Decolourization of anthraquinone reactive dye by electrochemical reduction on reticulated glassy carbon electrode

Abstract

A remoção do corante reativo Reactive Blue 4 (RB4) por redução eletroquímica em solução aquosa foi investigada sobre eletrodo de carbono vítreo reticulado. O grupo antraquinona presente no corante RB4 é reduzido em pH < 8,0 em uma única etapa a hidroquinona, segundo um processo reversível de dois elétrons e reação de pré-protonação, via geração de um radical semiquinona detectado espectrotométricamente. Em pH > 8,0, ambas as formas não e pré-protonada da antraquinona são reduzidas em duas etapas reversíveis de dois elétrons. Após 3 horas de eletrólise em meio ácido e neutro o corante perde 60% de sua coloração, enquanto que em meio alcalino perde apenas 37%. Simultaneamente, 64% de remoção de carbono orgânico total foi obtida após eletrólise em meio ácido de pH 2,0.The electrochemistry reduction for the removal of Reactive Blue 4 (RB4) dye from aqueous solution using reticulated glassy carbon electrode is investigated. At pH < 8.0 the anthraquinone group of the RB4 dye are reduced in one cathodic step to hidroquinone after a reversible two-electron process involving a precedent two protons reaction. A stable semiquinone is detected by spectrophotometric technique. At pH > 8.0 the reduction process involves two reversible 2-electron steps, whose species are generated by a protonation equilibrium of anthraquinone group. The results shows that 60% of color removal was obtained after 3 hours of RB4 dye electrolysis at acidic and neutral conditions and only 37% at alkaline conditions. Simultaneously 64% of total organic carbon was removed after electrolysis at pH 2.0.Keywords: reactive dyes, electrochemical reduction, dye treatment, reactive blue 4 IntroductionReactive dyes are the main group of dyes used in the textile industry.1 They are very effective in fabric dyeing due to the reactive groups capable of forming covalent bonds with a hydroxyl or amino group on the fiber. Inefficiencies in the dyeing process results in 10-15% of all dyestuff being lost directly to wastewater.2 Therefore, their crescent world consumption has attracted the critical attention of the public and the authorities with respect to the toxicological and environmental aspects of the reactive dyes. 3,4 Dye wastewater is usually treated by physical or chemical treatment process. They include physicalchemical flocculation, electroflotation, membranefiltration, electrokinetic coagulation, ion-exchange, irradiation, precipitation and other treatment using activated carbon. 5 Over the past few years, alternative methods 6-10 for dye treatment have been investigated, including chemical oxidation with reagents such as: ozone, hydrogen peroxide, ozone/UV, hydrogen peroxide/UV and Fenton's reagent [hydrogen peroxide + Fe (II)]. The application of electrochemical oxidation with or without UV light as method for dye degradation have also been investigated, [11][12][13][14][15] but no mechanisms of the reduction were discussed. [16][17][18][19] Most of the electrochemical studies involving reduction of reactive dyes are based on mercury electrode [16][17...

Carbon Nanotube-Based Electrochemical Sensor for the Determination of Anthraquinone Hair Dyes in Wastewaters

“…On the bare electrode, the AG25 dye was voltammetrically reduced on the glassy carbon electrode in a single-step process at around −0.47 V (Peak I), attributed to the reduction of the anthraquinone/hydroquinone group, as described in the literature [39][40][41]. A small voltammetric peak was seen on the reverse scan, where the anode-to-cathode peak height ratio (Ipa/Ipc = 0.18) and Epa − Epc = 105 mV clearly indicated that the process was not completely reversible under the surface of the glassy carbon electrode without modification [42].…”

“…Taking into account that the process involves a transfer of two electrons (n = 2), according to the equation ΔE/ΔpH = (59.1 mV NH + /n)* and using the slope obtained, we can suggest that the number of protons (NH + ) transferred may be two [39,43]. These results indicated that the anthraquinone reduction occurred in a similar way to that obtained on a glassy carbon electrode, except for the faster electron transfer and partial protonation, which changed the reversibility of the cyclic voltammograms obtained on the CNTME.…”

“…for the activated CNTME, suggesting that reduction of the dye is favored on the activated surface. In order to confirm this effect on the charge-transfer resistance (Rct) and the double-layer capacitance (Cdl), measurements of electrochemical impedance spectroscopy (EIS) were carried out [39]. AG25 using the activated and inactivated CNTME (Figure 4).…”

Application of voltammetric technique to the analysis of indanthrene dye in alkaline solution

“…As other compounds containing anthraquinone dyes, they are reduced in two consecutive one electron transfer reaction leading anthraquinone to generate the corresponding hydroquinone from Refs. [27,29] in the potential range of ÿ0.5 V to ÿ0.7 V. The reduction system is followed by new step around ÿ1.0 V, where the quinoid group (eC]O) is also reduced to the eCeOH (peak III). This last peak is higher and presents better analytical potentiality to monitor dye concentration, even in suspension.…”

Ozonation of azo dye acid black 1 under the suppression effect by chloride ion

“…The toxicity of theses dyes is often related to the amines employed or formed in their syntheses. 2 Dye wastewaters can be treated by conventional processes, such as activated carbon absorption or coagulation, or by alternative technologies including electrochemical treatment, 3,4 absorption using new materials and advanced oxidative processes (AOPs). 5 Despite the fact that ozonation in acid medium is not an AOP, O 3 proved to yield excellent results on dye effluents treatment.…”