In Situ Quick X-ray Absorption Fine Structure and Small-Angle X-ray Scattering Study of Metal Nanoparticle Growth in Water-in-Oil Microemulsions during Photoreduction

Abstract

Formation of metal nanoparticles (silver (Ag) and palladium (Pd) nanoparticles) in water/alkane/sodium bis(2-ethylhexyl) sulfosuccinate (AOT) water-in-oil (w/o) microemulsions consisting of AOT, water, and organic solvent (n-heptane, n-octane, n-decane, and isooctane) by photoreduction was monitored by means of a combination of in situ quick X-ray absorption fine structure (QXAFS) and small-angle X-ray scattering (SAXS) measurements. The stages of reduction–nucleation and the association process (aggregative particle growth and Ostwald ripening) of metal atoms to produce metal nanoparticles were discriminated in the course of the photoreduction time. In situ QXAFS results indicated that the aggregative growth follows a sigmoidal profile described both by the solid-state kinetic model, specifically the Avrami–Erofe’ev model, and by the chemical-mechanism-based kinetic Finke–Watzky model. The SAXS results clearly showed that the formation of Ag and Pd nanoparticles preferentially follows a reduction–nucleat...