Size and purity of gold nanoparticles changes with different types of thiolate ligands

Gold nanoparticles (Au-NPs) were prepared by a surfactant-free single-phase reduction of hydrogen tetrachloroaurate(III) hydrate in the presence of different organic thiol ligands. Sizes, size distributions, and crystallinity of the Au-NPs were determined by high-resolution transmission electron microscopy and powder X-ray diffraction, whereas thermogravimetric analysis provided information on the organic ligand-to-gold ratios as well as amounts of contaminants. A systematic decrease in size with increasing conical bulk of the thiolate ligand is observed but large size distributions and contamination of the generated Au-NPs prohibit detailed mechanistic studies. A first-generation Fréchet dendron thiol produced the smallest and cleanest Au-NPs of the narrowest size distribution.