Acta Phys. -Chim. Sin. ›› 2018, Vol. 34 ›› Issue (7): 786-791.doi: 10.3866/PKU.WHXB201709292

Special Issue: Toward_Atomically_Precise_Nanoclusters_and_Nanoparticles

• ARTICLE • Previous Articles     Next Articles

Controlled Synthesis of Au36(SR)24 (SR = SPh, SC6H4CH3, SCH(CH3)Ph, and SC10H7) Nanoclusters

Yang ZHOU1,2,Zhimin LI1,2,Kai ZHENG1,2,Gao LI1,*()   

  1. 1 State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning Province, P. R. China
    2 University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2017-09-13 Published:2018-03-26
  • Contact: Gao LI E-mail:gaoli@dicp.ac.cn
  • Supported by:
    the Natural Science Foundation of Liaoning Province, China(20170540897)

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Abstract:

In the past decade, gold nanoclusters of atomic precision have been demonstrated as novel and promising materials for potential applications in catalysis and biotechnology because of their optical properties and photovoltaics. The Au36(SR)24 nanocluster is one of the most well-known clusters, which is directly converted from the Au38(SR)24 cluster through a "ligand-exchange" process. It consists of an Au28 kernel with a truncated face-centered cubic (FCC) framework exposing the (111) and (100) facets. Here we report a simple protocol to prepare Au36(SR)24 nanoclusters, ligated by aliphatic and aromatic thiolate ligands (SR = SPh, SC6H4CH3, SCH(CH3)Ph, and SC10H7) via a "size-focusing" process. First, polydisperse Au nanoparticles were synthesized and isolated, and then reacted under harsh conditions in the presence of excess thiol ligands at relatively high etching temperatures (80 ℃). The as-synthesized Au36(SR)24 nanoclusters were characterized and analyzed by UV-Vis absorption spectroscopy, electrospray ionization (ESI), and matrix-assisted laser desorption ionization (MALDI) mass spectrometry, as well as thermogravimetric analysis (TGA). All the Au36(SR)24 nanoclusters showed two step-like optical absorption peaks at ~370 and 580 nm in the UV-vis spectra. Only one strong set of nanocluster-ion peaks centered at an m/z of 10517.0 was observed in the ESI mass spectrum of the Au36(SCH(CH3)Ph)24 nanocluster. This could be assigned to the [Au36(SCH(CH3)Ph)24Cs]+ species, and was a strong indicator of the high purity of the as-obtained Au36 cluster samples produced on a small scale. The TGA profile showed 31.67% organic weight loss of the nanocluster, matching well with the expected theoretical value of 31.71%. The Au-SR bond in the gold nanoclusters was broken at ~180 ℃ in a normal air atmosphere. Fragments of the Au36(SR)24 clusters capped with different thiolate ligands, which were mainly caused by the strong laser intensity during the analysis, were detected in the MALDI mass spectra. This interesting phenomenon was also observed in the case of Au25(SR)18, and could be due to the inherent properties of the Au-SR bond on the surface of the gold nanoclusters. Finally, the optical properties of the Au36(SR)24 nanoclusters were found to be influenced by the capping thiolate ligands. Compared to the UV-Vis spectrum of the Au36(SCH(CH3)Ph)24 cluster, the optical spectra of the other three Au36 clusters were red-shifted (~3 nm for Au36(SPh)24, 5 nm for Au36(SC6H4CH3)24, and 13 nm for the (Au36(SNap)24 clusters). This shift could be explained by the electron transfer occurring from the electron-rich aromatic ligands to the Au kernel. The electron transfer capacity followed the order ―SNap > ―SC6H4CH3 > ―SPh > ―SCH(CH3)Ph. Overall, this study demonstrates the effectiveness and promising application of ligand engineering for tailoring the electronic properties of Au nanoclusters.

Key words: Gold cluster, Au36(SR)24, Control synthesis, Size-focusing, Ligand effect