Coaxial conducting polymer nanotubes: polypyrrole nanotubes coated with polyaniline or poly(<Emphasis Type="Italic">p</Emphasis>-phenylenediamine) and products of their carbonisation

Polypyrrole nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in a reaction mixture containing methyl orange. They were subsequently coated with polyaniline or poly(p-phenylenediamine) in situ during the oxidation of respective monomers in their presence. A part of the coaxial nanotubes was deprotonated using ammonia solution. The conductivity of polypyrrole nanotubes of 60 S cm^?1, was reduced after the coating, and again after the deprotonation, but maintained at a level above 10^?4 S cm^?1. Infrared and Raman spectra reflect the presence of the polymer overlayer deposited on the polypyrrole template. Thermogravimetric analysis was used as a tool for the analytical carbonisation of samples in an inert nitrogen atmosphere. The conversion of conducting polymers to nitrogen-containing carbon nanotubes was confirmed using Raman spectra.     

The carbon nanotubes-polyaniline composites and their effect on catalytic properties of deposited catalysts

Composites of functionalized single-wall carbon nanotubes and polyaniline are deposited onto electrodes by in situ electrochemical polymerization. Their electrochemical behavior and differential capacitance are studied by cyclic voltammetry, electrochemical impedance spectroscopy, and chronovoltamperometry. The differential capacitance of the composite electrode exceeds that of pure polyaniline film deposited onto electrode, which can be explained by the nanotubes’ loosening effect on the polyaniline structure. The composite-electrode capacitance is as large as 1000 F g⁻¹ or higher. Thus obtained composite films were used as a support for deposited platinum-ruthenium catalyst. The Pt-Ru structure and catalytic properties in the methanol oxidation reaction are studied. It is shown that the specific current of methanol oxidation at Pt-Ru is larger by a factor of 7–15 than those measured when pure polyaniline, pure carbon nanotubes, or standard Vulcan XC-72 carbon black are used as supports. It is found that the catalytic activity is the same for all studied supports, provided the current is reduced to the unit of Pt-Ru true surface area. Thus, the observed large catalytic effect is associated with the structure and high dispersivity of the electrodeposited metals incorporated to the single-wall carbon nanotubes-polyaniline composite.     

Composite materials based on polyaniline and multiwalled carbon nanotubes: Morphology and electrochemical behavior

Composites based on polyaniline are prepared via the chemical oxidative polymerization of aniline in the presence of multiwalled carbon nanotubes modified by the sorption of the co-oxidants IrC ₆ ^2? and 2,2′-azino-bis(3-ethyl-benzthiazolin-6-sulfonate). The approach used here, in combination with corresponding conditions of polymerization, ensures the synthesis of composite materials with a high morphological homogeneity of the polymer phase. The study of the electrochemical properties of composites (the reversibility of redox transitions and the stability of capacity parameters) indicates that that they are strongly influenced by the morphological features of the polymer coating. The composite prepared with the use of nanotubes modified by 2,2′-azino-bis(3-ethyl-benzthiazolin-6-sulfonate) possesses better electrochemical characteristics. This effect is associated with a closer to perfect morphology of the polymer coating, a coaxial polyaniline shell highly uniform in thickness along the entire length of nanotubes.     

Conducting polyaniline/multi-wall carbon nanotubes composite paints on low carbon steel for corrosion protection: electrochemical investigations

The coaxial coating of multi-wall carbon nanotubes (MWCNT) with poly(aniline) (PANI) was synthesised and a paint was prepared containing conducting PANI-MWCNT composite. The corrosion protection performance was assessed by open circuit potential measurements, potentiodynamic polarisation, and electrochemical impedance spectroscopy. The corrosion rate of low-carbon steel coated with 1.5 mass % of PANI-MWCNT-based paint in 3.5 mass % sodium chloride solution was found to be 0.037 mm y^?1, about 5.2 times lower than that of unpainted low-carbon steel and 3.6 times lower than that of epoxy painted steel.     

A renewable bamboo carbon/polyaniline composite for a high-performance supercapacitor electrode material

A high-performance conducting polymer-activated carbon composite electrode material was prepared by potentiostatic deposition of aniline on a hierarchically porous carbon, which was carbonized from the natural bamboo. The obtained composite combined the contribution of the unique properties of the activated carbon and pseudocapacitance of the deposited polyaniline layer. This active material possessed excellent rate capability and good cycle performance, over 92% of the original capacitance is retained after 1,000 cycles. The energy density of the composite can reach 47.5 W h kg⁻¹ calculated only by active mass. It can be a good candidate for high-performance supercapacitor.     

Ultrasensitive determination of hydrazine using a glassy carbon electrode modified with Pyrocatechol Violet electrodeposited on single walled carbon nanotubes

A glassy carbon electrode (GCE) was modified with pyrocatechol violet (PCV) that was electrodeposited on single walled carbon nanotubes (SWCNTs) via continuous cycling between 0 and 0.9 V (vs. SCE). The resulting electrode exhibits excellent electrocatalytic activity towards the oxidation of hydrazine at 0.3 V. The apparent surface coverage of the electrode is at least 24 times higher (2.7?×?10^?10 mol cm^?2) than that obtained with a bare GCE (1.1?×?10^?11 mol cm^?2). This is attributed to a remarkably strong synergistic effect between the acid-pretreated SWCNTs and the electrodeposited PCV coating. Response is fast (2 s) and sensitive (281 mA M^?1 cm^?2). Other features include a wide linear range (150 nM to 0.4 mM) and a low detection limit (150 nM at an SNR of 3). The sensor has been successfully applied to the determination of hydrazine in water and cigarette samples with good accuracy and precision. In addition, the morphology and the wetting properties of the coating were studied by scanning electromicroscopy and contact angle measurements.

Electrochemical capacitance of the composite of poly (3,4-ethylenedioxythiophene) and functionalized single-walled carbon nanotubes

The homogenous coating of poly (3,4-ethylenedioxythiophene) (PEDOT) on carbon nanotubes was realized by using functionalization of single-walled carbon nanotubes (SWNTs) in this study. Consequently, the PEDOT/functionalized SWNTs (PEDOT/F-SWNTs) composites, with size of around 100nm, which is much smaller than that of PEDOT, were prepared by the electrochemical method. Its small granule increased the active/nonactive mass ratio and reduced the ions diffusion length. Therefore, its specific capacitance of the composite was up to 200F g^?1, which was remarkably greater than that of PEDOT. Furthermore, the PEDOT/F-SWNTs composites had very rapid charge/discharge ability with specific capacitance of 180F g^?1 at scanning rate of 200mV s^?1 and 170F g^?1 at frequency of 1Hz, which is an important practical advantage. In addition, such composite had a good cycling performance and a wide potential window.     

Electrochemical synthesis and characterization of solid-phase microextraction fibers using conductive polymers: application in extraction of benzaldehyde from aqueous solution

In this work, polyaniline, polypyrrole, and polyaniline/polypyrrole composite fibers were synthesized in the absence and presence of oxidized multiwalled carbon nanotubes using electrochemical cyclic voltammetry with CF₃COOH as dopant. Thermal stability of these fibers was studied by differential scanning calorimetry. Then, headspace solid-phase microextraction process coupled with gas chromatography and flame ionization detector was used for comparing extraction capability of benzaldehyde from aqueous solution. Since polyaniline fiber showed better extraction efficiency than the other fibers, its preparation conditions including acid concentration, aniline concentration, scan rate, and amount of multiwalled carbon nanotubes were studied by means of the “one-factor-at-a-time method”. The analytical performance of polyaniline fibers were investigated to determine benzaldehyde from the aqueous solution. The morphology and texture of polyaniline fibers were examined by field emission scanning electron microscopy and Fourier transform infrared spectroscopy analyses. The attained results revealed that the perfect conditions for acid concentration, aniline concentration, scan rate, and multiwalled carbon nanotubes content were 0.5 M, 0.2 M, 25 mV s^?1, and 0.02 wt%, respectively. The limit of detection for the proposed polyaniline fiber was 15 ng ml^?1.     

Influence of carbon shell structure on electrochemical performance of multi-walled carbon nanotube electrodes

Core/shell nanostructures have received considerable attention due to the synergistic effect of their combination of materials. In this work, core/shell carbon/multi walled carbon nanotubes (MWNTs) (C-MWNTs) composed of core MWNTs and carbon shells were prepared to obtain a new type of carbon electrode materials. Carbon shells containing nitrogen groups were prepared by coating polyaniline (PANI) onto the MWNTs by in situ polymerization and subsequent carbonization at 850 °C. After carbonization, the C-MWNTs contained 5.84% nitrogen and showed a hollow structure and crystallinity like that of pristine MWNTs. In addition, the C-MWNTs exhibited electrochemical performance superior to that of pristine MWNTs, and the highest specific capacitance (231 F g⁻¹) of the C-MWNTs was obtained at a scan rate of 0.1 A g⁻¹, as compared to 152 F g⁻¹ for pristine MWNTs. This superior performance is attributed to the maintenance of high electrical conductivity by the π–π interaction between the carbon layer and the MWNTs, increased specific surface area of C-MWNTs, and the presence of nitrogen groups formed on the carbon electrode after the carbonization of the shell PANI.     

Micelle-encapsulated multi-wall carbon nanotubes with photosensitive copolymer and its application in the detection of dopamine

Photosensitive copolymer P(St-alt-MAn)-co-P(VM-alt-MAn) was synthesized and employed to disperse multi-wall carbon nanotubes (MWCNTs). It was found that copolymer could form micelles in aqueous solution and adsorb onto the surface of MWCNTs to produce micelle-encapsulated MWCNTs (e-MWCNTs) by in situ photo crosslinking after irradiation with ultraviolet light and a stable suspension of e-MWCNTs in aqueous solution was obtained. When deposited onto polyaniline (PANI)-modified glassy carbon electrodes, a thin film of e-MWCNTs composite was obtained and the performance of the e-MWCNTs/PANI electrode toward dopamine was then evaluated. The experimental results suggest that the hybrid film modified electrode exhibits a dramatic electrocatalytic effect on the oxidation of dopamine (DA), as evidenced by a marked enhancement of the current response. A series of CVs was obtained by modified glassy-carbon electrodes with different size of micelles was also researched. The result shows that the peak current increased with the increasing size of micelles. A linear calibration plot was obtained in a wide range of 1.0?×?10^?7–1.0?×?10^?3 M and the detection limit was 5.0?×?10^?8 M. In addition, the interference from ascorbic acid (AA) was effectively suppressed due to the presence of the negatively charged carboxylate groups of copolymer on the outside of MWCNTs which repels AA anions and provides a transport channel only for DA cations.     

Porous carbon nanotubes improved sulfur composite cathode for lithium-sulfur battery

Porous multi-walled carbon nanotubes (PCNTs) with multiple mesopores structure are synthesized through activation of multi-walled carbon nanotubes (MWCNTs) by potassium hydroxide. The potassium hydroxide activation process results in a significantly enhanced specific surface area with numerous small pores. The as-obtained PCNTs are employed as the conductive matrix for sulfur in the sulfur cathode. Compared with the composite sulfur cathode based on the original MWCNTs, the sulfur-PCNTs cathode shows a significantly improved cycle performance and columbic efficiency. The reversible capacity is 530 mAh?g^?1 and columbic efficiency is 90 % after 100 cycles at a current density of 100 mA?g^?1. The improvement in the electrochemical performance for S-PCNT is mainly attributed to the enlarged surface area and the porous structure of the unique mesopores carbon nanotube host, which cannot only facilitate transport of electrons and Li⁺ ions, but also trap polysulfides, retard the shuttle effect during charge/discharge process.     

Carbon fiber microelectrodes modified with carbon nanotubes as a new support for immobilization of glucose oxidase

Carboxylated carbon nanotubes were coated onto carbon microfiber electrodes to create a micron-scale bioelectrode. This material has a high surface area and can serve as a support for immobilization of enzymes such as glucose oxidase. A typical carbon nanotube loading of 13???g?cm^?1 yields a coating thickness of 17???m and a 2000-fold increase in surface capacitance. The modified electrode was further coated with a biocatalytic hydrogel composed of a conductive redox polymer, glucose oxidase, and a crosslinker to create a glucose bioelectrode. The current density on oxidation of glucose is 16.6?mA?cm^?2 at 0.5?V (vs. Ag/AgCl) in oxygen-free glucose solution. We consider this approach to be useful for designing and characterizing surface treatments for carbon mats and papers by mimicking their local microenvironment.

The determination of acetaminophen using a carbon nanotube:graphite-based electrode

The oxidation of acetaminophen was studied at a glassy carbon electrode modified with multi-walled carbon nanotubes and a graphite paste. Cyclic voltammety, differential pulse voltammetry and square wave voltammetry at various pH values, scan rates, and the effect of the ratio of nanotubes to graphite were investigated in order to optimize the parameters for the determination of acetaminophen. Square wave voltammetry is the most appropriate technique in giving a characteristic peak at 0.52 V at pH 5. The porous nanostructure of the electrode improves the surface area which results in an increase in the peak current. The voltammetric response is linear in the range between 75 and 2000 ng.mL^?1, with standard deviations between 0.25 and 7.8%, and a limit of detection of 25 ng.mL^?1. The method has been successfully applied to the analysis of acetaminophen in tablets and biological fluids.     

Synthesis of Multishell Carbon Nanotube Composites via Template Method

Multishell nanotubes of polyaniline and carbon were synthesized via a template approach. A thin layer of MnO₂ coated on carbon nanotubes acts as a reactive template for the consequent formation of the polyaniline coating. The polyaniline-carbon nanotubes show enhanced dispersibility in water and can be possibly used as a functional material of electrochemical capacitors with improved performance. The general method operates by coating carbon nanotubes on functional materials such as poly (3,4-ethylenedioxythiophene), polypyrrole, silica, and carbon.     

Confined Nanospace Pyrolysis for the Fabrication of Coaxial Fe3O4@C Hollow Particles with a Penetrated Mesochannel as a Superior Anode for Li‐Ion Batteries

In this study, a method is developed to fabricate Fe₃O₄@C particles with a coaxial and penetrated hollow mesochannel based on the concept of “confined nanospace pyrolysis”. The synthesis involves the production of a polydopamine coating followed by a silica coating on a rod‐shaped β‐FeOOH nanoparticle, and subsequent treatment by using confined nanospace pyrolysis and silica removal procedures. Typical coaxial hollow Fe₃O₄@C possesses a rice‐grain morphology and mesoporous structure with a large specific surface area, as well as a continuous and flexible carbon shell. Electrochemical tests reveal that the hollow Fe₃O₄@C with an open‐ended nanostructure delivers a high specific capacity (ca. 864 mA h g^?1 at 1 A g^?1), excellent rate capability with a capacity of about 582 mA h g^?1 at 2 A g^?1, and a high Coulombic efficiency (>97 %). The excellent electrochemical performance benefits from the hollow cavity with an inner diameter of 18 nm and a flexible carbon shell that can accommodate the volume change of the Fe₃O₄ during the lithium insertion/extraction processes as well as the large specific surface area and open inner cavity to facilitate the rapid diffusion of lithium ions from electrolyte to active material. This fabrication strategy can be used to generate a hollow or porous metal oxide structure for high‐performance Li‐ion batteries.     

Chemically bonded carbon nanotubes on modified gold substrate as novel unbreakable solid phase microextraction fiber

A new technique is introduced for preparation of an unbreakable fiber using gold wire as a substrate for solid phase microextraction (SPME). A gold wire is used as a solid support, onto which a first film is deposited that consists of a two-dimensional polymer obtained by hydrolysis of a self-assembled monolayer of 3-(trimethoxysilyl)-1-propanthiol. This first film is covered with a layer of 3-(triethoxysilyl)-propylamine. Next, a stationary phase of oxidized multi-walled carbon nanotubes was chemically bound to the surface. The synthetic strategy was verified by Fourier transform infrared spectroscopy and scanning electron microscopy. Thermal stability of new fiber was examined by thermogravimetric analysis. The applicability of the novel coating was verified by its employment as a SPME fiber for isolation of diazinon and fenthion, as model compounds. Parameters influencing the extraction process were optimized to result in limits of detection as low as 0.2?ng?mL^?1 for diazinon, and 0.3?ng?mL^?1 for fenthion using the time-scheduled selected ion monitoring mode. The method was successfully applied to real water, and the recoveries for spiked samples were 104% for diazinon and 97% for fenthion.

A New Anode for Lithium‐Ion Batteries Based on Single‐Walled Carbon Nanotubes and Graphene: Improved Performance through a Binary Network Design

Carbon nanomaterials, especially graphene and carbon nanotubes, are considered to be favorable alternatives to graphite‐based anodes in lithium‐ion batteries, owing to their high specific surface area, electrical conductivity, and excellent mechanical flexibility. However, the limited number of storage sites for lithium ions within the sp²‐carbon hexahedrons leads to the low storage capacity. Thus, rational structure design is essential for the preparation of high‐performance carbon‐based anode materials. Herein, we employed flexible single‐walled carbon nanotubes (SWCNTs) with ultrahigh electrical conductivity as a wrapper for 3D graphene foam (GF) by using a facile dip‐coating process to form a binary network structure. This structure, which offered high electrical conductivity, enlarged the electrode/electrolyte contact area, shortened the electron‐/ion‐transport pathways, and allowed for efficient utilization of the active material, which led to improved electrochemical performance. When used as an anode in lithium‐ion batteries, the SWCNT‐GF electrode delivered a specific capacity of 953 mA h g^?1 at a current density of 0.1 A g^?1 and a high reversible capacity of 606 mA h g^?1 after 1000 cycles, with a capacity retention of 90 % over 1000 cycles at 1 A g^?1 and 189 mA h g^?1 after 2200 cycles at 5 A g^?1.     

Voltammetric Determination of Phenoxybenzyl‐Type Insecticides at Chemically Modified Conducting Polymer‐Carbon Nanotubes Coated Electrodes

The electrochemical reduction of three common insecticides such as cypermethrin (CYP), deltamethrin (DEL) and fenvalerate (FEN) was investigated at glassy carbon electrode (GCE), multiwalled carbon nanotubes modified GCE (MWCNT‐GCE), polyaniline (herein called as modifier M₁) and polypyrrole (herein called as modifier M₂) deposited MWCNT/GCE using cyclic voltammetry. Influences of pH, scan rate, and concentration were studied. The surface morphology of the modified film was characterized by scanning electron microscopy (SEM) and X‐ray diffraction analysis (XRD). A systematic study of the experimental parameters that affect differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived at. The calibration plots were linear over the insecticide's concentration range 0.1–100 mg L^?1 and 0.05–100 mg L^?1 for all the three insecticides at MWCNT‐GCE and MWCNT(M₁)‐GCE respectively. The MWCNT(M₂)‐GCE performed well among the three electrode systems and the determination range obtained was 0.01–100 mg L^?1 for CYP, DEL and FEN. The limit of detection (LOD) was 0.35 μg L^?1, 0.9 μg L^?1 and 0.1 μg L^?1 for CYP, DEL and FEN respectively on MWCNT(M₂)‐GCE modified system. Suitability of this method for the trace determination of insecticide in spiked soil sample was also determined.     

Activated carbon prepared from polyaniline base by K2CO3 activation for application in supercapacitor electrodes

An activated carbon was prepared from a polyaniline base using K₂CO₃ as an activating agent. The morphology, surface chemical composition, and surface area of the as-prepared carbon materials were investigated by scanning electron microscope, X-ray photoelectron spectroscopy, and Brunauer?CEmmett?CTeller measurement, respectively. Electrochemical properties of the as-prepared sample were studied by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 6?mol?L^?1 KOH aqueous solution. Compared with the non-activated carbon, activated carbon showed superior capacitive performance. The activation carbon presented a high specific gravimetric capacitance of 210?F?g^?1. The good electrochemical performance of the activated carbon was ascribed to well-developed micropores, high surface area, the presence of nitrogen and oxygen functional groups, and larger pore volume.     

Determination of 1-hydroxypyrene in human urine by a multi-wall carbon nanotubes-modified glassy carbon electrode

A multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (MWNT-GCE) was used to study the electrochemical behaviour of1-hydroxypyrene (1-OHP) and applied to its determination. The results showed that the modified electrode had a strong adsorptive ability to 1-OHP and enhances its electrochemical signal. By square wave voltammetry, the linear relationship of 1-OHP was 6?×?10^?9???8?×?10^?7?mol?L^?1 with a linear correlation coefficient of 0.996, and the detection limit was 1?×?10^?10?mol?L^?1. Compared with other published methods, this newly proposed method possesses many advantages such as very low detection limit, fast response, low cost and simplicity. And this method was applied successfully in the determination of 1‐OHP in real human urine samples.