Electropolymerization of phenol on a vitreous carbon electrode in alkaline aqueous solution at different temperatures

Electrochemical oxidation of phenol in basic aqueous solution has been studied on a vitreous carbon electrode at different temperatures in the range of 25–85 °C by cyclic voltammetry and chronoamperometry techniques. The electrochemical oxidation of phenol led to a complete deactivation of the electrode, whatever the temperature used, as a result of the deposition of an adhesive and insulating polymeric film. The electrochemical activity of the electrode was progressively restored by repeated potential scans in the range of water stability only when conducted at high temperatures; electrode reactivation was explained by an increase in the polymeric film permeability for both electrons (electron tunneling) and phenol molecules (diffusion). Chronoamperometric measurements carried out in the potential region of water stability have shown that electrode passivation was reduced or prevented at high temperatures. For chronoamperometry performed at the onset of oxygen evolution, the electrode remained active even at low temperatures because the discharge of water involved the production of hydroxyl radicals that destructively oxidized the polymeric film. The effect of temperature on electrode reactivation was determined by the measurement of current at an electrolysis time of 300 s; an increase of the temperature from 25 to 85 °C amplified the current from 0.212 to 5.373 mA

Effect of electropolymerisation conditions on the permeability of polyphenol films deposited on a vitreous carbon electrode

Polymeric films were prepared from alkaline (NaOH) phenol aqueous solutions on a vitreous carbon (VC) electrode by potentiostatic or galvanostatic electro-oxidation. Permeation through such films was studied by rotating-disk electrode using the ferricyanide redox couple, and by cyclic voltammetry using phenate ions. The influence of the electropolymerisation controllable parameters such as NaOH and phenol concentrations, potential or current applied, electrosynthesis time, temperature and hydrodynamic conditions (electrode rotation + solution magnetic stirring) on the permeability of these polymeric films was examined. Conditions for the removal of phenol by electropolymerisation are discussed on the basis of the permeability of polyphenol films obtained by electrosynthesis. Permeable films were formed for a concentration of free hydroxyl anion larger of 0.1 M. An increase of the temperature to 85°C favours the formation of highly permeable films, thus avoiding electrode fouling

Electropolymerization of phenol on a vitreous carbon electrode in acidic aqueous solution at different temperatures

Electrochemical oxidation of phenol in acidic aqueous solution was studied on a vitreous carbon electrode at different temperatures in the range of 25–85 °C by cyclic voltammetry and chronoamperometry. The kinetic aspect of the phenol oxidation was investigated as a function of its concentration and temperature. The electrode deactivation by formation of an adherent, compact, and insulating polymeric film was examined by monitoring the decrease in the peak current of phenol oxidation during the course of successive potential scans. Repeated potential scans in the region of water stability did not reactivate the electrode whatever the temperature used. Chronoamperometric curves recorded at different potentials in the region of water decomposition shown that the electrochemical activity of the electrode was partially restored even when performed at low temperature (25 °C)

Electrochemical removal of phenol in alkaline solution. Contribution of the anodic polymerization on different electrode materials

The removal of organic pollutants based on electropolymerization on an anode was performed in the case of phenol in alkaline solution. The polymer formed by a process involving less than two electrons per molecule of phenol, is then precipitated by decreasing the pH and finally filtered and disposed. The electrochemical polymerization of phenol (C0 = 0.105M) in alkaline solution (pH = 13) at 86 ◦C has been studied by galvanostatic electrolysis, using a range of anode materials characterized by different O2-overpotentials (IrO2, Pt and B-PbO2). Measurements of total organic carbon and HPLC have been used to follow phenol oxidation; the morphology of the polymer deposited on the electrode surface has been examined by SEM. Experimental data indicate that phenol concentration decreases by oxidation according to a first order reaction suggesting a mass transport limitation process. Polymeric films formed in alkaline solution did not cause the complete deactivation of the anodes. SEM results show that the polymeric films formed on Ti/IrO2 and Pt anodes cannot be mineralized. On the other hand, complex oxidation reactions leading to the partial incineration of polymeric materials can take place on the Ta/B-PbO2 surface due to electrogenerated HO• radicals which have an oxidizing power much higher than that of intermediaries formed respectively on IrO2 and Pt. It is assumed that the polymer films formed on these anodes have different permeability characteristics which determine the rate of mass transfer of the phenol. The fractions of phenol converted in polymers were 25, 32 and 39% respectively with Ti/IrO2, Pt and Ta/B-PbO2, a series of materials in which the O2-overvoltage increases

Electrochemical Treatment of Industrial Organic Effluents

The anodic oxidation of organics is a potentially powerful technique of controlling pollutants in industrial waste waters. Based on a fundamental analysis, this paper summarizes recent results in this field. Direct electrochemical processes catalyzed by the oxygen-transfer reaction are discussed for several anode materials. Ti/SnO2 is particularly efficient for cold combustion of aromatic pollutants. Potential candidate processes involving the electrochemical generation of oxidizer reactants (O3, H2O2), or the electrochemical regeneration of metallic redox couples are discussed

Voltammetric determination of the critical micellar concentration of surfactants by using a boron doped diamond anode

The electrochemistry of three surfactants has been studied by voltammetry at boron doped diamond (BDD) electrode in sodium sulphate solutions. The electrochemical behaviour of these surfactants is characterized by an oxidation signal (peak or wave) situated before the electrolyte oxidation. The anodic current is found to follow a linear relation with the concentration of the surfactants; the slope decreases abruptly above the critical micellar concentration (CMC) of the surfactants. The CMC values obtained for an anionic (sodium dodecylbenzenesulfonate, SDBS), a cationic (polyoxyethylene-23-dodecyl ether, BRIJ 35) and a neutral (1-(hexadecyl)trimethylammonium bromide, CTAB) surfactant are found in good agreement with those measured by the classical technique of surface tension. This voltammetric method has the advantage not to require the use of a redox active electrochemical probe

Kinetic Study of the Electrochemical Mineralization of m-Cresol on a Boron-Doped Diamond Anode.

The kinetics of the electrooxidation of m-cresol in aqueous solution was investigated in a one-compartment flow electrochemical cell with a boron-doped diamond electrode (BDD). Cyclic voltammograms recorded on BDD revealed that cresol oxidation takes place at a potential very close to the discharge of water. Under potentiostatic conditions, at a working potential lower than water discharge, a passive layer was rapidly formed on the electrode surface due to cresol polymerization. The anode fouling was not observed during electrolysis performed with the flow electrochemical cell operating under galvanostatic conditions. In this case, the decay of mcresol concentration followed a pseudo-first-order kinetics. The abatement of chemical oxygen demand (COD) showed that the kinetics of m-cresol oxidation was limited by mass transfer and that a full mineralization was achieved. A good agreement between predicted and experimental COD and instantaneous current efficiency values was obtained, although some deviations were observed at high current since the experimental data decreased faster than those predicted ones. These deviations can be explained by the occurrence of oxygen evolution which increases the mass transfer coefficient

Electrochemical preparation of peroxodisulfuric acid using boron doped diamond thin film electrodes

We have investigated the electrochemical oxidation of sulfuric acid on boron-doped synthetic diamond electrodes (BDD) obtained by HF CVD on p-Si. The results have shown that high current efficiency for sulfuric acid oxidation to peroxodisulfuric acid can be achieved in concentrated H2SO4 (>2 M) at moderate temperatures (8–10 °C). The main side reaction is oxygen evolution. Small amounts of peroxomonosulfuric acid (Caro's acid) have also been detected. A reaction mechanism involving hydroxyl radicals, HSO4− and undissociated H2SO4 has been proposed. According to this mechanism electrogenerated hydroxyl radicals at the BDD anode react with HSO4− and H2SO4 giving peroxodisulfate

New electrodes for silver(II) electrogeneration:comparison between Ti/Pt, Nb/Pt, and Nb/BDD

Electrochemical processes based on the regeneration of silver (II) are very efficient for the destruction or dissolution of persistent substances. The aim of this work is to assess new anode materials to replace the conventional platinum electrode. The electrochemical generation of Ag (II) by oxidation of Ag (I) in HNO3 (6mol/L) was evaluated at boron doped diamond on niobium substrate (Nb/BDD) anode and results are compared with those obtained on Ti/Pt and Nb/Pt anodes. The performance of these anodes was evaluated in a filter press reactor in batch operation mode. The rate of Ag (II) generation obtained on the Nb/BDD anode is similar to that obtained on platinized electrodes. A theoretical model is presented to predict the behavior of the system. Good agreement is found between experimental results and the theoretical model

Electrochemical incineration of cresols: A comparative study between PbO2 and boron-doped diamond anodes

The electrooxidation of aqueous solutions containing 5 mM of o-, m- and p-cresol at pH 4.0 has been investigated using a flow filter-press reactor with a boron-doped diamond (BDD) under galvanostatic electrolysis. All cresols are degraded at similar rate up to attaining overall mineralization. Comparable treatment of the m-cresol effluent on PbO2 leads to partial electrochemical incineration. However, this pollutant is more rapidly removed with PbO2 than with BDD. The decay kinetics of all cresols follows a pseudo-first-order reaction. Aromatic intermediates such as 2-methylhydroquinone and 2-methyl-p-benzoquinone and carboxylic acids such as maleic, fumaric, pyruvic, malonic, tartronic, glycolic, glyoxylic, acetic, oxalic and formic, have been identified and followed during the m-cresol treatment by chromatographic techniques. From these oxidation by-products, a plausible reaction sequence for m-cresol mineralization on both anodes is proposed. The energy consumption for the corresponding electrochemical process is also calculated