Monitoring Photo-Fenton and Photo-Electro-Fenton process of contaminants emerging concern by a gas diffusion electrode using Ca10-xFex-yWy(PO4)6(OH)2 nanoparticles as heterogeneous catalyst.

The catalytic performance of modified hydroxyapatite nanoparticles, Ca10-xFex-yWy(PO4)6(OH)2, was applied for the degradation of methylene blue (MB), fast green FCF (FG) and norfloxacin (NOR). XPS analysis pointed to the successful partial replacement of Ca by Fe. Under photo-electro-Fenton process, the catalyst Ca4FeII1·92W0·08FeIII4(PO4)6(OH)2 was combined with UVC radiation and electrogenerated H2O2 in a Printex L6 carbon-based gas diffusion electrode. The application of only 10 mA cm-2 resulted in 100% discoloration of MB and FG dyes in 50 min of treatment at pH 2.5, 7.0 and 9.0. The proposed treatment mechanism yielded maximum TOC removal of ∼80% and high mineralization current efficiency of ∼64%. Complete degradation of NOR was obtained in 40 min, and high mineralization of ∼86% was recorded after 240 min of treatment. Responses obtained from LC-ESI-MS/MS are in line with the theoretical Fukui indices and the ECOSAR data. The study enabled us to predict the main degradation route and the acute and chronic toxicity of the by-products formed during the contaminants degradation.

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.

Hydrogen peroxide electrogeneration from O2 electroreduction: A review focusing on carbon electrocatalysts and environmental applications.

Hydrogen peroxide (H2O2) stands as one of the foremost utilized oxidizing agents in modern times. The established method for its production involves the intricate and costly anthraquinone process. However, a promising alternative pathway is the electrochemical hydrogen peroxide production, accomplished through the oxygen reduction reaction via a 2-electron pathway. This method not only simplifies the production process but also upholds environmental sustainability, especially when compared to the conventional anthraquinone method. In this review paper, recent works from the literature focusing on the 2-electron oxygen reduction reaction promoted by carbon electrocatalysts are summarized. The practical applications of these materials in the treatment of effluents contaminated with different pollutants (drugs, dyes, pesticides, and herbicides) are presented. Water treatment aiming to address these issues can be achieved through advanced oxidation electrochemical processes such as electro-Fenton, solar-electro-Fenton, and photo-electro-Fenton. These processes are discussed in detail in this work and the possible radicals that degrade the pollutants in each case are highlighted. The review broadens its scope to encompass contemporary computational simulations focused on the 2-electron oxygen reduction reaction, employing different models to describe carbon-based electrocatalysts. Finally, perspectives and future challenges in the area of carbon-based electrocatalysts for H2O2 electrogeneration are discussed. This review paper presents a forward-oriented viewpoint of present innovations and pragmatic implementations, delineating forthcoming challenges and prospects of this ever-evolving field.

Exploring the Potential of Heteroatom-Doped Graphene Nanoribbons as a Catalyst for Oxygen Reduction.

In this study, we created a series of N, S, and P-doped and co-doped carbon catalysts using a single graphene nanoribbon (GNR) matrix and thoroughly evaluated the impact of doping on ORR activity and selectivity in acidic, neutral, and alkaline conditions. The results obtained showed no significant changes in the GNR structure after the doping process, though changes were observed in the surface chemistry in view of the heteroatom insertion and oxygen depletion. Of all the dopants investigated, nitrogen (mainly in the form of pyrrolic-N and graphitic-N) was the most easily inserted and detected in the carbon matrix. The electrochemical analyses conducted showed that doping impacted the performance of the catalyst in ORR through changes in the chemical composition of the catalyst, as well as in the double-layer capacitance and electrochemically accessible surface area. In terms of selectivity, GNR doped with phosphorus and sulfur favored the 2e- ORR pathway, while nitrogen favored the 4e- ORR pathway. These findings can provide useful insights into the design of more efficient and versatile catalytic materials for ORR in different electrolyte solutions, based on functionalized carbon.

Decentralized approach toward organic pollutants removal using UV radiation in combination with H2O2-based electrochemical water technologies.

The current literature lacks a comprehensive discussion on the trade-off between pollutant degradation/mineralization and treatment time costs in utilizing UV light in combination with H2O2-based electrochemical advanced oxidation processes (EAOPs). The present study sheds light on the benefits of using the photoelectro-Fenton (PEF) process with UVA or UVC for methylparaben (MetP) degradation in real drinking water. Although light boosts the photodegradation of refractory Fe(III) complexes and the photolysis of H2O2 (with UVC only), the energy-intensive nature of light-based treatments is acknowledged. To help tackle the high energy consumption issue, a novel approach was employed: partial application of UVA or UVC light after a predetermined electro-Fenton electrolysis time. The proposed treatment approach yielded satisfactory comparable results to those obtained from the application of PEF/UVA or PEF/UVC in terms of total organic carbon removal (ca. 100%), with notably lower energy consumption (ca. 50%). The study delves into the combined method's feasibility, analyzing pollutant degradation/mineralization process and overall energy consumption. The research identifies possible degradation routes based on intermediate detection and radical quenching experiments. Finally, toxicological assessments evaluate the toxicity levels of MetP and its intermediates. The findings of this study bring meaningful contributions to the fore and point to the highly promising potential of the proposed approach, in terms of sustainability and cost-effectiveness, when applied for decentralized water treatment.

Highly porous seeding-free boron-doped ultrananocrystalline diamond used as high-performance anode for electrochemical removal of carbaryl from water.

Boron-doped diamond (BDD) electrodes are regarded as the most promising catalytic materials that are highly efficient and suitable for application in advanced electrochemical oxidation processes targeted at the removal of recalcitrant contaminants in different water matrices. Improving the synthesis of these electrodes through the enhancement of their morphology, structure and stability has become the goal of the material scientists. The present work reports the use of an ultranano-diamond electrode with a highly porous structure (B-UNCDWS/TDNT/Ti) for the treatment of water containing carbaryl. The application of the proposed electrode at current density of 75 mA cm-2 led to the complete removal of the pollutant (carbaryl) from the synthetic medium in 30 min of electrolysis with an electric energy per order of 4.01 kWh m-3 order-1. The results obtained from the time-course analysis of the carboxylic acids and nitrogen-based ions present in the solution showed that the concentrations of nitrogen-based ions were within the established maximum levels for human consumption. Under optimal operating conditions, the proposed electrode was successfully employed for the complete removal of carbaryl in real water. Thus, the findings of this study show that the unique, easy-to-prepare BDD-based electrode proposed in this study is a highly efficient tool which has excellent application potential for the removal of recalcitrant pollutants in water.

Using Palladium and Gold Palladium Nanoparticles Decorated with Molybdenum Oxide for Versatile Hydrogen Peroxide Electroproduction on Graphene Nanoribbons.

Electrocatalytic production of H2O2 via a two-electron oxygen reduction reaction (ORR-2e-) is regarded as a highly promising decentralized and environmentally friendly mechanism for the production of this important chemical commodity. However, the underlying challenges related to the development of catalytic materials that contain zero or low content of noble metals and that are relatively more active, selective, and resistant for long-term use have become a huge obstacle for the electroproduction of H2O2 on commercial and industrial scales. The present study reports the synthesis and characterization of low metal-loaded (≤6.4 wt %) catalysts and their efficiency in H2O2 electroproduction. The catalysts were constructed using gold palladium molybdenum oxide (AuPdMoOx) and palladium molybdenum oxide (PdMoOx) nanoparticles supported on graphene nanoribbons. Based on the application of a rotating ring-disk electrode, we conducted a thorough comparative analysis of the electrocatalytic performance of the catalysts in the ORR under acidic and alkaline media. The proposed catalysts exhibited high catalytic activity (ca. 0.08 mA gnoble metal-1 in an acidic medium and ca. 6.6 mA gnoble metal-1 in an alkaline medium), good selectivity (over 80%), and improved long-term stability toward ORR-2e-. The results obtained showed that the enhanced ORR activity presented by the catalysts, which occurred preferentially via the two-electron pathway, was promoted by a combination of factors including geometry, Pd content, interparticle distance, and site-blocking effects, while the electrochemical stability of the catalysts may have been enhanced by the presence of MoOx.

A study of possible substitutes for the endocrine disruptor DEHP in two hormone receptors.

Bis(2-ethylhexyl) phthalate (DEHP) has been widely used for the production of plastics, and the compound has also been found to act as endocrine disruptor. Exposure to DEHP has been found to cause several hormonal problems, including decreased fertility. Due to the environmental and health risks posed by the use of DEHP, the present study employed molecular docking, molecular dynamics, and free energy analyses (MM-GBSA, MM-PBSA, and SIE) aiming at evaluating the action of DEHP and that of two other compounds (ATEC and DL9TH), tested as potential DEHP substitutes, on two hormone receptors (sex hormone-binding globulin - SHBG - and progesterone receptor - PR). The results obtained showed that ATEC may be a good substitute for DEHP in the production of plastics, such as PVC, considering that the compound recorded the greatest free energy values with respect to binding with SHBG (-31.36 kcal/mol obtained from MM-GBSA; -20.28 kcal/mol for MM-PBSA, and -7.40 for SIE) and PR (-36.40 kcal/mol for MM-GBSA; -27.00 kcal/mol for MM-PBSA, and -8.51 kcal/mol for SIE) - this shows that ATEC presented the least activity in the two hormone receptors. The findings of this study provide relevant insights on potential substitutes for DEHP and help shed light on the action of these new efficient substances, which have similar properties to DEHP (ATEC and DL9TH) yet do not act as endocrine disruptors.Communicated by Ramaswamy H. Sarma.

Degradation of antibiotic ciprofloxacin by different AOP systems using electrochemically generated hydrogen peroxide.

The present work reports the degradation of the antibiotic ciprofloxacin (CIP) by different advanced oxidative process systems (UV; Anodic Oxidation; H2O2; H2O2/UV; H2O2/Fe2+ and H2O2/UV/Fe2+) in an electrochemical cell using gas diffusion electrode (GDE) for the synthesis of hydrogen peroxide. CIP degradation and mineralization were evaluated by high efficiency liquid chromatography (HPLC) and total organic carbon (TOC) techniques. Of all the systems investigated, the photoelectro-Fenton system presented the best degradation efficiency; this system promoted highly significant mineralization percentages of 54.8% and 84.6% in 90 and 360 min, and relatively lower energy consumption rates of 4110.0 and 9808.2 kWh kg-1 TOC, respectively. In 6 h period of experiment, the main degradation products of ciprofloxacin were identified, and the aliphatic acids obtained helped confirm the rupture of the aromatic ring. The application of the photoelectro-Fenton process with in situ eletroctrogeneration of H2O2 using GDE has proved to be suitably promising for the treatment of organic pollutants.

Removal of Orange II (OII) dye by simulated solar photoelectro-Fenton and stability of WO2.72/Vulcan XC72 gas diffusion electrode.

The objectives of this study were to determine the viability of removing Orange II (OII) dye by simulated solar photoelectro-Fenton (SSPEF) and to evaluate the stability of a WO2.72/Vulcan XC72 gas diffusion electrode (GDE) and thus determine its best operating parameters. The GDE cathode was combined with a BDD anode for decolorization and mineralization of 350 mL of 0.26 mM OII by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF) at 100, 150 and 200 mA cm-2 and SSPEF at 150 mA cm-2. The GDE showed successful operation for electrogeneration, good reproducibility and low leaching of W. Decolorization and OII decay were directly proportional to the current density (j). AO-H2O2 had a reduced performance that was only half of the SSPEF, PEF and EF treatments. The mineralization efficiency was in the following order: AO-H2O2 < EF < PEF ≈ SSPEF. This showed that the GDE, BDD anode and light radiation combination was advantageous and indicated that the SSPEF process is promising with both a lower cost than using UV lamps and simulating solar photoelectro-Fenton process. The PEF process with the lowest j (100 mA cm-2) showed the best performance-mineralization current efficiency.

Rapid separation of post-blast explosive residues on glass electrophoresis microchips.

This study describes the development of an analytical methodology based on the use of microchip electrophoresis (ME) devices integrated with capacitively coupled contactless conductivity detection (C4 D) for the separation and detection of inorganic anions in post-blast explosive residues. The best separation condition was achieved using a running buffer composed of 35 mmol/L lactic acid, 10 mmol/L histidine and 0.070 mmol/L cetyl(trimethyl ammonium) bromide. For C4 D measurements, the highest sensitivity was obtained applying a 700 kHz sinusoidal wave with excitation voltage of 20 Vpp . The separation of Cl- , NO3- , NO2- , SO42- , ClO4- and ClO3- was performed within ca. 150 s with baseline resolution and efficiencies between 4.4 × 104 and 1.7 × 105 plates/m. The found limits of detection ranged between 2.5 and 9.5 µmol/L. Last, real samples of post-blast explosive residues were analyzed on the ME-C4 D devices obtaining successfully the determination of Cl- , NO3- and SO42- . The achieved concentration values varied between 12.8-72.5 mg/L for Cl- , 1.7-293.1 mg/L for NO3- and 1.3-201.3 mg/L for SO42- . The data obtained using ME-C4 D devices were in good agreement with the concentrations found by ion chromatography. The approach reported herein has provided short analysis time, instrumental simplicity, good analytical performance and low cost. Furthermore, the ME-C4 D devices emerge as a powerful and portable analytical platform for on-site analysis demonstrating to be a promising tool for the crime scene investigation.

Electrochemical and sonoelectrochemical processes applied to amaranth dye degradation.

Amaranth dye is an organic compound largely used in the food and beverage industries with potential toxicity effects on humans. It can be found as a pollutant species in aquatic environments and has been classified as an endocrine disruptor. This study describes amaranth degradation upon ultrasonication associated with an electrochemical system that uses a boron-doped diamond anode BDD, defined as a sonoelectrochemical process. Ninety-minute electrolyses were performed using current densities in the 10-50 mA cm(-2) range, and the concentration decay, pH, energy and current efficiencies, as well as the discoloration rate were evaluated. The amaranth concentration decayed as a function of electrolysis time and the reactions obeyed pseudo first-order kinetics, with an apparent constant rate between 10(-1) and 10(-3)min(-1). The electrochemical and sonoelectrochemical processes at 35 mA cm(-2) yielded TOC removal values between 92.1% and 95.1% respectively, after 90 min. Current efficiency values obtained for both processes were 18.2% and 23.6%. Exhaustive 5h electrolysis was performed and the degradation products were identified by HPLC-MS. A mechanism for the degradation of amaranth was proposed based on an analysis of the aromatic and aliphatic intermediates.

Application of the response surface and desirability design to the Lambda-cyhalothrin degradation using photo-Fenton reaction.

Lambda-cyhalothrin is a potent pyrethroid insecticide used widely in pest management. Detectable levels of the pyrethroid in agricultural watersheds are potentially toxic to aquatic organisms. There is little information in the scientific literature about degradation in aqueous media of the Lambda-cyhalothrin by Advanced Oxidative Process. A mathematical approach for the degradation of this compound has not yet been fully explored… The Central composite design (CCD) and response surface method (RSM) were applied to evaluate and optimize the interactive effects of two operating variables. The initial dosages of H2O2 and Fe(2+) on photo-Fenton degradation of an aqueous solution of Lambda-cyhalothrin in a recirculation flow-through UV photoreactor were used. The remaining concentration of Lambda-cyhalothrin (y1) and the percentage removal of total organic carbon (y2) were the monitored factors since they are dependent parameters of y1 and y2. According to analysis of variances (ANOVA) results, two proposed models can be used to navigate the design space with regression coefficient R(2) - 0.834 and 0.843 for y1 and y2, respectively. A multi-response optimization procedure, based on the global desirability of the factors, was performed to establish the best concentrations of hydrogen peroxide and ferrous sulfate that would allow the most efficient degradation of Lambda-cyhalothrin concomitant with a maximal removal of total organic carbon. The global desirability surface revealed that 0.295 mmol L(-1) of ferrous sulfate and 3.85 mmol L(-1) of hydrogen peroxide were close to the optimum conditions to satisfy both factors simultaneously using minimal amounts of reagents. These photo-Fenton conditions promoted 100% of Lambda-cyhalothrin degradation and 79.83% TOC removal (mineralization) in 120 min of reaction time.

Electrochemical detection of carbamate pesticides in fruit and vegetables with a biosensor based on acetylcholinesterase immobilised on a composite of polyaniline-carbon nanotubes.

A sensitive electrochemical acetylcholinesterase (AChE) biosensor was successfully developed on polyaniline (PANI) and multi-walled carbon nanotubes (MWCNTs) core-shell modified glassy carbon electrode (GC), and used to detect carbamate pesticides in fruit and vegetables (apple, broccoli and cabbage). The pesticide biosensors were applied in the detection of carbaryl and methomyl pesticides in food samples using chronoamperometry (CA). The GC/MWCNT/PANI/AChE biosensor exhibited detection limits of 1.4 and 0.95µmolL(-1), respectively, for carbaryl and methomyl. These detection limits were below the allowable concentrations set by Brazilian regulation standards for the samples in which these pesticides were analysed. Reproducibility and repeatability values of 2.6% and 3.2%, respectively, were obtained in the conventional procedure. The proposed biosensor was successfully applied in the determination of carbamate pesticides in cabbage, broccoli and apple samples without any spiking procedure. The obtained results were in full agreement with those from the HPLC procedure.

Photo-Fenton degradation of the insecticide esfenvalerate in aqueous medium using a recirculation flow-through UV photoreactor.

The aim of the study was to evaluate the efficiencies of photo-Fenton (Fe(2+)) and (Fe(3+)) processes in the degradation of high-concentrations of esfenvalerate (in the form of aqueous emulsion of a commercial formulation) using a recirculation flow-through photoreactor irradiated with UV light from a 15 W lamp (254 nm emission peak). The results obtained using a basic photo-Fenton (Fe(2+)) reaction (esfenvalerate 17 mg L(-1); ferrous sulphate 1 mM; hydrogen peroxide 25 mM; pH 2.5) were compared with those acquired when ferrioxalate (1, 3 or 5 mM) served as the iron source. Degradation of the active component of the commercial formulation was significantly greater, and the rate of oxidation more rapid, using a photo-Fenton (Fe(3+)) process compared with its Fe(2+) counterpart. The most efficient degradation of the insecticide (75% in 180 min) was achieved with a reaction mixture containing 5mM ferrioxalate. However, under the same experimental conditions, degradation of pure esfenvalerate preceded much faster (99% in 60 min) and was 100% complete within 180 min reaction time.

Development and application of a highly selective biomimetic sensor for detection of captopril, an important ally in hypertension control.

A biomimetic sensor is proposed as a promising new analytical method for determination of captopril in different classes of samples. The sensor was prepared by modifying a carbon paste electrode with iron (II) phthalocyanine bis(pyridine) [FePc(dipy)] complex. Amperometric measurements in a batch analytical mode were first carried out in order to optimize the sensor response. An applied potential lower than 0.2 V vs Ag|AgCl in 0.1 mol L-1 of TRIS buffer at pH 8.0 provided the best response, with a linear range of 2.5 x 10-5 to 1.7 x 10-4 mol L-1. A detailed investigation of the selectivity of the sensor, employing seventeen other drugs, was also performed. Recovery studies were carried out using biological and environment samples in order to evaluate the sensor's potential for use with these sample classes. Finally, the performance of the biomimetic sensor was optimized in a flow injection (FIA) system using a wall jet electrochemical cell. Under optimized flow conditions, a broad linear response range, from 5.0 x 10-4 to 2.5 x 10-2 mol L-1, was obtained for captopril, with a sensitivity of 210 ± 1 µA L mol-1.

Electrochemical sensor highly selective for estradiol valerate determination based on a modified carbon paste with iron tetrapyridinoporphyrazine.

This work reports the use of iron tetrapyridinoporphyrazine (FeTPyPz) as a highly selective catalyst in the construction of an electrochemical sensor for estradiol valerate (EV) determination. The sensor was prepared by modifying a carbon paste with FeTPyPz. The best results were obtained in a mixture of acetonitrile (MeCN) and 0.1 mol L(-1) phosphate buffer solution (pH 6.0) in a volume ratio of 47 : 53. A linear response range was observed between 45 and 450 micromol L(-1) with a sensitivity of 12160 +/- 306 microA L mol(-1) and quantification and detection limits of 45 and 13 micromol L(-1), respectively. The repeatability, expressed as the relative standard deviation (RSD) for n = 10, was 5.9% ([EV] = 50 micromol L(-1)). The reproducibility (RSD) for the sensor construction was better than 4% and the operational stability (RSD) over 50 measurements was 1.8%. A detailed investigation regarding the selectivity and electrochemical characteristics was carried out. Finally, in a first step to evaluate the application potential of the sensor, it was successfully applied to determine EV in a commercial formulation.