Fabrication and electrocatalytic properties of polyaniline/Pt nanoparticle composites

Polyaniline (PANI)/Pt nanoparticle composites can be prepared by the spontaneous redox reaction of K2PtCl4 with PANI, to yield thin films that show electrocatalytic properties in both acidic and neutral aqueous media.     

Electrochemical and morphological characterization of poly[(R)-(−)-3-(l-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-α-phenylglycinate] films deposited on ITO electrodes

Poly[(R)-(–)-3-(l-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-α-phenylglycinate] films were deposited on ITO electrodes using potentiodynamic and galvanostatic methods. Polymerization occurred as a charge dependent process at 1.0 V vs. Ag/Ag⁺(CH₃CN) and was not affected by the presence of nitro groups in the monomer. The surface morphology of the film and its electrochemical properties were studied as a function of deposition charge (Q_dep) and deposition method. Film thickness increased in a quasi-linear manner with respect to Q_dep within the range 40–80 mC cm². The galvanostatic method provided easier control of Q_dep compared with potentiodynamic deposition, and produced a more adherent film with homogeneous grain geometry. Cyclic voltammetry revealed a well defined redox couple at the anodic region, attributable to polymer p-doping, and a poorly defined redox pair at the cathodic region, attributable to the reduction of the nitro group.     

Crystallization kinetics of Pd in composite films of PEDT

The crystallization of palladium in poly-3,4-ethylenedioxythiophene (PEDT) films is studied in order to obtain nanosized palladium clusters in PEDT composite layers with high electrocatalytic activity. Nucleation and growth of Pd is investigated for dependences on overpotential, polymer layer thickness d and chemical state (active or overoxidized) of the PEDT films. It is found that before the onset of diffusion limitations the growth occurs under charge transfer control. The observed induction period t₀ indicates crystallization at the metal | polymer interface. The linear relation I^1/3 versus t found in the initial stage of the deposition process gives evidence for three-dimensional growth of the metal crystals. The number N₀ of sites active for nucleation decreases strongly with increasing d. A saturation in N₀ is reached for continuous thicker films. The overoxidized layers are less active for metal deposition and exhibit a 50-fold lower number of active sites. The electrocatalytic properties of the Pd/PEDT composite layers are studied with respect to hydrogen sorption. High electrocatalytic activity is found for composites obtained with thin PEDT films polymerized in the low potential region.     

Tuning of the electronic properties of self-assembling and highly sensitive chromic polyalkylthiophenes

The solvatochromic behaviour of different functional group-bearing and self-interacting polyalkylthiophenes with strong chromic responses in solution and self-assembling capacity in the solid state is investigated here. The menagerie of species deriving from the conformational freedom of the conjugated chains in solution has been examined in different solvent mixtures as their physico-chemical nature sensibly affects final material morphology in the solid (film) state. Memory of solution curling shape and of the degree of aggregation is in fact retained through casting or spin-coating procedures and permanently endures in the polymeric film. The efficiency of the final device based on the ICP (inherent conducting polymer) film may therefore be improved by simply acting on its morphology, which is directly determined by polymer dissolution conditions.     

Heme protein-gluten films: voltammetric studies and their electrocatalytic properties

Direct electrochemistry and electrocatalysis of heme proteins, such as hemoglobin (Hb), myoglobin (Mb), and horseradish peroxidase (HRP), incorporated in gluten biopolymer films cast on pyrolytic graphite (PG) electrodes, were studied by voltammetry and amperometry. All the three protein-gluten films exhibited a pair of well-defined, quasi-reversible cyclic voltammetric peaks at about −0.28 V versus saturated calomel electrode (SCE) in pH 5.5 buffers, respectively, characteristic of the heme Fe(III)/Fe(II) redox couples, indicating enhanced electron transfer between the proteins and PG electrodes in a gluten film environment. The protein-gluten hydrogel films showed excellent stability. Positions of Soret absorption band of protein-gluten films suggested that the heme proteins kept their secondary structure similar to their native state in the films in the medium pH range. The heme proteins in gluten films were act as a biologic catalyst to catalyze reduction of oxygen or hydrogen peroxide. The voltammetric or amperometric responses of H₂O₂ at the protein-gluten film electrodes could be used to determine the concentration of H₂O₂ in solution.     

Structures and electrical properties of ferroelectric copolymer ultrathin films

Ultrathin films of ferroelectric copolymer vinylidenefluoride and trifluoroethylene, P(VDF-TrFE), were successfully obtained by spin-coating and their nanoscale structures and electrical properties were studied utilizing atomic force microscopy (AFM). We succeeded in obtaining ultrathin copolymer films on graphite whose thickness ranged from 1 nm to several tens of nanometers by controlling concentration of copolymer solutions in methylethylketone. We found that ultrathin films thinner than 4 nm showed layered structures whose layer thickness was about 0.5 nm. On the other hand, films thicker than 4 nm formed typical edge-on lamellar crystal structures. Furthermore, we investigated surface potential distribution and piezoelectric property by AFM-based techniques and discussed interaction between electrical dipoles in the molecular chains and graphite substrate.     

Photoluminescence and Raman spectroscopy studies on polyaniline/PbI2 composite

Functionalization of PbI₂ with conjugated polymers (polyaniline-emeraldine base (PANI-EB) or polyaniline-emeraldine salt (PANI-ES)) is demonstrated by Raman and luminescence studies. PbI₂/PANI hybrid material was prepared by electrochemical polymerization of aniline onto the PbI₂ modified Pt electrode and mechanico-chemical reaction between the two constituents. PANI interacting with the PbI₂ gives rise to new Raman bands at 80, 144 and 170 cm⁻¹. First line reveals the formation of “stacking faults” that disrupt the I-Pb-I layers stacking along the c axis by the insertion of polymer molecules. The bands at 144 and 170 cm⁻¹ are attributed to the vibrational mode associated with Pb-NHR″₂ (R″=C₆H₄) bond. The functionalization of PbI₂ with PANI-EB brings forth the PANI-ES form. Depending on the semiconducting (PANI-EB) or conducting (PANI-ES) properties of the polymer in the PbI₂/PANI intercalated material, a partial or total collection of the charges generated under band to band irradiation is revealed by photoluminescence studies.     

Application of Polyfolates in the Development of Electrochemical Glucose Biosensors

Folic acid was polymerised electrochemically at a glassy carbon electrode surface from 0.1 mol L^?1 phosphate buffer saline solution, pH 5.0, containing 0.1 mmol L^?1 monomer. The obtained thin film was porous with a pore size of 50–60 nm. Since its electrochemical stability was rather short, the polyfolate film was covered with a graphene‐chitosan composite layer which increased its stability significantly. The best strategy to immobilise the enzyme was crosslinking with glutaraldehyde. The lifetime of this glucose biosensor in use was at least 12 days, on‐shelf life time was at least 30 days. The linear range was up to 1 mmol L^?1 and the LOD was 0.6 µmol L^?1. The first polyfolate‐based biosensor was applied to analysis of natural samples.     

Electrochemistry and scanning electron microscopy of polyaniline/peroxidase-based biosensor

An amperometric biosensor was prepared by in situ deposition of horseradish peroxidase (HRP) enzyme on a polyaniline (PANI)-doped platinum disk electrode. The PANI film was electrochemically deposited on the electrode at 100 mV s⁻¹/Ag-AgCl. Cyclic voltammetric characterization of the PANI film in 1 M HCl showed two distinct redox peaks, which prove that the PANI film was electroactive and exhibited fast reversible electrochemistry. The surface concentration and film thickness of the adsorbed electroactive species was estimated to be 1.85×10⁻⁷ mol cm⁻² and approximately 16 nm, respectively. HRP was electrostatically immobilized onto the surface of the PANI film, and voltammetry was used to monitor the electrocatalytic reduction of hydrogen peroxide under diffusion-controlled conditions. Linear responses over the concentration range 2.5×10⁻⁴ to 5×10⁻³ M were observed. Spectroelectrochemistry was used to monitor the changes in UV-vis properties of HRP, before and after the catalysis of H₂O₂. The biosensor surface morphology was characterized by scanning electron microscopy (SEM) using PANI-doped screen-printed carbon electrodes (SPCEs) in the presence and absence of (i) peroxidase and (ii) peroxide. The SEM images showed clear modifications of the conducting film surface structure when doped with HRP, as well as the effect of hydrogen peroxide on the morphology of biosensor.     

Template synthesis of polyaniline/Pd nanoparticle and its catalytic application

Pre-organization of Pd(II) species on polyaniline to form the corresponding d,π-conjugated complex provided a versatile route to a small and well-dispersed nanoparticle, which worked as an efficient redox catalyst for oxidative coupling reaction of 2,6-di-t-butylphenol.     

Constructing magnetic polyaniline/metal hybrid nanostructures using polyaniline/Fe3O4 composite hollow spheres as supports

Polyaniline (PANI)/Fe₃O₄ composite hollow spheres have been successfully synthesized in one step using sulfonated polystyrene (PS) spheres as templates. The magnetic PANI hollow spheres were used as supports for noble metal nanoparticles (NPs) such as Au and Pd. The morphology, composition and magnetic properties of the resulting products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, inductively coupled plasma (ICP) atomic spectra and vibrating sample magnetometer. The catalytic activity of magnetic PANI/Au composite shells on the oxidation of dopamine was investigated by cyclic voltammetry. The obtained results provide our product with a practical application for the detection of dopamine. On the other hand, the catalytic activity of magnetic PANI/Pd composite shells on the reduction of 4-nitroaniline was investigated by spectroscopic methods and compared with Pd/C catalyst which was already widely used in industrial production.     

Probing buried carbon nanotubes within polymer-nanotube composite matrices by atomic force microscopy

Multi-walled carbon nanotubes (MW-CNT) inside a polyamide-6 (PA6)-MW-CNT composite were visualized by atomic force microscopy (i) in a field-assisted intermittent contact and (ii) in the tunneling (TUNA) mode. Individual buried MW-CNTs were clearly discerned within the PA6 matrix. An average diameter of 33 ± 5 nm of the MW-CNTs was determined based on field-assisted intermittent contact mode AFM images, which is consistent with the expected size of PA6-coated MW-CNTs. Single well dispersed MW-CNTs that are located in the sub-surface region of the composite were also observed in the TUNA mode. These new AFM approaches circumvent the tedious sample preparation based on ultramicrotoming required for high resolution electron microscopy studies to obtain “in-depth” morphological information and hence are expected to facilitate the analysis of CNT-based and other nanocomposites in the future.     

Morphology and thermal properties of conductive polyaniline/polyamide composite films

Polyaniline (PANI) in an emeraldine‐base form, synthesized by chemical oxidation polymerization, was doped with camphor sulfonic acid (CSA). The conducting complex (PANI–CSA) and a matrix, polyamide‐66, polyamide‐11, or polyamide‐1010, were dissolved in a mixed solvent, and the blend solution was dropped onto glass and dried for the preparation of PANI/polyamide composite films. The conductivity of the films ranged from 10^?7 to 10⁰ S/cm when the weight fraction of PANI–CSA in the matrices changed from 0.01 to 0.09, and the percolation threshold was about 2 wt %. The morphology of the composite films before and after etching was studied with scanning electron microscopy, and the thermal properties of the composite films were monitored with differential scanning calorimetry. The results indicated that the morphology of the blend systems was in a globular form. The addition of PANI–CSA to the films resulted in a decrease in the melting temperature of the composite films and also affected the crystallinity of the blend systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2531–2538, 2002     

Platinum-modified polyaniline/polysulfone composite film electrodes and their electrocatalytic activity for methanol oxidation

The polyaniline/polysulfone (PAN/PSF) composite films were prepared by electropolymerization, and then platinum was deposited into this composite film to obtain the platinum-modified polyaniline/polysulfone(Pt/PAN/PSF) composite film electrodes. Their component, morphology and structure were characterized by FTIR spectra, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the composite film has a bi-layer structure with asymmetrical pores, and the platinum particles are homogeneously dispersed in the modified film electrodes. The cyclic voltammetry and electrochemical impedance spectroscopy techniques were applied to investigate the electrochemical properties and the electrocatalytic activity of the modified film electrodes, which show a promotive action for methanol oxidation and the methanol oxidation under a diffusion-controlled process.     

Study on the electrochemical behavior and differential pulse voltammetric determination of rhein using a nanoparticle composite film-modified electrode

A sensitive electrochemical method was developed for the differential pulse voltammetric determination of rhein at a glassy carbon electrode (GCE) modified with a nanoparticle composite film. In the present paper, multi-wall carbon nanotube (MWNT) was dispersed into dihexadecyl phosphate (DHP) to give a homogeneous suspension. After the solvent evaporation, a uniform film of MWNT-DHP composite film was obtained on the GCE surface. The MWNT-DHP composite film-modified GCE exhibited excellent electrocatalytic behavior toward the redox of rhein. Compared with an irreversible reduction of rhein at the bare GCE, a reversible redox behavior of rhein was observed at the MWNT-DHP composite film-modified GCE and the redox current was also enhanced greatly. Based on this, a cathodic differential pulse voltammetry (DPV) was applied for the determination of rhein. The experimental parameters, which influence the current of rhein, were optimized. Under optimal conditions, the cathodic DPV measurements were performed and a linear response of rhein was obtained in the range from 1.0 x 10(-8) to 5.0 x 10(-6) mol L(-1) and with a limit of detect (LOD) of 5.0 x 10(-9) mol L(-1). The proposed procedure was successfully applied to assay rhein in real samples with satisfactory results.     

Thermal stability study of conductive polyaniline/polyimide blend films on their conductivity and ESR measurement

Conductivity stability at thermal environment of conductive polyaniline‐complexes/polyimide (PANI‐complexes/PI) blends, which were doped by camphorsulfonic acid (CSA) and dodecylbenzenesulfonic acid (DBSA), respectively, were investigated by conductivity measurements, electron spin resonance (ESR) spectra, differential and scanning thermometer (DSC). In the conversion process of PANI/Polyamic acid (PAA) to PANI/PI, the blend endeavored some kinds of alteration such as decomplexation of moisture and solvent, dissociation of dopant, crosslinking of PANI chain, and the imidization of PAA chain. PANI‐DBSA/PI showed higher thermal stability of conductivity than PANI‐CSA/PI, and both samples showed nearly linear decay of conductivity with increasing temperature showing greatly enhancement of conductivity stability. When they were exposed at near or over glass transition temperature, the conductivity decay became faster. The conductivity stability at base environment was also higher for PANI‐DBSA/PI due to difficulty in accessing of hydroxyl ion to PANI, which were resulted from dopant. DBSA‐doped blends showed increased polaron mobility and concentration at relatively high temperature, which led to extremely higher conductivity and its stability at high temperature. Copyright © 2002 John Wiley & Sons, Ltd.     

Facile synthesis of highly conductive polyaniline/graphite nanocomposites

A facile process for the synthesis of exfoliated graphite and polyaniline/graphite (PANI/graphite) nanocomposite was developed. Graphite nanosheets were prepared via the microwave irradiation and sonication from synthesized expandable graphite. The nanocomposites were fabricated via in situ polymerization of aniline monomer in the presence of graphite nanosheets. The nanoscale dispersion of graphite sheets was evidenced by the SEM and TEM examinations. According to the electrical conductivity test, the conductivity of the final PANI/graphite nanocomposites were dramatically increased compared with pristine PANI. From the thermogravimetric analysis, the introduction of graphite exhibits a beneficial effect on the thermal stability of PANI.     

Wavelength dependence of nanoscale photodegradation in poly(3-octylthiophene) thin films

The use of conducting polymers in optoelectronic devices is subject to the understanding of the electro-optical processes that take place at the nanoscale. One of the photo-induced processes that limit their application is the photodegradation, which reduces the device working life. In this work the photodegradation of poly(3-octylthiophene) thin films was studied by combining Kelvin probe microscopy and optical microscopy. In this way, a direct correlation between morphological and contact potential changes with optical density changes as a function of the irradiation wavelength and intensity can be made. These results, complemented with Raman spectra help to clarify the degradation processes that are taking place. We find that the photodegradation strongly depends on the irradiation wavelength blue light being much more aggressive than UV. In addition, the optical properties change abruptly before any substantial change in the morphology is observed.     

Fabrication and characterization of copper nanoparticle thin-films and the electrocatalytic behavior

Copper nanoparticles, stabilized by cysteine, have been formed thin-films on indium tin oxide (ITO) electrodes with (3-mercaptopropyl) trimethoxysilane (MPTMS). Scanning electron micrograph (SEM) demonstrates that the films are uniform and the copper nanoparticles are homogeneously distributed on the ITO electrode surface. Electrochemical experiments reveal that the obtained copper nanoparticles modified electrodes show improved electron-transfer characteristics and exhibit high electrocatalytic activity to the reduction of nitrite and nitric oxide, which can be utilized as an efficient electrochemical sensor.     

Electrochemical properties of polyaniline in p-toluene sulfonic acid solution

Polyaniline was deposited potentiodynamically on a stainless steel substrate in the presence of an inorganic acids (sulfuric acid). The electrochemical characterization of the electrode was carried out by means of cyclic voltammetry and electrochemical impedance spectroscopy in the organic acids (p-toluene sulfonic acid) solution. The results show that polyaniline has a high specific capacitance of 431.8 F g⁻¹ at 1 mV s⁻¹, high coulombic efficiency of 95.6% at 20 mV s⁻¹, and exhibits a high reversibility. This indicates the promising feasibility of the polyaniline used as an electrochemical capacitor material in the electrolyte of p-toluene sulfonic acid solution especially at high charge–discharge process.