title: In situ XAFS studies of Au particle formation by photoreduction in polymer solutions.
abstract: Formation mechanisms of metal particles (gold (Au) particles) in an aqueous ethanol solution of HAuCl4 with poly(N-vinyl-2-pyrrolidone) (PVP) by the photoreduction method were investigated by UV-vis, transmission electron microscopy (TEM), and in situ and ex situ X-ray absorption fine structure (XAFS) analysis. The average diameters of the dilute and concentrated Au particles in PVP solution are estimated from TEM to be 106 A and 925 A, respectively. XAFS analysis was carried out to elucidate the reduction process of AuCl4- ionic species to metallic Au particles for the Au-L3 edge of the colloidal dispersions of the concentrated Au solutions. In the photoreduction process, the reduction of AuCl2- species to Au0 atoms is a slower process than that of AuCl4- to AuCl2-, and the reduction of AuCl2- to Au0 atoms and the association of Au0 atoms to form seed Au particles (particle diameter between 5.5 and 30 A) 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 the formation of larger Au particles (particle diameter larger than 500 A).
authors.affiliation: Department of Health Science and Clothing Environment, Faculty of Human Life and Environment, Nara Women's University, Nara 630-8506, Japan. harada@cc.nara-wu.ac.jp
authors.forename: Masafumi
authors.initials: M
authors.lastname: Harada
authors.forename: Hisahiro
authors.initials: H
authors.lastname: Einaga
mesh_terms: D017979:Gold Colloid / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D010316:Particle Size; D010777:Photochemistry; D011145:Polyvinyls / Q000737:chemistry*; D011759:Pyrrolidines / Q000737:chemistry*
chemical_list: D017979:Gold Colloid; D011145:Polyvinyls; D011759:Pyrrolidines; C505150:poly(N-vinylpyrrolidine)