Growth of Cu nanobelt and Ag belt-like materials by surfactant-assisted galvanic reductions

Surfactant-assisted galvanic synthesis and growth characteristics of copper nanowires

One-dimensional copper nanowires (CuNWs) are synthesized on a large-scale using a cetyltrimethylammonium chloride-assisted galvanic replacement reaction on aluminum substrates.

Removal and Recovery of Heavy Metal Ions by Two-dimensional MoS2 Nanosheets: Performance and Mechanisms

We investigated the removal of heavy metals from water by two-dimensional MoS₂ nanosheets suspended in aqueous solution, and restacked as thin film membranes, respectively. From these studies we elucidated a new heavy metal ion removal mechanism that involves a reduction-oxidation (redox) reaction between heavy metal ions and MoS₂ nanosheets. Ag⁺ was used as a model species and MoS₂ nanosheets were prepared via chemical exfoliation of bulk powder. We found that the Ag⁺ removal capacity of suspended MoS₂ nanosheets was as high as ∼4000 mg/g and adsorption accounted for less than 20% of removal, suggesting the reduction of Ag⁺ to metallic silver as a dominant removal mechanism. Furthermore, we demonstrated that MoS₂ membranes were able to retain a similar high removal capacity, and attribute this capability to the formation of a conductive, permeable multilayer MoS₂ structure, which enables a corrosion-type reaction involving electron transfer from a MoS₂ site inside the membrane (anode) to another site on membrane surface (cathode) where heavy metal ions are reduced to metallic particles. The membrane surface remains active to efficiently recover metallic particles, because the primary oxidation products are soluble, nontoxic molybdate and sulfur species, which do not form an insulating oxide layer to passivate the membrane surface. Therefore, MoS₂ membranes can be used effectively to remove and recover precious heavy metals from wastewater.

Syntheses and Properties of Metal Nanomaterials with Novel Crystal Phases

In recent decades, researchers have devoted tremendous effort into the rational design and controlled synthesis of metal nanomaterials with well-defined size, morphology, composition, and structure, and great achievements have been reached. However, the crystal-phase engineering of metal nanomaterials still remains a big challenge. Recent research has revealed that the crystal phase of metal nanomaterials can significantly alter their properties, arising from the distinct atomic arrangement and modified electronic structure. Until now, it has been relatively uncommon to synthesize metal nanomaterials with novel crystal phases in spite of the fact that these nanostructures would be promising for various applications. Here, the research progress regarding the fine control of noble metal (Au, Ag, Ru, Rh, Pd) and non-noble metal (Fe, Co, Ni) nanomaterials with novel crystal phases is reviewed. First, synthesis strategies and their phase transformations are summarized, while highlighting the peculiar characteristics of each element. The phase-dependent properties are then discussed by providing representative examples. Finally, the challenges and perspectives in this emerging field are proposed.

Size-tunable Synthesis of Silver Nanobelts Using a Polyaniline Derived Polymer as a Template

Silver nanobelts (AgNBs) have attracted a great interest due to their excellent electrical conductivity and mechanical strength, leading a facile synthesis of these AgNBs in great demand. In here, we are reporting a simple, aqueous phase, size tunable synthesis of smooth surfaced 1D-silver nanobelts using a Polyaniline (PANi) derived polymer at room temperature. The specifically designed PANi polymer, comprising a pendant carboxyl group in the chain, acted as both a reducing agent and template. The resulting Ag nanobelts have more than 10 μm of length, mean width values ranging from 41.1 (11.5) nm to 118.5 (8.8) nm and a mean thickness value of 36.7 (12.5) nm. The UV-Visible spectrum of the AgNBs has shown two Surface Plasmon Resonance peaks at 352 nm and 383 nm.

Visible-light-driven Ag/AgCl plasmonic photocatalysts via a surfactant-assisted protocol: enhanced catalytic performance by morphology evolution from near-spherical to 1D structures

Fibrous Ag/AgCl structures with boosted photocatalytic performances have been fabricatedviaa one-pot surfactant-assisted morphology evolution from near-spherical to 1D architectures.

Morphology and composition controlled synthesis of flower-like silver nanostructures

Flower-like silver nanostructures with controlled morphology and composition were prepared through wet-chemical synthesis. The reaction rate is simply manipulated by the amount of catalyzing agent ammonia added which is the key point to determine the ratio of hexagonal close-packed (HCP) to face-centered cubic (FCC) phase in silver nanostructures. The existence of formic acid that is the oxidation product of aldehyde group is demonstrated to play a crucial role in achieving the metastable HCP crystal structures by replacing ionic surfactants with polyvinylpyrrolidone (PVP). Utilizing flower-like silver nanostructures as surface-enhanced Raman scattering (SERS) substrates, Raman signal of Rhodamine 6G, or 4-aminothiophenol with concentration as low as 10(-7) M was detected. Moreover, it is demonstrated that phase composition has no direct relation to the SERS enhancing factor which is mainly determined by the amount of hot spots.

Preparation and characterization of highly planar flexible silver crystal belts

We report a novel simple one-pot strategy for fabricating pure and highly planar silver (Ag) crystal belts. Unique single-crystal Ag belts (high width-to-thickness ratio ~50) were successfully synthesized in high yield (80 wt%) by reducing AgNO3 using N,N,N',N'-tetramethylethylenediamine (TEMED) as a reducing and a structure-determining agent in the presence of polyethylene glycol (PEG) under mild conditions.

Responsive helical self-assembly of AgNO3 and melamine through asymmetric coordination for Ag nanochain synthesis

Responsive nanohelices can be self-assembled via asymmetric coordination bonding between AgNO3 and melamine. Silver nanochains composed of nanoparticles can be synthesized simply by photo-reduction of the above complex.

Surface-enhanced Raman scattering imaging of a single molecule on urchin-like silver nanowires

Urchin-like silver nanowires are prepared by reacting AgNO(3)(aq) with copper metal in the presence of cetyltrimethylammonium chloride and HNO(3)(aq) on a screen-printed carbon electrode at room temperature. The diameters of the nanowires are about 100 nm, and their lengths are up to 10 μm. Using Raman spectroscopy, the detection limit of Rhodamine 6G (R6G) on the urchin-like silver nanowire substrate can be as low as 10(-16) M, while the analytical enhancement factor is about 10(13). Raman mapping images confirm that a single R6G molecule on the substrate can be detected.

(110)-exposed gold nanocoral electrode as low onset potential selective glucose sensor

A straightforward electrochemical deposition process was developed to grow gold nanostructures, including nanocoral, nanothorn, branched belt, and nanoparticle, on carbon electrodes by reducing HAuCl4 under constant potentials in mixtures containing CTAC and/or NaNO3. Among the nanostructures, the quasi-one-dimensional nanocoral electrode showed the highest surface area. Because of this, it provided excellent electrochemical performances in cyclic voltammetric (CV) studies for kinetic-controlled enzyme-free glucose oxidation reactions. In amperometric studies carried out at 0.200 V in PBS (pH 7.40, 0.100 M), the nanocoral electrode showed the highest anodic current response. It also offered the greatest sensitivity, 22.6 μAmM(-1)cm(-2), an extended linear range, 5.00×10(-2) mM to 3.00×10(1) mM, and a low detection limit, 1.00×10(1) μm among the electrodes investigated in this study. In addition, the glucose oxidation by the nanocoral electrode started at -0.280 V, more negative than the one of using a commercial Au electrode as the working electrode. This is attributed to the presence of exposed Au (110) surfaces on the electrode. The feature was applied to oxidize glucose selectively in the presence of ascorbic acid (AA) and uric acid (UA), common interferences found in physiological analytes. With an applied voltage at -0.100 V, the AA oxidation (started at -0.080 V) can be avoided while the glucose oxidation still provides a significant response.

Growth of pagoda-topped tetragonal copper nanopillar arrays

Growth of arrays of pagoda-topped tetragonal Cu nanopillar (length 1- 6 mum; width 150 +/- 25 nm) with {100} side faces on Au/glass is achieved by a simple electrochemical reduction of CuCl(2)(aq) by Al(s) in aqueous dodecyltrimethylammonium chloride. Field-emission measurement shows that the Cu nanopillars can emit electrons (10 muA cm(-2)) at a turn-on field of 12.4 V mum(-1) with a calculated field enhancement factor of 713.

Synthesis of flexible, ultrathin gold nanowires in organic media

Gold nanoparticles are very interesting because of their potential applications in microelectronics, optical devices, analytical detection schemes, and biomedicine. Though shape control has been achieved in several polar solvents, the capability to prepare organosols containing elongated gold nanoparticles has been very limited. In this work we report a novel, simplified method to produce long, thin gold nanowires in an organic solvent (oleylamine), which can be readily redispersed into nonpolar organic solvents. These wires have a characteristic flexible, hairy morphology arising from a small thickness (<2 nm) and an enormous length (up to several micrometers), with the possibility of adjusting the dimensions through modification of the growth conditions, in particular, the gold salt concentration. Despite their extreme aspect ratio, the wires are stable in solution for long periods of time but easily break when irradiated with high-energy electron beams during transmission electron microscopy.

Growth of high-aspect-ratio gold nanowires on silicon by surfactant-assisted galvanic reductions

A simple galvanic reduction for direct growth of Au nanowires on silicon wafers is developed. The nanowires were prepared by reacting HAuCl4aq with Sns in the presence of CTACaq (cetyltrimethylammonium chloride) and NaNO3aq, which were important to the product morphology development. The nanowire diameter was 50-100 nm, and the length was more than 20 microm.

In situ electrical measurements of polytypic silver nanowires

Novel 4H structure silver nanowires (4H-AgNWs) have been reported to coexist with the usual face-centered cubic (FCC) ones. Here we report the electrical properties of these polytypic AgNWs for the first time. AgNWs with either 4H or FCC structures in the diameter range of 20-80 nm were measured in situ inside a transmission electron microscope (TEM). Both kinds of AgNW in the diameter range show metallic conductance. The average resistivity of the 4H-AgNWs is 19.9 μΩ cm, comparable to the 11.9 μΩ cm of the FCC-AgNWs. The failure current density can be up to ∼10(8) A cm(-2) for both 4H-and FCC-AgNWs. The maximum stable current density (MSCD) is introduced to estimate the AgNWs' current-carrying ability, which shows diameter-dependence with a peak around 34 nm in diameter. It is attributed to fast annihilation of the current-induced vacancies and the enhanced surface scattering. Our investigations also suggest that the magnetic field of the electromagnetic lens may also introduce some influence on the measurements inside the TEM.

Arrays of iso-oriented gold nanobelts

For the first time single crystalline gold nanobelt arrays with identical crystallographic orientation were obtained. A combined method consisting of directional solid-state transformation of a Fe-Au eutectoid and a well controlled electrochemical treatment enables production of arrays of nanobelts with a desired length. They have an average thickness of 25 nm and width of 200-250 nm, respectively. The obtained gold nanobelt arrays were characterized by electron backscattered diffraction (EBSD), X-ray diffraction, and XPS. The underlying mechanisms and the potential of this method for the production of nanosensors are discussed.