Electro-Fenton Process and Related Electrochemical Technologies Based on Fenton’s Reaction Chemistry

Novel electro-fenton approach for regeneration of activated carbon

An electro-Fenton-based method was used to promote the regeneration of granular activated carbon (GAC) previously adsorbed with toluene. Electrochemical regeneration experiments were carried out using a standard laboratory electrochemical cell with carbon paste electrodes and a batch electrochemical reactor. For each system, a comparison was made using FeSO4 as a precursor salt in solution (homogeneous system) and an Fe-loaded ion-exchange resin (Purolite C-100, heterogeneous system), both in combination with electrogenerated H2O2 at the GAC cathode. In the two cases, high regeneration efficiencies were obtained in the presence of iron using appropriate conditions of applied potential and adsorption-polarization time. Consecutive loading and regeneration cycles of GAC were performed in the reactor without great loss of the adsorption properties, only reducing the regeneration efficiency by 1% per cycle during 10 cycles of treatment. Considering that, in the proposed resin-containing process, the use of Fe salts is avoided and that GAC cathodic polarization results in efficient cleaning and regeneration of the adsorbent material, this novel electro-Fenton approach could constitute an excellent alternative for regenerating activated carbon when compared to conventional methods.

Regulation of electrochemically generated ferrous ions from an iron cathode for Pd-catalytic transformation of MTBE in groundwater

A novel Pd-based electro-Fenton (E-Fenton) process has recently been developed to transform organic contaminants in groundwater. However, it only produces H2O2 and requires addition of Fe(2+). In this study, an innovative approach is developed to effectively regulate the generation of Fe(2+) from an iron cathode in a three-electrode system in addition to H2O2 production. The Fe(2+) is then used for the Pd-catalytic transformation of methyl tert-butyl ether (MTBE) in groundwater. Results from batch experiments suggest Fe(2+) accumulation follows pseudo-first-order kinetics with rate quantitatively regulated by current and pH, and MTBE can be completely transformed. In a specially configured three-electrode column using iron as the first cathode, the localized acidic conditions develop automatically in the iron cathode and Pd zone by partitioning the current between the two cathodes, leading to controllable generation of Fe(2+) and H2O2. Effects of electrolyte concentrations and types as well as humic acid on MTBE transformation are slight. The stable transformation (~70%) in a long-term study (20 days) suggests this improved Pd-based E-Fenton process is sustainable to produce Fe(2+), H2O2, and appropriate pH conditions simultaneously for transforming organic contaminants. This study presents a new concept of generating Fe(2+) from an iron cathode for the processes requiring Fe(2+).

Electrochemical generation of hydroxyl radicals for examining protein structure

The use of hydroxyl radicals to covalently label the solvent-exposed surface of proteins has been shown to be a powerful tool to examine the structure of proteins and intermolecular interfaces. Current methods to generate hydroxyl radicals for footprinting experiments rely on the laser photolysis of H2O2 or the synchrotron radiolysis of water, which adds significant costs and/or complexity to the experiments. In this work, we develop the electro-Fenton reaction as a means to generate hydroxyl radicals for structural footprinting mass spectrometry experiments to complement current laser and synchrotron-based methods, while reducing the costs and complexity of initiating such experiments. The use of an electrochemical flow cell also enables control of the timing and extent of the radical generation process, while reducing the complexity typically associated with radical footprinting experiments. Ubiquitin, a model protein, was labeled with electro-Fenton generated hydroxyl radicals and top-down proteomics was used to verify oxidation sites on the protein surface.

Bio-electro-Fenton system for enhanced estrogens degradation

The feasibility of removing estrogens including 17β-estradiol (E2) and 17α-ethynyl-estradiol (EE2) was studied in a bio-electro-Fenton (BEF) system equipped with a Fe@Fe2O3/non-catalyzed carbon felt (NCF) composite cathode. E2 and EE2 were removed by reactive oxidants, produced by bio-electro-Fenton system and zero-valent iron/O2 system, as well as adsorption. Under closed-circuit condition, 81% of E2 and 56% of EE2 were removed within 10h in the system, in which the highest concentration of total iron ions and H2O2 reached 81 and 1.2mg/L, respectively. The maximum power density of BEF system equipped with Fe@Fe2O3/NCF electrode was 4.35 W/m(3). Two intermediates of E1 and 6-OH-E2 were identified during Fenton oxidation of E2. This study demonstrates the degradation fate of E2 and EE2 in a BEF system equipped with Fe@Fe2O3/NCF electrodes, which provides a promising and cost-effective solution for the removal of recalcitrant contaminants with simultaneous power generation.

Mineralization of citric acid wastewater by photo-electrochemical chlorine oxidation

This work demonstrates a novel chloride photo-electrochemical method for mineralizing citric acid. The electrolytic reactor with a length of 12 cm, a width of 12 cm and a height of 30 cm held 2.5 L of solution, which was involved in the batch reaction. Both anode and cathode were made of titanium coated with RuO2/IrO2. The results revealed that the solution pH dominated the production of hypochlorous acid (HOCl) oxidant in the presence of NaCl as direct current electricity was used. The chloride electrochemical process at pH 5.5 removed 59% of total organic carbon (TOC) in 4 h (NaCl = 200 mM, current = 5 A). UV irradiation (254 nm) in the reactor induced the photo-electrochemical reaction, increasing the TOC removal from 59% to 99.4%. Finally, the reaction pathway for citric acid mineralization was discussed with reference to the detection of intermediates using a liquid chromatography-mass spectrometry (LC-MS).

Core-shell structure dependent reactivity of Fe@Fe₂O₃ nanowires on aerobic degradation of 4-chlorophenol

In this study, core-shell Fe@Fe₂O₃ nanowires with different iron oxide shell thickness were synthesized through tuning water-aging time after the reduction of ferric ions with sodium borohydride without any stirring. We found that these Fe@Fe₂O₃ nanowires exhibited interesting core-shell structure dependent reactivity on the aerobic degradation of 4-chlorophenol. Characterization results revealed that the core-shell structure dependent aerobic oxidative reactivity of Fe@Fe₂O₃ nanowires was arisen from the combined effects of incrassated iron oxide shell and more surface bound ferrous ions on amorphous iron oxide shell formed during the water-aging process. The incrassated iron oxide shell would gradually block the outward electron transfer from iron core for the subsequent two-electron molecular oxygen activation, but more surface bound ferrous ions on iron oxide shell with prolonging aging time could favor the single-electron molecular oxygen activation, which was confirmed by electron spin resonance spectroscopy with spin trap technique. The mineralization of 4-chlorophenol was monitored by total organic carbon measurement and the oxidative degradation intermediates were analyzed by gas chromatography-mass spectrometry. This study provides new physical insight on the molecular oxygen activation mechanism of nanoscale zerovalent iron and its application on aerobic pollutant removal.

Electrochemical degradation of m-cresol using porous carbon-nanotube-containing cathode and Ti/SnO2-Sb2O5-IrO2 anode: kinetics, byproducts and biodegradability

The degradation of m-cresol solution was studied using an electrochemical oxidation system with Ti/SnO2-Sb2O5-IrO2 anode for anodic oxidation and porous carbon-nanotube-containing cathode for H2O2 electrogeneration along with Fe(3+) reduction. Organic pollutants were oxidized by hydroxyl radical (OH) formed simultaneously in the medium from electro-Fenton reaction in the presence of Fe(2+) and at the anode surface from water oxidation. The porous cathode made of graphite, carbon nanotube (CNT) and polytetrafluoroethene (PTFE) exhibited a higher catalytic activity toward O2 reduction producing H2O2 and Fe(3+) reduction for Fe(2+) regeneration, favoring organics degradation by electro-Fenton oxidation. The degradation kinetics results revealed that the reaction of m-cresol cleavage with hydroxyl radicals could be described by pseudo first-order kinetics. The progress of organics mineralization demonstrated some byproducts were formed during m-cresol degradation. Based on the byproducts identified by GC-MS and HPLC, the sequential process of m-cresol degradation was proposed. Furthermore, the aerobic biological treatment showed that the electrochemical treatment was able to evidently enhance the biodegradability of m-cresol solution.

Using single-chamber microbial fuel cells as renewable power sources of electro-Fenton reactors for organic pollutant treatment

Electro-Fenton reactions can be very effective for organic pollutant degradation, but they typically require non-sustainable electrical power to produce hydrogen peroxide. Two-chamber microbial fuel cells (MFCs) have been proposed for pollutant treatment using Fenton-based reactions, but these types of MFCs have low power densities and require expensive membranes. Here, more efficient dual reactor systems were developed using a single-chamber MFC as a low-voltage power source to simultaneously accomplish H2O2 generation and Fe(2+) release for the Fenton reaction. In tests using phenol, 75 ± 2% of the total organic carbon (TOC) was removed in the electro-Fenton reactor in one cycle (22 h), and phenol was completely degraded to simple and readily biodegradable organic acids. Compared to previously developed systems based on two-chamber MFCs, the degradation efficiency of organic pollutants was substantially improved. These results demonstrate that this system is an energy-efficient and cost-effective approach for industrial wastewater treatment of certain pollutants.

Mineralization of sulfanilamide by electro-Fenton and solar photoelectro-Fenton in a pre-pilot plant with a Pt/air-diffusion cell

The mineralization of sulfanilamide solutions at pH 3.0 was comparatively studied by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) using a 2.5 L pre-pilot plant containing a Pt/air-diffusion cell coupled with a solar photoreactor. Organics were primordially oxidized by hydroxyl radical (OH) formed from Fenton's reaction between H₂O₂ generated at the cathode and added Fe(2+) and/or under the action of sunlight. A mineralization up to 94% was achieved using SPEF, whereas EF yielded much poorer degradation. The effect of current density and Fe(2+) and drug concentrations on the degradation rate, mineralization current efficiency and energy cost per unit DOC mass of EF and/or SPEF was examined. The sulfanilamide decay always followed a pseudo first-order kinetics, being more rapid in SPEF due to the additional generation of OH induced by sunlight on Fe(III) species. Catechol, resorcinol, hydroquinone and p-benzoquinone were identified as aromatic intermediates. The final solutions treated by EF contained Fe(III) complexes of maleic, fumaric, oxamic and mainly oxalic acids, which are hardly destroyed by OH. The quick photolysis of Fe(III)-oxalate complexes by sunlight explains the higher oxidation ability of SPEF. The N content of sulfanilamide was mainly mineralized as NH₄⁺ ion and in much lesser extent as NO₃⁻ ion, whereas most of its initial S was converted into SO₄²⁻ ion.

Electrochemical degradation of the antibiotic sulfachloropyridazine by hydroxyl radicals generated at a BDD anode

The treatment of aqueous solutions of the antibiotic sulfachloropyridazine (SCP) was carried out at the natural pH of the solution (pH 4.5) with hydroxyl radicals (OH) generated at a BDD anode surface by electro-oxidation using an undivided electrochemical cell equipped with a three-dimensional carbon-felt cathode. Hydroxyl radicals are powerful oxidants and react with the antibiotic leading to its overall mineralization. The kinetic study showed that oxidative degradation of SCP follows pseudo first-order reaction kinetics, with a relatively short degradation time. The degree of mineralization of SCP solutions increased with the applied current, being higher than 95% after 8 h of electrolysis at 350 mA or higher current. To determine the degradation pathway upon the action of hydroxyl radicals, the cyclic and aliphatic by-products, as well as the released inorganic ions, were identified and quantified over electrolysis time. The values of the rate constants of reactions between OH and the SCP and its intermediates were determined by the competition kinetics method using p-hydroxybenzoic acid. The absolute rate constant for the OH-mediated degradation of SCP was found to be 1.92 × 10(9)M(-1)s(-1). Toxicity assessment by the Microtox method during the electro-oxidation of SCP solutions revealed the formation of compounds that can be more toxic than the parent molecule, but the overall results confirm the effectiveness of this electrochemical process for the removal of the antibiotic SCP and its by-products from aqueous media.

A new insight into Fenton and Fenton-like processes for water treatment: Part II. Influence of organic compounds on Fe(III)/Fe(II) interconversion and the course of reactions

The interconversion of Fe(III)/Fe(II) in Fenton (Fe(2+)/H2O2) and Fenton-like (Fe(3+)/H2O2) reactions has been studied to better understand their intrinsic mechanisms. The reactions were conducted at an initial pH of 3.0, with H2O2 in excess and iron in catalytic concentrations, and with nitrobenzene and atrazine as model organic compounds. The results of this study have shown that some intermediate species in the degradation of aromatic compounds can influence the interconversion of Fe(III)/Fe(II) in the Fenton and Fenton-like reactions, and hence influence the rate and course of the reactions. Thus, from the point of view of Fe(III)/Fe(II) interconversion, a Fenton-like reaction inevitably involves a classical Fenton reaction, and a Fenton reaction may also involve a Fenton-like reaction step. These two reactions may be somewhat interchangeable and proceed simultaneously. In the case of the degradation of aromatic compounds, the Fenton-like reactions display autocatalytic character, but no such effect is observed for non-aromatic compounds.

Electro-Fenton decolourisation of dyes in an airlift continuous reactor using iron alginate beads

In this study, electro-Fenton dye degradation was performed in an airlift continuous reactor configuration by harnessing the catalytic activity of Fe alginate gel beads. Electro-Fenton experiments were carried out in an airlift reactor with a working volume of 1.5 L, air flow of 1.5 L/min and 115 g of Fe alginate gel beads. An electric field was applied by two graphite bars connected to a direct current power supply with a constant potential drop. In this study, Lissamine Green B and Reactive Black 5 were selected as model dyes. Fe alginate gel beads can be used as an effective heterogeneous catalyst for the degradation of organic dyes in the electro-Fenton process, as they are more efficient than the conventional electrochemical techniques. At optimal working conditions (3 V and pH 2), the continuous process was performed. For both dyes, the degree of decolourisation increases when the residence time augments. Taking into account hydrodynamic and kinetic behaviour, a model to describe the reactor profile was obtained, and the standard deviation between experimental and theoretical data was lower than 6%. The results indicate the suitability of the electro-Fenton technique to oxidise polluted effluents in the presence of Fe alginate gel beads. Moreover, the operation is possible in a continuous airlift reactor, due to the entrapment of iron in the alginate matrix.

Degradation of dyes from aqueous solution by Fenton processes: a review

Several industries are using dyes as coloring agents. The effluents from these industries are increasingly becoming an environmental problem. The removal of dyes from aqueous solution has a great potential in the field of environmental engineering. This paper reviews the classification, characteristics, and problems of dyes in detail. Advantages and disadvantages of different methods used for dye removal are also analyzed. Among these methods, Fenton process-based advanced oxidation processes are an emerging prospect in the field of dye removal. Fenton processes have been classified and represented as "Fenton circle". This paper analyzes the recent studies on Fenton processes. The studies include analyzing different configurations of reactors used for dye removal, its efficiency, and the effects of various operating parameters such as pH, catalyst concentration, H2O2 concentration, initial dye concentration, and temperature of Fenton processes. From the present study, it can be conclude that Fenton processes are very effective and environmentally friendly methods for dye removal.

Electrochemical incineration of omeprazole in neutral aqueous medium using a platinum or boron-doped diamond anode: degradation kinetics and oxidation products

The electrochemical incineration of omeprazole, a widely prescribed gastrointestinal drug which is detected in natural waters, has been studied in a phosphate buffer of pH 7.0 by anodic oxidation with electrogenerated H(2)O(2) (AO-H(2)O(2)) operating at constant current density (j). The experiments were carried out in a cell equipped with either a Pt or a boron-doped diamond (BDD) anode and an air-diffusion cathode to continuously produce H(2)O(2). In these systems, organics are mainly oxidized by hydroxyl radicals formed at the Pt or BDD surface from water oxidation. A partial total organic carbon (TOC) abatement close to 78% for omeprazole was achieved by AO-H(2)O(2) with a BDD anode after consumption of 18 Ah L(-1) at 100 mA cm(-2), whereas the alternative use of Pt did not allow mineralizing the drug. However, the drug was totally removed using both anodes, although it decayed more rapidly using BDD. In this latter system, increasing j accelerated the degradation process, but lowering the mineralization current efficiency. Greater drug content also enhanced the degradation rate with higher mineralization degree and current efficiency. The kinetics for omeprazole decay always followed a pseudo-first-order reaction and its rate constant increased with increasing j and with decreasing its concentration. Seven heteroaromatic intermediates and four hydroxylated derivatives were detected by LC-MS, while nine short-linear carboxylic acids were identified and quantified by ion-exclusion HPLC. These acids were largely accumulated using Pt and rapidly removed using BDD, thus explaining the partial mineralization of omeprazole achieved by AO-H(2)O(2) with the latter anode. The release of inorganic ions such as NO(3)(-), NH(4)(+) and SO(4)(2-) was followed by ionic chromatography. A plausible reaction sequence for omeprazole mineralization involving all intermediates detected is proposed.

On the application of nanostructured electrodes prepared by Ti/TiO2/WO3 "template": a case study of removing toxicity of indigo using visible irradiation

New assays with HepG2 cells indicate that Indigo Carmine (IC), a dye that is widely used as additive in many food and pharmaceutical industries exhibited cytotoxic effects. This work describes the development of a bicomponent nanostructured Ti/TiO2/WO3 electrode prepared by "template" method and investigates its efficiency in a photoelectrocatalytic method by using visible light irradiation and applied potential of 1V. After 2h of treatment there are reduction of 97% discoloration, 62% of mineralization and formation of three byproducts assigned as: 2-amine-5-sulfo-benzoic acid, 2,3-dioxo-14-indole-5-sulfonic acid, and 2-amino-α-oxo-5-sulfo-benzeneacetic acid were identified by HPLC-MS/MS. But, cytotoxicity was completely removed after 120 min of treatment.

Kinetic behavior of anti-inflammatory drug ibuprofen in aqueous medium during its degradation by electrochemical advanced oxidation

The electrochemical abatement of the drug ibuprofen (2-(4-isobutylphenyl)propionic acid) from aqueous solution has been carried out by anodic oxidation. The electrolyses have been performed at constant current using a small, undivided cell equipped with a Pt or thin-film boron-doped diamond (BDD) anode and a carbon-felt cathode. The results have shown that ibuprofen has been destroyed under all the conditions tested, following pseudo-first-order kinetics; however, BDD enables higher removal rates than Pt, because the former produces greater quantity of (•)OH. Using BDD anode, the pseudo-first-order rate constant increased with applied current and when NaCl replaced Na2SO4 as supporting electrolyte, while it is almost unaffected by ibuprofen concentration. Mineralization of ibuprofen aqueous solutions was followed by total organic carbon (TOC) measurements. After 8 h of electrolysis, TOC removal varied from 91% to 96% applying a current in the range of 50-500 mA. The reaction by-products were quantified by chromatographic techniques, and in particular, aliphatic acids (oxalic, glyoxylic, formic, acetic, and pyruvic) have been the main intermediates formed during the electrolyses. The absolute rate constant for the oxidative degradation of ibuprofen have also been determined, by competition kinetic method, as 6.41 × 10(9) M(-1) s(-1).

Optimisation of decolourisation and degradation of Reactive Black 5 dye under electro-Fenton process using Fe alginate gel beads

The aim of this work was to improve the ability of the electro-Fenton process using Fe alginate gel beads for the remediation of wastewater contaminated with synthetic dyes and using a model diazo dye such as Reactive Black 5 (RB5). Batch experiments were conducted to study the effects of main parameters, such as voltage, pH and iron concentration. Dye decolourisation, reduction of chemical oxygen demand (COD) and energy consumption were studied. Central composite face-centred experimental design matrix and response surface methodology were applied to design the experiments and to evaluate the interactive effects of the three studied parameters. A total of 20 experimental runs were set, and the kinetic data were analysed using first-order and second-order models. In all cases, the experimental data were fitted to the empirical second-order model with a suitable degree for the maximum decolourisation of RB5, COD reduction and energy consumption by electro-Fenton-Fe alginate gel beads treatment. Working with the obtained empirical model, the optimisation of the process was carried out. The second-order polynomial regression model suggests that the optimum conditions for attaining maximum decolourisation, COD reduction and energy consumption are voltage, 5.69 V; pH 2.24 and iron concentration, 2.68 mM. Moreover, the fixation of iron on alginate beads suggests that the degradation process can be developed under this electro-Fenton process in repeated batches and in a continuous mode.

Complete removal of the insecticide azinphos-methyl from water by the electro-Fenton method--a kinetic and mechanistic study

The removal of organophosphorous insecticide azinphos-methyl (AZPM) from water has been investigated by the electro-Fenton method which produces hydroxyl radicals electro-catalytically. The reaction between these radicals and AZPM has led to the oxidation of AZPM up to carbon dioxide and inorganic ions indicating its complete removal from water. The oxidation kinetics was fitted to pseudo-first order reaction and absolute rate constant of the second order reaction kinetic was determined as (6.82 ± 0.18) × 10(9) M(-1) s(-1) by using competitive kinetics method. The oxidation of AZPM by hydroxyl radicals leads to the formation of different intermediates species; such as aromatic derivatives, short-chain carboxylic acids and inorganic ions as end products. The identification and quantification of these intermediates were deeply investigated by HPLC, GC-MS and ion chromatography analyses. Based on the identified intermediates, a general oxidation mechanism was proposed. Mineralization ability of the process was also tested by using aqueous AZPM solutions and its commercial formulation, Gusathion M WP 25 (GMWP25). Mineralization efficiency was followed by the chemical oxygen demand (COD) analysis of treated solutions. The overall mineralization of synthetic AZPM solution and that of commercial formulation at the end of treatment highlights the outstanding mineralization power of the electro-Fenton process.

Superparamagnetic iron oxide nanoparticles: amplifying ROS stress to improve anticancer drug efficacy

Superparamagnetic iron oxide nanoparticles (SPION) are an important and versatile nano- platform with broad biological applications. Despite extensive studies, the biological and pharmacological activities of SPION have not been exploited in therapeutic applications. Recently, β-lapachone (β-lap), a novel anticancer drug, has shown considerable cancer specificity by selectively increasing reactive oxygen species (ROS) stress in cancer cells. In this study, we report that pH-responsive SPION-micelles can synergize with β-lap for improved cancer therapy. These SPION-micelles selectively release iron ions inside cancer cells, which interact with hydrogen peroxide (H₂O₂) generated from β-lap in a tumor-specific, NQO1-dependent manner. Through Fenton reactions, these iron ions escalate the ROS stress in β-lap-exposed cancer cells, thereby greatly enhancing the therapeutic index of β-lap. More specifically, a 10-fold increase in ROS stress was detected in β-lap-exposed cells pretreated with SPION-micelles over those treated with β-lap alone, which also correlates with significantly increased cell death. Catalase treatment of cells or administration of an iron chelator can block the therapeutic synergy. Our data suggest that incorporation of SPION-micelles with ROS-generating drugs can potentially improve drug efficacy during cancer treatment, thereby provides a synergistic strategy to integrate imaging and therapeutic functions in the development of theranostic nanomedicine.

Three-dimensional homogeneous ferrite-carbon aerogel: one pot fabrication and enhanced electro-Fenton reactivity

This work focuses on constructing a high catalytic activity cathode of an electro-Fenton system, to overcome the defects of low activity, poor stability, and intricate fabrication of supported catalysts. A series of ferrite-carbon aerogel (FCA) monoliths with different iron/carbon ratios was synthesized directly from metal-resin precursors accompanied by phase transformation. Self-doped ferrite nanocrystals and carbon matrix were formed synchronously via moderate condensation and sol-gel processes, leading to homogeneous texture. An optimal 5% ferric content FCA was composed of coin-like carbon nano-plate with continuous porous structure, and the ferric particles with diameters of dozens of nanometers were uniformly embedded into the carbon framework. The FCA exhibited good conductivity, high catalytic efficiency, and distinguished stability. When it was used as an electro-Fenton cathode, metalaxyl degradation results demonstrated that 98% TOC elimination was realized after 4 h, which was 1.5 times higher than that of the iron oxide supported electrode. It was attributed to self-doped Fe@Fe(2)O(3) ensuring Fe(II) as the mediator, maintaining high activity via reversibe oxidation and reduction by electron transfer among iron species with different valences. Meanwhile, an abundance of independent reaction microspaces were provided for every ferric crystal to in situ decompose electrogenerated H(2)O(2). Moreover, the possible catalytic mechanism was also proposed. The FCA was a promising candidate as potential cathode materials for high-performance electro-Fenton oxidation.

Bio-distribution and in vivo antioxidant effects of cerium oxide nanoparticles in mice

Cerium oxide nanoparticles have oxygen defects in their lattice structure that enables them to act as a regenerative free radical scavenger in a physiological environment. We performed a comprehensive in vivo analysis of the biological distribution and antioxidant capabilities of nanoceria administered to mice perorally (PO), intravenously (IV), or intraperitoneally (IP) by dosing animals weekly for 2 or 5 weeks with 0.5 mg kg(-1) nanoceria. Next, we examined if nanoceria administration would decrease ROS production in mice treated with carbon tetrachloride (CCl(4)). Our results showed that the most extensive and cumulative nano-deposition was via IV and IP administered while PO administration showed mice excreted greater than 95% of their nanoceria within 24 h. Organ deposition for IV and IP mice was greatest in the spleen followed by the liver, lungs, and kidneys. Elimination for all administration routes was through feces. Nanoceria administration showed no overt toxicity, however, WBC counts were elevated with IV and IP administration. Our in vivo studies show that nanoceria administration to mice with induced liver toxicity (by CCl(4)) showed similar findings to mice treated with N-acetyl cystine (NAC), a common therapeutic to reduce oxidative stress. Taken together, our studies show that nanoceria remains deposited in tissues and may decrease ROS, thereby suggesting that cerium oxide nanoparticles may be a useful antioxidant treatment for oxidative stress.

Application of Fered-Fenton process for m-phenylenediamine degradation

This study was undertaken to investigate the feasibility of applying the Fered-Fenton process to the degradation of m-phenylenediamine, by examining the effect of varying the initial H2O2 and Fe(2+) concentrations, the initial pH and electric current on the process efficiency. The degradation behavior of m-phenylenediamine was also compared to that of aniline. The Fered-Fenton reactor consists of anodes and cathodes with mesh-type titanium metal coated with IrO2/RuO2 and stainless steel, respectively. The experiments showed that m-phenylenediamine was rapidly degraded by the Fered-Fenton process. Initial pH of 3.2 is optimal for the removal of m-phenylenediamine and chemical oxygen demand (COD). m-Phenylenediamine and COD removal efficiencies increased with the increasing electrical current from 0 A to 4 A, and decreased with a further increase in electrical current. Optimum efficiency resulting in 100% degradation of m-phenylenediamine and elimination of 30% of COD was achieved at pH 3.2 at 60 min in the presence of 10 mM of m-phenylenediamine, 0.268 mM of Fe(2+), 43.6 mM of H2O2, and under a current of 4 A.

Kinetics of acetaminophen degradation by Fenton oxidation in a fluidized-bed reactor

Acetaminophen (ACT), an analgesic and antipyretic substance, is one of the most commonly detected pharmaceutical compound in surface waters and wastewaters. In this study, fluidized-bed Fenton (FB-Fenton) was used to decompose ACT into its final degradation products. The 1.45-L cylindrical glass reactor had inlet, outlet and recirculating sections. SiO(2) carrier particles were supported by glass beads with 2-4 mm in diameter. ACT concentration was determined by high performance liquid chromatography (HPLC). During the first 40 min of reaction, a fast initial ACT removal was observed and the "two-stage" ACT degradation conformed to a pseudo reaction kinetics. The effects of ferrous ion dosage and [Fe(2+)]/[H(2)O(2)] (FH ratio) were integrated into the derived pseudo second-order kinetic model. A reaction pathway was proposed based on the intermediates detected through SPME/GC-MS. The aromatic intermediates identified were hydroquinone, benzaldehydes and benzoic acids while the non-aromatic substances include alcohols, ketones, aldehydes and carboxylic acids. Rapid initial ACT degradation rate can be accomplished by high initial ferrous ion concentration and/or low FH ratio.

A three-electrode column for Pd-catalytic oxidation of TCE in groundwater with automatic pH-regulation and resistance to reduced sulfur compound foiling

A hybrid electrolysis and Pd-catalytic oxidation process is evaluated for degradation of trichloroethylene (TCE) in groundwater. A three-electrode, one anode and two cathodes, column is employed to automatically develop a low pH condition in the Pd vicinity and a neutral effluent. Simulated groundwater containing up to 5 mM bicarbonate can be acidified to below pH 4 in the Pd vicinity using a total of 60 mA with 20 mA passing through the third electrode. By packing 2 g of Pd/Al(2)O(3) pellets in the developed acidic region, the column efficiency for TCE oxidation in simulated groundwater (5.3 mg/L TCE) increases from 44 to 59 and 68% with increasing Fe(II) concentration from 0 to 5 and 10 mg/L, respectively. Different from Pd-catalytic hydrodechlorination under reducing conditions, this hybrid electrolysis and Pd-catalytic oxidation process is advantageous in controlling the fouling caused by reduced sulfur compounds (RSCs) because the in situ generated reactive oxidizing species, i.e., O(2), H(2)O(2) and OH, can oxidize RSCs to some extent. In particular, sulfite at concentrations less than 1 mM even greatly increases TCE oxidation by the production of SO(4)(•-), a strong oxidizing radical, and more OH.

Role of electrode materials for the anodic oxidation of a real landfill leachate--comparison between Ti-Ru-Sn ternary oxide, PbO(2) and boron-doped diamond anode

In this paper the electrocatalytic properties of Ti-Ru-Sn ternary oxide (TiRuSnO(2)), PbO(2) and boron-doped diamond (BDD) anodes have been compared for the electrochemical oxidation of a real landfill leachate from an old municipal solid waste landfill (average values of COD 780 mg dm(-3) and NH(4)(+)-N266 mg dm(-3)). The experiments have been performed using an undivided flow cell equipped with a stainless steel cathode, under constant current of 2 A and flow-rate of 420 dm(3) h(-1). The performance of the electrodes has been compared measuring the time evolution of aromatic compounds, COD, ammonium, colour removal, current efficiency and energy consumption. The experimental results indicated that after 8 h of electrolyses TiRuSnO(2) anode yields only 35% COD, 52% colour and 65% ammonium removal. Using PbO(2) ammonium and colour were completely removed but a residual COD (i.e. 115 mg dm(-3)) was present. On the contrary BDD enables complete COD, colour and ammonium removal due to the electrogeneration of hydroxyl radicals from water discharge and active chlorine from chloride ions oxidation. BDD also exhibits greater current efficiency along with a significantly lower energy cost than other electrodes. These results indicated that the electrochemical oxidation with BDD anode is an effective process for the treatment of landfill leachate.

Formation of sulfonyl aromatic alcohols by electrolysis of a bisazo reactive dye

Five sulfonyl aromatic alcohols, namely 4-((2-hydroxyethyl)sulfonyl)phenol, 4-((2-(2-((4-hydroxyphenyl)sulfonyl)ethoxy)vinyl)sulfonyl)phenol, 4-(ethylsulfonyl)phenol, 4-(vinylsulfonyl)phenol and 5-((4-aminophenyl)sulfonyl)-2-penten-1-ol were identified by LC-ESI-Qq-TOF-MS as products formed by electrolysis of the bisazo reactive dye Reactive Black 5 (RB5). Since electrolyses were performed in an undivided cell equipped with Ni electrodes in alkaline medium, amines like 4-(2-methoxyethylsulfonyl)benzene-amine (MEBA) with m/z 216 were also suspected to be formed due to the plausible chemical reaction in the bulk or the cathodic reduction of RB5 and its oxidation by-products. Aiming to check this hypothesis, a method was used for the preparation of MEBA with 98% purity, via chemical reduction also of the dye RB5. The logP of the synthesized sulfonyl aromatic compounds was calculated and their logk_w values were determined chromatographically. These data were discussed in regard to the relationship between hydrophobicity/lipophilicity and toxicity.

Design of a neutral three-dimensional electro-Fenton system with foam nickel as particle electrodes for wastewater treatment

In this work, we demonstrate a novel three-dimensional electro-Fenton system (3D-E-Fenton) for wastewater treatment with foam nickel, activated carbon fiber and Ti/RuO(2)-IrO(2) as the particle electrodes, the cathode, and the anode respectively. This 3D-E-Fenton system could exhibit much higher rhodamine B removal efficiency (99%) than the counterpart three-dimensional electrochemical system (33%) and E-Fenton system (19%) at neutral pH in 30 min. The degradation efficiency enhancement was attributed to much more hydroxyl radicals generated in the 3D-E-Fenton system because foam nickel particle electrodes could activate molecular oxygen to produce O(2)(-) via a single-electron transfer pathway to subsequently generate more H(2)O(2) and hydroxyl radicals. This is the first observation of molecular oxygen activation over the particle electrodes in the three-dimensional electrochemical system. These interesting findings could provide some new insight on the development of high efficient E-Fenton system for wastewater treatment at neutral pH.

A ferrous oxalate mediated photo-Fenton system: toward an increased biodegradability of indigo dyed wastewaters

This study assessed the applicability of a ferrous oxalate mediated photo-Fenton pretreatment for indigo-dyed wastewaters as to produce a biodegradable enough effluent, likely of being derived to conventional biological processes. The photochemical treatment was performed with ferrous oxalate and hydrogen peroxide in a Compound Parabolic Concentrator (CPC) under batch operation conditions. The reaction was studied at natural pH conditions (5-6) with indigo concentrations in the range of 6.67-33.33 mg L(-1), using a fixed oxalate-to-iron mass ratio (C(2)O(4)(2-)/Fe(2+)=35) and assessing the system's biodegradability at low (257 mg L(-1)) and high (1280 mg L(-1)) H(2)O(2) concentrations. In order to seek the optimal conditions for the treatment of indigo dyed wastewaters, an experimental design consisting in a statistical surface response approach was carried out. This analysis revealed that the best removal efficiencies for Total Organic Carbon (TOC) were obtained for low peroxide doses. In general it was observed that after 20 kJ L(-1), almost every treated effluent increased its biodegradability from a BOD(5)/COD value of 0.4. This increase in the biodegradability was confirmed by the presence of short chain carboxylic acids as intermediate products and by the mineralization of organic nitrogen into nitrate. Finally, an overall decrease in the LC(50) for Artemia salina indicated a successful detoxification of the effluent.

Electro-Fenton treatment of mature landfill leachate in a continuous flow reactor

The treatment of mature landfill leachate by EF-Fere (also called Fered-Fenton) method was carried out in a continuous stirred tank reactor (CSTR) using Ti/RuO(2)-IrO(2)-SnO(2)-TiO(2) mesh anodes and Ti mesh cathodes. The effects of important parameters, including initial pH, inter-electrode gap, H(2)O(2) to Fe(2+) molar ratio, H(2)O(2) dosage and hydraulic retention time, on COD removal were investigated. The results showed that the complete mixing condition was fulfilled in the electrochemical reactor employed in this study and COD removal followed a modified pseudo-first order kinetic model. The COD removal efficiency increased with the decrease of H(2)O(2) to Fe(2+) molar ratio and hydraulic retention time. There existed an optimal inter-electrode gap or H(2)O(2) dosage so that the highest COD removal was achieved. Nearly the same COD removal was obtained at initial pH 3 and 5, but the steady state was quickly achieved at initial pH 3. The organic pollutants in the leachate were analyzed through a gas chromatography coupled with mass spectrometry (GC-MS) system. About 73 organics were detected in the leachate, and 52 of which were completely removed after EF-Fere process.

Design of a visible light driven photo-electrochemical/electro-Fenton coupling oxidation system for wastewater treatment

In this study, we report on a photo-electrochemical/electro-Fenton oxidation (PEC/EF) system by coupling visible light driven photo-electrochemical oxidation (PEC) and electro-Fenton oxidation (EF) in an undivided cell. Bi2WO6 nanoplates deposited on FTO glass (Bi2WO6/FTO) and Fe@Fe2O3 core-shell nanowires supported on activated carbon fiber (Fe@Fe2O3/ACF) were used as the anode and the cathode in the PEC/EF system, respectively. This novel PEC/EF system showed much higher activity than the single PEC and EF systems on degradation of rhodamine B in aqueous solution at natural pH. Moreover, the degradation and the instantaneous current efficiencies of the PEC/EF system were increased by 154% and 26% in comparison with the sum of those of single PEC and EF systems, respectively. These significant enhancements could be attributed to the synergetic effect from better separation of photo-generated carriers in the photo-anode and the transfer of photo-electrons to the oxygen diffusion cathode to generate more electro-generated H2O2 and hydroxyl radicals on the Fenton cathode. The better separation of photo-generated carriers contribute more to the overall degradation enhancement than the photo-electrons generated H2O2 and the subsequent Fenton reaction on the cathode during the PEC/EF process.

Degradation of paracetamol by advance oxidation processes using modified reticulated vitreous carbon electrodes with TiO(2) and CuO/TiO(2)/Al(2)O(3)

The degradation of paracetamol in aqueous solutions in the presence of hydrogen peroxide was carried out by photochemistry, electrolysis and photoelectrolysis using modified 100 pores per inch reticulated vitreous carbon electrodes. The electrodes were coated with catalysts such as TiO(2) and CuO/TiO(2)/Al(2)O(3) by electrophoresis followed by heat treatment. The results of the electrolysis with bare reticulated vitreous carbon electrodes show that 90% paracetamol degradation occurs in 4 h at 1.3 V vs. SCE, forming intermediates such as benzoquinone and carboxylic acids followed by their complete mineralisation. When the electrolysis was carried out with the modified electrodes such as TiO(2)/RVC, 90% degradation was achieved in 2 h while with CuO/TiO(2)/Al(2)O(3)/RVC, 98% degradation took only 1 h. The degradation was also carried out in the presence of UV reaching 95% degradation with TiO(2)/RVC/UV and 99% with CuO/TiO(2)/Al(2)O(3)/RVC/UV in 1 h. The reactions were followed by spectroscopy UV-Vis, HPLC and total organic carbon analysis. These studies show that the degradation of paracetamol follows a pseudo-first order reaction kinetics.