Small-angle X-ray scattering study of metal nanoparticles prepared by photoreduction in aqueous solutions of sodium dodecyl sulfate

Photoreduction formation mechanisms of metal particles (gold (Au) and platinum (Pt) particles) in aqueous solution of sodium dodecyl sulfate (SDS) have been investigated using transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) measurements. The anionic surfactant SDS was used as a stabilized reagent to disperse metal particles in aqueous solutions. The average particle diameter of Au and Pt particles was estimated from TEM as 4.5 and 2.7 nm, respectively. The SAXS analysis showed that in high concentration of SDS the size of Au and Pt particles is consistent with those obtained from TEM and EXAFS measurements, and the micelles of SDS retain a core–shell structure in aqueous solutions after the formation of metal particles. In the particle formation process, metal particles were photochemically produced in the core of micelles and they did not significantly affect the morphology of micelles, although these metal ions were almost randomly distributed in solution before the photoreduction. The particle growth rate of Au and Pt could be evaluated on the basis of the weight fraction of these metal particles, and it was found that Au particle growth occurs more rapidly than Pt particle growth in the aqueous SDS solutions.