Stability of Silver Oxide (Ag2O): its Synthetic Relevance and Importance on the Silver Nanoparticles Passivity

M. A. MACCHIONE ; J. GODOY; O. A. DOUGLAS; R. MOIRAGHI; F. Y. OLIVA; M. A. PÉREZ; E. A. CORONADO; V. A. MACAGNO

Florianópolis

Congreso; 10 th ISE sponsored meeting Passivity of Metals and Semiconductors; 2011

International Society of Electrochemistry

Stability of aqueous Ag2O colloids is studied with UV-Visible spectroscopy, transmission electronic microscopy (TEM) and theoretical calculations with the Electrodynamic Theory. Despite dry Ag2O is stable up to 170 ºC1, aqueous Ag2O colloids undergo thermal decomposition at room temperature (20-25 ºC) to produce silver nanoparticles (AgNPs). The existence of this process is analyzed in light of UV-Visible spectroscopic evidence, TEM characterization and electrodynamic calculations performed with the Mie theory. Experimental results obtained for the decomposition of aqueous Ag2O colloids varying the oxide particle size-population, the temperature and the electrolyte composition help us analyze some alternatives in formulating the decomposition reaction mechanism. Although our study aimed at unraveling the nature of the reaction in physicochemical terms is still in progress, the knowledge of the existence of such a decomposition process constitutes a useful fact in designing new synthetic routes to obtain AgNPs and nanostructures (NSs). Since O2 or H2O2 are the more probable products of the Ag2O decomposition, AgNPs produced with this reaction route can be easily purified, constituting one of its most important advantages. Our studies using this reaction have been focused in the production of NPs in aqueous media and in water/acetone as well as for the production of hybrid TiO2/Ag NPs. The morphology of AgNPs is sensitive to the water/acetone volume ratio as well as to the Silver(I) ligand concentration (NH3). In a similar approach, the interplay between NH3 and OH- concentrations allows the heterogeneous nucleation of Ag2O onto TiO2 surface particles (and its further decomposition) to be favored over the path silver oxide homogenous nucleation followed by its decomposition. UV-Vis spectral evolution of 0.1 mM AgNO3, 1 mM NaOH solutions at 25 ºC aged over 30 days and AgNPs formed (inset) after that aging period.      References 1 A. F. Benton, L.C. Drake, J. Am. Chem. Soc. 56 (1934) 255.