Ultrathin Au Nanowires Research Articles

Water-phase synthesis of Au and Au-Ag nanowires and their SERS activity.

Metal nanowires (NWs) with a diameter of a few nanometers have attracted considerable attention as a promising one-dimensional nanomaterial due to their inherent flexibility and conductive properties and their weak plasmon absorption in the visible region. In a previous paper, we reported the synthesis of ultrathin 1.8 nm-diameter Au NWs using toluene-solubilized aqueous solutions of a long-chain amidoamine derivative (C18AA). This study investigates the effect of different organic solvents solubilized in C18AA aqueous solutions on the morphology of the Au products and demonstrates that solubilizing methylcyclohexane yields thick 2.7 nm-diameter Au NWs and 3.3 nm-diameter Au-Ag alloy NWs. Further, the surface-enhanced Raman scattering sensitivity of ultrathin Au NWs, thick Au NWs, and thick Au-Ag alloy NWs were assessed using 4-mercaptopyridine and found that their enhancement factors are 104-105 and the order is Au-Ag NWs > thick Au NWs > ultrathin Au NWs.

Designing anisotropic inorganic nanocapsules via self-assembly of polymer-like ultrathin Au nanowires.

Anisotropic assembly of nanomaterials into hollow structures is an attractive technique in biomedicine and biosensing. Commonly used polymer materials are easy to assemble yet it is hard to form anisotropic morphologies. Here in this work, we successfully prepared a novel gold nanocapsule with an anisotropic ellipsoidal shape and cavity structure by the self-assembly of ultrathin Au nanowires. The assembly mechanism is further studied by tuning the assembly conditions such as nanowire concentration, solvent composition, and temperature. It is found that the controlling forces of the nanowire assembly process are mainly the symmetric interfacial tension and the asymmetric nanowire deformation potential, which contribute together to result in anisotropic nanocapsules. Finally, the obtained Au nanocapsules were used as nanocarriers to load pyrene as a model drug, showing great drug loading ability and pH-responsive drug release behavior. We believe that this unique anisotropic assembly product will bring new insights into nanostructure design and soft matter research.

Template-less Synthesis of Coded Au Nanowires.

Morphological coding of nanostructures represents a capability in rapid modulation of structural features and most importantly, the transcription of information into nanoscale. Exploiting the regioselectivity in the template-less electrochemical synthesis of ultrathin Au nanowires, we show that rapid alternation of applied potential would cause corresponding change in the width of the emerging nanowire segments. By understanding the growth kinetics, a strong correlation between the nanowire morphologies and the deposition potential is established and applied in emulating the Morse code.

Cold welding assisted self-healing of fractured ultrathin Au nanowires

In nano-electronic field, cold welding is a simple novel method to join ultrathin noble metal nanowires (NWs) without introducing extra energy and defects. In previous works, it always occurred between ultrathin noble metal NWs, tensile fracture parts of a single NW, or a NW formation from nanoparticles. However, some external force is still needed to drive the materials as close to each other as possible before the process. Here, we proposed a new method to achieve cold welding without introducing artificial loadings. The bending fractured ultrathin gold (Au) NW can be self-healed assisted by cold welding during the removal of the tungsten (W) tip by in situ transmission electron microscope (TEM). A new interface with lattice mismatch formed in the welding zone after multiple periodic cycles, leaving an angle between the two rebonded fracture parts. Furthermore, the cold welding assisted self-healing of the bending fractured ultrathin Au NW and atom evolutions were also confirmed by molecular dynamics (MD) simulations. The successful implementation of cold welding makes the self-healing come true when the ultrathin Au NW fractures under the unexpected vibrations.

Water-Phase Synthesis of Ultrathin Au Nanowires with a Two-Dimensional Parallel Array Structure

Abstract Ultrathin Au nanowires (NWs) with a diameter below 2 nm have attracted considerable attention as a promising one-dimensional nanomaterial. However, they are practically synthesized in organic solvents. Here, for the first time, we report the synthesis of ultrathin Au NWs with ∼1.7 nm diameter in water using a water-soluble long-chain amidoamine derivative (C18AA) as a key compound. The resultant Au NWs were naturally dispersible in water, which is an environment-friendly solvent. We also demonstrate that the formation of the Au NWs is based on oriented-attachment growth mechanism, and that the presence of Cl− ion facilitates its effective elongation over a length of a few µm. Further, cryogenic transmission electron microscopy (cryo-TEM) of the aqueous dispersion revealed that the Au NWs self-assembled into a bundle structure with two-dimensional parallel arrays in water.

Trimetallic Au@PdPb nanowires for oxygen reduction reaction

The development of highly efficient and stable Pd-based catalysts is crucial to improve their sluggish oxygen reduction reaction (ORR) kinetics in acid media. To improve ORR activity and utilization efficiency of Pd, an ideal catalyst should have ORR-favorable chemical environment, optimized geometric structure, and long periods of operation. In this work, we first synthesize a novel trimetallic Au@PdPb core-shell catalyst consisting of PdPb alloy nano-layers grown on the surface of ultrathin Au nanowires (NWs) by a two-step water-bath method. The Au@PdPb NWs have the merits of anisotropic one-dimensional nanostructure, high utilization efficiency of Pd atoms and doping of Pb atoms. Because of the structural and multiple compositional advantages, Au@PdPb NWs exhibit remarkably enhanced ORR activity with a high half-wave potential (0.827 V), much better than those of commercial Pd black (0.788 V) and bimetallic Au@Pd NWs (0.803 V). Moreover, Au@PdPb NWs display better electrocatalytic stability for the ORR than those of Pd black and Au@Pd NWs. This study demonstrates the validity of our approach for deriving highly ORR-active Pd-based catalysts by modifying their structure and composition.

Controllable syngas production on gold nanowires/nickel foam electrode in non-aqueous system

A hierarchical electrode is prepared with Au nanowires grown on nickel foam. With large specific active surface area, it is used for producing syngas (H2/CO) with controllable ratio, through electrochemical process in DMF. The synthetic innovation lies in the use of 3-cyanopropyltriethoxysilane, to achieve the adsorption of appropriate amount of Au seeds for the one-dimensional growth of ultrathin Au nanowires (d ≈ 5 nm). With the nanowires forest on the three-dimensional porous nickel foam substrate, syngas is produced by electro-catalysis with high overall Faradic efficiency and tunable H2/CO ratios. This synthetic strategy opens a facile way to synthesize the hierarchical nanostructured materials, and broaden the choice of the catalysts for electrochemical applications.

Braiding Ultrathin Au Nanowires into Ropes.

Braiding is a common skill in daily life but rare at the nanoscale. Most of the current nanohelices are directly grown or assembled without involving mechanical interactions, and they are thus distinctively different from ropes in terms of functions and mechanisms. Here, by coaxially twisting multiple ultrathin Au nanowires, nanoropes are synthesized with elegant helical patterns that are consistent with the macroscopic equivalents. The strain relaxation of lattice transformation causes the nanowires to pursue the maximum degree of twisting, while the mutual packing interactions in a bundle prevent sideways emergence of U-turns. The consistent chirality of the seemingly independent strands can only arise when a first twisting strand causes morphological deformation in its neighbors, which induces the collective uni-directional twisting. The spontaneous braiding and the "remote" control of the nanowires involve mechanical interactions and possibly energy transmission, thus opening doors to chiral assembly and future smart nanodevices.

1-nm-Wide Hydrated Dipole Arrays Regulate AuNW Assembly on Striped Monolayers in Nonpolar Solvent

Summary We show that striped phases of horizontally oriented phospholipids presenting 1-nm-wide orientable dipole arrays can order and straighten flexible 2-nm-diameter gold nanowires (AuNWs) with lengths (up to 1 μm) that greatly exceed the template pitch (∼7.5 nm). AuNW ordering can extend over areas > 100 μm2. Whereas wires bundle in solution, with contact between ligand shells, wires adsorbing to the template separate to much larger center-to-center distances (e.g., 12–30 nm) near multiples of the template pitch, consistent with repulsive interactions between wires emerging during interactions with dipole arrays in the template. AuNW assembly was carried out in cyclohexane, a nonpolar solvent. Interestingly, we found that wire ordering was contingent on the extent of phospholipid headgroup hydration and the presence of excess oleylamine, which assembled into hemicylindrical micelles around the hydrated headgroups. Together, these components generated a protected polar environment that enabled the phospholipid headgroups to function collectively to regulate AuNW assembly.

Enhancement of Raman signal from analytes on ultrathin Au and AuCu alloy nanowire network substrates

Network of ultrathin Au and AuCu alloy nanowires of diameter ∼3.5 nm were used to design novel substrates for surface-enhanced Raman spectroscopy (SERS) for detection of ppm level of analyte molecule, Rhodamine 6 G. The ultrathin morphology and geometry of the wire network resulted in a 20-fold enhancement in the signal as compared to a substrate with Au or AuCu particles of the same concentration. Raman signal enhancement on AuCu nanowire array has been found to be higher than on Au nanowire array. This observation has been corroborated by theoretical simulations as well. The effect of excitation wavelength on the enhancement has been studied for different analyte molecules on Au and AuCu nanowire ensemble as the SERS substrate. The effect of polarization of the laser source with respect to the anisotropic bunch of nanowires on the Raman signal was also studied.

Sequential Ligand Exchange of Coordination Polymers Hybridized with In Situ Grown and Aligned Au Nanowires for Rapid and Selective Gas Sensing.

Combining polymeric materials and conductive one-dimensional metal nanostructures is able to achieve enhanced chemical and electrical properties, but the control over their morphology and spatial arrangement remains a big challenge. Herein, by replacing benzenedicarboxylate (BDC) in ZnBDC nanoplates with oleylamine (OAM) in the presence of HAuCl4, Zn-OAM nanobelts with a highly ordered laminar structure were obtained, on which ultrathin Au nanowires (Au NWs) were deposited and aligned along the long axes of the nanobelts. The resulting Zn-OAM/Au NW hybrid further underwent an OAM-to-2-methylimidazole ligand exchange, resulting in the formation of porous nanobelts composed of ZIF-8 nanocrystals interwound with aligned Au NWs. Due to the synergistic effect between the polymeric and metallic structures, the Zn-OAM/Au NW hybrid nanobelts and ZIF-8/Au NW porous nanobelts demonstrated fast and selective gas sensing at ambient conditions, in sharp contrast to the nonresponsive Au NWs or Zn-based polymers alone.

Solution synthesis of helical gold nanowire bundles

Helical nanostructures are important nanoscale building blocks. While only a few methods are available for synthesizing helical metal nanostructures, those involving collective twisting behaviour are even fewer. Here, we report a solution synthesis of Au nanowire bundles with hierarchical helical constructions. Ultrathin nanowires with diameters of only about 10 nm formed huge ribbon bundles that have a width of 0.5-1 μm and thickness of a few hundreds of nanometres. These bundles extended to hundreds of micrometres and curled into helices. Mechanism studies revealed that the white floccules formed by Au(i) and a thiol ligand are of critical importance for both the nanowire growth and helical bundle formation. The nanowire growth took place in the floccules following the previously reported active surface growth mode, and the bundle formation was due to the splitting of the active surface. Most importantly, the floccules assisted the strain-induced curling process that yielded helices. As the length of the bundles keeps increasing and they break out from the surrounding floccules, they would have to pass through the pores of the floccules. The imbalanced squeezing at the pore caused the bundles to curl into helices.

New Insights into the Growth Mechanism of Ultrathin Au Nanowires from Combined in Situ EXAFS and SAXS Studies

The synthesis of Au nanowires (NWs) in hexane solution of HAuCl4·3H2O, oleylamine and triisopropylsilane at room temperature was “in situ” monitored by means of X-ray absorption fine structure spectroscopies and small-angle X-ray scattering to determine, under identical synthesis conditions, both the changes in the oxidation state of gold atoms and the evolution of the size and shape of the objects involved in the formation of Au NWs. We propose a multistage process for the formation of the NWs: first, Au(III) atoms form a planar-square geometry complex that is continuously reduced to give Au(I) disk-like structures with diameters bigger than that of the final NWs. In a second stage, characteristic length/thickness ratio of these disk-like objects increases to form cylinders, presumably through aurophilic interactions between Au(I) centers and stacking of the disks. When most of the Au atoms have been reduced to Au(I), the reduction to Au(0) begins (third stage), and the NWs grow to form an hexagonal arra...

Twisting Ultrathin Au Nanowires into Double Helices

Previously, double helix nanowire was reported by coating Pd/Pt/Au onto Au-Ag alloy nanowire. Here, straight oleylamine-stabilized ultrathin Au nanowires with single crystalline fcc lattice are surprisingly converted into double helix helices upon reacting with Ag in tetrahydrofuran (THF). The obtained Au-Ag helical nanowires contain lattice distinctively different from the fcc lattice and are different in many aspects with the previous system. The discovery may expand the scope of nanoscale double helix formation and the understanding of lattice transformation among ultrafine nanostructures.

Robust bifunctional oxygen electrocatalyst with a \u201crigid and flexible\u201d structure for air-cathodes

The development of highly active air-cathodes with robust stability and a low price is of crucial significance for rechargeable Zn–air batteries and remains a great challenge. Herein, for the first time, we report a “rigid and flexible” material consisting of three-dimensional (3D) porous nickel-manganese oxide (Ni6MnO8) coupled with 1D ultrathin Au nanowires (Au-NWs) as an efficient bifunctional oxygen electrocatalyst, adopting α-naphthol-Au(III) as a precursor of Au-NWs and pre-formed Ni6MnO8 as a support. Ni6MnO8 acts not only as a robust carbon-free support that is stable in alkaline electrochemical conditions, but also as a highly active component for the oxygen evolution reaction (OER), while flexible Au-NWs contribute to the excellent oxygen reduction reaction (ORR) activity and act as a flexible conductive electronic network. The coupling of Ni6MnO8 and Au-NWs plays a complementary role in the two types of oxygen electrocatalytic reactions. Accordingly, their advantages have been optimally harnessed while overcoming their deficiencies. Moreover, a Zn–air battery assembled with such a rigid and flexible air-cathode has lower charge and discharge overpotentials and a higher cyclic stability than those with a mixed Pt/C+RuO2 catalyst.

Separation of gold nanowires and nanoparticles through a facile process of centrifugation

Abstract We demonstrate a facile process of centrifugation for the successful separation of Au nanowires (NWs) and nanoparticles (NPs). The products before/after separation were characterized by transmission electron microscopy (TEM, high-resolution TEM, bright and conical dark filed TEM) and UV–vis absorption spectroscopy. In addition, Au NWs exhibit stronger surface-enhanced Raman scattering ability relative to that of Au NPs. The current process could be used for separation and purification of other metal nanomaterials with different shapes. The further assembling ultrathin Au NWs and monodispersed Au NPs have great potential applications including sensors and electronic devices.

Ultrathin Au nanowires assisted magnetic graphene-silica ZIC-HILIC composites for highly specific enrichment of N-linked glycopeptides

Protein glycosylation has been proven to participate in a variety of complex biological processes; however, the low abundance of glycopeptides in natural samples makes it essential to develop methods to isolate and enrich glycopeptides. In this study, a novel ultrathin Au nanowire assisted zwitterionic hydrophilic magnetic graphene oxide (GO-Fe3O4/SiO2/AuNWs/L-Cys) was synthesized with the good biocompatibility of GO, strong magnetic responses of Fe3O4, large surface area of ultrathin Au nanowires and excellent hydrophilicity of L-Cys via four simple and rapid steps. The ultrathin Au nanowires have a one-dimensional structure and were easily grafted with an abundant amount of L-Cys for the enrichment of glycopeptides. After the GO-Fe3O4/SiO2/AuNWs/L-Cys composites were applied to glycopeptide enrichment, 26 glycopeptides from a human IgG digest could be identified, with a detection limit as low as 10 fmol. Due to the abundant amount of grafted L-Cys, the composites also showed a large binding capacity (150 μg mg−1). Furthermore, the composites were applied for the analysis of real biological samples. A total of 793 glycopeptides from 467 glycoproteins were identified in three replicate analyses of 40 μg of mouse liver proteins. The results demonstrated the great potential of GO-Fe3O4/SiO2/AuNWs/L-Cys composites for the analysis of glycoproteins.

Assembly of Ultrathin Gold Nanowires into Honeycomb Macroporous Pattern Films with High Transparency and Conductivity

Because of its promising properties, honeycomb macroporous pattern (HMP) film has attracted increasing attention. It has been realized in many artificial nanomaterials, but the formation of these HMPs was attributed to templates or polymer/supermolecule/surfactant assistant assembly. Pure metal HMP film has been difficult to produce using a convenient colloidal template-free method. In this report, a unique template-free approach for preparation of Au HMP film with high transparency and conductivity is presented. Ultrathin Au nanowires, considered a linear polymer analogue, are directly assembled into HMP film on various substrates using a traditional static breath figure method. Subsequent chemical cross-linking and oxygen plasma treatment greatly enhance the stability and conductivity of the HMP film. The resulting HMP film exhibits great potential as an ideal candidate for transparent flexible conductive nanodevices.

Exploring the Multifunctionality of a Novel Long-Chain Amidoamine Amphiphile.

In this review, we demonstrate that the practical applications of a novel long-chain amidoamine derivative with a simple molecular structure (C18AA) are equivalent to or higher in number than those of supramolecules with complex molecular structures. Molecular assemblies of C18AA exhibit distinctive thermal responsiveness; namely, C18AA can form a gel with apolar organic solvents, while O/W emulsions of C18AA act as a heat-induced gelator that undergoes a phase transition from solution to gel upon heating. We also show that C18AA emulsions containing a quaternary ammonium salt develop an iridescent color over a specific temperature range. Further, molecular assemblies of C18AA serve as high-performance soft templates for the preparation of shape-controlled metal nanocrystals such as ultrathin Au nanowires and Pd nanowires.

Atomic-Level-Designed Catalytically Active Palladium Atoms on Ultrathin Gold Nanowires.

A Ag monolayer facilitates the deposition of isolated Pd atoms rather than continuous ones on ultrathin Au nanowires. During the hydrogenation of nitrophenol and the electrooxidation of ethanol, these two groups of Pd atoms show distinctive but geometry-dependent catalytic activity. This new atomic geometry maneuvering strategy is ready for the atomically precise design of nanocatalysts.