Silver organosol: synthesis, characterisation and localised surface plasmon resonance study

Abstract

In this article a simple and reproducible technique for the synthesis of a silver organosol is reported from a specific silver precursor, solid silver acetate. Molten hexadecylamine acts as a solvent for silver acetate and imparts stability to the evolved nanoparticles. The amine-capped organosol shows unique stability as neither agglomeration nor oxidation takes place over one year. The synthesised silver particles have been characterised by UV-visible, TEM, XRD, XPS, FTIR and thermogravimetric studies. The hexadecylamine-stabilised silver organosol was employed to examine the altered optical properties in different solvent systems and with different ligands by accounting for the changes in the localised surface plasmon resonance (LSPR) spectrum. It was observed that the position of the surface plasmon band of silver nanoparticles is greatly affected by the solvents and ligands under consideration. The quantitative alteration of the LSPR spectrum involving encapsulated nanoparticles in a dielectric ligand shell has been rationalised from Mie theory. It has also been shown that cationic and anionic surfactants of different chain lengths induce changes in the optical properties of silver nanoparticles whereas, zwitterionic amino acid molecules reflect insignificant changes in the LSPR spectrum. The λ_max of the LSPR gradually shifts to red with the increase in chain length of both the cationic and anionic surfactants, indicating specific binding of the surfactant molecules around silver nanoparticles. Finally the affinity of the synthesised silver nanoparticles for amine molecules has been accounted for by taking the HSAB principle into consideration.