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We report a niche route to the fabrication of Au-based hybrid nanostructures in the form of homojunction via seeded growth mediated with etching regrowth. In particular, the trioctahedral Au nanoparticles are initially doped with limited amounts of Pt/Ag atoms on the surface, followed by oxidative etching using HAuCl4. Instead of truncation on sharp corners/edges, the resulting products maintain the trioctahedral morphology but with an extra segment anchored on one side of the particle. Due to the structural advantages in metal–metal interface engineering and elemental doping, the current Au-based nanoscale homojunctions exhibit improved specific activity, reaction kinetics, and long-term durability in electrooxidation of methanol, as compared to pure Au trioctahedral counterparts. As verified by DFT simulation, such high catalytic performance can be ascribed to the favorable adsorption of the reactive species and low energy barrier for the rate determining step of Pt/Ag doping on the Au-Au interface. The present study introduces a niche synthetic strategy to create noble metal hybrid nanostructures based on oxidative etching and validates their promising use in electrocatalysis, which could be beneficial for the rational design of advanced fuel cell catalysts with versatile interface engineering. [ABSTRACT FROM AUTHOR]

Noble metal Janus nanocrystals involving components with the same crystal structure and close lattice constants are technically difficult to produce as anisotropic growth is not favored under general deposition conditions. Herein, taking Au and Ag, we describe a feasible synthetic strategy to create Au–Ag Janus nanoparticles (JNPs) with tunable sizes, which exhibit multiple plasmonic absorptions in the UV-vis range. The success of the current synthesis lies in the surface doping of trisoctahedral (TOH) Au seeds with limited amount of Pt/Ag atoms to introduce a relatively large lattice strain during the seeded growth, which is found crucial to facilitate the anisotropic deposition of Ag. In contrast, the use of undoped Au seeds leads to the formation of Au@Ag core–shell nanoparticles. The size of resulting products could be tuned by varying the amount of the added Ag precursor or the size/quantity of Au seeds. Compared to core–shell counterparts, the current Au–Ag Janus nanoparticles exhibit more plasmonic absorption peaks. Owing to such advantages, the current Au–Ag Janus nanoparticles show enhanced catalytic properties in the reduction of 4-nitrophenol under UV-vis light irradiation. The current study provides a feasible strategy that allows the fabrication of Janus bimetallic nanocrystals with elements having a close lattice constant and validates the promising use as plasmonic catalysts, which could be potentially extended to other metals or alloys. [ABSTRACT FROM AUTHOR]

We report the preparation of gold (Au) nanosheets with a quasi‐square morphology and curved edges (Au QSNSs). The atomic packing on the edge, corner, and central part of an individual Au QSNS is carefully observed via spherical aberration corrected high‐resolution transmission electron microscopy, and the atomic‐resolution images confirm the dominant presence of {100} facets on all these regions. Such type of two‐dimensional nanostructure is of great interest, as conventional gold nanoplates/nanoprisms are mainly enclosed with {111} facets on upper/bottom faces. The use of glutathione and octadecyltrimethylammonium chloride as the shape‐directing agent and the capping agent, respectively, at appropriate amounts, together with a dropwise addition of Au precursor at controlled rate, have been validated to be crucial for the formation of such a unique two‐dimensional nanostructure. When acting as electrocatalysts for the methanol oxidation reaction in alkaline medium, the Au QSNSs/C exhibited noticeable enhancement, compared to spherical counterparts, in terms of mass activity, reaction kinetics, and long‐term durability, demonstrating their structural advantage. [ABSTRACT FROM AUTHOR]

Controlled synthesis of two-dimensional noble metal nanomaterials with an in-plane branching morphology has been of great research interest recently, but has so far achieved limited success for AuAg-based nanocrystals. Herein, we report the fabrication of gold–silver (AuAg) nanosheets with abundant in-plane cracking and sub-10 nm thickness via one-pot kinetics-controlled synthesis. In particular, the dropwise addition of Au/Ag precursor solutions into a mixture of octadecyltrimethylammonium chloride and ascorbic acid, kept in an ice–water bath, leads to the formation of nanobelts/nanowires initially, followed by their growth into branched nanosheets. These AuAg products can further convert to AuAgM (M = Pd or Pt) nanosheets via galvanic replacement reaction under ambient conditions. Interestingly, the AuAgPd nanosheets are obtained with a Au@PdAg core–shell elemental distribution with many zigzag edges. In contrast, the AuAgPt nanosheets show a homogeneous distribution of all three metals, together with a highly stippled surface. All these AuAg-based nanosheets exhibit strong absorbance in the near-infrared region and thus show superb activities as photocatalysts for UV-vis light-assisted reduction of 4-nitrophenol due to the effect of plasmon enhancement. The present study provides a feasible route to generating AuAg-based multimetallic nanocrystals with a two-dimensional structure, in-plane branching morphology, and effective control over the elemental distribution, which could be potentially extended to other noble metals and/or alloys for the rational design of plasmonic photocatalysts. [ABSTRACT FROM AUTHOR]

We report a niche synthetic strategy to manipulate the shape of gold‐silver (AuAg) nanocrystals based on kinetics control. The success of current work relies on the use of two syringe pumps to add Au and Ag precursor solutions independently at distinct injection rates, which allows the separate control over the feeding rate of Au and Ag atoms, respectively. Such strategy is validated effective in both one‐pot reduction and seeded growth involving spherical and rod‐likes Au seeds. By conducting orthogonal experiments setting two injection rates at three levels, a set of morphologies are obtained. Interestingly, AuAg alloy nanocrystals in the form of multipod, hollow protruded particles, and branched hollow nanoplate, that are rare to obtain via conventional routes, are successfully screened out, exhibiting the unique advantage of this strategy. The current work provides a feasible approach to applying kinetics control over AuAg bimetallic nanocrystals, which could be extended to other noble metals or material combinations. [ABSTRACT FROM AUTHOR]

Etching and regrowth are two typical processes involved during wet-chemical synthesis of noble-metal nanocrystals. In the present study, we demonstrate that by rationally manipulating the two processes, trimetallic nanocrystals with a unique multilayered structure can be successfully prepared in high purity, as well as with tunable sizes. In particular, by conducting co-reduction of Pd and Pt precursors in the presence of spherical Au seeds, the continuous etching of Pt(IV) ions as enabled by insufficient reducing power, together with the regrowth of Au and Pd atoms during the growth stage, allows the resultant products to exhibit a multi-layered elemental distribution, where Pd and Pt are in the inner shell while Au and Pt are dominant in the outer shell. When supported on carbon and used as electrocatalysts, these AuPdPt multilayered nanodendrites with controlled sizes in the range of 32–88 nm show an improved electrocatalytic activity and long-term durability for formic acid oxidation, as compared to commercial Pt/C. The present study offers a facile method to prepare tri-metallic nanocrystals with a controlled shape and spatial elemental distribution, which could be further extended to other noble metals or alloys. [ABSTRACT FROM AUTHOR]

We report a seeded growth of gold (Au) nanoplates with two distinct morphologies, which are similar to a lotus leaf and a donut, respectively. The success of this synthesis relies on the use of flat Au nanoplates in high purity as seeds, followed by a controlled deposition. In particular, the presence of Ag+ led to the deposition of Au atoms preferentially occurred at the central part of one face of the nanoplate and thus the formation of lotus leaf‐like shape. In contrast, when Ag+ was absent, the growth mainly occurred to the edge region. Then, cold‐welding of newly‐formed branches and further diffusion of Au atoms created holes in the nanoplate, resulting in the formation of donut‐like shape. The Au nano‐lotus leaves with tunable sizes exhibited absorbance in near‐infrared region and enhanced chemical activities in electrochemical measurements. The current strategy is extended to fabricate Au−Ag nanoplates with a similar lotus leaf‐like morphology, which also exhibited strong absorbance in near‐infrared region in UV‐vis extinction spectra. The current work allows the fabrication of two‐dimensional Au‐based nanomaterials with concave shape and three‐dimensional architecture and could be potentially extended to other noble metals and alloys. [ABSTRACT FROM AUTHOR]

We report a facile synthesis of Au@PdAg alloy core‐shell nanocrystals in dendrite form, having tunable size and composition. In particular, using spherical Au nanoparticles as seeds, the co‐reduction of Pd and Ag precursor in growth stage results in the formation of PdAg alloy shells with a dendrite shape. Their size and elemental composition can be tuned by varying the seed amount and feeding ratio in Pd and Ag precursor, respectively, illustrating the versatility of the current synthetic strategy. The size, morphology, and elemental composition of the products have been characterized using a set of techniques, including SEM, TEM, XRD, XPS, HAADF‐STEM, and EDX‐STEM mapping. When working as electrocatalysts, the current Au@PdAg alloy core‐shell nanocrystals supported by carbon black exhibit enhanced activity and excellent operation stability for electroxidation of ethanol as compared to commercial Pd/C. The current work offers a feasible strategy to preparation of multi‐metallic core‐shell dendritic nanocrystals with controllable size and composition and could find important use in fuel cells and related fields. [ABSTRACT FROM AUTHOR]

• A facile method for fabrication of AuAg alloy nanoplates with controlled elemental compositions was developed. • They were characterized with a unique morphology of wavy nanoplate, together with sub-15 nm in thickness. • Tunable LSPR properties and satisfying photothermal performance were demonstrated. Gold-silver alloy wavy nanoplates with tunable elemental compositions are successfully prepared, exhibiting strong NIR absorbance and excellent photothermal properties. [Display omitted] We report a facile synthesis of AuAg alloy nanoplates in high purity, together with tunable elemental compositions and uniformity in size and morphology. The success of current work relies on the one-pot co-reduction of Au and Ag precursor in an ice-water bath with the presence of octadecyltrimethylammonium chloride (OTAC) as a capping agent. With the increase in Ag content, the localized surface plasmon resonance (LSPR) of AuAg alloy nanoplates exhibited a noticeable blue-shift from near-infrared (NIR) to visible region. Thanks to the well-defined NIR LSPR properties and broad spectral range, the current products exhibit a remarkably integrated high-quality photothermal feature as well as the efficient photothermal conversion. Meanwhile, the current AuAg alloy nanoplates demonstrate satisfying photothermal stability verified via continuous exposure and cyclic irradiation by an 808-nm laser. The present study offers a facile route to the preparation of two-dimensional AuAg alloy nanocrystals with tunable elemental compositions and validates their excellent responses towards photothermal measurements, which could find promising use in photothermy-based diagnosis and therapy. [ABSTRACT FROM AUTHOR]