Synthesis of Au Nanoparticles with Benzoic Acid as Reductant and Surface Stabilizer Promoted Solely by UV Light.

Photoreductive synthesis of colloidal gold nanoparticles (AuNPs) from Au is one important process for nanoprocessing. Several methods have been proposed; however, there is no report of a method capable of producing AuNPs with inexpensive reagents acting as both reductant and surface stabilizer, promoted solely under photoirradiation. We found that UV irradiation of water with Au and benzoic acid successfully produces monodispersed AuNPs, where thermal reduction does not occur in the dark condition even at elevated temperatures. Photoexcitation of a benzoate-Au complex reduces Au while oxidizing benzoic acid. The benzoic acid molecules are adsorbed on the AuNPs and act as surface stabilizers. Change in light intensity and benzoic acid amount successfully creates AuNPs with controllable sizes. The obtained AuNPs can easily be redispersed in an organic solvent or loaded onto a solid support by simple treatments.