Oxidation of gold nanoparticles by Au(III) complexes in toluene

Abstract

The rapid, stoichiometric oxidation of gold nanoparticles by tetraalkylammonium and tetraalkylphosphonium Au(III) complexes in toluene is reported here. Nanoparticle oxidation proceeds via a comproportionation mechanism and generates stable Au(I) complexes of the ammonium and phosphonium cations used. These reactions are studied for several organo-soluble nanoparticle systems, employing different cations and halides in the Au(III) oxidant complex, and a mechanism for the comproportionation reaction is proposed. It is demonstrated that Au nanorods stabilized in toluene can be progressively "sculpted" by Au(III) complexes. Measurement artifacts caused by the reduction of Au(I) and Au(III) species during conventional TEM imaging are also demonstrated and discussed. The results presented here provide insight into a host of issues in the chemistry of Au nanoparticles: nanoparticle oxidation, reduction of Au(III) species to Au(0) nanoparticles, galvanic replacement reactions using Au(III), and sample changes induced by TEM imaging. The oxidation of Au nanoparticles by Au(III) complexes in nonpolar solvents is expected to be a valuable new tool for nanoparticle sculpting, dissolution of nanogold templates, Au content determination, ligand removal from nanoparticles, nanoparticle purification, and Au recovery processes. © 2012 American Chemical Society.