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This article describes a systematic study of the oxidative etching and regrowth behaviors of Pd nanocrystals, including single‐crystal cubes bounded by {100} facets, single‐crystal octahedra and tetrahedra enclosed by {111} facets; and multiple‐twinned icosahedra covered by {111} facets and twin boundaries. During etching, Pd atoms are preferentially oxidized and removed from the corners regardless of the type of nanocrystal, and the resultant Pd2+ ions are then reduced back to elemental Pd. For cubes and icosahedra, the newly formed Pd atoms are deposited on the {100} facets and twin boundaries, respectively, due to their relatively higher energies. For octahedra and tetrahedra, the Pd atoms self‐nucleate in the solution phase, followed by their growth into small particles. We can control the regrowth rate relative to etching rate by varying the concentration of HCl in the reaction solution. As the concentration of HCl is increased, 18‐nm Pd cubes are transformed into octahedra of 23, 18, and 13 nm, respectively, in edge length. Due to the absence of regrowth, however, Pd octahedra are transformed into truncated octahedra, cuboctahedra, and spheres with decreasing sizes whereas Pd tetrahedra evolve into truncated tetrahedra and spheres. In contrast, Pd icosahedra with twin boundaries on the surface are converted to asymmetric icosahedra, flower‐like icosahedra, and spheres. This work not only advances the understanding of etching and growth behaviors of metal nanocrystals with various shapes and twin structures but also offers an alternative method for controlling their shape and size. [ABSTRACT FROM AUTHOR]

Gold–palladium (AuPd) alloy nano-corolla are successfully prepared in high purity, followed by exploration as electrocatalysts for electroxidation of ethanol (EOR) in alkaline medium. Applying kinetics control on the one-pot formation process using a syringe pump is emphasized, where the Au/Pd precursor solution is dropwise titrated into the reaction mixture containing capping agent and reductant at an elevated temperature. We perform systematical investigation towards the morphology evolution pathway and effects of several key parameters. After loading on carbon black, the current AuPd alloy nano-corolla exhibit superb specific activity, reaction kinetics, and operation stability for EOR, showing morphological and structural merit. The present study provides insight into fabrication of bimetallic alloy nanocrystals with open structure, which could find important use in crystal engineering for multimetallic nanocrystals and rational design of fuel cell electrocatalyst. Gold–palladium (AuPd) alloy nanocrystals in the form of corolla are successfully prepared via kinetic-controlled synthesis in high purity, exhibit improved activity and stability as EOR electrocatalysts in KOH solution [ABSTRACT FROM AUTHOR]

Wavy gold@palladium-gold (Au@PdAu) core-shell nanoplates are successfully prepared via seeded growth. Starting with the use of plate-like Au nanocrystals with the thickness of ~10 nm as seeds, the preferential deposition of Pd atoms vertical to the upper/bottom surface plane allows the formation of the core-shell structure with tunable thickness, where the shell thickness can be limited to sub-10 nm. As confirmed by X-ray diffraction (XRD) analyses, further atomic diffusion allows the generation of PdAu alloy phase in the products, leading to the formation of Au@PdAu core-shell nanostructure. With the strong absorbance in near-infrared (NIR) region, they could work as efficient catalysts towards reduction of 4-nitrophenol under visible light irritation. In particular, the enhancement factor (the ratio of apparent rate constant in light to that in dark) reaches as high as 6.76 arising from the plasmonic-enhancement effect. The current work provides a feasible strategy to fabricate Pd-based bimetallic nanocrystals with plasmonic properties and validates their promising application in the plasmonic-enhanced catalysis. [ABSTRACT FROM AUTHOR]

We report a niche strategy to fabricate planar trimetallic nanocrystals with in‐plane branches and a unique hybrid structure. The success of current work relies on the use of seeded growth to produce Au@Ag core‐shell nanocubes, followed by the reaction with an excessive third metal precursor (i. e. Pd) via galvanic replacement reaction (GRR) in the presence of controlled reduction. The morphology of resulting products varied in the order of cube, concave cube, hollow cage, yolk‐shell frame, and finally branched nanoplates with Au‐PdAg hybrid structure. The controlled reduction involved in the GRR process, together with the use of Au seed at appropriate amounts and docosyltrimethylammonium chloride as the capping agent, is demonstrated to be crucial for the formation of such unique structure. When loaded on carbon black and working as electrocatalysts for electroxidation of ethanol in alkaline media, the current products exhibit satisfying electrocatalytic activity (e. g. 591 mA mgPd−1 in mass activity and 10.01 A m−2 in specific activity), improved kinetics, and long‐term durability, as compared to commercial Pt/C. The present study offers a feasible route to applying precise spatial control over elemental metals for two‐dimensional dendritic noble metal nanocrystals and could be potentially extended to other metals or alloy. [ABSTRACT FROM AUTHOR]

Localized surface plasmon resonance (LSPR) has drawn much interest in photocatalysis due to the advantages in extending light-absorption and improving charge-separation efficiency. In this work, Au nanocubes with exposed {100} facets and Au nanotrioctahedrons with exposed {221} facets are synthesized via the seed-growth method with the aim of demonstrating the photocatalytic performance under the LSPR effect using a typical TiO2 photocatalyst. The modification of Au nanocrystals results in accelerated charge separation in the TiO2 photocatalyst, which is attributed to the synergetic effect of local electromagnetic field enhancement from the LSPR effect and the Schottky junction established in Au and TiO2. Consequently, the photocatalytic hydrogen-production from the TiO2 photocatalyst is greatly improved. Moreover, Au nanotrioctahedrons modified TiO2 exhibits superior photocatalytic performance due to the stronger local electromagnetic field of the LSPR and the more efficient electron trapping originated from the unique morphology with exposed {221} facets. [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 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]

We offer new insights into the roles played by surface capping in controlling the pattern of growth involving Pd cubic seeds and a HAuCl4 precursor. The final products can take different surface structures (concave vs. flat side faces) depending on the presence or absence of surface capping. [ABSTRACT FROM AUTHOR]

Abstract: A series of Mn2+ doped CdS photocatalysts were prepared by a co-precipitation method and characterized by XRD, DRS, TEM, and XPS techniques. While the band gap, crystal phase and the morphology of CdS nanocrystal were not found to be affected noticeably by Mn2+ doping, there was an optimal Mn2+ doping content of wt 0.5% where the hydrogen production was more than doubled compared to pure CdS. Calculations of density functional theory (DFT) with plane waves and pseudopotentials were used to characterize the doping effect of Mn in cubic CdS. It is assumed that Mn2+ serving as shallow trapping sites can separate e−/h+ pairs at surface of nanosized CdS, so as to greatly reduce their surface recombination and which in turn leads to improved hydrogen yield. [Copyright &y& Elsevier]

We report the fabrication of "Pt-on-PdAg" heterogeneous nanocrystals in the form of trigonal/hexagonal plate (THNPs) and explored their applications in electroxidation of methanol (MOR) in alkaline medium. In particular, PdAg polyhedral nanoparticles are prepared in advance, followed by the addition of Pt salts to allow in situ galvanic replacement reaction (GRR) between them, leading to the formation of Pt nano-islands on PdAg particle surface and the transformation of the overall morphology into trigon/hexagon. The deliberately designed Pt-"PdAg alloy" interface arising from the hybrid structure greatly enriches the absorption sites, showing noticeable structural advantages in MOR electrocatalysis. Particularly, the carbon-supported Pt-on-PdAg THNPs exhibit nearly 30-fold increase in specific activity as compared to that of commercial Pt/C, as well as enhanced reaction kinetics and long-term durability. DFT calculations suggest that the reaction of CH 3 OH oxidation mediated by PtAgPd is energetically more favorable compared to the similar reaction promoted by Pt, which rationalizes the experimental observation that PtAgPd shows the improved catalytic performance. The present study offers a feasible route to construct trimetallic nanocrystals with successful interface engineering, and validates their promising use as fuel cell electrocatalyst from both experimental validation and fundamental insights. It may help enlighten the rational design of heterostructured electrocatalysts with regulated multiple active sites. • Stepwise synthesis of trigonal/hexagonal plate-like Pt-on-PdAg hybrid nanostructures is proved. • The density of Pt nano-islands and the overall elemental composition can be tuned. • Interface engineering, tensile strain and multimetallic synergy, contribute to enhanced MOR. • DFT calculations show that MOR mediated by PtAgPd is energetically more favorable. [ABSTRACT FROM AUTHOR]

Oxidativeetching plays an important role in the synthesis of metalnanocrystals. This is because the zerovalent species, including atoms,clusters, and nanocrystallites, can all be oxidized back to the ionicform and thus altering the types and distributions of products formedin both the nucleation and growth steps. In the first part of thisreview, we discuss the critical components needed for oxidative etching,as well as methods for enabling or preventing oxidative etching ina synthesis. We then present and analyze a number of interesting experimentalobservations caused by oxidative etching. In the following sections,we highlight four major applications of oxidative etching in the synthesisof metal nanocrystals, with regards to experimental controls overthe crystallinity, size, shape, morphology, and growth kinetics. [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]

The successful phosphorization of gallium indium zinc oxynitride consists of GaInZnON core and InP shell with an ideal type-II band alignment. With efficient charge separation during photocatalytic pure water splitting, the AQE can be up to 10.6% at 430 nm and 13.8% at 350 nm, respectively. • A core-shell GaInZnON@InP heterojunction photocatalyst is prepared. • The heterojunction displays an ideal type-Ⅱ band alignment. • The band alignment enables efficient charge separation. • Photocatalytic overall water splitting with an AQY of 10.6% is achieved. Overall water splitting via solar-driven photocatalysis provides an ideal way to realizing a viable and sustainable hydrogen economy, while the development of efficient photocatalysts remains a grand challenge to date. Herein, we report the successful surface phosphorization of a gallium indium zinc oxynitride (GaInZnON) photocatalyst, which comprises a GaInZnON core and a thin InP shell. The success to the synthesis relies on the rapid diffusion of In from the bulk to the crystal surface and preferential combination of In with P to form an outer layer. The enhanced charge migration was confirmed with characterization and the charge redistribution difference around the heterojunction. The core-shell composite having an ideal type-II band alignment enables efficient charge separation within the particle scale and significantly improved photocatalytic activity toward pure water splitting for simultaneous and stoichiometric H 2 and O 2 evolution. The apparent quantum efficiencies can be up to 10.6% at 430 nm and 13.8% at 350 nm, respectively. Our results suggest that such core-shell GaInZnON@InP architectures hold great potential for efficient and scalable solar hydrogen generation. [ABSTRACT FROM AUTHOR]

Review: 83 refs. [ABSTRACT FROM AUTHOR]