Fabrication of CuInS2/CNTs absorber layers by sol–gel method

In this work, CuInS₂/multiwalled carbon nanotube (MWCNT) layers are fabricated by the sol–gel spin-coating method. We introduce two forms of MWCNTs into a CIS₂ solution, washed functional multiwalled carbon nanotubes (W-FMWCNTs) and unwashed-functional multiwalled carbon nanotubes (UW-FMWCNTs), in order to investigate the effects of MWCNTs and an acidic environment on the physical properties of the CIS₂ absorber layers. The structure and morphology of the samples are investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD study shows that all samples crystallize in a tetragonal structure. The results obtained from the optical, thermo-electric, and electrical measurements indicate that the two groups of CIS₂ layers prepared using W- and UW-FMWCNTs show the opposite behaviors. The Seebeck coefficient (SC) measurements indicate possible formation of a p–n junction.     

In Situ Growth of Mesoporous SnO2 on Multiwalled Carbon Nanotubes: A Novel Composite with Porous‐Tube Structure as Anode for Lithium Batteries

A novel mesoporous‐nanotube hybrid composite, namely mesoporous tin dioxide (SnO₂) overlaying on the surface of multiwalled carbon nanotubes (MWCNTs), was prepared by a simple method that included in situ growth of mesoporous SnO₂ on the surface of MWCNTs through hydrothermal method utilizing Cetyltrimethylammonium bromide (CTAB) as structure‐directing agents. Nitrogen adsorption–desorption, X‐ray diffraction and transmission electron microscopy analysis techniques were used to characterize the samples. It was observed that a thin layer tetragonal SnO₂ with a disordered porous was embedded on the surface of MWCNTs, which resulted in the formation of a novel mesoporous‐nanotube hybrid composite. On the base of TEM analysis of products from controlled experiment, a possible mechanism was proposed to explain the formation of the mesoporous‐nanotube structure. The electrochemical properties of the samples as anode materials for lithium batteries were studied by cyclic voltammograms and Galvanostatic method. Results showed that the mesoporous‐tube hybrid composites displayed higher capacity and better cycle performance in comparison with the mesoporous tin dioxide. It was concluded that such a large improvement of electrochemical performance within the hybrid composites may in general be related to mesoporous‐tube structure that possess properties such as one‐dimensional hollow structure, high‐strength with flexibility, excellent electric conductivity and large surface area.     

Structural and optical properties of functionalized multi-walled carbon nanotubes

Herein, we report the functionalization of multiwalled carbon nanotubes (MWCNTs) using meta-Chloroperoxybenzoic acid (mCPBA) as an oxidizing agent. Epoxy groups are incorporated into the sidewall of MWCNTs and the prepared functionalized multiwalled carbon nanotubes (F-MWCNTs) were characterized using FT-IR spectroscopy, X-ray diffraction, Raman spectroscopy and UV–visible spectroscopy. Morphology of MWCNTs and F-MWCNTs was determined using Scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM results clearly indicated that the diameter of F-MWCNTs is increased by 120% as compared to neat MWCNTs. From UV–visible spectroscopy data, band gap of F-MWCNTs was calculated using Tauc equation and it was found to be 3.9 eV. Photo emission property of F-MWCNTs was analyzed using photoluminescence spectroscopy. F-MWCNTs showed nice emission in the visible region and it depended upon the excited wavelength. These functionalized carbon nanotubes could find use as tunable optoelectronic devices in future nanotechnology.     

Acidified multi-wall carbon nanotubes/polyaniline composites with high negative permittivity

Acidified multi-wall carbon nanotubes (MWCNTs-COOH) have been synthesized using mixed acid acidification, and then acidified multi-wall carbon nanotubes (MWCNTs-COOH)/polyaniline (PANI) composites with negative permittivity have been successfully synthesized by in situ polymerization. At the same time, the effects of composition and structure on the permittivity of MWCNTs-COOH/PANI composites have been systematically studied. The effects of MWCNTs-COOH content on the generation and variation of negative permittivity are illuminated by the structure model of “nano wires”. XRD analysis indicates that MWCNTs-COOH becomes the crystal nucleus and affects the crystallinity of the MWCNTs-COOH/PANI composites. SEM results indicate that different contents of MWCNTs-COOH cause various dispersion states of MWCNTs-COOH, thus lead to different morphologies of MWCNTs-COOH/PANI composites and variation of permittivity.     

Efficient Lightweight Supercapacitor with Compression Stability

This paper reports the fabrication of an electrochemical supercapacitor (ES) with high gravimetric and areal capacitances, achieved at a high mass ratio of active material to current collector. The active material, polypyrrole, is in situ polymerized in an aerogel‐based current collector composed of crosslinked cellulose nanocrystals (CNCs) and multiwalled carbon nanotubes (MWCNTs). Mechanical robustness, flexibility, and low impedance of the current collectors are achieved by the chemical crosslinking of CNC aerogels and efficient dispersion of MWCNTs through the use of bile acid as a dispersant. Furthermore, the advanced electrode design results in low contact resistance. A single‐electrode areal capacitance of 2.1 F cm^?2 is obtained at an active mass loading of 17.8 mg cm^?2 and an active material to current collector mass ratio of 0.57. Large area ES electrodes and devices show flexibility, excellent compression stability at 80% compression, and electrochemical cyclic stability over 5000 cycles. Moreover, good retention of capacitive properties is achieved at high charge–discharge rates and during compression cycling. The results of this investigation pave the way for the fabrication of advanced lightweight ES, which can be used for energy storage in wearable electronic devices and other applications.     

A Reusable Interface Constructed by 3‐Aminophenylboronic Acid‐Functionalized Multiwalled Carbon Nanotubes for Cell Capture,Release, and Cytosensing

A newly developed electrochemical cell sensor for the determination of K562 leukemia cells using 3‐aminophenylboronic acid (APBA)‐functionalized multiwalled carbon nanotubes (MWCNTs) films is demonstrated. The films are generated by the covalent coupling between the ? NH₂ groups in APBA and the ? COOH group in the acid‐oxidized MWCNTs. As a result of the sugar‐specific affinity interactions, the K562 leukemia cells are firmly bound to the APBA‐functionalized MWCNTs film via boronic acid groups. Compared to electropolymerized APBA films, the presence of MWCNTs not only provides abundant boronic acid domains for cell capture, their high electrical conductivity also makes the film suitable for electrochemical sensing applications. The resulting modified electrodes are tested as cell detection sensors. This work presents a promising platform for effective cell capture and constructing reusable cytosensors.     

One‐Step Electrochemical Synthesis of Graphene/Polyaniline Composite Film and Its Applications

This work describes a new one‐step large‐scale electrochemical synthesis of graphene/polyaniline (PANI) composite films using graphite oxide (GO) and aniline as the starting materials. The size of the film could be controlled by the area of indium tin oxide (ITO). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible absorption spectrum (UV–vis) results demonstrated that the graphene/PANI composite film was successfully synthesized. The obtained graphene/PANI composite film showed large specific area, high conductivity, good biocompatibility, and fast redox properties and had perfect layered and encapsulated structures. Electrochemical experiments indicated that the composite film had high performances and could be widely used in applied electrochemical fields. As a model, horseradish peroxidase (HRP) was entrapped onto the film‐modi?ed glassy carbon electrode (GCE) and used to construct a biosensor. The immobilized HRP showed a pair of well‐de?ned redox peaks and high catalytic activity for the reduction of H₂O₂. Furthermore, the graphene/PANI composite film could be directly used as the supercapacitor electrode. The supercapacitor showed a high specific capacitance of 640 F g^?1 with a retention life of 90% after 1000 charge/discharge cycles.     

Novel PEN/BaTiO3/MWCNT Multicomponent Nanocomposite Film with High Thermal Stability for Capacitor Applications

In this work, novel nanocomposite films formed from polyarylene ether nitrile (PEN), barium titanate (BaTiO₃), and multiwalled carbon nanotubes (MWCNTs) were successfully prepared by the solution casting method combined with continuous ultrasonic dispersion technology. The micromorphology, thermal, mechanical, and dielectric properties of the nanocomposite films are investigated. All of the nanocomposite films exhibited excellent thermal stability and mechanical strength almost the same as pure PEN film. Their initial decomposition temperatures were up to 492°C, and the tensile strength was over 82 MPa. Besides, the nanocomposite films had excellent flexibility, as the films could be curled easily into cylinders with several layers. Furthermore, it was found that the film with 1.5 wt.% MWCNTs and 20 wt.% BaTiO₃ had the best comprehensive dielectric properties, with potential for application in organic film capacitors.     

Surface chemical sensitivity of polyaniline doped with palladium or platinum compounds

The chemical and structural surface-aging effects brought about by the presence of water in emeraldine base (EB) polyaniline (PANI) doped with Pd or Pt protonic acids were studied. IR spectroscopy, XRD, XPS and heterogeneous catalytic hydrogenation (alkyne→alkene→alkane) were applied to characterise the PANI–Pd and PANI–Pt. Interpretation of the results gave the surface characteristics, structure, chemical catalytic activity and stability mainly of PANI–Pd specimens. The unique form of catalytically active centres therein was the surface complex [PdCl₄]²⁻ with Pd 3d_5/2 BE=337·7 eV. The most promising among the PANI–Pd catalysts studied were those dried in a slow, long procedure (3 months, zeolite 5A). Copyright © 1998 John Wiley & Sons, Ltd.     

Hybrid electrochromic film based on polyaniline and TiO2 nanorods array

Titanium dioxide (TiO₂) nanorods (NRs) array was successfully prepared via hydrothermal method on fluorine doped tinoxide (FTO) coated transparent conductive glass substrate. The hybrid film of polyaniline (PANI)/TiO₂ NRs was achieved through electrochemical polymerization of aniline onto the TiO₂ NRs array film. The electrochromic and optical properties of the hybrid film were investigated by cyclic voltammetry (CV), amperometric i–t and UV–vis spectroscopy. The results indicate that the hybrid film has long term stability and reversible color changes after cyclic voltammetry scans for 200 circles. The PANI/TiO₂ NRs hybrid film can show three different colors. Response time of PANI/TiO₂ NRs hybrid film is about 0.7 s and 2.6 s at different states, respectively. The TiO₂ NRs array and the loose, porous surface among the hybrid film facilitate charge transmission and also provide large surface area for electrochemical reaction.     

Enhanced photoelectrocatalytic activity of Cr-doped TiO2 nanotubes modified with polyaniline

A facile method for preparation of Cr-doped TiO₂ nanotubes (Cr–TiO₂ NTs) modified with polyaniline (PANI) was developed. The obtained materials were analyzed with scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy. The photoelectrochemical property of PANI/Cr–TiO₂ nanotubes was studied by voltammetry, photocurrent and electrochemical impedance spectroscopy (EIS). Using PANI/Cr–TiO₂ NTs as photoanode, the removal of p-nitrophenol (PNP) by photoelectrocatalytic oxidation technique was investigated. Compared with Cr–TiO₂ NTs, PANI/Cr–TiO₂ NTs showed an increased efficiency in the photoelectrocatalytic degradation of PNP. Moreover, photoelectrocatalysis was more efficient for PNP degradation than electrochemical oxidation, direct photolysis, and photocatalysis. The influences of applied bias potential, initial concentration of PNP and solution pH on the photoelectrocatalytic degradation of PNP were investigated. Under optimized conditions, almost all PNP could be degraded on PANI/Cr–TiO₂ NTs after 2-h photoelectrocatalytic treatment.     

Cover Picture: Preparation of Rectangular WO3·H2O Nanotubes Under Mild Conditions (Adv. Funct. Mater. 11/2007)

The synthesis of WO₃ · H₂O nanotubes under mild conditions is reported by Limin Wu and co‐workers, of Fudan University, P.R. China on p. 1790. The synthesis is carried out with the aid of polyaniline (PANI). The PANI molecules are intercalated into tungsten oxide layers to provide a driving force for the formation of nanotubes from nanosheets. By this approach, the nanosheets can be directly rolled into nanotubes. This method could be applied to many other materials that possess layered/lamellar structures for forming nanotubes. WO₃·H₂O nanotubes are successfully synthesized with the aid of intercalated polyaniline (PANI) under relatively mild conditions. More interestingly, the WO₃·H₂O nanotubes have a rectangular cross‐section structure formed through a rolling mechanism. Scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, Fourier‐transform infrared analysis, UV‐vis‐near‐IR spectroscopy, selected‐area electron diffraction, and vibrating‐sample magnetometry analysis are employed to characterize the morphology, structure, and properties of the nanotubes.     

Platinum Nanoparticle Clusters Immobilized on Multiwalled Carbon Nanotubes: Electrodeposition and Enhanced Electrocatalytic Activity for Methanol Oxidation

3D flowerlike Pt nanoparticle clusters are electrodeposited onto multiwalled carbon nanotubes (MWCNTs) by using a three‐step protocol, which is all‐electrochemical and involves a key, second step of a potential pulse sequence. This 3D fractal morphology is in marked contrast to the 2D uniform nanoparticle dispersion of MWCNTs, which is achieved when the second step adopts cyclic voltammetry instead of a potential‐step method. The former is found to exhibit significantly higher electrocatalytic activity and better stability than the latter for oxidation of methanol. These attractive features are attributable to the unique 3D flowerlike structure of Pt nanoparticle clusters on MWCNTs with much higher electrochemically active surface areas. Our work points to a new path for the preparation of 3D Pt/MWCNT nanocomposites, which are promising as electrocatalysts in direct methanol fuel cells.     

Electropolymerization of Stable Leucoemeraldine Base Polyaniline Film and Application for Quantitative Detection of <Emphasis Type="Italic">Escherichia coli</Emphasis> O157:H7

A stable leucoemeraldine base polyaniline (PANI) has been optimally electrodeposited on a bare screen-printed carbon electrode (SPCE) using a potentiostatic method and a nonenzymatic electrochemical immunosensor for quantitative detection of Escherichia coli O157:H7 (E. coli O157:H7) fabricated. The stability, electroactivity, and surface morphology of the PANI film were studied by cyclic voltammetry and scanning electron microscopy. The PANI film formed by the potentiostatic method was firmly attached to the SPCE, being more stable than PANI film electrodeposited by a cyclic voltammetric method. Gold nanoparticles (AuNPs) were linked to the PANI film and used as a connector to an antibody against E. coli O157:H7 (Ab). E. coli O157:H7 was quantitatively detected by differential pulse voltammetry based on the PANI/Ab-modified SPCE. The principle of this quantitative method is based on a prominent decrease of the current after specific binding to E. coli O157:H7. Under the optimized conditions, a linear relationship between the peak current change (ΔI) and the logarithm of the E. coli O157:H7 concentration was obtained in the range from 4.0 × 10⁴ colony-forming units (CFU)/mL to 4.0 × 10⁹ CFU/mL, with limit of detection (LOD) of 7.98 × 10³ CFU/mL at signal-to-noise ratio (S/N) of 3. The immunoassay exhibited acceptable specificity, reproducibility, and stability for detection of E. coli O157:H7. In future work, the proposed approach could be used to prepare stable films which can withstand sonication and strong acid.     

Nanostructured CuO/PANI composite as supercapacitor electrode material

An in-situ polymerization method has been employed to prepare CuO/PANI nanocomposite. The prepared samples have been characterized by X-ray diffraction (XRD), FTIR spectroscopy, field emission scanning electron microscopy (FESEM), and BET analysis. Application of the prepared samples has been evaluated as supercapacitor material in 1 M Na₂SO₄ solution using cyclic voltammetry (CV) in different potential scan rates, ranging from 5 to 100 mV s⁻¹, and electrochemical impedance spectroscopy (EIS). The specific capacitance of CuO/PANI has been calculated to be as high as 185 F g⁻¹, much higher than that obtained for pure CuO nanoparticles (76 F g⁻¹). Moreover, the composite material has shown better rate capability (75% capacitance retention) in various scan rates in comparison with the pure oxide (30% retention). EIS results show that the composite material benefits from much lower charge transfer resistance, compared to CuO nanoparticles. Moreover, much better cyclic performance has been achieved for the composite material.     

Structural,Magnetic, and Reflection Loss Characteristics of Ni/Co/Sn-Substituted Strontium Ferrite/Functionalized MWCNT Nanocomposites

Ni/Co/Sn-substituted strontium ferrite [SrFe_12?x (Ni_0.5Co_0.5Sn) _x/2O₁₉]/multiwalled carbon nanotube (MWCNT) nanocomposites were produced by assembling ferrite particles on the external surfaces of MWCNTs. Various techniques including x-ray diffraction (XRD) analysis, transmission electron microscopy, field-emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared (FTIR) spectroscopy were used to demonstrate the successful attachment of ferrite particles onto the external surfaces of the MWCNTs. XRD analysis and FTIR spectroscopy confirmed the presence of strontium ferrite and carbon nanotube phases in ferrite and nanocomposite samples, respectively. FE-SEM micrographs indicated the formation of ferrite particles on the outer surfaces of MWCNTs in nanocomposite samples. Furthermore, vibrating-sample magnetometer (VSM) and reflection loss (RL) measurements were performed to assess the magnetic and microwave characteristics of the synthesized samples. VSM loops confirmed a relatively strong dependence of the saturation magnetization and coercivity on the volume percentage of MWCNTs. With the introduction of MWCNTs or an increase in the substitution, the saturation magnetization and coercivity were decreased. The RL properties of the nanocomposites were investigated in the 8 GHz to 12 GHz frequency range. The sample with 80 wt.% nanocomposite content showed a maximum RL of ?35 dB at 8.3 GHz with a 4 GHz absorption bandwidth over the extended frequency range of 8 GHz to 12 GHz for absorber thickness of 1.8 mm. The RL evaluations indicated that these nanocomposites have high potential for application as wide-band electromagnetic wave absorbers at GHz frequencies.     

Fabrication and performance evaluation of symmetrical supercapacitor based on manganese oxide nanorods–PANI composite

Manganese oxide nanorods distributed over polyaniline (PANI) network was prepared by one step facile synthesis condition. pH of the reactant solution was tuned using sulfuric acid. Effect of pH on the morphology, chemical composition, structure and electrochemical performance of the prepared materials were studied. Thermal investigation reveals the decomposition of PANI at temperatures below 600 °C. Structural details and chemical composition of the compound was obtained from XRD, FTIR and XPS studies. α type MnO₂ was found to be crystallized in the prepared MnO₂–PANI composite. Single crystal manganese oxide nanorods distributed over the PANI network was cognizant from the FESEM and HRTEM investigations. Nanorods of average diameter 82 nm and length 482 nm were obtained without deploying any surfactants or templates. Electrochemical techniques like Cyclic Voltammetry (CV), Chronopotentiometry (CP) and Electrochemical Impedance Spectroscopy (EIS) were utilized. Study results indicate that the composites prepared shows excellent electrochemical performance. Among the prepared materials, MnP-46 exhibits a maximum specific capacitance of 687 Fg⁻¹ at 5 mV s⁻¹ scan rate and a capacitance retention of 95% over 2000 cycling. Promising performance of MnP-46 was further tested in a symmetrical two cell configuration. The cell was operative upto 1 V potential window. MnP-46 in a symmetrical arrangement demonstrates 179 Fg⁻¹ at 5 mV/s scan rate. High conductivity of the electrode material was confirmed from the Nyquist plot.     

Effects of hydrogen peroxide on the electrical conductivity of graphite/polyaniline composites

The effects of hydrogen peroxide (H₂O₂) on the direct current (dc) electrical conductivity of graphite (G)/polyaniline (PANI) composites are studied. It was found that the conductivity of G/PANI composite reacted with H₂O₂ decreases with increasing time. Results are confirmed by UV–vis, FTIR absorption measurements, X-ray diffraction analysis and Raman spectroscopy. From X-ray diffraction and Raman spectroscopy measurements we prove that H₂O₂ affects only PANI but not Graphite particles. After their treatment with H₂O₂ only G(10%)/PANI, G(20%)/PANI and G(30%)/PANI samples show a semi-conductor behavior. The charge transport mechanisms in these three samples are due to hopping and tunneling and are described by both Mott's three-dimensional variable range hopping model and Sheng's fluctuation induced tunneling model. The transition in the nature of charge transport in G(10%)/PANI, G(20%)/PANI and G(30%)/PANI samples after treatment with H₂O₂ is caused by disorder and localization, whereas the inverse semi-conductor-metal transition which occurs at above G(30%) in the same samples arises essentially from percolation in G/PANI composites.     

Influence of polyaniline on electrode materials

Polyaniline (PANI) has been used for modification of the electrochemical behaviour of a carbon fluoride ((CF_x)_n) cathode in a lithium cell. PANI and (CF_x)_n powders were carefully mixed and the electrochemical properties and kinetic parameters of the composite (CF_x)_n–PANI cathode were evaluated by galvanostatic and potentiodynamic techniques. An increase in exchange current has been found for electrodes with addition of polyaniline in the form of emeraldine base (EB). During the reduction process of carbon fluoride using 1 M lithium perchlorate solution in organic solvent, the ternary intercalation compound CLi_xF is formed and then irreversibly decomposed into carbon and lithium fluoride. The insertion of lithium cations into the (CF_x)_n layered structure is diffusionally controlled, hence improvement in electronic properties of this fluoride material by the presence of conducting PANI chains and enhancement of discharge performance were found for 25% addition of PANI. Copyright © 1998 John Wiley & Sons, Ltd.     

Evaluation of Pd Nanoparticle-Decorated CeO<Subscript>2</Subscript>-MWCNT Nanocomposite as an Electrocatalyst for Formic Acid Fuel Cells

In this work, CeO₂-modified Pd/CeO₂-carbon nanotube (CNT) electrocatalyst for the electro-oxidation of formic acid has been investigated. The support CNT was first modified with different amounts (5–30 wt.%) of CeO₂ using a precipitation-deposition method. The electrocatalysts were developed by dispersing Pd on the CeO₂-CNT supports using the borohydride reduction method. The synthesized electrocatalysts were analyzed for composition, morphology and electronic structure using x-ray diffraction (XRD), scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) techniques. The formation of Pd nanoparticles on the CeO₂-CNT support was confirmed using TEM. The activity of Pd/CeO₂-CNT and of Pd-CNT samples upon oxidation of formic acid was evaluated by using carbon monoxide stripping voltammetry, cyclic voltammetry, and chronoamperometry. The addition of moderate amounts of cerium oxide (up to 10 wt.%) significantly improved the activity of Pd/CeO₂-CNT compared to the unmodified Pd-CNT. Pd/10 wt.% CeO₂-CNT showed a current density of 2 A mg^?1, which is ten times higher than that of the unmodified Pd-CNT (0.2 A mg^?1). Similarly, the power density obtained for Pd/10 wt.% CeO₂-CNT in an air-breathing formic acid fuel cell was 6.8 mW/cm² which is two times higher than Pd-CNT (3.2 mW/cm²), thus exhibiting the promotional effects of CeO₂ to Pd/CeO₂-CNT. A plausible justification for the improved catalytic performance and stability is provided in the light of the physical characterization results.