Electrochemical decolorization of Rhodamine B dye: Influence of anode material, chloride concentration and current density

Abstract

A B S T R A C TSurface water contamination by dyes released from a variety of industries is an environmental problem of great concern. However, electrochemical oxidation is a promising alternative for water treatment. In this paper, we studied the electrochemical oxidation of Rhodamine B (RhB) dye on the Ti/RuO 2 -IrO 2 (DSA ® ) and SnO 2 anodes comparing their efficiencies. The effect of some parameters, such as current density, initial pH (pH 0 ), nature, concentration of electrolyte and temperature at the electrochemical oxidation was investigated evaluating the decolorization and the chemical oxygen demand (COD) removal at optimal conditions. Complete decolorization of RhB was achieved in the presence of chloride ions at different times using both electrodes. An optimum efficiency was obtained at pH 6.5, T = 25°C. Also, the current density of 40 mA cm −2 using the DSA electrode in NaCl 0.05 mol L −1 + Na 2 SO 4 0.1 mol L −1 mixture solution as a supporting electrolyte, 100% color removal and 61.7% chemical oxygen demand removal after 90 min of electrolysis were achieved. DSA showed better performance than SnO 2 in wide operating conditions and was proved to be more cost-effective and more efficient. The effectiveness of the degradation is explained by indirect electrochemical oxidation, where in the presence of chlorides electrolyte leads to the electro-generation of strong oxidant species, such as Cl 2 and ClO − ions, improving the efficiency of treatment at both electrodes.The DSA has been classified as 'active' or 'non-active' depending on

Decolorization and Degradation of a Mixture of Industrial Azo Dyes by Anodic Oxidation Using a Ti/Ru0.3Ti0.7O2 (DSA‐Cl2) Electrode.

“…As previously commented, a higher degradation of azo dye was observed with respect to the performance in basic medium, because in acidic solutions Cl – is oxidized to Cl 2 , which is the dominant oxidizing agent. In a basic medium, the efficiency of degradation is slightly lower, as in the mineralization of the azo AB29 dye, due to the decrease in the production of Cl 2 /HClO …”

“…Operating conditions such as electrolyte composition, supporting electrolyte, reactor design and electrode material are main factors to be considered for the efficiency of the electrochemical oxidation process . As mentioned above, the anode material strongly influences both the selectivity and the efficiency of AO.…”

“…The most common DSA‐type anode in wastewater treatment is Ti/Ru 0.3 Ti 0.7 O 2 (DSA‐Cl 2 ) due to its high catalytic activity, high stability to anodic corrosion and mechanical steadiness, as well as high electrocatalytic activity for chlorine evolution as a consequence of the surface redox reactions taking place at transition metal ions that act as active sites for the absorption of chlorine atoms . Several studies have addressed the effects of dye concentration, pH, supporting electrolyte, electrode material and current density on dye removal efficiency,− but limited works analyze intermediates, by‐products and dye degradation mechanisms …”

Removal of the Rhodamine B Dye at Ti/Ru0.3Ti0.7O2 Anode Using Flow Cell System

“…Consequently, most studies have reported that an increase of the mass transport coefficient has an adverse effect on the degradation of the organic pollutants mediated by electrogenerated active chlorine [33,[56][57][58]. However, the formation of hydroxyl radicals (OH • ) depends only on the density of electrical current used.…”

“…e application of a DSA electrode to remove organic pollutants was typically accomplished with the presence of NaCl as supporting electrolyte due to its high electrocatalytic activity for chlorine evolution, and it can be used efficiently for organic degradation by indirect electrolysis by in situ generations of active chlorine through the oxidation of chloride ions that are present in the solution [31][32][33][34]. e Ti/Ru 0.3 Ti 0.7 O 2 composition is one of the most common DSA materials, and it has been widely used in the chloroalkali industry for the last 30 years [35,36].…”