Gold nanowire networks: synthesis, characterization, and catalytic activity

Gold nanowire networks (AuNWNs) with average widths of 17.74 nm (AuNWN(1)) or 23.54 nm (AuNWN(2)) were synthesized by direct reduction of HAuCl(4) with sodium borohydride powder in deep eutectic solvents, such as ethaline or reline, at 40 °C. Their width and length were dependent on the type of solvent and the NaBH(4)/HAuCl(4) molar ratio (32 in ethaline and 5.2 in reline). High resolution transmission electron microscopy (HR-TEM) analysis of the gold nanowire networks showed clear lattice fringes of polycrystalline nanopowder of d = 2.36, 2.04, 1.44, and 1.23 ? corresponding to the (111), (200), (220), or (311) crystallographic planes of face centered cubic gold. The purified AuNWNs were used as catalysts for the chemical reduction of p-nitroaniline to diaminophenylene with sodium borohydride in aqueous solution. The reaction was monitored in real time by UV-vis spectroscopy. The results show that the reduction process is six times faster in the presence of gold nanowire networks stabilized by urea from the reline (AuNWN(2)) than in the presence of gold nanowire networks stabilized by ethylene glycol from ethaline (AuNWN(1)). This is due to a higher number of corners and edges on the gold nanowires synthesized in reline than on those synthesized in ethaline as proven by X-ray diffraction (XRD) patterns recorded for both types of gold nanowire networks. Nevertheless, both types of nanomaterials determined short times of reaction and high conversion of p-nitroaniline to diaminophenylene. These gold nanomaterials represent a new addition to a new generation of catalysts: gold based catalysts.     

Synthesis and Characterization of ZnO Nanowires

Zinc oxide is a wide bandgap (3.37 eV) semiconductor with a hexagonal wurtzite crystal structure. ZnO prepared in nanowire form may be used as a nanosized ultraviolet light-emitting source. In this study, ZnO nanowires were prepared by vapor-phase transport of Zn vapor onto gold-coated silicon substrates in a tube furnace heated to 900 ?C. Gold serves as a catalyst to capture Zn vapor during nanowire growth. Size control of ZnO nanowires has been achieved by varying the gold film thickness…     

Surfactantless synthesis of multiple shapes of gold nanostructures and their shape-dependent SERS spectroscopy

A useful method for the synthesis of various gold nanostructures is presented. The results demonstrated that flowerlike nanoparticle arrays, nanowire networks, nanosheets, and nanoflowers were obtained on the solid substrate under different experimental conditions. In addition, surface-enhanced Raman scattering (SERS) spectra of 4-aminothiophenol (4-ATP) on the as-prepared gold nanostructures of various shapes were measured, and their shape-dependent properties were evaluated. The intensity of the SERS signal was the smallest for the gold nanosheets, and the flowerlike nanoparticle arrays gave the strongest SERS signals.     

Effect of (L:D) Aspect Ratio on Single Polypyrrole Nanowire FET Device

Effect of different aspect ratio (length to diameter ratio, L:D) on single polypyrrole (Ppy) nanowire based field effect transistor (FET) sensor for real time pH monitoring was studied. Ppy nanowires with diameters of ~60, ~80 and ~200 nm were synthesized using electrochemical deposition inside anodized aluminium oxide (AAO) template and were assembled using AC dielectrophoretic alignment followed by maskless anchoring on a pair of gold electrodes separated with different gap lengths. Microfabricated gold electrode patterns with gap size between 1 - 4 μm were developed by means of MEMS technique (photolithography). Using field effect transistor geometry with pair of microfabricated gold contact electrodes serving as a source and a drain, and a platinum (Pt) mesh (anchored in a microfluidic channel) was used as a gate electrode. When effect of different aspect ratio of the nanowire were compared, higher sensitivity was recorded for higher aspect ratio. The sensitivity was further improved by modulating the gate potential. These FET sensors based on single polypyrrole nanowire exhibited excellent and tunable sensitivity towards pH variations.     

Wires, plates, flowers, needles, and core-shells: diverse nanostructures of gold using polyaniline templates

A simple and versatile method for the synthesis of a wide range of polyaniline (PANI)-based 1D and 2D gold nanostructures of uniform size distribution with high colloidal stability is demonstrated. All the nanostructures were synthesized from oligoaniline-coated gold nanoparticle precursors. The nanostructures include nanowires of various sizes, nanoplates, and flower-like nanoparticles. These nanowires showed a pH-dependent shape transformation. Needle-like aggregates of Au/PANI were formed as the pH of the nanowire solution changed to 2.5. At higher pH (10.2), nanowires converted into spherical nanoparticles. Core-shell particles of Au/PANI composites have been achieved by the reversal of the pH of the nanowire from 10.2 to 2.9. The morphology of the nanostructures was studied by TEM and SEM. FTIR, UV-vis, XRD, and LDI MS were utilized for the characterization of the chemical composition of the nanostructures. A mechanism for the nanowire growth is proposed.     

Single on-chip gold nanowires for electrochemical biosensing of glucose

The development of glucose diagnostic devices with low detection limits is of key importance in diabetes-related research. New highly sensitive sensors are required for non-invasive detection of glucose in bodily fluids, other than blood, and an electrochemical sensor based on a single gold nanowire for rapid, reliable and quantitative detection of low glucose concentrations (10 μM-1 mM), is presented in this paper. Single gold nanowire devices are fabricated at silicon chip substrates using a hybrid electron beam-photolithography approach. Critical dimensions of the nanowires are characterised using a combination of scanning electron and atomic force microscopies. Fabricated nanowire devices are characterised by direct electrical probing and cyclic voltammetry to explore functionality. The voltammetric detection of glucose was performed using ferrocene monocarboxylic acid as an oxidising mediator in the presence of glucose oxidase. The biosensor can be applied to the quantification of glucose in the range of 10 μM-100 mM, with an extremely high sensitivity of 7.2 mA mM(-1) cm(-2) and a low detection limit of 3 μM (S/N = 3). The sensor demonstrated high selectivity towards glucose with negligible interference from other oxidizable species including uric acid, ascorbic acid, mannose, fructose, salicylic acid (Aspirin) and acetaminophen (Paracetamol).     

柔性不锈钢基底上一维TiO_2纳米线薄膜的制备及表征

采用直流磁控溅射的方法在柔性不锈钢基底(50μm)上沉积纯钛薄膜,后在NaOH碱溶液中经水热法制备了非钛基大长径比的一维TiO2纳米线薄膜,并通过场发射扫描电子显微镜(FESEM)、X射线衍射(XRD)、透射电子显微镜(TEM)以及光电化学的方法对不锈钢基一维TiO2纳米线薄膜进行了表征.结果表明,纯钛薄膜的致密度、结晶性能以及与基底的结合强度均随衬底温度的升高而加强;在10mol·L-1NaOH浓度下,生长一维TiO2纳米线结构的适宜温度为130-150℃;TiO2纳米线长度达到几个微米,直径在10-30nm之间,并且相互交叉生长,构成一个三维网络结构.此外,在Na2SO4溶液中对TiO2纳米线薄膜进行了线性扫描和瞬态光电流测试,结果表明,一维TiO2纳米线薄膜电极较TiO2纳米颗粒电极表现出更优异的光电化学性能.这种磁控溅射与水热反应相结合的方法,为非钛异质基底上制备一维TiO2纳米线薄膜提供了新的思路.     

Reduced graphene oxide conjugated Cu2O nanowire mesocrystals for high-performance NO2 gas sensor

Reduced graphene oxide (rGO)-conjugated Cu(2)O nanowire mesocrystals were formed by nonclassical crystallization in the presence of GO and o-anisidine under hydrothermal conditions. The resultant mesocrystals are comprised of highly anisotropic nanowires as building blocks and possess a distinct octahedral morphology with eight {111} equivalent crystal faces. The mechanisms underlying the sequential formation of the mesocrystals are as follows: first, GO-promoted agglomeration of amorphous spherical Cu(2)O nanoparticles at the initial stage, leading to the transition of growth mechanism from conventional ion-by-ion growth to particle-mediated crystallization; second, the evolution of the amorphous microspheres into hierarchical structure, and finally to nanowire mesocrystals through mesoscale transformation, where Ostwald ripening is responsible for the growth of the nanowire building blocks; third, large-scale self-organization of the mesocrystals and the reduction of GO (at high GO concentration) occur simultaneously, resulting in an integrated hybrid architecture where porous three-dimensional (3D) framework structures interspersed among two-dimensional (2D) rGO sheets. Interestingly, "super-mesocrystals" formed by 3D oriented attachment of mesocrystals are also formed judging from the voided Sierpinski polyhedrons observed. Furthermore, the interior nanowire architecture of these mesocrystals can be kinetically controlled by careful variation of growth conditions. Owing to high specific surface area and improved conductivity, the rGO-Cu(2)O mesocrystals achieved a higher sensitivity toward NO(2) at room temperature, surpassing the performance of standalone systems of Cu(2)O nanowires networks and rGO sheets. The unique characteristics of rGO-Cu(2)O mesocrystal point to its promising applications in ultrasensitive environmental sensors.     

Formation of gold-silver nanowires in thin surfactant solution films

Thin, long gold/silver nanowires were grown on substrates in thin surfactant solution films. This growth process occurred exclusively in thinning aqueous films as the water evaporated, and elongated surfactant template structures were formed. The nanowire growth depended on the presence of a relatively high concentration of silver ions (typical Ag:Au mole ratio of 1:1). Tuning the pH value to about 5 in the growth solution was crucial for the nanowire growth. Further development of this process may lead to a simple wet chemical technique for the fabrication of relatively uniform arrays of metal nanowires on surfaces.     

Metallic Co4N Porous Nanowire Arrays Activated by Surface Oxidation as Electrocatalysts for the Oxygen Evolution Reaction

Designing highly efficient electrocatalysts for oxygen evolution reaction (OER) plays a key role in the development of various renewable energy storage and conversion devices. In this work, we developed metallic Co₄N porous nanowire arrays directly grown on flexible substrates as highly active OER electrocatalysts for the first time. Benefiting from the collaborative advantages of metallic character, 1D porous nanowire arrays, and unique 3D electrode configuration, surface oxidation activated Co₄N porous nanowire arrays/carbon cloth achieved an extremely small overpotential of 257 mV at a current density of 10 mA cm⁻², and a low Tafel slope of 44 mV dec⁻¹ in an alkaline medium, which is the best OER performance among reported Co‐based electrocatalysts to date. Moreover, in‐depth mechanistic investigations demonstrate the active phases are the metallic Co₄N core inside with a thin cobalt oxides/hydroxides shell during the OER process. Our finding introduces a new concept to explore the design of high‐efficiency OER electrocatalysts.     

Interactions of neutral and cationic transition metals with the redox system of hydroquinone and quinone: theoretical characterization of the binding topologies, and implications for the formation of nanomaterials

To understand the self-assembly process of the transition metal (TM) nanoclusters and nanowires self-synthesized by hydroquinone (HQ) and calix[4]hydroquinone (CHQ) by electrochemical redox processes, we have investigated the binding sites of HQ for the transition-metal cations TM(n+)=Ag(+), Au(+), Pd(2+), Pt(2+), and Hg(2+) and those of quinone (Q) for the reduced neutral metals TM(0), using ab initio calculations. For comparison, TM(0)-HQ and TM(n+)-Q interactions, as well as the cases for Na(+) and Cu(+) (which do not take part in self-synthesis by CHQ) are also included. In general, TM-ligand coordination is controlled by symmetry constraints imposed on the respective orbital interactions. Calculations predict that, due to synergetic interactions, silver and gold are very efficient metals for one-dimensional (1D) nanowire formation in the self-assembly process, platinum and mercury favor both nanowire/nanorod and thin film formation, while palladium favors two-dimensional (2D) thin film formation.     

Evaporation‐Induced Ordered Honeycomb Structures of Gold Nanoparticles at the Air/Water Interface

The breath figure method was used to prepare dodecanethiol‐capped gold nanoparticle macroporous structures with pore diameters from 1.7 to 3.5 μm on an air/water interface. A two‐step procedure is proposed for the fabrication of these macroporous structures, by forming a surfactant monolayer on water, and drop‐casting a gold nanoparticle dispersion in chloroform onto the surfactant monolayer. The self‐assembled films are easily transferred from the water surface onto different substrates and were characterized by TEM, SEM, and AFM. Ordered honeycomb structures with different pore arrays (perforated monolayer films, hexagonal networks and alveoli‐like porous films) were obtained. The change in morphology is concentration dependent, and deformed structures with elliptic honeycomb networks are also observed. In addition, honeycomb films using gold nanoparticles stabilized by a weakly bound ligand (dioctadecyldimethylammonium chloride) were formed by the same technique. These films have potential as substrates for surface‐enhanced Raman spectroscopy.     

Rapid charge transport in dye-sensitized solar cells made from vertically aligned single-crystal rutile TiO(2) nanowires

A rapid solvothermal approach was used to synthesize aligned 1D single-crystal rutile TiO(2) nanowire (NW) arrays on transparent conducting substrates as electrodes for dye-sensitized solar cells. The NW arrays showed a more than 200 times faster charge transport and a factor four lower defect state density than conventional rutile nanoparticle films.     

Preparation of Ag Nanowire @ Au Nanoparticle Hybrid Nanowires and their Influence on the Fluorescence Properties of P3HT

In this study, the galvanic displacement reaction between silver and AuCl₄⁻ was carried out to synthesize a series of silver nanowire (Ag NW) @ gold nanoparticle (Au NP) hybrid nanowires. The influence of Ag NW @ Au NP hybrid nanowires on the fluorescence properties of the poly (3‐hexylthiophene) (P3HT) was investigated. The particle sizes of Au NPs on the hybrid nanowires could be adjusted by varying the reaction time and the concentration of the HAuCl₄ solution. Furthermore, steady‐state fluorescence measurements showed that the fluorescence intensity of the P3HT films was higher on various Ag NW @ Au NP hybrid nanowires compared to that on a bare silicon substrate. This was due to the increase in the intensity of electromagnetic field by the localized surface plasmon resonances of Au NPs and surface plasmon polaritons of Ag NWs from the hybrid nanowires. The results were further confirmed by the Raman spectra of the P3HT films on different substrates.     

Flexible transparent PES/silver nanowires/PET sandwich-structured film for high-efficiency electromagnetic interference shielding

We have developed a kind of high-yield synthesis strategy for silver nanowires by a two-step injection polyol method. Silver nanowires and polyethylene oxide (PEO) (M(w) = 900,000) were prepared in a homogeneous-coating ink. Wet composite films with different thicknesses were fabricated on a PET substrate by drawn-down rod-coating technology. Silver nanowires on PET substrates present a homogeneous distribution under the assistance of PEO. Then PEO was thermally removed in situ at a relatively low temperature attributed to its special thermal behavior under atmospheric conditions. As-prepared metallic nanowire films on PET substrates show excellent stability and a good combination of conductivity and light transmission. A layer of transparent poly(ethersulfones) (PESs) was further coated on silver nanowire networks by the same coating method to prevent the shedding and corrosion of silver nanowires. Sandwich-structured flexible transparent films were obtained and displayed excellent electromagnetic interference (EMI) shielding effectiveness.     

Characterization and Application of Surface Plasmon-Enhanced Optical Diffraction from Electrodeposited Gold Nanowire Arrays

Arrays of gold nanowires formed by the process of lithographically patterned nanowire electrodeposition (LPNE) were characterized by a combination of SEM, polarized UV-visible absorption spectroscopy and optical diffraction measurements. A transverse localized surface plasmon resonance (LSPR) was observed for gold nanowire arrays with an absorption maximum (λ(max)) that varied with nanowire width. Transmission optical diffraction measurements were measured with the even and odd diffraction orders creating an alternating, out of phase sinusoidal intensity pattern characteristic of the LPNE nanowire arrays. The intensities of the even diffraction order maxima were the strongest for nanowires with a width of 115 ± 10 nm; nanowires of this width exhibit a λ(max) of 635 ± 10 nm, verifying that the transverse LSPR has enhanced the optical diffraction signal. Real time total internal reflection diffraction intensity measurements were used to monitor in situ the electrodeposition of silver monolayers onto the gold nanowire arrays.     

Three-dimensional electrically interconnected nanowire networks formed by diffusion bonding

We demonstrate a new strategy to bond nanowires (NWs) using diffusion bonding of gold (Au). The strategy was used to form very large scale, electrically interconnected 3D NW networks composed of both homogeneous and heterogeneous (multisegmented) NWs. The size of the networks ranged from tens of micrometers to millimeters. We have measured the electrical characteristics of the networks and explored one application of the networks in 3D spatial chemical sensing.     

3-Halotetrahydropyran-4-one Derivatives from Homopropargyl Acetal

A gold(I)-catalyzed regioselective method for the preparation of 3-bromo/iodo-tetrahydropyran-4-one derivatives from homopropargyl acetal is reported. A one-pot procedure based on a gold(I)-catalyzed Petasis–Ferrier rearrangement/cyclization and subsequent electrophilic halogenation was developed. Corresponding hemiacetals were not suitable substrates for the formation of the 3-halo-pyran derivatives. The present transformation is a useful method to readily afford highly substituted 3-halo-tetrahydropyran-4-ones, which are suitable substrates in a variety of reactions in further synthesis.     

Freestanding mesoporous quasi-single-crystalline CO3O4 nanowire arrays

We report a facile template-free method for the large-area growth of freestanding hollow Co3O4 nanowire arrays on a variety of substrates including transparent conducting glass, Si wafer, and copper foil, et al. These nanowires have the interesting combined properties of mesoporosity and quasi-single-crystallinity. With their high surface area and crystallinity, and their direct growth on conductive substrate, these Co3O4 nanowire arrays will have promising applications in lithium-ion batteries, chemical sensing, and field-emission and electrochromic devices. Using the prepared nanowire arrays as electrode, an electrochemical sensor for hydrogen peroxide sensing has been demonstrated.     

Synthesis of Large‐Area Three‐Dimensional Polyaniline Nanowire Networks Using a “Soft Template”

Summary: Three‐dimensional polyaniline (PANI) nanowire networks were synthesized in high yield using a “soft template” self‐assembled with hexadecyltrimethylammonium bromide and oxalic acid. The PANI nanowire networks had diameters from 35–100 nm depending on synthesis conditions and/or procedures. The networks and the “cross‐linking points” were clearly observed by field‐emission scanning electron microscopy and transmission electron microscopy. A possible mechanism for the formation of three‐dimensional PANI nanowire networks is discussed.

FESEM image of PANI with three‐dimensional nanowire networks.