The preparation and characterization of the cross-linked Ag–AgCl/polypyrrole nanocomposite

The cross-linked Ag–AgCl/polypyrrole (PPy) nanocomposite was synthesized using silver nanowires as templates. In the process, FeCl₃ served not only as the oxidant for pyrrole monomer but also as the etching-agent for silver nanowires. The morphologies of the product were observed by transmission electron microscopy. The existence of silver chloride and silver in PPy matrix was confirmed by X-ray diffraction and X-ray photoelectron spectroscope technologies. A possible formation mechanism of the cross-linked Ag–AgCl/PPy nanocomposite was also discussed.     

Mechanism of polypyrrole and silver nanorod formation in lauric acid–cetyl trimethyl ammonium bromide coacervate gel template: Physical and conductivity properties

Polypyrrole (PPy) and silver (Ag) nanorods are synthesized in cetyl trimethylammonium bromide–lauric acid (CTAB–LA) complex coacervate gel template. When PPy–CTAB–LA system is polymerized with AgNO₃, Ag nanorods are produced while use of ammonium persulphate (APS) as initiator yields PPy nanorods. Ag-nanorods are produced from the initial stage while PPy nanorods take a longer time. The average diameter of Ag nanorods varies from 60 to 145 nm by increasing AgNO₃ concentration from 0.27 M to 1.08 M and that of PPy varies from 145 nm to 345 nm by changing pyrrole concentration from 1 × 10^?4 to 2 × 10^?4 M, respectively. Fourier transformed infrared (FTIR) spectra indicate stabilization of Ag nanorods through complexation of PPy with adsorbed Ag⁺ ions. PPy nanoparticles are stabilized by adsorbed sulphate ions and lauric acid, both are acting as dopant to it. FFT pattern and EDX spectra clearly indicate the presence of Ag nanocrystals and PPy on the surface of Ag nanorods, respectively. The mechanism of nanorod formation is attributed from UV–Vis spectra showing a red shift of surface plasmon band of Ag and π–π* transition band of PPy with time. The highest dc conductivity of PPy–Ag composite is found to be 414.2 S/cm, 7 orders higher than that of PPy nanorods (9.3 × 10^?4 S/cm). PPy–Ag systems show Ohmic behavior while PPy nanorods exhibit semi-conducting behavior. The preferential formation of Ag nanorod in AgNO₃ initiated polymerization is attributed to the higher cohesive force of Ag than that of PPy. With two times higher LA and CTAB concentration in the gel the Ag nanorod diameter decreases only 12% while that of PPy nanorod decreases by 50%. Possible reasons are discussed from the hard and soft nature of the two nanorods and from the elasticity of the gel template.     

Fabrication of Ag/polypyrrole coaxial nanocables through common ions adsorption effect

According to the common ions adsorption effect, Ag⁺ ions will be adsorbed onto the closest surface of silver nanowires after being immersed in AgNO₃ solution. This makes the surface of silver nanowires become the active sites to oxidize pyrrole monomer to form PPy sheath without adding other oxidizing agent. The results of FT-IR and UV–vis spectra show the formation of PPy chain when pyrrole monomer was added to the reaction mixture containing the disposed silver nanowires. TEM images further prove that the Ag/polypyrrole (PPy) coaxial nanocables have been fabricated. The thickness of PPy sheath can be controlled by adjusting the concentration of AgNO₃ aqueous solution, which used to dispose silver nanowires. To some extent, the thickness of PPy layer would increase with the increasing of the concentration of AgNO₃ solution. After the adsorbed Ag⁺ ions on the surface of silver nanowires reach to the saturation, the thickness of PPy layer would not change greatly with continuously increasing of AgNO₃ concentration.     

Preparation and characterization of visible light-driven AgCl/PPy photocatalyst

Visible light photoactive AgCl/polypyrrole (PPy) composites were prepared via the reaction between excessive Ag⁺ and Cl⁻ ions in the presence of PPy_. The AgCl/PPy composites were systematically characterized using Fourier transform infrared (FTIR) spectroscopy, Raman spectra, X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM) and Thermal gravity analysis (TGA). It was found that face-centered cubic AgCl nanocrystallite and 0.2 wt% PPy component existed in the composite and spherical AgCl/PPy nanoparticles were in the range of 200-600 nm. The AgCl/PPy composites showed higher visible light-driven photocatalytic activity and stability than that of AgCl. A photoreduction mechanism was postulated for AgCl/PPy photocatalyst on dye methyl orange (MO). The used AgCl/PPy photocatalyst was facilely regenerated by an oxidation process in aqueous FeCl₃ solution.     

Synthesis and characterization of Ag@PPy yolk–shell nanocomposite

Ag@SiO₂@polypyrrole (PPy) nanocomposites were fabricated by a simple method. Ag@PPy yolk–shell nanocomposite was obtained after the removal of the midlayer SiO₂. TEM confirmed that the movable Ag cores were encapsulated in the interior of the hollow PPy nanoparticles. The structure of the resultant product was characterized by the Raman spectrum and X-ray diffraction technologies. Thermogravimetric analysis (TGA) revealed that the thermal stability of the nanocomposites was improved as compared with the pure PPy.     

Fabrication of Pt nanoparticles decorated PPy–MWNTs composites and their electrocatalytic activity for methanol oxidation

Here we report the synthesis and characterization of a catalyst material constituted of Pt, polypyrrole (PPy) and multi-walled carbon nanotubes (MWNTs). The catalyst supports (PPy–MWNTs nanocomposites) were synthesized via in situ chemical polymerization in advance, in which MWNTs were regarded as the matrix material. The supports were characterized by SEM & TEM, elemental analysis, XRD, FTIR and conductivity measurements. Then the catalysts were synthesized by a chemical reduction using sodium borohydride (NaBH₄) as reducing agent and acetic acid buffer (pH = 4) containing trace K₂C₂O₄ as reaction media. FTIR spectra showed that there existed relations between PPy and MWNTs during in situ polymerization. SEM and TEM micrographs of the catalyst samples exhibited that the existence of PPy layer which was evenly wrapped on the surface of MWNTs resulted in significant improvement in helping Pt particles well dispersed. XRD results showed that higher Pt(1 1 1) content in the catalyst deposited on PPy–MWNTs supports than that on MWNTs. The cyclic voltammetry (CV) tests of methanol electrocatalytic oxidation demonstrated that the electrode modified by Pt/PPy–MWNTs ternary composite catalyst showed higher catalytic stability than Pt/MWNTs binary catalyst, due to the synergic interaction between Pt and the carrier.     

Influence of Ag doped graphene on electrochemical behaviors and specific capacitance of polypyrrole-based nanocomposites

In this work, silver (Ag) nanoparticles were deposited on graphene sheets by chemical reduction and Ag-doped graphene (Ag-GR)/polypyrrole (PPy) nanocomposites were prepared by oxidation polymerization. The effect of the Ag-GR incorporation on the electrochemical properties of the PPy nanocomposites was investigated. It was found that highly dispersed Ag nanoparticles (2–5 nm) could be deposited onto the GR and that Ag-GR was successfully coated by PPy. From the cyclic voltammograms, Ag-GR showed higher electrocatalytic activity than that of pristine GR. Furthermore, the Ag-GR/PPy showed remarkably increased current density, quicker response, and better specific capacitance compared with GR/PPy. This indicates that, due to their high electrocatalytic activity, the Ag nanoparticles deposited onto the GR serve as an efficiency catalyst to improve electrochemical performance of the GR/PPy and that they resulted in the increase of the charge transfer between GR and PPy by bridge effect.     

A study on the preparation of poly(vinyl alcohol) nanofibers containing silver nanoparticles

In this study, two practical methods for the facile and controlled preparation of poly(vinyl alcohol) (PVA) nanofibers containing Ag nanoparticles were investigated for use in antimicrobial applications. In the first method, PVA nanofibers containing Ag nanoparticles were successfully electrospun from PVA/silver nitrate (AgNO₃) aqueous solutions after first refluxing them. The Ag nanoparticles in the PVA/AgNO₃ aqueous solutions were generated by refluxing them. Interestingly, it was found that the Ag nanoparticles were also spontaneously generated during the electrospinning process. In the second method, Ag nanoparticles were generated by annealing the PVA nanofibers electrospun from PVA/AgNO₃ aqueous solutions. Residual Ag⁺ ions and the Ag nanoparticles generated during the electrospinning process in the PVA nanofibers were diffused and aggregated into larger Ag nanoparticles during the annealing process. All of the Ag nanoparticles were sphere shaped and evenly distributed in the PVA nanofibers prepared by the two methods.     

Facile decoration of polypyrrole nanoparticles onto graphene nanosheets for supercapacitors

A facile approach was developed to prepare the graphene nanosheets (GNS) supported polypyrrole (PPy) nanoparticles via the in situ chemical oxidative polymerization of pyrrole onto the surfaces of the GNS modified with sodium dodecyl sulfonate (SDS) as surfactant for GNS and dopant for PPy simultaneously. The morphologies of the graphene nanosheets supported polypyrrole nanoparticles (GNS/PPy nanocomposites) with different feeding ratios were characterized with transition electron microscopy (TEM). It indicated that the PPy nanoparticles had been successfully decorated onto the GNS surfaces. The electrochemical performances of the GNS/PPy nanocomposites were investigated with cyclic voltammetry (CV), constant current charge–discharge and electrochemical impedance spectroscopy (EIS) techniques. The nanocomposite exhibited specific capacitance of 294 F g⁻¹ at the charge–discharge current density of 10 mA cm⁻² in 1.0 M NaNO₃ electrolyte. It showed that the GNS/PPy nanocomposites might be promising electrode materials for supercapacitors.     

Polypyrrole/thermally sensitive polyelectrolyte composite (I)

Polypyrrole (PPy) was prepared by electrochemical polymerization with the polyelectrolyte (PE) as a dopant. The PEs were copolymers of the water soluble polymers and 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS). The water soluble polymers were thermally sensitive poly(N-isopropyl acrylamide), P(NiPAAm) and thermally insensitive poly(acrylamide), P(AAm). The surface of PPy/PE film observed by SEM was smoother than that of PPy film doped with a monoelectrolyte. PPy/PE composites were fairly conductive, whose electrical conductivities measured by the four-probe method were in the range of 10⁻¹ to 10⁻² S/cm. The characteristics of cation and anion exchange during redox processes were investigated by applying potential from −0.8 to 0.5 V vs. an Ag/AgCl reference electrode to the PPy. The effect of temperature on the doping–dedoping behavior and mass change of PPy composites was investigated by potentiodynamic voltammetry and electrochemical quartz crystal microbalance (EQCM). The electrochemical activity of the PPy/PE gradually decreased with increasing temperature. PPy/P(NiPAAm/AMPS) showed much greater mass change with increasing temperature than PPy/P(AAm/AMPS), mainly because of a decrease in the degree of swelling of thermally sensitive moiety. This confirms that PPy/P(NiPAAm/AMPS) possesses temperature-dependent electrochemical activity, which indicates that it can be utilized for many attractive applications. The thermal volume transition temperature of PPy/P(NiPAAm/AMPS) was estimated from the slope change of mass decrease. The transition temperature of the oxidized state of PPy/P(NiPAAm/AMPS) was higher than that of the reduced state.     

Carbon nanotube–metal–oxide nanocomposites: microstructure,electrical conductivity and mechanical properties

Carbon nanotube–metal–oxide composites (metal=Fe, Co or Fe/Co alloy; oxide=Al₂O₃, MgO or MgAl₂O₄) have been prepared by hot-pressing the corresponding composite powders, in which the carbon nanotubes, mostly single or double-walled, are very homogeneously dispersed between the metal–oxide grains. For the sake of comparison, ceramic and metal–oxide nanocomposites have also been prepared. The microstructure of the specimens has been studied and discussed in relation to the nature of the matrix, the electrical conductivity, the fracture strength and the fracture toughness. The carbon nanotube–metal–oxide composites are electrical conductors owing to the percolation of the carbon nanotubes.     

Preparation of oligoaniline derivative/polyvinylpyrrolidone nanofibers containing silver nanoparticles

Oligoaniline derivative/polyvinylpyrrolidone nanofibers containing silver nanoparticles have been successfully prepared by electrospinning technique. Silver nanoparticles were prepared through reduction of Ag⁺ by oligoaniline derivative, and the process of redox was monitored by UV–vis spectra. The morphology of Ag-polymer blends nanocomposites and the distribution of Ag nanoparticles were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical analysis of nanocomposites was checked by cyclic voltammetry (CV) in the 0.5 M H₂SO₄. In addition, the presence of Ag nanoparticles was indicated by X-ray diffractometer (XRD).     

Slow strain rate stress corrosion testing at elevated temperatures and high pressures

Slow strain rate stress corrosion cracking experiments have been performed on single phase and duplex phase 304 stainless steels at 290°C. Environmental variables included chloride concentrations (0–1000 ppm), oxygen concentration (0–2 ppm) and potential (?_corr to + 500 mV vs Ag/AgCl). These experiments have shown that s.c.c. resistance is relatively unaffected by Cl^? if O₂ concentrations approach zero. However, at 2 ppm O₂ concentration, there is a large decrease in resistance with increasing Cl^? concentrations. Anodic polarization of the steels during straining in solutions containing 100 ppm Cl^? and 0 ppm O₂ showed a threshold potential for s.c.c. at ～ 500 mV more noble than the corrosion potential (? 650 ± 60 mV vs Ag/AgCl at temperature).     

Electrochemical synthesis of polypyrrole films over each of well-aligned carbon nanotubes

Polypyrrole (PPy) films were uniformly electropolymerized over each carbon nanotube of the well-aligned carbon nanotube arrays. For comparison, PPy films were also coated on flat metallic titanium (Ti) and platinum (Pt) substrates by the same technique. The synthesis and the redox performance of the PPy films were conducted by cyclic voltammetry (CV). The structural characterization including the thickness and uniformity of the PPy films was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is observed that the coating of the PPy film over carbon nanotubes is much faster than that on flat Ti/Pt surface. Furthermore, the redox performance of the PPy-coated carbon nanotube electrodes over flat Ti/Pt electrodes was significantly improved due to the high accessible surface area of the carbon nanotubes in the aligned arrays, especially in large film formation charge (Q_film). It is very promising that the electrode developed in this study could be used as high performance electrode in rechargeable batteries.     

Self-assembled polyaniline nanotubes and nanoribbons/titanium dioxide nanocomposites

Self-assembled polyaniline (PANI) nanotubes, accompanied with nanoribbons, were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous medium, in the presence of colloidal titanium dioxide (TiO₂) nanoparticles of 4.5 nm size, without added acid. The morphology, structure, and physicochemical properties of the PANI/TiO₂ nanocomposites, prepared at various initial aniline/TiO₂ mole ratios, were studied by scanning (SEM) and transmission (TEM) electron microscopies, FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), conductivity measurements, and thermogravimetric analysis (TGA). The electrical conductivity of PANI/TiO₂ nanocomposites increases in the range 3.8 × 10^?4 to 1.1 × 10^?3 S cm^?1 by increasing aniline/TiO₂ mole ratio from 1 to 10. The morphology of PANI/TiO₂ nanocomposites significantly depends on the initial aniline/TiO₂ mole ratio. In the morphology of the nanocomposite synthesized using aniline/TiO₂ mole ratio 10, nanotubes accompanied with nanosheets prevail. The nanocomposite synthesized at aniline/TiO₂ mole ratio 5 consists of the network of nanotubes (an outer diameter 30–40 nm, an inner diameter 4–7 nm) and nanorods (diameter 50–90 nm), accompanied with nanoribbons (a thickness, width, and length in the range of 50–70 nm, 160–350 nm, and ～1–3 μm, respectively). The PANI/TiO₂ nanocomposite synthesized at aniline/TiO₂ mole ratio 2 contains polyhedral submicrometre particles accompanied with nanotubes, while the nanocomposite prepared at aniline/TiO₂ mole ratio 1 consists of agglomerated nanofibers, submicrometre and nanoparticles. The presence of emeraldine salt form of PANI, linear and branched PANI chains, and phenazine units in PANI/TiO₂ nanocomposites was proved by FTIR and Raman spectroscopies. The improved thermal stability of PANI matrix in all PANI/TiO₂ nanocomposites was observed.     

Conducting polymer functionalized multi-walled carbon nanotubes with noble metal nanoparticles: Synthesis,morphological characteristics and electrical properties

We report the synthesis of conducting polyaniline-functionalized multi-walled carbon nanotubes (MWCNTs-f-PANI) containing noble metal (Au and Ag) nanoparticles composites (MWCNTs-f-PANI-Au or Ag-NC). MWCNTs-f-PANI was initially synthesized by functionalizing acyl chloride terminated carbon nanotubes (MWCNTs-COCl) with 2,5-diaminobenzenesulphonic acid (DABSA) via amide bond formation, followed by surface initiated in situ chemical oxidative graft polymerization of aniline in the presence of the ammonium persulphate (APS) as an oxidizing agent. MWCNTs-f-PANI was then dispersed into an aqueous Au or Ag metal salt solution followed by the addition of sodium citrate, which acted as a reducing agent. The resulting composite contained a high level of well dispersed Au or Ag nanoparticles (MWCNTs-f-PANI/Au-NC or MWCNTs-f-PANI-Ag-NC). Morphological and structural characteristics, as well as electrical conducting properties of the hybrid nanocomposites were characterized using various techniques including high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis) and four-probe measurements. FT-IR spectra confirmed that PANI was covalently bonded to MWCNTs. TEM images revealed the presence of Au or Ag nanoparticles finely dispersed in the composites with a size of <15 nm. XRD analysis revealed the presence of strong interactions between the metal nanoparticles and MWCNTs-f-PANI, where the metal particles were present in a phase-pure crystalline state with face centered cubic (fcc) structure. The room temperature electrical conductivity of the MWNCTs-f-PANI/Au or Ag composites was 4.8–5.0 S/cm, respectively, which was much higher than that of CNTs-f-PANI (0.18 S/cm) or pure PANI (2.5 × 10^?3 S/cm). A plausible mechanism for the formation of nanocomposites is presented. We expect that the new synthesis strategy reported here will be applicable for the synthesis of other hybrid CNTs–polymer/metal nanocomposites with diverse functionalities. This new type of hybrid nanocomposite material may have numerous applications in nanotechnology, gas sensing, and catalysis.     

Gas sensitivity study of polypyrrole/WO3 hybrid materials to H2S

Polypyrrole (PPy) and WO₃ were prepared by chemical oxidation polymerization and emulsion method, respectively. PPy/WO₃ hybrid materials with different PPy mass percent were prepared by mechanical mixing. WO₃ and PPy/WO₃ hybrids were characterized by XRD, SEM and HRTEM, and the sensitivity studies of PPy, WO₃ and PPy/WO₃ to toxic gases NH₃, H₂S, NO_x were also carried out. It was found that the particle size of WO₃ was about 29 nm, and PPy/WO₃ was about 50–100 nm. Gas sensitivity tests showed that when operated at 90 °C, PPy/WO₃ hybrids had better reversibility to H₂S than PPy higher sensitivity and selectivity to H₂S than WO₃. PPy/WO₃ materials had short response–recovery time to H₂S and their sensitivities had linear relationship with the concentration of H₂S. The sensitive mechanism of PPy/WO₃ materials to H₂S may be the co-effect of proton doping process and the n-type semiconductor's effect.     

Controlled fabrication of nanostructured polypyrrole on ion association template: Tubes,rods and networks

Polypyrrole (PPy) with variable nanostructure such as nanotubes, nanorods and networks has been fabricated by employing an ion association of heparin–methylene blue as new morphology-directing agent. The ion association exhibited both advantages of hard and soft template in template-induced chemical polymerization of pyrrole. By altering the ration of ion association component, PPy could be easily switched in morphology between nanotubes and nanorods. With the coordination effect of ion association and oxidant Fe³⁺, PPy networks with high conductivity could also be obtained in static condition. The achieved nanostructured polypyrrole were all doped with heparin, a biochemical material, and had potential exploitation value in electrochemistry and biochemistry.     

Electrospinning PVDF/PPy/MWCNTs conducting composites

Conducting PVDF/PPy composites (PPy composites) were prepared by using the highly porous electrospun (e-spun) nonwoven web as a host polymer. E-spun nonwoven web was made by electrospinning a solution of PVDF and CuCl₂·2H₂O in solvent of N,N-dimethylacetamide (DMAc). The PPy composites were fabricated by exposing a nonwoven web containing oxidant to pyrrole vapors. Field-emission scanning electron microscopy (FE-SEM) analysis was conducted to show the microstructure of the nonwoven webs and the uniform coating of PPy on the e-spun fiber surfaces of the PPy composite. The information of PPy on the e-spun fibers surface was confirmed by attenuated Fourier-transform infrared spectrometer (ATR FT-IR) and X-ray photoelectron spectroscope (XPS). The thermal property of PPy composites was also investigated by differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The electrical conductivity of the PPy composites was affected by the fabrication method and oxidant content in the nonwoven web. The electrical conductivity and mechanical strength of the PPy composites were improved when surface-modified multi-walled carbon nanotubes (MWCNTs) were added to the e-spun fibers. Energy-filtered transmission electron microscopy (EF-TEM) results confirmed that the MWCNTs were well arranged and embedded in the e-spun fibers. The observed conductivity of the conducting PPy-MWCNTs composite was 10^?1 S/cm.     

The preparation and gas sensitivity study of polypyrrole/zinc oxide

Polypyrrole (PPy) was prepared by chemical oxidation polymerization, analyzed by FT-IR, elemental analysis and HRTEM, and studied for gas sensitivity. It suggested that PPy had sensitivity to NH₃, H₂S and NO_x, and showed irreversibility to NO_x gas. The organic–inorganic hybrid materials PPy/ZnO with different PPy weight percents were prepared by mechanical mixing, and the sensitivity study of the materials to toxic gases NH₃, H₂S, NO_x was carried out at different operating temperatures 30, 60, and 90 °C. It was found that PPy/ZnO materials (PPy(1%)/ZnO, PPy(3%)/ZnO, PPy(5%)/ZnO, PPy(10%)/ZnO, PPy(20%)/ZnO) had better selectivity and reversibility to NO_x than pure PPy, and much lower working temperature than the reported working temperature of ZnO (about 350–450 °C). Their sensitivity increased with the increasing concentration of NO_x at particular working temperature, and among them PPy(10%)/ZnO had the maximum sensitivity to NO_x in the same condition. They showed no response to 1000, 1500, 2000 ppm NH₃ or H₂S. The response mechanism of PPy/ZnO materials to NO_x was discussed.