Dendritic Gold Nanostructures Research Articles

Facile Synthesis of Dendritic Gold Nanostructures with Hyperbranched Architectures and Their Electrocatalytic Activity toward Ethanol Oxidation

Gold dendritic nanostructures with hyperbranched architectures were synthesized by the galvanic replacement reaction between nickel wire and HAuCl4 in aqueous solution. The study revealed that the morphology of the obtained nanostructures strongly depended on experimental parameters such as the HAuCl4 solution concentration, reaction temperature, and time, as well as stirring or not. According to the investigation of the growth process, it was proposed that gold nanoparticles with rough surfaces were first deposited on the nickel substrate and that subsequent growth preferentially occurred on the preformed gold nanoparticles, finally leading to the formation of hyperbranched gold dendrites via a self-organization process under nonequilibrium conditions. The electrochemical experiment results demonstrated that the as-obtained gold dendrites exhibited high catalytic activity toward ethanol electrooxidation in alkaline solution, indicating that this nanomaterial may be a potential catalyst for direct ethanol fuel cells.

Facile and controlled electrochemical route to three-dimensional hierarchical dendritic gold nanostructures

In this work, a facile, feasible and controlled electrochemical route was developed to prepare well-defined three-dimensional (3D) gold hierarchical dendrites (Au HDs) on a glassy carbon electrode by one-step electrodeposition, using the applied potential of 0.0V for 600s in the electrolyte containing 20mM HAuCl4, 150mM cytosine and 0.5M H2SO4. Cytosine played important roles in the synthesis of the Au HDs, while no seed, template or surfactant involved. The corresponding growth mechanism was discussed in some detail. The as-prepared Au nanocrystals were applied as Raman-active substrates for surface-enhanced Raman scattering (SERS) amplification detection of Pb2+ with high sensitivity.

One-Pot Synthesis of Dendritic Gold Nanostructures in Aqueous Solutions of Quaternary Ammonium Cationic Surfactants: Effects of the Head Group and Hydrocarbon Chain Length

Hierarchical, three-fold symmetrical dendritic gold was prepared in an aqueous solution of the quaternary ammonium cationic surfactant dodecyltrimethylammonium bromide (DTAB). Similar surfactants with different head groups and hydrocarbon chain lengths were also used for comparison. Two-fold and one-fold symmetrical dendritic gold nanostructures were obtained in N-dodecyl-N-methylpyrrolidinium bromide (C(12)-MPB) and dodecyltriethylammonium bromide (DTEAB) aqueous solutions, respectively. Longer hydrocarbon chain lengths were unfavorable for the formation of dendritic nanostructures. The interaction energies between the individual surfactants and Au (111) plane were calculated using molecular dynamics simulations. Based on a series of contrast experiments and molecular dynamics simulations, the possible growth mechanism and fabrication process of the dendritic structures were proposed. The DTAB-capped, three-fold gold dendrites exhibited good surface-enhanced Raman scattering (SERS) sensitivity toward rhodamine 6G (R6G), indicating their potential for use in SERS-based detections and analysis. This work provides a simple and effective strategy for fabricating dendritic gold nanostructures in aqueous solutions.

One-step growth of needle and dendritic gold nanostructures on silicon for surface enhanced Raman scattering

Light-induced deposition of gold nanostructures onto both n-type and p-type silicon was performed by galvanic displacement. On illuminating the n-type silicon with a 530 nm laser during the deposition process, a clustered deposit was observed whereas on using a 635 nm laser, gold nano-needles were formed. In comparison, on depositing gold on p-type silicon, flat dendritic structures were obtained and no significant changes in morphology were observed in the presence or absence of light. In the dark, only irregular gold clusters formed. The influence of light in changing the morphology was related to the surface plasmon resonance of the gold nuclei as well as the excess charge present in the conduction band of the silicon. To evaluate the sensoric property of the substrates, Raman spectroscopy was conducted on the metal–semiconductor couple for the detection of ruthenium red molecule. Among the substrates, the gold needle–silicon couple gave the highest surface enhanced Raman scattering (SERS) enhancement. We could also conclude from the SERS measurements that the metal–semiconductor interface plays an important role in increasing the SERS signal.

Seeded growth of two-dimensional dendritic gold nanostructures

We show that seeded growth can be applied to creating two-dimensional (2D) dendritic Au nanostructures on sample grids, which can be directly characterized by transmission electron microscopy (TEM). The 2D synthesis of highly consistent structures offers a novel mechanistic perspective on the aggregation of colloidal Au nanocrystals on a surface.

Ultrafast Preparation of Three-Dimensional Dendritic Gold Nanostructures in Aqueous Solution and Their Applications in Catalysis and SERS

Three-dimensional dendritic gold nanostructures were prepared via an ultrafast one-step homogeneous solution method. Cationic surfactants, decane-1,10-bis(methylpyrrolidinium bromide) ([mpy-C10-mpy]Br2), were used as the capping agent and l-ascorbic acid (AA) was used as the reducing agent. The as-prepared gold dendrites present a [111] plane and grow along the ⟨211⟩ direction. The AA plays an important role in the formation of the dendritic nanostructures. The methylpyrrolidinium quaternary ammonium headgroups and bolaform nanostructures of the surfactants are the key factors for the formation of dendritic structures. Further investigation revealed that the reaction time and concentration of HAuCl4 weakly affect the formation of the dendrites. Moreover, the obtained gold dendrites exhibit excellent activity toward the catalytic reduction of p-nitraniline and higher enhancement of surface-enhanced Raman scattering when using Rhodamine 6G as the model molecules.

Galvanic replacement mediated growth of dendritic gold nanostructures with a three-fold symmetry and their applications to SERS

Hierarchical, three-fold symmetrical, single-crystalline gold dendrites are synthesized on different metal substrates including Al, Zn, and Ni in a mixture of ethanol and water with the assistance of an ionic liquid. Structural characterizations suggest that the obtained gold dendrites are grown along the <211> directions. Such <211>-oriented gold dendrites are seldom reported. Both the metal substrate and the volume ratio of ethanol and water have demonstrated a significant effect on the dendrite morphologies. The obtained gold dendrites are found to yield large SERS enhancement factors for rhodamine 6G (R6G) and the morphology of the branches is a key for the enhancement.

Ultrafast growth of dendritic gold nanostructures and their applications in methanol electro-oxidation and surface-enhanced Raman scattering

A simple and rapid solution-phase synthesis of dendritic gold nanostructures with hyperbranched architecture is demonstrated in this report. Further investigations revealed that the morphology of the synthesized sample depended on proper parameters such as reagent concentration, reaction temperature, reagent addition sequence and stir. Moreover, the dendritic gold nanostructures exhibited a good electrocatalytic activity toward methanol electro-oxidation. When compared with sea-urchinlike and flowerlike gold nanostructures which were prepared by varying the parameters of experiment, dendritic gold nanostructures showed the highest surface-enhanced Raman scattering (SERS) sensitivity using 4-aminothiophenol (4-ATP) as probe molecules. The dendritic gold nanostructures may find potential applications in catalysis, SERS and biosensor.

A Facile Synthesis of Two-Dimensional Dendritic Gold Nanostructures at the Air/Water Interface

Two-dimensional dendritic gold nanostructures are synthesized at the air/water interface with the assistance of a special additive, [camphorC2mim]Cl, which can form a precipitate with AuCl4−. Interestingly, the precipitate is essential to the formation of dendritic nanostructures. Transmission electron microscopy (TEM) characterization reveals that the ratio of [camphorC2mim]Cl to HAuCl4 rather than the concentration is crucial to the morphology of the obtained dendritic nanostructures. A reasonable mechanism based on diffusion-limited aggregation (DLA) theory is proposed according to the high resolution TEM (HRTEM) characterization. The obtained gold dendrites are shown to yield a large surface-enhanced Raman scattering (SERS) enhancement for rhodamine 6G.

Facile fabrication of 3D dendritic gold nanostructures with an AuSn alloy by square wave potential pulse

Multifunctional three dimensional (3D) dendritic gold (DG) nanostructures have been synthesized facilely by square wave potential pulse (SWPP) with an Au 45Sn 55 (wt.%) alloy in an electrolyte of NaOH or H 2SO 4. The dendrite formation involves combined actions of selective removal of Sn, oxidation–reduction cycles (ORCs) of gold and intensive hydrogen evolution, wherein the nanopores from dealloying and the movement of hydrogen bubbles facilitate the dendrite formation by rearranging the newly produced Au atoms from the ORCs. An alkaline medium is preferable and the dendritic structure can be obtained as quickly as in 100 s. Some applications have been demonstrated with the prepared DG including electrocatalytic oxidation of glucose, surface-enhanced Raman scattering, and superhydrophobicity.

3D dendritic gold nanostructures: seeded growth of a multi-generation fractal architecture

In this report, we focus on the synthetic challenges for nanoscale 3D fractal architectures, namely the multi-generation growth with control in both size uniformity and colloidal stability; by directing the simultaneous growth of Au and polyaniline on Au seeds, fractal nanoparticles can be achieved with a topology distinctively different from those of spheres, cubes or rods.

Controlled Synthesis of Dendritic Gold Nanostructures Assisted by Supramolecular Complexes of Surfactant with Cyclodextrin

Controlled synthesis of well-defined planar Au nanodendrites with a symmetric single-crystalline structure consisting of trunks and side branches grown along the 211 directions was realized by reducing chloroauric acid in aqueous mixed solutions of dodecyltrimethylammonium bromide (DTAB) and beta-cyclodextrin (beta-CD). It has been revealed that the formation of the supramolecular complexes of DTAB with beta-CD due to host-guest interaction is indispensable for the fabrication of these unique planar Au nanodendrites, and a proper CD-to-DTAB molar ratio is essential to their exclusive formation. A variety of Au nanostructures, such as branched particles consisting of rodlike branches and flowerlike particles consisting of platelike petals, could be readily obtained by simply changing the CD-to-DTAB molar ratio. Moreover, the obtained Au nanodendrites exhibited both a good electrocatalytic activity toward the oxidation of methanol and a good surface-enhanced Raman scattering (SERS) sensitivity for detecting p-aminothiophenol (PATP) molecules, indicating their potential applications including catalysis, biosensing, and nanodevices.

Surfactant-Directed Multiple Anisotropic Gold Nanostructures: Synthesis and Surface-Enhanced Raman Scattering

A facile and effective method for the synthesis of gold nanostructures using beta-cyclodextrin in aqueous alkaline medium is reported. The results demonstrate that leaf-like, rugged, dendritic, and tadpole-shaped gold nanostructures are obtained with high yield for the first time under the same experimental conditions by using four different surfactants. To study the effect of surfactant on the shape of the nanoparticles, the experiments were also carried out in the absence of surfactant and in the presence of poly(1-vinyl-2-pyrrolidone). The growth process of the dendritic gold nanostructures formed was investigated by withdrawing samples from the heated solution and examining the intermediate products formed by transmission electron microscopic analysis. The formation mechanism of the anisotropic gold nanostructures is discussed, and it is demonstrated that the cooperative effect of cyclodextrin and the surfactant molecules determines the ultimate morphology of the gold nanostructures obtained. In addition, the effect of the as-prepared nanostructures as an active material in surface-enhanced Raman scattering has been investigated by employing 4-aminothiophenol as a probe molecule. Thus, different enhancement signals are obtained for the different nanostructures; the dendritic nanostructures showed the strongest intensity of the SERS signals and smallest for the leaf-like nanostructures.

Implantation and Growth of Dendritic Gold Nanostructures on Graphene Derivatives: Electrical Property Tailoring and Raman Enhancement

Interfacing electron-rich metal nanoparticles with graphene derivatives can sensitively regulate the properties of the resultant hybrid with potential applications in metal-doped graphene field-effect transistors (FETs), surface-enhanced Raman spectroscopy, and catalysis. Here, we show that by controlling the rate of diffusion and catalytic reduction of gold ions on graphene oxide (GO), dendritic "snowflake-shaped" gold nanostructures (SFGNs) can be templated on graphene. The structural features of the SFGNs and their interfacing mechanism with GO were characterized by microscopic analysis and Raman-scattering. We demonstrate that (a) SFGNs grow on GO-surface via diffusion limited aggregation; (b) SFGN's morphology (dendritic to globular), size (diameter of 150-500 nm and a height of 45-55 nm), coverage density, and dispersion stability can be controlled by regulating the chemiophysical forces; (c) SFGNs enhance the Raman signal by 2.5 folds; and (d) SFGNs act as antireduction resist during GO-SFGN's chemical reduction. Further, the SFGNs interfacing with graphene reduces the apparent band gap (from 320 to 173 meV) and the Schottky barrier height (from 126 to 56 meV) of the corresponding FET.

Ionic Liquid-Assisted Growth of Single-Crystalline Dendritic Gold Nanostructures with a Three-Fold Symmetry

Hierarchical, three-fold symmetrical, single-crystalline gold dendrites were synthesized by the reaction between a zinc plate and a solution of HAuCl4 in the ionic liquid [BMIM][PF6]. The unique dendritic gold nanostructures show a three-order hierarchy (i.e., a three-fold symmetrical <111>-oriented trunk, three groups of trident-like <111>-oriented branches grown on the trunk, and many <111>-oriented nanorod leaves grown on the branches symmetrically), indicating an interesting fractal growth. According to the investigation on the growth process of the gold dendrites, it was proposed that gold nuclei nanocrystals first formed on the zinc substrate through a direct surface reaction and that the subsequent crystal growth preferentially took place on the preformed gold crystals through a primary cell reaction, leading to the formation of the final hyperbranched dendrites under nonequilibrium conditions. In contrast, AuZn alloy dendrites consisting of aggregated primary nanoparticles were produced when the ionic liquid solution was replaced by an aqueous solution. It was proposed that the significantly lowered ion diffusivity and reaction rate in the ionic liquid medium could largely contribute to the formation of the pure single-crystalline gold dendrites. Moreover, electrocatalytic measurements performed in alkaline solution suggested that the obtained dendritic gold nanostructures exhibited good electrocatalytic activity toward the oxidation of methanol, which might be related to the special three-order hierarchical architectures.

Synthesis and Characterization of 3D Dendritic Gold Nanostructures and Their Use as Substrates for Surface-Enhanced Raman Scattering

Three-dimensional dendritic gold nanostructures (3D-DGNs) were prepared at room temperature through an aqueous/organic interfacial reaction of hydrogen tetrachloroaurate (HAuCl4, in aqueous phase) and 3,4-ethylenedioxythiophene (EDOT, in organic phase) without the use of any seeds, templates, surfactants, or stabilizers. SEM and TEM studies indicated that the 3D-DGNs compose of numerous nanowires with diameters around 30 nm and each wire brings a nanosheet head with thickness of 80 ± 5 nm. The effects of reaction conditions including the concentrations of HAuCl4 and EDOT, the reaction temperature, and the organic solvents on the morphology of 3D-DGNs were systematically investigated and a possible mechanism for the formation of 3D-DGNs was proposed. The 3D-DGNs can be used as substrates for surface-enhanced Raman scattering (SERS). They exhibited much higher surface enhancement than those of conventional electrochemically roughed gold surfaces and gold nanorods when 4-mercaptopyridine (4MP) was used as a molecule probe. The enhancement factor of 3D-DGN substrate was measured to be (1.9 ± 0.4) × 106, and the limit of detection (LOD) was determined to be lower than 1 × 10-10 M.