Electrochemical and Photochemical Oxidation of Cationic Dyes: A Comparative Study (original) (raw)
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Coloration Technology, 2004
The degradation of two commercial reactive dyes, CI Reactive Red 141 (homo‐bireactive) and CI Reactive Red 238 (hetero‐bireactive), using Fenton's reagent in the dark and under either artificial or solar irradiation, has been investigated. The main parameters that govern the complex reactive system, i.e. type of irradiation, temperature and initial concentrations of iron(II) and hydrogen peroxide, have been studied at pH 3. Temperature and the use of light have beneficial effects on the removal of colour, aromatic compounds, total organic carbon, acute toxicity, given as changes in EC50 values (against the marine photobacteria Vibrio fischeri) and changes in the biodegradability. The advanced oxidation processes used in this study have proven to be highly effective for the treatment of such types of reactive dyes and several advantages concerning the technique application arise from the study. The possibility of a combined advanced oxidation process‐biological treatment is propo...
Solar Energy, 2004
The degradation of different commercial reactive dyes: a monoreactive dye (Procion Red H-E7B), an hetero-bireactive dye (Red Cibacron FN-R) and a Standard Trichromatic System, by using solar light assisted Fenton and photo-Fenton reaction is investigated. The reaction efficiencies have been compared with the ones obtained for the same system in the dark or under the assistance of an artificial light source. The use of solar light is clearly beneficial for the removal of color, aromatic compounds (UV 254 ), total organic carbon (TOC), and the increase of the BOD 5 /COD ratio. The possibility of a combined advanced oxidation process (AOP)/biological treatment based on the use of sunlight is suggested.
2021
The current study was aimed at the decolorization and mineralization of six newly synthesized hetero-functional (vinyl sulfone and cyanuric chloride) azo reactive dyes (D-1 to D-6) using two advanced oxidation processes (Fenton and photo-Fenton). Results showed that both oxidation mechanisms effectively mineralized the synthesized hetero-functional azo reactive dyes. However, decolorization and mineralization of dyes through photo-Fenton oxidation were more effective than Fenton oxidation. The data revealed that process parameters (pH, Fe2+ dosage, concentration of H2O2, and reaction time) greatly affect the mineralization of the selected dyes. Decolorization efficiency (98%) and chemical oxygen demand (COD) removal (78%) was obtained for the six degraded azo reactive dyes under optimum conditions; pH (3), Fe2+ concentration (20 mg/L), H2O2 (500 mg/L), and contact time (80 min) using Fenton oxidation. On the other hand, 99% decolorization and 82% COD removal was achieved for the pho...
Applied Catalysis B: Environmental, 2015
The degradation of solutions with 0.260 mM of the diazo dye Congo Red at pH 3.0 has been studied by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation with electrogenerated H 2 O 2 (AO-H 2 O 2 ), electro-Fenton (EF) and photoelectro-Fenton (PEF) with a 6 W UVA light. Experiments were made in a 100 mL stirred tank reactor with a boron-doped diamond (BDD) anode and an air-diffusion cathode at constant current density (j). In these systems, organics were mainly destroyed by • OH formed at the anode surface from water oxidation and/or in the bulk from Fenton's reaction between added Fe 2+ and cathodically generated H 2 O 2 . The oxidation power of the EAOPs increased in the sequence AO-H 2 O 2 < EF < PEF. Almost total mineralization was attained after 360 min of PEF at j ≥ 66.7 mA cm −2 due to the parallel photolytic action of UVA light. In all the EAOPs, increasing j enhanced the degradation process, but with a loss of mineralization current efficiency and higher energy consumption. Congo Red decay always obeyed a pseudo-first-order kinetics. The study of the Congo Red degradation in a 2.5 L solar flow plant with a Pt/air-diffusion cell confirmed the viability of the solar PEF (SPEF) treatment at industrial scale. Optimum conditions were found for 0.260 mM of Congo Red with 0.50 mM Fe 2+ at 100 mA cm −2 , yielding almost total mineralization in 240 min with about 49% current efficiency and 0.45 kWh (g DOC) −1 energy consumption. LC-MS analysis of treated solutions allowed the identification of 21 aromatic intermediates and 13 hydroxylated derivatives, including diazo, monoazo, biphenyl, benzene, naphthalene and phthalic acid compounds. Tartatic, tartronic, acetic, oxalic and oxamic acids were detected as final carboxylic acids in all the EAOPs. The fast photodecarboxylation of the Fe(III)-carboxylate complexes explained the higher oxidation ability of the photo-assisted methods of PEF and SPEF. The initial N of the dye was mainly lost as N-volatile products and mineralized to NO 3 − ion and in lesser extent to NH 4 + ion, whereas its initial S was converted into SO 4 2− ion. (C.A. Martínez-Huitle), brillas@ub.edu (E. Brillas). generated in situ at the anode surface at high current and/or in the bulk from Fenton's reaction chemistry. • OH is the second strongest oxidant known, after fluorine, and its high standard redox potential (E • = 2.80 V/SHE) allows complete combustion of most organics to CO 2 , inorganic ions and water .
Journal of Electroanalytical Chemistry, 2012
The degradation of 100 ml of a 200 mg l À1 Direct Yellow 4 (DY4) solution in 0.05 M Na 2 SO 4 with 0.5 mM Fe 2+ of pH 3.0 has been comparatively studied by electro-Fenton (EF), photoelectro-Fenton (PEF) with UVA light and a novel photo-assisted EF (PA-EF). The latter method consists of the application of EF for a given time, followed by UVA illumination alone. Electrolytic experiments were made with a boron-doped diamond (BDD) anode and an air-diffusion cathode generating H 2 O 2 at constant current density. In this system, oxidant Å OH was produced at the BDD surface from water oxidation and in the bulk from Fenton's reaction. The DY4 solution was rapidly decolorized in EF and PEF due to the action of Å OH. The PEF process yielded an almost total mineralization of DY4, being more powerful than EF that only allowed partial mineralization. The proposed PA-EF was as potent as PEF if the initial electrolysis was prolonged until the production of intermediates that can be mineralized by UVA light. At 33.3 mA cm À2 , the best PA-EF was found by stopping the electrolysis and starting UVA irradiation at 120 min. The PA-EF process was always more economic than PEF and even less expensive than EF at high current density. Oxalic and oxamic acids were detected as ultimate by-products by ion-exclusion HPLC. The Fe(III) complexes of both acids were slowly mineralized with Å OH in EF, but rapidly photolyzed by UVA light in PEF and PA-EF. In these processes, the photolysis of N-intermediates produced oxamic acid. NH þ 4 ion was released in much larger proportion than NO À 3 ion, but the major part of the initial N was lost as volatile N-compounds. The photolytic removal of Fe(III)-oxalate complexes and N-intermediates accounts for the high effectiveness of the PEF and PA-EF processes.
Journal of Photochemistry and Photobiology A: Chemistry, 2003
This paper evaluates the degradation of two azo reactive dyes, C.I. Reactive Yellow 84 (RY84) and C.I. Reactive Red 120 (RR120) by photo-Fenton and Fenton-like oxidation. All experiments were performed on a laboratory scale set-up. The effects of different reaction parameters such as initial pH, contact time, effect of light and hydrogen peroxide concentrations on the oxidation of the dye aqueous solutions have been assessed. Effective system conditions were found to be pH of 3, hydrogen peroxide-to-iron molar ratio of 20:1 and UV or solar irradiation. The color removal efficiency at the optimum conditions during different Fenton-like processes was also evaluated. The results show that the color removal of RY84 after 15 min reaction time follows the decreasing order: solar/Fe(II)/H 2 O 2 > UV/Fe(II)/H 2 O 2 > UV/Cu(II)/Fe(III)/H 2 O 2 > UV/Fe(III)oxalate/H 2 O 2 > UV/Fe(III)/H 2 O 2 > dark/Fe(II)/H 2 O 2 > solar/Fe(III)oxalat/H 2 O 2 > UV/H 2 O 2 > UV/Fe(II) = UV. During the same reaction period the relative order for RR120 removal rate was slightly different: solar/Fe(II)/H 2 O 2 > UV/Fe(II)/H 2 O 2 > UV/Fe(III)/H 2 O 2 = UV/Cu(II)/Fe(III)/H 2 O 2 > UV/Fe(III)oxalate/H 2 O 2 = UV/H 2 O 2 > UV.
Electro-Fenton process is a potentially useful oxidation process for destroying toxic organic compounds in aqueous medium. In this study, the electro-Fenton degradation of a solution mixture of Malachite Green (MG) and Orange II catalyzed by ferric ions was examined. Results showed that this system could degrade and mineralize the dye mixture. It was shown that absorbance decrease in MG was accelerated in the presence of Orange II, whereas absorbance decrease of Orange II at the same conditions was depressed. This behavior was attributed to generation of hydroquinone-like intermediates from degradation of Orange II that can accelerate Fenton reaction by reduction of Fe 3+ to Fe 2+ ions. GC-MS detection of the products formed in the Orange II electro-Fenton degradation showed the generation of dihydroxynaphthalene compounds that are probably responsible for acceleration of MG degradation.
Electrochimica Acta, 2015
The degradation of 100 cm 3 of 177 mg dm À3 of the triphenylmethane dye Malachite Green oxalate at pH 3.0 was studied by anodic oxidation with stainless steel cathode (AO-SS), AO with air-diffusion cathode (AO-H 2 O 2), electro-Fenton (EF) and photoelectro-Fenton (PEF) with UVA light. The main oxidizing species were hydroxyl radicals formed from either water oxidation at the anode surface or in the bulk between added Fe 2+ and H 2 O 2 generated at the air-diffusion cathode. The use of a Pt anode led to slower decolorization and mineralization than BDD in all treatments because of the higher oxidation power of the latter. The decolorization was much faster for EF and PEF compared to AO-SS and AO-H 2 O 2 due to the contribution of hydroxyl radicals in the bulk. PEF allowed the quickest color removal by the rapid Fe 2+ regeneration from the photolysis of Fe(III) complexes with oxalate. The most powerful process was PEF with BDD, which yielded total decolorization in 6 min and 97% mineralization at 240 min operating at 100 mA cm À2 , thanks to hydroxyl radicals formed at the anode surface and in the bulk along with the photolytic action of UVA radiation. The evolution of final carboxylic acids like maleic, fumaric, succinic, acetic, oxalic, formic and oxamic was followed by ion-exclusion HPLC. All these acids and their Fe(III) complexes were removed more slowly with Pt anode. The initial N atoms of the dye were pre-eminently accumulated as NH 4 + ion, along with small amounts of NO 3 À ion.
A Photo-Fentontreatment of a Mixture of Three Cationic Dyes
Application of photo-Fenton process, UV/Fe 3+ /H 2 O 2 , to treatment for a mixture of three cationic dyes was investigated. The effect of the oxidative agent's initial concentration was investigated as well as the effect of the initial concentration of Fe +3 and H2O2 on the dyes degradation was studied. The best results were obtained using 0.6 mM of Fe 3+ and 12 mM hydrogen peroxide. Under these experimental conditions, 90% of TOC and 100% of color removal were achieved.
Journal of Electroanalytical Chemistry, 2019
Brazil is the fifth biggest global manufacturer of textiles and the fourth in cotton textile exports. Textile effluents contain organic dyes that are highly recalcitrant and difficult to oxidize by conventional physico-chemical and biological treatments. Mid-sized textile factories require reliable water treatment technologies of small physical footprint that do no produce solid wastes to treat their manufacturing effluents. Electrochemically-driven technologies emerge as feasible alternative technologies that overcome barriers in the management of these industrial effluents. This work studies the application of electrochemical advanced oxidation processes on the treatment of dye bath effluents containing cotton dye Reactive Blue 4. Electro-Fenton treatment attains complete color removal with an electrical energy per order (E EO) of 7.4 kWh m-3 order-1 , which represents an order of magnitude lower operational expenditure than electrochemical oxidation (54.8 kWh m-3 order-1). Simultaneous irradiation with UVA light in photoelectron-Fenton systems did not show any effect on RB4 degradation kinetics. But UVA irradiation increased the mineralization achieved after treatment, which enhanced current efficiencies ca. 2-fold respect to electro-Fenton.