One-phase controlled synthesis of Au25 nanospheres and nanorods from 1.3 nm Au : PPh3 nanoparticles: the ligand effects

We report the controlled synthesis of [Au-25(PPh3)(10)(SR1)(5)X-2](2+) nanorods (H-SR1: alkyl thiol, H-SC2H4Ph and H-S(n-C6H13)) and Au-25(SR2)(18) nanospheres (H-SR2: aromatic thiol, H-SPh and H-SNap) under the one-phase thiol etching reaction of the polydisperse Au-n(PPh3)(m) parent-particles (core diameter: 1.3 +/- 0.4 nm, 20 < n < 50). These as-obtained gold nanoclusters are identified by UV-vis spectroscopy and matrix-assisted laser desorption ionization mass spectrometry. Furthermore, the conversion process, from Au-n(PPh3)(m) nanoparticles to Au-25(SNap)(18) nanospheres, is monitored by UV-vis spectroscopy. It is observed that the Au-25(PPh3)(10)(SR1)(5)X-2 nanorods cannot convert to Au-25(SR)(18) nanospheres in the presence of excess thiol (both the alkyl and aromatic thiol) even under thermal conditions (e.g., 55 and 80 degrees C), indicating that both the Au-25 nanorods and nanospheres are in a stable state during the alkyl and aromatic thiol etching reactions, respectively. The two different conversion pathways (i.e., to Au-25(PPh3)(10)(SR1)(5)X-2 nanorods and Au-25(SR2)(18) nanospheres) mainly are attributed to the different electronic properties and the steric effects of the alkyl and aromatic thiol ligands. The significant ligand effect also is observed in catalytic CO oxidation. The Au-25(SC2H4Ph)(18)/CeO2 catalyst shows catalytic activity at 80 degrees C and reaches up to 80.7% and 98.5% (based on CO conversion) at 100 and 150 degrees C, while Au-25(SNap)(18)/CeO2 and Au-25(PPh3)(10)(SC2H4Ph)(5)X-2/CeO2 give rise to a low activity at 100 degrees C with only 3.3% and 10.2% CO conversion and 98.0% and 94.6% at 150 degrees C.