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Surface-enhanced Raman scattering was used to resolve the chemical species, including chloride ions, on the surface of Ag nanocrystals in their original reaction solution, avoiding changes to the surface while eliminating possible artifacts. 

We present an overview of the opportunities provided by bimetallic core–shell nanocrystals, followed by a discussion of the challenges and promising solutions regarding the elucidation of the true surface composition and its dynamics. 

Silver is an excellent catalyst for oxidation reactions such as ethylene epoxidation, but it shows limited activity toward reduction reactions. Here we report a strategy to revitalize Ag nanocrystals as a redox catalyst for the production of an aromatic azo compound by modifying their surface with an isocyanide-based compound. We also leverage in situ fingerprint spectroscopy to acquire molecular insights into the reaction mechanism by probing the vibrational modes of all chemical species at the catalytic surface with surface-enhanced Raman spectroscopy. We establish that binding of isocyanide to Ag nanocrystals makes it possible for Ag to extract the oxygen atoms from the nitro-groups of nitroaromatics and then use these atoms to oxidize isocyanide to isocyanate. Concurrently, the coupling between two adjacent deoxygenated nitroaromatic molecules leads to the formation of an aromatic azo compound. 

Silver nanocubes have found use in an array of applications but their performance has been plagued by the shape instability arising from the oxidation and dissolution of Ag atoms from the edges and corners. Here we demonstrate that the shape of Ag nanocubes can be well preserved by covering their edges and corners with a corrosion-resistant metal such as Ir. In a typical process, we titrate a Na 3 IrCl 6 solution in ethylene glycol (EG) into a suspension of Ag nanocubes in an EG solution in the presence of poly(vinylpyrrolidone) (PVP) held at 110 °C. The Ir atoms derived from the reduction of Na 3 IrCl 6 by EG and Ag are deposited onto the edges and then corners for the generation of Ag–Ir core-frame nanocubes. Remarkably, our results indicate that a small amount of Ir atoms on the edges and corners is adequate to prevent the Ag nanocubes from transforming into nanospheres when heated in a PVP/EG solution up to 110 °C. We further demonstrate that these Ag–Ir nanocubes embrace plasmonic properties comparable to those of the original Ag nanocubes, making them immediately useful in a variety of applications. This strategy for stabilizing the shape of Ag nanocubes should be extendible to Ag nanocrystals with other shapes or nanocrystals comprised of other metals. 

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. 

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 Ru^IIIprecursor 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 anhcpstructure 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.