Electrochemical degradation of RB-5 dye by anodic oxidation, electro-Fenton and by combining anodic oxidation–electro-Fenton in a filter-press flow cell

Abstract

Keywords:Boron-doped diamond Electrochemical oxidation Electro-Fenton process Filter-press flow cell Reactive Black 5 dye Reticulated vitreous carbon This paper reports the removal of a recalcitrant and toxic dye, Reactive Black 5 (RB-5) by three methods; 1) anodic oxidation (AO) on Boron-Doped Diamond (BDD), 2) by electro-Fenton (EF) process where hydrogen peroxide was produced by oxygen reduction on reticulated vitreous carbon (RVC) electrodes and 3) by the combination of AO-EF. The BDD and RVC electrodes were fitted in a filter-press flow cell in recycle batch mode of operation. The experimental set-up for the AO and EF processes consisted of two electrolyte compartments separated by a Nafion membrane with the dye contained in the anolyte and the catholyte, respectively. The combined AO-EF process used only one electrolyte compartment. The colour and total organic carbon (TOC) removal were more efficient when the AO and EF processes were used separately than the combined process, AO-EF. The influence of current density and initial concentration of ferrous ions were examined. The lowest energy efficiency (208 kWh kg −1 ) with the EF process was found when −0.4 V vs. Ag/AgCl was applied to a RVC electrode and the concentration of Fe 2+ was 1.0 × 10 −4 mol dm −3 achieving total colour and 74% of TOC removals in less than 90 min electrolysis. All proposed processes were able to promote high percentages of TOC removal following a pseudo-first order kinetic oxidation. The BDD electrode was the most effective material to remove RB-5 dye within 7.5 min and presented the highest apparent rate constant (0.835 min −1 ) with 82% TOC removal within 30 min at an energy consumption of 291 kWh kg −1 and 41.1 mA cm −2 current density. In the case of the combined process AO-EF the electrodegradation rate of RB-5 was at least three times lower, apparent rate constant (0.269 min −1 ), and 32% of TOC was removed with a high EC (682 kWh kg −1 ). Therefore oxidation process applied separately was more efficient.

The continued development of reticulated vitreous carbon as a versatile electrode material: Structure, properties and applications

“…A recent paper has reported the oxidation of Reactive Black 5 via an electro-Fenton process in a divided flow cell employing RVC electrodes and comparing this method to direct oxidation on boron-doped diamond electrodes [78]. The concentration of Fe 2+ has a direct relationship to the removal rate of the dye in Figure 16, reaching total colour removal in under 90 min.…”

“…A wide variety of contaminants, electrolytes and reactions is evident in Table 3, ranging from deposition of single metals from uncomplexed media [19,69], anionic complexes [35] or reduction of toxic metal ions [72,73], deposition of one metal from a mixture [35] and the effect of the electrolyte medium [74]. In the case of organic contaminants, such as model or actual dyes, oxidation can be achieved by direct anodic treatment, in-situ peroxide generation [75], an oxygen transfer anode [76] or an electro-Fenton [77,78] process.…”

Fe(II)-Based GDE Electrodes for the Demineralization of Methylene Blue Dye

“…Currently, hydrogen peroxide can be produced by using many synthesis techniques including electro-Fenton [5], photo electro-Fenton [6], and solar electro-Fenton [7]. These technologies produce hydrogen peroxide in situ and thus negate the hazards and costs of handling and transporting bulk hydrogen peroxide.…”

Electrochemical Degradation of Reactive Blue 19 Dye by Combining Boron‐Doped Diamond and Reticulated Vitreous Carbon Electrodes

“…In previous study we quantified the amount of H 2 O 2 generation from the reduction of dissolved oxygen which was constantly bubbled in the electrolyte. [26] The degradations efficiency was evaluated using a UV-VIS spectrophotometer from Scinco (NEOSYS-2000) in the range of 200 to 800 nm, begin the area in the visible (400-700 nm) part of spectra used to calculate colour removal promoted through equation (12). The concentration of RB-19 was monitored during the electrochemical degradation assays using the calibration curve at 593 nm.…”