The effect of initiation method on the size, monodispersity and shape of gold nanoparticles formed by the Turkevich method

The growth of gold nanoparticle (Au NP) colloids was initiated either thermally, by sonolysis, microwave (MWA) or hard ultra-violet (UVC; 254 nm) irradiation. The solutions were formulated analogous to Turkevich et al. and contained an auric acid gold source and different amounts of sodium tri-citrate reductant and stabiliser. A comparison of the initiation methods, using reagent solutions of equal concentration, was used to make gold nanoparticles. This showed marked differences in the final colloid, with variance in the monodispersity, size and shape of particles with initiation method. The physical size, shape and monodispersity of colloids formed were ascertained from transition electron microscopy (TEM) imaging. Properties such as average particle size and shape were directly related to changes in the surface plasmon resonance (SPR) band from UV-visible spectra. We demonstrate how a variety of simple initiation methods can be used to synthesise near monodisperse gold nanoparticles. More importantly, it is shown how the initiation method is fundamental to the eventual particle size of the resulting colloids; with sizes ranging from 11.0-11.9 nm in thermal reactions, 16.9-18.0 nm in sonolysis reactions, 11.3-17.2 nm in MWA reactions and 8.0-11.2 nm in UVC initiated reactions. Possible reaction pathways and mechanisms are put forward to explain these marked differences.