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We report a silver‐free synthesis of gold (Au) concave nanocubes (CNCs) that involves the direct deposition of Au atoms over spherical Au seeds under well‐controlled reaction kinetics and surface capping. The elementally‐pure composition makes them ideal research candidate towards validating structural advantage of concave surface in electrocatalytic oxidation of ethanol. In particular, the as‐obtained Au CNCs exhibited an enhanced specific activity and reaction kinetics, but weakened long‐term stability, as compared to quasi‐spherical counterparts. Theoretical simulations suggest that the high‐index planes represent a high catalytic performance for ethanol oxidation. The current work offers an effective synthetic strategy that successfully excludes the necessary and wide use of Ag+ ions in controlled synthesis of pure Au nanocrystals with a concave cubic shape, shedding light on the rational design of fuel cell electrocatalyst from the perspective of crystal facet effect. [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]

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]

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]

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 an ultrafast synthesis of wavy gold‐silver (AuAg) nanowires with tunable diameters via a seed‐mediated co‐reduction. The success of current strategy relies on the use of an elevated reaction temperature to accelerate the synthesis to be completed within several minutes and the use of Au seeds with controlled sizes to enable the manipulation over their diameters in the range of 2–10 nm. The presence of chloride‐contained quaternary ammonium surfactant and excessive reductant have been demonstrated to be critical for the high‐yield formation of AuAg products with the unique morphology of wavy nanowire. Due to the advantage in size control, the size effect on the plasmonic behavior of AuAg alloy wavy nanowires is investigated, where the products with sub‐5 nm diameter exhibit a broad shoulder absorbance peak in their spectrum. [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 report the seeded growth of gold@silver (Au@Ag) core‐shell nanocrystals with the shape of truncated right bipyramids (TRB) and their hollow derivatives obtained via a galvanic replacement reaction. In particular, by depositing Ag on single‐crystal Au seeds under kinetic control, the resultant Au@Ag core‐shell products exhibit planar defects. Morphology and structure characterization is performed to confirm the crystallinity variation and the resultant TRB shape. Considering that elemental Au and Ag have similar lattice constants and negligible lattice mismatch, this phenomenon is quite unique, as the crystallinity of product is typically governed by the seed. The size of final product can be controlled in the range of 37–85 nm by varying the volume of the Au seed solution. In addition, by reacting with gold precursor, the as‐prepared Au@Ag TRBs can be converted into Au‐based nanostructures with hollow interiors, showing absorbance properties continuously tuned in the visible range, which could find important use in photocatalysis, sensing, and fluorescence enhancement, among others. [ABSTRACT FROM AUTHOR]

A synthetic case is reported that demonstrates the cationic additive, Ag+, can influence the crystallinity and thus shape of final product during seeded growth of Au nanocrystals. Using single‐crystal Au seeds as reference, the crystallinity difference between seed and final product could be directly compared. In particular, three different types of crystallinity/morphology can be obtained by varying the concentration of Ag+ in the particle growth solutions: single‐crystal quasi‐spheres, multiply twinned particles (MTPs), and protruded MTPs, with no Ag+ added and solution Ag+ /Au3+ ratios of 1 : 20 and 1 : 5, respectively. The reaction kinetics are investigated using extinction spectroscopy, indicating the presence of Ag+ leads to a dampened growth of Au nanocrystals. This principle is validated using single‐crystal Au seeds with different morphology and amounts. We also test the anti‐corrosion performance of as‐prepared Au nanocrystals with different crystallinity by treating them with sodium thiosulfate. Interestingly, in addition to reduction in size, the morphology of single‐crystal ones varies from quasi‐sphere to cube, indicating the anisotropy in oxidative etching of Au nanocrystals. [ABSTRACT FROM AUTHOR]

A synthetic case is reported that demonstrates the cationic additive, Ag+, can influence the crystallinity and thus shape of final product during seeded growth of Au nanocrystals. Using single‐crystal Au seeds as reference, the crystallinity difference between seed and final product could be directly compared. In particular, three different types of crystallinity/morphology can be obtained by varying the concentration of Ag+ in the particle growth solutions: single‐crystal quasi‐spheres, multiply twinned particles (MTPs), and protruded MTPs, with no Ag+ added and solution Ag+ /Au3+ ratios of 1 : 20 and 1 : 5, respectively. The reaction kinetics are investigated using extinction spectroscopy, indicating the presence of Ag+ leads to a dampened growth of Au nanocrystals. This principle is validated using single‐crystal Au seeds with different morphology and amounts. We also test the anti‐corrosion performance of as‐prepared Au nanocrystals with different crystallinity by treating them with sodium thiosulfate. Interestingly, in addition to reduction in size, the morphology of single‐crystal ones varies from quasi‐sphere to cube, indicating the anisotropy in oxidative etching of Au nanocrystals. [ABSTRACT FROM AUTHOR]

A variety of hexagonal sodium yttrium fluoride (NYF) crystals with tunable shapes have been grown, and their up-conversion (UC) emission has been greatly improved after post-treatment in an aqueous solution of NH4HF2 and NaF. The enhancement has been attributed to topotactic ion insertion of sodium cations into the channels of Na3 xY2- xF6. As sodium-ion insertion continues to occur and the sodium content rises, the up-conversion emission intensity and green-to-red ratio increase up to the saturation level. However, the X-ray diffraction patterns and SEM images suggest that both the crystallographic structure and geometric morphology remain unchanged during this topotactic sodium ion insertion. This strategy is very different to previous reports on the use of ion exchange in the preparation of sodium yttrium fluoride crystals and improvement of UC emission. The results of this work demonstrate that sodium vacancy in the hexagonal Na3 xY2- xF6 crystal is the key to the clear reduction in the up-conversion photoluminescence properties of the crystals, but the topotactic sodium ion insertion can revive the up-conversion efficiency greatly. [ABSTRACT FROM AUTHOR]

The photoluminescent properties of Tb3+/Yb3+-, Ce3+/Tb3+/Yb3+-, and Eu2+/Yb3+-doped KSrPO4 are investigated by photoluminescence excitation and emission spectroscopy. [ABSTRACT FROM AUTHOR]