Journal
ACS NANO
Volume 10, Issue 2, Pages 2607-2616Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.5b07665
Keywords
seed-mediated growth; surface capping concave nanocrystal; surface-enhanced Raman spectroscopy; Au-catalyzed reduction and oxidation
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Funding
- National Science Foundation [CHE-1412006]
- Georgia Institute of Technology
- 3M nontenured faculty award
- China Scholarship Council
- Center for Functional Nanomaterials a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory [DE-SC0012704]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [1412006] Funding Source: National Science Foundation
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We report a facile synthesis of Ag@Au concave cuboctahedra by titrating aqueous HAuCl4 into a suspension of Ag cuboctahedra in the presence of ascorbic add (AA), NaOH, and poly(vinylpyrrolidone) (PIT) at room temperature. Initially, the Au atoms derived from the reduction of Au3+ by AA are conformally deposited on the entire surface of a Ag cuboctahedron. Upon the formation of a complete Au shell, however, the subsequently formed Au atoms are preferentially deposited onto the Au{100} facets, resulting in the formation of a Ag@Au cuboctahedron with concave structures at the sites of {111} facets. The concave cuboctahedra embrace excellent SERS activity that is more than 70-fold stronger than that of the original Ag cuboctahedra at an excitation wavelength of 785 nm. The concave cuboctahedra also exhibit remarkable stability in the presence of an oxidant such as H2O2 because of the protection by a complete Au shell. These two unique attributes enable in situ SERS monitoring of the reduction of 4-nitrothiophenol (4-NTP) to 4-aminothiophenol (4-ATP) by NaBH4 through a 4,4'-dimercaptoazobenzene (trans-DMAB) intermediate and the subsequent oxidation of 4 -ATP back to trans-DMAB upon the introduction of H2O2.
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