Abstract
Adsorbed Ag
+ ions on the surface of Ag
2O formed by the reaction of Ag
+ ions and OH
−, are reduced by the adsorbed aspartic acid.
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► Alkaline solution is required to the formation of perfect transparent silver sol. ► Size and rates of silver nanoparticle formation strongly depends on the aspartic acid concentrations. ► Amino and α-carboxylate groups undergo chemical transformation. ► Aspartic acid oxidized by the adsorbed silver ions onto the surface of silver oxide.
Spectrophotometric, kinetic, and transmission electron microscopic (TEM) data for the formation of Ag-nanoparticles using aspartic acid (Asp) as reductant are reported for the first time. In the formation of transparent silver sols, an alkaline medium is required. The silver nanoparticles are spherical, uniform particle size, and strongly depend on the [Asp]. The apparent rate constant decreases with [Asp] (from 4.0 to 24.0
×
10
−4
mol
dm
−3, the rate constants decreased from 2.6
×
10
−4 to 0.3
×
10
−4
s
−1). For a certain reaction time, i.e., 30
min, the absorbance of the silver sol first increased until it reached a maximum, and then decreased with [Asp]. Kinetic and TEM results indicate that the size of the Ag-nanoparticles depends on the [Asp]. It is proposed that the oxidation of Asp occurs by the adsorbed Ag
+ ions on the surface of Ag
2O particles.