We report a facile route to the synthesis of Ag@Au–Pt trimetallic nanocubes in which the Ag, Au, and Pt atoms are exposed at the corners, side faces, and edges, respectively. Our success relies on the use of Ag@Au nanocubes, with Ag 2 O patches at the corners and Au on the side faces and edges, as seeds for the site-selective deposition of Pt on the edges only in a reaction system containing ascorbic acid (H 2 Asc) and poly(vinylpyrrolidone). At an initial pH of 3.2, H 2 Asc can dissolve the Ag 2 O patches, exposing the Ag atoms at the corners of a nanocube. Upon the injection of the H 2 PtCl 6 precursor, the Pt atoms derived from the reduction by both H 2 Asc and Ag are preferentially deposited on the edges, leading to the formation of Ag@Au–Pt trimetallic nanocubes. We demonstrate the use of 2,6-dimethylphenyl isocyanide as a molecular probe to confirm and monitor the deposition of Pt atoms on the edges of nanocubes through surface-enhanced Raman scattering (SERS). We further explore the use of these bifunctional trimetallic nanoparticles with integrated plasmonic and catalytic properties for in situ SERS monitoring the reduction of 4-nitrothiophenol by NaBH 4 . Upon the removal of Ag via H 2 O 2 etching, the Ag@Au–Pt nanocubes evolve into trimetallic nanoboxes with a wall thickness of about 2 nm and well-defined openings at the corners. The trimetallic nanoboxes embrace plasmon resonance peaks in the near-infrared region with potential in biomedical applications.
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Fabrication of Ag–Pd concave nanocrystals through facet-selective oxidation of Ag atoms
We report the fabrication of Ag–Pd concave nanocrystals by introducing the Pd( ii ) precursor into an aqueous suspension of Ag nanocubes in the presence of cetyltrimethylammonium chloride (CTAC) under ambient conditions. Different from the previously reported work that involved the oxidation of Ag and deposition of Pd at random sites on the surface for the generation of Ag–Pd hollow nanocrystals, we demonstrate that the Cl − ions from CTAC can confine the oxidation of Ag atoms to the side faces of a nanocube while the resultant Pd atoms are deposited on the edges in an orthogonal manner. By controlling the amount of the Pd( ii ) precursor involved in a synthesis, we can transform Ag nanocubes into Ag–Pd nanocrystals with different degrees of concaveness for the side faces and controllable Pd contents. We characterize the outermost layer of concave surfaces for the as-obtained Ag–Pd nanocrystals by surface-enhanced Raman scattering (SERS) through the use of an isocyanide probe. This facile approach would enable the fabrication of Ag-based concave nanocrystals for applications in plasmonics and catalysis.
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- Award ID(s):
- 1708300
- NSF-PAR ID:
- 10106051
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 11
- Issue:
- 14
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 6710 to 6718
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Facet‐selective etching and deposition, as determined by the landscape of surface energy, represent two powerful methods for the transformation of noble‐metal nanocrystals into nanostructures with complex shapes or morphologies. This review highlights the use of these two methods, including integration of them, for the fabrication of novel monometallic and bimetallic nanostructures with enhanced properties. We start with an introduction to the role of surface capping in controlling the facet‐selective etching or deposition on the surface of Ag nanocrystals, followed by a case study of how to maneuver etching and deposition at different facets of Pd nanocrystals for the fabrication of nanoframes. We then introduce the use of galvanic replacement to accomplish selective etching and deposition on two different facets in an orthogonal manner, transforming Pd nanocubes into Pd−Pt octapods. By complementing galvanic replacement with a chemical reduction reaction, it is also feasible to control the rates of these two reactions for the conversion of Ag nanocubes into Ag@Ag−Au concave nanocubes and Ag@Au core‐shell nanocubes. These transformation methods not only greatly increase the shape diversity of metal nanocrystals but also offer nanocrystals with enhanced plasmonic and/or catalytic properties.
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Abstract This article reports a facile method for the synthesis of Pd‐Ru nanocages by activating the galvanic replacement reaction between Pd nanocrystals and a Ru(III) precursor with I
‐ ions. The as‐synthesized nanocages feature a hollow interior, ultrathin wall of ≈2.5 nm in thickness, and a cubic shape. Our quantitative study suggests that the reduction rate of the Ru(III) precursor can be substantially accelerated upon the introduction of I‐ ions and then retarded as the ratio of I‐ /Ru3+is increased. The Pd‐Ru nanocages take an alloy structure, with the Ru atoms in the nanocages crystallized in a face‐centered cubic structure instead of the hexagonal close‐packed phase taken by bulk Ru. Using Pd nanocubes with different edge lengths, the dimensions of the nanocages in the range of 6−18 nm can readily be tuned. When tested as catalysts toward the electro‐oxidation of ethylene glycol and glycerol, respectively, the Pd‐Ru cubic nanocages prepared from 18 nm Pd cubes exhibit 5.1‐ and 6.2‐fold enhancements in terms of mass activity relative to the commercial Pd/C. After 1000 cycles of accelerated durability test, the mass activities of the nanocages are still 3.3 and 3.7 times as high as that of the pristine commercial Pd/C catalyst, respectively. -
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Abstract Noble‐metal nanoboxes offer an attractive form of nanomaterials for catalytic applications owing to their open structure and highly efficient use of atoms. Herein, we report the facile synthesis of Ag−Ru core−shell nanocubes and then Ru nanoboxes with a hexagonal close‐packed
(hcp ) structure, as well as evaluation of their catalytic activity toward a model hydrogenation reaction. By adding a solution of Ru(acac)3in ethylene glycol (EG) dropwise to a suspension of silver nanocubes in EG at 170 °C, Ru atoms are generated and deposited onto the entire surface of a nanocube. As the volume of the RuIIIprecursor is increased, Ru atoms are also produced through a galvanic replacement reaction, generating Ag−Ru nanocubes with a hollow interior. The released Ag+ions are then reduced by EG and deposited back onto the nanocubes. By selectively etching away the remaining Ag with aqueous HNO3, the as‐obtained Ag−Ru nanocubes are transformed into Ru nanoboxes, whose walls are characterized by anhcp structure and an ultrathin thickness of a few nanometers. Finally, we evaluated the catalytic properties of the Ru nanoboxes with two different wall thicknesses by using a model hydrogenation reaction; both samples showed excellent performance. -
We report the fabrication of Ag–Au cuboctahedral nanoboxes enclosed by {100} and {111} facets, respectively, through the orthogonal deposition of Au on two different facets of Ag cuboctahedra. Specifically, we titrate aqueous HAuCl 4 into an aqueous mixture containing Ag cuboctahedra, ascorbic acid, and NaOH (under basic conditions), in the presence of poly(vinylpyrrolidone) (PVP) and cetyltrimethylammonium chloride (CTAC), respectively. In the case of PVP, the oxidation of Ag was initiated from the {111} facets of the cuboctahedra through the galvanic replacement reaction between Au( iii ) and Ag, accompanied by the deposition of Au onto the {100} facets. Because the dissolved Ag( i ) ions could react with NaOH to form Ag 2 O on the {111} facets and thus terminate the galvanic reaction, the Au( iii ) ions would be further reduced by the ascorbate monoanion (HAsc − ) to generate Au atoms for their continuing deposition on the {100} facets, converting Ag cuboctahedra to Ag@Au {100} cuboctahedra. Upon the etching of Ag from the core, we obtained Ag–Au cuboctahedral nanoboxes enclosed by {100} facets. In contrast, when CTAC was present, the oxidation of Ag through a galvanic reaction could continuously proceed on {100} facets as the dissolved Ag( i ) ions would react with the excessive amount of Cl − ions derived from CTAC to produce soluble AgCl 2 − ions rather than insoluble Ag 2 O. As a result, the dissolved Ag( i ) and Au( iii ) ions would be co-reduced by HAsc − for the generation of Ag and Au atoms, followed by their co-deposition onto {111} facets for the generation of Ag@Au {111} concave cuboctahedra. After the removal of Ag from the core by etching, we obtained Ag–Au {111} cuboctahedral nanoboxes enclosed by {111} facets. Both samples of cuboctahedral nanoboxes exhibited strong optical absorption in the infrared region. Interestingly, the cuboctahedral nanoboxes enclosed by {111} facets showed significantly enhanced catalytic activity toward the reduction of 4-nitrophenol by NaBH 4 relative to their counterparts encased by {100} facets.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9nr01250h
