Enric Brillas

University of Barcelona, Barcino, Catalonia, Spain

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Publications (293)1038.08 Total impact

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    ABSTRACT: A novel carbon felt cathode coated with iron oxides has been prepared by Fe3 + electrodeposition. The deposited iron content was analyzed by X-ray fluorescence, the composition of iron oxides formed by X-ray diffraction and the morphology of deposits by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Freshly prepared electrodes were used as air-diffusion cathodes in a stirred tank reactor with a boron-doped diamond (BDD) anode to degrade solutions of Malachite Green dye at pH 3.0 by heterogeneous electro-Fenton (EF) and photoelectro-Fenton (PEF) processes. Oxidizing agents were hydroxyl radicals formed at the BDD surface from water oxidation and at the cathode surface or in the bulk from Fenton's reaction between deposited or leached Fe2 + and electrogenerated H2O2 in both treatments, along with the photo-oxidation by UVA light in heterogeneous PEF. The decolorization and mineralization of dye solutions were faster for the latter process due to the photolysis of Fe(III) complexes with initial oxalate and generated carboxylic acids. TOC decay always obeyed a pseudo-first-order kinetics. The increase in dye concentration decelerated the decolorization efficiency and mineralization rate, but enhanced the mineralization current efficiency. A test of 10 consecutive cycles of heterogeneous EF treatment of 50 mg L− 1 of Malachite Green at 21.7 mA cm− 2 showed a gradual loss of iron oxides from the cathode with decreasing dye mineralization rate. An improvement of the stability of the novel cathode is then necessary for its reuse with a better keeping of the oxidation power of heterogeneous EF and PEF treatments of organic pollutants in waters.
    No preview · Article · Feb 2016
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    ABSTRACT: The degradation of 100 mL of 2.08 mM oxalic acid (OXL) and oxamic acid (OXM) solutions in 0.10 M Na2SO4 at pH 3.0 has been studied by solar photolysis (SP), electro-Fenton (EF) and solar photoelectro-Fenton (SPEF). EF and SPEF experiments were performed with a stirred electrochemical cell containing a 3 cm2 boron-doped diamond (BDD) anode and a 3 cm2 air-diffusion cathode that generates H2O2. Natural sunlight was directly exposed to the solution in SP and SPEF. Catalytic contents of 0.50 mM Fe3+, 0.50 mM Cu2+ or mixtures up to 0.50 mM of both metallic ions were added to the solution and a current density of 33.3 mA cm−2 was applied in EF and SPEF. OXM presented a remarkable slower decay than OXL by SP due to the lower photoactivity of metallic-oxamate complexes. OXL concentration decayed 90% in the presence of Fe3+ and Fe3+/Cu2+ mixtures, whereas the OXM drop decreased directly with increasing Cu2+ concentration. In EF, OXL was more slowly removed than OXM due to higher recalcitrant character of the Fe(III)-oxalate complexes which can only be mineralized by OH formed at the anode surface but not by those generated from Fenton’s reaction in the bulk. Upon Cu2+ addition, higher removal percentages were found because Cu(II)-carboxylate complexes are attacked by OH, thus accelerating the mineralization. In contrast, OXL destruction was largely enhanced in SPEF using the mixture of catalysts as a result of the photolysis of Fe(III)-oxalate complexes and the parallel mineralization of Cu(II)-carboxylate complexes by the high quantity of oxidant OH induced from photolysis of Fe(III)-aquo species. In all cases, the decay of OXL and OXM concentration obeyed a pseudo-first-order reaction, with an apparent rate constant dependent on the applied current in EF and SPEF.
    No preview · Article · Feb 2016
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    ABSTRACT: The performance of three electrochemical advanced oxidation processes, namely electro-oxidation with electrogenerated H2O2 (EO–H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF) for the treatment of aqueous solutions of the food azo dye Ponceau 4R in an undivided cell with a BDD anode and an air-diffusion cathode was compared in terms of colour, dye concentration and total organic carbon (TOC) removals. PEF treatments in ultrapure water with Na2SO4 were performed to assess the effect of current density, as well as supporting electrolyte and dye concentrations. At 100 mA cm−2, solutions of 130 mL of 254 mg L−1 of the dye in 0.05 M Na2SO4 became colourless and totally mineralized after 50 and 240 min, respectively, which can be explained by the synergistic action of BDD(OH) at the anode surface and homogeneous OH formed in the bulk from Fenton’s reaction promoted in the presence of Fe2+ catalyst. Furthermore, UVA photons induced the continuous Fe2+ regeneration and photolytic decomposition of refractory intermediate complexes. In that aqueous matrix, the cleavage of the dye molecules proceeded through several reaction routes to yield N-containing and non-N-containing derivatives with one or two aromatic rings, short-chain aliphatic carboxylic acids and inorganic ions. Oxalic and oxamic acids and sulfate ions were accumulated at different rates in EO–H2O2, EF and PEF. The three methods allowed the progressive decontamination of Ponceau 4R solutions in a real water matrix even without the addition of electrolyte, although complete TOC abatement after 360 min at 33.3 mA cm−2 was only ensured by the iron-catalyzed PEF process.
    Full-text · Article · Jan 2016 · Applied Catalysis B Environmental
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    ABSTRACT: Coupled electrochemical advanced oxidation processes like electro-Fenton (EF) and photoelectro-Fenton (PEF) were evaluated for the treatment of an aqueous solution containing 100 mg L–1 total organic carbon of the low biodegradable azo dye Orange-G (Acid Orange 10) using a boron-doped diamond (BDD)/air-diffusion cell. It was confirmed the existence of synergic effects between UVA light photo-oxidation and/or hydroxyl radicals (•OH) formed from water oxidation at the BDD anode and the Fenton reaction between added Fe2+ and H2O2 produced at the air-diffusion cathode. A rapid discoloration of the solution was always obtained, mainly attributed to the oxidation of the azo dye with •OH generated from Fenton’s reaction in EF and PEF. The color loss followed a pseudo-first-order kinetics, controlled by the applied current. The dye mineralization was enhanced with increasing current due to the greater production of •OH and finally, short-linear carboxylic acids like oxalic and oxamic were pre-eminently accumulated. The Fe(III) complexes of these acids were slowly removed by •OH in EF and rapidly photodecomposed by UVA light in PEF up to 98% mineralization. Sulfate and nitrate ions were accumulated in the medium during both EF and PEF treatments. The more powerful coupled PEF process is then able to efficiently degrade streams contaminated with Orange G.
    No preview · Article · Jan 2016 · Separation and Purification Technology
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    ABSTRACT: Acidic solutions of trans-cinnamic acid at pH 3.0 have been comparatively treated by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), and photoelectro-Fenton (PEF). The electrolytic experiments were carried out with a boron-doped diamond (BDD)/air-diffusion cell. The substrate was very slowly abated by AO-H2O2 because of its low reaction rate with oxidizing (•)OH produced from water discharge at the BDD anode. In contrast, its removal was very rapid and at similar rate by EF and PEF due to the additional oxidation by (•)OH in the bulk, formed from Fenton's reaction between cathodically generated H2O2 and added Fe(2+). The AO-H2O2 treatment yielded the lowest mineralization. The EF process led to persistent final products like Fe(III) complexes, which were quickly photolyzed upon UVA irradiation in PEF to give an almost total mineralization with 98 % total organic carbon removal. The effect of current density and substrate concentration on all the mineralization processes was examined. Gas chromatography-mass spectrometry (GC-MS) analysis of electrolyzed solutions allowed identifying five primary aromatics and one heteroaromatic molecule, whereas final carboxylic acids like fumaric, acetic, and oxalic were quantified by ion exclusion high-performance liquid chromatography (HPLC). From all the products detected, a degradation route for trans-cinnamic acid is proposed.
    No preview · Article · Jan 2016 · Environmental Science and Pollution Research
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    ABSTRACT: Solutions of pH 3.0 containing trans-ferulic acid, a phenolic compound in olive oil mill wastewater, have been comparatively degraded by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). Trials were performed with a BDD/air-diffusion cell, where oxidizing OH was produced from water discharge at the BDD anode and/or in the solution bulk from Fenton's reaction between cathodically generated H2O2 and added catalytic Fe(2+). The substrate was very slowly removed by AO-H2O2, whereas it was very rapidly abated by EF and PEF, at similar rate in both cases, due to its fast reaction with OH in the bulk. The AO-H2O2 process yielded a slightly lower mineralization than EF, which promoted the accumulation of barely oxidizable products like Fe(III) complexes. In contrast, the fast photolysis of these latter species under irradiation with UVA light in PEF led to an almost total mineralization with 98% total organic carbon decay. The effect of current density and substrate concentration on the performance of all treatments was examined. Several solar PEF (SPEF) trials showed its viability for the treatment of wastewater containing trans-ferulic acid at larger scale. Four primary aromatic products were identified by GC-MS analysis of electrolyzed solutions, and final carboxylic acids like fumaric, acetic and oxalic were detected by ion-exclusion HPLC. A reaction sequence for trans-ferulic acid mineralization involving all the detected products is finally proposed.
    No preview · Article · Dec 2015 · Journal of hazardous materials
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    ABSTRACT: The degradation of 100 cm3 of 177 mg dm-3 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-H2O2), 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 Fe2+ and H2O2 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-H2O2 due to the contribution of hydroxyl radicals in the bulk. PEF allowed the quickest color removal by the rapid Fe2+ 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-2, 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 NH4+ ion, along with small amounts of NO3- ion.
    Full-text · Article · Nov 2015 · Electrochimica Acta
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    Abdoulaye Thiam · Ignasi Sirés · Enric Brillas
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    ABSTRACT: The degradation of 130 mL of mixtures of food azo dyes E122, E124 and E129 has been studied by electro-Fenton (EF) and UVA photoelectro-Fenton (PEF) using a stirred tank reactor with either a boron-doped diamond (BDD) or Pt anode and an air-diffusion cathode. The main oxidant was hydroxyl radical formed at the anode from water oxidation and in the bulk from Fenton's reaction between added Fe(2+) and H2O2 generated at the cathode. In sulfate medium, fast decolorization was found for all systems, but the almost total mineralization was more rapidly achieved by PEF with BDD. The performance with a real water matrix was slightly worse, although the removal of total organic load was still as high as 95%. The solar PEF (i.e., SPEF) treatment of dye mixtures using a 2.5 L flow plant with a BDD/air-diffusion cell coupled to a planar solar photoreactor is also reported. Fast decolorization and almost total mineralization was found in the presence of either sulfate, perchlorate, nitrate or a mixture of sulfate + chloride ions. In chloride medium, however, the formation of recalcitrant chloroderivatives decelerated the degradation process. Greater current efficiency and lower specific energy consumption were attained in sulfate medium at lower current density and higher azo dye content. A plausible reaction sequence based on 18 aromatic intermediates identified by GC-MS and 6 short-linear carboxylic acids detected by ion-exclusion HPLC has been proposed. The SPEF process promoted the photodegradation of Fe(III)-oxalate complexes and other undetected products. Sulfate and nitrate ions were always released to the medium. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Full-text · Article · Sep 2015 · Water Research
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    ABSTRACT: The effect of various parameters on the performance of electrochemical advanced oxidation processes (EAOPs) like electro-Fenton (EF), photoelectro-Fenton (PEF) and solar PEF (SPEF) was assessed for the treatment of a sanitary landfill leachate previously subjected to biological and coagulation processes. The tested operational variables included: (i) anode material (boron-doped diamond (BDD) and Pt), (ii) initial total dissolved iron concentration (20-80mgL-1), (iii) pH (2.8-4.0), (iv) initial addition of 1:3 Fe(III)-to-oxalate molar ratio at various pH values (2.8-5.0), (v) temperature (15-40°C) and (vi) radiation source (UVA, UVA-Vis and UVC lamps and natural sunlight). The BDD anode showed high superiority over the Pt one for EF, PEF with UVA light (PEF-UVA) and SPEF processes, thereby advising an important role of the physisorbed hydroxyl radicals (OH) at the anode surface on landfill leachate oxidation even under the potent solar radiation. An initial total dissolved iron content of 60mgL-1 was chosen as the best dose for the PEF-UVA process with the BDD anode (PEF-BDD-UVA). While PEF-BDD-UVA without external addition of oxalic acid yielded the best results at pH 2.8, the initial addition of 1:3 Fe(III)-to-oxalate molar ratio allowed operating at pH 3.5 with even higher efficiency and at pH 4.0 with only slightly lower efficiency. Effluent temperatures from 20 to 40°C led to similar mineralization rates for the PEF-BDD-UVA technique. The use of UVA and UVC lamps and natural sunlight as radiation sources in PEF-BDD and SPEF-BDD systems led to similar mineralization profiles as a function of time. The UVA-Vis lamp induced lower effluent mineralization mainly for longer reaction times.
    No preview · Article · Sep 2015 · Applied Catalysis B Environmental
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    ABSTRACT: Levofloxacin is a large spectrum antibiotic from fluoroquinolones family, widely used and detected in natural waters. Here, this drug was degraded by a novel heterogeneous electro-Fenton (EF) process, so-called EF-pyrite, in which pyrite powder in suspension regulates the solution pH to 3.0 and supplies 0.2mM Fe(2+) as catalyst to the solution. Trials were performed with a stirred boron-doped diamond (BDD)/carbon-felt cell under O2 bubbling for cathodic H2O2 generation. Hydroxyl radicals formed from water oxidation at the BDD anode and in the bulk from Fenton's reaction between Fe(2+) and H2O2 were the main oxidizing agents. The effect of applied current and antibiotic concentration over the mineralization rate and degree, mineralization current efficiency and specific energy consumption was studied. An almost total mineralization was achieved for a 0.23mM drug solution operating at 300mA for 8h. The kinetic decay of the drug was followed by reversed-phase HPLC and obeyed a pseudo-first-order reaction. Ion-exclusion HPLC analysis of treated solutions revealed that oxalic and oxamic acids, the most persistent final products, were the predominant pollutants remaining in solution at long electrolysis time. Ion chromatography analysis confirmed the release of F(-), NO3(-) and NH4(+) ions during levofloxacin mineralization. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Full-text · Article · Aug 2015 · Chemosphere
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    ABSTRACT: The degradation of the copper-phthalocyanine dye Reactive Blue 15 dye in sulfate medium has been comparatively studied by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). Experiments with 100cm3 solutions of 0.203mmoldm-3 dye were performed with a stirred tank reactor containing a boron-doped diamond (BDD) anode and an air-diffusion cathode for continuous H2O2 production. Experimental conditions of pH 3.0 and 0.50mmoldm-3 Fe2+ as catalyst were found optimal for the EF process by the predominant oxidation with hydroxyl radicals formed in the bulk from Fenton's reaction between added Fe2+ and generated H2O2. The kinetics of Reactive Blue 15 abatement was followed by reversed-phase HPLC and always obeyed a pseudo-first-order reaction. The decolorization rate in EO-H2O2 was much lower than dye decay due to the formation of large quantities of colored intermediates under the action of hydroxyl radicals generated at the BDD anode from water oxidation. In contrast, the color and dye removals were much more rapid in EF and PEF by the most efficient oxidation of hydroxyl radicals produced from Fenton's reaction. PEF was the most powerful treatment owing to the photolytic action of UVA irradiation, yielding 94% mineralization after 360min at 66.7mAcm-2. The effect of current density over the performance of all methods was examined. LC-MS analysis of treated solutions allowed the identification of 25 aromatic and heteroaromatic products and 30 hydroxylated derivatives. Tartaric, acetic, oxalic and oxamic acids were quantified by ion-exclusion HPLC. Acetic acid was the only product remaining after PEF and its large persistence explained the almost total mineralization achieved by this process. Chloride, sulfate, nitrate and in smaller proportion, ammonium ions were released to the solution in all cases. A plausible reaction sequence for Reactive Blue 15 mineralization has been finally proposed.
    No preview · Article · Aug 2015
  • Sergi Garcia-Segura · Enric Brillas

    No preview · Article · Aug 2015
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    ABSTRACT: The occurrence of food color additives in waters is becoming a hot topic due to their potential health effects, especially on children. The treatment of Ponceau 4R solutions by electro-oxidation (EO) with or without H2O2 production, electro-Fenton (EF) and photoelectro-Fenton (PEF) using small undivided and divided batch cells with either Pt or BDD as the anode has been thoroughly studied. The electrolyses were performed in different electrolytes like Na2SO4, NaCl, NaNO3 and LiClO4 in order to elucidate the changes in reactivity. Depending on the anode, cathode, process and electrolyte, the azo dye could be degraded due to the single or combined action of: (i) direct cathodic reduction and/or anodic oxidation, (ii) •OH-mediated oxidation at the anode vicinity or in the solution bulk, and (iii) active chlorine-mediated oxidation. The presence of Cl− led to the fastest decolorization, whereas it became detrimental for total organic carbon abatement. The oxidation of Cl− to active chlorine (Cl2 and HClO) and oxychlorine anions (ClO3− and ClO4−) by direct charge transfer or by M(•OH) and •OH was investigated. Color removal was much slower in SO42−, ClO4− and NO3− media, although the latter was particularly beneficial in PEF and/or using BDD. Regarding the mineralization, PEF outperformed the other technologies. Similar trends were observed in SO42− and ClO4− media, being slightly favored in NO3−. In contrast, Cl− medium tended to be detrimental due to the formation of refractory chloroderivatives, the destruction of M(•OH) to form less oxidizing (oxy) chloro radicals, oxychlorine anions and active chlorine, and the reaction between HClO and H2O2. Experiments in divided cells demonstrated the very small contribution of cathodic reduction of the dye and its by-products. Linear sweep voltammetry revealed the direct oxidation of both, Ponceau 4R and Cl− on the anode surface.
    Full-text · Article · Aug 2015 · Electrochimica Acta
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    ABSTRACT: The degradation of 100 mL of 0.245 mM of the antibiotic ciprofloxacin in 0.05 M Na2SO4 at pH 3.0 has been studied by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF), UVA photoelectro-Fenton (PEF) and solar PEF (SPEF). Electrolyses were performed with a stirred tank reactor using either a boron-doped diamond (BDD) or Pt anode and an air-diffusion cathode. In EF, PEF and SPEF, ciprofloxacin was rapidly removed due to its oxidation with (•)OH formed from Fenton's reaction between added Fe(2+) and H2O2 generated at the cathode. The larger electrochemical incineration of the antibiotic was achieved by SPEF with BDD with 95% mineralization thanks to the additional attack by hydroxyl radicals formed from water oxidation at the BDD anode surface and the photolysis of final Fe(III)-oxalate and Fe(III)-oxamate species from sunlight. Up to 10 primary intermediates and 11 hydroxylated derivatives were identified by LC-MS, allowing the proposal of a reaction sequence for ciprofloxacin mineralization. A different behavior was found when the same antibiotic concentration was oxidized in a synthetic urine matrix with high urea content and a mixture of PO4(3-), SO4(2-) and Cl(-) ions. Since Fenton's reaction was inhibited in this medium, only EO and EO-H2O2 processes were useful for mineralization, being the organics mainly degraded by HClO formed from Cl(-) oxidation. The EO process with a BDD/stainless steel cell was found to be the most powerful treatment for the urine solution, yielding 96% ciprofloxacin removal and 98% mineralization after 360 min of electrolysis at optimum values of pH 3.0 and current density of 66.6 mA cm(-2). The evolution of released inorganic ions was followed by ion chromatography. Copyright © 2015 Elsevier Ltd. All rights reserved.
    No preview · Article · Jun 2015 · Water Research
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    ABSTRACT: The decolorization and mineralization of solutions containing 230mgL(-1) of the food azo dye Allura Red AC at pH 3.0 have been studied upon treatment by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). Experiments were performed with a stirred tank reactor containing a boron-doped diamond (BDD) or Pt anode and an air-diffusion cathode to generate H2O2. The main oxidants were hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between H2O2 and added Fe(2+). The oxidation ability increased in the sequence EO-H2O2<EF<PEF and faster degradation was always obtained using BDD. PEF process with BDD yielded almost total mineralization following similar trends in SO4(2-), ClO4(-) and NO3(-) media, whereas in Cl(-) medium, mineralization was inhibited by the formation of recalcitrant chloroderivatives. GC-MS analysis confirmed the cleavage of the NN bond with formation of two main aromatics in SO4(2-) medium and three chloroaromatics in Cl(-) solutions. The effective oxidation of final oxalic and oxamic acids by BDD along with the photolysis of Fe(III)-oxalate species by UVA light accounted for the superiority of PEF with BDD. NH4(+), NO3(-) and SO4(2-) ions were released during the mineralization. Copyright © 2015 Elsevier B.V. All rights reserved.
    Full-text · Article · Jun 2015 · Journal of Hazardous Materials
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    ABSTRACT: A solution with 0.245 mM of the diazo dye Evans Blue and 0.50 mM Fe2+ as catalyst of pH 3.0 was comparatively degraded by electrochemical processes based on Fenton’s reaction chemistry like electro-Fenton (EF), photoelectro-Fenton (PEF) with a 6 W UVA light and solar photoelectro-Fenton (SPEF). Electrolytic trials 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. Organics were destroyed by OH produced at the anode surface from water oxidation and in the bulk from Fenton’s reaction between added Fe2+ and H2O2 generated at the cathode. Evans Blue decay obeyed a pseudo-first-order kinetics and was much faster than solution decolorization due to the formation of colored aromatic products. The mineralization rate rose in the sequence EF < PEF < SPEF. Almost total mineralization was rapidly achieved in SPEF at current density ⩾66.7 mA cm−2 because of the potent UV radiation from sunlight. Up to 19 aromatic intermediates and 16 hydroxylated derivatives including diazo, monoazo, biphenylic, benzenic, naphthalenic and phthalic acid compounds were detected by LC–MS. The SPEF process was performed in a 10 L flow plant with a Pt/air-diffusion cell coupled to a CPC photoreactor in order to confirm its viability at industrial scale. 88% mineralization with 42% current efficiency and 2.13 kWh kg−1 DOC energy consumption were obtained after 300 min of treatment at 55.4 mA cm−2. Nine short-linear carboxylic acids were identified as final products, oxalic, formic and oxamic acids being the most persistent. The photodecarboxylation of Fe(III)–carboxylate complexes explained the good oxidation ability of PEF and SPEF. The initial S of the diazo dye was transformed into SO42− ion, whereas its initial N was mineralized to NO3− ion but largely lost as N-volatile products.
    No preview · Article · Jun 2015 · Journal of electroanalytical chemistry
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    ABSTRACT: 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 H2O2 (AO-H2O2), 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 Fe2+ and cathodically generated H2O2. The oxidation power of the EAOPs increased in the sequence AO- H2O2 < 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 Fe2+ 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 NO3− ion and in lesser extent to NH4+ ion, whereas its initial S was converted into SO42− ion.
    Full-text · Article · Jun 2015 · Applied Catalysis B Environmental
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    ABSTRACT: Here, 2.5 L of solutions of the pharmaceutical ranitidine (RNTD) at pH 3.0 have been comparatively degraded by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) processes using a pre-pilot flow plant with a Pt/air-diffusion cell. RNTD was oxidized by hydroxyl radicals coming from water oxidation at the Pt anode and Fenton’s reaction between added Fe2+ and H2O2 generated at the air-diffusion cathode. In SPEF, the cell was coupled to a flat solar photoreactor to irradiate the solution with sunlight. The potent combined action of hydroxyl radicals and photolysis by sunlight explains the higher oxidation ability of SPEF compared to EF, attaining 80% mineralization as maximal. The optimum Fe2+ content as catalyst was 0.50 mM. The effect of current density and drug concentration on the degradation rate of RNTD, mineralization current efficiency and energy consumption for EF and SPEF was examined. The RNTD decay always followed a pseudo-first-order kinetics, having a greater oxidation rate for SPEF by the additional generation of hydroxyl radicals induced by photolysis of Fe(III) species. Malic, pyruvic, acetic, oxalic, oxamic and formic acids were detected as final carboxylic acids. The three latter acids were the main components of the final treated solution in EF because their Fe(III) complexes were not destroyed by generated hydroxyl radicals. The quick photolysis of such Fe(III)-carboxylate species by sunlight explains the greater oxidation power of SPEF. The initial S atom of RNTD was released as sulfate ion, whereas its initial N atoms were converted into ammonium ion along with a smaller proportion of nitrate ion.
    No preview · Article · May 2015 · Separation and Purification Technology
  • Enric Brillas · Ignasi Sirés
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    ABSTRACT: Electrochemical technology has attracted increasing interest in recent years as an environment-friendly solution to many industrial problems and challenges. First, we give an overview on the fundamentals of electrochemical processes for the removal of pharmaceuticals from water, particularly electrochemical oxidation and Fenton-based processes, such as electro-Fenton, and ultraviolet (UV) and solar photoelectro-Fenton, that have improved performance. We also mention other less studied methods, although the main focus is on reactivity elucidation by chromatography with UV or conductivity detection, especially by mass spectrometry techniques (e.g., coupled to gas chromatography or liquid chromatography), in order to discuss the degradation pathways of pharmaceuticals on the basis of the reactive species electrogenerated in each technology. In some cases, simultaneous assessment of toxicity adds crucial information for the future integration of these technologies in water-treatment facilities where pharmaceuticals and their byproducts can occur.
    No preview · Article · May 2015 · TrAC Trends in Analytical Chemistry
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    Enric Brillas · Carlos A. Martínez-Huitle
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    ABSTRACT: As the environment preservation gradually becomes a matter of major social concern and more strict legislation is being imposed on effluent discharge, more effective processes are required to deal with non-readily biodegradable and toxic pollutants. Synthetic organic dyes in industrial effluents cannot be destroyed in conventional wastewater treatment and consequently, an urgent challenge is the development of new environmentally benign technologies able to mineralize completely these non-biodegradable compounds. This review aims to increase the knowledge on the electrochemical methods used at lab and pilot plant scale to decontaminate synthetic and real effluents containing dyes, considering the period from 2009 to 2013, as an update of our previous review up to 2008. Fundamentals and main applications of electrochemical advanced oxidation processes and the other electrochemical approaches are described. Typical methods such as electrocoagulation, electrochemical reduction, electrochemical oxidation and indirect electro-oxidation with active chlorine species are discussed. Recent advances on electrocatalysis related to the nature of anode material to generate strong heterogeneous OH as mediated oxidant of dyes in electrochemical oxidation are extensively examined. The fast destruction of dyestuffs mediated with electrogenerated active chlorine is analyzed. Electro-Fenton and photo-assisted electrochemical methods like photoelectrocatalysis and photoelectro-Fenton, which destroy dyes by heterogeneous OH and/or homogeneous OH produced in the solution bulk, are described. Current advantages of the exposition of effluents to sunlight in the emerging photo-assisted procedures of solar photoelectrocatalysis and solar photoelectro-Fenton are detailed. The characteristics of novel combined methods involving photocatalysis, adsorption, nanofiltration, microwaves and ultrasounds among others and the use of microbial fuel cells are finally discussed.
    Full-text · Article · May 2015 · Applied Catalysis B: Environmental