Characterization of metal nanoparticles prepared by photoreduction in aqueous solutions of various surfactants using UV–vis, EXAFS and SAXS

Photoreduction formation mechanisms of metal particles (gold (Au) and platinum (Pt) particles) in aqueous surfactant solutions of dodecyltrimethylammonium chloride (DTAC) and polyethylene glycol lauryl ether (PEG) have been studied by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) measurements. EXAFS results confirmed the metallic nature of the nanoparticles, and showed that the average particle size significantly depends neither on the metal species nor on the charged properties (cationic, anionic, or nonionic) of surfactants. The SAXS analysis indicated that the structure of DTAC and PEG micelles could be fitted with the hard-sphere model having the interaction radius RHS and the spherically shaped core–shell structure. At the beginning of the photoirradiation, the increase of the SAXS intensity at q < 1.0 nm−1 was not due to the change of the size and shape of the produced metal particles, but due to the increase in number of produced metal particles in the growth process. Once the radius of metal particles produced during the photoirradiation exceeded a radius (Rshell) of the individual micelles, the metal particle growth was noticeably accelerated and the larger aggregates were formed, which were not stabilized by adsorbed surfactant molecules on their metal surface.