Evidence of Fenton-like reaction with active chlorine during the electrocatalytic oxidation of Acid Yellow 36 azo dye with Ir-Sn-Sb oxide anode in the presence of iron ion

Abstract

The degradation of 2.5 L of Acid Yellow 36 solutions at pH 3.0 by electro-oxidation (EO) has been studied in a flow plant with a reactor containing an Ir-Sn-Sb oxide anode and a stainless steel cathode. The anode was prepared onto Ti by the Pechini method and characterized by SEM-EDX and XRD. It showed a certain ability to electrocatalyze both, the generation of adsorbed OH from water oxidation in sulfate medium and, more largely, the production of active chlorine in a mixed electrolyte containing Cl − ion. The EO treatment of the dye solution in the latter medium led to a rapid decolorization because active chorine destroyed the colored by-products formed, but color removal was much slower in pure NaClO 4 or Na 2 SO 4 due to the limited formation of OH. In contrast, greater mineralization was obtained in both pure electrolytes since the by-products formed in the presence of Cl − became largely persistent. The effect of liquid flow rate, current density and dye content on the EO performance in the mixed electrolyte was examined. The drop of absorbance and dye concentration obeyed a pseudo-first-order kinetics. Interestingly, the decolorization rate, dye concentration decay and TOC removal were enhanced upon catalysis with 1.0 mM Fe 2+. Such better performance can be accounted for by the formation of OH in the bulk from the electro-Fenton-like reaction between electrogenerated HClO and added Fe 2+. Even larger mineralization was achieved by the photoelectro-Fenton-like process upon irradiation of the solution with UVA light due to photolysis of some refractory intermediates. Maleic and acetic acids were detected as final short-chain linear carboxylic acids. The loss of Cl − and the formation of ClO 3 − , ClO 4 − , SO 4 2− , NO 3 − and NH 4 + were evaluated as well.

On the performance of HOCl/Fe2+, HOCl/Fe2+/UVA, and HOCl/UVC processes using in situ electrogenerated active chlorine to mineralize the herbicide picloram

“…Further improvements in the conversion to CO 2 might be expected if a powerful UVA light had been used, such as the sunlight; however, due to experimental limitations concerning the assembled system, this was not feasible. Similar results concerning the increasing removal levels during oxidation of the acid yellow 36 azo dye for the Fenton type and photo-Fenton type processes (using a Ir-Sn-Sb oxide anode for the in situ electrogeneration of active chlorine species) were obtained by Aguilar et al [22].…”

“…On the other hand, mass transfer limitation and the choice of adequate electrode materials limit the application of the electrochemical technology, resulting in excessive energy expenses and limited space-time yields [18]. In order to try to overcome these limitations, considering the solution pH, mass transfer limitation and anode material, Fenton type based reactions (particularly the reaction between HOCl and Fe 2+ ions) have been proposed [19] and seems to be an alternative process [20,21] to treat solutions contaminated with organic compounds, as also recently shown by Brillas and coworkers [22]. A Fenton type reaction is based on the homolysis reaction of the HOCl species (electrochemically produced using mixed oxide anodes or added as a chemical reagent) by Fe 2+ ions (or other Fe 2+ complex ion [23]) to produced HO% and Cl% species.…”

“…A Fenton type reaction is based on the homolysis reaction of the HOCl species (electrochemically produced using mixed oxide anodes or added as a chemical reagent) by Fe 2+ ions (or other Fe 2+ complex ion [23]) to produced HO% and Cl% species. The process performance can be increased if a suitable combination of the electrochemical and photochemical (using a UVA light to eliminate Fe complexes with carboxylic acids [24]) methods are carried out [22].…”

Antituberculosis drug isoniazid degraded by electro-Fenton and photoelectro-Fenton processes using a boron-doped diamond anode and a carbon-PTFE air-diffusion cathode

“…The most important operation parameter in the EF process is the applied j, since it limits the quantity of oxidant • OH originated under Fenton's conditions and at the BDD surface (Sirés et al 2014;Aguilar et al 2017). The increase of this parameter promotes the formation of more H2O2 at the cathode from reaction (3), which gives rise to greater quantity of • OH from Fenton's reaction (1), as well as BDD( • OH) by accelerating reaction (6).…”

“…The performance of the EF process can be improved with the use of UVA radiation (315-400 nm), which is typical in photoelectro-Fenton (PEF) since it promotes: (i) the photoreduction reaction (4) from Fe(III) species formed by Fenton's reaction (1), and (ii) the photodecomposition of Fe(III)-carboxylate complexes from reaction (5) (Brillas et al 2009;Aguilar et al 2017;Moreira et al 2017).…”