An Electrochemical Study on the Corrosion Inhibition of Stainless Steel by Polyaniline Film

Polyaniline(PANI)film was electrosynthesized on 304 stainless steel by cyclic voltammetry using aqueous oxalic acid as supporting electrolyte.The potential sweep rates were changed to achieve the PANI film with different thickness and structures.Protective properties of the PANI film for corrosion of stainless steel in 3% NaC1 aqueous solution were investigated by monitoring potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS).The results showed that the PANI film which was formed with lower sweep rate led to more positive shift of corrosion potential and greater charge transfer resistance,reflecting higher inhibition for corrosion of the stainless steel.     

纳米纤维聚苯胺膜在不锈钢电极表面的生长过程

研究了脉冲电流法(PGM)聚合苯胺时, 纳米纤维聚苯胺(PANI)膜在不锈钢(SS)电极表面的生长过程. 用计时电位法和扫描电子显微镜(SEM)表征了聚苯胺生长过程的电化学特征和微观形貌; 并通过循环伏安(CV)法研究了苯胺的聚合速率. 结果表明, 聚苯胺的生长经历了两个阶段, 首先是在裸不锈钢电极表面上形成颗粒状聚苯胺, 此时聚合电位约为1.10 V, 经历了30 s后, 电极表面被一层颗粒状聚苯胺膜所覆盖; 在此基础上, 聚苯胺以纳米纤维状结构继续生长, 当颗粒状聚苯胺被纳米纤维状聚苯胺膜完全覆盖时, 聚合电位降至0.75 V左右并保持稳定.     

Enhancement of photoelectric catalytic activity of TiO2 film via Polyaniline hybridization

A Polyaniline (PANI)/TiO₂ film coated on titanium foil was successfully prepared using the sol-gel method followed by a facile chemisorption. Compared with pristine TiO₂, the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation rates of 2,4-dichlorophenol (2,4-DCP) with the PANI/TiO₂ film were enhanced by 22.2% and 57.5%, respectively. 2,4-DCP can be mineralized more effectively in the presence of PANI/TiO₂ film. The best PEC degradation efficiency of 2,4-DCP with the PANI/TiO₂ film was acquired at an external potential of 1.5 V with a layer of 1 nm thick PANI. The PANI/TiO₂ film was characterized by Raman spectra, Fourier transform infrared spectra (FT-IR), Auger electron spectroscopy (AES), and electrochemical analysis. These results indicated that there was a chemical interaction on the interface of PANI and TiO₂. This interaction may be of significance to promote the migration efficiency of carriers and induce a synergetic effect to enhance the PC and PEC activities.     

The resistance to over-oxidation for polyaniline initiated by the resulting quinone-like molecules

Polyaniline (PANI) suffers electrochemical over-oxidation at high anodic potentials, which leads to severe degradation, forming quinone-like molecules (hydroquinone/benzoquinone, HQ/BQ). A research area usually neglected is the influence of the newly-produced HQ/BQ on the over-oxidation of PANI. In this study, it has been examined by cyclic voltammetry (CV) and FT-IR spectroscopy. When HQ was intentionally added into sulfuric acid solutions, the cyclic voltammograms demonstrate that the rate of degradation turned to be lower as the concentration of introduced HQ increased. First-order rate constants obtained from kinetic study were shown to vary between 0.1399 and 0.1027 s⁻¹ within the concentration range of HQ from 0 to 0.05 M. An important finding is that the quinone-like molecules may have a great electronic exchange with the nitrogen atoms of the intact PANI chain when adsorbed on it, which leads to the changes in PANI structure at the molecule level. Less pernigraniline (PEB) was finally obtained and thus slower degradation was observed. This conclusion is supported by the phenomenon that the peak potentials for emeraldine/pernigraniline (EM/PEB) transitions shifted to more positive values when HQ was added. Moreover, from FT-IR analyses, it seemed that the relative content of the reduced form of PANI ascended with the degradation. So, the existence of HQ/BQ enhances the stability of PANI structure, endows PANI with resistance to over-oxidation and protects it from further degradation to a certain extent.     

聚苯胺的化学合成及其电化学表征

本文用化学聚合法合成了在Ｎ－甲基吡咯烷酮（ＮＭＰ）中可溶的聚苯胺（ＰＡＮＩ）。通过溶液法定量（浓度与体积）制膜，对ＰＡＮＩ膜修饰电极的循环伏安（ＣＶ）性质进行了研究，证实了ＰＡＮＩ膜在１０．０ｍｏｌ／Ｌ ＨＣｌ的介质中，－０．１５￣０．６５Ｖ（ｖｓ．ＳＣＥ）的电位范围内氧化还原单元为八隅体单元。比较了恒电流聚合与化学聚合所得的聚苯胺的ＣＶ性质，发现两者有很好的一致性。     

Studies on metallofullerene (Dy@C82) embedded in a DDAB film in aqueous solution

The electrochemical behavior of metallofullerene (Dy@C82) in didodecyldimethylammonium bromide (DDAB) films deposited on glassy carbon, quartz crystal microbalance (QCM) gold crystals, and indium tin oxide (ITO) electrodes in aqueous solution was investigated in detail. Four pairs of reversible redox peaks were observed, and for the first time, these peaks were characterized by vis/NIR spectroscopy. Different from previous fullerene/cationic lipid modified electrodes, one oxidation and three reduction processes were observed. The stability of Dy@C82 and its ions in the film toward air was detected by measuring its cyclic voltammogram after holding the potentials for 10 s, followed by introducing 10 microL of air to the solution. Dy@C82 and its first three anions are stable toward air and water, while some chemical reactions take place when the third anion is further reduced in the film. Dy@C82+ is less stable than Dy@C82- toward water and air. The electrochemical processes were measured in different electrolytes, which showed pronounced anionic dependence on either its cation or anions. The electrochemical processes were also monitored using electrochemical quartz crystal microbalance (EQCM), and from the result a possible electron-transfer mechanism of a Dy@C82/DDAB electrode in aqueous solution was presented. It showed that the anions of Dy@C82 were bound to the DDA+ cation in the film, while the anions of electrolyte diffused into the film to compensate the positive charges when a cation of Dy@C82 was generated.     

The effect of the polyaniline morphology on the performance of polyaniline supercapacitors

The polyaniline (PANI) prepared by the pulse galvanostatic method (PGM) or the galvanostatic method on a stainless steel substrate from an aqueous solution of 0.5 mol/l H₂SO₄ with 0.2 mol/l aniline has been studied as an electroactive material in supercapacitors. The electrochemical performance of the PANI supercapacitor is characterized by cyclic voltammetry, a galvanostatic charge–discharge test and electrochemical impedance spectroscopy in NaClO₄ and HClO₄ mixed electrolyte. The results show that PANI films with different morphology and hence different capacitance are synthesized by controlling the synthesis methods and conditions. Owing to the double-layer capacitance and pseudocapacitance increase with increasing real surface area of PANI, the capacitive performances of PANI were enhanced with increasing real surface area of PANI. The highest capacitance is obtained for the PANI film with nanofibrous morphology. From charge–discharge studies of a nanofibrous PANI capacitor, a specific capacitance of 609 F/g and a specific energy density of 26.8 Wh/kg have been obtained at a discharge current density of 1.5 mA/cm². The PANI capacitor also shows little degradation of capacitance after 1,000 cycles. The effects of discharge current density and deposited charge of PANI on capacitance are investigated. The results indicate that the nanofibrous PANI prepared by the PGM is promising for supercapacitors.     

Characterization of stainless steel electrode modified by a thin film of polyaniline containing pt particles and its electrocatalytic activity for methanol oxidation

The catalytic behavior of stainless steel (SS) electrode modified by a thin film of polyaniline (PANI) containing platinum particles was studied for electrooxidation of methanol and compared with a platinated Pt/PANI electrode in acidic aqueous solution. Cyclic voltammetry (CV), chronoamperometry, CO stripping techniques were used to investigate electrochemical properties and electrocatalytic activity of SS/PANI/Pt and Pt/PANI/Pt electrodes. The morphology and particle size of Pt catalysts were characterized by Transmission Electron Microscopy (TEM) measurement. The effects of various parameters such as thickness of polymer film, medium temperature and stability of the modified electrodes on methanol oxidation were also investigated. The results indicated that the modified SS electrode exhibited a considerably high electrocatalytic activity on the methanol oxidation as well as the modified Pt electrode.     

Study the effect of inorganic salts on the chemically polymerized aniline films using quartz crystal microbalance

The chemical oxidation of aniline with ammonium peroxydisulfate to form polyaniline (PANI) films has been studied in different aqueous acid mediums such as HCl, HNO₃, and H₂SO₄. The yield and the growth rate of the PANI film deposition were measured using the quartz crystal microbalance (QCM) technique. The effect of different salts such as KCl, NaNO₃, and K₂SO₄ and their concentration on the yield and the growth rate of the film formation are investigated. The yield of PANI film deposition depends on the acid used and the type of salts as well as their concentrations. When HCl and HNO₃ were used as media, the addition of salts with the same anion has no effect. However, when H₂SO₄ was used as media, the addition of salts with the same anions as the medium enhances the yield of PANI film deposition. The UV–visible spectra of the produced PANI films in the absence and presence of the salts are also studied. Copyright © 2007 John Wiley & Sons, Ltd.     

Electrodepositions and capacitive properties of hybrid films of polyaniline and manganese dioxide with fibrous morphologies

Electrocodepositions were conducted in solutions of aniline and MnSO₄ through potential cycling to afford hybrid films of polyaniline (PANI) and manganese dioxide (PANI/MnO₂). The films obtained displayed characteristic redox peaks of PANI on cyclic voltammograms in acidic aqueous solution. While in 1.0 M NaNO₃ at pH 1, the films showed pseudocapacitive behaviors from 0 to 0.65 V vs. SCE. MnO₂ was detected through XRD and XPS measurements on the films. The codeposition of PANI with MnO₂ had dramatic effects on morphologies of the obtained hybrid films that displayed fibrous morphologies instead of granular one of PANI. Hybrid film PM50 obtained in the presence of 50 mM Mn²⁺ displayed a specific capacitance of 532 F g⁻¹ at 2.4 mA cm⁻² discharging current, 26% higher than that of similarly prepared PANI. It showed a coulombic efficiency (η) of 97.5% over 1200 cycles with 76% specific capacitance maintained.     

Polyaniline film deposition from the oxidative polymerization of aniline using K2Cr2O7

The deposition of the polyaniline (PANI) films was monitored using the quartz crystal microbalance (QCM) technique. The films were grown from an aqueous dilute hydrochloric acid solution by the chemical oxidation of aniline using potassium dichromate (KDC). The effect of the initial molar ratio of the KDC/aniline on the yield and the growth rate of the PANI films were studied. There is no optimum initial molar ratio of KDC/aniline of PANI film deposition. Also there was a small depletion period and no degradation to the deposited PANI films. The order of the polymerization kinetics was studied with respect to KDC. The UV-visible spectra of the PANI films grown onto a glass support immersed into the bulk solution were measured. The absorption of the PANI film with the time of polymerization was compared to the growth of the PANI film thickness with time determined from the QCM technique. The characteristics of the PANI film deposition were compared to the corresponding ones that were observed during the oxidative polymerization of aniline with ammonium persulphate (APS).     

Electrochemical Response of Polyaniline (PANI)/Thiokol Rubber (TR) Films in Cysteine Solution

The electrochemical character of polyaniline/thiokol rubber (PANI/TR) composite film on a Pt electrode was investigated in a cysteine sulphuric acid solution by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The significant change of the peak current and peak potential in the cyclic voltammograms was observed. The irreversible peaks of cyclic voltammetry for cysteine/cystine redox couple at a platinum electrode have turned into one pair of nearly reversible peaks at the above electrode; the reversibility of the redox couple has been greatly improved. We found that thiokol rubber could improve the electrocatalysis of the PANI film to the electrochemical reaction with S‐S bonds, as well as the adhesion of the PANI film to the Pt substrate. Several effective factors, such as the concentration of thiokol rubber in the nonaqueous electrodeposition solution, different potential scan rate, immersing time of the film electrode in the studied electrolyte were all taken into account.     

基底材料对脉冲电流法制备的聚苯胺膜性能的影响

本文采用脉冲电流法(PGM)在不同的基底材料表面沉积PANI, 通过平均电位\|时间曲线及扫描电子显微镜(SEM)等方法研究了基底材料对PGM法制备PANI的影响; 并采用循环伏安(CV)和电化学阻抗谱(EIS)研究了不同电极材料表面PANI的电化学性能.     

The polymerization of aniline at a solution-gelatin gel interface

Gelatin gel swollen with the solution of aniline hydrochloride was exposed to a solution of ammonium peroxydisulfate. The reactants met at the gel interface, and the redox reaction between them produced a polyaniline (PANI) interlayer, a PANI membrane, at first. The electrons abstracted from the aniline molecules in the gel during the oxidation are transferred through a conducting PANI membrane to oxidant molecules in the external solution. The reaction between aniline and peroxydisulfate thus takes place without the need for the reactant molecules to physically meet. PANI, therefore, grows from the interface into the gelatin gel. When the loci of reactants are reversed, i.e. the oxidant is inside the gelatin gel and aniline hydrochloride in the surrounding solution, PANI grows from the gel interface into the aniline solution but some PANI is produced inside the gelatin gel, too. Composite PANI-gelatin gels were separated and gelatin was removed from them by acid hydrolysis. The resulting PANI had a granular morphology and a conductivity of the order of units S cm⁻¹, slightly lower compared with PANI prepared in a common way by mixing the solutions of reactants. The differences in the details of molecular structure are discussed on the basis of FTIR spectra.     

The stability of polyaniline in strongly alkaline or acidic aqueous media

Polyaniline (PANI) base has been suspended in 9 M potassium hydroxide at 20 °C or 90 °C for various time intervals extending to 4 months. The fraction of acetone-soluble material increased from 1.2 wt.% to 4.5 wt.% after exposure to an alkaline medium for 60 days at 20 °C. Gel-permeation chromatography indicates that the aggregation of PANI is reduced, while the chain degradation itself is negligible. FTIR spectroscopy confirms this trend and the absence of hydrolytic changes in the PANI structure. Polyaniline retains the ability to be reprotonated with a 1 M sulfuric acid to a conducting form. No marked changes in the molecular structure have been found, even after suspension of PANI in 9 M KOH at 90 °C for 60 days.Similar immersion of PANI salt in 5 M sulfuric acid at 20 °C was responsible for changes in the protonation, and the mass increased by 11 wt.%. This was explained by the exchange of the original sulfate or chloride counter-ions for hydrogen sulfate anions or by the protonation of secondary amine sites in PANI in addition to imine ones. The changes in the molecular structure are discussed on the basis of FTIR spectra. The conductivity decreased from 1.2 S cm⁻¹ to ∼10⁻³ S cm⁻¹ but no time-dependence of conductivity was observed. There was no fraction of PANI soluble in acetone. PANI in the protonated state is thus stable also in the strongly acidic medium.The study is supplemented by the assessment of the thermal stability of PANI base, which is of importance for the processing of PANI. Loss of moisture has been observed after exposure to 250 °C for 10 h in both nitrogen atmosphere and in air. Good stability was found at 350 °C only in the nitrogen atmosphere, while a marked mass loss in weight was registered in air.     

The kinetics and spectral studies of the in situ polyaniline film formation

The chemical oxidation of aniline with ammonium persulfate (APS) in an aqueous acidic solution to form polyaniline (PANI) films has been studied using the quartz crystal microbalance (QCM) technique. The kinetics of the film formation was investigated. The reaction exhibited half-order with respect to APS and first-order to aniline. The effect of temperature on the growth rate of PANI films was studied. The activation energy is 39.79 kJ/mol. This is in agreement with the corresponding one determined for the chemical polymerization of PANI in the bulk. The UV-visible spectra of the PANI films grown onto a glass support immersed into the bulk solution were measured. The absorption of the PANI film with time was also studied and compared to the growth of the PANI film thickness using the QCM technique.     

Voltammetric behavior of benzo[a]pyrene at boron-doped diamond electrode: a study of its determination by adsorptive transfer stripping voltammetry based on the enhancement effect of anionic surfactant, sodium dodecylsulfate

Benzo[a]pyrene (BaP), a member of the polycyclic aromatic hydrocarbon (PAH) class, is one of the most potent PAH carcinogens. The electrochemical oxidation of BaP was first studied by cyclic voltammetry at the boron-doped diamond electrode in non-aqueous solvent (dimethylsulphoxide with lithium perchlorate). The compound was irreversibly oxidized in a single step at high positive potential, resulting in the well-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure in aqueous and aqueous/surfactant solutions over the pH range of 2.0-8.0. The technique in aqueous solutions had little value in practice because of too small oxidation peak current. This problem was solved when surfactants were added into the sample solution, by which the oxidation peak currents of BaP were found enhanced dramatically. The employed surfactants were sodium dodecylsulfate (anionic, SDS), cetyltrimethylammonium bromide (cationic, CTAB) and Tween 80 (non-ionic). Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 2.0 containing 2.5 × 10⁻⁴ M SDS at +1.07 V (vs. Ag/AgCl) (after 120 s accumulation at +0.10 V). The process could be used to determine BaP in the concentration range of 16-200 nM (4.04-50.46 ng mL⁻¹), with a detection limit of 2.86 nM (0.72 ng mL⁻¹). This method was also applied to determine BaP in model water sample prepared by adding its different concentrations into tap water.     

Electrochemical immunoassay of benzo[a]pyrene based on dual amplification strategy of electron-accelerated Fe3O4/polyaniline platform and multi-enzyme-functionalized carbon sphere label

An electrochemical immunosensor, basing on a dual amplification strategy by employing a biocompatible Fe₃O₄/polyaniline/Nafion (Fe₃O₄/PANI/Nafion) layer as sensor platform and multi-enzyme-antibody functionalized highly-carbonized spheres (multi-HRP-HCS-Ab₂) as label, was constructed for sensitive detection of benzo[a]pyrene (BaP). The stable film, Fe₃O₄/PANI/Nafion, can not only immobilize biomolecules, but also catalyze the reduction of hydrogen peroxide, indicating an accelerated electron transfer pathway of the platform. The experimental conditions, including the concentration of Nafion, concentration of Fe₃O₄/polyaniline (Fe₃O₄/PANI), pH of the detection solution and concentrations of biomolecules, were studied in detail. Basing on a competitive immunoassay, the current change was proportional to the logarithm of BaP concentration in the range of 8 pM and 2 nM with the detection limit of 4 pM. The proposed immunosensor exhibited acceptable reproducibility and stability. This new type of dual amplification strategy may provide potential applications for the detection of environmental pollutants.     

Determination of ibuprofen and novocaine hydrochloride with the use of water-micellar solutions of surfactants

The solubility and acid-base properties of ibuprofen in water-micellar media of surfactants were studied. A new visual method for the titrimetric determination of ibuprofen in pure form was proposed. The smallest pK value (4.43) and the greatest solubility (8.1 mg ml⁻¹) of ibuprofen were achieved using an aqueous cationic micellar medium of 0.1 M tridecylpyridinium bromide. The titration was performed with 0.05 M potassium hydroxide aqueous solution and the exact end-point was determined with the use of xylenol blue as indicator. Conditions for the individual determination of ibuprofen and novocaine hydrochloride in their 1:1 mixtures with the use of 0.1 M tridecylpyridinium bromide were proposed.     

In situ electrochemical SERS studies on electrodeposition of aniline on 4-ATP/Au surface

The electrochemical polymerization of 0.01 M aniline in 1 M H₂SO₄ aqueous solution on roughened Au surface modified with a self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) has been investigated by in situ electrochemical surface-enhanced Raman scattering spectroscopy (SERS). The repeat units and possible structures of the electrodeposited polyaniline (PANI) film were proposed; i.e., aniline monomer is coupled in head-to-tail predominately at the C₄ of aniline and amine of 4-ATP, and the thin PANI film is orientated vertically to substrate surface. Simultaneous Raman spectra during potential scanning indicate clearly that the ultrathin PANI film (in initial growth of the film) consists of semiquinone radical cation (IP⁺), para-disubstituted benzene (IP and IP⁺) and quinine diimine (NP) while it is oxidized, and without quinine diimine and semiquinone radical cation while reduced. Meanwhile, the results confirm that 4-ATP monolayer shows a strong promotion on the electrodeposition of aniline monomer, and a possible polymerization mechanism was proposed.