectron transfer occurs from EDTA towards the silver aggregates, until all the excess Ag+ ions are reduced, thereby allowing their slow coale scence: this growth results in flat, triangular, single crystals (100- 150 nm side) which are only 10 nm thick. They display previously unrep orted spectra with three absorption bands related to their non-spheric al shape: a small peak at 330 nm, a band in the 400 nm region and a ma in broad band in the infra-red, the position of which depends on R = [ EDTA]/[Ag+]. At pH = 10 the aggregates are slowly corroded due to a re dox potential shift caused by both size and complexation effects.