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Abstract Shape control has been a major theme of nanocrystal research in terms of synthesis, property tailoring, and optimization of performance in a variety of applications. Among the possible shapes, bipyramids are unique owing to their symmetry, planar defects, and exposed facets. In this article, we focus on the colloidal synthesis of noble‐metal nanocrystals featuring a triangular bipyramidal shape, together with highlights of their properties and applications. We start with a brief discussion of the general classification and requirements for the nucleation and growth of bipyramidal nanocrystals, followed by specific aspects regarding the synthetic methods with a focus on the roles of reduction, etching, and capping, as well as controls of facet, size, aspect ratio, and corner truncation. In the end, we illustrate how these aspects affect the properties of bipyramidal nanocrystals for plasmonic and catalytic applications, together with future perspectives. 

Abstract It remains a challenge to accomplish colloidal synthesis of noble‐metal nanocrystals marked by high quality, large quantity, and batch‐to‐batch consistency. Here we report a self‐airtight setup for achieving robust, reproducible, and scalable production of Ag nanocubes with uniform and controlled sizes from 18 to 60 nm. Different from the conventional open‐to‐air setup, the self‐airtight system makes it practical to stabilize the reaction condition by minimizing the loss of volatile reagents. The new setup also allows us to easily optimize the amount of O₂(from air) trapped in the system, ensuring burst nucleation of single‐crystal seeds, followed by their slow growth into nanocubes. Most significantly, the new setup allows for the production of Ag nanocubes at gram quantities without sacrificing uniformity, corner/edge sharpness, controlled size, and high purity across different batches. The availability of high‐quality Ag nanocubes in such a large quantity is anticipated to substantially boost their use in applications related to plasmonics, catalysis, and biomedicine. 

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. 

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.