Molecular numbers in core and shell: structural dependence of reactivity of alkylcarboxylate-stabilized silver nanoparticles

Spectroscopic, chemical, thermal, and voltammetric analyses on six kinds of alkylcarboxylate-stabilized silver nanoparticles 4.7 nm in diameter were carried out with an aim to reveal the effect of alkylcarboxylates on the optical, thermal, geometric, and electrochemical properties of the nanoparticles. These nanoparticles are composed of silver atoms and silver alkylcarboxylates having even numbers, m, of carbon atoms from 8 to 18. As a measure of the structure of the nanoparticles, the ratio of the number of silver atoms (nAg) to that of alkylcarboxylates (ns) per nanoparticle was evaluated by means of titration through chemical oxidation, voltammetric currents, and thermal gravimetric analysis. It increased with an increase in m and ranged from 1.3 to 9.8. Properties of the nanoparticle have been exhibited in absorbance of the UV-vis spectra at the point of the proportionality to n(Ag), voltammetric currents of which values were close to the theoretical values at the diffusion of particle itself, and the m-independent kinetic energy of the thermal decomposition and the overpotential of the reduction. They are not observed for the composed species, that is, silver atoms and silver alkylcarboxylate molecules.