Artur J. Motheo

Investigation of corrosion protection of steel by polyaniline films

In the present study potentiodynamic polarisation curves were obtained for carbon and stainless steel in contact with 3% sodium chloride aqueous solution saturated with air in order to evaluate the capacity of polyaniline in the emeraldine oxidation state to protect the surface against corrosion processes. A high stability of the PAni films was observed with a gain of the corrosion potential around 270 mV more positive in the substrate covered with PAni than in the case without it. Corrosion of steel could be prevented using the conducting polymers as a protective layer.

Electro-oxidation of ethanol on gold : analysis of the reaction products and mechanism

Although the electrocatalytic properties of gold are not as good as those of platinum, the oxidation of small alcohol molecules, such as ethanol, is possible at gold both in acid and alkaline media. By using programmed potential electrolysis coupled with chromatographic analysis of the products formed, the nature and the variation of their concentrations as a function of pH and time have been determined. In alkaline medium, the only product detected was acetic acid. On the other hand, in perchloric acid medium, the reaction products are highly dependent on the value of the oxidation potential, with the following successive steps: ethanol→acetaldehyde→acetic acid. A general tentative mechanism is proposed and discussed.

Electro-oxidation of glycerol on platinum dispersed in polyaniline matrices

Abstract Films of polyaniline (PAni) were electrosynthesized on gold and glassy carbon substrates. The morphology of the films was verified using scanning electron microscopy (SEM) and, as expected, the PAni film formed on glassy carbon presented fibrillar morphology, while that formed on gold presented fibrils on top of a more compact structure. Different amounts of platinum were electrodeposited into the polymer matrices at constant potential and the electrocatalytic activities of the electrodes were evaluated for glycerol electro-oxidation in acidic medium. Furthermore, the active areas of such modified electrodes were determined from the charges involved in the electro-oxidation of an adsorbed carbon monoxide monolayer. Considering the real active areas, the modified electrode with the gold substrate presents higher electrocatalytic activity for glycerol oxidation than that with the glassy carbon substrate. This difference is mainly related to their morphological characteristics and platinum particle sizes.

Electrochemical degradation of humic acid.

The treatment of natural water for drinking water production goes through the degradation of humic substances. In this study, humic acid, extracted from a peat area located at the margins of the Mogi Guaçu River at São Paulo State, Brazil, was used to perform electro-oxidation essays in order to evaluate the possibilities of electrochemical methods in the degradation of humic substances. The working electrodes were dimensionally stable anodes (DSA) type with the following compositions: Ti/Ir0.3Ti0.7O2; Ti/Ru0.3Ti0.7O2; and Ti/Ir0.2Ru0.2Ti0.6O2. The electrolyses were performed by using a solution composed of an electrolyte support (0.1 mol l(-1) KCL) and 30 mg l-1 of the humic acid. Samples were taken during the electrolyses and analysed by the pH, transmittance, UV-vis spectra and chromatography. The results show that the Ti/Ru0.3Ti0.7O2 electrode presents the best performance considering the elimination of most of the electro-oxidation products after approximately 2 h of electrolysis at 40 mA cm(-2).

Influence of different types of acidic dopant on the electrodeposition and properties of polyaniline films

The effect of different types of acidic dopant namely, poly(vinyl sulfonic) (PVS), camphor sulfonic (CSA) and hydrochloric acids on the electrodeposition of polyaniline (PANI) films by cyclic voltammetry has been investigated and correlated with the morphology and properties of the polymers produced. The polymer films were studied by cyclic voltammetry, electron microscopy, u.v.–visible spectroscopy, X-ray diffraction and conductivity measurements. The nucleation step of the electrodeposition of PANI depends on the counter-ion of the dopant and significantly affects polymer growth as well as the morphology of the polymers produced. The properties of the polymeric films were also greatly influenced by the type of acid dopant used in the electrodeposition. Although all dopants used were protonic acids the conductivity of the polymer was affected by the counter-ion and could be enhanced by exposition to m-cresol due to secondary doping effects.

Effect of monomer ratio in the electrochemical synthesis of poly(aniline-co-o-methoxyaniline)

Abstract Copolymers poly(aniline-co-o-methoxyaniline) were electrosynthesized from aqueous solutions containing 1 mol l−1 HCl and a constant total concentration of monomer (0.1 mol l−1). By varying the aniline/o-methoxyaniline ratio, it was possible to observe that the electrochemical growth depends on the initial amount of o-methoxyaniline present in the solution. The UV–vis spectra show that in the doped state the copolymers containing concentration of o-methoxyaniline lower than 50% present optical absorption for λ≥1000 nm comparable to polyaniline (PAni). The conductivity measurements present a similar behavior. The infrared spectra also show a decrease of the oxidation degree with the increase of o-methoxyaniline concentration. By determining the copolymer compositions by elemental analysis, the reactivity ratios were estimated for aniline and o-methoxyaniline, and this values suggest a possible block copolymer structure.

Decolourisation of real textile waste using electrochemical techniques: Effect of electrode composition

The present paper presents the study of the decolourisation of real textile effluent by constant current electrolysis in a flow-cell using a DSA type material. The effect of using different anode materials (Ti/Ru(0.3)Ti(0.7)O(2); Ti/Ir(0.3)Ti(0.7)O(2); Ti/Ru(X)Sn(1-X)O(2), where X=0.1, 0.2 or 0.3) on the efficiency of colour removal is discussed. Attempts to perform galvanostatic oxidation (40 and 60 mA cm(-2)) on the as-received effluent demonstrate that colour removal and total organic carbon (TOC) removal are limited. In this case the greatest degree of colour removal is achieved when anode containing 90% SnO(2) is used. If the conductivity of the effluent is increased by adding NaCl (0.1 mol L(-1)) appreciable colour/TOC removal is observed. The efficiencies of colour and TOC removal are discussed in terms of the energy per order (E(EO)/kW h m(-3)order(-1)) and energy consumption (E(C)/kW h kg(-1)TOC), respectively. Finally, the extent of colour removal is compared to consent levels presented in the literature.

Electrochemical immittance spectroscopy applied to the study of the single crystal gold/aqueous perchloric acid interface

The technique of electrochemical immittance spectroscopy has been used for characterisation of the interface at gold single crystal electrodes in aqueous solutions of perchloric acid in the absence of Faradaic processes. The results obtained for low index crystallographic orientations, namely, (100), (110) and (111) are compared to those obtained earlier for the (210) orientation. The experimental results are analysed by fitting them to a simple equivalent circuit consisting of a resistor in series with a constant phase element representing respectively, the solution resistance, Rs, and the distributed impedance of the double layer, ZCPE. The dependence of the parameters constituting the constant phase element, namely the pre-exponential factor, Y0, and the fractional exponent, nf, on the orientation of the electrode surface, on the electrode potential and on the solution concentration are discussed. The relationship of these parameters to the surface energy of the single crystals is discussed.

Electrochemical and sonoelectrochemical processes applied to amaranth dye degradation

Amaranth dye is an organic compound largely used in the food and beverage industries with potential toxicity effects on humans. It can be found as a pollutant species in aquatic environments and has been classified as an endocrine disruptor. This study describes amaranth degradation upon ultrasonication associated with an electrochemical system that uses a boron-doped diamond anode BDD, defined as a sonoelectrochemical process. Ninety-minute electrolyses were performed using current densities in the 10-50 mA cm(-2) range, and the concentration decay, pH, energy and current efficiencies, as well as the discoloration rate were evaluated. The amaranth concentration decayed as a function of electrolysis time and the reactions obeyed pseudo first-order kinetics, with an apparent constant rate between 10(-1) and 10(-3)min(-1). The electrochemical and sonoelectrochemical processes at 35 mA cm(-2) yielded TOC removal values between 92.1% and 95.1% respectively, after 90 min. Current efficiency values obtained for both processes were 18.2% and 23.6%. Exhaustive 5h electrolysis was performed and the degradation products were identified by HPLC-MS. A mechanism for the degradation of amaranth was proposed based on an analysis of the aromatic and aliphatic intermediates.

Avaliação dos tratamentos eletroquímico e fotoeletroquímico na degradação de corantes têxteis

This paper presents the study of the oxidation of three textile dyes (Remazol black B, Remazol Brilliant Orange 3R and Remazol Golden Yellow RNL) using electrochemical and photoelectrochemical methods. In both methods, electrolysis experiments were performed at a current density of 50 mA cm-2 in an aqueous solution of each dye (30 mg L-1), using a photoelectrochemical flow-cell. For all the dyes studied, the photoelectrochemical method was demonstrated to be more efficient than the electrochemical one. Photoelectrochemical oxidation resulted in complete decoloration after 90 min of electrolysis and total organic carbon (TOC) removal reached up to 36%. It was observed that the dyes presenting chromophores at higher wavelengths are removed the quickest, which indicates that photosensitised (photoassisted) oxidation occurs. The level of color was reduced to levels below the standards presented in the literature, which indicates the viability of the photoelectrochemical process as part of the treatment of textile effluents.