1978 Current Organic Chemistry, 2012, 16, 1978-1985 Electrochemical Degradation of Anthraquinone Dye Alizarin Red: Role of the Electrode Material Salah Ammar a,c , Mhemdi Asma a , Nihal Oturan b , Ridha Abdelhédi a and Mehmet A. Oturan b,* a Unité de Recherche d’Electrochimie et Environnement, Ecole Nationale d’Ingénieurs de Sfax, BPW, 3038, Sfax, Tunisie b Université Paris-Est Marne-la-Vallée, Laboratoire Géomatériaux et Environnement, 5 boulevard Descartes, Champs-sur-Marne, 77454 Marne-la-Vallée, Cedex 02, France c Département de chimie Faculté des Sciences de Gabès, Cité Erriadh, 6027 Gabès, Tunisie Abstract: Anodic oxidation is a promising process for degrading toxic and biologically refractory organic pollutants present in wastewa- ter. Proper selection of electrodes is the key to reach effective and economic treatment. In this study, the electrochemical oxidation of Al- izarin Red has been studied in neutral media using lead dioxide (PbO2), boron-doped diamond (BDD) and platinum (Pt) anodes in bulk electrolysis experiments under same conditions. Obtained results have clearly shown that the electrode material is an important parameter for the optimization of such process. Kinetics analysis showed that Alizarin Red is readily oxidized on PbO2 and BDD anodes, Pt anode having a moderate ability to oxidize it. Different current efficiencies were obtained for PbO2 and BDD, depending on the applied current density in the range from 33 to 150 mA cm -2 . The effect of the initial Alizarin Red concentration on the performance of PbO2, BDD and Pt anodes, as well as, their comparative oxidation ability was studied. Faster Alizarin Red elimination and TOC removal were obtained using BDD anode with current density of 33 mA cm -2 . Bulk electrolysis showed that the complete TOC and color removal were achieved using PbO2 and BDD anodes while Pt anode performed only a partial oxidation of Alizarin Red. Keywords: Alizarin, Degradation kinetics, Anodic oxidation, BDD anode, Hydroxyl radical, TOC removal. 1. INTRODUCTION Synthetic dyes are extensively used in many fields of up-to-date technology. The more common chemical classes of dyes employed at industrial scale are the azo, indigoid, triphenyl methyl and an- thraquinone dyes. Because of their commercial importance, the impact [1] and toxicity [2] of dyes released in the environment have been extensively studied. Traditional physico-chemical treatments applied to the purification of dyeing wastewaters include adsorption with inorganic supports, filtration and ion exchange [3-5]. These procedures lead to effective discoloration, but their application is restricted by the formation of sludge to be disposed or by the need to regularly regenerate the adsorbent materials [6]. On the other hand, the application of micro organisms to the biodegradation of synthetic dyes is an attractive and simple method by operation. A large number of activated sludge processes, mixed cultures with aerobic and anaerobic destruction of dyes were used [7, 8]. Unfortunately, these processes are often inefficient because the majority of these compounds are persistent and resistant to mi- crobiological degradation. More powerful chemical methods such as ozonation [9] and oxidation with hypochlorite ion as well as advanced oxidation proc- esses (AOPs) such as photocatalytic systems involving TiO 2 /UV, H 2 O 2 /UV, H 2 O 2 /Fe 3+ /UV and O 3 /UV provide fast discoloration along with degradation of dyes [10-14]. However, the use of these methods is not completely accepted at present because they are mostly energy-consuming and require the use of chemicals having a negative effect on cost-effectiveness of the treatment. *Address correspondence of this author at the Université Paris-Est Marne-la-Vallée, Laboratoire Géomatériaux et Environnement, 5 boulevard Descartes, Champs-sur- Marne, 77454 Marne-la-Vallée, Cedex 02, France; Tel: +33 1 49 32 90 65; E-mail: mehmet.oturan@univ-paris-est.fr In recent decades the electrochemical technology has been largely developed for its alternative use in wastewater treatment [15-18]. One of the approaches for electrochemical treatment of organic pollutants is the indirect electrolysis generating in situ chemical oxidizing agents such as chlorine and hydrogen peroxide to react with the pollutants [19]. Hydrogen peroxide is an environ- mentally friendly chemical that leaves no hazardous residuals dur- ing its self-degradation since it decomposes only to water and oxy- gen. It is electrogenerated in acidic solution by two electron reduc- tion of oxygen on the cathode surface: O 2 + 2H + + 2 e -  H 2 O 2 (1) This reaction can take place at different cathode such as mer- cury pool [20], reticulated vitreous carbon [21], activated carbon fibber [22], carbon felt [23-26], carbon sponge [27] and O 2 diffu- sion [28-30] cathodes. The oxidation power of electrogenerated weak oxidant H 2 O 2 can be enhanced in the presence of Fe 2+ ions at acidic medium through the Fenton reaction (reaction (2)) for which Fenton's reagent is electrochemically generated (electro-Fenton process) [31, 32]: H 2 O 2 + Fe 2+ + H +  Fe 3+ + H 2 O +  OH (2) Fe 3+ ions formed by Fenton reaction (reaction (2)) are reduced at the cathode at the potential of oxygen reduction in order to re- generate ferrous ions: Fe 3+ + e -  Fe 2+ (3) Another approach to the electrochemical treatment of organic pollutants is the direct electro-oxidation that called "anodic oxida- tion process" constituting a promising alternative that has the poten- tial to replace or complete already existing processes and compati- Send Orders of Reprints at reprints@benthamscience.org 1 5- 8/12 $58.00+.00 © 2012 Bentham Science Publishers