Degradation of the fluoroquinolone enrofloxacin by electrochemical advanced oxidation processes based on hydrogen peroxide electrogeneration

Solutions of the veterinary fluoroquinolone antibiotic enrofloxacin in 0.05 M Na₂SO₄ of pH 3.0 have been comparatively degraded by electrochemical advanced oxidation processes such as anodic oxidation with electrogenerated H₂O₂ (AO-H₂O₂), electro-Fenton (EF), photoelectro-Fenton (PEF) and solar photoelectro-Fenton (SPEF) at constant current density. The study has been performed using an undivided stirred tank reactor of 100 ml and a batch recirculation flow plant of 2.5 l with an undivided filter-press cell coupled to a solar photoreactor, both equipped with a Pt or boron-doped diamond (BDD) anode and a carbon-polytetrafluoroethylene gas diffusion cathode to generate H₂O₂ from O₂ reduction. In EF, PEF and SPEF, hydroxyl radical (OH) is formed from Fenton's reaction between added catalytic Fe²⁺ and generated H₂O₂. Almost total decontamination of enrofloxacin solutions is achieved in the stirred tank reactor by SPEF with BDD. The use of the batch recirculation flow plant showed that this process is the most efficient and can be viable for industrial application, becoming more economic and yielding higher mineralization degree with raising antibiotic content. This is feasible because organics are quickly oxidized with OH formed from Fenton's reaction and at BDD from water oxidation, combined with the fast photolysis of complexes of Fe(III) with generated carboxylic acids under solar irradiation. The lower intensity of UVA irradiation used in PEF with BDD causes a slower degradation. EF with BDD is less efficient since OH cannot destroy the most persistent Fe(III)-oxalate and Fe(III)-oxamate complexes. AO-H₂O₂ with BDD yields the poorest mineralization because pollutants are only removed with OH generated at BDD. All procedures are less potent using Pt as anode due to the lower production of OH at its surface. Enrofloxacin decay always follows a pseudo first-order reaction. Its primary aromatic by-products and short intermediates including polyols, ketones, carboxylic acids and N-derivatives are detected by GC-MS and chromatographic techniques. The evolution of F⁻, NO₃⁻ and NH₄⁺ ions released to the medium during each process is also determined.     

Photoelectro-Fenton combined with photocatalytic process for degradation of an azo dye using supported TiO2 nanoparticles and carbon nanotube cathode: Neural network modeling

In this work, treatment of an azo dye solution containing C.I. Basic Red 46 (BR46) by photoelectro-Fenton (PEF) combined with photocatalytic process was studied. Carbon nanotube-polytetrafluoroethylene (CNT-PTFE) electrode was used as cathode. The investigated photocatalyst was TiO₂ nanoparticles (Degussa P25) having 80% anatase and 20% rutile, specific surface area (BET) 50 m²/g, and particle size 21 nm immobilized on glass plates. A comparison of electro-Fenton (EF), UV/TiO₂, PEF and PEF/TiO₂ processes for decolorization of BR46 solution was performed. Results showed that color removal follows the decreasing order: PEF/TiO₂ > PEF > EF > UV/TiO₂. The influence of the basic operational parameters such as initial pH of the solution, initial dye concentration, the size of anode, applied current, kind of ultraviolet (UV) light and initial Fe³⁺ concentration on the degradation efficiency of BR46 was studied. The mineralization of the dye was investigated by total organic carbon (TOC) measurements that showed 98.8% mineralization of 20 mg/l dye at 6 h using PEF/TiO₂ process. An artificial neural network (ANN) model was developed to predict the decolorization of BR46 solution. The findings indicated that artificial neural network provided reasonable predictive performance (R² = 0.986).     

A comparative study on the efficiency of electro-Fenton process in the removal of propham from water

Electro-Fenton process has been widely used in the treatment of organic pollutants lately. Its oxidation efficiency mainly depends on the electrode materials. In this study, boron doped diamond (BDD), carbon sponge (CS) and platinum (Pt) electrodes were used at four different configurations as anode and cathode. The oxidation efficiencies of BDD anode and CS cathode were investigated together for the first time in the electro-Fenton process. Propham was used as the model pollutant. The obtained results indicate that the decay rate of propham and the mineralization rate of propham aqueous solutions were highest in the case of BDD and CS electrodes as expected. The obtained mineralization current efficiency (MCE) value was 81% at 100 mA in the presence of 0.2 mM Fe³⁺ for 30 min electrolysis. The oxidative degradation intermediates of propham showed different accumulation characteristics in all configurations. The oxamic acid resisted to mineralization but it rapidly degraded in the presence of BDD anode.     

Electro-Fenton, UVA photoelectro-Fenton and solar photoelectro-Fenton degradation of the drug ibuprofen in acid aqueous medium using platinum and boron-doped diamond anodes

The degradation of a 41 mg dm⁻³ ibuprofen (2-(4-isobutylphenyl)propionic acid) solution of pH 3.0 has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) like electro-Fenton, UVA photoelectro-Fenton and solar photoelectro-Fenton at constant current density. Experiments were performed in a one-compartment cell with a Pt or boron-doped diamond (BDD) anode and an O₂-diffusion cathode. Heterogeneous hydroxyl radical (OH) is generated at the anode surface from water oxidation, while homogeneous OH is formed from Fenton's reaction between Fe²⁺ and H₂O₂ generated at the cathode, being its production strongly enhanced from photo-Fenton reaction induced by sunlight. Higher mineralization is attained in all methods using BDD instead Pt, because the former produces greater quantity of OH enhancing the oxidation of pollutants. The mineralization rate increases under UVA and solar irradiation by the rapid photodecomposition of complexes of Fe(III) with acidic intermediates. The most potent method is solar photoelectro-Fenton with BDD giving 92% mineralization due to the formation of a small proportion of highly persistent final by-products. The effect of Fe²⁺ content, pH and current density on photoelectro-Fenton degradation has been studied. The ibuprofen decay always follows a pseudo-first-order kinetics and its destruction rate is limited by current density and UV intensity. Aromatics such as 1-(1-hydroxyethyl)-4-isobutylbenzene, 4-isobutylacetophenone, 4-isobutylphenol and 4-ethylbenzaldehyde, and carboxylic acids such as pyruvic, acetic, formic and oxalic have been identified as oxidation by-products. Oxalic acid is the ultimate by-product and the fast photodecarboxylation of its complexes with Fe(III) under UVA or solar irradiation explains the higher oxidation power of photoelectro-Fenton methods in comparison to electro-Fenton procedures.     

Degradation of disperse azo dyes from waters by solar photoelectro-Fenton

Solutions of the azo dyes Disperse Red 1 (DR1) and Disperse Yellow 3 (DY3), commonly used in the Chilean textile industry, in 0.1 mol dm⁻³ Na₂SO₄ and 0.5 mmol dm⁻³ Fe²⁺ of pH 3.0 were comparatively degraded by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) using a 2.5 dm³ recirculation flow plant containing a BDD/air-diffusion cell coupled with a solar photoreactor. Organics were oxidized in EF with hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between electrogenerated H₂O₂ and added Fe²⁺. The oxidizing power of SPEF was enhanced by the additional production of hydroxyl radicals from the photolysis of Fe(III) hydrated species and the photodecomposition of Fe(III) complexes with intermediates by UV light of solar irradiation. Total decolorization, complete dye removal and almost overall mineralization for both dye solutions were only achieved using the most potent SPEF process, yielding higher current efficiencies and lower energy consumptions than EF. Final carboxylic acids like pyruvic, acetic, oxalic and oxamic were detected during the SPEF treatments. NO₃⁻ ion was released as inorganic ion. The use of a solution pH of 2.0–3.0 at 50 mA cm⁻² was found preferable for SPEF. Synthetic textile dyeing solutions containing the dyes were treated under these conditions yielding lower decolorization rate, slower dye removal and smaller mineralization degree than only using 0.1 mol dm⁻³ Na₂SO₄ due to the parallel oxidation of organic dyeing components. However, lower energy consumptions were obtained by the destruction of more amounts of total organic carbon, indicating that SPEF is a useful and viable method for the remediation of textile industrial wastewaters with high contents of disperse azo dyes.     

Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode

The degradation of herbicides 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in aqueous medium of pH 3.0 has been comparatively studied by anodic oxidation and electro-Fenton using a boron-doped diamond (BDD) anode. All solutions are totally mineralized by electro-Fenton, even at low current, being the process more efficient with 1 mM Fe²⁺ as catalyst. This is due to the production of large amounts of oxidant hydroxyl radical (OH) on the BDD surface by water oxidation and from Fenton’s reaction between added Fe²⁺ and H₂O₂ electrogenerated at the O₂-diffusion cathode. The herbicide solutions are also completely depolluted by anodic oxidation. Although a quicker degradation is found at the first stages of electro-Fenton, similar times are required for achieving overall mineralization in both methods. The decay kinetics of all herbicides always follows a pseudo first-order reaction. Reversed-phase chromatography allows detecting 4-chlorophenol, 4-chloro-o-cresol, 2,4-dichlorophenol and 2,4,5-trichlorophenol as primary aromatic intermediates of 4-CPA, MCPA, 2,4-D and 2,4,5-T, respectively. Dechlorination of these products gives Cl⁻, which is slowly oxidized on BDD. Ion-exclusion chromatography reveals the presence of persistent oxalic acid in electro-Fenton by formation of Fe³⁺-oxalato complexes, which are slowly destroyed by OH adsorbed on BDD. In anodic oxidation, oxalic acid is mineralized practically at the same rate as generated.     

A dual-chamber microbial fuel cell with conductive film-modified anode and cathode and its application for the neutral electro-Fenton process

This study reports on the modification of the anode and the cathode in a dual-chamber microbial fuel cell (MFC) with a polypyrrole (PPy)/anthraquinone-2,6-disulfonate (AQDS) conductive film to boost its performance and the application of the MFC to drive neutral electron-Fenton reactions occurring in the cathode chamber. The MFC equipped with the conductive film-coated anode and cathode delivered the maximum power density of 823 mW cm⁻² that was one order of magnitude larger than that obtained in the MFC with the unmodified electrodes. This was resulted from the enhanced activities of microbial metabolism in the anode and oxygen reduction in the cathode owing to the decoration of both electrodes with the PPy/AQDS composite. The MFC with the modified electrodes resulted in the largest rate of H₂O₂ generation in the cathode chamber by the two-electron reduction of O₂. The increase in the concentration of H₂O₂ was beneficial for the enhancement in the amount of hydroxyl radicals produced by the reaction of H₂O₂ with Fe²⁺, thus allowing an increased oxidative ability of the electro-Fenton process towards the decolorization and mineralization of an azo dye (i.e., Orange II) at pH 7.0.     

Electro-Fenton degradation of azo dye using polypyrrole/anthraquinonedisulphonate composite film modified graphite cathode in acidic aqueous solutions

Amaranth azo dye has been degraded by electro-Fenton method using an undivided cell containing the polypyrrole (PPy)/anthraquinonedisulphonate (AQDS) composite film modified graphite cathode and Pt anode. In acidic media, the PPy/AQDS composite film exhibits the characteristic of gas diffusion cathode and is highly efficient for hydrogen peroxide electrogeneration with high generation rate and current efficiency. This new electro-Fenton system can degrade amaranth azo dye efficiently in various acidic solutions. The amaranth decay and total organic carbon (TOC) removal were determined as a function of pH, cathode potential, Fe²⁺ and doping AQDS concentrations. Total dye decay and 80.3% mineralization were achieved at the optimum conditions (pH 3.0, E_cath = −0.65 V vs. SCE, 2.0 mM Fe²⁺ concentration). The electrochemical stability and electrocatalytic activity of the composite film after use in electro-Fenton process were also investigated using cyclic voltammetry (CV) and Fourier transfer infrared (FTIR) spectroscopy technologies.     

Complete mineralization of the antibiotic amoxicillin by electro-Fenton with a BDD anode

On April 30, 2014, the World Health Organization’s first global report on the presence of antibiotics in waters focused on their negative consequences, which may include the growth of microorganisms with antimicrobial resistance. The β-lactam antibiotic amoxicillin (AMX) is widely used in human and veterinary medicine, and it has been recently detected in sewage treatment plants and effluents. In this paper, the degradation of acidic aqueous solutions of AMX by electro-Fenton process has been studied at constant current. Experiments have been performed in an undivided cell equipped with a carbon-felt cathode and a Pt or boron-doped diamond (BDD) anode. In such systems, the organic molecules are mainly oxidized by hydroxyl radical (^?OH) simultaneously formed on the anode surface from water oxidation as well as in the bulk from Fenton’s reaction between Fe²⁺ catalyst and electrogenerated H₂O₂. The decay and mineralization of AMX was monitored by means of high performance liquid chromatography (HPLC) and TOC measurements. The evolution of the concentration of the final aliphatic carboxylic acids and inorganic ions like ammonium, nitrate and sulfate was assessed by HPLC and ion chromatography, respectively. The effect of the anode material, initial AMX concentration and current density was thoroughly studied. The AMX decay always followed a pseudo-first-order kinetics using either Pt or BDD, and the apparent rate constant increased with applied current. A quicker mineralization was reached with BDD because of the larger production of active ^?OH. The absolute rate constant between hydroxyl radical and AMX determined by the competition kinetics method using p-hydroxybenzoic acid as the reference compound was found to be (2.02 ± 0.01) × 10⁹ M^?1 s^?1.     

Solar photoassisted anodic oxidation of carboxylic acids in presence of Fe using a boron-doped diamond electrode

This paper reports a comparative study on the anodic oxidation of 2.5 l of 50 mg l⁻¹ TOC of formic, oxalic, acetic, pyruvic or maleic acid in 0.1 M Na₂SO₄ solutions of pH 3.0 with and without 1.0 mM Fe³⁺ as catalyst in the dark or under solar irradiation. Experiments have been performed with a batch recirculation flow plant containing a one-compartment filter-press electrolytic reactor equipped with a 20 cm² boron-doped diamond (BDD) anode and a 20 cm² stainless steel cathode, and coupled to a solar photoreactor. This system gradually accumulates H₂O₂ from dimerization of hydroxyl radical (OH) formed at the anode surface from water oxidation. Carboxylic acids in direct anodic oxidation are mainly oxidized by direct charge transfer and/or OH produced on BDD, while their Fe(III) complexes formed in presence of Fe³⁺ can also react with OH produced from Fenton reaction between regenerated Fe²⁺ with electrosynthesized H₂O₂ and/or photo-Fenton reaction. Fast photolysis of Fe(III)-oxalate and Fe(III)-pyruvate complexes under the action of sunlight also takes place. Chemical and photochemical trials of the same solutions have been made to better clarify the role of the different catalysts. Solar photoassisted anodic oxidation in presence of Fe³⁺ strongly accelerates the removal of all carboxylic acids in comparison with direct anodic oxidation, except for acetic acid that is removed at similar rate in both cases. This novel electrochemical advanced oxidation process allows more rapid mineralization of formic, oxalic and maleic acids, without any significant effect on the conversion of acetic acid into CO₂. The synergistic action of Fe³⁺ and sunlight in anodic oxidation can then be useful for wastewater remediation when oxalic and formic acids are formed as ultimate carboxylic acids of organic pollutants, but its performance is expected to strongly decay in the case of generation of persistent acetic acid during the degradation process.     

The improvement of boron-doped diamond anode system in electrochemical degradation of p-nitrophenol by zero-valent iron

Boron-doped diamond (BDD) electrodes are promising anode materials in electrochemical treatment of wastewaters containing bio-refractory organic compounds due to their strong oxidation capability and remarkable corrosion stability. In order to further improve the performance of BDD anode system, electrochemical degradation of p-nitrophenol were initially investigated at the BDD anode in the presence of zero-valent iron (ZVI). The results showed that under acidic condition, the performance of BDD anode system containing zero-valent iron (BDD-ZVI system) could be improved with the joint actions of electrochemical oxidation at the BDD anode (39.1%), Fenton's reaction (28.5%), oxidation–reduction at zero-valent iron (17.8%) and coagulation of iron hydroxides (14.6%). Moreover, it was found that under alkaline condition the performance of BDD-ZVI system was significantly enhanced, mainly due to the accelerated release of Fe(II) ions from ZVI and the enhanced oxidation of Fe(II) ions. The dissolved oxygen concentration was significantly reduced by reduction at the cathode, and consequently zero-valent iron corroded to Fe(II) ions in anaerobic highly alkaline environments. Furthermore, the oxidation of released Fe(II) ions to Fe(III) ions and high-valent iron species (e.g., FeO²⁺, FeO₄²⁻) was enhanced by direct electrochemical oxidation at BDD anode.     

Mineralization of herbicide 3,6-dichloro-2-methoxybenzoic acid in aqueous medium by anodic oxidation, electro-Fenton and photoelectro-Fenton

The mineralization of acidic aqueous solutions with 230 and 115 ppm of herbicide 3,6-dichloro-2-methoxybenzoic acid (dicamba) in 0.05 M Na₂SO₄ of pH 3.0 has been studied by electro-Fenton and photoelectro-Fenton using a Pt anode and an O₂-diffusion cathode, where oxidizing hydroxyl radicals are produced from Fenton's reaction between added Fe²⁺ and H₂O₂ generated by the cathode. While electro-Fenton only yields 60-70% mineralization, photoelectro-Fenton allows a fast and complete depollution of herbicide solutions, even at low currents, by the action of UV irradiation. In both treatments, the initial chlorine is rapidly released to the medium as chloride ion. Comparative electrolyses by anodic oxidation in the absence and presence of electrogenerated H₂O₂ give very poor degradation. The dicamba decay follows a pseudo-first-order reaction, as determined by reverse-phase chromatography. Formic, maleic and oxalic acids have been detected in the electrolyzed solutions by ion-exclusion chromatography. In electro-Fenton, all formic acid is transformed into CO₂, and maleic acid is completely converted into oxalic acid, remaining stable Fe³⁺-oxalato complexes in the solution. The fast mineralization of such complexes by UV light explains the highest oxidative ability of photoelectro-Fenton.     

Electro-Fenton degradation of antimicrobials triclosan and triclocarban

The antimicrobials triclosan (2,4,4′-trichloro-2′-hydroxydiphenyl ether) and triclocarban (N-(4-chlorophenyl)-N′-(3,4-dichlorophenyl)urea) have been degraded by four electro-Fenton systems using undivided electrolytic cells with a Pt or boron-doped diamond (BDD) anode and a carbon felt or O₂ diffusion cathode. The main oxidant is hydroxyl radical (OH) produced both on the anode surface from water oxidation and in the medium by Fenton's reaction, which takes place between electrogenerated H₂O₂ and Fe²⁺ coming from cathodic reduction of O₂ and Fe³⁺, respectively. Triclosan from saturated aqueous solutions of pH 3.0 is completely removed in all cells, decreasing its decay rate in the order: Pt/carbon felt > BDD/carbon felt > Pt/O₂ diffusion > BDD/O₂ diffusion, in agreement with their OH generation ability from Fenton's reaction. Glyoxylic, maleic and oxalic acids are identified as aliphatic intermediates. Complexes between oxalic acid and iron ions persist largely in solution, although Fe²⁺-oxalato complexes are mineralized by OH in the medium and Fe³⁺-oxalato complexes are destroyed by OH on BDD. Analogous treatments of more concentrated triclosan solutions using a 20:80 (v/v) acetonitrile/water mixture as solvent evidence the role of hydroxyl radicals along the degradation. In this hydroorganic medium hydroxylated derivatives such as 2,4-dichlorophenol, 4-chlorocatechol, chlorohydroquinone and chloro-p-benzoquinone, and carboxylic acids such as maleic, oxalic, formic and acetic acids are detected as products. Complete destruction of iron-oxalato complexes and released Cl⁻ ion involves some oxidizing species coming from parallel acetonitrile oxidation. The same electro-Fenton systems also yield the overall removal of triclocarban in acetonitrile/water mixtures, giving rise to urea, hydroquinone, chlorohydroquinone, 1-chloro-4-nitrobenzene and 1,2-dichloro-4-nitrobenzene as primary intermediates.     

Advances in the Electro‐Fenton Process for Remediation of Recalcitrant Organic Compounds

The electro‐Fenton (EF) process is a promising method combining electrochemical reactions and Fenton's reagent. In this hybrid process, the electrical current induces the in situ generation of H₂O₂ via reduction of oxygen, and the catalytic reaction is propagated by Fe²⁺ regeneration, which can take place by reduction of Fe³⁺ with H₂O₂, hydroperoxyl radical, organic radical intermediates, or directly at the cathode. Recent advances in the EF process are discussed and several key variables analyzed, including electrode material, initial pH, and Fenton's reagents, in order to extend the applicability of this technology.     

Catalytic behavior of the Fe/Fe system in the electro-Fenton degradation of the antimicrobial chlorophene

The catalytic behavior of the Fe³⁺/Fe²⁺ system in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O₂-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05 M Na₂SO₄ as supporting electrolyte and Fe³⁺ as catalyst. In these processes the drug is oxidized with hydroxyl radical (OH) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe²⁺ + H₂O₂, both of them generated at the cathode). The catalytic behavior of the Fe³⁺/Fe²⁺ system mainly depends on the cathode tested. In the cells with an O₂-diffusion cathode, H₂O₂ is largely accumulated and the Fe³⁺ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe³⁺ concentration, because this leads to a higher quantity of Fe²⁺ regenerated at the cathode and, subsequently, to a greater OH production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H₂O₂ is electrogenerated in small extent, whereas Fe²⁺ is largely accumulated because the regeneration of this ion from Fe³⁺ reduction at the cathode is much faster than its oxidation to Fe³⁺ at the anode. In this case, an Fe³⁺ concentration as low as 0.2 mM is required to obtain the maximum OH generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O₂ diffusion cell because the final Fe³⁺–oxalate complexes are difficult to oxidize with OH. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount of OH generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2 mM Fe³⁺, because oxalic acid and its Fe²⁺ complexes are directly oxidized with OH in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution.     

An electrolyte-free system for ozone generation using heavily boron-doped diamond electrodes

An electrolyte-free system for electrochemical ozone generation was developed using boron-doped diamond (BDD) electrodes as the anode and cathodes in combination with Nafion® N117/H⁺ as the separating membrane. Trials using BDD with various B/C ratios suggested that heavily boron-doped BDD with sp² impurities yielded high concentration of ozone. Further experiments by replacement of the feedstock solutions with 0.85 M Na₂SO₄ or 0.85 M NaCl resulted in no significant difference, suggesting that the use of pure water as the feedstock is the most appropriate method for ozone production. A high efficiency could be achieved by applying water as a feedstock for the anode and the cathode chambers. In addition, comparison with Pt electrodes confirmed that the excellent structural stability of BDD was the main factor contributing to this success.     

Electrochemical reforming of CH4−CO2 mixed gas using porous Gd-doped ceria electrolyte with Cu electrode

This paper reports on the composition and flow rate of outlet gas and current density during the reforming of CH₄ with CO₂ using three different electrochemical cells: cell A, with Ni−GDC (Gd-doped ceria: Ce_0.8Gd_0.2O_1.9) cathode/porous GDC electrolyte/Cu−GDC anode, cell B, with Cu−GDC cathode/ porous GDC electrolyte/Cu−GDC anode and cell C, with Ru−GDC cathode/ porous GDC electrolyte/ Cu−GDC anode. In the cathode, CO₂ reacts with supplied electrons to form CO fuel and O²⁻ ions (CO₂+2e⁻→CO+O²⁻). Too low affinity of Cu cathode to CO₂ in cell B reduced the reactivity of the CO₂ with electrons. The CO fuel, O²⁻ ions and CH₄ gas were transported to the anode through the porous GDC mixed conductor of O²⁻ ions and electrons. In the anode, CH₄ reacts with O²⁻ ions to produce CO and H₂ fuels (CH₄+O²⁻→2 H₂+CO+2e⁻). The reforming efficiency at 700−800 °C was lowest in cell B and highest in cell A. The Cu anode in cells A and C worked well to oxidize CH₄ with O²⁻ ions (2Cu+O²⁻→Cu₂O+2e⁻, Cu₂O+CH₄→2Cu+CO+2H₂). However, a blockage of the outlet gas occurred in all the cells at 700−800 °C. The gas flow is inhibited due to a reduction in pore size in the cermet cathode, as well as sintering and grain growth of Cu metal in the anode during the reforming.     

Electrocatalytic oxidation of coal on Ti-supported metal oxides coupled with liquid catalysts for H2 production

Electrocatalytic oxidation of coal on Ti-supported metal/metal oxides coupled with liquid catalysts is systematically investigated as a method of producing hydrogen at the cathode. The composition of the liquid catalyst was varied to determine its effect on the coal electrolysis. A spectrum of byproducts from the coal oxidation at the anode was analyzed. The Ti-supported metal oxide electrodes were prepared by thermal decomposition and characterized by scanning electron microscopy (SEM). X-ray diffraction results show that the composition of the electrodes was Ti/Pt, Ti/RuO₂, Ti/IrO₂ and Ti/IrO₂–RuO₂. Coal oxidation tests on these electrodes indicate that Ti/IrO₂ has the best electrocatalytic activity. Polarization curves reveal that redox catalysts, such as Fe³⁺, K₃Fe(CN)₆, KBr and V₂O₅, bridge the coal particles and the solid electrode surface, thus increasing the rates of coal oxidation. The dynamic transition of Fe³⁺/Fe²⁺ is proven by a KMnO₄ titration experiment, and the possible catalytic mechanism is discussed. Product analysis shows that pure H₂ is generated at the cathode and that CO₂ is the main product at the anode.     

Degradation study of some pharmaceuticals in commercial formulation by electro-Fenton process using a dimensionally stable anode cathode: Analytical technique,optimization conditions,and energy consumption

The aim of this work was to degrade pharmaceuticals such as amoxicillin (AMX), ceftriaxone (CTX), and Telebrix (TLX) by electro-Fenton (EF) process using a dimensionally stable anode (DSA) cathode, Pt-RuO₂-IrO₂ (PRI). For this purpose, the optimal conditions of degradation, the pseudo-first-order kinetics, the current efficiency, the electrochemical energy consumption (EEC), and the energy cost have been investigated. A spectrophotometric analysis technique has been developed. It is a simple, fast, linear, reliable, and selective technique with LOD = 0.013 g/L and LOQ = 0.04 g/L. The optimum working conditions determined are: Fe²⁺ = 0.2 mM, pH = 3, j = 20 mA/cm², and (Pt, PRI) as electrode pair. Under these conditions, the EF process leads to a conversion of the parent compound. In addition, the degradation of compounds by EF follows pseudo-first-order kinetics. The EEC for the degradation of 1 kg COD of an organic compound is 99.48, 66.86, and 50.32 kWh kg COD⁻¹ for AMX, CTX, and TLX respectively. The energy cost for processing these compounds is $4.92 (AMX), $10.03 (CTX), and $7.55 (TLX) with current efficiencies between 26% and 51%. Ultimately, the EF process using PRI at the cathode can be used for the treatment of real wastewater from health centres under optimal conditions.     

Mineralization of an azo dye Acid Red 14 by photoelectro-Fenton process using an activated carbon fiber cathode

The mineralization of an azo dye Acid Red 14 (AR14) by the photoelectro-Fenton (PEF) process was studied in an undivided electrochemical reactor with a RuO₂/Ti anode and an activated carbon fiber (ACF) cathode able to electrochemically generate H₂O₂. Anodic oxidation and UV irradiation of AR14 were also examined as comparative experiments. Results indicate that the electro-Fenton process yielded about 60–70% mineralization of AR14, while the photoelectro-Fenton could mineralize AR14 more effectively (more than 94% total organic carbon (TOC) removal) even at low current densities assisted with UV irradiation after 6 h electrolysis. The mineralization current efficiency (MCE) of the PEF process increased with the increasing AR14 concentrations. In addition, the initial solution pH ranging from 1.49 to 6.72 had little influence on the TOC removal probably due to the formation of organic carboxylic acids which balanced the pH increase caused by the cathodic generation of hydrogen gas. The ACF cathode showed a long-term stability during multiple experimental runs for degradation of AR14, indicating its good potential for practical application in treating refractory organic pollutants in aqueous solutions.