| Abstract
| - Formation mechanisms of metal particles (gold (Au) particles) in an aqueous ethanol solution of HAuCl4 withpoly(N-vinyl-2-pyrrolidone) (PVP) by the photoreduction method were investigated by UV−vis, transmission electronmicroscopy (TEM), and in situ and ex situ X-ray absorption fine structure (XAFS) analysis. The average diametersof the dilute and concentrated Au particles in PVP solution are estimated from TEM to be 106 Å and 925 Å, respectively.XAFS analysis was carried out to elucidate the reduction process of AuCl4- ionic species to metallic Au particlesfor the Au-L3 edge of the colloidal dispersions of the concentrated Au solutions. In the photoreduction process, thereduction of AuCl2- species to Au0 atoms is a slower process than that of AuCl4- to AuCl2-, and the reduction ofAuCl2- to Au0 atoms and the association of Au0 atoms to form seed Au particles (particle diameter between 5.5 and30 Å) concurrently proceeds in the short-duration photoirradiation. In addition, in the long-duration photoirradiation,the slow progression of Au particle growth occurs with the association of Au0−Au0 metallic bonds, resulting in theformation of larger Au particles (particle diameter larger than 500 Å).
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