We report the synthesis of bifunctional Ag@SiO2/Au nanoparticles with an “islands in the sea” configuration by titrating HAuCl4solution into an aqueous suspension of Ag@SiO2core–shell nanocubes in the presence of NaOH, ascorbic acid, and poly(vinyl pyrrolidone) at pH 11.9. The NaOH plays an essential role in generating small pores in the SiO2shell
We report a facile synthesis of Ag‐enriched Ag‐Pd bimetallic nanoframes with ridges as thin as 1.7 nm. The synthesis involves co‐titration of aqueous AgNO3and Na2PdCl4solutions into an aqueous suspension of Ag nanocubes at room temperature in the presence of ascorbic acid and poly(vinyl pyrrolidone). The Ag and Pd atoms derived from the co‐reduction by ascorbic acid are co‐deposited on the edge and corner sites of Ag nanocubes for the generation of Ag@Ag‐Pd core–frame nanocubes. When subjected to H2O2etching, the Ag cores are selectively removed to generate Ag‐Pd bimetallic nanoframes made of ultrathin ridges enriched in Ag. In comparison to both the Ag nanocubes and Ag@Ag‐Pd core‐frame nanocubes, the Ag‐Pd bimetallic nanoframes exhibit markedly enhanced activity in catalyzing the reduction of 4‐nitrophenol by NaBH4.
more » « less- NSF-PAR ID:
- 10234109
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemNanoMat
- Volume:
- 2
- Issue:
- 6
- ISSN:
- 2199-692X
- Format(s):
- Medium: X Size: p. 494-499
- Size(s):
- ["p. 494-499"]
- Sponsoring Org:
- National Science Foundation
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Abstract in situ , followed by the epitaxial deposition of Au from the Ag surface through the pores, leading to the formation of Au islands (6–12 nm in size) immersed in a SiO2sea. By controlling the amount of HAuCl4titrated into the reaction system, the Au islands can be made to pass through and protrude from the SiO2shell, embracing catalytic activity toward the reduction of 4‐nitrophenol to 4‐aminophenol by NaBH4. While the Ag in the core provides a strong surface‐enhanced Raman scattering activity, the SiO2sea helps maintain the Au component as compact, isolated, and stabilized islands. The Ag@SiO2/Au nanoparticles can serve as a bifunctional probe to monitor the stepwise Au‐catalyzed reduction of 4‐nitrothiophenol to 4‐aminothiophenol by NaBH4and Ag‐catalyzed oxidation of 4‐aminothiophenol totrans ‐4,4′‐dimercaptoazobenzene by the O2from air in the same reaction system. -
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.more » « less
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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
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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
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