Electrochemical discolouration and degradation of reactive dichlorotriazine dyes: reaction pathways

Abstract

Results of electrochemical oxidation of two reactive dichlorotriazine dyes: Reactive Red 2 and Reactive Blue 81, are presented in this paper. Two electrode materials: Ti/TiO 2 (70%)-RuO 2 (30%) and carbon felt, were applied in the investigations as anodes. Voltammetric measurements show that Reactive Blue 81 electrooxidation proceeds easier and with higher rate than electrooxidation of Reactive Red 2. Both dyes are oxidised irreversibly in at least one electrode step before oxygen evolution starts at the electrode. Effectiveness of electrochemical oxidation under potentiostatic conditions achieved for Reactive Blue 81 was higher than for Reactive Red 2, with application of a carbon felt anode. Pulse radiolysis measurements prove addition of • OH radical to the dye molecule and formation of cyclohexadienyl and naphthoxyl radicals. Results of voltammetric analysis, pulse radiolysis measurements and GC-MS identification of intermediate products suggest two possible pathways of the dyes electrochemical oxidation.

Comparative electrochemical oxidation of methyl orange azo dye using Ti/Ir-Pb, Ti/Ir-Sn, Ti/Ru-Pb, Ti/Pt-Pd and Ti/RuO 2 anodes

“…The effectiveness of AO with dimensionally stable anodes to decolorize and partially mineralize dye solutions in the presence of sulfate or chloride ions has been well proven [5]. Active MO such as Ti/RuO2 [3], Ti/IrO2 [23,24] and Ti/Pt [25], non-active MO like Ti/ PbO2 [9,26] and active mixed MO (MMO) such as Ti/Ru-Ti [25,27], Ti/Ir-Ru [28], Ti/Sn-Sb-Pt [29] and C/Pt-Bi [30] have been utilized. Faster decolorization was found in chloride compared to sulfate medium due to the Cl− oxidation to active chlorine (Cl2/HClO/ ClO−), which attacks the organics much more rapidly than MOx( OH) formed from reaction (1) [5,7,8].…”

Real-time in situ monitoring using visible spectrophotometry as a tool for probing electrochemical advanced oxidation processes for dye decolorisation

“…It is rare for researchers to assess the degradation of more than one dye, and when multiple dyes are studied, their structures are typically too dissimilar to be able to draw any meaningful comparisons. 7,16,17,[19][20][21][22][23][24][25][26] To address this, we have employed our continuous-monitoring apparatus to study the AO and EAP decolorisation of nine electronically-diverse dyes from the common azo, triarylmethane, and xanthene structural families, and we present our results here. We have probed the impact of dye structure and oxidant identity on the rate of decolorisation.…”

Electrochemical treatment of trypan blue synthetic wastewater and its degradation pathway

“…HOCl, ClOare generated in presence of chloride electrolyte and these species can oxidize the organics into simple biodegradable molecules [5,6]. The electrochemical degradation of methyl violet 2B, acridine, eosin yellow [7], alphazurine dye [8], reactive blue 81, reactive red 2 [9], reactive blue-4, reactive orange-16 [10], reactive red 120 [11], reactive brilliant red K-2BP [12], methyl green [13], methyl red [14] and other dyes has been successfully achieved in presence of suitable electrolyte and operating conditions. Furthermore, the results from these works infer that the extent of degradation of an organic pollutant not only depends on the operating conditions employed, but also on the structural, chemical and electrochemical properties of the pollutant itself [7].…”