ORIGINAL PAPER Electrochemical degradation of the Acid Blue 62 dye on a b-PbO 2 anode assessed by the response surface methodology Jose ´ M. Aquino • Romeu C. Rocha-Filho • Nerilso Bocchi • Sonia R. Biaggio Received: 2 January 2010 / Accepted: 26 March 2010 / Published online: 10 April 2010 Ó Springer Science+Business Media B.V. 2010 Abstract The electrochemical degradation of the anthra- quinonic dye Acid Blue 62 in a filter-press reactor on a Ti/Pt/ b-PbO 2 anode was investigated using the response surface methodology with the variables: current density, pH, [NaCl], and temperature. The system’s modeling was carried out with the charge required for 90% decolorization (Q 90 ) and the chemical oxygen demand removal percentage after a 30 min electrolysis (COD 30 ), with good correlations between predicted and observed values. Best conditions for decolorization were attained in acidic solutions (pH = 4) with medium to high [NaCl] (1.0–2.0 g L -1 ) and lower temperature due to the prevalent oxidant species HOCl and Cl 2 . Optimal conditions for COD 30 removal were attained at high current densities in pH [ 5 solutions with high [NaCl], when the prevalent oxidant species are HOCl and OCl - . The lowest charge per unit volume of the electrolyzed solution necessary for total mineralization was attained at pH 11. Keywords Electrooxidation  Dye degradation in the presence of chlorine  Acid Blue 62 dye  PbO 2 anode  Factorial design 1 Introduction Synthetic dyes are a class of organic compounds exten- sively used for innumerable industrial applications, mainly textile. Among these compounds, the azo (–N=N–) ones are the most produced and consumed in dyeing processes, but other classes of dyes such as the anthraquinonic ones are also used [1]. As a consequence of their use, significant quantities of effluents are produced and have to be treated before disposal into the environment. Textile effluents are mainly characterized by intense colors originated by non- reacted dyestuff and high organic loads (due to the pres- ence of auxiliary chemicals). The presence of synthetic dyes in water can interfere with sun light penetration [2] and cause health risks [1, 3, 4]. Furthermore, dye molecules are known to be stable and thus may remain in the envi- ronment for long periods [3]. Hence, the use and imple- mentation of various methods to decolorize and degrade synthetic dyes are of great importance, due to increasingly rigid environmental regulations [5]. As described in the literature [1, 6, 7], there are several methods for the remediation of textile effluents, such as: biological, chemical, physico-chemical, advanced oxida- tion, and electrochemical processes. Among them, elec- trochemical methods [1, 8, 9] might be a reasonable option due to the combination of easy implementation with pol- lutants high removal rates. Their main drawback regards the use of electrical energy. However, the development of new electrode materials with a high oxidation power can lead to better efficiencies for the removal of pollutants. In conventional electrooxidation, pollutants can be removed by: (i) direct oxidation, through the direct transfer of electrons from the adsorbed pollutant on the electrode surface and (ii) indirect oxidation, in which electrons are transferred to other species adsorbed on the electrode sur- face [9]. The most common electrogenerated species in indirect oxidation (anodic process) is the hydroxyl radical (•OH). According to the interaction between this radical and anode materials, Kapalka et al. [10] classified them from low to high oxidation power anodes. Furthermore, when chloride ions are used, the pollutants oxidation may J. M. Aquino  R. C. Rocha-Filho (&)  N. Bocchi  S. R. Biaggio Departamento de Quı ´mica, Universidade Federal de Sa ˜o Carlos, C.P. 676, 13560-970 Sa ˜o Carlos, SP, Brazil e-mail: romeu@ufscar.br 123 J Appl Electrochem (2010) 40:1751–1757 DOI 10.1007/s10800-010-0115-9