Decahedral Seeds Research Articles

Highly controlled synthesis of symmetrically branched tripod and pentapod nanocrystals with enhanced photocatalytic performance

Anisotropic nanostructures with tunable optical properties induced by controllable size and symmetry have attracted much attention in many applications. Herein, we report a controlled synthesis of symmetrically branched AuCu alloyed nanocrystals. By varying Au:Cu atom ratio in precursor, Y-shaped tripods with three-fold symmetry and star-shaped pentapods with five-fold symmetry are synthesized, respectively. The growth mechanism of AuCu tripods from icosahedral seeds and AuCu pentapods from decahedral seeds is revealed. Aiming to excellent photocatalytic performance, CdS nanocrystals are controlled grown onto the sharp tips of AuCu tripods and pentapods. In addition, a carrier-selective blocking layer of Ag2S is introduced between AuCu and CdS, for achieving effective charge separation in AuCu-Ag2S-CdS nanohybrids. Through evaluating the photocatalytic performance by hydrogen generation experiments, the AuCu-Ag2S-CdS tripod nanocrystals exhibit an optimized hydrogen evolution rate of 2182 μmol·g−1·h−1. These findings will contribute greatly to the understanding of complex nanoparticle growth mechanism and provide a strategy for the design of anisotropic nanoalloys for widely photocatalytic applications.

Homochiral Nanopropeller via Chiral Active Surface Growth.

Under the control of chiral ligand glutathione and in the presence of hexadecyltrimethylammonium bromide, Au deposition on Au seeds is known to give chiral nanostructures. We have previously shown that the protruding chiral patterns, as opposed to flat facets, are likely caused by active surface growth, where nonuniform ligand coverage could be responsible for the focused growth at a few active sites. By pushing the limit of such a growth mode, here, we use decahedral seeds to prepare homochiral nanopropellers with intricate patterns of deep valleys and protruding ridges. Control experiments show that the focused growth depends on the rates of Au deposition by changing either the seed concentration or the reductant concentration, consistent with the proposed mechanism. The dynamic growth competition between the ligand-deficient active sites and the ligand-rich surfaces gradually focuses the growth onto a few active sites, causing the expansion of grooves, squeezing of steep ridges, and a surprising 36° rotation of the pentagonal outline. The imbalanced deposition on the prochiral slopes is responsible for the tilted grooves, the twisted walls, and thus the well-separated and distorted blades, which become the origin of the chiroptical responses.

Diffusion growth mechanism of penta-twinned Ag nanocrystals from decahedral seeds.

Crystals with penta-twinned structures can be produced from diverse fcc metals, but the mechanisms that control the final product shapes are still not well understood. By using the theory of absorbing Markov chains to account for the growth of penta-twinned decahedral seeds via atom deposition and surface diffusion, we predicted the formation of various types of products: decahedra, nanorods, and nanowires. We showed that the type of product depends on the morphology of the seed and that small differences between various seed morphologies can lead to significantly different products. For the case of uncapped decahedra seeds, we compared predictions from our model to nanowire morphologies obtained in two different experiments and obtained favorable agreement. Possible extensions of our model are indicated.

Pd–Au Asymmetric Nanopyramids: Lateral vs Vertical Growth of Au on Pd Decahedral Seeds

Pd–Au Asymmetric Nanopyramids: Lateral vs Vertical Growth of Au on Pd Decahedral Seeds

Understanding the Solution-Phase Growth of Cu and Ag Nanowires and Nanocubes from First Principles.

In this feature article, we provide an account of the Langmuir Lecture delivered by Kristen Fichthorn at the Fall 2020 Virtual Meeting of the American Chemical Society. We discuss how multiscale theory and simulations based on first-principles DFT were useful in uncovering the intertwined influences of kinetics and thermodynamics on the shapes of Ag and Cu cubes and nanowires grown in solution. We discuss how Ag nanocubes can form through PVP-modified deposition kinetics and how the addition of chloride to the synthesis can promote thermodynamic cubic shapes for both Ag and Cu. We discuss kinetic factors contributing to nanowire growth: in the case of Ag, we show that high-aspect-ratio nanowires can form as a consequence of Ag atom surface diffusion on the strained surfaces of Marks-like decahedral seeds. On the other hand, solution-phase chloride enhances Cu nanowire growth due to a synergistic interaction between adsorbed chloride and hexadecylamine (HDA), which leaves the {111} nanowire ends virtually bare while the {100} sides are fully covered with HDA. For each of these topics, a synergy between theory and experiment led to significant progress.

Aqueous Synthesis of Pd–M (M = Pd, Pt, and Au) Decahedra with Concave Facets for Catalytic Applications

Noble-metal nanocrystals with structural features such as high-index facets and twin defects on the surface are desirable for various catalytic applications. Here we report an aqueous route to the facile synthesis of Pd–M (M = Pd, Pt, and Au) decahedra covered with concave facets by controlling the deposition and diffusion of M atoms on Pd decahedral seeds. Our mechanistic studies indicate that the preferential deposition of M atoms on the twin boundaries of Pd decahedral seeds under limited surface diffusion is instrumental to their evolution into decahedra enclosed by concave facets. Due to the presence of high-index facets and twin boundaries on the surface, the Pd concave decahedra show enhanced catalytic activity towards formic acid oxidation. The present work not only offers a general route to the facile synthesis of decahedral nanocrystals with concave facets but also provides an additional knob for enhancing the catalytic performance of noble-metal nanocrystals.

One-Pot Synthesis of Penta-twinned Palladium Nanowires and Their Enhanced Electrocatalytic Properties.

This article reports the design and successful implementation of a one-pot, polyol method for the synthesis of penta-twinned Pd nanowires with diameters below 8 nm and aspect ratios up to 100. The key to the success of this protocol is the controlled reduction of Na2PdCl4 by diethylene glycol and ascorbic acid through the introduction of NaI and HCl. The I- and H+ ions can slow the reduction kinetics by forming PdI42- and inhibiting the dissociation of ascorbic acid, respectively. When the initial reduction rate is tuned into the proper regime, Pd decahedral seeds with a penta-twinned structure appear during nucleation. In the presence of I- ions as a selective capping agent toward the Pd(100) surface, the decahedral seeds can be directed to grow axially into penta-twinned nanorods and then nanowires. The Pd nanowires are found to evolve into multiply twinned particles if the reaction time is extended beyond 1.5 h, owing to the involvement of oxidative etching. When supported on carbon, the Pd nanowires show greatly enhanced specific electrocatalytic activities, more than five times the value for commercial Pd/C toward formic acid oxidation and three times the value for Pt/C toward oxygen reduction under an alkaline condition. In addition, the carbon-supported Pd nanowires exhibit greatly enhanced electrocatalytic durability toward both reactions. Furthermore, we demonstrate that the Pd nanowires can serve as sacrificial templates for the conformal deposition of Pt atoms to generate Pd@Pt core-sheath nanowires and then Pd-Pt nanotubes with a well-defined surface structure.

Oxidative Etching of Pd Decahedral Nanocrystals with a Penta-twinned Structure and Its Impact on Their Growth Behavior

We report a systematic study of the oxidative etching of penta-twinned Pd decahedral nanocrystals by O2/I– under different conditions and its impact on their subsequent growth behavior. Analysis by transmission electron microscopy shows significant rounding of the decahedral structure. More specifically, the etching is found to begin at the equatorial vertices, due to their high surface free energy, and proceed along the adjacent, equatorial edges through the dissolution of low-coordination atoms. Comparison of the etching behaviors under different conditions reveals the critical role of a reductive environment for the initiation of oxidative etching, possibly due to the presence of a protective oxide layer on the surface of Pd decahedra. Overgrowth on the seeds with a rounded profile generates penta-twinned Pd nanorods with an asymmetric, tapered structure as a result of simultaneous axial and radial growth. In comparison, the original decahedral seeds only show axial growth, leading to the formation of ...

Helical Growth of Ultrathin Gold–Copper Nanowires

In this work, we report the synthesis and detailed structural characterization of novel helical gold-copper nanowires. The nanowires possess the Boerdijk-Coxeter-Bernal structure, based on the pile up of octahedral, icosahedral, and/or decahedral seeds. They are self-assembled into a coiled manner as individual wires or into a parallel-ordering way as groups of wires. The helical nanowires are ultrathin with a diameter of less than 10 nm and variable length of several micrometers, presenting a high density of twin boundaries and stacking faults. To the best of our knowledge, such gold-copper nanowires have never been reported previously.

Penta‐Twinned Copper Nanorods: Facile Synthesis via Seed‐Mediated Growth and Their Tunable Plasmonic Properties

The use of seed‐mediated growth as a versatile approach to the synthesis of penta‐twinned Cu nanorods with uniform diameters and controllable aspect ratios is reported. The success of this approach relies on our recent synthesis of uniform Pd decahedra, with sizes in the range of 6–20 nm. The Pd decahedral seeds can direct the heterogeneous nucleation and growth of Cu along the fivefold axis to produce nanorods with uniform diameters defined by the lateral dimension of the original seeds. Due to a large mismatch in the lattice constants between Cu and Pd (7.1%), the deposited Cu is forced to grow along one side of the Pd decahedral seed, generating a nanorod with an asymmetric distribution of Cu, with the Pd seed situated at one of the two ends. According to extinction spectra, the as‐obtained Cu nanorods can be stored in water under the ambient conditions for at least six months without noticeable degradation. This excellent stability allows us to systematically investigate the size‐dependent surface plasmon resonance properties of the penta‐twinned Cu nanorods. With the nanorod transverse modes positioned at 560 nm, the longitudinal modes can be readily tuned from the visible to the near‐infrared region by controlling the aspect ratio.

One-pot polyol synthesis of highly monodisperse short green silver nanorods.

Green silver nanorods (Ag NRs) of a low aspect ratio (2.8) have been produced in high yields via an optimized, simple, and robust one-pot polyol method in the presence of tannic acid, which favors the nucleation of decahedral seeds needed for the production of monodisperse Ag NRs. These Ag NRs were further used as sacrificial templates to produce Au hollow nanostructures via galvanic replacement reaction with HAuCl4 at room temperature.

Pd@Pt Core-Shell Concave Decahedra: A Class of Catalysts for the Oxygen Reduction Reaction with Enhanced Activity and Durability.

We report a facile synthesis of multiply twinned Pd@Pt core-shell concave decahedra by controlling the deposition of Pt on preformed Pd decahedral seeds. The Pt atoms are initially deposited on the vertices of a decahedral seed, followed by surface diffusion to other regions along the edges/ridges and then across the faces. Different from the coating of a Pd icosahedral seed, the Pt atoms prefer to stay at the vertices and edges/ridges of a decahedral seed even when the deposition is conducted at 200 °C, naturally generating a core-shell structure covered by concave facets. The nonuniformity in the Pt coating can be attributed to the presence of twin boundaries at the vertices, as well as the {100} facets and twin defects along the edges/ridges of a decahedron, effectively trapping the Pt adatoms at these high-energy sites. As compared to a commercial Pt/C catalyst, the Pd@Pt concave decahedra show substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). For the concave decahedra with 29.6% Pt by weight, their specific (1.66 mA/cm(2)Pt) and mass (1.60 A/mgPt) ORR activities are enhanced by 4.4 and 6.6 times relative to those of the Pt/C catalyst (0.36 mA/cm(2)Pt and 0.32 A/mgPt, respectively). After 10,000 cycles of accelerated durability test, the concave decahedra still exhibit a mass activity of 0.69 A/mgPt, more than twice that of the pristine Pt/C catalyst.

Twinned Gold Nanoparticles under Growth: Bipyramids Shape Controlled by Environment

The structure of (Au) bipyramids, very promising for their specific plasmonic properties, is fully analyzed for gradual stages of growth. From combined use of HRTEM (high resolution transmission electronic microscopy) in specific conditions and SAED (selected area electronic diffraction) analysis, the atomic structure of these elongated objects of different sizes is extracted (from 2 to 60 nm). In the case of silver(I)-assisted growth from citrate capped seeds, a clear pentatwinned structure, made by the superimposition of specific pairs of crystallographic zones is found for the different size nanoparticles representing the different steps of the growing bipyramids. The experimental results were analyzed in the framework of a recent atomistic approach developed for metal–environment interactions to account for the stability of multitwinned nanorods or bipyramids in a complex environment. Efficient in describing the multitwinned nanoparticles and the drastic effects of environment on the stabilization of elongated multitwinned shapes, this model supports the experimental features of bipyramids and nanorods formation from citrate seeds as a function of the nature of the surface chemical ligands: citrate seeds in a growth solution prepared without silver(I) yields the formation of a few pentatwinned nanorods, while the silver(I)-assisted growth process mainly leads to pentatwinned bipyramids. The conservation of a bulk pentatwinned structure inherited from isotropic decahedral (i-Dh) seeds all along the growth is retrieved by this approach for two different environments.

Five‐Fold Twinned Pd Nanorods and Their Use as Templates for the Synthesis of Bimetallic or Hollow Nanostructures

AbstractWe report the use of seed‐mediated growth for the facile synthesis of five‐fold twinned Pd nanorods with controlled diameters in the range of 6–16 nm and tunable lengths up to 81 nm. In this approach, the formation of decahedral seeds and their anisotropic growth could be deliberately performed under different conditions to obtain samples with high purity. Transmission electron microscopy studies revealed that the nanorods were formed through the deposition of Pd atoms onto the surfaces of decahedral seeds along the <110> direction. Subsequent mechanistic studies indicated that a combination of a proper reduction rate and an effective capping agent was crucial to the formation of Pd nanorods. With the use of these Pd nanorods as templates, we also demonstrated the synthesis of Pd–Pt bimetallic nanotubes, as well as Pd@Au and Pd@Ag core–sheath nanorods.

Ag−Au−Ag Heterometal Nanowires: Synthesis, Diameter Control, and Dual Transversal Modes with Diameter Dependency

We report on the synthesis of Ag−Au−Ag heterometal nanowires through an epitaxial seed-mediated growth of silver nanowires from gold decahedral seeds. The diameter of the Ag−Au−Ag nanowires is precisely controlled in a range of 60−150 nm by using gold decahedral seeds with corresponding edge sizes. The three transversally excited bulk, localized, and propagating modes exhibit optical signatures in the UV−vis spectra. In particular, the end-on incidence propagating mode is highly sensitive to the nanowire diameter. Such exact control of diameters and diameter-dependent surface plasmon modes are expected to be useful for photonic circuit elements and chemical and biosensors.

Silver/Gold Heterometallic Nanostructures and Their Surface Plasmon-related Behaviors

AbstractA combination of silver and gold is demonstrated in nanoscale objects. Silver and gold have similar but distinct chemical and physical properties. We employed three main chemistry related to silver and gold – underpotential deposition, epitaxial growth, and Galvanic replacement. Selective underpotential deposition of silver guided the growth direction of gold and generated gold octahedrons, cuboctahedrons, cubes, and rods. Epitaxial growth of silver on gold decahedral seeds formed silver-gold-silver heterometallic nanorods and wires. Galvanic replacement of silver for gold yielded asymmetric single hollow and symmetric double hollow structures. All silver/gold nanostructures exhibited characteristic optical features in the UV-vis-NIR ranges. Such structural variation and corresponding optical properties are useful for diverse applications in electronics, photonics, biology, and catalysis.

Process window for the synthesis of Ag wires through polyol process

A process window for the synthesis of Ag wires through the polyol process was established, in which long and uniform size of silver wires is obtained. The formation of decahedral seeds (leading to the formation of wires) is in competition with ordinary seeds (becoming spherical colloids) and heterogeneous nucleation and deposition on vessel walls. All of the various processes are in turn influenced by the supply rate of silver from reduction reactions. Adding silver nuclei before the reduction reaction could effectively decrease the wire diameter.

One-Dimensional Gold Nanostructures through Directed Anisotropic Overgrowth from Gold Decahedrons

One-dimensional gold nanorods were synthesized from gold decahedrons in the presence of silver ions by a systematic overgrowth approach. Both the diameters and lengths of the nanorods were independently varied by using distinct-sized decahedrons and gold precursor concentrations. The key factors of anisotropic growth are three-dimensional decahedral seed structures and energetic differentiation of the distinct facets. A series of copper and silver underpotential deposition (UPD) experiments confirmed that the silver components were mainly located on the Au(100) facets, which constitute the side walls of the nanorods. The growth mechanism of the gold nanorods could be clarified by an arbitrary elongation of the decahedral seeds and selective restriction of the {100} growth by silver UPD. Low temperature growth without silver generated very long nanowires by preferential adsorption of poly(vinyl pyrrolidone) on the {100} surface.

Photochemical Synthesis of Monodisperse Size-Controlled Silver Decahedral Nanoparticles and Their Remarkable Optical Properties

Monodisperse decahedral silver nanoparticles have been synthesized with excellent shape selectivity (>99%) by novel photochemical transformation of aqueous silver nanoparticle precursors. The procedure employs intense white light and is very robust and reproducible. The precursor solution transforms from a mixture of shapes dominated by small silver platelets into the decahedra, driven by superior stability of decahedral seeds. The decahedra size can be varied by adjusting intensity and spectral properties of the irradiating light. Furthermore, the decahedra can be controllably photochemically regrown to larger sizes, while fully preserving the monodispersity. Silver decahedra exhibit remarkable optical properties featuring a bicolored appearance due to the interplay between plasmonic adsorption and scattering. The sharp plasmon resonances of silver decahedra were tunable from 455 to 570 nm through size variation. Finally, silver decahedra exhibited greatly superior enhancement of Raman scattering compare...

Shape Adjustment between Multiply Twinned and Single-Crystalline Polyhedral Gold Nanocrystals: Decahedra, Icosahedra, and Truncated Tetrahedra

Polyhedral gold nanocrystals with decahedral, icosahedral, and truncated tetrahedral shapes are synthesized by a simple one-pot polyol process in the prescence of poly(vinyl pyrrolidone) (PVP). High PVP concentration up to 360 equiv of the gold precursor, HAuCl4, effectively stabilizes decahedral seeds to yield uniform decahedra with various edge sizes. Decreased PVP concentration subsequently leads to selective formation of icosahedra and truncated tetrahedra. This results from a combination between the relative energy difference of the polyhedral structures and the oxidative etching rate of the seeds by Cl-/O2 during the reaction. The distinct morphologies of gold nanocrystals exhibit characteristic extinction patterns in the UV−vis−NIR ranges, and these properties are successfully analyzed by the discrete dipole approximation (DDA) calculation. Most extinctions stem from the polar and azimuthal dipolar excitations, and azimuthal quardrupole resonance appears between two dipolar bands in the 88-nm decahedra. Given these shape- and size-dependent optical properties, gold nanocrystals hold considerable promise for biomedical and photonic applications.