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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]

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]

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 the fabrication of gold@palladium–gold (Au@PdAu) nanocrystals with a highly branched shape via seeded growth. The success of the current work relies on the use of a syringe pump for dropwise addition of a bimetallic precursor to apply control over the reaction kinetics and an elevated reaction temperature to promote island growth mode as enabled by the coupling between surface diffusion and lattice mismatch. In particular, the one-shot injection of the bimetallic precursor at 60 °C and room temperature, respectively, resulted in the production of Au@PdAu nanocrystals with the shape of a concave cube and segmented branches, respectively, while dropwise addition of the bimetallic precursor at 60 °C led to the formation of a dendritic Pd–Au shell over the spherical Au seeds. When working as electrocatalysts, as compared to solid counterparts, the Au@PdAu core–shell nanodendrites exhibit an improved operation stability for electrooxidation of ethanol in alkaline media, demonstrating the advantage in morphology and structure. [ABSTRACT FROM AUTHOR]

We report the facile synthesis of gold–silver (Au–Ag) nanostructures in a niche hybrid form of ultrathin wire–dots, where the ultrathin nanowires are embedded with quasi-spherical dots along the longitudinal direction. The key to the success of this work relies on the use of seeded growth and the introduction of excessive Ag ions in the growth stage to facilitate the formation of such a unique architecture. Several reaction parameters, including the amount of silver and reductant, seed quantity and size/morphology, are systematically investigated to reveal their role in determining the morphology of the final products. We also recorded their UV-vis extinction spectra and compared them with pure ultrathin wires to investigate the effect of dot regions on the optical properties. [ABSTRACT FROM AUTHOR]

We report a facile synthesis of silver (Ag) nanoplates with rough edges via seeded growth. The key to this success is relies on the manipulation of the competitive relationship between surface diffusion and kinetics-controlled growth. In particular, Ag atoms initially deposit on the corners and edges of seed plates and then diffuse towards the low-curvature region in a controlled way to form edges with rough features. The as-prepared Ag plate-shaped products were also tested for surface enhanced Raman spectroscopy (SERS), which exhibited the dependence of SERS enhancement on edge roughness. The current work offers an effective synthetic route to control the shape of Ag nanoplates and could find important use in shape-controlled synthesis of other noble metals. [ABSTRACT FROM AUTHOR]

Rechargeable lithium-ion batteries (LIBs) for potentially low-cost and high-energy-density storage have been intensively researched to meet ever-growing demands. Achieving higher storages and understanding the transporting and storing diffusion process of Li ions are still great challenges. Herein, a porous crystalline polyoxometalate-based metal–organic framework (POM@MOF), H2[Cu II4 (Htrz)5(H2O)2][Mo VI4 Cu II4 O26]0.5·3H2O, with defect sites as a LIB electrode material is reported. The Li-ion diffusion process in the material was investigated using ex situ X-ray photoelectron spectroscopy (XPS) and off-line powder X-ray diffraction (PXRD), indicating that O atoms of POM nano-clusters can be regarded as Li-ion acceptors (storage sites); meanwhile the defect sites (uncoordinated N atoms or –N–H groups) in the crystalline material also participate in the Li-ion storage. The reported porous crystalline POM@MOF material with defects delivers a remarkable Li-ion storage capacity of ca. 700 mA h g−1 in 200 cycles at a current density of 100 mA g−1. [ABSTRACT FROM AUTHOR]

A new fluconazole-functionalized polyoxometalate-based metal–organic framework (POMOF) [Ag3(FKZ)2(H2O)2][H3SiW12O40] (AgFKZSiW12) was successfully constructed, and its polypyrrole (PPy) coated composite AgFKZSiW12@PPy was also obtained via a facile ‘in situ’ oxidation polymerization process. The peroxidase-like activity evaluation indicates that the maximized synergistic effect from the integration of PPy, SiW12 clusters, HFKZ drug molecules, and Ag ions deeply enhanced the overall performance. More importantly, AgFKZSiW12@PPy exhibits the fastest response time (30 s) among all the reported peroxidase mimics to date, including the pristine AgFKZSiW12 (2 min). Moreover, the AgFKZSiW12@PPy-based colorimetric biosensing platform towards H2O2 and ascorbic acid (AA) exhibits limits of detection (LOD) as low as 0.12 μM and 2.7 μM, respectively. This work reveals a promising prospect in medical diagnosis and biotechnology for colorimetric biosensor fabrication with high performance through the introduction of PPy. [ABSTRACT FROM AUTHOR]

Rechargeable lithium-ion batteries (LIBs) for potentially low-cost and high-energy-density storage have been intensively researched to meet ever-growing demands. Achieving higher storages and understanding the transporting and storing diffusion process of Li ions are still great challenges. Herein, a porous crystalline polyoxometalate-based metal-organic framework (POM@MOF), H 2 [Cu(Htrz) 5 (H 2 O) 2 ][MoCuO 26 ] 0.5 ·3H 2 O, with defect sites as a LIB electrode material is reported. The Li-ion diffusion process in the material was investigated using ex situ X-ray photoelectron spectroscopy (XPS) and off-line powder X-ray diffraction (PXRD), indicating that O atoms of POM nano-clusters can be regarded as Li-ion acceptors (storage sites); meanwhile the defect sites (uncoordinated N atoms or -N-H groups) in the crystalline material also participate in the Li-ion storage. The reported porous crystalline POM@MOF material with defects delivers a remarkable Li-ion storage capacity of ca. 700 mA h g -1 in 200 cycles at a current density of 100 mA g -1 .

A new fluconazole-functionalized polyoxometalate-based metal-organic framework (POMOF) [Ag 3 (FKZ) 2 (H 2 O) 2 ][H 3 SiW 12 O 40 ] (AgFKZSiW 12 ) was successfully constructed, and its polypyrrole (PPy) coated composite AgFKZSiW 12 @PPy was also obtained via a facile 'in situ' oxidation polymerization process. The peroxidase-like activity evaluation indicates that the maximized synergistic effect from the integration of PPy, SiW 12 clusters, HFKZ drug molecules, and Ag ions deeply enhanced the overall performance. More importantly, AgFKZSiW 12 @PPy exhibits the fastest response time (30 s) among all the reported peroxidase mimics to date, including the pristine AgFKZSiW 12 (2 min). Moreover, the AgFKZSiW 12 @PPy-based colorimetric biosensing platform towards H 2 O 2 and ascorbic acid (AA) exhibits limits of detection (LOD) as low as 0.12 μM and 2.7 μM, respectively. This work reveals a promising prospect in medical diagnosis and biotechnology for colorimetric biosensor fabrication with high performance through the introduction of PPy.