The corrosion-inhibiting effect of polypyrrole films doped with p-toluene-sulfonate,benzene-sulfonate or dodecyl-sulfate anions,as coating on stainless steel in NaCl aqueous solutions

This article presents a study of the conditions for electro-synthesis of polypyrrole (PPy) films on stainless steel, in the presence of the anions p-toluene-sulfonate (pTS), benzene-sulfonate (BS) or dodecyl-sulfate (DS). Cyclic voltammetry (CV) was used in the synthesis of the polypyrrole films on the stainless steel (SS). These polymeric films were characterized by IR and UV–vis spectroscopy and their morphology and thickness were analyzed by scanning electron microscopy (SEM). Their performance as protective films against corrosive processes presented by the SS/PPy-pTS, SS/PPy-BS or SS/PPy-DS systems was evaluated in 0.1 M NaCl aqueous solution. The study of the corrosion processes of the stainless steel/polymer systems was conducted through measurements of open circuit potential (E_OCP), polarization curves (PC) and electrochemical impedance spectroscopy (EIS). The results showed that the protective capacity of these polymeric systems on stainless steel, mainly with regard to pitting, depends on the nature of the anion dopant used during electro-synthesis of the PPy film. The best performance was seen with the dopants pTS and BS.     

Glassy carbon electrode modified with a bilayer of multi-walled carbon nanotube and polypyrrole doped with new coccine: Application to the sensitive electrochemical determination of Sumatriptan

A promising electrochemical sensor was developed based on a layer by layer process by electro-polymerization of pyrrole in the presence of new coccine (NC) as dopant anion on the surface of the multi-walled carbon nanotubes (MWCNTs) pre-coated glassy carbon electrode (GCE). The modified electrode was used as a new and sensitive electrochemical sensor for voltammetric determination of sumatriptan (SUM). The electrochemical behavior of SUM was investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results showed a remarkable increase (∼12 times) in the anodic peak current of SUM in comparison to the bare GCE. The effect of experimental variables such as, drop size of the casted MWCNTs suspension, pH of the supporting electrolyte, accumulation conditions and the number of cycles in the electro-polymerization process on the electrode response was investigated. Under the optimum conditions, the modified electrode showed a wide linear dynamic range of 0.02–10.0 μmol L⁻¹ with a detection limit of 6 nmol L⁻¹ for the voltammetric determination of SUM. The prepared electrode showed high sensitivity, stability and good reproducibility in response to SUM. This sensor was successfully applied for the accurate determination of trace amounts of SUM in pharmaceutical and clinical preparations.     

Electrochemistry of conductive polymers XXXV: Electrical and morphological characteristics of polypyrrole films prepared in aqueous media studied by current sensing atomic force microscopy

Electrical and morphological characteristics of polypyrrole (PPy) films electro-deposited in four different aqueous electrolyte solutions including p-toluenesulfonate, dodecylsulfate, poly(styrenesulfonate), and perchlorate have been investigated using current-sensing atomic force microscopy. Experimental parameters including the electrolyte, applied current density, and deposition time were shown to affect the morphologies and current images of PPy films thus prepared. The PPy films were galvanostatically prepared under the identical conditions except for different electrolytes; the globular-shaped topographic structures with the unusually large sizes were obtained in dodecylsulfate. The p-toluenesulfonate doped PPy film showed the highest average conductivity whereas the perchlorate doped one showed the lowest of all the films prepared.     

Electrochemical preparation and properties of polypyrrole and its blend with poly(vinyl sulfonate) doped with perchlorate anions

In this article, we report polypyrrole (PPy)/poly(vinyl sulfonate) (PVS) and PPy/perchlorate (ClO) composite films generated by the electrochemical oxidation of pyrrole on a glassy carbon electrode (GCE) in an aqueous solution. The response of the produced films to an applied potential at 0.7 V was obtained by a cyclic voltammetry study in acetonitrile media. The films were significantly similar in their electrochemical behavior when ClO ions doped during the redox process. We concluded that with an increasing number of cycles, the anodic current increased because the number of the electroactive participants transported in the copolymer matrix was increased. Theoretical studies based on the Nernst and Butler–Volmer equations indicated that the ClO ion was transported during the oxidation/reduction process of the PPY/PVS and PPY/ClO films. The produced films were characterized further by means of IR spectroscopy, electrochemical impedance spectroscopy, and scanning electron microscopy to verify that the anion of ClO was doped into the copolymer matrix as well. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Understanding of electrochemical and structural changes of polypyrrole/polyethylene glycol composite films in aqueous solution

Electrochemical monitoring of electrical and structural changes of both PPy and PPy–PEG films electrochemical deposited, in order to highlight if the structural stability offered by PEG has an influence on electrical properties and stability in aqueous solution over immersion time was investigated.Electrochemical analysis suggests that PPy–PEG film inserts cations easier than PPy film for a short immersion time probably due to ability of PEG to form complexes with metal cations.The FTIR spectra showed that the PEG incorporation decreases the rate of PPy overoxidation probably by restraining the electron release and by rendering O₂ inaccessible to PPy.Mott–Schottky analysis based on capacitance measurement reveal p-type conductance for both films.The in situ AFM analysis sustains electrochemical behaviour and has permitted elaboration of a model of PPy and PPy–PEG films behaviour during immersion in testing solution.     

ac-Electrogravimetry study of ionic and solvent motion in polypyrrole films doped with an heteropolyanion, SiMo12O40

One way to immobilize heteropolyanions on an electrode is to entrap them into a film of conducting polymer. In the present work, a polypyrrole film doped with a Keggin-type heteropolyanion, SiMo₁₂O₄₀⁴⁻, obtained by electrochemical way was studied.We focus on the charge compensation process, which occurs when the heteropolyanions entrapped into the polymer are reduced or re-oxidized. First, electrochemical quartz crystal microbalance analyses were performed, then, to determine if solvent motion takes place, ac-electrogravimetry measurements were carried out. In fact, in concentrated acidic solution, only protons are involved in the charge compensation. In low acidic solution (pH 3) having a high potassium concentration (0.5 M) both proton and potassium ions are involved whereas at pH 5.2 only potassium motion takes place. These findings are in good agreement with the acido-basic properties of SiMo₁₂O₄₀⁶⁻. In all cases, no solvent motion was pointed out.     

Amperometric urea biosensors based on the entrapment of urease in polypyrrole films

Urease (Urs) was immobilized in electrochemically prepared polypyrrole (PPy) and the resulting films were characterized by cyclic voltammetry, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and ultraviolet visible spectroscopy (UV-VIS). The enzymatic activity of Urs entrapped in the PPy matrix was confirmed by the catalytic conversion of urea into carbon dioxide and ammonia, when urea was detected amperometrically at different concentrations in standard samples and commercial fertilizers. The PPy/Urs biosensors exhibited selectivity, a relatively high efficiency at urea concentrations below 3.0 mmol L⁻¹, and a sensitivity to urea of 2.41 μA cm⁻² mmol⁻¹ L.     

Polypyrrole materials doped with weakly coordinating anions: influence of substituents and the fate of the doping anion during the overoxidation process

The influence of weakly coordinating anions with different shapes and substituents has been studied to get the overoxidation resistance limit of the material, ORL. The anions utilized are derivatives of [Co(C₂B₉H₁₁)₂]⁻, [B₁₂H₁₂]²⁻ and [B₁₂H₁₁NH₃]⁻. The following tendencies have been established (1) boron cluster monoanions are to date the anions that offer the highest stability to overoxidation of PPy doped materials (2) the ORL stability of the material can not be attributed only to the shape of the cluster (3) monoanionic clusters are far superior than dianionic to get an ORL rise (4) cluster charge density reduction results in ORL rise as has been observed in [Co(C₂B₉H₁₁)₂]⁻ after incorporation of electron-withdrawing substituents with no electron back-donation (5) globular, rigid and large monoanions are less suitable for enhanced ORL values than elongated and non-rigid species (6) adequate anion's substitution produce a rise in the ORL of the material, thus polyether side-arms are beneficial with [Co(C₂B₉H₁₁)₂]⁻, whereas, T-shaped methylaryl groups are appealing in [B₁₂H₁₁NH₃]⁻ based materials, respectively, (7) substituents on the anions usually imply higher difficulty in the materials' growth. The high boron contents in these materials has permitted to learn on the fate of the doping anions during the overoxidation process. There is a built-up of the concentration of the doping anion in the electrolyte near surface area, whereas, a depletion is observed in the nearest inner layers.     

The effect of electrolyte anions incorporated into anodic oxide films on the experimental transport numbers of ions

The growth of barrier anodic film is considered theoretically with regard to the migration of three ionic carriers: oxygen and metal ions and electrolyte anions. It is shown that the consideration of anion transport leads to the conclusion that the film grows at three interfaces: the metal/oxide and oxide/electrolyte interfaces and the interface between an oxide layer containing electrolyte anions (contaminated layer) and the oxide layer free of them (“pure” layer). The error in the measured transport numbers of metal and oxygen, which is caused by ignoring a contribution of electrolyte anions to the total charge transport, is maximum in the absence of anion motion.     

Study of the coupling reactions between electrochemically generated aromatic radical anions and methyl, alkyl and benzyl radicals

Alkyl radicals produced in the indirect reduction of alkyl halides or alkyldimethylsulfonium salts by electrochemically generated aromatic radical anions couple fast with the latter and alkylated or dialkylated dihydro compounds are formed. Rate constants measured for the coupling reaction between on one hand methyl, primary, secondary and tertiary alkyl radicals as well as benzyl and cumyl radicals and on the other hand a wide spectrum of electrochemically generated aromatic radical anions are found to be about 1×10⁹ M⁻¹ s⁻¹. Previous measurements of coupling rate constants for primary alkyl radicals have been re-evaluated since they were affected by the presence of an S_N2 reaction occurring between the alkyl halides used as radical precursors and the aromatic radical anions. New experiments are also included using alkyldimethylsulfonium salts as precursors in order to prevent such S_N2 artefacts. It is concluded that sterical hindrance does not play a significant role for the radical-radical anion coupling reactions. In general the rate constants for the coupling reactions are all close to 10⁹ M⁻¹ s⁻¹.     

Anion and cation transport in composite films of polypyrrole with a sulphonated silica (ormosil) hydrogel

Composite films of polypyrrole with a sulphonated organically modified silica (ormosil) have been prepared on electrodes by the electrochemical oxidation of pyrrole in a liquid sol-gel electrolyte. The ormosil is incorporated into the polypyrrole matrix as an immobile polymeric counterion in addition to mobile Cl⁻ counterions from the sol-gel electrolyte. Ion transport in the composites was investigated by impedance spectroscopy and electron microprobe analysis. The presence of both mobile and immobile counterions allows potential control of the mode of ion transport, with anion transport dominating at high potentials and cation transport dominating at low potentials. As the polymer is un-doped (reduced), its ionic conductivity first decreases as mobile anions are expelled, and then increases as cations and excess electrolyte are incorporated.     

水溶液中硼氧配阴离子的存在形式及影响因素

综述了硼酸盐水溶液中硼氧配阴离子的存在形式、振动光谱研究结果及影响其变化的因素.硼酸盐水溶液中,硼氧配阴离子除了常见的[B(OH)4]-,B(OH)3,[B3O3(OH)4],[B4O5(OH)4]2-,[B5O6(OH)4]-,[B6O7(OH)6]2-以外,还存在着[B2O(OH)6]-2,[B3O3(OH)5]2-等,各种硼氧配阴离子相互作用、相互影响.FT-IR和Raman光谱研究结果进一步明确了硼氧配阴离子的存在形式及相互作用.同时指出了各种硼氧配阴离子的存在形式及相互作用与溶液总硼浓度、pH、金属阳离子、温度及水热条件等有关,且主要依赖于溶液总硼浓度和pH.高的总硼浓度和较低的pH有利于高聚合度的硼氧配阴离子的存在,反之则利于低聚合度的硼氧配阴离子的存在.     

Investigation by EQCM of the electrosynthesis and the properties of polypyrrole films doped with sulphate ions and/or a Keggin-type heteropolyanion, SiMo12O40

The first part of this paper describes in detail the electrochemical synthesis of polypyrrole (PPy) films monitored by electrochemical quartz crystal microbalance (EQCM). These films are either doped only with a Keggin-type heteropolyanion (HPA), SiMo₁₂O₄₀⁴⁻, or co-doped with such polyanions and sulphate ions. It is evidenced that this HPA catalyses the electropolymerisation of the pyrrole since it is able to oxide pyrrole monomer, and on the other hand, that HPAs are definitively entrapped into the polypyrrole film as shown by their electrochemical response. All the PPy film is electroactive. When the co-doped film is obtained by potentiodynamic method, its anion composition is not homogeneous in depth, there is a concentration gradient of the doping anions. In the second part of this paper, the morphology of the films is shown as well as their electrochemical characterisations that were carried out by EQCM in order to focus on the charge compensation process that occurs during SiMo₁₂ reduction and re-oxidation. In a wide domain of potentials, only the HPA response is observed, the polymer remains in its conducting form. The SiMo₁₂O₄₀⁴⁻ doped PPy films are cationic films. When several types of cations are present in the medium, the influence of the pH on the nature of the cations implied in the charge compensation that occurs during SiMo₁₂ reduction and re-oxidation is important. When the PPy film is co-doped, it is possible to obtain a mixed PPy film. Another important finding is the stability of trapped SiMo₁₂ ions in contact with solutions of pH higher than 4, on the contrary to what occurs when they are in solution.     

Characterization of polypyrrole films electrosynthesized onto titanium in the presence of sodium bis(2-ethylhexyl) sulfosuccinate (AOT)

Films of polypyrrole (PPy) were successfully electrosynthesized onto titanium in neutral and alkaline solutions of sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT or AOT) by potentiodynamic, galvanostatic and potentiostatic techniques. Results of the characterization of the films by cyclic voltammetry, scanning electron microscopy (SEM) and adhesion measurements are presented. It was found that the AOT molecule remains entrapped within the polymer matrix. The initial growth of the polymer produces electroactive toroidal deposits whereas for electropolymerization of longer duration the typical globular structure is developed. Adherence to Ti increases with deposition time and this result is interpreted as a consequence of the growth of a composite PPy/Ti oxide.     

Voltammetric determination of ascorbic acid and dopamine in the same sample at the surface of a carbon paste electrode modified with polypyrrole/ferrocyanide films

Functionalized polypyrrole film were prepared by incorporation of [Fe(CN)₆]⁴⁻ as a doping anion, during the electropolymerization of pyrrole onto a carbon paste electrode in an aqueous solution by potentiostatic method. The electrochemical behavior of dopamine (DA) and ascorbic acid (AA) in one solution was studied at the surface of bare and modified carbon paste electrodes using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and differntial pulse voltammetry (DPV) methods. The well separated anodic peaks for oxidation of DA and AA were observed at the surface of the modified carbon paste electrode under optimum condition (pH 6.00), which can be used for determination of these species simultaneously in mixture by LSV and DPV methods. The linear analytical curves were obtained in the ranges of 0.10-1.00 mM and 0.10-0.95 mM for ascorbic acid and 0.10-1.20 mM and 0.20-0.95 mM for dopamine concentrations using LSV and DPV methods, respectively. The detection limits (2σ) were determined as 3.38 × 10⁻⁵ M and 1.34 × 10⁻⁵ M of ascorbic acid and 3.86 × 10⁻⁵ M and 1.51 × 10⁻⁵ M of dopamine by CV and DPV methods.     

Enhanced mineralization of phenol and other hydroxylated compounds in a photocatalytic process assisted with ferric ions

This study shows that the presence of low ferric ion concentrations accelerates the rate of photocatalytic oxidation and mineralization of different phenolic components. Ferric ions not only considerably affect the rates of disappearance and total mineralization of phenol, but also the concentration-time profiles of its major intermediates. At reaction conditions, three major aromatic intermediates were identified: ortho-dihydroxybenzene (o-DHB), para-dihydroxybenzene (p-DHB), and 1,4-benzoquinone (1,4-BQ). Additionally, four carboxylic acids were also detected as intermediates: fumaric acid (FuAc), maleic acid (MeAc), oxalic acid (OxAc) and formic acid (FoAc). Fe ions also increase the rate of disappearance and mineralization of the aromatic intermediates when tested separately. A new refined series-parallel kinetic network for the photocatalytic mineralization of phenol is proposed describing the reaction in higher detail than previous studies. It is concluded that the proposed mechanism adequately describes both unpromoted photocatalytic oxidation (unpromoted PC) and Fe-assisted photocatalytic oxidation (Fe-assisted PC) of phenol with the various mechanistic steps involving detectable species. Experimental data also reveal that while unpromoted PC and Fe-assisted PC reactions share a close mechanism, the latter leads to changes in the step-related kinetic constants. It is found that the overall quantum yield (OQY) increase in the Fe-assisted PC reactions for phenol ranges between 30% and 50%. For the aromatic intermediates the increment is between 25% and 38%. Two kinetic models are developed to represent the oxidation of phenol in both unpromoted PC and Fe-assisted PC systems. The first model predicts the rate of disappearance of the major aromatic components while the second one includes the carboxylic acids and allows the prediction of the total mineralization rate of phenol. Estimates of the parameters along with their statistical indicators are also reported for both systems.     

炉水中侵蚀性阴离子对碳钢腐蚀的试验研究

为了研究低磷酸盐—低氢氧化钠水处理工艺下侵蚀性阴离子对碳钢的腐蚀 ,通过高压釜静态试验 ,计算在不同浓度下碳钢的腐蚀速度 ,测定溶液中总铁离子浓度以及对表面的 EPMA(Electron probe microanalysis,电子探针微量分析 )分析。结果表明 :高温下 ,Cl-、SO42 -是引起碳钢腐蚀的主要原因。它们能阻碍膜的形成。随着离子浓度的增大 ,当 CCl- >0 .4m g/L 时 ,碳钢的腐蚀速率明显增加 ,蚀孔增多 ,耐蚀性能降低     

Ionic association of Ce(IV)-decatungstate in the context of heteroatom reduction

The kinetics of single electron heteroatom reduction in Ce(IV)-decatungstate anion is demonstrated to be strongly dependent on the nature of the supporting electrolyte cation. DC polarography reveals an increase of both reduction rate at a positively charged mercury electrode and a limiting diffusion current in the Li⁺…Cs⁺ sequence. Both effects look anomalous in the framework of traditional concepts of electrode kinetics. To clarify the nature of these observations, ionic association of Ce(IV)-decatungstate with various alkali metal cations was addressed experimentally by means of the potentiometric technique. Finally, our self-consistent interpretation of various cation nature effects rests on a difference in the number of bound cations and their location around the polyanion. The ionic association is modeled by using the results of DFT calculations of the CeW₁₀ anion, non-local electrostatics and an extended version of the Bjerrum model.     

活性炭掺杂WO_3/ZnO复合薄膜制备及其光催化性能研究

采用溶胶-凝胶法在铝箔上制备WO3/ZnO复合薄膜,并用活性炭对其改性,以甲基橙水溶液模拟有机污染物,研究了WO3/ZnO薄膜的光催化降解性能。实验结果表明:白炽灯照射2h、WO3质量分数为2.5%时,WO3/ZnO/铝箔对甲基橙的降解率达到78.54%;紫外光照射下降解率达到99.89%。当活性炭掺杂量为10g/L时,制得的WO3/ZnO复合薄膜均匀一致且光催化性能良好,可见光照射下甲基橙降解率达到85.71%。     

Accumulation of Cu(II) cations in poly(3,4-ethylenedioxythiophene) films doped by hexacyanoferrate anions and its application in Cu-selective electrodes with PVC based membranes

Electrochemical properties of poly(3,4-ethylenedioxythiophene) doped with hexacyanoferrate(II,III) ions (PEDOT(HCF)) were studied in the presence of Cu²⁺ ions. Voltammetric and EDAX studies revealed retention of hexacyanoferrate anions in the polymer film and accumulation of Cu(II) cations, as well as formation of solid copper hexacyanoferrate near the polymer surface.Accumulation of Cu²⁺ ions was found to be advantageous from the point of view of PEDOT(HCF) applications as a solid contact (ion-to-electron transducer) in all-solid-state Cu²⁺-selective electrodes with solvent polymeric polyvinyl chloride (PVC) based membrane, containing Cu²⁺-selective ionophore. Binding of Cu²⁺ ions in the conducting polymer layer results in analyte ions flux into the transducer phase. Thus, pronounced enhancement of selectivity of the all-solid-state Cu²⁺-selective electrode or lower detection limit of the potentiometric response range was achieved, reaching under optimised conditions 10⁻⁷ M CuSO₄.