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Gold–silver (Au–Ag) nanocrystals with a combination of concave surface and hollow interior are of great interest due to their distinctive structural merits. Herein, we introduce a facile strategy based on seed surface doping to create concave Au@AuAg yolk–shell nanocubes with surface concavity (Au@AuAg YSCNCs), and examine their intriguing properties in optics and catalysis. In particular, the Au@Ag core–shell nanocubes are generated and reacted with sodium thiosulfate, followed by the addition of HAuCl4 to remove Ag atoms on the side walls and deposit Au/Ag atoms on the corners/edges via the galvanic replacement reaction. UV-vis extinction spectra show that compared to Au@Ag core–shell nanocubes, the current Au@AuAg YSCNCs enable a redshift in the major absorption peak, which should be attributed to the increase in charge polarization regions. Meanwhile, the structural advantage is validated using the reduction of 4-nitrophenol as the model reaction. In particular, the current Au@AuAg YSCNCs exhibit an enhanced catalytic efficiency compared to the Au@Ag core–shell nanocubes. Mechanism study using density functional theory reveals that the structural advantage boosts the catalytic activity by upshifting the d-band center and thus lowering the activation barrier. The current study provides a feasible strategy to integrate two structural features (e.g., concave surface and hollow interior) into one AuAg nano-entity, which could be potentially extended to other metals and/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]

The photocatalyst surface is central to photocatalytic reactions. However, it has been a challenge to explicitly understand both the surface configuration and the structure-dependent photocatalytic properties at the atomic level. First-principles density functional theory (DFT) calculations provide a versatile method that makes up for the lack of experimental surface studies. In DFT calculations, the initial surface model greatly affects the accuracy of the calculation results. Consequently, establishing a more realistic and more reliable material surface models is undoubtedly the first step and the most important link in theoretical calculations. The aim of this Perspective is to provide a general understanding of the methods for the surface modeling of photocatalytic materials in recent years. We begin with a discussion of the basic theories applied in photocatalytic surface research, followed by an explanation of the importance of surface modeling in photocatalysis. We then elaborate on the advantages and disadvantages of the basic surface model and briefly describe the latest surface modeling methods. Finally, we evaluate the rationality of current surface modeling methods. We summarize this Perspective by prospecting the developing directions of photocatalytic surface research in the future. It is believed that a reasonable surface model should be verified by both experimental characterization and theoretical computation with negative feedback. [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 preparation of a series of heterojunctions made of Ta3N5 and TiO2 nanoparticles that show good properties for photocatalytic hydrogen production. The composite photocatalyst with a light-response range up to 620 nm shows a hydrogen evolution rate of 250 μmol h−1. The apparent quantum efficiency at 330 nm can be as high as 46%. Particularly, normalized spectral studies indicate that the heterojunction is more active upon full-spectrum (without using optical filters) irradiation, and its activity is even superior  to the total activity exhibited upon UV-light irradiation (λ ≤ 420 nm) and visible-infrared light irradiation (λ ≥ 420 nm). Moreover, in situ photodeposition of platinum nanoparticles on the surface of the photocatalyst as well as the band alignment analysis demonstrate the Z-scheme mechanism associated with the photocatalytic process. Specifically, photogenerated electrons from TiO2 will rapidly combine with the photogenerated holes from Ta3N5 through interfacial charge transfer, leaving the more active electrons and holes in Ta3N5 and TiO2, respectively, to facilitate redox reactions. Basically, TiO2 is only UV-light active, while Ta3N5 can be activated under visible-light irradiation. In this case, a synergy effect, upon simultaneous UV-light excitation and visible-light excitation, can be achieved by full-spectrum irradiation, leading to a much higher photocatalytic activity. This work thus provides a favorable and upward direction for the establishment of heterojunctions for high-efficiency hydrogen production and solar energy applications. [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]

Atomically ordered intermetallic nanocrystals have been extensively explored in electrocatalysis due to their outstanding catalytic performances and excellent stabilities. However, controllable synthesis of intermetallic nanocrystals in terms of their size and structure remains a grand challenge due to the generally involved high-temperature thermal annealing synthetic method, largely hindering the optimization of their catalytic properties. Herein, we report a versatile approach to the synthesis of atomically ordered Pd3Pb multiply twinned intermetallic nanowire networks (MT-IM-NNs) with a tunable diameter and microstructure. The use of preformed Pd seeds, which were converted to a Pd3Pb intermetallic phase via the diffusion of Pb atoms into the seeds, as well as an oriented attachment growth mode, accounted for the formation of such a unique structure. Importantly, the diameter and microstructure of Pd3Pb MT-IM-NNs could be engineered by controlling the size and type of Pd seeds. In addition, the Pd3Pb multiply twinned intermetallic porous nanowire networks exhibited a high faradaic efficiency of 21.46% and an NH3 yield rate of 18.2 μg h−1 mgcat−1 at −0.2 V vs. the reversible hydrogen electrode toward N2 electroreduction. [ABSTRACT FROM AUTHOR]

Sluggish C–C bond cleavage during the ethanol oxidation reaction (EOR) in acidic media results in a lowered energy yield and gravely hinders the commercialization of direct ethanol fuel cells. Here we report an elaborate synthesis of sub-10 nm concavity-tunable Rh@Pt core–shell nanocubes with an engineered Rh–Pt interface and Pt atomic surface steps to facilitate the C–C bond cleavage in the EOR. Using a microsyringe pump, the surface concavity of the Rh@Pt core–shell nanocubes is successfully manipulated through kinetically adjusting the ratio of the atom deposition rate and surface diffusion rate (Vdep./Vdiff.) during the overgrowth process. Compared to the samples with shallow surface concavity and a flat surface, the deeper concaved Rh@Pt core–shell nanocubes possess richer surface Pt atomic steps and exhibit a greater enhancement in EOR catalysis, achieving mass activity and specific activity that are 3.74 times and 6.89 times higher than those of the state-of-the-art Pt/C catalysts, respectively. Electrochemical in situ FTIR studies indicate that the Rh–Pt interfacial interaction and the surface Pt atomic steps on the Rh@Pt concave nanocubes can effectively facilitate the C–C bond cleavage towards the complete oxidation of ethanol to CO2. [ABSTRACT FROM AUTHOR]

A new analytical method is described for the colorimetric detection of sulfide. This approach involves the use of Pd nanocubes (PdNCs) as artificial peroxidases that can effectively generate a colored signal by catalyzing the oxidation of peroxidase substrates. In the presence of sulfide, the colored signal is greatly diminished because of the specific and efficient inhibition of the peroxidase-like activity of the PdNCs through their surface inactivation by the formation of PdS. Based on this finding, sulfide assay can be achieved in the 0.125–2.75 μM concentration range with a detection limit of 80 nM. This method shows high selectivity to sulfide besides other ions, and has been applied for the determination of sulfide in spiked real samples. It also features simplicity and rapidness since the assay can be conducted at room temperature, in aqueous solution, and requires only ∼5 min. [ABSTRACT FROM AUTHOR]

Coating an ultrathin platinum-rich skin on nanosubstrates made of other cheaper metals is an effective strategy for fabricating active electrocatalysts with low Pt-content. We developed a facile one-pot synthesis of Pd@Pt3Ni core–shell nanobranches with ultrathin Pt3Ni{111} skins that have active and durable catalytic performances for ethanol electrooxidation. [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]

CdS is a well-known and efficient photocatalyst for photocatalytic hydrogen production. However, CdS is prone to photocorrosion in the photocatalytic reaction, in which CdS itself is oxidized by the photogenerated holes. Most of the work reported, to date, has focused only on the structure of CdS. However, less attention was paid to the kinetic changes of CdS during the photocatalytic reaction, which, in our opinion, is a crucial step for its practical utilization. In this report, we have developed a facile in situ Raman analysis, aiming to clarify the microstructural changes of CdS during the photocatalytic reaction process. In this study, photocatalytic hydrogen production over CdS in an Ar or air atmosphere was studied using various techniques in addition to in situ Raman spectroscopy. With Raman spectroscopy, a significant increase in the surface lattice strain of CdS was only observed when it was exposed to air, while the electron–phonon interactions remained the same regardless of the atmosphere. A direct correlation between the interfacial crystal lattice and photocorrosion of the CdS photocatalyst during photocatalytic hydrogen production was found based on our in situ Raman investigation. Finding the photocorrosion of the CdS photocatalyst at its very early stage using our in situ Raman technique is expected to provide meaningful guidance for the design of active and stable chalcogenide photocatalysts, which, however, cannot be achieved using traditional characterization techniques. [ABSTRACT FROM AUTHOR]

This article describes a facile synthesis of Pd–Ir bimetallic nanostructures in the forms of core–shell octapods and alloyed nanocages. The success of this synthesis relies on the use of Pd nanocubes as the sacrificial templates and interplay of two different processes: the galvanic replacement between an Ir precursor and the Pd nanocubes and the co-reduction of Pd2+ and Ir3+ by ethylene glycol. The galvanic replacement played a dominant role in the initial stage, through which Pd atoms were dissolved from the side faces whereas Ir atoms were deposited at the corner sites to generate Pd–Ir core–shell octapods. As the concentration of Pd2+ in the reaction mixture was increased, co-reduction of Pd2+ and Ir3+ occurred in the late stage of synthesis. The resultant Pd and Ir atoms were deposited onto the octapods while the Pd atoms in the interiors continued to be etched away due to the galvanic replacement, finally leading to the formation of Pd–Ir alloyed nanocages. The octapods and nanocages were then evaluated as catalysts for the selective generation of hydrogen from the decomposition of hydrous hydrazine. The nanocages exhibited better selectivity for hydrogen generation than octapods (66% versus 29%), which can be attributed to the presence of an alloyed, porous structure on the surface. [ABSTRACT FROM AUTHOR]

Multifaceted Cu2O with controlled crystal facet exposure was synthesized via a facile one-step method. It was found that photogenerated electrons prefer to accumulate on high index planes, while holes tend to migrate to {100} facets of a Cu2O polyhedron, leading to efficient charge separation and enhanced photocatalytic reforming of glucose. [ABSTRACT FROM AUTHOR]

Coating an ultrathin platinum-rich skin on nanosubstrates made of other cheaper metals is an effective strategy for fabricating active electrocatalysts with low Pt-content. We developed a facile one-pot synthesis of Pd@Pt3Ni core-shell nanobranches with ultrathin Pt3Ni{111} skins that have active and durable catalytic performances for ethanol electrooxidation.

Multifaceted Cu2O with controlled crystal facet exposure was synthesized via a facile one-step method. It was found that photogenerated electrons prefer to accumulate on high index planes, while holes tend to migrate to {100} facets of a Cu2O polyhedron, leading to efficient charge separation and enhanced photocatalytic reforming of glucose.