Recent advances in synthesis, physical properties and applications of conducting polymer nanotubes and nanofibers

This article summarizes and reviews the various preparation methods, physical properties, and potential applications of one-dimensional nanostructures of conjugated polyaniline (PANI), polypyrrole (PPY) and poly(3,4-ethylenedioxythiophene) (PEDOT). The synthesis approaches include hard physical template method, soft chemical template method, electrospinning, and lithography techniques. Particularly, the electronic transport (e.g., electrical conductivity, current-voltage (I-V) characteristics, magnetoresistance, and nanocontact resistance) and mechanical properties of individual nanowires/tubes, and specific heat capacity, magnetic susceptibility, and optical properties of the polymer nanostructures are presented with emphasis on size-dependent behaviors. Several potential applications and corresponding challenges of these nanofibers and nanotubes in chemical, optical and bio-sensors, nano-diodes, field effect transistors, field emission and electrochromic displays, super-capacitors and energy storage, actuators, drug delivery, neural interfaces, and protein purification are also discussed.     

Self-assembly Ag2O nanoparticles into nanowires with the aid of amino-functionalized silica nanoparticles

This paper describes a novel self-assembly behavior of Ag₂O nanoparticles to Ag₂O nanowires. In the alkaline water-alcohol solution, Ag⁺ ions reacted with OH⁻ ions on silica nanoparticles functionalized by N-(2-aminoethyl)-3-aminopropyl-trimethoxy-silane (AEAPTS) to form Ag₂O nanoparticles. The Ag₂O nanoparticles further self-assembled into Ag₂O nanowires. The morphology of Ag₂O nanowires could be controlled by adjusting Ag/Si molar ratios in the systems. With low Ag/Si molar ratio, uniform Ag₂O nanowires were obtained with diameter of about 50 nm and length of tens micrometers. With the increase of Ag/Si molar ratio, Ag₂O nanowires became thicker, shorter and irregular. It was shown by high-resolution transmission electron microscopy (HRTEM) that all Ag₂O nanowires consisted of tiny Ag₂O nanoparticles with diameter of 10-20 nm. The self-assembly of Ag₂O nanoparticles into Ag₂O nanowires was observed by transmission electron microscopy (TEM) and the corresponding growth mechanism was proposed.     

Enhanced thermoelectric power factor and low thermal conductivity in one-dimensional Te/Ag2Te composites

We reports the synthesis and characterization of Te/Ag₂Te nanorod composites with various Ag₂Te contents. The composite samples were prepared by mixing Te and Ag₂Te nanorods synthesized by polyvinylpyrrolidone (PVP)-assisted solution-phase mixing. The thermoelectric properties of the prepared composites vary according to the Ag₂Te content. Furthermore, the samples exhibit an enhancement in electrical conductivity and a reduction in the Seebeck coefficient with increasing Ag₂Te content. The maximum power factor (350.71 µV/K at room temperature) is observed for the sample containing 30% Ag₂Te. The samples were assembled as 1D nanostructures, which led to a decrease in thermal conductivity owing to the strong phonon scattering effect. The maximum thermoelectric figure of merit (ZT) at room temperature, 0.34 was obtained for the sample with 30% Ag₂Te content. This value is 480% larger than that obtained for the pristine Te nanorod samples.     

Fabrication and photocatalytic performance of one-dimensional Ag3PO4 sensitized SrTiO3 nanowire

The 1D Ag₃PO₄ sensitized SrTiO₃ nanowires are prepared by simple route of electrospinning-in situ deposition technique. The results of the thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive Spectrometer (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–Visible diffuse reflectance spectroscopy (UV–Vis) indicate that the Ag₃PO₄ nanoparticles has been deposited on the surface of the SrTiO₃ nanowires successfully. Experimental results showed that compared with pure SrTiO₃, the as-prepared 1D Ag₃PO₄ sensitized SrTiO₃ nanowires exhibit obvious enhancement of photocatalytic performance and stability. Especially, the Ag₃PO₄/SrTiO₃ (3AS sample) had a satisfactory photocatalytic activity for degrading methylene blue (MB) more than 98% under visible light irradiation. As to pure SrTiO₃ and Ag₃PO₄, only 9.8% and 49% of MB was decomposed after 35?min irradiation respectively. Furthermore, the mechanism of the enhancing photocatalytic activity could be ascribed to the nano-heterojunction of the Ag₃PO₄/SrTiO₃, the visible light response of the Ag₃PO₄, and the 1D structure of the nanowires.     

Effect of metallic Ag growth on the electrical resistance of 3D flower‐like Ag4V2O7 crystals

In this communication, we report for the first time the nucleation and growth of metallic Ag nanoparticles on the surface of 3D flower‐like Ag₄V₂O₇ crystals, induced by accelerated electron beam irradiation. The growth of metallic Ag on the surfaces of Ag₄V₂O₇ crystals were studied by transmission electron microscopy (TEM) and energy dispersive X‐ray spectroscopy (EDXS). According to TEM images and EDXS analyses, exposure to the electron beam induces a reduction process and the growth of metallic Ag nanoparticles on the surface of Ag₄V₂O₇ crystals. Moreover, the inductively coupled plasma optical emission spectrometry measurements indicated an excess of Ag and V vacancies at Ag₄V₂O₇ lattice. Finally, it was observed that the electrical resistance varies considerably with the exposure time to electron beam irradiation.     

Hydrothermal synthesis of vanadium pentoxide nanostructures and their morphology control

Different morphologies of vanadium pentoxide (V₂O₅) from 1D to 3D, including nanospheres, nanowires, urchin-like and flower-like nanostructures, have been synthetized by a simple hydrothermal method. Some parameters, such as the reaction temperature, the volume of polyvinyl pyrrolidone (PVP) and possible formation mechanisms of different V₂O₅ nanostructures were discussed. The results demonstrate that PVP and the reaction temperature play a critical role on the morphology of vanadium pentoxide.     

Ag nanowires and its application as electrode materials in electrochemical capacitor

Silver nanowires were synthesized on a large scale by using anodic aluminum oxide (AAO) film as templates and serving ethylene glycol as reductant. Their morphological and structural characterizations were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and selected area electron diffraction (SAED). The electrochemical properties of silver nanowires as electrode materials for electrochemical capacitors were investigated by cyclic voltammetry (CV) and galvanostatic charge/discharge technique in 6 M KOH aqueous electrolyte. The Ag₂O/Ag coaxial nanowires were formed by the incomplete electrochemical oxidation during the charge step. The maximum specific capacitance of 987 F g^?1 was obtained at a charge–discharge current density of 5 mA cm^?2.     

Electrodeposition of silver telluride thin films from non-aqueous baths

We describe a method for preparation of crystalline silver telluride films by cathodic deposition from dimethyl sulfoxide (DMSO) solutions containing 0.1 M NaNO₃, 5.0 mM AgNO₃ and 3.5-7.0 mM TeCl₄. X-ray diffraction data indicated that the deposited silver telluride films could be adjusted from Ag excess and stoichiometric monoclinic Ag₂Te to hexagonal Ag₇Te₄ by increasing the concentration of TeCl₄ in the electrolyte or lowering the deposition potential. The Ag₂Te film is gray and the Ag₇Te₄ film is dark blue-gray and mirror like adhered strongly to the substrates. Scanning electron microscopy images show that Ag₂Te films were formed with globular grains with average diameters of more than 1 μm. In contrast, Ag₇Te₄ film consists of triangles characteristic of a (1 1 1) single-crystal with a hexagonal structure in average sizes of about 0.4 μm. The X-ray photoelectron spectra (XPS) indicated that the binding energies deviation of Te3d in Ag₇Te₄ is less than that in Ag₂Te, which is consistent with the apparent valences of Te in Ag₂Te and Ag₇Te₄. Finally, the cathodic deposition reactions were studied by cyclic voltammetry.     

Orientation-controlled synthesis and characterization of Bi2Te3 nanofilms, and nanowires via electrochemical co-deposition

An electrochemical deposition technique based on co-deposition was used to deposit preferentially oriented Bi₂Te₃ nanostructures (nanofilm, and nanowire). The shared underpotential deposition (UPD) potentials for both Bi and Te co-deposition were determined by cyclic voltammetric measurements. The scanning probe microscopy (scanning tunneling microscopy (STM) and atomic force microscopy (AFM)) and the X-ray diffraction (XRD) data indicated that the electrodeposition of Bi₂Te₃ results in nanofilm-structured deposits with a preferential orientation at (0 1 5) and nanowired-structured deposits with a preferential orientation at (1 1 0) in acidic and basic (in the presence of ethylenediaminetetraacetic acid (EDTA)) medium, respectively. The results show that the nucleation and growth mechanism follows 3D mode in acidic solutions and 2D mode in basic solution containing EDTA additive. The optical characterization performed by reflection absorption Fourier transform infrared (RA-FTIR) spectroscopy showed that the band gap energy of Bi₂Te₃ nanostructures depends on the thickness, size, and shape of the nanostructures and the band gap increases as the deposition time decreases. Moreover, the quantum confinement is strengthened in the wire-like deposits relative to the film-like deposits. Energy dispersive X-ray spectroscopy (EDS) analysis demonstrated that Bi₂Te₃ nanostructures were always in 2:3 stoichiometry, and they were made up of only pure Bi and Te.     

Role of tellurium addition on the linear and non-linear optical,structural, morphological properties of Ag60-xSe40Tex thin films for nonlinear applications

The tellurium (Te)-doped Ag_60-xSe₄₀Te_x (x = 0%, 5%, 10%, 15%) thin films of thickness ∼800 nm were prepared from the bulk sample by thermal evaporation method on a glass substrate. The X-ray diffraction study revealed the amorphous nature of the films whereas the change in vibrational modes was noticed from the Raman spectroscopy. The composition of the films was verified by energy dispersive X-ray analysis and the surface morphology pictures were taken by field emission scanning electron microscopy and atomic force microscope. The changes in optical properties (linear and non-linear) with Te addition were studied from UV-Visible spectroscopy data and related empirical formulas. The addition of Te reduced the bandgap values significantly and the reduction in transmission resulted in the increase of the linear refractive index. The decrease in optical bandgap is due to an increase in disorder while the width of the tail in the gap increased with Te%. The optical density, dispersion energy, extinction coefficient, carrier concentration, dielectric constant, oscillator wavelength increased while the oscillator energy, oscillator strength, optical electronegativity decreased with Te content. The electrical susceptibility increased with Te content. The non-linear susceptibilities and the non-linear refractive index increased which is good for the nonlinear photonic devices.     

Sonochemical Synthesis and Characterization of the New Plate-Shaped Lead(II)–Iodo Coordination Polymer: A Precursor to Produce a Pure Phase Nano-Sized Lead(II) Oxide

Preparation of plate-shaped nanostructures of a new 1D polymeric lead(II) complex containing the Pb₂-(μ-I)₂ motif, [Pb(neo)I₂] _n ,(1) where neo is the abbreviation of neocuproine, using a sonochemical method is described. The new coordination polymer is characterized by scanning electron microscopy, X-ray diffraction (XRD), elemental analysis and infrared spectroscopy. The single crystalline material is obtained using a heat gradient applied to a solution of the reagents. Single-crystal XRD analysis indicates that a coordination number of six for Pb^II ions, (i.e., PbN₂I₄) with an asymmetrical coordination sphere and “stereo-chemically active” electron lone pairs. They also show that the chains interact with each other through π–π stacking interactions creating a 3D framework. PbO nanoparticles are obtained by thermolysis of 1 at 180?°C with oleic acid as a surfactant. Scanning electron microscopy confirms formation of PbO particles with a size of ~25?nm.     

Two novel self-interpenetrating 3D iron(II) coordination frameworks: Synthesis,spectroscopic and structural characterizations with magnetic properties

Two novel self-interpenetrating 3D Fe(II) coordination frameworks namely {Fe(4,4′-bpy)[Ag₂(CN)₃]₂}_n (I) and {Fe(4,4′-bpy)[Ag(CN)₂]₂[AgCN]₂}_n (II) have been synthesized and fully characterized. The 3D architectures and degree of interpenetration of these coordination frameworks were significantly affected by silver(I) cyanide species. The crystal structure of I presents 4-fold interpenetrating 3D framework with 4,4′-bpy and [Ag₂(CN)₃]⁻ species. While, that of II constructed by 4,4′-bpy and two different silver(I) cyanide species, AgCN and [Ag(CN)₂]⁻ resulting to 2-fold interpenetrating 3D framework. The stability and rigidity of both coordination frameworks are mainly supported dominantly by Ag^I ⋯ Ag^I interactions. Their magnetic properties exhibit high spin behavior.     

Some thermodynamic,electrical and electrochemical properties of silver vanadium bronzes

Silver vanadium bronzes (Ag_xV₂O₅) were investigated for their electrical, electrochemical and thermodynamic properties. The specific conductivity of β  Ag_xV₂O₅ as a function of temperature and composition parameter x is measured.From emf measurements values are obtained for the partial thermodynamic functions ΔH?_Ag and ΔS?_Ag for Ag_xV₂O₅ as a function of x. By aid of these values an integral curve for ΔH?_Ag and Δ?_Ag(500 K) as a function of x is constructed. It follows that silver vanadium bronzes have remarkable thermodynamic properties.Finally some current density — voltage curves are given at different temperatures for galvanic cells with a Ag_0.30V₂O₅  bronze as a cathode material.     

Electrochemical synthesis of silver oxide nanowires,microplatelets and application as SERS substrate precursors

We describe the electrochemical synthesis of silver oxide nanowires and nanowire bundles, filled platelets and hollow microplatelets in either basic or acidic N,N-dimethylformamide solution. We propose that these nanostructures are formed at the electrode surface via two competing reactions namely, silver dissolution off the electrode in the presence of NH₃ or HF during the anodization of silver, and silver oxide precipitation. Results show that the precipitated silver oxide nanoparticles aggregate into nanowires as well as into filled and hollow microscale platelets, depending upon the nuclei concentration and the anodization current density. X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and Raman scattering spectroscopy show that the nanowires and microplatelets are mainly composed of Ag₂O. Nanowire bundles are used as substrates for surface-enhanced Raman scattering (SERS) where single molecule detection is achieved and evidenced using a bianalyte Raman technique.     

The ionic hall effect in the solid electrolyte C5H6NAg5I6

The ionic Hall effect was measured in polycrystalline C₅H₆NAg₅I₆ at 25°C using an ac electric field and a dc magnetic field. The Hall voltages ranged between 10 and 100nV for magnetic fields of 0.1-T. From these data we calculated the average Ag⁺ ion mobility, the number of mobile Ag⁺ ions per cm³, the percentage of free silver ions, and the average relaxation time. We conclude that the exceptionally high ionic conductivity in C₅H₆NAg₅I₆ at 25°C probably arises from a relatively small number of mobile Ag⁺ ions.     

Effects of electrolyte in dye-sensitized solar cells and evaluation by impedance spectroscopy

Effects of the electrolyte of DSCs on impedance spectra were evaluated by changing concentration of redox couple, viscosity, and additives to electrolyte. The relation with current-voltage characteristics (I-V characteristics) was investigated. In many cases, the impedance component attributed to charge transfer at TiO₂|electrolyte interface demonstrated strong relation with the I-V characteristics. The recombination of electrons in TiO₂ with I₃⁻ in electrolyte was a key factor in determining performance of DSCs. To evaluate the effect of I₃⁻, diffusion-limiting current in the electrolyte for various viscosities was evaluated by cyclic voltammetry. When the short circuit current (SCC) was almost equal to the diffusion-limiting current, strong influence of the diffusion coefficient on the impedance spectra was observed: impedance arcs were enlarged as the diffusion coefficient was decreased. On the other hand, when the diffusion-limiting current was larger than the SCC, photo-excitation and electron injection processes became dominating factors in the DSCs performance. The SCC was regulated by the charge recombination process at TiO₂|electrolyte interface, and thus the impedance component ω₃ was related to the performance in such condition.     

Synthesis and transport properties of La0.67Sr0.33MnO3 conformally-coated on carbon nanotubes

We report for the first time the fabrication of nanostructured ferromagnetic lanthanum strontium manganite La_0.67Sr_0.33MnO₃ (LSMO) conformally coated onto bamboo-like carbon nanotubes (BCNTs) by pulsed laser deposition. Scanning electron microscopy revealed that one-dimensional LSMO/BCNTs with diameters ranging from 100-160 nm and lengths over 10 μm were obtained. Line-scanned energy-dispersive X-ray spectroscopy profiles, selected area electron diffraction rings, and energy-filtered transmission electron microscopy maps provided further insight into the hybrid nanostructures. LSMO/BCNT and BCNT were also investigated via in situ electrical probing in a transmission electron microscope using a piezo-driven scanning tunneling microscopy holder. Modeling of the I–V characteristics of individual hybrid nanotubes yielded the resistivity, bandgap, and electron density of LSMO and BCNT. The results show that the transport properties of LSMO/BCNT are superior to those of BCNT. This research advances the integration of oxide materials and carbon nanotubes, bringing forth new avenues for miniaturization and fabrication of one-dimensional core-multishell materials with multifunctional properties that can be used as building blocks in nanodevices.     

Horizontal transfer of aligned Si nanowire arrays and their photoconductive performance

An easy and low-cost method to transfer large-scale horizontally aligned Si nanowires onto a substrate is reported. Si nanowires prepared by metal-assisted chemical etching were assembled and anchored to fabricate multiwire photoconductive devices with standard Si technology. Scanning electron microscopy images showed highly aligned and successfully anchored Si nanowires. Current-voltage tests showed an approximately twofold change in conductivity between the devices in dark and under laser irradiation. Fully reversible light switching ON/OFF response was also achieved with an I_ON/I_OFF ratio of 230. Dynamic response measurement showed a fast switching feature with response and recovery times of 10.96 and 19.26 ms, respectively.     

Model bulk Mo–V–Te–O catalysts for selective oxidation of propane to acrylic acid

The crystal structures and chemical compositions of the M1 and M2 phases proposed as active and selective in propane oxidation to acrylic acid over the bulk mixed Mo–V–Te–O catalysts were investigated by the transmission electron microscopy, coupled with energy dispersive analysis of X-rays. The results revealed that the crystal structure of the M1 phase is orthorhombic with space group Pbca, lattice parameters a=21.25 Å, b=27.14 Å, c=4.03 Å and composition Mo_0.64V_0.32Te_0.1O_3.05 (Mo/V ∼2), whereas M2 is hexagonal with space group P6mm, lattice parameters a=7.10 Å, c=4.05 Å and composition Mo_1.79V_1.85Te_0.1O_11.36 (Mo/V ∼1). The M1 phase was dominant in the Mo–V–Te–O catalyst. The results obtained indicated that the bulk Mo–V–Te oxides represent a well-defined model catalytic system for the studies of the surface molecular structure-activity/selectivity relationships in propane oxidation to acrylic acid.     

Oxidation effects on toughness and slow crack growth in polycrystalline graphites

The fracture toughness (K_Ic) and slow crack growth behavior of four fine-grained polycrystalline graphites, oxidized to 5, 10 and 20% weight losses, were measured in air at room temperature. Exponential decreases in the elastic moduli as well as decreases in the fracture surface energy contributed to lowering K_Ic. Oxidation generally shifted the stress intensity-crack velocity (K_I-V_I) diagram to lower stress intensity values, and decreased the slope, or N-value. Scanning electron microscope fractography revealed that a combination of filler particle and binder phase degradation with increasing oxidation was responsible for the decreased toughness and changes in the (K_I-V_I) characteristics. Oxidation conditions were shown to significantly affect the magnitude of decreases in the physical, elastic and mechanical properties of these graphites.