Electrochemical Oxidation Of Aniline Research Articles

Influence of surfactant on conductivity, capacitance and doping of electrodeposited polyaniline films

The electrodeposition of polyaniline films is usually carried out in acid solutions such as hydrochloric acid, perchloric acid or sulfuric acid, and more rarely in organic acids such as camphorsulfonic acid (CSA). In this study, the impact of the presence of a surfactant in the electrolytic solution based on hydrochloric acid or CSA was evaluated by successively using anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethylammonium bromide, CTAB), and non-ionic (Tritonx100) surfactants. Whatever the surfactant and the acid used, the electrochemical oxidation of aniline has successfully led to the formation of a thick polyaniline (PANI) film through a quasi-reversible reaction controlled by the diffusion of aniline monomers. The nature of the surfactant was shown to affect physico-chemical properties of the film, in particular its morphological features (morphology, thickness, roughness), electrochemical activity, specific capacitance, and conductivity. For example, PANI films containing SDS had a spongy morphology when PANI films containing Tritonx100 had a more fibrous and compact structure. Glow Discharge Optical Emission Spectroscopy (GDOES) experiments also highlighted differences depending on the acid used since chloride anions, from HCl, were present only on the top surface of the PANI films when camphorsulfonate anions were present everywhere throughout the polymer film, which impacts the doping process and electrochemical activity of the films. Moreover, the specific capacitance of the PANI/CSA films is higher and more sensitive to current density variation than the one of PANI/HCl films. Finally, electrochemical impedance experiments evidenced that the conductivity of PANI films electrodeposited from CSA solutions was much higher than the one of PANI films prepared from HCl solutions, and highly dependent on the nature of the surfactant, the most conductive films being obtained in the presence of SDS and Tritonx100. Therefore, the originality of this work comes from the possibility of modulating the conductivity, capacitance and electroactivity of electrodeposited polyaniline films using surfactants of different polarity, and from the determination of the distribution of ions in the films using the GDOES technique, which is rarely used to characterise organic films.

Electrochemical oxidation of aniline using a high-flux CNT filter

Carbon nanotube (CNT) membrane electrochemical filtration has been found to provide effective solutions for water contaminant removal. However, bubble elimination, water flux increase, and CNT membrane robustness enhancement still remain great challenges for CNT electrochemical filtration technologies. To improve the performance of the electrochemical CNT filter, a ceramic flat membrane is used as the CNT electrode support. Aniline (AN) is chosen as the target pollutant to investigate the effects of water quality (initial pH, initial AN concentration, and support electrolyte concentration) and running conditions (anode potential and water flux). In addition, the current efficiencies (CE) of the two different modes (single-pass filtration and recirculated filtration) are also estimated. The results showed that the effects of various impact factors on the AN degradation were generally similar in both modes. Overall, the CEs of the sing-pass filtration mode with the stable influent conditions were higher than those of the recirculation filtration mode. Increasing the flux and applied anode potential did increase the AN degradation rate. The maximum water flux density of the high-flux CNT electrochemical filter reached 83.9 mL/(cm2·h), 4.0–16.1 fold of that of a typical CNT electrochemical filter, addressing the defects of bubble formation and CNT fragility of the free-standing BUCKYPAPER membrane in a conventional electrochemical filter. The configuration with a ceramic membrane support greatly improved the practicability of CNT-based electrochemical filtration technology for real wastewater treatment.

Understanding the electro-catalytic effect of benzene ring substitution on the electrochemical oxidation of aniline and its derivatives using BDD anode: Cyclic voltammetry, bulk electrolysis and theoretical calculations

The use of boron doped diamond (BDD) films in environmental applications has been extensively proved. This electrocatalytic material produces higher concentrations of free‑hydroxyl radicals on its surface, favoring a complete mineralization of many organic pollutants. Although efficient degradation levels are achieved using BDD films, effects such as the chemical structure of the contaminant, waste by-products, oxidants produced, weak/strong surface interactions and bulk reactions influence the electro/chemical catalytic reactions as well as on the effectiveness of the process. In this frame, this study aims to investigate the effect of benzene ring substitution on the electrochemical oxidation of aniline and its derivatives using BDD anode. To do that, the electrochemical behavior of aniline, nitro and chloro‑aniline derivatives in aqueous solution on BDD anode using cyclic voltammetry and bulk electrolysis was examined as well as their environmental elimination was explained by quantum mechanics (QM) calculations. The results clearly allowed associating the experimental measurements to theoretical estimations to comprehend the catalytic relationship between the molecular electronic properties of aniline and its derivatives and their elimination from water.

The First Stages of Chemical and Electrochemical Aniline Oxidation—Spectroscopic Comparative Study

There are several types of aniline oligomers that can be formed in the early stages of aniline oxidation: linear oligomers with repeating units joined in para positions, and various branched and polycyclic oligomers, being the two most important groups. The fraction of these different oligomeric groups depends upon the reaction conditions of aniline oxidation. The aim of this study was to analyze the first products of the chemical and electrochemical oxidation of aniline at the (starting) pH 1 and 7, in order to specify the conditions of the formation of phenazine-like oligomers, and to test the theory that they have an important role in polyaniline film formation. We have confirmed that phenazine-like oligomers do not form at pH 1, neither in the chemical nor the electrochemical oxidation of aniline; however, they form in both chemical and electrochemical oxidation of aniline at pH 7. Phenazine-like oligomers are thus definitely not necessary intermediates for PANI film formation, not even in the chemical polymerization of aniline. Finally, the redox behavior of phenazine-like oligomers was demonstrated in a medium at pH 1.

π-Conjugated polyaniline-assisted flexible titania nanotubes with controlled surface morphology as regenerative medicine in nerve cell growth

Biologically active conjugated polymers, for example polyaniline (PANI), have drawn attention as emerging materials for applications in bio-medical implant devices, due to their inherent abilities with regard to charge-carrier properties, and their ability to immobilize biomolecules or proteins. Herein, we report an electrocoating of PANI on titania nanotubes (TNTs) via electrochemical oxidation of aniline with PANI layers of appropriate thickness (∼274 nm). Uniform titanium oxide nanotubes were first developed from titanium (Ti) foil through an anodization process, followed by calcination to obtain high purity TNTs vertically aligned on a Ti substrate. These had a large surface area, controllable tube height and diameter, and were highly biocompatible, and doping with PANI further improved their properties, like being antibacterial, having a lower charge transfer resistance (22.51 Ω) and strong anti-corrosion behavior (Ecorr ∼ − 184 mV, Icorr ∼ 9.7 × 10−7 Amp). In vitro experiments revealed that the cellular functions of PC12 and S42 cells on TNTs-PANI scaffolds show characteristic improvement in proliferation and differentiation owning to approach neuronal cells activation associated with axonal growth and migration in the peripheral nervous system (PNS). Thus, the flexible bioactive substrate is capable of stimulating neuronal cells, and can inspire neural transduction through direct neural interfaces.

Electrochemical oxidation of aniline by a novel Ti/TiOxHy/Sb-SnO2 electrode

Electrochemical oxidation of aniline in aqueous solution was investigated over a novel Ti/TiOxHy/Sb-SnO2 electrode prepared by the electrodeposition method. Scanning electron microscopy, X-ray diffraction, and electrochemical measurements were used to characterize its morphology, crystal structure, and electrochemical properties. Removal of aniline by the Ti/TiOxHy/Sb-SnO2 electrode was investigated by ultraviolet-Visible spectroscopy and chemical oxygen demand (COD) analysis under different conditions, including current densities, initial concentrations of aniline, pH values, concentrations of chloride ions, and types of reactor. It was found that a higher current density, a lower initial concentration of aniline, an acidic solution, the presence of chloride ions (0.2 wt% NaCl), and a three-dimensional (3D) reactor promoted the removal efficiency of aniline. Electrochemical degradation of aniline followed pseudo-first-order kinetics. The aniline (200 mL of 100 mg L−1) and COD removal efficiencies reached 100% and 73.5%, respectively, at a current density of 20 mA cm−2, pH of 7.0, and supporting electrolyte of 0.5 wt% Na2SO4 after 2 h electrolysis in a 3D reactor. These results show that aniline can be significantly removed on the Ti/TiOxHy/Sb-SnO2 electrode, which provides an efficient way for elimination of aniline from aqueous solution.

Fabrication of a stable Ti/TiOxHy/Sb−SnO2 anode for aniline degradation in different electrolytes

A novel anode Ti/TiOxHy/Sb−SnO2 with excellent oxidation ability and long lifetime was successfully fabricated by introducing a TiOxHy interlayer through a simple way. The Ti substrate was modified through thermal oxidation followed by an electrochemical reduction process. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), accelerated lifetime test, scanning electron microscope (SEM) and X-ray diffraction (XRD) were adopted to characterize its morphology, crystal structure and electrochemical properties. These studies indicated that TiOxHy interlayer played a critical role in improving electrode stability. Besides, the electrochemical oxidation of aniline in the NaCl and Na2SO4 were both investigated to test the application of this Ti/TiOxHy/Sb−SnO2 electrode. Results showed that nearly 70% of aniline could be degraded within 2h. After characterization of the intermediates and products, a possible electrochemical degradation mechanism of aniline was proposed. It was worth noting that due to electro-polymerization, some nonconductive oligo(aniline)s could accumulate on the anode surface and lower the oxidation ability of the anode. However, the anode could be recovered repeatedly (at least 5 times) by essential electrochemical activation process, which also relied on the high electrode stability.

Electrochemical oxidation of aniline at mono and bimetallic electrocatalysts supported on carbon nanotubes

Abstract The electrochemical mineralization of aniline, a compound that causes serious environmental problems, was investigated at Pt, Pd and Ru–Cu catalysts supported on multiwalled carbon nanotubes (CNTs). The modified electrodes, based on commercial CNT samples, were prepared and dispersed onto Toray carbon (CT) using a Nafion/water solution. The electroreactivity of aniline at the electrocatalysts based on CNTs, and the kinetic parameters of the redox reactions, were determined using cyclic voltammetry. In order to determine the conditions that allow an efficient mineralization, the electrochemical oxidation of aniline was carried out in a membrane separated electrochemical cell. The reaction products were identified and quantified using chromatographic methods in order to evaluate the mineralization efficiency. The highest conversions were obtained with the Ru–Cu/CNT/CT modified electrode.

Electrochemical oxidation and protein adduct formation of aniline: a liquid chromatography/mass spectrometry study

Historically, skin sensitization tests are typically based on in vivo animal tests. However, for substances used in cosmetic products, these tests have to be replaced according to the European Commission regulation no. 1223/2009. Modification of skin proteins by electrophilic chemicals is a key process associated with the induction of skin sensitization. The present study investigates the capabilities of a purely instrumental setup to determine the potential of commonly used non-electrophilic chemicals to cause skin sensitization by the generation of electrophilic species from the parent compound. In this work, the electrophiles were generated by the electrochemical oxidation of aniline, a basic industrial chemical which may also be released from azo dyes in cosmetics. The compound is a known sensitizer and was oxidized in an electrochemical thin-layer cell which was coupled online to electrospray ionization-mass spectrometry. The electrochemical oxidation was performed on a boron-doped diamond working electrode, which is able to generate hydroxyl radicals in aqueous solutions at high potentials. Without any pretreatment, the oxidation products were identified by electrospray ionization/time-of-flight mass spectrometry (ESI-ToF-MS) using their exact masses. A mass voltammogram was generated by plotting the obtained mass spectra against the applied potential. Oligomerization states with up to six monomeric units in different redox states of aniline were observed using this setup. This approach was extended to generate adducts between the oxidation products of aniline and the tripeptide glutathione. Two adducts were identified with this trapping experiment. Protein modification was carried out subsequently: Aniline was oxidized at a constant potential and was allowed to react with β-lactoglobulin A (β-LGA) or human serum albumin (HSA), respectively. The generated adducts were analyzed by liquid chromatography coupled to ESI-ToF-MS. For both β-LGA and HSA, aniline adducts were successfully generated and identified.

Electrochemical degradation of sulfonated amines on SI/BDD electrodes

The electrochemical oxidation of aniline (AN) and ortanilic (OA), metanilic (MA) and sulfanilic (SA) acids was performed using as anode a boron-doped diamond (BDD) electrode. Tests were performed with model solutions of the different amines, with concentrations of 200 mg L −1, using as electrolyte 0.035 M Na 2SO 4, in a batch cell, with re-circulation, at different current densities (200 and 300 A m −2). Samples were collected at pre-selected intervals and absorbance measurements, Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), Total Kjeldahl Nitrogen, Ammonia Nitrogen, Nitrates and Nitrites and HPLC analysis were performed. Results have shown a good elimination of the persistent pollutant, with COD and TOC removals always higher than, respectively: AN – 91% and 90%; OA – 75% and 82%; MA – 88% and 87%; and SA – 85% and 79%. The combustion efficiencies, calculated for the first hour of the runs, for the 300 A m −2 assays, were the following: AN – 0.93; OA – 0.28; MA – 0.82; and SA – 0.83. For all the amines studied, after 6 h degradation only oxalic and maleic acids were identified by HPLC.

Electrochemical gold deposition from sulfite solution: application for subsequent polyaniline layer formation

Electrochemical gold deposition from sulfite solutions was studied by means of voltammetry, EIS and EQCM. A gold film electrode was used for polyaniline layer formation by electrochemical oxidation of aniline. The standard electrochemical reduction potential of the reaction (Au(SO3)2) 3- + e - = Au + 2S O 3- was deter- mined, and is equal to 0.116 V (vs. NHE). Both solution stirring and temperature increase accelerate the electro- chemical reduction of gold, when the electrode potential is below -0.55 V. When the potential is above -0.55 V the electrochemical reduction proceeds via passive layer for- mation. Our study suggests that the passive layer consists of chemically adsorbed sulfite ions and sulfur. The gold film deposited from sulfite solution is a high quality sub- strate suitable for conducting polymer layer formation. This technique, where a polymer layer electrode is pre- pared by thin gold film deposition onto a metal surface and by subsequent polymer layer formation, can be applied in sensor research and technology.

Theoretical study of the structure and electronic spectra of fully protonated emeraldine oligomers

AbstractPolyaniline (PANI) is one of the most studied conducting polymers. Obtained in its conducting form (known as “emeraldine salt”) by chemical or electrochemical oxidation of aniline in aqueous acidic medium, this polymer manifests an array of attractive properties. Nevertheless, these properties still need to be described at the molecular level. Intense theoretical investigations during the past few years aim at explaining the chain organization, conductivity mechanism, and other structural and spectral characteristics. Most studies adopt simplified models in which hydration effect is underestimated, since all simulations are performed either in vacuum or in the presence of a limited number of water molecules. The present computational study sheds light on the molecular organization of a number of model PANI hydrated clusters with different alignment and multiplicity, which can explain the experimentally recorded UV/VIS spectra. The influence of hydration and interaction with adjacent oligomers is estimated. Short‐chain doubly protonated emeraldine oligomers are used as model systems. The calculations are performed at the semi‐empirical (AM1) and/or molecular mechanics (AMBER96) level. Proper configurations of the clusters are selected using Monte Carlo simulations. Electron correlation (CIS) is accounted for upon evaluation of the absorption spectra of the clusters. The relative strength of the interchain coupling is estimated by simulation of PANI clusters consisting of two PANI tetramers in water. Comparison to experimental results is made. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Ion-Selective Electrodes Prepared with Polyaniline Membranes

Polyaniline is a conductive polymer that has electrochemical activity. For this reason, it has many different uses in electrochemical area. In this study, polyaniline was prepared by electrochemical oxidation of aniline in concentrated H2SO4 and HCl solutions. Then, membranes were obtained from a mixture of these polymers and paraffin at a weight ratio of 50%. Ion-selective electrodes were prepared with these membranes and AgCl/Ag electrodes. Properties of prepared membranes were investigated with potentiometric measurements made in HCl, KCl, H2SO4, and HClO4 solutions of different concentrations. The E–logc plots obtained with these ion-selective electrodes were found to be linear in a distinct concentration range. Their slopes depend on the membrane type and the doping ion in the test solution. The difference between these membranes was explained according to the morphological structures of polyaniline membranes.

Electrochemical oxidation of aniline at boron-doped diamond electrodes

The electrochemical oxidation of aniline at boron-doped diamond (BDD) electrodes was investigated by cyclic voltammetry, steady-state polarization measurements and bulk electrolysis under potentiostatic control. It was found that acidic media is suitable for efficient electrochemical oxidation of aniline, because at low pH, the potential required for avoiding electrode fouling is lower than in neutral and alkaline media. The results of the longtime polarization measurements suggested that more anodic potentials ensure slightly higher efficiency for the conversion of aniline to CO2, while the direct oxidation process does not play a prominent part in the overall electrochemical incineration of aniline. The current efficiencies (∼44%) and the efficiency of aniline conversion to CO2 (∼80%) favourably compare with those reported for other electrochemical methods for aniline destruction. The results demonstrate the possibility of using BDD as an electrode material for electrochemical wastewater treatment, mainly when very high anodic potentials are required.

Simultaneous multimode experiments for studies of electrochemical reaction mechanisms: demonstration of concept.

An instrumental setup has been configured for a simultaneous real time recording of electrochemical, spectroelectrochemical, and mass data on an electrode from a single measurement for studies of complex electrochemical reaction mechanisms. This was achieved by combining a few pieces of equipment: a potentiostat/galvanostat for electrochemical measurements, the near-normal incidence reflectance spectrometer for spectroelectrochemical measurements, and a quartz crystal analyzer (QCA) for mass changes on the electrode. The latter two were coupled through a bifurcated optical fiber on the reflective QCA electrode. The experimental setup thus assembled was demonstrated to be very powerful in elucidating reaction mechanisms of the reaction sequence for a complex reaction, for example, electrochemical oxidation of aniline, which accompanies spectral, as well as weight, changes upon oxidation. The system was also applied to the study of the lithium intercalation reaction of tungsten trioxide thin films in a nonaqueous solution.

Conducting films obtained by electro-oxidation of p-aminodiphenylamine (ADPA) in the presence of aniline in buffer aqueous solution at pH 5

The electrochemical oxidation of aniline and p-aminodiphenylamine (ADPA) was carried out in a phosphate buffer solution at pH 5. Cyclic voltammetry and “in situ” FTIR spectroscopy were combined to study the redox behavior of the oxidation products. When ADPA is oxidized in the presence of aniline, two redox processes are observed. One of these redox processes is related to a soluble species, while the other pertains to a species attached to the electrode surface. Only those films synthesized from ADPA oxidation in the presence of aniline are electroactive in this buffered medium. No evidence pointing to the occurrence of autocatalytic polymerization exists under the experimental conditions employed.

The characteristic of electrochemical oxidation of aniline on SnO2/Ti electrode

The characteristic of electrochemical oxidation of aniline on SnO2/Ti electrode is studied. The results indicate that SnO2/Ti electrode dopedF plays a wonderful role in the oxidation of aniline comparing with Pt electrode. The kinetics factors that influence the oxidation rate of aniline on the SnO2/Ti electrode are determined by the dissolving of the film on the electrode. The dissolving of the film consisted of intermediate products on the electrode is the slow step. The effects of aniline concentration, pH in aniline solution and the current density (i) on the rate of aniline oxidation, the complexity of intermediate products and the basic category of the intermediate products consisted of the film are introduced.

Destruction of aniline by mediated electrochemical oxidation with Ce(IV) and Co(III) as mediators

Mediated electrochemical oxidation has been employed to test the feasibility of treating soluble organic wastes. We report Ce(IV)- and Co(III)-mediated electrochemical oxidation of aniline at various electrodes in acidic media as an example of organic waste. Aniline was oxidized by an electrogenerated electron transfer mediator, Ce4+ or Co3+, in the anolyte and carbon dioxide was produced as a final oxidation product. Carbon dioxide was collected by bubbling through a barium hydroxide solution. When a powerful oxidizing agent, Ce(IV) or Co(III), was used as an electron shuttling mediator, parameters affecting the coulombic efficiency for aniline oxidation were the standard oxidation potentials of the mediators, their concentrations and the reaction temperature. Intermediate species produced during the oxidation of aniline were identified by cyclic voltammetric and absorption spectroscopic measurements.

Efficient Polymerization of Aniline at Carbon Nanotube Electrodes

High surface area conducting polymers with nanoscale dimensions are an important aim for device applications. Here is reported the polymerization and electrochemical oxidation of aniline at multiwalled carbon nanotube electrodes. Polyaniline films formed on these nanotube whiskers are oxidized more easily and produce a higher current density during the anodic oxidation compared to conventional electrodes such as those made from Pt. Scanning electron microscopy images indicate that the morphology of the films is granular, consisting of nanosized domains.

The kinetic behavior for the electrochemical polymerization of aniline in aqueous solution

The electrochemical oxidation of aniline in 0.8 M HCl solution is carried out using repeated potential cycling between 0 and 1.1 V (versus SCE). Its anodic peak current at 1.0 V for the first scan is markedly retarded in the presence of resorcinol or phloroglucinol, and decreases with increasing their concentrations. However, this peak current is slightly affected by hydroquinone, because it is oxidized electrochemically before oxidation of aniline. The experiment of the rotating ring-disk electrode shows that both the disk current at 1.0 V and the ring current for electrolysis of aniline are simultaneously decreased in the presence of resorcinol. This means that a soluble intermediate cation generated at the disk electrode is captured by resorcinol. There are four anodic peaks and three reduction peaks on the cyclic voltammograms during oxidation of aniline by repeated potential cycling. From the temperature dependence of the separate anodic peak currents, the activation energy of each reaction is calculated. For the first scan, the oxidation of aniline at 1.0 V involves two different activation energies at temperatures from 1 to 35 °C. Both activation energies are smaller than 21 kJ mol −1. The values fall into the range of activation energies for a general propagation reaction and termination reaction of free radical polymerization. These experimental facts indicate that the initial stage of aniline oxidation is the most likely to involve the formation of a radical cation.