Electrochemical preparation and kinetic study of poly(o-tolidine) in aqueous medium

Poly(o-tolidine), PoT, film was prepared by electrochemical oxidation of the monomer, oT, in 0.1 M HCl + 0.1 M KClO₄. The presence of KClO₄ in the formation medium was found to be essential for the electropolymerization process to proceed. Increasing the upper potential limit up to +1.5 V, instead of +1.0 V, leads to appearance of a new anodic peak at +1.36 V and enhancement of the polymer formation of PoT without changing the film structure. The electrochemical behavior of the formed polymer films was investigated in 1.0 M HClO₄. The kinetic parameters were calculated from the values of the charge consumed during the electropolymerization process. The rate of the polymerization reaction was found to depend on the concentration of the monomer rather than the electrolyte. The polymerization rate is first order with respect to the monomer concentration and zero order with respect to the electrolyte. The electrolyte plays no active role in the kinetics of the electropolymerization process and its role is most likely limited to polymer doping.     

Electropolymerization of 4-nitro-1,2-phenylenediamine and electrochemical studies of poly(4-nitro-1,2-phenylenediamine) films

In this work, we report the anodic electropolymerization of 4-nitro-1,2-phenylenediamine (4NoPD) in different supporting electrolytes at different pH. The feasibilities of forming the polymer poly(4-nitro-1,2-phenylenediamine) (P4NoPD) on gold and glassy carbon electrodes (GCE) were shown. The P4NoPD films were generated by continuous potential cycling between −0.15 V and +1.10 V (versus Ag|AgCl, saturated KCl). The pH of the electropolymerization medium, the nature of the background electrolyte and the number of cycles used were found to influence strongly the amount of polymer deposited. The reduction of nitro-groups of the P4NoPD films was also found to be dependent on solution conditions, especially pH.     

Potentiodynamic deposition of poly (o-anisidine-co-metanilic acid) on mild steel and its application as corrosion inhibitor

For the first time, poly (o-anisidine-co-metanilic acid) (PASM) was deposited on mild steel substrate by electrochemical polymerization of o-anisidine and metanilic acid monomers in aqueous solution of 0.1 M H₂SO₄. The electrochemical polymerization of o-anisidine takes place in the presence of metanilic acid monomer and uniform, strongly adherent coating was obtained on the substrate. The electroactivity of copolymer was studied by cyclic voltammetry and AC impedance techniques. There is an increasing anodic current due to oxidation of metanilic acid monomer at the surface of the electrode when the applied potential is cycled from −0.2 V to 0.8 V. These deposits were characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis and TG/DTA techniques. The effect of various concentrations of PASM copolymer solution in acid rain corrosive media has been studied through potentiodynamic polarization, AC impedance and I-E curve methods. The soluble form of polymeric solution provided better anti-corrosive behavior in artificial acid rain solution.     

Characterization of ultrathin electroactive films synthesized via the self-limiting electropolymerization of o-methoxyaniline

The electropolymerization of o-methoxyaniline under self-limiting deposition conditions yields ultrathin (<20 nm) coatings of an insoluble, low-molecular-weight polymer on planar indium-tin-oxide electrode substrates. The self-limiting nature of the electropolymerization is achieved by using citrate-buffered aqueous electrolytes (pH 4.7) in which the developing polymer that deposits at the electrified interface is neither conductive nor permeable to monomer. Although non-conductive as electrodeposited, the resulting poly(o-methoxyaniline) coating becomes electroactive when transferred to acidic aqueous electrolytes. The morphology and chemical structure of the poly(o-methoxyaniline) coatings are characterized by surface-sensitive methods including atomic force microscopy, specular-reflectance infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemistry. Fundamental understanding of the structure/property relationships derived from these investigations on planar substrates will ultimately be applied to three-dimensional electrode nanoarchitectures that incorporate such electroactive coatings for enhanced charge-storage functionality.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

Electrochemical and in situ TM-AFM studies of the polymerization conditions on poly(o-methoxyaniline) film morphology

The in situ atomic force microscopy and the electrochemical studies on electropolymerization of the o-methoxyaniline in the 0.0-0.8 V versus NHE range of the electrode potential are described. It is proved that in the 0.0-0.3 V versus NHE a redox process takes place, resulting in the formation of poly(o-methoxyaniline) in its reduced form, leucoemeraldine. The different morphologies are exhibited by poly(o-methoxyaniline) under different polymerization conditions. The microscopic results show that with the increase of the monomer concentration in the bulk of electrolyte solution the globular morphology, related to the coil like molecular structure, is replaced by the fibrilar one, related to the opened-up, more conductive extended coil structure. It is shown that oxidation of a leucoemeraldine state of polymer to its emeraldine state results in the change of the morphology from the chain like structure to the massive fibrilar like structure. The reduction of oxidized polymer results in its irreversible fragmentation.     

Protective properties of polyaniline and poly(aniline-co-o-anisidine) films electrosynthesized on brass

Polyaniline and poly(aniline-co-o-anisidine) films were deposited on brass (Cu40Zn). The synthesis processes of homo and copolymer film were carried out under cyclic voltammetric condition from 0.12 M aniline and 0.06 M aniline + 0.06 M o-anisidine containing 0.2 M sodium oxalate solutions. Homo and copolymer films were characterized by scanning electron microscopy (SEM). SEM images clearly show that one of the brass electrodes was covered with a black copolymer film of strongly adherent homogeneous characteristic while the other one with a porous dark green homo polymer one. The corrosion performances of coated and uncoated electrodes in 3.5% NaCl were evaluated with the help of AC impedance spectroscopy, anodic polarization plots and open circuit potential–time curves. The protective effect of homo and copolymer films formed on brass grew in parallel with extended exposure time. It was only observed with copolymer-coated electrode that changes in the charge transfer resistance of copolymer-coated electrode were related to strong adsorption of copolymer film on the brass surface which led to the formation of a protective oxide layer due to its catalytic behaviour.     

Methanol electrooxidation on platinum microparticles electrodeposited on poly (o-methoxyaniline) films

In this paper we have studied the electrooxidation of methanol on electrodes obtained through the electrodeposition of platinum microparticles on poly (o-methoxyaniline) films. The dependence of the electroactivity on the electrodes preparation parameters has been detailed. It has been shown that the concentration of the monomer during the formation of the polymeric films influences the rate of polymer growth and the electrocatalytic activity. A maximum methanol electrooxidation peak current has been observed for polymers grown to an anodic voltammetric charge of approximately 75 mC cm⁻². It has been observed that the electroactivity increases when the platinum deposition is carried out in several steps instead of a single potential electrolysis. The conditions that favour a slower deposition process, i.e., smaller H₂PtCl₆ concentrations and smaller electrodeposition overpotential, lead to an enhancement of the methanol electrooxidation currents. This enhancement is attributed to an increase in the platinum surface area as a consequence of a decrease in the platinum particle size.     

Effects of polymerization potential on the permselectivity of poly(o-phenylenediamine) coatings deposited on Pt-Ir electrodes for biosensor applications

In attempts to improve the permselectivity of poly-o-phenylenediamine (PoPD) for biosensor applications, we investigated the influence of applied electropolymerization potential on the permeability properties of the non-conducting, non-ionic form of PoPD deposited on Pt-Ir wire electrodes in neutral media, using fixed potential amperometry and cyclic voltammetry. The analytes chosen were hydrogen peroxide (the signal transduction molecule in many oxidase-based biosensors) and ascorbic acid (AA, the archetypal interference species in biological applications of biosensors). The permselectivity (S%) of Pt/PoPD, expressed as the percentage interference by AA in hydrogen peroxide calibrations carried out at +0.7 V versus SCE, showed three distinct ranges: very poor (∼70%) for mild anodic applied polymerization potentials (<200 mV), indicating little or no PoPD coating formed on the electrode surface; moderate (∼2%) when the PoPD was generated using intermediate potentials (250-300 mV); and excellent (<0.3%) for polymerization potentials >400 mV. There was also a trend in this last S% range for further improvement with increasing polymerization potential, which reached an optimum value of 0.10 ± 0.02% (n = 19 sensors) when the PoPD electrodeposition was carried out at 700 mV versus SCE. This enhancement in S% was due to a surprising combination of increases in permeability for hydrogen peroxide and decreases in AA permeability for the higher values of applied polymerization potential. In addition, the data indicate that, for the conditions used here, electropolymerization at the fixed applied potential of 0.7 V was superior to CV in terms of permselectivity for hydrogen peroxide detection by PoPD-modified electrodes in media containing AA.     

Electrochemical composite formation of thiophene and N-methylpyrrole polymers on carbon fiber microelectrodes: Morphology,characterization by surface spectroscopy,and electrochemical impedance spectroscopy

Electrochemical composite thin film formation (∼0.6–0.7 μm) of thiophene and N-methylpyrrole on carbon fiber microelectrodes (diameter ∼7 μm) was carried out by cyclic voltammetry in order to understand and improve the surface properties and capacitance behaviour of carbon fibers. Carbon fiber microelectrodes were coated with polythiophene and N-methylpyrrole was electrografted onto the thiophene electrode. The electrocoated carbon fiber surface mophology was characterized by scanning electron microscopy and atomic force microscopy and by FTIR-reflectance spectroscopy for their composition. The effect of monomer concentration and scan number on electropolymerization has also been investigated. The impedance behaviour of composite electrodes was characterized by electrochemical impedance spectroscopy. The composite of polythiophene and poly-N-methylpyrrole exhibits better charge storage properties than polythiophene coated carbon fiber microelectrodes.     

In situ UV-vis spectroelectrochemistry of poly(o-phenylenediamine-co-m-toluidine)

Results of in situ UV-vis spectroelectrochemical studies of the electropolymerization of o-phenylenediamine (OPD), m-toluidine (MT) and the copolymerization of OPD with MT are reported. Electropolymerization was performed in aqueous acidic medium at a constant potential of E_SCE = 1.0 V at an indium doped tin oxide (ITO) coated glass electrode. The course of homopolymerization was followed for MT and OPD solutions with various monomer concentrations. The spectral characteristics of the mixed solutions were studied at a constant concentration of MT and various concentrations of OPD in the comonomer feed. An absorption band at λ = 497 nm was assigned to the head-to-tail mixed dimer/oligomer resulting from the cross reaction between OPD and MT cation radicals. UV-vis spectra recorded during copolymerization show dependence of the growth of the band at λ = 497 nm on OPD concentration in the feed. At lower OPD feed concentration it appears as the major band in the corresponding spectra. The UV-vis spectra recorded for the copolymer films suggest the incorporation of both monomer units in the copolymer. The FT-IR spectra of the copolymers show the presence of phenazine type structures in the copolymer backbone.     

Electrochemical copolymerization of m-toluidine and o-phenylenediamine

Electroactive copolymers of m-toluidine (MT) and o-phenylenediamine (OPD) were prepared electrochemically in aqueous sulfuric acid by potential cycling and characterized with cyclic voltametry, in situ conductivity measurements and FT-IR spectroscopy. The voltammograms of the copolymers exhibit different behavior for different concentrations of OPD in the comonomer feed. At optimum conditions the resulting poly(OPD-co-MT) shows an extended useful potential range of the redox activity as compared to the corresponding homopolymers. The effect of scan rate and pH on the electrochemical activity was studied. The copolymer was electrochemically active even at pH 8.0. The stability of the copolymer film was also tested. The copolymer has a potential region of maximum conductivity different from that of PMT and POPD. The conductivity of the copolymer is between the conductivity of the homopolymers. The vibrational bands at 3122/3450 and 2922/875 cm⁻¹ in the FT-IR spectra of the copolymer indicate the presence of both OPD and MT units, respectively, in the copolymer backbone.     

Poly(o-ethylaniline) coatings for stainless steel protection

The poly(o-ethylaniline) coatings were electrochemically synthesized on 304-stainless steel by using cyclic voltammetry from an aqueous salicylate medium. Cyclic voltammetry, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize these coatings, which indicates that the aqueous salicylate solution is a suitable medium for the electrochemical polymerization of o-ethyaniline on 304-stainless steel. The performance of poly(o-ethylaniline) as protective coating against corrosion of 304-stainless steel in aqueous 3% NaCl was evaluated by the open circuit potential measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The results of the potentiodynamic polarization and cyclic potentiodynamic polarization demonstrate that the poly(o-ethylaniline) coating provides excellent protection to both localized and general corrosion of 304-stainless steel. The corrosion potential was about 0.190 V more positive in aqueous 3% NaCl for the poly(o-ethylaniline) coated steel than that of bare steel and reduces the corrosion rate of steel almost by a factor of 20.     

Photosensitive poly(benzoxazole) based on precursor from diphenyl isophthalate and bis(o-aminophenol)

A new synthetic method for the preparation of poly(benzoxazole) (PBO) precursor, poly(o-hydroxyamide) (7) from bis(o-aminophenol) (5) and diphenyl isophthalate (6) has been developed. Polymer 7 was prepared by the polycondensation of 5 and 6 in 1-methyl-2-pyrrolidinone (NMP) at 185-205 °C. Model reactions were carried out in detail to elucidate appropriate conditions for the formation of 2-hydroxybenzanilide (3) from o-aminophenol (1) and phenyl benzoate (2). The photosensitive (PBO) precursor based on polymer 7 containing a 22% of benzoxazole unit and 30 wt% 1-{1,1-bis[4-(2-diazo-1-(2H)naphthalenone-5-sulfonyloxy)phenyl]ethyl}-4-{1-[4-(2-diazo-1(2H)naphthalenone-5-sulfonyloxy)phenyl]methylethyl}benzene (S-DNQ) showed a sensitivity of 110 mJ cm⁻² and a contrast of 5.0 when it was exposed to 436 nm light followed by developing with a 2.38 wt% aqueous tetramethylammonium hydroxide solution at room temperature. A fine positive image featuring 8 μm line and space patterns was observed on the film of the photoresist exposed to 200 mJ cm⁻² of UV-light at 436 nm by the contact mode.     

Electrochemical tolazoline sensor based on gold nanoparticles and imprinted poly-o-aminothiophenol film

Amperometric detection of tolazoline (TL) was carried out on a gold nanoparticles (AuNPs)/poly-o-aminothiophenol (PoAT)-modified electrode by a molecular imprinting technique and electropolymerization method. The modification procedure was characterized via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The recognition between the imprinted sensor and target molecule was observed by measuring the variation of amperometric response of the oxidation-reduction probe, K₃Fe(CN)₆ on electrode. Under the optimal experimental conditions, the peak currents were proportional to the concentrations of tolazoline in two ranges of 0.05-5.0 μg mL⁻¹ and 5.0-240 μg mL⁻¹ with the detection limit of 0.016 μg mL⁻¹. Meanwhile the prepared sensor showed sensitive and selective binding sites for tolazoline. The enhancement of sensitivity was attributed to the presence of AuNPs which decreased the electron-transfer impedance.     

Electrochemical incineration of p-cresol and o-cresol in the filter-press-type FM01-LC electrochemical cell using BDD electrodes in sulfate media at pH 0

This work shows a comparative study of the incineration of 2-mM p-cresol and o-cresol in 1 M-H₂SO₄ in aqueous media. Microelectrolysis studies indicated that both the p-cresol and o-cresol oxidation were carried out via hydroxyl radicals (OH) formed by water oxidation in the boron-doped diamonds (BDD)-H₂O-H₂SO₄-p-cresol and o-cresol interface. In both cases, the potential and current density ranges, where great amounts of OH are formed, were between 2.3 V ≤ E ≤ 2.75 V versus SHE and J = 10 mA cm⁻². Electrolyses in an undivided FM01-LC reactor were performed at different Reynolds values 27,129 ≤ Re ≤ 42,631, and at J = 10 mA cm⁻². For p-cresol and o-cresol, the rate of degradation was slow, however it increases slightly as a function of the Re, indicating that the oxidation involves a complex pathway; current efficiency also rises as a function of the Re. For p-cresol, the mineralization at Re = 42,631 reached 90%, with 71% current efficiency and an energy consumption of 7.84 kWh m⁻³; whereas o-cresol was mineralized to 84%, with 67% current efficiency and an energy consumption of 6.56 kWh m⁻³. The results obtained in this work demonstrated that o-cresol is more recalcitrant than p-cresol.     

Electrochemical synthesis and corrosion performance of poly(pyrrole-co-o-anisidine)

The electrochemical synthesis of poly(o-anisidine) homopolymer and its copolymerization with pyrrole have been investigated on mild steel. The copolymer films have been synthesized from aqueous oxalic acid solutions containing different ratios of monomer concentrations: pyrrole:o-anisidine, 9:1, 8:2, 6:4, 1:1. The characterization of polymer films were achieved with FT-IR, UV–visible spectroscopy and cyclic voltammetry techniques. The electrochemical synthesis of homogeneous-stable poly(o-anisidine) film with desired thickness was very difficult on steel surface. Therefore its copolymer with pyrrole has been studied to obtain a polymer film, which could be synthesized easily and posses the good physical–chemical properties of anisidine. The kinetics and rate of copolymer film growth were strongly related to monomer feed ratio. The introduction of pyrrole unit into synthesis solution increased the rate of polymerization and the substrate surface became covered with polymer film soon, while this process required longer periods in single o-anisidine containing solution. The protective behavior of coatings has been investigated against steel corrosion in 3.5% NaCl solution. For this aim electrochemical impedance spectroscopy (EIS) and anodic polarization curves were utilized. The synthesized poly(o-anisidine) coating exhibited significant protection efficiency against mild steel corrosion. It was shown that 6:4 ratio of pyrrole and anisidine solution gave the most stable and corrosion protective copolymer coating.     

Protection of type 430 stainless steel against pitting corrosion by ladder conductive polymer

Poly(o-phenylenediamine) (PoPD) was electropolymerized by cyclic voltammetry (CV) on 430 stainless steel from sulfuric acid solution containing o-phenylenediamine monomer. The formation of the polymer film is slower than that of polyaniline (PANI) film. Transparent and compact layers (∼1.0 μm) of PoPD deposited after 100 cycles, while thicker (∼3 μm), grainy and porous layers of PANI formed after 50 cycles. The PoPD layers protect the steel substrate from pitting in 3% NaCl but the layers of PANI fail, and pitting and crevice corrosion were observed on the steel surface. Both polymers keep the steel substrate in a passive state in sulfuric acid. After aging in acid solution the underlying oxides were investigated after peeling off the polymer layers; this showed an excellent passive film formed under PoPD. The passive steel was completely free from pitting after immersion in the chloride solution for 1 week.     

A new method for characterizing the growth and properties of polyaniline and poly(aniline-co-o-aminophenol) films with the combination of EQCM and in situ FTIR spectroelectrochemisty

A new method of in situ piezoelectric Fourier transform infrared (FTIR) spectroelectrochemisty, i.e., the combination of in situ FTIR and electrochemical quartz crystal microbalance (EQCM), was developed to study the electropolymerization of aniline and aniline-co-o-aminophenol, to investigate the properties of the polymers in 0.2 M HClO₄. The piezoelectric electrochemical studies showed that the copolymerization process was changed in the presence of o-aminophenol and the copolymer exhibited different electrochemical behaviors from polyaniline and poly-o-aminophenol. The effects of the molar ratio of o-aminophenol on the copolymerization speed and the scan rate or pH values on the electroactivity of the copolymer were also investigated. The results suggested that the copolymer formed in the case of F = 0.1 had good stability and electroactivity than polyaniline at different pH values. The results obtained by the way of in situ piezoelectric FTIR spectroelectrochemisty indicated that the copolymerization process and the properties of the copolymer were different from that of polyaniline. The polymerization mechanisms and the structure of the two polymers were also different from each other. The copolymer formed through head-to-tail coupling of the two monomers via NH groups was a new polymer rather than a mixture of polyaniline and poly-o-aminophenol.     

The influence of polyaniline (PANI) coating on corrosion behaviour of zinc–cobalt coated carbon steel electrode

Zinc–cobalt alloy plating (ZnCo) was successfully deposited on carbon steel (CS) applying current of 2 mA with galvanostatic technique. Polyaniline film (PANI) was synthesized with cyclic voltammetry technique from 0.20 M aniline containing 0.20 M sodium tartrate solution on zinc–cobalt plated carbon steel (CS/ZnCo) electrode. PANI film characterized by scanning electron microscopy (SEM), was covered with a dark green-brown homopolymer film of strongly adherent homogeneous characteristic while the other one was plated with a porous light ZnCo one. The corrosion behaviour of zinc–cobalt deposited carbon steel electrodes with and without polyaniline (PANI) film in 3.5% NaCl solution was investigated with AC impedance spectroscopy (EIS) technique and anodic polarization curves. The results showed that PANI coating led to decrease of the permeability of metallic plating. The PANI homopolymer film provided an effective barrier property on zinc–cobalt coating and a remarkable anodic protection to substrate for longer exposure time.