Surfactant-free sub-2 nm ultrathin triangular gold nanoframes

Plate-Like Colloidal Metal Nanoparticles

The pseudo-two-dimensional (2D) morphology of plate-like metal nanoparticles makes them one of the most anisotropic, mechanistically understood, and tunable structures available. Although well-known for their superior plasmonic properties, recent progress in the 2D growth of various other materials has led to an increasingly diverse family of plate-like metal nanoparticles, giving rise to numerous appealing properties and applications. In this review, we summarize recent progress on the solution-phase growth of colloidal plate-like metal nanoparticles, including plasmonic and other metals, with an emphasis on mechanistic insights for different synthetic strategies, the crystallographic habits of different metals, and the use of nanoplates as scaffolds for the synthesis of other derivative structures. We additionally highlight representative self-assembly techniques and provide a brief overview on the attractive properties and unique versatility benefiting from the 2D morphology. Finally, we share our opinions on the existing challenges and future perspectives for plate-like metal nanomaterials.

A Reversible Moisture-Responsive Plasmonic Color-Raman and Transmittance Modulation Device by Dispersing Hyaluronan-Functionalized Ag into Nanofibers

Plasmonic physical color generation, which mostly depends on selective absorption, creates unique colors by light transmission and scattering. Based on this, regulating plasmon and transparency with external stimulation is a promising approach for fabricating optical devices with enhanced visual displays; however, few studies have addressed the implementation of dual-optical modulation. In addition, developing a color response to environmental stimuli through the highly shape-sensitive plasmon depth modulation has long remained a significant challenge once the nanostructure is determined. Some stimulations also require high amounts of electricity, which can be costly. In this study, strategically designed hyaluronan-functionalized triangular silver nanoparticles (AgNPs) were embedded in polyvinyl alcohol-polyethylene nanofiber films to achieve a breakthrough in the moisture-responsive dual-optical modulation of the plasmonic color-Raman and transparency. Switchable colors that are reversible were induced in plasmon-resonance-modulation AgNPs via moisture stimulation, adjusting the expansion-tunable dielectric constant of hyaluronan-functionalized AgNPs and varying the electron density due to electron transfer. Furthermore, a moisture gradient was used to decrease the Raman scattering and increase the photoluminescence, which is a significant demonstration of smart-plasmonic evolution. This effect occurred due to the gradual transition from plasmon-driven photoluminescence quenching to photoluminescence enhancement as the interval of the Ag and hyaluronic acid molecules was increased. The transparency of the composite film was also dynamically regulated by turning moisture on/off. This occurred because of the significant difference in hygroscopic expansion between hyaluronan and the nanofibers, which generated a large variation in the total refractive index and caused changes in the surface roughness.

Au Nanorings with Intertwined Triple Rings

We designed complex Au nanorings with intertwined triple rings (ANITs) in a single entity to amplify the efficacy of near-field focusing. Such a complex and unprecedented morphology at the nanoscale was realized through on-demand multistepwise reactions. Triangular nanoprisms were first sculpted into circular nanorings, followed by a series of chemical etching and deposition reactions eventually leading to ANITs wherein thin metal bridges hold the structure together without any linker molecules. In the multistepwise reaction, the well-faceted growth pattern of Au, which induces the growth of two distinctive flat facets in a lateral direction, is important to evolve the morphology from single to multiple nanorings. Although our synthesis proceeds through multiple steps in one batch without purification steps, it shows a remarkably high yield (>∼90%) at the final stage. The obtained high degree of homogeneity (in both shape and size) of the resulting ANITs allowed us to systematically investigate the corresponding localized surface plasmon resonance (LSPR) coupling with varying nanoring arrangements and observe their single-particle surface enhanced Raman scattering (SERS). Surprisingly, individual ANITs exhibited an enormously large enhancement factor (∼10⁹), which confirms their superior near-field focusing relative to other reported nanoparticles.

Catalytic Nanoframes and Beyond

The ever-increasing need for the production and expenditure of sustainable energy is a result of the astonishing rate of consumption of fossil fuels and the accompanying environmental problems. Emphasis is being directed to the generation of sustainable energy by the fuel cell and water splitting technologies. Accordingly, the development of highly efficient electrocatalysts has attracted significant interest, as the fuel cell and water splitting technologies are critically dependent on their performance. Among numerous catalyst designs under investigation, nanoframe catalysts have an intrinsically large surface area per volume and a tunable composition, which impacts the number of catalytically active sites and their intrinsic catalytic activity, respectively. Nevertheless, the structural integrity of the nanoframe during electrochemical operation is an ongoing concern. Some significant advances in the field of nanoframe catalysts have been recently accomplished, specifically geared to resolving the catalytic stability concerns and significantly boosting the intrinsic catalytic activity of the active sites. Herein, general synthetic concepts of nanoframe structures and their structure-dependent catalytic performance are summarized, along with recent notable advances in this field. A discussion on the remaining challenges and future directions, addressing the limitations of nanoframe catalysts, are also provided.

One-Pot Self-Templated Growth of Gold Nanoframes for Enhanced Surface-Enhanced Raman Scattering Performance

As one of the representative metallic hollow nanostructures, Au nanoframes have shown fascinating properties such as strong localized surface plasmon resonance associated with emerging applications such as surface-enhanced Raman scattering (SERS) sensors. In this study, for the first time, a facile one-pot synthetic approach for hollow Au nanoframes is demonstrated by directly etching Au nanoplates, that is, the so-called self-templates. A novel growth mechanism has been revealed that involves a synergistic function of Ag and Br ions. The presence of Ag⁺ leads to the observation of self-limiting Au film thickness, whereas Au{111} facets are preferentially attacked by the presence of Br^- in the reaction ambient. More importantly, graphene is introduced to prevent/minimize aggregation during the formation of Au nanoframes. The combined simulation and experimental studies show that the hybrid platform made of graphene/Au nanoframes is capable of detecting analytes at concentration levels down to 10^-9 M by using the SERS technique.

Gold nanobipyramid-embedded ultrathin metal nanoframes for in situ monitoring catalytic reactions

Metal nanoframes, especially ultrathin ones, with excellent plasmonic properties are synthetically interesting and highly attractive. Herein we report on the synthesis of Au nanobipyramid-embedded ultrathin metal nanoframes with one of the plasmon modes very similar to that of the Au nanobipyramids. The synthesis is mediated by silver coating on Au nanobipyramids. The excellent plasmonic properties of the Au nanobipyramid-embedded ultrathin metal nanoframes are ascribed to the little influence of the ultrathin metal nanoframes on the Au nanobipyramids, as verified by electrodynamic simulations. The increase in the amount of the added metal atoms changes the nanostructure from the nanoframe to a nanocage shape. The method has also been successfully applied to (Au nanobipyramid)@Ag nanorods with different lengths and Au nanobipyramids with different longitudinal dipolar plasmon wavelengths, suggesting the generality of our approach. We have further shown that the Au nanobipyramid-embedded ultrathin metal nanoframes possess an excellent surface-enhanced Raman scattering and outstanding in situ reaction probing performance. Our study opens up a route for the construction of plasmonic ultrathin metal nanoframes based on Au nanobipyramids for plasmon-enabled applications.

Colloidal Gold Nanorings and Their Plasmon Coupling with Gold Nanospheres

Gold nanorings are attractive as plasmonic metal nanocrystals because they have a hollow inner cavity. Their enhanced electric field inside the ring cavity is accessible, which is highly desirable for assembling with other optical components and studying their plasmon-coupling behaviors. However, the lack of robust methods for synthesizing size-controllable and uniform Au nanorings severely impedes the study of their attractive plasmonic properties and plasmon-driven applications. Herein, an improved wet-chemistry method is reported for the synthesis of monodisperse colloidal Au nanorings. Using circular Au nanodisks with different thicknesses and diameters as templates, Au nanorings are synthesized with thicknesses varied from ≈30 to ≈50 nm and cavity sizes varied from ≈90 to ≈40 nm. The produced Au nanorings are assembled with colloidal Au nanospheres to yield Au nanoring-nanosphere heterodimers in sphere-in-ring and sphere-on-ring configurations on substrates. The sphere-in-ring heterodimers exhibit the interesting feature of plasmonic Fano resonance upon the excitation of the dark quadrupolar plasmon mode of the Au nanorings. The open cavity in a nanoring holds a great promise for studying plasmon-coupled systems, which will facilitate the construction of advanced metamaterials and high-performance Fano-based devices.

Noble Metal Based Alloy Nanoframes: Syntheses and Applications in Fuel Cells

Noble metal nanostructures are being used broadly as catalysts for energy conversion in fuel cells. To overcome the future energy crises, fuel cells are anticipated as clean energy sources because they can be operated at low temperature, their energy conversion is high and their carbon release is almost zero. However, an active and stable electrocatalyst is essential for the electrochemical reactions in fuel cells. Therefore, properties of the nanostructures greatly depend on the shape of the nanostructures. Individual as well as interaction properties are greatly affected by changes in the surface area of the nanostructures. By shape controlled synthesis, properties of the nanostructures could be further enhanced by increasing the surface area or active sites for electrocatalysts. Therefore, an efficient approach is needed for the fabrication of nanostructures to increase their efficiency, activity, or durability in fuel cells by reducing the usage of noble metals. Different types of hollow nanostructures until now have been prepared including nanoboxes, nanocages, nanoshells, nanoframes (NFs), etc. NFs are the hollow unique three-dimensional structure which have no walls-they only contain corners or edges so they have large surface area. In electrocatalytic reactions, the molecules involved in the reaction can easily reach the inner surface of the nanoframes, thus noble metals' utilization efficiency increases. NFs usually have high surface area, greater morphological and compositional stabilities, allowing them to withstand harsh environmental conditions. By considering the current challenges in fabrication of noble metal based alloy NFs as electrocatalysts, this review paper will highlight recent progress, design, and fabrication of noble metal alloy NFs through different strategies-mainly photocatalytic template, electrodeposition, Kirkendall effect, galvanic replacement, chemical/oxidative etching, combination of both and other methods. Then, electrochemical applications of NFs in fuel cells toward formic acid, methanol, ethanol, oxygen reduction reaction as well as bifunctional catalyst will also be highlighted. Finally, we will summarize different challenges in the fabrication of highly proficient nanocatalysts for the fuel cells with low cost, high efficiency and high durability, which are the major issues for the highly commercial use of fuel cells in the future.

Preparation of Pt-skin PtRhNi Nanoframes Decorated with Small SnO2 Nanoparticles as an Efficient Catalyst for Ethanol Oxidation Reaction

Pt-based nanoframes are one of the most promising catalysts for ethanol oxidation reaction in direct ethanol fuel cells. It is important to understand the mechanisms responsible for creating these hollow nanoframe-based catalysts. Herein, for the first time, Pt-skin PtRhNi rhombic dodecahedral nanoframes were decorated with small SnO₂ nanoparticles and were used as an efficient catalyst for the ethanol oxidation reaction. Moreover, by combining the ex situ scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy observations at various stages of synthesis, along with density functional theory calculations, it was possible to track the synthesis route of solid rhombic dodecahedral PtRhNi nanoparticles, which are the precursors of PtRhNi nanoframes. After the chemical etching of the Ni core from solid PtRhNi nanoparticles, the obtained nanoframes were decorated with SnO₂ nanoparticles. The resulting SnO₂@PtRhNi heteroaggregates were deposited on high-surface-area carbon and electrochemically tested, showing a 6-fold higher mass activity and 10-fold higher specific activity toward ethanol oxidation reaction than commercially available Pt catalysts.

Shaping well-defined noble-metal-based nanostructures for fabricating high-performance electrocatalysts: advances and perspectives

This review highlights recent advances in shaping protocols and structure-activity relationships of noble-metal-based catalysts with well-defined nanostructures in electrochemical reactions.

Spectral dependence of plasmon-enhanced fluorescence in a hollow nanotriangle assembled by DNA origami: towards plasmon assisted energy transfer

The precise positioning of plasmonic nanoscale objects and organic molecules can significantly boost our ability to fabricate hybrid nanoarchitectures with specific target functionalities. In this work, we used a DNA origami structure to precisely localize three different fluorescent dyes close to the tips of hollow gold nanotriangles. A spectral dependence of plasmon-enhanced fluorescence is evidenced through co-localized AFM and fluorescence measurements. The experimental results match well with explanatory FDTD simulations. Our findings open the way to the bottom-up fabrication of plasmonic routers operating through plasmon energy transfer. They will allow one to actively control the direction of light propagation.

Triangular AgAu@Pt core-shell nanoframes with a dendritic Pt shell and enhanced electrocatalytic performance toward the methanol oxidation reaction

Triangular AgAu@Pt nanoframes with a dendritic Pt shell were synthesized by employing Ag nanoprisms as sacrificial templates. Due to the unique frame-like nanostructure and ternary components, the AgAu@Pt nanoframes exhibit impressive electrocatalytic performance toward the methanol oxidation reaction with much higher activity, and better anti-poisoning capability than commercial Pt/C catalysts.

Controlled growth and optical response of a semi-hollow plasmonic nanocavity and ultrathin sulfide nanosheets on Au/Ag platelets

Herein, we report a strategy to construct a semi-hollow plasmonic nanocavity and grow ultrathin sulfide nanosheets inside. The competition and cooperation of Au deposition with Ag etching based on flat Ag nanoplates are proposed. For the establishment of the semi-hollow nanocavity, Au shells are grown on Ag nanoplates, which serve as a stable frame, followed by partial etching of the Ag nanoplates. By controlling the thickness of the initial Ag nanoplates or the injected amount of etchant, the nanocavity size is fine-tuned. Significantly, the remaining unetched Ag layers provide a flat platform for the growth of 2D ultrathin sulfides of Ag₂S and CdS inside the semi-hollow plasmonic nanocavity. Strong plasmon resonance and large local field enhancement are exhibited inside the plasmonic cavity where the ultrathin semiconductor sulfides are grown, indicating strong plasmon-exciton interactions in the hybrids. Furthermore, this synthetic approach is extended to grow other metal sulfides such as Bi₂S₃ and PbS. The combination of a flat plasmonic cavity with ultrathin semiconductor nanosheets in this study provides a new strategy for the development of unique plasmon-based hybrids with excellent optical properties.

Suppressing Nanoparticle-Mononuclear Phagocyte System Interactions of Two-Dimensional Gold Nanorings for Improved Tumor Accumulation and Photothermal Ablation of Tumors

The clearance of nanoparticles (NPs) by mononuclear phagocyte system (MPS) from blood leads to high liver and spleen uptake and negatively impacts their tumor delivery efficiency. Here we systematically evaluated the in vitro and in vivo nanobio interactions of a two-dimensional (2D) model, gold (Au) nanorings, which were compared with Au nanospheres and Au nanoplates of similar size. Among different shapes, Au nanorings achieved the lowest MPS uptake and highest tumor accumulation. Among different sizes, 50 nm Au nanorings showed the highest tumor delivery efficiency. In addition, we demonstrated the potential use of Au naonrings in photoacoustic imaging and photothermal therapy. Thus, engineering the shape, surface area, and size of Au nanostructures is important in controlling NP-MPS interactions and improving the tumor uptake efficiency.

Iridium-Based Multimetallic Nanoframe@Nanoframe Structure: An Efficient and Robust Electrocatalyst toward Oxygen Evolution Reaction

Nanoframe electrocatalysts have attracted great interest due to their inherently high active surface area per a given mass. Although recent progress has enabled the preparation of single nanoframe structures with a variety of morphologies, more complex nanoframe structures such as a double-layered nanoframe have not yet been realized. Herein, we report a rational synthetic strategy for a structurally robust Ir-based multimetallic double-layered nanoframe (DNF) structure, nanoframe@nanoframe. By leveraging the differing kinetics of dual Ir precursors and dual transition metal (Ni and Cu) precursors, a core-shell-type alloy@alloy structure could be generated in a simple one-step synthesis, which was subsequently transformed into a multimetallic IrNiCu DNF with a rhombic dodecahedral morphology via selective etching. The use of single Ir precursor yielded single nanoframe structures, highlighting the importance of employing dual Ir precursors. In addition, the structure of Ir-based nanocrystals could be further controlled to DNF with octahedral morphology and CuNi@Ir core-shell structures via a simple tuning of experimental factors. The IrNiCu DNF exhibited high electrocatalytic activity for oxygen evolution reaction (OER) in acidic media, which is better than Ir/C catalyst. Furthermore, IrNiCu DNF demonstrated excellent durability for OER, which could be attributed to the frame structure that prevents the growth and agglomeration of particles as well as in situ formation of robust rutile IrO₂ phase during prolonged operation.

Synthesis of circular and triangular gold nanorings with tunable optical properties

This communication describes a robust wet-chemical synthetic strategy for the preparation of monodispersed circular and triangular gold nanorings.

Seed-Mediated Growth of Colloidal Metal Nanocrystals

Seed-mediated growth is a powerful and versatile approach for the synthesis of colloidal metal nanocrystals. The vast allure of this approach mainly stems from the staggering degree of control one can achieve over the size, shape, composition, and structure of nanocrystals. These parameters not only control the properties of nanocrystals but also determine their relevance to, and performance in, various applications. The ingenuity and artistry inherent to seed-mediated growth offer extensive promise, enhancing a number of existing applications and opening the door to new developments. This Review demonstrates how the diversity of metal nanocrystals can be expanded with endless opportunities by using seeds with well-defined and controllable internal structures in conjunction with a proper combination of capping agent and reduction kinetics. New capabilities and future directions are also highlighted.

Rational design and synthesis of noble-metal nanoframes for catalytic and photonic applications

Nanoframes are unique for their 3D, highly open architecture. When made of noble metals, they are attractive for use as heterogeneous catalysts because of their large specific surface areas, high densities of catalytically active sites and low vulnerability toward sintering. They promise to enhance the catalytic activity and durability while reducing the material loading and cost. For nanoframes composed of Au and/or Ag, they also exhibit highly tunable plasmonic properties similar to those of nanorods. This article presents a brief account of recent progress in the design, synthesis and utilization of noble-metal nanoframes. We start with a discussion of the synthetic strategies, including those involving site-selected deposition and etching, as well as dealloying of both hollow and solid nanocrystals. We then highlight some of the applications enabled by noble-metal nanoframes. Finally, we discuss the challenges and trends with regard to future development.

Gold core@silver semishell Janus nanoparticles prepared by interfacial etching

Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface.

Ag-Ag2S Hybrid Nanoprisms: Structural versus Plasmonic Evolution

Recently, Ag-Ag2S hybrid nanostructures have attracted a great deal of attention due to their enhanced chemical and thermal stability, in addition to their morphology- and composition-dependent tunable local surface plasmon resonances. Although Ag-Ag2S nanostructures can be synthesized via sulfidation of as-prepared anisotropic Ag nanoparticles, this process is poorly understood, often leading to materials with anomalous compositions, sizes, and shapes and, consequently, optical properties. In this work, we use theory and experiment to investigate the structural and plasmonic evolution of Ag-Ag2S nanoprisms during the sulfidation of Ag precursors. The previously observed red-shifted extinction of the Ag-Ag2S hybrid nanoprism as sulfidation occurs contradicts theoretical predictions, indicating that the reaction does not just occur at the prism tips as previously speculated. Our experiments show that sulfidation can induce either blue or red shifts in the extinction of the dipole plasmon mode, depending on reaction conditions. By elucidating the correlation with the final structure and morphology of the synthesized Ag-Ag2S nanoprisms, we find that, depending on the reaction conditions, sulfidation occurs on the prism tips and/or the (111) surfaces, leading to a core(Ag)-anisotropic shell(Ag2S) prism nanostructure. Additionally, we demonstrate that the direction of the shift in the dipole plasmon is a function of the relative amounts of Ag2S at the prism tips and Ag2S shell thickness around the prism.

Synthesis and optical property characterization of elongated AuPt and Pt@Au metal nanoframes

We report a facile method to synthesize elongated nanoframes consisting of Pt and Au in solution. Pentagonal Au nanorods served as templates and successfully led to an elongated AuPt nanoframe after etching the core Au. Subsequently, the coating of Au around Pt ridges resulted in Pt@Au metal nanoframes. The resulting elongated nanostructure exhibited 5 well-defined ridges continuously connected along the long axis. During the shape evolution from pure Au nanorods to elongated Pt@Au metal nanoframes, their corresponding localized surface plasmon resonance bands were monitored. Especially, unique surface plasmon features were observed for elongated Pt@Au nanoframes where the short-axis oscillation of surface free electrons is strongly coupled but the long-axis oscillation is not coupled among the ridges.

The alloying effect and AgCl-directing growth for synthesizing a trimetallic nanoring with improved SERS

We report the synthesis of high quality trimetallic Au/Ag/Pt nanorings (TAAPNs) by using Au/Ag alloy decahedra (AAAD) as templates. The alloying effect and AgCl-directing growth have been investigated in detail during the formation of TAAPN. It was found that the doping of Ag in AAAD changes the surrounding environment of Au atoms and decreases the oxidization reduction potential (ORP) of [AuCl(2)](-)/Au because of the alloying effect, resulting in the dissolved O(2) molecules that serve as an effective etchant for oxidizing Au to Au(I). Ascorbic acid (AA) and chloroplatinic acid (H(2)PtCl(6)) are weak acids which can accelerate the etching by increasing the concentration of H(+). The AgCl selectively absorbs on {100} of the decahedra and induces the preferential deposition of H(2)PtCl(6) here via their complexing interaction. AA reduces Pt(IV) and Ag(I) to atoms which grow on {100} facets. The formed Pt/Ag layer changes the etching direction from along [100] to [111] and generates the TAAPN. Besides, it has been noted that the TAAPNs exhibit good Surface Enhanced Raman Scattering (SERS) performance.

Face the Edges: Catalytic Active Sites of Nanomaterials

Edges are special sites in nanomaterials. The atoms residing on the edges have different environments compared to those in other parts of a nanomaterial and, therefore, they may have different properties. Here, recent progress in nanomaterial fields is summarized from the viewpoint of the edges. Typically, edge sites in MoS2 or metals, other than surface atoms, can perform as active centers for catalytic reactions, so the method to enhance performance lies in the optimization of the edge structures. The edges of multicomponent interfaces present even more possibilities to enhance the activities of nanomaterials. Nanoframes and ultrathin nanowires have similarities to conventional edges of nanoparticles, the application of which as catalysts can help to reduce the use of costly materials. Looking beyond this, the edge structures of graphene are also essential for their properties. In short, the edge structure can influence many properties of materials.

Rational Design of Metal Nanoframes for Catalysis and Plasmonics

Recently, metal nanoframes have received increased attention due to their unique spatial and physicochemical, e.g., catalytic and plasmonic properties. So far, a variety of synthetic procedures have been developed to fabricate metal nanoframes with different shapes, sizes and compositions. Typical synthesis of metal nanoframes involves two stages: 1) formation of solid nanocrystals and 2) hollowing out the interiors and side faces. In this review, solution-phase synthetic strategies are summarized, based on galvanic replacement reactions, oxidative etching, the Kirkendall effect, electrodeposition, and template-assisted growth, as well as one-pot synthesis. Their potential applications in catalysis and optical sensing are overviewed as well.

Transformation of truncated gold octahedrons into triangular nanoprisms through the heterogeneous nucleation of silver

Described is a straightforward procedure for forming organized substrate-immobilized nanoprisms which are single crystalline, surfactant-free and which form a heteroepitaxial relationship with the underlying substrate. The devised route utilizes truncated Au octahedrons formed through solid state dewetting techniques as high temperature heterogeneous nucleation sites for Ag adatoms which are arriving to the substrate surface in the vapour phase. Observed is a morphological and compositional transformation of the Au structures to triangular nanoprisms comprised of a homogeneous AuAg alloy. During this transformation, the localized surface plasmon resonance red-shifts, broadens and increases in strength. The shape transformation, which cannot be rationalized using thermodynamic arguments dependent on the surface energy minimization, is described in terms of a kinetically driven growth mode, previously predicted by molecular dynamic simulations. The so-formed structures, when coated with a thin layer of Pd, are demonstrated as plasmonic sensing elements for hydrogen detection.

Silver/gold core-shell nanoprism-based plasmonic nanoprobes for highly sensitive and selective detection of hydrogen sulfide

A simple and highly sensitive and selective hydrogen sulfide assay utilizing plasmonic nanoprobes is presented in this report. The assay employs the etching of silver in the Ag/Au core-shell nanoprisms, accompanied by surface plasmon resonance (SPR) signal depression and shift. Briefly, thin layers of gold are first coated onto silver nanoprisms. The thin gold layer not only guarantees the high stability of the plasmonic nanoprobes but also ensures the high selectivity toward hydrogen sulfide. Once hydrogen sulfide is introduced, the silver core is converted to Ag2S mainly from its lateral walls. Moreover, the SPR peak is located in the NIR region that makes these plasmonic nanoprobes more appealing for the detection of hydrogen sulfide in real-world samples and in in vivo applications.

Triangular Ag-Pd alloy nanoprisms: rational synthesis with high-efficiency for electrocatalytic oxygen reduction

We report the generation of triangular Ag-Pd alloy nanoprisms through a rationally designed synthetic strategy based on silver nanoprisms as sacrificial templates. The galvanic replacement between Ag nanoprisms and H2PdCl4 along with co-reduction of Ag(+)/Pd(2+) is responsible for the formation of final prismatic Ag-Pd alloy nanostructures. Significantly, these Ag-Pd alloy nanoprisms exhibited superior electrocatalytic activity for the oxygen reduction reaction (ORR) as compared with the commercial Pd/C catalyst. Such a high catalytic activity is attributed to not only the alloyed Ag-Pd composition but also the dominant {111} facets of the triangular Ag-Pd nanoprisms. This work demonstrates the rational design of bimetallic alloy nanostructures with control of selective crystal facets that are critical to achieve high catalytic activity for fuel cell systems.