Gold nanoparticle formation from photochemical reduction of Au3+ by continuous excitation in colloidal solutions. A proposed molecular mechanism

TitleGold nanoparticle formation from photochemical reduction of Au3+ by continuous excitation in colloidal solutions. A proposed molecular mechanism
Publication TypeJournal Article
Year of Publication2005
AuthorsEustis, S, Hsu, HY, EL-Sayed, MA
JournalJournal of Physical Chemistry B
Volume109
Pagination4811-4815
Date PublishedMar
ISBN Number1520-6106
Accession NumberWOS:000227734500003
Abstract

A photochemical reduction of Au3+ with continuous 250-400 nm excitation is studied in ethylene Zalycol, and poly (vinylpyrrolidone) (PVP) is used as a capping material. After the absorption of Au3+ disappears, excitation is stopped. The surface plasmon absorption of gold as well as the thermal reappearance of the Au3+ absorption are found to increase as a function of time. The rates of these changes are studied as a function of the mole fraction of ethylene glycol in water. Experimental results show that a small amount of ethylene glycol increases the formation of gold nanoparticles and decreases the reformation of the Au3+ absorption after irradiation. Increasing the glycol concentration first increases the rate of formation of gold nanoparticles to a maximum at a mole fraction 0.40. As the glycol concentration is further increased, the rate of formation of the gold nanoparticles and the rate of re-formation of Au3+ decrease. A mechanism is proposed that involves the reduction of the excited Au3+ to Au2+ by ethylene glycol. This is followed by the disproportionation of Au2+ to Au3+ and Au1+. Both the reduction of Au1+ by ethylene glycol and its disproportionation lead to the formation of Au-0, which upon nucleation and growth form An nanoparticles.

DOI10.1021/jp0441588