Improved Operation of Chloralkaline Reversible Cells with Mixed Metal Oxide Electrodes Made Using Microwaves.

This study focuses on the synthesis of mixed metal oxide anodes (MMOs) with the composition Ti/RuO2Sb2O4Ptx (where x = 0, 5, 10 mol) using hybrid microwave irradiation heating. The synthesized electrodes were characterized using scanning electron microscopy, X-ray energy-dispersive analysis, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. These electrodes were then evaluated in both bulk electrolytic and fuel cell tests within a reversible chloralkaline electrochemical cell. The configurations using the electrodes Ti/(RuO2)0.7-(Sb2O4)0.3 and Ti/(RuO2)66.5-(Sb2O4)28.5-Pt5 presented lower onset potential for oxygen and chlorine evolution reactions and reduced resistance to charge transfer compared to the Ti/(RuO2)63-(Sb2O4)27-Pt10 variant. These electrodes demonstrated notable performance in reversible electrochemical cells, achieving Coulombic efficiencies of up to 60% when operating in the electrolytic mode at current densities of 150 mA cm-2. They also reached maximum power densities of 1.2 mW cm-2 in the fuel cell. In both scenarios, the presence of platinum in the MMO coating positively influenced the process. Furthermore, a significant challenge encountered was crossover through the membranes, primarily associated with gaseous Cl2. This study advances our understanding of reversible electrochemical cells and presents possibilities for further exploration and refinement. It demonstrated that the synergy of innovative electrode synthesis strategies and electrochemical engineering can lead to promising and sustainable technologies for energy conversion.

Toxicological aspect of water treated by chlorine-based advanced oxidation processes: A review.

As well established in the literature, residual toxicity is an important parameter for evaluating the sanitary and environmental safety of water treatment processes, and this parameter becomes even more crucial when chlorine-based processes are applied for water treatment. Eliminating initial toxicity or preventing its increase after water treatment remains a huge challenge mainly due to the formation of highly toxic disinfection by-products (DBPs) that stem from the degradation of organic contaminants or the interaction of the chlorine-based oxidants with different matrix components. In this review, we present a comprehensive discussion regarding the toxicological aspects of water treated using chlorine-based advanced oxidation processes (AOPs) and the recent findings related to the factors influencing toxicity, and provide directions for future research in the area. The review begins by shedding light on the advances made in the application of free chlorine AOPs and the findings from studies conducted using electrochemical technologies based on free chlorine generation. We then delve into the insights and contributions brought to the fore regarding the application of NH2Cl- and ClO2-based treatment processes. Finally, we broaden our discussion by evaluating the toxicological assays and predictive models employed in the study of residual toxicity and provide an overview of the findings reported to date on this subject matter, while giving useful insights and directions for future research on the topic.

Recent advances on modified reticulated vitreous carbon for water and wastewater treatment - A mini-review.

Recently, modifications on reticulated vitreous carbon (RVC) have attracted attention as a promising strategy to produce low-cost, stable, and highly active electrodes leading to significant advances in the water/wastewater treatment field compared with raw RVC. Modified RVC materials have been used as cathode, anode, and membrane. Improvements on physical and electrocatalytic properties are achieved by RVC modification via diverse strategies, including the deposition of metal oxides, the introduction of surface functional groups, and the formation of composites, which were used to remove organic contaminants and pathogens from water matrices, as summarized in this mini-review. This mini-review mainly focused on papers published from 2015 to 2020 that reported modified RVC electrodes to eliminate pollutants and pathogens from water matrices by electrochemical advanced oxidation processes. Likewise, news challenges and opportunities are discussed, and perspectives for the ongoing and future studies in this research field are also given.

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.

Improved 4-nitrophenol removal at Ti/RuO2-Sb2O4-TiO2 laser-made anodes.

In this study, binary and ternary mixed metal oxide anodes of Ti/RuO2-Sb2O4 and Ti/RuO2-Sb2O4-TiO2 were prepared using two different heating methods: conventional furnace and alternative CO2 laser heating. The produced anodes were physically and electrochemically characterized by using different techniques. The main difference found in the laser-made anodes was their more compact morphology, without the common deep cracks found in anodes made by typical thermal decomposition, which showed an important correlation with the prolonged accelerated service life. The correlation between the physicochemical properties of the anodes with their performance towards the 4-nitrophenol oxidations is discussed. The results demonstrated that the ternary anode (Ti/RuO2-Sb2O4-TiO2) is very promising, presenting a kinetic 5.7 times faster than the respective binary anode and the highest removal efficiency when compared with conventionally made anodes. Also, the lowest energy consumption per unit of mass of contaminant removed is seen for the laser-made Ti/RuO2-Sb2O4-TiO2 anode, which evidences the excellent cost-benefit of this anode material. Finally, some by-products were identified, and a degradation route is proposed. Graphical abstract.

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.

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.