Electrochemical degradation of crystal violet with BDD electrodes: Effect of electrochemical parameters and identification of organic by-products Ricardo E. Palma-Goyes a,b , Fernando L. Guzmán-Duque a , Gustavo Peñuela b , Ignacio González c , Jose L. Nava d , Ricardo A. Torres-Palma a,b, * a Grupo de electroquímica, Instituto de química, Facultad de ciencias exactas y naturales, Universidad de Antioquia, A.A. 1226, Medellín, Colombia b Grupo de diagnóstico y control de la contaminación, Facultad de ingeniería, Universidad de Antioquia, A.A. 1226, Medellín, Colombia c Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Química, Av. San Rafael Atlixco No. 186, C.P. 09340, México D.F., Mexico d Universidad de Guanajuato, Departamento de Ingeniería Geomática e Hidráulica, Av. Juárez No. 77, C.P. 36000, Guanajuato, Mexico article info Article history: Received 24 February 2010 Received in revised form 12 July 2010 Accepted 14 July 2010 Available online 14 August 2010 Keywords: Electrochemical oxidation Triphenylmethane dye Crystal violet BDD electrode Water treatment Dye treatment abstract This paper explores the applicability of electrochemical oxidation on a triphenylmethane dye compound model, hexamethylpararosaniline chloride (or crystal violet, CV), using BDD anodes. The effect of the important electrochemical parameters: current density (2.5–15 mA cm 2 ), dye concentration (33– 600 mg L 1 ), sodium sulphate concentration (7.1–50.0 g L 1 ) and initial pH (3–11) on the efficiency of the electrochemical process was evaluated. The results indicated that while the current density was lower than the limiting current density, no side products (hydrogen peroxide, peroxodisulphate, ozone and chlorinated oxidizing compounds) were generated and the degradation, through  OH radical attack, occurred with high efficiency. Analysis of intermediates using GC–MS investigation identified several prod- ucts: N-methylaniline, N,N-dimethylaniline, 4-methyl-N,N-dimethylaniline, 4-methyl-N-methylaniline, 4- dimethylaminophenol, 4-dimethylaminobenzoic acid, 4-(N,N-dimethylamino)-4 0 -(N 0 ,N 0 -dimethylamino) diphenylmethane, 4-(4-dimethylaminophenyl)-N,N-dimethylaniline, 4-(N,N-dimethylamino)-4 0 -(N 0 ,N 0 - dimethylamino) benzophenone. The presence of these aromatic structures showed that the main CV deg- radation pathway is related to the reaction of CV with the  OH radical. Under optimal conditions, practically 100% of the initial substrate and COD were eliminated in approximately 35 min of electrolysis; indicating that the early CV by-products were completely degraded by the electrochemical system. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Triphenylmethane dye compounds, such as crystal violet (CV), are largely used in the paper, leather, cosmetic, and food industries. The textile industry consumes large amounts of these substances for dyeing nylon, wool, cotton, and silk, as well as for colouring oil, fats, waxes, varnish and plastics (Gessner and Mayer, 2001). Furthermore, some of the triphenylmethane dyes are used as med- icine and biological stains (Azmi et al., 1998). These compounds not only cause coloration of water, but also pose a serious risk to aquatic life (Nassar and Magdy, 1997) and their presence in drink- ing water constitutes a possible human health hazard (Pielesz, 1999). Biological processes are the most economical option to eliminate organic pollutants. However, these methods cannot be applied to many textile wastewaters due to the toxicity of commercial dyes against the microorganisms used in the processes (Robinson et al., 2001). Physicochemical methods, based on the production and use of hydroxyl radical called Advanced Oxidation Processes (AOPs) (e.g. H 2 O 2 /UV, UV/O 3 ,H 2 O 2 /O 3 , TiO 2 photocatalysis, Fenton’s re- agent, photo-Fenton), have been successfully tested for elimination of this kind of compounds in water (Ruppert et al., 1994; Azbar et al., 2004). These processes are all based on the generation and use of a powerful oxidant, the  OH radical. However, because of the hydroxyl radical scavenger effect, they have limited applica- tions in waters containing appreciable quantities of inorganic ions. Guillard et al. (2005) demonstrated how the TiO 2 photocatalytic efficiency, under acidic conditions, decreased due to the  OH radical scavenging effect by anions such as NO  3 , Cl  , SO 2 4 , PO 3 4 . Siedlecka et al. (2007) studied the effect of selected inorganic anions on the effectiveness of the Fenton advanced oxidative treatment of waters contaminated with methyl t-butyl ether (MTBE). SO 2 4 , Cl  and H 2 PO  4 led to competition between the organics and the  OH radicals, 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.07.020 * Corresponding author at: Grupo de electroquímica, Instituto de química, Facultad de ciencias exactas y naturales, Universidad de Antioquia, A.A. 1226, Medellín, Colombia. Tel.: +57 4 219 56 00; fax: +57 4 219 56 66. E-mail addresses: rtorres@matematicas.udea.edu.co, ricardo.torrespalma@utor- onto.ca (R.A. Torres-Palma). Chemosphere 81 (2010) 26–32 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere