Photoelectrolysis of clopyralid wastes with a novel laser-prepared MMO-RuO2TiO2 anode

This paper studies the applicability of a novel laser-prepared mixed metal oxide (MMO-RuO2TiO2) anode in the photoelectrochemical degradation of clopyralid, a toxic and biorefractory herbicide. Results are compared to those obtained using the well-known boron-doped diamond (BDD) anode and demonstrate that, although the electrolysis with diamond is more effective than that obtained with the new electrode, the irradiation of UVC light makes the novel MMO material more effective in chloride media. It was explained in terms of the homolysis of hypochlorous acid/hypochlorite to form chloride and hydroxyl radicals. Photoelectrochemical degradation with MMO produced a marked synergistic effect in TOC removal, especially in the presence of chloride ions. On the contrary, for the BDD anode, at the tested conditions, antagonisms were found in both sulfate and chloride media. These important synergisms allows finding conditions in which the novel anode can be competitive with the BDD

Biodegradability improvement of clopyralid wastes through electrolysis using different diamond anodes

The use of boron-doped (BDDs) anodes for efficient removal of complex organic molecules, such as organochlorine compounds, is well stated in the literature. However, the role of the different characteristics of this anode on the transformation of these type of contaminants into more biodegradable molecules is a topic of interest that need to be clarified when aimed an efficient combination of an electrochemical system as a previous step to biological treatment. In this work, improvement in the biodegradability of synthetic wastes polluted with clopyralid, as an organochlorine model compound, is studied after electrolysis with different BDDs in the presence of the two most common supporting electrolytes (containing sulfate or chloride ions). For that, clopyralid removal, mineralization, aromatics intermediates, short-chain carboxylic acids, and inorganic ions were monitored. Improved results were found in sulfate media for BDD with 200 ppm, capable of removing 88.7% of contaminants and 85% of TOC, resulting in an improvement in biodegradability of almost 7-fold compared to the initial sample. These findings point out that lower doping levels are preferable when coupling studied technologies

Testing the role of electrode materials on the electro-Fenton and photoelectro-Fenton degradation of clopyralid

This work studies the effect of the anode and cathode materials on the degradation of the herbicide clopyralid. Different electrochemical advanced oxidation processes (EAOPs), including electrochemical oxidation with electrogenerated hydrogen peroxide (EO-H2O2), electro-Fenton (EF), and photoelectro-Fenton (PEF) were carried out. The first experiments were focused on the effect of the cathode, where the use of the hydrophobic carbon felt modified by the deposition of carbon black & PTFE mixture (MCF) improves the H2O2 production in comparison to a conventional carbon felt (CF), regardless of the anode material employed. On the other hand, a laser-made Ti/Ru0.3Ti0.7O2 mixed metal oxide (MMO) and a commercial boron-doped diamond (BDD) were compared as anodes. Results obtained point out that the MMO anode promotes the accumulation of this oxidant (H2O2) in bulk. Once characterized by the production of hydrogen peroxide, the second part of this study focused on the degradation of clopyralid with the MCF cathode with different EAOPs. Results demonstrate that clopyralid fastly degrades in the sequence EO-H2O2 < EF < PEF, and almost complete mineralization occurs for EF and PEF employing MMO or BDD as the anode. Synergy effect study shows that irradiation of 9 W UVC produces a positive synergistic effect of 81.7% and 41.55% (for the PEF-MMO and PEF-BDD, respectively), ascribed to the additional removal of aromatic intermediates by the UVC and the activation of H2O2. At the end of the treatment, mineralization of the herbicide was attained at 1.22 kW h (g−1 TOC). Finally, considering the lower cost of the prepared MMO, these findings demonstrate the potentiality of using modified carbon felt combined with the laser-made Ti/Ru0.3Ti0.7O2 anode for the treatment of polluted waters

Understanding the electrolytic generation of sulfate and chlorine oxidative species with different boron-doped diamond anodes

The electrochemical generation of several oxidative species was studied at the surfaces of five commercial boron-doped diamond anodes with different doping levels (100–8000 ppm). These insights can open the possibility of tailoring anodes for a more efficient application in environmental remediation processes. All materials evaluated were characterized by linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, contact angle, and scanning electron microscopy, as well as by bulk electrolysis. As a result, it was confirmed that the boron doping level influences the physical and electrochemical properties of the electrodes, indicating distinct behavior of the electrodes on the production of chlorine and sulfate oxidative species. The higher the boron doping, the lower is the crystallite size, and the higher is the conductivity, the hydrophilic behavior, and the electron-transfer activity. Voltammetric characterization demonstrates that low boron doping favors the formation of hydroxyl radicals, while high doping levels favor the direct electrochemical oxidation of sulfate or chloride. Moreover, when operating at high overpotentials in bulk electrolysis (typical conditions in environmental applications), the formation of chlorine and sulfate oxidative species is favored at low boron doping levels. This behavior is attributed to the very efficient mediated formation of these oxidants from the hydroxyl radicals, whose production is promoted with these electrodes at those conditions. It means that only operating at much softer conditions, the unique direct generation of hydroxyl oxidant occurs, opening a way for the potential prevention of perchlorate formation during disinfection by using highly boron-doped diamond anodes

New laser-based method for the synthesis of stable and active Ti/SnO2–Sb anodes

The main drawback impairing the application of highly electrocatalytic SnO2–Sb anodes in the removal of recalcitrant pollutants from wastewater is their short service life. Here, we report the synthesis of Ti/SnO2–Sb anodes with improved stability through a CO2 laser as the primary heating source. The influence of different calcination temperatures (400, 500, 600 °C), and varied composition of the solvent in the precursor solution, on the stability and activity of the anodes, were investigated. Notably, the use of the CO2 laser heating method at 600 °C improves the service life up to 5-fold as compared to the conventionally prepared anodes. The laser-made Ti/SnO2–Sb anode calcined at 600 °C exhibits the best electrocatalytic performance with the fastest color removal rates in the oxidation of methylene blue dye. Therefore, for the first time, Ti/SnO2–Sb anodes with superior properties were produced by a fast method employing CO2 laser, envisaging its future applications in wastewater treatment

Improving biodegradability of clopyralid wastes by photoelectrolysis: The role of the anode material

In this work, the removal of the non-readily biodegradable herbicide clopyralid by electrochemical (EC) and photoelectrochemical (PhEC) oxidation with different anode materials were conducted looking to improve not only its oxidation but also its biodegradability. First, in order to find out optimal conditions, it was carried out EC and PhEC degradations in chloride medium, at current densities ranging from 30 to 100 mA cm−2 during 1 h (0.8–2.7 A h L−1), using as anodes MMO-RuO2TiO2, MMO-RuO2IrO2, MMO-IrO2Ta2O5 and boron-doped diamond (BDD). Results show better efficiencies on clopyralid removal for MMO-RuO2IrO2 and BDD anodes at lower current densities. Then, the influence of all anodes on clopyralid transformation was evaluated, extending the electrolysis and photoelectrolysis for 8 h applying 30 mA cm−2 (6.4 A h cm−3). At these conditions, better outcomes are observed for PhEC degradation, where complete pollutant removal is attained for BDD anode and 88.7% for MMO-RuO2IrO2, while COD removal is 47.7% for MMO and 43.1% for BDD anode. Then, short-term biodegradability tests, conducted for EC and PhEC processes, pointed out that MMO-RuO2TiO2 is the most promising anode material, being capable of improving biodegradability in 48.2% and 53% for EC and PhEC degradation, respectively. The toxicity of treated solutions using MMO-RuO2TiO2 and BDD anodes in both EC and PhEC degradation were compared, employing the inhibitory effect in the bioluminescence of marine bacteria Vibrio Fisheri. Toxicity assessments show that toxicity significantly reduces by using the MMO-RuO2TiO2 in NaCl and Na2SO4 medium for both processes. Finally, this study demonstrates that photoelectrolysis with MMO anodes was the most effective strategy in order to increase biodegradability in chloride media, as well as to reduce the toxicity of the treated waste

Enhancement of wastewater treatment using novel laser-made Ti/SnO2–Sb anodes with improved electrocatalytic properties

In this study, a novel Ti/SnO2–Sb anode, improved using a laser heating manufacturing procedure, was applied in wastewater treatment. For comparison purposes, similar anodes were manufactured using the conventional furnace heating procedure. Electrochemical characterizations in the background electrolyte confirmed that the novel material has improved electric conductivity, as compared to the furnace-made one and, hence, it may lead to much lower operating costs in real applications. The electrocatalytic properties of the novel anode in comparison with the conventional were evaluated using a standard and well-known reaction: the phenol oxidation. Different operational conditions were evaluated. Concentrations of phenol were monitored by HPLC and analysis of organic matter by TOC analyzer. The best condition of phenol removal was associated with a relatively low energy consumption of 0.80 kWh (gTOC)−1 and specific electrical energy consumption of 0.81 kWh m−3 order−1. Interestingly, the phenol is not completely removed after 60 min of treatment using the furnace-made anode under the same operating conditions in which was fully depleted with the new electrode. Moreover, chlorinated by-products remained in the final solution with the conventional electrode and were exhausted with the novel one. Finally, after an extensive comparison with literature about the oxidation of phenol, the Ti/SnO2–Sb produced by laser-manufacturing procedure presented the best phenol removal as compared with both non-active and active anodes

Towards a higher photostability of ZnO photo-electrocatalysts in the degradation of organics by using MMO substrates

In this work, it is proposed a novel strategy to increase the photostability of the ZnO photoelectrocatalyst under prolonged light irradiation, without the addition or deposition of metals and/or semiconductor oxides during their synthesis. This strategy is based on the use of a mixed metal oxide (MMO-Ru0.3Ti0.7O2) coating as the substrate for the electrodeposition of ZnO. To assess it, the electrodeposition of ZnO films on Ti and Ti/MMO substrates and the photoelectrocatalytic activity of these materials for the degradation of the herbicide clopyralid were studied. The results showed that the substrate directly influenced the photo-stability of the ZnO film. Under the incidence of UV light and polarization, the novel Ti/MMO/ZnO electrode showed greater photocurrent stability as compared to Ti/ZnO, which is a very important outcome because the behavior of these electrodes was similar when compared in terms of the degradation of clopyralid. Single electrolysis was not able to degrade efficiently clopyralid at the different potentials studied. However, the irradiation of UV light on the polarized surface of the Ti/ZnO and Ti/MMO/ZnO electrodes increased markedly the degradation rate of clopyralid. A synergistic effect was observed between light and electrode polarization, since the rate of degradation of clopyralid was twice as high in photoelectrocatalysis (PhEC) than in photocatalysis (PhC) and different intermediates were formed. From these results, mechanisms of degradation of clopyralid for the PhC and PhEC systems with the Ti/ZnO and Ti/MMO/ZnO electrodes were presented. Therefore, the Ti/MMO/ZnO electrode could be a cheap and simple alternative to be applied in the efficient photodegradation of organic pollutants, presenting the great advantage of having a facile synthesis and high capacity to work at relatively low potentials.En este trabajo se propone una estrategia novedosa para incrementar la fotoestabilidad del fotoelectrocatalizador de ZnO bajo irradiación de luz prolongada, sin la adición o deposición de metales y / o óxidos semiconductores durante su síntesis. Esta estrategia se basa en el uso de un óxido de metal mixto (MMO-Ru 0.3 Ti 0.7 O 2) revestimiento como sustrato para la electrodeposición de ZnO. Para evaluarlo se estudió la electrodeposición de películas de ZnO sobre sustratos de Ti y Ti / MMO y la actividad fotoelectrocatalítica de estos materiales para la degradación del herbicida clopyralid. Los resultados mostraron que el sustrato influyó directamente en la fotoestabilidad de la película de ZnO. Bajo la incidencia de la luz ultravioleta y la polarización, el nuevo electrodo de Ti / MMO / ZnO mostró una mayor estabilidad de fotocorriente en comparación con Ti / ZnO, lo cual es un resultado muy importante porque el comportamiento de estos electrodos fue similar en términos de degradación de clopyralid. La electrólisis simple no fue capaz de degradar eficazmente la clopiralida a los diferentes potenciales estudiados. Sin embargo, la irradiación de luz ultravioleta sobre la superficie polarizada de los electrodos de Ti / ZnO y Ti / MMO / ZnO aumentó notablemente la tasa de degradación del clopiralida. Se observó un efecto sinérgico entre la luz y la polarización del electrodo, ya que la tasa de degradación de clopiralida fue dos veces mayor en fotoelectrocatálisis (PhEC) que en fotocatálisis (PhC) y se formaron diferentes intermedios. A partir de estos resultados, se presentaron los mecanismos de degradación de clopiralida para los sistemas PhC y PhEC con los electrodos Ti / ZnO y Ti / MMO / ZnO. Por tanto, el electrodo Ti / MMO / ZnO podría ser una alternativa barata y sencilla para ser aplicada en la fotodegradación eficiente de contaminantes orgánicos, presentando la gran ventaja de tener una síntesis fácil y alta capacidad para trabajar a potenciales relativamente bajos. Se observó un efecto sinérgico entre la luz y la polarización del electrodo, ya que la tasa de degradación de clopiralida fue dos veces mayor en fotoelectrocatálisis (PhEC) que en fotocatálisis (PhC) y se formaron diferentes intermedios. A partir de estos resultados, se presentaron los mecanismos de degradación de clopiralida para los sistemas PhC y PhEC con los electrodos Ti / ZnO y Ti / MMO / ZnO. Por tanto, el electrodo Ti / MMO / ZnO podría ser una alternativa barata y sencilla para ser aplicada en la fotodegradación eficiente de contaminantes orgánicos, presentando la gran ventaja de tener una síntesis fácil y alta capacidad para trabajar a potenciales relativamente bajos. Se observó un efecto sinérgico entre la luz y la polarización del electrodo, ya que la tasa de degradación de clopiralida fue dos veces mayor en fotoelectrocatálisis (PhEC) que en fotocatálisis (PhC) y se formaron diferentes intermedios. A partir de estos resultados, se presentaron los mecanismos de degradación de clopiralida para los sistemas PhC y PhEC con los electrodos Ti / ZnO y Ti / MMO / ZnO. Por tanto, el electrodo Ti / MMO / ZnO podría ser una alternativa barata y sencilla para ser aplicada en la fotodegradación eficiente de contaminantes orgánicos, presentando la gran ventaja de tener una síntesis fácil y alta capacidad para trabajar a potenciales relativamente bajos. dado que la tasa de degradación de clopiralida fue dos veces más alta en fotoelectrocatálisis (PhEC) que en fotocatálisis (PhC) y se formaron diferentes intermedios. A partir de estos resultados, se presentaron los mecanismos de degradación de clopiralida para los sistemas PhC y PhEC con los electrodos Ti / ZnO y Ti / MMO / ZnO. Por tanto, el electrodo Ti / MMO / ZnO podría ser una alternativa barata y sencilla para ser aplicada en la fotodegradación eficiente de contaminantes orgánicos, presentando la gran ventaja de tener una síntesis fácil y alta capacidad para trabajar a potenciales relativamente bajos. dado que la tasa de degradación de clopiralida fue dos veces más alta en fotoelectrocatálisis (PhEC) que en fotocatálisis (PhC) y se formaron diferentes intermedios. A partir de estos resultados, se presentaron los mecanismos de degradación de clopiralida para los sistemas PhC y PhEC con los electrodos Ti / ZnO y Ti / MMO / ZnO. Por tanto, el electrodo Ti / MMO / ZnO podría ser una alternativa barata y sencilla para ser aplicada en la fotodegradación eficiente de contaminantes orgánicos, presentando la gran ventaja de tener una síntesis fácil y alta capacidad para trabajar a potenciales relativamente bajos

Platinum: A key element in electrode composition for reversible chloralkaline electrochemical cells

In this work, the performance of a reversible electrochemical cell using three different electrodes (Ti/Ru0.5Ir0.5O2, Ti/Ru0.3Ti0.7O2, and Ti/Ru0.3Ti0.6O2Pt0.1) is evaluated and compared for the oxidation of chlorides and reduction of chlorine. Results indicate that this technology is successful and that its efficiency depends significantly on the composition of the electrode in charge of the chlorine electrochemistry. Operating at 0.5 V allows us to obtain near 7 mA cm−2 and power efficiencies around 120 Wh mmol−1 hydrogen supplied. In electrolytic mode, efficiencies around 4 mol Cl2 mWh−1 can be obtained. The best performance is shown by the Ti/Ru0.3Ti0.6O2Pt0.1 electrode resulting from its roughest morphology and the presence of Pt. In shifting from electrolyzer to fuel cell mode, the current produced is rapidly stabilized for Ti/Ru0.3Ti0.6O2Pt0.1 and Ti/Ru0.5Ir0.5O2 electrodes. However, the electrode Ti/Ru0.5Ir0.5O2 showed a progressive change, which suggests a change in its composition that negatively affects the system.En este trabajo se evalúa y compara el desempeño de una celda electroquímica reversible utilizando tres electrodos diferentes (Ti/Ru 0.5 Ir 0.5 O 2 , Ti/Ru 0.3 Ti 0.7 O 2 , y Ti/Ru 0.3 Ti 0.6 O 2 Pt 0.1 ). para la oxidación de cloruros y reducción de cloro. Los resultados indican que esta tecnología es exitosa y que su eficiencia depende significativamente de la composición del electrodo a cargo de la electroquímica del cloro . Operando a 0,5 V nos permite obtener cerca de 7 mA cm −2y eficiencias energéticas de alrededor de 120 Wh mmol- 1 de hidrógeno suministrado. En modo electrolítico se pueden obtener eficiencias en torno a 4 mol Cl 2 mWh− 1 . El electrodo Ti/Ru 0.3 Ti 0.6 O 2 Pt 0.1 presenta el mejor comportamiento debido a su morfología más rugosa ya la presencia de Pt. Al pasar del modo electrolizador al modo de pila de combustible, la corriente producida se estabiliza rápidamente para los electrodos Ti/Ru 0,3 Ti 0,6 O 2 Pt 0,1 y Ti/Ru 0,5 Ir 0,5 O 2 . Sin embargo, el electrodo Ti/Ru0.5 Ir 0.5 O 2 mostró un cambio progresivo, lo que sugiere un cambio en su composición que afecta negativamente al sistema