Effect of Ligands on the Redox Reactions of Silver Metal Clusters

Abstract

The reduction of silver ions and their subsequent agglomeration was studied in aqueous solutions in the presence of N-(hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), iminodiacetic acid, 5-aminotetrazole, benzotriazole, and 2-mercaptobenzimidazole as ligands. The presence of ligands in the solution affects the early processes via the complexation of Ag+ ions with the carboxyl and amino moieties of the ligands. Also, it reduces somewhat the rate of reduction by hydrated electrons. The transient absorption spectra of Ag0, Ag2+ and Ag20 and their successive rate constants have been determined. The red shift in the band of silver atoms was found to be more pronounced when the ligand interaction is stronger. This was correlated with the ligand-induced redox properties of the silver couple. These effects are also more pronounced in the presence of excess silver ions in the solution. It was observed that silver N-(hydroxyethyl)ethylenediaminetriacetic acid and silver nitrilotriacetic acid are not directly reduced by (CH3)2CO•-. This confirms that the redox potential of the silver couple is lowered in the presence of HEDTA and NTA. In addition, HEDTA stabilizes silver metal particles against corrosion due to the shift in the redox potential. Silver particles prepared by γ irradiation and combined with hydrothermal treatment were characterized using transmission electron microscopy and showed particle sizes of 10−20 nm.