Evolution of Electronic State and Properties of Silver Nanoparticles during Their Formation in Aqueous Solution

The electron density of a nanoparticle is a very important characteristic of the properties of a material. This paper describes the formation of silver nanoparticles (NPs) and the variation in the electronic state of an NP’s surface upon the reduction in Ag⁺ ions with oxalate ions, induced by UV irradiation. The calculations were based on optical spectrophotometry data. The NPs were characterized using Transmission electron microscopy and Dynamic light scattering. As ~10 nm nanoparticles are formed, the localized surface plasmon resonance (LSPR) band increases in intensity, decreases in width, and shifts to the UV region from 402 to 383 nm. The interband transitions (IBT) band (≤250 nm) increases in intensity, with the band shape and position remaining unchanged. The change in the shape and position of the LSPR band of silver nanoparticles in the course of their formation is attributable to an increasing concentration of free electrons in the particles as a result of a reduction in Ag⁺ ions on the surface and electron injection by ${\mathrm{CO}}_2^{-}$ radicals. The ζ-potential of colloids increases with an increase in electron density in silver nuclei. A quantitative relationship between this shift and electron density on the surface was derived on the basis of the Mie–Drude theory. The observed blue shift (19 nm) corresponds to an approximately 10% increase in the concentration of electrons in silver nanoparticles.