Synthesis and Characterization of Carboxylate-Modified Gold Nanoparticle Powders Dispersible in Water

Carboxylate-modified gold nanoparticles have been synthesized in a single-phase system based on the reduction of hydrogen tetrachloroaurate(III) by sodium borohydride in methanol using mercaptosuccinic acid (MSA) as the stabilizing thiol ligand. Five samples with diameters of 10.2, 10.8, 12.8, 19.4, and 33.6 Å have been prepared as water-redispersible powders through decreasing the initial MSA/HAuCl4 molar ratio from 2.5 to 0.5. These samples were characterized by X-ray diffraction, transmission electron microscopy, elemental analysis, thermogravimetric analysis, ζ-potential measurement, Fourier transform infrared spectroscopy, and UV−vis spectroscopy. The results show that a large number of the particles are fcc single crystals with the polyhedral morphology of a truncated octahedral motif and that a self-assembled monolayer of thiolates has indeed formed through the adsorption of mercapto groups on the gold particle surface; the maximum packing density of the thiolates is 15.23 Å2 per mercapto group. The surface structures of the powders are clearly defined; MSA on the particle surface exists in the form of sodium carboxylate, and one MSA unit combines with one H2O molecule.