Wire-like Morphology Research Articles

Room-temperature growth (“farming”) and high-performance supercapacitor applications of highly crystalline CuO nanowires/graphene nanoplatelet nanopowders

We report a first-of-its-kind farming-like growth of nanopowders of CuO nanowires (NWs) via room-temperature thermal oxidation. Compared to conventional thermal annealing methods for producing copper oxide nanostructures, which require elevated temperatures (300–600 °C), the present method yields a large amount of highly crystalline CuO NW nanopowders at a much lower temperature (i.e., room temperature). Two-dimensional carbon nanostructures such as graphene nanoplatelets (GNPs) were used as supports for the growth of the CuO NWs. The GNPs were coated with Cu seed layers by the electroless plating method, which is suitable for mass production. After electroplating of Cu layers, the GNP supports were kept at room temperature and under constant humidity (50 or 60% relative humidity) for over 24 h, resulting in the dense wire-like morphology of copper oxide. Scanning electron microscopy, energy dispersive X-ray diffraction, X-ray diffraction, and Raman spectroscopy measurements revealed that the NWs consisted of highly crystalline monoclinic CuO. Once the NWs were formed, their morphology was stable for up to 168 h at room temperature. The as-prepared CuO nanopowders were tested as electrodes of electrochemical capacitors (or supercapacitors). In a three-electrode configuration, a working electrode made of CuO NWs exhibited an excellent mass-specific capacitance of 145 F g−1 at 5 mV s−1 in a 3 M KOH aqueous electrolyte. The growth of CuO nanopowders on GNPs illustrated in this study demonstrates a novel approach for the room-temperature synthesis of nanopowders, with promising applications in next-generation energy devices.

Inkjet-Based Fabrication Process with Control over the Morphology of SERS-Active Silver Nanostructures

Morphological control of silver nanostructures is sought after due to the dependence of optical properties on size and shape. Herein, we report a facile printing process for fabricating silver nanostructured films with wire-like or particle-like morphologies on paper by merely varying the halide composition of precursor salt from potassium bromo-iodide to potassium chloride. Silver was efficiently retained on the top surface of porous paper substrates by printing an excess of potassium halide salt first, leading to more conductive films at lower silver loadings. Furthermore, Raman characterization results show that silver films having nanoparticle morphology have higher SERS activity than samples with nanowire morphology, although the roughness factor of nanowire films is higher than the corresponding nanoparticulate film. Overall, these findings highlight a facile process for controlling the morphology of SERS-active silver nanostructures, which are fabricated on paper using a desktop inkjet printer.

Annealing led conversion from polypyrrole to carbon nitride nanowires and the fabrication of highly efficient ammonia sensing device

In this work, first of all, polypyrrole (PPy) nanowires have been successfully prepared using template synthesis technique at room temperature by chemical polymerisation of pyrrole within the pores of anodic alumina template. Secondly, the effect of 4 h annealing on morphological, optical and ammonia gas sensing device properties has been studied at 200 °C and 300 °C. The characterization of unanealed and annealed samples was done by using scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and time resolved photoluminescence. IV measurements are done for studying gas sensing device. The SEM confirms the flexible wire-like morphology of unannealed and annealed nanowires whereas XRD investigation shows the amorphous nature of unannealed and annealed nanowires. Characteristic peaks of FTIR confirm the formation of PPy nanowires synthesized at room temperature and transition from polypyrrole to carbon nitride nanowires after annealing PPy nanowires at 200 and 300 °C. The transition from PPy to CNx nanowires after annealing is proved by the characteristic FTIR peaks corresponding to C=C and C=N bond and the time resolved photoluminescence spectra recorded at different wavelengths corresponding to polypyrrole and carbon nitride well known transitions. I–V studies of nanowires show the increase in sensitivity of annealed nanowires towards NH3 at about thousand times than that of unannealed nanowires.

Controlled synthesis and magnetic properties of Ni nanotubes and nanowires

Ni nanotubes and nanowires with an average diameter of about 140nm are synthesized by a template-assisted sol-gel autocombustion method using nickel nitrate, citric acid and ammonia as the starting materials. The anodic aluminum oxide templates are prepared by a facile anodizing method. By adjusting the experimental conditions in the sol-gel process, the final products having tubular or wire-like morphologies can be perfectly controlled. Transmission electron microscope characterization indicates that the Ni nanotubes are very friable and can be easily broken into pieces of short nanotubes, but the Ni nanowires are compact and have very high aspect ratios. Magnetic measurements indicate that both the Ni nanowires and the Ni nanotubes possess superparamagnetism at room temperature.

On the strain-induced stabilization of microstructural features formed along dislocations

Capillarity-driven mass transport limits the stability of microstructures with a high surface-to-volume ratio. Fiber reinforcements, dendritic structures, and other wire-like morphologies may be susceptible to Rayleigh instabilities and to concurrent or subsequent coarsening. Decreases in the characteristic length scales of microstructures to the nanoscale make such forms of evolution and instability evident at lower values of homologous temperature, consistent with expectations based on size scaling. Herein, we present a simple continuum theory that predicts that sufficiently small second-phase wires exhibiting dislocation character are stable to both Rayleigh instabilities and coarsening. Thus, defects such as hollow-core dislocations will tend to be stabilized while a freestanding nanowire will tend to be unstable. More generally, the effects of surface-energy anisotropy and strain energy on morphological stability are evaluated in a manner that allows their individual and combined effects on stability to be assessed and mapped.

In Situ Wire Drawing of Phosphate Glass in Polymer Matrices for Material Extrusion 3D Printing

A strategy to increase the amount of materials available for additive manufacturing platforms such as material extrusion 3D printing (ME3DP) is the creation of printable thermoplastic composites. Potential limiters to the incorporation of filler materials into a thermoplastic resin include agglomeration of the filler materials, which can compromise the mechanical properties of the material system and a static morphology of the filler material. A potential solution to these issues is the use of filler materials with low glass transition temperatures allowing for a change in morphology during the extrusion process. Here, we successfully demonstrate the drawing of phosphate glass particles into a wire-like morphology within two polymeric systems: (1) a rubberized acrylonitrile butadiene styrene (ABS) blend and (2) polylactic acid (PLA). After applying a normalization process to account for the effect of air gap within the 3D printed test specimens, an enhancement in the mechanical properties was demonstrated where an increase in strength was as high as 21% over baseline specimens. Scanning electron microanalysis was used to characterize the fracture surface and wire drawing efficacy. Factors affecting the ability to achieve wire drawing such as polymer viscosity and print temperature are also highlighted.

Construction of 1D SnO2-coated ZnO nanowire heterojunction for their improved n-butylamine sensing performances.

One-dimensional (1D) SnO2-coated ZnO nanowire (SnO2/ZnO NW) N-N heterojunctions were successfully constructed by an effective solvothermal treatment followed with calcination at 400 °C. The obtained samples were characterized by means of XRD, SEM, TEM, Scanning TEM coupled with EDS and XPS analysis, which confirmed that the outer layers of N-type SnO2 nanoparticles (avg. 4 nm) were uniformly distributed onto our pre-synthesized n-type ZnO nanowire supports (diameter 80~100 nm, length 12~16 μm). Comparisons of the gas sensing performances among pure SnO2, pure ZnO NW and the as-fabricated SnO2/ZnO NW heterojunctions revealed that after modification, SnO2/ZnO NW based sensor exhibited remarkably improved response, fast response and recovery speeds, good selectivity and excellent reproducibility to n-butylamine gas, indicating it can be used as promising candidates for high-performance organic amine sensors. The enhanced gas-sensing behavior should be attributed to the unique 1D wire-like morphology of ZnO support, the small size effect of SnO2 nanoparticles, and the semiconductor depletion layer model induced by the strong interfacial interaction between SnO2 and ZnO of the heterojunctions. The as-prepared SnO2/ZnO NW heterojunctions may also supply other novel applications in the fields like photocatalysis, lithium-ion batteries, waste water purification, and so on.

Electrodeposited Iron(III) Oxide (α-Fe<sub>2</sub>O<sub>3</sub>) Thermoelectric Thin Films

α-Fe2O3 thermoelectric thin films were electrodeposited onto copper substrates using chloride-based electrolytes by means of potentiostatic electrodeposition. The influence of several electrodeposition parameters on the surface morphology, elemental composition and electrical conductivity of the deposited films was studied and analyzed. The deposits formed porous, wire-like morphology, with the smallest width measured to be ~60 nm. The wires tend to aggregate to form clusters, in addition to multi-layered growth of the wires. Between the parameters studied, electrolyte concentration and deposition time parameters have higher influences on the electrical conductivity of the deposited films, with the increment up to two fold higher. Deposition potential parameter offered the lowest capability to improve on the electrical conductivity in addition to the non-uniform distribution of the measured electrical conductivities. The tunable electrical conductivity is favorable for improving the performance of α-Fe2O3 films for thermoelectric applications.

Dealloying monolithic Pt-Cu alloy to wire-like nanoporous structure for electrocatalysis and electrochemical sensing

Micrometer wire-like PtCu catalysts with nanoporous structure and tunable composition were fabricated by dealloying Pt3Cu97. When the Pt:Cu ratio is lower than 1:99, dealloying results in dispersed PtCu nanoporous nanoparticles and/or single nanoparticles. Material characterization by X-ray diffraction and electron microscope shows that the formation of wire-like morphology is due to the large-scale shrink of the long rod-like alloy grains during the dealloying. The composition of the dealloyed nanoporous PtCu can be widely tuned by changing the concentration of the dealloying solution. Electrochemical test shows that the wire-like porous PtCu alloys show enhanced and composition-dependent catalytic activity for H2O2 electro-reduction.

Controllable one-dimensional FePt nanomaterials synthesised by chemical method

Controllable FePt nanowires have been synthesised by tuning the reaction conditions. The growth mechanism of the FePt nanowires was investigated by analysing the samples obtained at different reaction stages in situ. The results show that there are two steps during formation of nanowires. The first step is nuclei and assembly process, in which FePt nuclei appear and grow up to fractions of the nanowire, and then the fractions with similar lattice fringes self-assemble to wire-like morphology under surfactant driving. The first step is foremost to control one-dimensional nanomaterials. The powerful surfactant and enough assembling time are key roles. The second step is the jointing and growing process. During this step, the connected fractions join onto each other and grow into nanowires. Based on this mechanism, we can easily achieve various one-dimensional nanomaterials from nanorods to nanowires with good quality by modifying surfactant and reactive temperature.

Effect of Heat Treatment on the Micro-Structural, Crystallinity and Photocatalytic Properties of Hydrothermally Prepared Titanate Nanowires

Titanate nanowires were synthesised by hydrothermal process in 10M NaOH aqueous solution at 200oC for 24h. The samples were washed repeatedly in HCl aq. solution and deionized water until pH ~7. Subsequently, the samples were heat-treated at 400-850°C in air for 2h. The X-ray diffraction (XRD) analysis of the sample heat-treated at 800°C showed the crystalline structure of sodium titanate (Na2Ti6O13 ), while the presence of anatase phase was detected from the sample heat-treated at 850°C. Wire-like morphology of the synthesized sample was observed using FE-SEM. The photocatalytic activity of the samples heat-treated at 600,800, 850°C and 900°C was investigated by measuring the degradation of methylene blue (MB) in aqueous solution under UV-light irradiation and more than 90% of the dye was efficiently degraded by the sample heat-treated at 850°C within 45 minutes irradiation time as compared to other tested samples.

Several millimeters long SiC–SiOx nanowires synthesized by carbon black and silica sol

Several millimeters long SiC–SiOx nanowires with the diameters of 50–300nm were successfully synthesized by carbothermal reduction using the raw materials of carbon black, silica sol and alumina at 1400°C. The morphology and microstructure of nanowires have been studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron energy scattering (EDX), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The nanowires were mainly in a straight wire-like morphology and consisted of 3C-SiC. Alumina played an important role in regulating the content of SiO2 in the reaction to produce SiO and keep nanowires subsequently growth along one-dimensional direction, and then an alumina-assisted growth of vapor–solid (VS) mechanism was proposed for the growth mechanism of several millimeters long SiC–SiOx nanowires.

Shape-selective synthesis and photoluminescence of SnO2 nanostructures under different catalyst conditions

We have successfully synthesized various SnO2 nanostructures on p-type Si (100) substrates via three different processes: (1) using an as-deposited Au thin-film catalyst, (2) by adjusting the particle size of the Au catalyst via annealing treatment, and (3) without using any Au catalyst. Scanning electron microscopy images indicate that nanostructures processed by methods (1) and (2) show wire-like morphology. The rod-like nanostructures obtained under “catalyst-free” conditions in method (3) present square cross sections and faceted surfaces. Transmission electron microscopy analysis shows that the SnO2 nanostructures obtained from processes (1) and (2) are single crystalline, while those from process (3) are polycrystalline with tetragonal SnO2 structures. Investigations on the room-temperature photoluminescence (PL) spectra reveal that the PL intensity and energy of the individual SnO2 nanostructures differ significantly according to the synthesis method. The SnO2 nanostructures synthesized using the “thin-film catalyst” method show a somewhat broad blue (440 nm) and an orange (620 nm) emission peak. The PL emission of the nanomaterial obtained through the “annealed catalyst” process (2) was considerably enhanced near 620 nm. The “catalyst-free” process (3) resulted in a material with only very weak orange emission at 620 nm and without any blue emission. Based on these results, the growth, microstructure, and PL mechanism of SnO2 nanostructures are discussed in this paper.

Hydrothermal synthesis of AgInS2@Ag2S nanocomposites by using Ag-carminic acid nanofibers as a novel precursor

This work introduces a new silver precursor based on the coordination compounds for the preparation of AgInS2@Ag2S nanocomposites. Carminic acid extracted from cochineal dye is used as chelating ligand to synthesize (Ag-carminic acid) complex. Thermal decomposition of the as-synthesized complex with wire-like morphology in the presence of InNO3·5H2O and thioacetamide at 200 °C for 10 h leads to the formation of AgInS2@Ag2S nanocomposites. To control particle sizes of the nanocomposites, various amounts of propylene glycol as solvent are applied. Based on the images of scanning electron microscopy, it can be found that by increasing the amount of propylene glycol, agglomeration of AgInS2@Ag2S particles increases. Additionally, photovoltaic properties of AgInS2@Ag2S nanocomposites have been studied by measuring the photocurrent density–voltage (J–V) curves.

DNA-encapsulated chain and wire-like β-MnO2 organosol for oxidative polymerization of pyrrole to polypyrrole.

A DNA-encapsulated chain and wire-like β-MnO2 organosols have been synthesized utilizing a two-phase water-toluene extraction procedure at room temperature (RT). The β-MnO2 organosol was prepared by transferring KMnO4 and DNA from aqueous solution separately to an organic solvent (toluene) using a phase transfer catalyst, mixing both organic solutions together, and subsequent reduction with NaBH4. The eventual diameters of the MnO2 particles in chain-like and wire-like morphologies were ∼1-2 nm and ∼1.8 ± 0.2 nm, respectively, whereas the nominal length of the DNA-MnO2 chains was ∼2-3 μm. Different morphologies of the MnO2 organosol were synthesized by simply tuning the DNA to KMnO4 molar ratio. The synthesized particles were successfully re-dispersed in different organic solvents for application in various organic reactions. The potential of the DNA-MnO2 organosol as a catalyst has been tested in the organic catalytic reaction for the oxidative polymerization of pyrrole to polypyrrole, using the DNA-MnO2 organosol as a potential catalyst. The synthesis process was simple, reproducible and robust. In future, the present process might be utilized for the formation of other nanomaterials in organic solvents, with specific morphologies and uses in a variety of catalytic reactions and energy storage applications.

Platinum-Tin Nanowires Anchored on a Nitrogen-Doped Nanotube Composite Embedded with Iron/Iron Carbide Particles as an Ethanol Oxidation Electrocatalyst

One-pot synthesis of Fe/Fe3C particles embeded within nitrogen-doped nanotube composite (Fe-C) is achieved by pyrolyzing a mixture of melamine and iron (III) chloride. PtSn alloys with atomic ratios of 3:1, 1:1, and 1:3 supported on Fe-C are formed using an ethylene glycol reduction method. PtSn alloys exhibit a wire-like morphology when supported on Fe-C (PtSn/Fe-C) as opposed to spherical morphology of PtSn nanoparticles formed on commercial carbon nanotubes (CNTs). The length of the PtSn nanowires is inversely proportional to the Pt:Sn atomic ratio. All three PtSn/Fe-C catalysts have higher ethanol oxidation activity and durability than the PtSn/CNT catalyst, and the highest activity is produced by a 1:1 Pt:Sn ratio. We conclude that Fe/Fe3C particles embedded within the N-doped carbon composite offers a promising PtSn suppport for direct ethanol fuel cells.

Synthesis and structural characterization of group 4 metal carboxylates for nanowire production.

The synthesis and characterization of a series of group 4 carboxylate derivatives ([M(ORc)4] where M = Ti, Zr, Hf) was undertaken for potential utility as precursors to ceramic nanowires. The attempted syntheses of the [M(ORc)4] precursors were undertaken from the reaction of [M(OBu(t))4] with a select set of carboxylic acids (H-ORc where ORc = OPc (O2CCH(CH3)2), OBc (O2CC(CH3)3), ONc (O2CCH2C(CH3)3)). The products were identified by single-crystal X-ray diffraction studies as [Ti(η(2)-OBc)3(OBu(t))] (1), [Zr2(μ3-O)(μ-OPc)4(μ,η(2)-OPc)(η(2)-OPc)]2 (2), [H]2[Zr(η(2)-OBc)2(OBc)2(OBc)2] (3), [Zr(μ-ONc)2(η(2)-ONc)2]2 (4), or [Hf(μ-ORc)2(η(2)-ORc)2]2 [ORc = OPc (5), OBc (6, shown), ONc (7)]. The majority of compounds (4-7) were isolated as dinuclear species with a dodecahedral-like (CN-8) bonding mode around the metals due to chelation and bridging of the ORc ligand. The two monomers (1 and 3) were found to adopt a capped trigonal prismatic and CN-8 geometry, respectively, due to chelating ORc and terminal ORc or OBu(t) ligands. The metals of the oxo-species 2 were isolated in octahedral and CN-8 arrangements. These compounds were then processed by electrospinning methods (applied voltage 10 kV, flow rate 30-60 μL/min, electric field 0.5 kV/cm), and wire-like morphologies were isolated using compounds 4, 6 (shown), and 7.

Diatom mimics: directing the formation of biosilica nanoparticles by controlled folding of lysine-leucine peptides.

Silaffins, long chain polyamines, and other biomolecules found in diatoms are involved in the assembly of a large number of silica nanostructures under mild, ambient conditions. Nanofabrication researchers have sought to mimic the diatom's biosilica production capabilities by engineering proteins to resemble aspects of naturally occurring biomolecules. Such mimics can produce monodisperse biosilica nanospheres, but in vitro production of the variety of intricate biosilica nanostructures that compose the diatom frustule is not yet possible. In this study we demonstrate how LK peptides, composed solely of lysine (K) and leucine (L) amino acids arranged with varying hydrophobic periodicities, initiate the formation of different biosilica nanostructures in vitro. When L and K residues are arranged with a periodicity of 3.5 the α-helical form of the LK peptide produces monodisperse biosilica nanospheres. However, when the LK periodicity is changed to 3.0, corresponding to a 310 helix, the morphology of the nanoparticles changes to elongated rod-like structures. β-strand LK peptides with a periodicity of 2.0 induce wire-like silica morphologies. This study illustrates how the morphology of biosilica can be changed simply by varying the periodicity of polar and nonpolar amino acids.

Enhanced catalytic and supercapacitor activities of DNA encapsulated β-MnO2nanomaterials

A new approach is developed for the aqueous phase formation of flake-like and wire-like β-MnO2 nanomaterials on a DNA scaffold at room temperature (RT) within a shorter time scale. The β-MnO2 nanomaterials having a band gap energy ∼3.54 eV are synthesized by the reaction of Mn(II) salt with NaOH in the presence of DNA under continuous stirring. The eventual diameter of the MnO2 particles in the wire-like and flake-like morphology and their nominal length can be tuned by changing the DNA to Mn(ii) salt molar ratio and by controlling other reaction parameters. The synthesized β-MnO2 nanomaterials exhibit pronounced catalytic activity in organic catalysis reaction for the spontaneous polymerization of aniline hydrochloride to emeraldine salt (polyaniline) at RT and act as a suitable electrode material in electrochemical supercapacitor applications. From the electrochemical experiment, it was observed that the β-MnO2 nanomaterials showed different specific capacitance (Cs) values for the flake-like and wire-like structures. The Cs value of 112 F g(-1) at 5 mV s(-1) was observed for the flake-like structure, which is higher compared to that of the wire-like structure. The flake-like MnO2 nanostructure exhibited an excellent long-term stability, retaining 81% of initial capacitance even after 4000 cycles, whereas for the wire-like MnO2 nanostructure, capacitance decreased and the retention value was only 70% over 4000 cycles. In the future, the present approach can be extended for the formation of other oxide-based materials using DNA as a promising scaffold for different applications such as homogeneous and heterogeneous organic catalysis reactions, Li-ion battery materials or for the fabrication of other high performance energy storage devices.

Shape-selective formation of MnWO4nanomaterials on a DNA scaffold: magnetic, catalytic and supercapacitor studies

A new route for the aqueous phase synthesis of single crystalline, shape-selective, magnetic MnWO4 nanomaterials on a DNA scaffold has been reported. The synthesis was done by the reaction of MnCl2·4H2O with Na2WO4 in DNA within five minutes of microwave heating. The process exclusively generates wire-like, flake-like and rice-like morphology just by tuning the DNA to Mn(II) salt and WO42− ion concentration and changing other reaction parameters. The field-cooled (FC) and zero-field-cooled (ZFC) magnetization study reveals that the flake-like structure shows the highest magnetization at 5 K compared to that of the wire-like and rice-like structures. The potential of the shape-selective MnWO4 nanomaterials has been tested in two different applications, firstly in a catalysis study for the decomposition of toxic KMnO4 and secondly in electrochemical supercapacitor applications. It was found that the MnWO4 nanomaterials showed different specific capacitance (SC) values for the various shapes and the order of the SC values is: wire-like > flake-like > rice-like. The highest SC of 34 F g−1 was observed for MnWO4 having wire-like shape. The yields of the products with uniform shapes have been found to be significantly high and the synthesized materials are stable for more than six months under ambient conditions. The present work will find a new platform for the generation of other mixed oxides using bio-molecules as scaffolds at low temperature and in short time scales. Moreover, the synthesized material might be useful for other potential applications in the fields of catalysis, sensors, energy storage materials and so on.