Rodnei Bertazzoli

Removal of Zn(II) from chloride medium using a porous electrode: current penetration within the cathode

An electrolytic process for the removal of zinc from aqueous solutions using a flow-through cell with a reticulated vitreous carbon cathode is proposed. The operational conditions for the reactor were optimized as a function of the electrolyte pH, the cathode porosity and the solution flow rate. Both a synthetic solution and a real effluent from an industrial electroplating plant were processed until zinc concentration dropped from 50 to 0.1 mg dm−3 and from 152 to 0.5 mg dm−3, respectively. After the processing of the real effluent, tomographic images of the cathode were taken in order to investigate the current depth penetration during electrolysis. Results have shown that the current density decreases from the outer surface to the centre of the RVC cathode.

Studies of the mechanism for the electrodeposition of FeCo alloys

Abstract The electrodeposition of FeCo alloy onto vitreous carbon has been investigated from a sulphate bath containing boric acid at pH 4. It is shown that the composition of the alloy is mainly determined by the ratio of Fe(II)/Co(II) in solution and only slightly by temperature or potential/current density. The Fe content of the alloy is always higher than the ratio of Fe(II)/Co(II) in solution despite the observation from studies of the solutions of Fe(II) and Co(II) alone that the Fe(II) is more difficult to reduce than Co(II) by 200 mV. The kinetics of the nucleation and early growth of the metal lattices as well as the kinetics of the M/M 2+ couples have been studied. The equilibrium potentials of the alloys in the plating solutions are close to that for the Co/Co(II) couple but the presence of Fe(II) in solution changes the mechanism for cobalt deposition as well as inhibiting the early stages of nucleation and growth.

Comparative Study of Commercial Oxide Electrodes Performance in Electrochemical Degradation of Organics in Aqueous Solutions

In this paper the potentiality of two types of DSAâ commercial electrodes, for electrochemical treatment of effluents, is investigated. Oxide anodes, with nominal composition of 70TiO2/30RuO2 and 45IrO2/55Ta2O5, were used in a flow-cell reactor for the electrooxidation of phenol. Comparative results were presented as phenol concentration decay as a function of electrolysis time, as well as COD and TOC concentration reduction. The cell reactor was operated at current densities, ranging from 15 to 150 mA cm-2 and solution linear velocity was 0.24 m s-1. Results reported in this paper showed that phenol and quinones were degraded to a very low concentration, besides only a small portion of the organic carbon is reduced. Starting from 100 mg L-1, after five hours of electrolysis at 100 mA cm-2, concentrations reached 0.4 mg L-1 of phenol, 1 mg L-1 of hydroquinone, 7 mg L-1 of benzoquinone and TOC was reduced by 35%.

Thirty minutes laser calcination method for the preparation of DSA® type oxide electrodes

Abstract In this paper, a new approach for the preparation of dimensionally stable anodes DSA® type oxide electrodes, using a CO2 laser as a heat source, is proposed. Commercial composition of (TiO2)0.7(RuO2)0.3 was used for this feasibility study in which thermal decomposition of precursor chlorides, for the growth of a coating 2–3 μm thick, is carried out in 30 min. The resulting oxide layer presented the usual cracked-mud morphology that lasted 8 h in an accelerated service life test at 400 mA cm −2 , in a H2SO4 1 M solution. The results involving the effects of laser beam power and scan rate are examined. Voltammetric anodic charge was maximized by the combination of 15 W beampower, focal distance of 210 mm and beam scan rate of 35 mm s −1 . By cycling potential between 0.2 and 1.1 V vs SCE the oxide coating behaved as a capacitor capable of being charged and discharged reversibly and the cathodic/anodic charge ratio remained close to one. Currents related to oxygen evolution reaction were observed after 1.37 V vs SCE.

Considerações sobre a eletrogeração de peróxido de hidrogênio

This paper presents some results that may be used as previous considerations to a hydrogen peroxide electrogeneration process design. A kinetic study of oxygen dissolution in aqueous solution is carried out and rate constants for oxygen dissolution are calculated. Voltammetric experiments on vitreous carbon cathode shown that the low saturation concentration drives the oxygen reduction process to a mass transfer controlled process which exhibits low values of limiting currents. Results have shown that the hydrogen peroxide formation and its decomposition to water are separated by 400 mV on the vitreous carbon surface. Diffusion coefficients for oxygen and hydrogen peroxide are calculated using data taken from Levich and Tafel plots. In a series of bulk electrolysis experiments hydrogen peroxide was electrogenerated at several potential values, and concentration profiles as a function of the electrical charged passed were obtained. Data shown that, since limiting current plateaus are poorly defined onto reticulated vitreous carbon, cathodic efficiency may be a good criterion for choosing the potential value in which hydrogen peroxide electrogeneration should be carried out.

MASS TRANSPORT PROPERTIES OF A FLOW-THROUGH ELECTROLYTIC REACTOR USING A POROUS ELECTRODE: PERFORMANCE AND FIGURES OF MERIT FOR Pb(II) REMOVAL

The removal of lead from an acid borate-nitrate solution containing Pb(II) was used to characterize the mass transport properties of an electrolytic reactor with reticulated vitreous carbon cathodes, operated in the flow-through mode. Current potential curves recorded at a rotating vitreous carbon disc electrode were used to determine the diffusion coefficient for Pb(II) under the conditions of the experiments. The performance and figures of merit of the electrolytic reactor were investigated by using different flowrates and cathode porosities. Dimensionless Sherwood and Reynolds numbers were correlated to characterize the mass transport properties of the reactor, and they were fitted to the equation Sh=24Re0.32Sc0.33.

Studies of the electrodeposition of cobalt on a vitreous carbon electrode

Neste trabalho foram feitos experimentos usando tecnicas de voltametria ciclica e pulso de potencial para o estudo do mecanismo de deposicao do cobalto em meio de sulfato. A voltametria ciclica mostrou dois picos de dissolucao, o que foi atribuido a dissolucao de uma fase rica em hidrogenio e outra do metal quase puro. A analise cinetica das curvas I-E na varredura reversa mostraram que, para uma solucao com 0,37 M Co(II) e pH 6, o potencial de equilibrio do par Co/Co(II) e -0,58 V vs. SCE e a corrente de troca, Io = 4,8 x 10-6 A cm-2. Os experimentos de pulso de potencial mostraram que o deposito de cobalto sobre o eletrodo de carbono vitreo apresenta nucleacao progressiva seguido de crescimento tridimensional. Ambas as tecnicas confinnaram que a deposicao do cobalto acontece em duas etapas, com a transferencia de um eletron cada.

Photoelectrochemical discoloration and degradation of organic pollutants in aqueous solutions

Organic compounds responsible for the color of wastewaters are usually refractory to biological digestion. In this paper the photo-assisted electrolysis process is used for color removal from three of the most colored wastewaters, which are daily generated in large amounts: the E1 bleach Kraft mill effluent, a textile reactive dye effluent and a landfill leachate. Electrolysis was carried out at 26,5 mA cm-2 in a flow reactor in which the anode surface was illuminated by a 400 W high pressure Hg bulb. In all experiments 70-75% of color reduction was observed which was also followed by a net organic load oxidation.

Effects of the modification of gas diffusion electrodes by organic redox catalysts for hydrogen peroxide electrosynthesis

This paper reports a comparative study of the electrochemical performance of in situ hydrogen peroxide electrogeneration on gas diffusion electrodes modified by organic redox catalysts 2-ethylanthraquinone, 2-terc-butylanthraquinone and azobenzene in medium of 0.1 mol L-1 H2SO4 plus 0.1 mol L-1 K2SO4, pH = 1. Hydrogen peroxide generation proved strongly dependent on the applied potential and on the concentration of added catalysts. Electrode modifications led to a significant increase in H2O2 yield (30%) reaching 850 mg L-1, and the overpotential for oxygen reduction shifted to less negative values (400 mV vs Ag/AgCl for electrodes modified by quinones and 300 mV vs Ag/AgCl for electrodes modified by azobenzene) compared to noncatalyzed gas diffusion electrodes, resulting in reduced energy consumption of 596.5 to 232.4 kWh kg-1. The results indicated that the best electrode for H2O2 electrogeneration is the gas diffusion electrode modified with 10% of 2-ethylanthraquinone, offering the best cost to benefit ratio.

Photo-assisted electrochemical degradation of the commercial herbicide atrazine.

This paper presents a degradation study of the pesticide atrazine using photo-assisted electrochemical methods at a dimensionally stable anode (DSA(®)) of nominal composition Ti/Ru(0.3)Ti(0.7)O(2) in a prototype reactor. The effects of current density, electrolyte flow-rate, as well as the use of different atrazine concentrations are reported. The results indicate that the energy consumption is substantially reduced for the combined photochemical and electrochemical processes when compared to the isolated systems. It is observed that complete atrazine removal is achieved at low current densities when using the combined method, thus reducing the energy required to operate the electrochemical system. The results also include the investigation of the phytotoxicity of the treated solutions.