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Chitosan is an abundant and non-toxic natural polysaccharide rich in nitrogen, which is used here to obtain N-doped mesoporous carbons (NMCs) as supports for Pt-saving PtCu alloy elecrocatalysts, which can be of interest for low-temperature fuels cells. NMCs with different textural properties were synthesized from cheap silica templates. They presented relative dominance of disordered graphitic lattice and comparable amounts of pyrrolic and pyridinic N, with different specific BET surface areas (715-1040 m2 g−1) and mesopore (1.2-2.4 cm3 g−1) and micropore volumes (0.1-0.6 cm3 g−1). PtCu nanoparticles were deposited by Cu electroless deposition and further galvanic exchange with Pt, with overall Pt loadings about 20 wt.%. Pt-rich PtCu alloy crystallites with contracted Pt fcc lattices and sizes of 3.1-4.7 nm were formed. The synthesized PtCu/NMCs catalysts presented better specific current densities for the oxygen reduction and better CO tolerance and specific current densities for the methanol oxidation reaction than those of commercial Pt/C and PtCu/CMK-3. The PtCu/NMC prepared with the H2SO4-activated NMC was the most active catalyst. The different textural properties of the carbonaceous materials appeared to determine the surface structure of the PtCu nanoparticles.

In this study, the applicability of factorial design to the treatment of greywater (GW) containing dodecyl-benzene sulfonic acid (LAS) by electrochemical advanced oxidation processes (EAOPs) is demonstrated. At bench scale, anodic oxidation with electrogenerated H2O2 (AO-H2O2) and photoelectro Fenton (PEF) processes were studied following a 23 factorial design with central point insertion, using a first-order mathematical polynomial. In the former process, the combination of a boron-doped diamond (BDD) anode with a carbon-PTFE air-diffusion cathode, both of 3 cm2, yielded a 76% degradation of LAS at 40 mg L-1 along with 52% TOC removal under optimized conditions. The PEF process with 5 mg L-1 Fe2+ at current density of 77.5 mA cm-2 allowed attaining a 63% of LAS degradation and 78% of TOC abatement. The best conditions found for PEF according to the factorial design, in terms of Fe2+ concentration and current density, were applied for the treatment of 10 L of raw GW by solar PEF (SPEF) using a compound parabolic collector (CPC) as solar reactor and a filter-press electrochemical cell. A 70% of LAS removal and a 55% of GW mineralization were attained after 240 min of treatment. Artemia salina toxicity tests were performed with effluents resulting from the different methods under optimum conditions, and the SPEF process was proven to be the most effective and promising EAOP for the reduction of GW toxicity.

This work assesses the effectiveness of an artificial intelligence (AI) model based on an artificial neural networks (ANN) – genetic algorithm (GA) in the prediction of the behavior and optimization of the treatment of sulfate wastewaters with Bromophenol blue dye using an electro-oxidation (EO) process. Trials were made with a filter press-type reactor with a boron-doped diamond (BDD) anode. The ANN model was trained with 51 electrolytic experiments by using the electrolysis time, flow, current density, pH and dye concentration as input variables and the discoloration efficiency as the output one. The performance of ANN was measured with RMSE and MAPE values of 10.73 % and 8.81 %, respectively, calculated from real and predicted values. Optimum conditions determined by GA were reached for the inputs of 10 min, 11.9 L min−1, 31.25 mA cm−2, 2.8 and 41.25 mg L−1, giving a discoloration efficiency of 88.8 ± 0.3 %, close to 95.5 % predicted by the model. To validate the AI model, the same experimental conditions were applied to treat wastewaters with Bromothymol blue and Thymol blue, with analogous structures to Bromophenol blue, and a mixture of the three dyes by EO. In all cases, the loss of color decayed following a pseudo-first-order kinetics, with similar apparent rate constants. For the dye mixture, 69 % COD was reduced at 60 min, with 13 % average current efficiency and 0.26 kW h (g COD)-1 energy consumption. The AI model is a strong tool to design, control and operate the EO process with a BDD anode to treat wastewaters with similar dyes.

The urgency to move from critical raw materials to highly available and renewable feedstock is currently driving the scientific and technical developments. Within this context, the abundance of natural resources like chitosan paves the way to synthesize biomass-derived nitrogen-doped carbons. This work describes the synthesis of chitosan-derived N-doped mesoporous carbon in the absence (MC-C) and presence (N-MC-C) of 1,10-phenanthroline, which acted as both a porogen agent and a second nitrogen source. The as-prepared MC-C and N-MC-C were thoroughly characterized and further employed as catalytic materials in gas-diffusion electrodes (GDEs), aiming to develop a sustainable alternative to conventional GDEs for H2O2 electrogeneration and photoelectro-Fenton (PEF) treatment of a drug pollutant. N-MC-C presented a higher content of key surface N-functionalities like the pyrrole group, as well as an increased graphitization degree and surface area (63 vs 6 m2/g), comparable to commercial carbon black. These properties entailed a superior activity of N-MC-C for the oxygen reduction reaction, as confirmed from its voltammetric behavior at a rotating ring-disk electrode. The GDE prepared with the N-MC-C catalyst showed greater H2O2 accumulation, attaining values close to those obtained with a commercial GDE. N-MC-C- and MC-C-derived GDEs were employed to treat drug solutions at pH 3.0 by the PEF process, which outperformed electro-oxidation. The fastest drug removal was achieved using N-MC-C, requiring only 16 min at 30 mA/cm2 instead of 20 min required with MC-C. The replacement of the dimensionally stable anode by a boron-doped diamond accelerated the degradation process, reaching an almost complete mineralization in 360 min. The main degradation products were identified, revealing the formation of six different aromatic intermediates, alongside five aliphatic compounds that comprised three nitrogenated structures. The initial N was preferentially converted into ammonium.

Pt(Cu) nanoparticles supported on carbon nanofibers (CNFs), multi-walled carbon nanotubes (MWCNTs) and Vulcan carbon XC72, have been synthesized by electroless deposition and galvanic exchange. The structural analyses show contracted Pt fcc lattices due to the formation of a PtCu alloy core covered by a Pt-rich shell, mean crystallite sizes of about 3 nm, as well as good dispersion and carbon attachment. The electrochemical surface areas (ECSAs) of Pt(Cu)/CNF and Pt(Cu)/XC72 are comparable to those of commercial Pt/C and PtCu/C. The Pt(Cu) electrocatalysts show more negative onset potentials for CO oxidation than Pt/C and PtCu/C, thus indicating their greater CO tolerance. Pt(Cu)/CNF and Pt(Cu)/MWCNT present the highest mass activity and specific activity for the O2 reduction, respectively, both with better relative stability than Pt(Cu)/XC72. Pt(Cu)/CNF and Pt(Cu)/MWCNT are then considered good cathode catalysts, yielding estimated savings of about 50 wt% Pt, when applied to low-temperature fuel cells.

The degradation and mineralization of the drug norfloxacin (NFX) has been assessed in a model solution, containing 15 mM NaCl +45 mM Na2SO4 at pH 3.0, using a flow plant with an FM01-LC filter-press reactor equipped with a Ti|Ir-Sn-Ru oxides anode to electrogenerate HClO from Cl- oxidation and a stainless-steel cathode. Unexpectedly, anodic oxidation with active chlorine (AO-HClO) outperformed electro-Fenton (EF-HClO), photoelectro-Fenton (PEF-HClO) and solar photoelectro-Fenton (SPEF-HClO) due to: (i) the formation of refractory complexes between iron ions and carboxyl group of NFX, and (ii) the conversion of HClO into less effective ¿OH upon its Fenton-like reaction with added Fe2+ catalyst. SPEF-HClO was superior among Fentonbased treatments because the ¿OH concentration was largely increased by the photolysis of Fe(III) species. At an initial NFX concentration in the range 0.103-0.146 mM, the optimum conditions for SPEF-HClO were 0.40 mM Fe2+ and 15 mA cm􀀀 2. A BDD anode allowed a higher production of ¿OH, accelerating the degradation and mineralization, with similar energy requirements as compared to trials with Ti|Ir-Sn-Ru oxides anode. The SPEFHClO process in urban wastewater was less powerful because of the parallel oxidation of natural organic matter. HClO, Fe2+ and Fetotal were quantified in both water matrices. The initial degradation sequence for NFX, proposed from 10 primary by-products identified by LC-MS/MS, revealed the occurrence of hydroxylation, chlorination and defluorination steps. Additionally, 5 stable by-products were detected by GC-MS.

The excessive cost, unsustainability or complex production of new highly selective electrocatalysts for H2O2 production, especially noble-metal-based ones, is prohibitive in the water treatment sector. To solve this conundrum, biomass-derived carbons with adequate textural properties were synthesized via agarose double-step pyrolysis followed by steam activation. A longer steam treatment enhanced the graphitization and porosity, even surpassing commercial carbon black. Steam treatment for 20 min yielded the greatest surface area (1248 m2 g-1), enhanced the mesopore/micropore volume distribution and increased the activity (E1/2 = 0.609 V) and yield of H2O2 (40%) as determined by RRDE. The upgraded textural properties had very positive impact on the ability of the corresponding gas-diffusion electrodes (GDEs) to accumulate H2O2, reaching Faradaic current efficiencies of ~95% at 30 min. Acidic solutions of ß-blocker acebutolol were treated by photoelectro-Fenton (PEF) process in synthetic media with and without chloride. In urban wastewater, total drug disappearance was reached at 60 min with almost 50% mineralization after 360 min at only 10 mA cm-2. Up to 14 degradation products were identified in the Cl--containing medium.

Antibiotics are widely supplied over all the world to animals and humans to fight and heal bacteriological diseases. The uptake of antibiotics has largely increased the average-life expectancy of living beings. However, these recalcitrant products have been detected at low concentrations in natural waters, with potential health risks due to alterations in food chains and an increase in the resistance to bacterial infection, control of infectious diseases, and damage of the beneficial bacteria. The high stability of antibiotics at mild conditions prevents their effective removal in conventional wastewater treatment plants. A powerful advanced oxidation processes such as the electro-Fenton (EF) process is being developed as a guarantee for their destruction by

Paracetamol (PCT) or acetaminophen is a widely prescribed drug to treat fever and mild to moderate pain. The PCT uptake by animals and humans is not complete, being excreted through their urine to contaminate the aquatic/natural environments. Trace amounts of this drug have been found in sewage sludge, hospital wastewaters, wastewater plant treatments, surface waters, and even drinking water. PCT denatures proteins and oxidize lipids in cells with damage of their genetic code. Its toxicity over macrophytes, protozoan, algae, bacteria, and fishes has been reported. Ozonation methods have been proposed as efficient treatments to solve this pollution. This comprehensive and critical review is focused on the application of ozonation processes to remove PCT polluted water from different sources, like natural waters, synthetic waters, and real wastewaters. The fundamentals, operating variables, and best results by direct ozonation and hybrid catalytic ozonation are described, with attention to produced reactive oxygen species and their oxidative action. Single ozonation, catalytic modification of materials, and hybrid non-catalytic processes are detailed as direct ozonation methods. Ozonation with metal-based catalysts and photolytic and photocatalytic ozonation as hybrid catalytic methods are analyzed. Sequential non-biological and biological treatments with ozone and ozonation for wastewater remediation in treatment plants are described. Reaction sequences proposed for PCT mineralization are finally discussed, showing the initial formation of hydroquinone and 2-hydroxy-4-(N-acetyl)-aminophenol and their consecutive evolution to ultimate carboxylic acids like oxalic and oxamic. The ability of the methods to destroy these acids and their iron- and/or copper-complexes explains their mineralization performance.

Groundwater nitrate contamination is an emerging threat in stressed regions under intensive farming although, lately, efforts to valorize such residues are highly encouraged. Here, electrochemical nitrate removal has been investigated as a versatile strategy for this purpose, using a reactor equipped with a cheap central Fe-based rotating cylinder electrode (RCE) as cathode and six concentric Ti|IrO2 plates as anodes. The study of the effect of Ecath and rotational speed (ω) on NO3- electroreduction from a synthetic aqueous solution with high conductivity revealed the feasibility of complete nitrate removal, which only required 100-120 min at Ecath = -1.80 V vs Hg|Hg2SO4|sat. K2SO4 within the ω-range of 100-500 rpm. The concentration decays agreed perfectly with a first-order kinetics. NH3 was accumulated as main product, being partly volatilized due to the quick solution alkalization, whereas NO2- was not found. Linear sweep voltammetries demonstrated the high electrocatalytic activity of carbon steel RCE as compared to inactive stainless steel. Koutecky-Levich analysis showed that the reduction process with carbon steel at Ecath from -1.80 V involved 8 electrons. The participation of H radical in the reduction mechanism was ascertained by electron paramagnetic resonance. The mass transport and charge transfer of the RCE reactor were characterized under turbulent flow by means of the dimensionless Damköhler (Da) number, as well as from the Sherwood-Reynolds-Schmidt (Sh-Re-Sc) analysis. A mixed regime with a prevalence of mass transport control was determined at Ecath from -1.8 V. The Sh = 0.70Re0.46Sc0.356 correlation obtained for this reactor may serve to guide the scale-up of electrochemical NO3- removal as more electrocatalytic cathode materials are developed. Successful NO3- elimination from solutions with low conductivity that mimicked groundwater is finally reported.

Most commonly employed anodes for photoelectrochemical degradation of organic contaminants in water are too thick, resulting in a low degradation efficiency due to the excessive electron-hole recombination. Multilayer-type TiO 2 /Au/TiO 2 nanocomposites have been prepared as photoanode thin films by pulsed laser deposition (PLD). The films were composed of six TiO 2 and five Au alternate layers, with total thickness of about 212 nm, aimed to optimize the absorption of photons and minimize the recombination. The influence of gold on the optical, structural, and chemical properties of the semiconductor nanocomposites was investigated. The band gap determined from Tauc model was 3.22 eV, close to that obtained by spectroscopic ellipsometry and lower than that of the TiO 2 film, revealing an enhancement of visible light absorption. The catalytic performance of PLD films was evaluated by using them as anodes in electro-oxidation (EO) and photoanodes in photoelectrocatalysis (PEC) to degrade 39-157 mg L ⁻¹ paracetamol in sulfate medium. The drug removal was very slow in EO, due to the low ability to form [rad] OH on the anode surface, which was significantly enhanced upon UVA irradiation in PEC. The presence of Cl ⁻ allowed a faster degradation by produced active chlorine. Finally, a hybrid process involving PEC + photoelectro-Fenton (PEF) with an air-diffusion cathode yielded total paracetamol decay in 4-5 min at an anodic potential of +4.0 V because of the efficient [rad] OH generation from Fenton's and photo-Fenton reactions. Hydroquinone, p-benzoquinone and hydroxylated products were detected during EO and PEC. The generation of active chlorine was confirmed by identifying a chlorinated derivative, N-(4-chloro-2-hydroxyphenyl)acetamide, in PEC + PEF treatment.

En este artículo, se discutirá la degradación de los ácidos trans-cinámico y trans-ferúlico a través de procesos electroquímicos de oxidación avanzados (PEOAs) tales como la oxidación anódica con H2O2 electro generado (OA-H2O2), electro-Fenton (EF) y fotoelectro-Fenton (FEF). En un reactor de tanque agitado, a 25 ° C, equipado con un ánodo de 3 cm2 de diamante dopado con boro (BDD) y un cátodo de carbono de difusión de aire de politetrafluoroetileno de 3 cm2, se electrolizó 100 ml de soluciones conteniendo 200 mg L-1 de carbono orgánico total (COT) en Na2SO4 0.05 M a pH 3.0 aplicando densidades de corriente desde 16.67 hasta 100 mA cm-2 durante 360 minutos. En los experimentos de EF y FEF, se añadió Fe2+ 0.50 mM como catalizador de la reacción de Fenton, mientras que en FEF, la solución se irradió con luz UVA. La capacidad de oxidación de los ácidos con los PEOAs aumentó en secuencia OA-H2O2

This article reports the electrochemical advanced oxidation treatment of 2.5 L of acidic aqueous solutions with 0.320 mM of the drug procaine hydrochloride in 0.050 M Na2SO4 using a pre-pilot flow plant. This was equipped with a cell, containing a boron-doped diamond (BDD) anode and an air-diffusion cathode for H2O2 generation, which was connected to an annular photoreactor with a 160 W UVA lamp for the study of photoelectro-Fenton (PEF) process. Poor degradation and mineralization was attained by electrochemical oxidation with electrogenerated H2O2 due to the limited attack of both, hydroxyl radical ( OH) formed at the BDD surface from water oxidation and H2O2 on organic matter. The electro-Fenton process became more effective thanks to the simultaneous oxidation with OH formed from Fenton’s reaction in the presence of Fe2+. The most powerful process was PEF because of the additional photolysis of photoactive intermediates by UVA radiation. This method allowed achieving 91% mineralization after 360 min of electrolysis at 33.3 mA cm−2. The effect of current density and drug concentration on PEF performance was examined. The mineralization current efficiency and energy consumption were determined for each treatment. Two N-containing derivatives were identified by gas chromatography-mass spectrometry. The quantification of generated carboxylic acids revealed that the final solution in PEF was composed of a mixture of acetic and formic acids.

(Co, S, P)-decorated multiwalled carbon nanotubes (MWCNTs) have been synthesized following a hydrothermal route as electrocatalysts to manufacture large surface area air-diffusion cathodes with carbon cloth as substrate. The enhanced electrocatalytic H2O2 production as compared with Co-free MWCNTs cathodes was demonstrated in a 2.5-L pre-pilot plant with either a RuO2-based or boron-doped diamond (BDD) anode, accumulating between 2- and 3-fold greater H2O2 contents with the catalyzed cathode. The good stability of this new material was ensured from the low Co leaching, with less than 9% Co released to solutions upon repeated usage. Aqueous solutions of the brominated organic preservative bronopol with 0.050 M Na2SO4 at pH 3.0 were comparatively treated by electro-oxidation (EO-H2O2), electro-Fenton (EF), UVA-assisted photoelectro-Fenton (PEF) and solar PEF (SPEF) at constant current density. SPEF with BDD anode and the catalyzed cathode showed the best performance, with total bronopol removal at 210 min and 94% mineralization after 360 min at 40 mA cm−2, thanks to the action of OH, BDD( OH) and sunlight. Formic acid was identified as main reaction by-product, whereas Br and N atoms were mainly converted to Br–, BrO3– and NO3–. Some unidentified organic by-product containing Br and N was formed as well.

The use of cobalt (II) salts (Co2+) for the catalytic decomposition of peroxymonosulfate (PMS) and the subsequent production of free radicals has demonstrated high efficiency in removing organic contaminants from water. However, only a few reports are available on the systematic analysis of PMS decomposition by Co2+ and its effect on contaminant degradation kinetics. In this study, PMS decomposition was evaluated at different initial PMS (5, 10, and 15 mM) and cobalt (0.05, 0.10, and 0.20 mM) concentrations. For all of the cases in this study, over 60% PMS decomposition was achieved after 30 min. A general degradation mechanism for any contaminant was proposed, as well as a kinetic model that incorporates the PMS/contaminant molar ratio. To validate the kinetic model, acetaminophen (ACT) was used as a target contaminant along with a response surface methodology (RSM) statistical analysis. Once validated, the model was used to determine ACT degradation by the Co2+/PMS process, the chemical oxygen demand (COD), and carboxylic acid evolution using the best experimental conditions.

Paracetamol (PCT), also known as acetaminophen, is a drug used to treat fever and mild to moderate pain. After consumption by animals and humans, it is excreted through the urine to the sewer systems, wastewater treatment plants, and other aquatic/natural environments. It has been detected in trace amounts in effluents of wastewater plant treatments, sewage sludge, hospital wastewaters, surface waters, and drinking water. PCT can cause genetic code damage, oxidative degradation of lipids, and denaturation of protein in cells, and its toxicity has been well-proven in bacteria, algae, macrophytes, protozoan, and fishes. To avoid its harmful health problems over living beings, powerful Fenton and Fenton-based treatments as pre-eminent advanced oxidation processes (AOPs) have been developed because of the inefficient treatment by conventional treatments. This paper presents a comprehensive and critical review over the application of such Fenton technologies to remove PCT from natural waters, synthetic wastewaters, and real wastewaters. The characteristics and main results obtained using Fenton, photo-Fenton, electro-Fenton, and photoelectro-Fenton are described, making special emphasis in the oxidative action of the generated reactive oxygen species. Hybrid processes based on the coupling with ultrasounds, gamma radiation, photocatalysis, photoelectrocatalysis, zero-valent iron-activated persulfate, adsorption, and microbial fuel cells, are analyzed. Sequential treatments involving the initiation with plasma gliding arc discharge and post-biological process are detailed. Comparative results with other available AOPs are also described and discussed. Finally, 13 aromatic by-products and 9 short-linear aliphatic carboxylic acid detected during the PCT removal by Fenton and Fenton-based processes are reported, with the proposal of three parallel pathways for its initial degradation.

Photoelectrocatalysis is a hybrid photon/electron-driven process that benefits from the synergistic effects of both processes to enhance and stabilize the generation of disinfecting oxidants. Photoelectrocatalysis is an easy to operate technology that can be scaled-up or scaled-down for various water treatment applications as low-cost decentralized systems. This review article describes the fundamentals of photoelectrocatalysis, applied to water disinfection to ensure access to clean water for all as a sustainable development goal. Advances in reactor engineering design that integrate light-delivery and electrochemical system requirements are presented, with a description of photo-electrode material advances, including doping, nano-decoration, and nanostructure control. Disinfection and cell inactivation are described using different model microorganisms such as E. coli, Mycobacteria, Legionella, etc., as well the fungus Candida parapsilosis, with relevant figures of merit. The key advances in the elucidation of bacterial inactivation mechanisms by photoelectrocatalytic treatments are presented and knowledge gaps identified. Finally, prospects and further research needs are outlined, to define the pathway towards the future of photoelectrocatalytic disinfection technologies.

The excessive cost, unsustainability or complex production of new highly selective electrocatalysts for H

The electrochemical oxidation of 4,6-dimethyldibenzothiophene (4,6-DMDBT) at low concentrations on a BDD anode was investigated in a monophasic acetonitrile (93.5% v/v)–water (6.5% v/v, 0.01 M LiClO4) solution. Two oxidation steps related to the sequential formation of sulfoxide and sulfone derivatives were identified. Kinetic parameters such as the electron transfer coefficient α, the number of electrons nα involved in the rate-determining step, the total number of electrons n, the reaction rate constant k0 and the diffusion coefficient D of 4,6-DMDBT for the first transformation were determined by cyclic voltammetry, differential pulse voltammetry (DPV), square wave voltammetry and bulk electrolysis under potentiostatic conditions. The process was bielectronic with α = 0.57, nα = 1, k0 = 7.46 × 10−6 cm s−1 and D = 2.30 × 10−6 cm2 s−1. DPV was the most sensitive electroanalytical technique. Using 27 mg L−1 of 4,6-DMTDB, DPV allowed determining a conversion of 91% to sulfoxide after 60 min of electrolysis in a BDD/BDD cell at an anodic potential of 1.50 V, with an apparent rate constant of 0.034 min−1. The electrochemical characterization was corroborated via gas chromatography–mass spectrometry and ultra-high performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry, confirming the formation of the sulfoxide in the first step and the sulfone in the second one as main products, alongside a minor proportion of dimers.

Groundwater is one of the main freshwater resources on Earth, but its contamination with NO3− and pesticides jeopardizes its viability as a source of drinking water. In this work, a detailed study of single electro-oxidation (EO) and electrodenitrification and paired EO/electrodenitrification processes has been undertaken with simulated and actual groundwater matrices containing 100 mg dm−3 NO3− and/or 5 mg dm−3 terbuthylazine pesticide. Galvanostatic electrolyses were made with 500 cm3 of solutions at pH 4.0-10.5 and 250-1000 mA in tank reactors with a RuO2 or boron-doped diamond (BDD) anode and one or two Fe cathodes, all of them in the form of meshes. Most of NO3− removals agreed with a pseudo-first-order kinetics. In Cl−-free media, NH4+ predominated as electroreduction product. In chloride media, a greater amount of N-volatiles was determined alongside a slower electrodenitrification, especially with RuO2 due to the partial re-oxidation of electroreduction products like NH4+ by active chlorine. The pesticide decays were also fitted to a pseudo-first order kinetics, and its presence led to a smaller release of N-volatiles. Overall, BDD always favored the pesticide degradation thanks to the action of BDD( • OH), whereas RuO2 was preferred for electrodenitrification under some conditions. The EO/electrodenitrification of groundwater was successful once the matrix was softened to minimize its hardness. The NO3− concentration was reduced below the limit established by the WHO. Overall, the BDD/Fe cell was more suitable than the RuO2/Fe cell because it accelerated the pesticide removal with a simultaneous high degree of NO3− electroreduction. However, it produced toxic chlorate and perchlorate. A final post-treatment with an anion exchange resin ensured a significant removal of both ions, thus increasing the viability of the electrochemical approach to treat this type of water. Chromatographic analyses revealed the formation of ten heteroaromatic products like desethyl-terbuthylazine and cyanuric acid, alongside oxalic and oxamic as final short-chain carboxylic acids.

International audience; Electrochemical advanced oxidation processes (EAOPs) have shown excellent capabilities to the abatement of recalcitrant organic pollutants. The Fenton-based electrochemical systems have shown great performance for in-situ generation of H2O2, allowing an efficient • OH production for the mineralization of organic pollutants. These systems have been widely applied at bench scale; however, studies to scale-up to a higher technology readiness level (TRL) are lacking. One of the main scale-up challenges of the Fenton-based systems is the implementation of air diffusion electrodes (ADE) in flow-by electrochemical cells. The ADE adds additional complexity with respect to mass transfer effects due to hydraulic reactor design and ADE gas pressure control. Therefore, this work experimentally investigated residence time distribution and platinum-sheet electrode mass transfer effects due to (a) the liquid cross-flow velocity through the electrochemical cell, (b) the gas pressure of the air-diffusion electrode (ADE), and (c) the presence of mesh sheet mass transfer promoters between the electrodes. Analysis of experimental results revealed a synergistic improvement of mass transfer with the ADE gas flow and the presence of mesh promoters. Engineers could exploit this synergistic effect to design electrochemical cells with significantly lower capital cost.

Pt(Cu) nanoparticles supported on CMK3 and CMK8 ordered mesoporous carbons (OMCs) have been synthesized by electroless deposition of Cu followed by galvanic exchange with Pt. The structural characterization by high-resolution transmission electron microscopy and X-ray diffraction showed the formation of Pt(Cu) nanoparticles of 4–5 nm, in which PtCu alloys with contracted fcc Pt lattice and 70–80 at.% Pt was identified. The X-ray photoelectron spectroscopy analyses indicated that the Pt(Cu) nanoparticles were mainly composed of a PtCu alloy core covered by a Pt-rich shell, in agreement with the steady cyclic voltammograms, which did not show any Cu oxidation peaks. Electroactive surface areas up to about 70 m2 gPt−1 were obtained. The onset potentials for CO oxidation and the oxygen reduction reaction were more negative and positive, respectively, as compared to Pt/C, thus indicating higher activity of these Pt(Cu) catalysts with respect to the latter. Based on the corresponding binding energies, these better activities were attributed to the favorable geometric and ligand effects of Cu on Pt, which were able to reduce the adsorption energy of the intermediates on Pt. Pt(Cu)/CMK3 showed competitive mass and specific activities, as well as better stability than Pt/C.

The relative oxidation power of dimensionally stable anodes, namely Ti/Ir-Pb, Ti/Ir-Sn, Ti/Ru-Pb, Ti/Pt-Pd and Ti/RuO₂, has been determined from the anodic oxidation (AO) treatment of 2 dm³ of methyl orange azo dye solutions in 0.050 mol dm¯³ Na₂SO₄ of pH 7.0 at constant current density. The anodes were synthesized by the dip-coating method using the corresponding metallic chlorides in isopropanol/water and their morphology, surface roughness, crystallographic structure and composition were analyzed. A mixture of IrO₂, Pb₂O₃ and Pb₃O₄ were the components in the outperforming Ti/Ir-Pb anode. The effect of current density, Na₂SO₄ concentration, and cathode nature on the decolorization of azo dye solutions by AO with Ti/RuO₂ was examined. Under favorable conditions, 96%-98% color removal was achieved using Ti/Ir-Pb, Ti/Ir-Sn and Ti/Ru-Pb, with lower decolorization for Ti/Pt-Pd and Ti/RuO₂ anodes. In all cases, a pseudo-first-order decolorization process was found. The oxidation ability of anodes rose in the order Ti/RuO₂< Ti/Pt-Pd < Ti/Ru-Pb < Ti/Ir-Sn < Ti/Ir-Pb, achieving 76.0% mineralization for the latter electrode. The mixture of active and non-active materials then gave rise to anodes with higher oxidation power than those made solely of active materials, due to the enhancement of the oxidation action of hydroxyl radicals formed in the non-active oxide. The superiority of Ir over Ru in the mixed metal oxides was related to the greater adsorption of organics on its surface, thereby favoring their oxidation. Ammonium and sulfate ions were released as pre-eminent ions. Stable byproducts and final short-linear aliphatic carboxylic acids were identified by gas chromatography-mass spectrometry and ion-exclusion high-performance liquid chromatography. Based on these compounds, a reaction sequence for methyl orange mineralization is proposed.

Model solutions of bisphenol A (BPA) in 0.050 M Na

One of the main challenges of electrochemical Fenton-based processes is the treatment of organic pollutants at near-neutral pH. As a potential approach to this problem, this work addresses the use of a low content of soluble chelated metal catalyst, formed between Fe(III) and ethylenediamine-N,N'-disuccinic (EDDS) acid (1:1), to degrade the herbicide triclopyr in 0.050 M Na

This work reports the novel application of an Fe-based 2D metal−organic framework (MOF), prepared with 2,2′-bipyridine-5,5′-dicarboxylate (bpydc) as organic linker, as highly active catalyst for heterogeneous photoelectro-Fenton (PEF) treatment of the lipid regulator bezafibrate in a model matrix and urban wastewater. Well-dispersed 2D structures were successfully synthesized and their morphological, physicochemical and photocatalytic properties were assessed. UV/Vis PEF using an IrO2/air-diffusion cell with an extremely low catalyst concentration (0.05 g L−1, tenfold lower than reported 3D MOFs) outperformed electro-oxidation with electrogenerated H2O2, electro-Fenton and visible-light PEF. Its excellent performance was explained by: (i) the enhanced mass transport of H2O2 (and organic molecules) at the 2D structure, providing active sites for heterogeneous Fenton's reaction and in-situ Fe(II) regeneration; (ii) the ability of photoinduced electrons to reduce H2O2 to •OH, and Fe(III) to Fe(II); and (iii) the enhanced charge transfer and excitation of Fe–O clusters, which increased the number of electron-hole pairs. LC-QToF-MS and GC-MS allowed the identification of 16 aromatic products of bezafibrate. The complete removal of four micropollutants mixed in urban wastewater at pH 7.4 revealed the great potential of (Fe−bpydc)-catalyzed PEF process.

11 pags., 10 figs., 2 tabs., The development of heterogeneous Fenton-based electrochemical advanced oxidation processes is important for the removal of organic pollutants at industrial level in the near future. This work reports the application of heterogeneous photoelectro-Fenton (HPEF) with UVA light as an enhanced alternative to the more widespread heterogeneous electro-Fenton (HEF) process. The treatment of the antibiotic cephalexin using chalcopyrite as a sustainable catalyst was studied using an undivided IrO/air-diffusion cell. XPS analysis showed the presence of Fe(III), Cu(I) and Cu(II) species on the surface. The amount of Fe ions dissolved upon chalcopyrite exposure to continuous stirring and air bubbling was proportional to chalcopyrite content. In all cases, the occurrence of pH self-regulation to an optimum value near 3 was observed. The HEF and HPEF treatments of 100 mL of 50 mg L cephalexin solutions with 0.050 M NaSO have been studied with 1.0 g L chalcopyrite at 50 mA cm. Comparative homogeneous EF and PEF with dissolved Fe and Cu catalysts were also performed. HPEF was the most effective process, which can be mainly explained by the larger production of homogeneous and heterogeneous [rad]OH and the photodegradation of the complexes formed between iron and organics. The effect of applied current and catalyst concentration on HPEF performance was assessed. Recycling experiments showed a long-term stability of chalcopyrite. Seven initial aromatics and six cyclic by-products of cephalexin were identified, and a plausible degradation route that also includes five final carboxylic acids is proposed., Financial support from FONDECYT project 11180772 (CONICYT, Chile) as well as from project CTQ2016-8616-R (AEI/FEDER, EU) is acknowledged. A. Thiam is grateful to the ‘Becas Iberoamérica. Santander Universidades’ program.

The development of new or upgraded electrochemical water treatment technologies is considered a topic of great interest. Here, Tartrazine azo dye solutions were treated by means of a quite innovative dual electrochemical persulfate (S

Pt(Ni)/C and PtRu(Ni)/C catalysts were synthesized by electroless deposition of Ni on a carbon dispersion followed by sequenced Pt deposition and spontaneous deposition of Ru species. The structural analyses of the catalysts with 88:12 and 98:2 Pt:Ni atomic ratios pointed out to the formation of small hexagonal Ni crystallites covered by thin cubic Pt surface structures with no evidence about PtNi alloy formation. The onset potentials for CO oxidation on Pt(Ni)/C and PtRu(Ni)/C were about 0.10 and 0.24 V more negative than those of Pt/C, thus indicating their better CO tolerance. The surface Ru species appeared to have the major effect by facilitating the CO removal by the bifunctional mechanism. The onset potential for the methanol oxidation reaction (MOR) of Pt(Ni)/C was about 0.15 V lower than that of Pt/C. The mass and specific activities together with the exchange current densities of the Pt(Ni)/C catalysts were also higher than those of Pt/C, making in evidence their higher activity in front of the MOR. The Tafel slopes for the MOR on Pt(Ni)/C suggested different reaction mechanism than on Pt/C. The electronic (ligand) effect of Ni on Pt was considered the main reason to explain the higher activity of Pt(Ni)/C in front of the CO oxidation and the MOR.

This work addresses the mineralization of the widely used Methyl Orange (MO) azo dye by technologies based on H

Fast and total inactivation of Gram-negative Pseudomonas aeruginosa in suspensions at natural pH 5.9 has been achieved by photoelectrocatalyisis (PEC), using Ag-decorated TiO2 photoanodes onto transparent conducting indium tin oxide (ITO) under UVA irradiation. The assays were made with 100 mL of bacterial suspensions in an undivided cell equipped with a photoanode, a stainless steel cathode and Ag|AgCl (3 M KCl) as reference electrode. Total inactivation was obtained in only 5 min using coatings with 4 wt.% Ag, 25 mM Na2SO4 as the electrolyte and 1.70 V as applied bias potential. Comparative photocatalytic treatments reached total inactivation at much longer time, suggesting the crucial role of hydroxyl radicals in PEC. These oxidants, which were detected by electron spin resonance, attacked the outer cell wall very effectively, since the recombination of the electron/hole pairs photoinduced under UVA irradiation was reduced. As characterized by high-resolution transmission electron microscopy (HRTEM), the best synthesized Ag-TiO2 thin-film photoanode mainly contains anatase TiO2 nanopowder decorated with Ag nanoparticles of ca. 45 nm. Analyses by X-ray powder diffraction and UV/Vis spectroscopy were also performed. The potential use of PEC for bacterial disinfection was confirmed for the rod-shaped Gram-positive Bacillus atrophaeus, which was more slowly inactivated due to its different cell wall structure. Scanning electron micrographs of both bacteria showed that PEC induced a high roughness, cell lysis and accumulation of cellular debris.

CoS2/MWCNTs have been previously described as potentially viable catalysts to enhance the classical two-electron H2O2 production from O2 reduction reaction (ORR) for in situ water treatment, but their poor stability still limits their large-scale application. Here, the synthesis and characterization of a novel electrocatalyst made of CoSP nanoparticles supported onto multi-walled carbon nanotubes (MWCNTs) is reported. X-ray diffraction data demonstrated the much higher stability conferred upon partial sulfur substitution by phosphorus. Linear and cyclic voltammograms of CoSP/MWCNTs showed a potential window from 0.9 to 0.1 V for the ORR at pH 3.0, along with greater H2O2 production ability. Large area air-diffusion cathodes were manufactured by depositing the catalyst onto carbon paper, being further used in a pre-pilot filter-press cell containing a boron-doped diamond anode. A stable H2O2 accumulation, with maximum current efficiency of 72.0%, was found upon electrolysis of 2.5 L of 0.050 M Na2SO4 at pH 3.0 and 25 mA cm−2. As a crucial finding, Co leaching was negligible. Solutions with 20 mg L−1 of the herbicide bentazon in the same electrolyte could not be mineralized by electrochemical oxidation, whereas photoelectro-Fenton with an UVA lamp and 0.50 mM Fe2+ led to total removal of the herbicide with 77.0% mineralization.

The degradation of the antibiotic thiamphenicol has been studied by photoelectro-Fenton (PEF) process with UVA light using pyrite particles as catalyst source. Pyrite is a sulfide mineral that naturally acidifies the reaction medium and releases Fe

This paper reports the degradation of a solution of 0.314 mM diclofenac (DCF), while using 5–15 mM Oxone as oxidizing agent with the catalytic action of 0.05–0.2 mM Co2+. The best performance was obtained for 10 mM Oxone and 0.2 mM Co2+, achieving the total DCF abatement and 77% removal of chemical oxygen demand after 30 min. Oxidizing of sulfate () and hydroxyl (•OH) radicals was formed by the Co2+/Oxone system. Oxone was firstly oxidized to persulfate ion that was then quickly converted into the above free radicals. For Oxone contents ≥10 mM, the decay of DCF concentration followed a second-order kinetic reaction, but the apparent rate constant changed with the Co2+ concentration used. High-performance liquid chromatography (HPLC) analysis of treated solutions showed the formation of some intermediates, whereas oxalic acid was identified as the prevalent final short-linear carboxylic acid by ion-exclusion HPLC.

An Au-TiO2 photoanode on carbon cloth has been synthesized by microwave-assisted sol-gel method to treat paracetamol solutions at pH 3.0 by photocatalysis (PC), electro-oxidation (EO), photoelectrocatalysis with UVA light (PEC), solar PEC (SPEC) and hybrid methods with photoelectro-Fenton under UVA (PEC + PEF) and sunlight (SPEC + SPEF) irradiation at constant anodic potential (Ean). The photoanode has been characterized by XRD, Raman spectroscopy, HRTEM and SEM-EDS. The counter electrode was a 316L stainless steel plate, which was replaced by an air-diffusion electrode for H2O2 generation in hybrid treatments. The most powerful process was SPEC + SPEF, yielding total paracetamol removal in

The degradation and mineralization ability of electrochemical processes like electro-oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and UVA-assisted photoelectro-Fenton (PEF) has been comparatively studied for solutions of the herbicide S-metolachlor. Solutions of 100 mL have been treated using an undivided cell equipped with an air-diffusion cathode and a boron-doped diamond (BDD) anode. The effect of pH, current density, and Fe2+ and S-metolachlor concentrations has been thoroughly studied. The total organic carbon removal profiles have demonstrated the feasibility of almost overall mineralization by EF and PEF after 9 h at 300 mA. The herbicide decays in both treatments informed about the complexation of Fe(III) ions formed from Fenton’s reaction, which decelerated S-metolachlor removal. However, the high oxidation power of BDD anode allowed the gradual mineralization of such complexes. The identification of chlorinated and non-chlorinated degradation byproducts by GC–MS has allowed the proposal of main degradation routes.

This work compares the ability of physical and chemical treatments, namely adsorption and electrochemical advanced oxidation processes, to remove tyrosol from aqueous medium. Adsorption on graphene nanoplatelets (GNPs) performed much better than a graphite intercalation compound. Adsorption isotherm fit with Freundlich model (R2 = 0.96), which is characteristic of a chemisorption process. Successful electrochemical regeneration enables 5 successive adsorption/regeneration cycles before corrosion of GNPs occurs. Other typical aromatic contaminants that may coexist with tyrosol can be also adsorbed on GNPs. Percentage of regeneration efficiency of GNPs showed a higher affinity towards Lewis acids group compounds and a lower one towards Lewis base. The treatment of 100 mL of 0.723 mM tyrosol solutions in non-chlorinated and chlorinated matrices at pH 3.0 was carried out by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and UVA photoelectro-Fenton (PEF). Trials were made with a BDD anode and an air-diffusion cathode at 10-30 mA cm-2. Hydroxyl radicals formed at the anode from water oxidation and/or in the bulk from Fenton's reaction between added Fe2+ and generated H2O2, along with active chlorine produced in chlorinated medium, were the main oxidants. Tyrosol concentration always decayed following a pseudo-first-order kinetics and its mineralization rose as EO-H2O2 < EF < PEF, more rapidly in the chlorinated matrix. The potent photolysis of intermediates under UVA radiation explained the almost total mineralization achieved by PEF in the latter medium. The effect of current density and tyrosol content on the performance of all processes was examined.

Aqueous mixtures of methyl, ethyl and propyl paraben (MeP, EtP and PrP) prepared in real urban wastewater with low conductivity were treated by solar photoelectro-Fenton (SPEF) process at low input current ( j = 10 mA cm −2 ) using a pre-pilot plant with an electrochemical reactor equipped with an air-diffusion cathode to electrogenerate H 2 O 2 and a boron-doped diamond (BDD) or RuO 2 -based anode. Comparative trials in simulated water matrices with or without Cl − in the absence of natural organic matter (NOM) always led to a slower decay of parabens concentration and total organic carbon (TOC). This was mainly due to the superior regeneration of Fe 2+ from photoreduction of Fe(III) complexes formed with NOM in real wastewater compared to that from Fe(OH) 2+ . In all matrices, a catalyst concentration as low as 0.20 mM Fe 2+ was enough to ensure the production of OH in the bulk from Fenton’s reaction. SPEF with BDD yielded a complete removal of parabens in 180 min and 66% mineralization at 240 min. This gave rise to the greatest mineralization current efficiencies reported so far, up to 1000%, with a low energy consumption of 84 kWh (kg TOC) −1 . The synergy between homogeneous and heterogeneous catalysis, which allowed the efficient dosage of OH and M( OH) at low j , with simultaneous action of high UV power from sunlight justified such a good performance. Analogous apparent rate constants were determined for MeP, EtP and PrP. Slower decays were found with RuO 2 -based anode due to its lower oxidation power. As a result, the MCE was 425% as maximum, but a lower energy consumption of 52 kWh (kg TOC) −1 was needed. Since the role of active chlorine was of minor importance, the formation of toxic, refractory chloroderivatives was minimized. All by-products were transformed into malic, formic and oxalic acids prior to total mineralization.