An amperometric enzyme biosensor based on in situ electrosynthesized core–shell nanoparticles

This work describes a new approach to the construction of an amperometric biosensor for hydrogen peroxide detection based on in situ electrosynthesized gold/polyaniline core–shell nanocomposites on conducting ITO electrode. The immobilization of the enzyme, horseradish peroxidase (HRP), on the polyaniline nanofilm was carried out by electrostatic attachment approach. Results showed that the immobilized HRP exhibited enhanced performance toward the reduction of H₂O₂, in comparison with other bulk polyaniline (PANI)-based H₂O₂ biosensor and metallic nanoparticles incorporated PANI systems. The resulting biosensor shows a fast amperometric response (<2 s) to H₂O₂. A linear range from 0.2 to 80 μM for the detection of H₂O₂ was observed with a sensitivity of 20.5 μA/mM and a detection limit of 0.16 μM at a signal-to-noise ratio of 3. Moreover, the biosensor has a good reproducibility, and long-term stability.     

Polyaniline synthesis with iron(III) chloride–hydrogen peroxide catalyst system: Reaction course and polymer structure study

We report on the catalytic polymerization of aniline (ANI) with FeCl₃/H₂O₂ system, which can considerably lower contamination of neat polyanilines (PANIs) by side-products characteristic of stoichiometric polymerization. However, catalytically prepared PANIs exhibit reduced conductivity related most probably to side reactions involving radicals generated as integral components of the FeCl₃/H₂O₂ system. Catalytic polymerization of ANI with FeCl₃/H₂O₂ system was found to be the reaction of approximately 2nd order with respect to ANI and gives PANIs of a good quality only when [H₂O₂] in the reaction mixture was kept low, i.e., at under-stoichiometric ratios [H₂O₂]/[ANI]. At over-stoichiometric ratio [H₂O₂]/[ANI], PANIs of lowered conductivity, worse spectroscopic characteristics and increased size of PANI nanostructures were obtained; nevertheless, these PANIs were not over-oxidized to pernigraniline state. The reaction-time profiles of the open-circuit potential of reaction mixtures exhibited an inflection related to the H₂O₂ depletion from the system. Total consumption of H₂O₂ exceeded its consumption necessary on ANI polymerization, which proves partial decomposition of H₂O₂ by Fe ions. UV/vis and resonance Raman spectra indicate incomplete deprotonization of PANIs prepared with FeCl₃/H₂O₂ system and subsequently treated with aqueous ammonia, which proves partial self-doping of these PANIs. However, IR and NMR spectra indicate rather low extent of self-doping. It has been proposed that self-doping of PANI involves phenolic OH groups originated from side reactions involving radical species formed from H₂O₂.     

The effect of epoxy coating containing emeraldine base and hydrofluoric acid doped polyaniline on the corrosion protection of AZ91D magnesium alloy

Corrosion protection of epoxy coatings containing emeraldine base polyaniline (PANI) or hydrofluoric acid doped PANI on AZ91D magnesium alloy were studied by EIS and Pull-Off Adhesion Test. The results indicated that the addition of emeraldine base PANI or hydrofluoric acid doped PANI could improve the corrosion resistance of epoxy coating. The epoxy coating containing hydrofluoric acid doped PANI had the best performance of the corrosion protection among three systems under investigation. The corrosion product film was analyzed by XPS indicating that PANI changed the chemical structure of the corrosion film. The protective mechanism imparted by PANI was discussed.     

Effect of Aspergillus niger Tiegh. L-10 on the physical and chemical properties of a polyaniline coating in the growth substrate

The influence of the growth of Aspergillus niger Tiegh. fungi on the morphological, chemical and electrochemical properties of the polyaniline (PANI) modified Ni surface has been investigated. The strain of Aspergillus niger Tiegh. L-10 was cultivated on the malt extract agar (DIFCO OXOID). A PANI film was synthesized by potentiodynamic polymerization in an aqueous 0.3 M H₂C₂O₄ solution containing 0.1 M aniline on the Ni electrode. The electrochemical behaviour of polymer films was determined in a 0.05 M H₂SO₄ solution by the cyclic voltammetry method. The composition of PANI and Aspergillus niger Tiegh. treated PANI surfaces have been characterized using X-ray photoelectron spectroscopy (XPS). The morphology has been studied using scanning electron microscopy (SEM). The attachment of a polymer film via the metabolic product resulted in oxidation of the surface. It was estimated that at the PANI/microorganism interface, a Ca-complexed carboxylate interfacial reaction product was formed.     

Magnetic properties of polyaniline doped with FeCl3

Magnetic properties of polyaniline (PANI) doped with FeCl₃ were investigated as a function of temperature and magnetic field. The temperature dependence of the magnetic susceptibility (χ) of PANI doped with FeCl₃ exhibits dominant paramagnetic component (well described by Curie–Weiss law with a negative Curie–Weiss temperature Θ) accompanied by a small temperature-independent paramagnetic contribution. Magnetization measured as the function of magnetic field shows smaller saturation effect than expected for non-interacting iron ions. These two observations suggest weak antiferromagnetic (AF) interactions between Fe ions.     

Preparation of polyaniline–TiO2 composite and its comparative corrosion protection performance with polyaniline

Due to strict environmental regulations on the usage of chromate in the coating industries, search for effective inhibitive pigment in replacing those chromate pigments has become necessary. In recent years it has been shown that electrically conducting polymers such as polyaniline (PANI) incorporated coatings are able to protect steel due to their passivating ability similar to that of chromates. This work presents the comparative corrosion protection performance of the coatings containing polyaniline and polyaniline–TiO₂ composite (PTC) on steel in acrylic binder. The PANI and PTC were prepared by chemical oxidative method of aniline by ammonium persulfate. The polymers were characterized by FTIR, XRD and SEM. The corrosion protection performance of the coatings containing PANI and PTC on steel was evaluated by immersion test in 3% NaCl for 60 days and salt fog test for 35 days. The performance of the coatings in both the tests was investigated by open circuit potential measurements and EIS technique. It has been found that the open circuit potential values of PTC containing coating are more nobler by 50–200 mV in comparison to that of coatings with PANI. Besides, the resistance values of the coating containing PTC were more than 10⁷ Ω cm² in the 3% NaCl immersion test after 60 days and 10⁹ Ω cm² in the salt fog test of 35 days which were two orders high in comparison to that of PANI containing coatings. The better performance of PTC containing coatings may be due to uniform distribution of polyaniline which can form uniform passive film on the iron surface.     

Electro-Synthesis of Nano-Colloidal PANI/ND Composite for Enhancement of Corrosion-Protection Effect of PANI Coatings

The polyaniline/nanodiamond (PANI/ND) nanocomposite coating was prepared on mild steel via electrochemical polymerization using cyclic voltammetry technique. The ultrasonic irradiation was used for effectively dispersing ND particles in electropolymerization solution. The prepared nanocomposite films were found to be nano-colloidal, and very adherent with low porosity. The corrosion performance of the coatings was investigated in 0.5 M H₂SO₄ solution by electrochemical impedance spectroscopy and polarization methods. The obtained results showed that the presence of ND particles significantly enhanced the corrosion protection performance of the PANI films in 0.5 M H₂SO₄ corrosive medium. X-ray diffraction and FT-IR techniques confirmed the intercalation of the nanoparticles in PANI matrix.     

Application of polyaniline to galvanic anodic protection on stainless steel in H2SO4 solutions

A stand-alone polyaniline (PANI) film electrode was made and then applied to protect 1Cr13 stainless steel (a type of stainless steel typically used in China, 0–15% C, 13% Cr) from corrosion in highly acidic solution, up to 5 M H₂SO₄. The stand-alone PANI electrode and 1Cr13 were coupled to study their galvanic interactions. PANI is a cathode while 1Cr13 is an anodic. The results indicate that PANI with a certain area can quickly passivate the stainless steel and effectively maintain the steady passive state for a long period of time. This specific method of PANI preventing 1Cr13 from corrosion is called galvanic anodic protection (GAP). Moreover, the efficiency, mechanism, and security of GAP were discussed. The results demonstrate that the stand-alone PANI electrode may have a potential application to galvanic anodic protection on stainless steel in highly corrosive H₂SO₄ solutions.     

Synthesis of polyaniline nanotubes using Mn2O3 nanofibers as oxidant and their ammonia sensing properties

In this work, a new method for the synthesis of polyaniline (PANI) nanotubes was presented. Experimentally, Mn₂O₃ nanofibers prepared by electrospinning technique were used as the oxidant template to initiate the polymerization of aniline in acid solution. After reaction, polyaniline shells were formed on the Mn₂O₃ nanofiber surface, and the Mn₂O₃ nanofibers were spontaneously removed. As a result, PANI nanotubes were obtained. As-prepared PANI nanotubes show an average diameter of 80 nm and inner diameter of 38 nm. The final PANI nanotubes were characterized by SEM, EDX, TEM, FTIR and XRD. The gas sensing of as-obtained PANI nanotubes was also investigated. It was found that the PANI nanotube sensing device could detect as low as 25 ppb NH₃ in air at room temperature with good reversibility.     

Dependence of the corrosion performance of polyaniline films applied on stainless steel on the nature of electropolymerisation solution

Polyaniline (PANI) films were deposited under cyclic voltammetric conditions on 304L stainless steel by aniline electropolymerisation from acidic and slightly basic solutions containing respectively the followed support-electrolytes: H₂C₂O₄ and KNO₃.It was found that the film produced in oxalic acidic medium was more conductive than that obtained in potassium nitrate one.The PANI coatings corrosion performances in 0.5 M NaCl were investigated and compared using standard electrochemical methods, electrochemical impedance spectroscopy (EIS) and SEM analysis.The highest corrosion resisting efficiency was obtained for PANI_nitrate which exhibited a significant physical barrier property against the attack of corrosive products. However, the corrosion protection of conductive PANI_oxalic coating was related to its catalytic behavior.     

Electrical and magnetic properties of the Fe3O4–polyaniline nanocomposite pellets containing DBSA-doped polyaniline and HCl-doped polyaniline with Fe3O4 nanoparticles

DBSA-doped polyaniline (DBSA–PANI) powder and HCl-doped polyaniline with Fe₃O₄ nanoparticles (HCl–PANI–Fe₃O₄) powder were mechanically mixed to obtain the Fe₃O₄–polyaniline nanocomposites. Powders of the nanocomposites were pressed to the pellets. Micromorphology, electrical and magnetic properties of the nanocomposite pellets were studied by using scanning electron microscopy and by measuring the conductivity in 100–300 K and the magnetization curve at room temperature. The DBSA–PANI pellets consist of long fibrils while the HCl–PANI–Fe₃O₄ pellets consist of granular particles. Thus the Fe₃O₄–polyaniline nanocomposites pellets consist of long fibrils and granular particles. The conductivity of the nanocomposite pellets linearly decreases from 0.19 ± 0.06 to 0.05 ± 0.01 S/cm when the HCl–PANI–Fe₃O₄ content increases from 0 to 100 wt.%. The variation of conductivity with temperature reveals that the charge transport mechanism can be considered to be one-dimensional variable-range-hopping (1D-VRH). All the Fe₃O₄–polyaniline nanocomposites show the magnetization curves. The saturation magnetization monotonously increases with increasing HCl–PANI–Fe₃O₄ content while the coercivity is estimated to be about zero independent of the HCl–PANI–Fe₃O₄ content. The saturation magnetization of the HCl–PANI–Fe₃O₄ is 11 emu/g.     

Corrosion protection of aluminum alloy by epoxy coatings containing polyaniline modified graphene additives

In the study, polyaniline/reduced‐graphene oxide (PANI‐RGO) composites, fabricated by loading 2, 5, and 8wt% graphene oxide, was prepared by in‐situ emulsion polymerization and reduction. They are characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy. Epoxy coatings adding PANI and PANI‐RGO composites were coated on the surface of AA5083 Al alloy. The anticorrosion performance of the coatings is measured by electrochemical impedance spectroscopy and potentiodynamic polarization curve in 3.5wt% NaCl solution. The results demonstrate that the epoxy/PANI‐RGO coating exhibits a better protection against AA5083 alloy corrosion compared with the epoxy/PANI coating. Enhancement of the passivation performance of PANI was obtained by the addition of RGO into epoxy/PANI coating system.     

Preparation and characterization of polyaniline/nano-Fe3O4 composites via a novel Pickering emulsion route

Polyaniline/nano-Fe₃O₄ composites were prepared by a novel solids-stabilized emulsion (Pickering emulsion) route for the first time. The products were characterized by SEM, XRD, FTIR spectra and particle size analyzer. Sphere-like morphology and sub-micrometer fibers of polyaniline/nano-Fe₃O₄ composites were synthesized in a toluene/water emulsion stabilized by Fe₃O₄ nanoparticles. It was found that the morphology of the resulting PANI/nano-Fe₃O₄ composites depended not only on the volume ratio of toluene to water (R), but also the amount of Fe₃O₄ in the reaction system. A possible mechanism for the formation of the different morphologic composites has been proposed. The room-temperature conductivity of PANI/nano-Fe₃O₄ composites also depended not only on the volume ratio of toluene to water (R), but also the amount of Fe₃O₄ in the reaction system. In addition, it was found that the magnetization under applied magnetic field for the as prepared the PANI/nano-Fe₃O₄ composites exhibited a clear hysteretic behavior, and both M_S and H_C for the PANI/nano-Fe₃O₄ composites exhibited a decrease with decreasing the nano-Fe₃O₄ content.     

Properties of electropolymerised polyaniline thin films obtained from different supporting electrolytes

This work reports on the properties of polyaniline (PANI) films electrochemically synthesised onto indium tin oxide (ITO) coated glass substrate from a mixed solution of 0.1?M aniline with three different types of supporting electrolytes: HNO₃, H₂SO₄ and H₃PO₄. In order to investigate the effect of dopant on the behaviour of polyaniline different techniques have been employed. These characterisations were made using photoelectrochemical, FTIR and Raman spectroscopies, field-emission scanning electron microscopy, UV–vis spectroscopy, diffuse reflectance spectrophotometry and photoluminescence techniques. The potocurent transients show a change of PANI films conductivity from p-type to n-type by changing the supporting electrolytes. The FTIR technique and Raman spectroscopy confirmed the formation of PANI thin film on ITO substrates. The morphology of the electropolymerised PANI thin films is closely related to the supporting electrolytes. Compact and spongy morphologies were observed for PANI films deposited in different supporting electrolytes. The optical measurements show an optical transmittance in the visible region, with variations depending on the nature of electrolytes.     

Direct involvement of acid centers of polyaniline in charge transfer on organic acceptor

Electrochemical behavior of hydroquinone and 4F-hydroquinone has been studied on Pt/polyaniline (PANI) electrodes in 1 M H₂SO₄ solution. Redox transformation of quinone/hydroquinone systems takes place on PANI practically without overpotential and, probably, the two-electron charge transfer processes are realized in such systems. Reaction currents depend on PANI quantities deposited on the Pt electrode and the molecular complex is formed. There exists a great electronic exchange between acid centers of PANI and quinone/hydroquinone molecules, resulting in electronic conjugation of this surface state (adsorbed molecule) with the polymer. Existence of such complexes was confirmed by FT-IR analysis which has been carried out on free-standing polymer films. Based on these findings we have assumed that the charge transfer complexes form along the polymer chain and the acceptor molecules participate in the doping and conductivity processes.     

Polyaniline and polypyrrole oxygen reversible electrodes

The effect of oxygen on the potential of reduced forms of polyaniline and polypyrrole were investigated. These forms of polyaniline and polypyrrole were not stable in the presence of oxygen. Zinc–polyaniline, zinc–polypyrrole, polyaniline–polyaniline (PANI–PANI), and polypyrrole–polypyrrole (PPy–PPy) batteries were constructed and studied. The effect of oxygen on the short-circuit current of these batteries showed that the cathode material, i.e., polyaniline and polypyrrole, can be regenerated by oxygen oxidation after discharge. These materials are potential candidates for the use as O₂ “fuel cell” type electrocatalytic electrodes.     

Synthesis and properties of high performance nanostructured polyaniline: Effect of initiator dosage and molecular oxygen

The effects of ammonium persulfate (APS)/aniline feed molar ratio or O₂ bubbling on the polymerization of polyaniline (PANI) in self-stabilized dispersion polymerization (SSDP) were examined. As the APS/aniline feed molar ratio was increased from 0.25/1.00 to 1.50/2.00, the polymerization yield was enhanced from 20% to 80%. However the molecular weight reduction with increased feed ratio, that is normally observed when PANI was polymerized in aqueous medium, was little. The O₂ bubbling during polymerization made the nanostructure of PANI to be finer, and this improved the solubility of PANI in solvent. The FT-IR spectra showed that the PANI prepared by SSDP, which have high conductivity in the range of 600–800 S/cm, contained less amount of the structures by ortho-coupling or Michael reductive addition of aniline compared to that synthesized by the standard method in an aqueous medium.     

Preparation,FTIR spectroscopic characterization and isothermal stability of differently doped conductive fibers based on polyaniline and polyacrylonitrile

Conductive fibers based on polyaniline (PANI) and polyacrylonitrile (PAN) were obtained by stirring with magnetic bar. This research was conducted to investigate conducting fibers of polyaniline:polyacrylonitrile (PANI:PAN) composite with different weight ratios of aniline in PAN matrix. The fibers were prepared by stirring process. The best conductivity behavior of the fibers was obtained with 5 mL of aniline. The fibers obtained were characterized using Fourier-transform infrared spectra (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The variation of electrical conductivity with different type doping agents (HCl, H₂SO₄ and HClO₄) and the stability in terms of DC electrical conductivity retention was studied in an oxidative environment by isothermal characteristics.     

Influence of tungstate ion dopants in corrosion protection behavior of polyaniline coating on mild steel

Electropolymerization of polyaniline (PANI) and polyaniline‐tungstate (PANIW) coatings on mild steel were successfully performed using cyclic voltammetry technique. Processes were carried out in aqueous electrolyte solutions of 0.3 M oxalic acid + 0.1 M aniline and 0.3 M oxalic acid + 0.1 M aniline + 0.001 M sodium tungstate dehydrate. Corrosion protection of PANI and PANIW coatings was evaluated with the help of open circuit potential (E_ocp) monitoring and electrochemical impedance spectroscopy (EIS) methods. All the results reveal the influence of additional doping agent (i.e., tungstate) in corrosion protection behavior of PANI coating.     

A study on mechanism of corrosion protection of polyaniline coating and its failure

Polyaniline (PANI) coatings were electrochemically deposited on substrates of stainless steel and platinum in solutions of 0.2 M H₂SO₄ and 0.1 M aniline by cyclic voltammetry. The corrosion protection of the PANI coatings and their failure were investigated in 0.2 M H₂SO₄ solution. It was observed that the corrosion protection ability of the coating to steel substrate was increased with the increase of the coating thickness. The corrosion protection ability was mainly attributed to the passivating effect of PANI due to its oxidizing ability in its emeraldine state. During its operation, the PANI coating in emeraldine state tended to gradually lose its corrosion protection ability. This gradual failure of the PANI coating, but faster than expected, was confirmed to be related to a gradual reduction of the emeraldine PANI and a gradually increased resistance between the PANI coating and the stainless steel substrate. These findings lead to a new mechanism for the corrosion protection of PANI coating and its failure.