In this work, the gas diffusion electrode (GDE) cathode of Vulcan XC72 carbon modified with nanoparticles of WO2.72 (WO2.72 / Vulcan XC72) was used for H2O2 electrogeneration and degradation of 350 mL of Orange II (OII) and Sunset Yellow FCF (SY) azo dyes by electro-Fenton (EF) and photoelectro-Fenton (PEF) processes with different Fe2+ initial content (1.00, 0.50 and 0.25 mmol L-1). The WO2.72 / Vulcan XC72 GDE electrolyzed approximately 3 times more H2O2 than the Vulcan XC72 GDE. Decolorizations and mineralizations of the dye solutions were more efficient at higher concentrations of Fe2+. The decolorization decay showed pseudo-first-order kinetics. The most promising decolorization results obtained at processes of WO2.72 / Vulcan XC72 cathode combined with Pt anode (100% color removal of OII and SY at 30 and 20 min of electrolysis with 1.00 mmol L-1 Fe2+, respectively). The best mineralization achieved in trials of WO2.72 / Vulcan XC72 cathode combined with boron-doped diamond (BDD) anode (82% total organic carbon (TOC) removal of OII by PEF / 1.00 after 3 h and 90% TOC removal of SY by PEF / 0.50 after 4 h). It was found that SY decolorization was faster and mineralization showed a similar yield independent of oxidized dye.
Lambda-cyhalothrin is a widely employed pyrethroid insecticide and is potentially toxic to the environment and to human health. Several reports indicate the presence of this insecticide in water samples worldwide, but more data about its behavior in waters and its derivative products are required. This study shows the behavior of the pesticide lambda-cyhalothrin in aqueous solution at different pH and temperature that were simulated by using water contaminated with a toxic concentration of lambda-cyhalothrin and chemical oxidative process. Lambda-cyhalothrin and its derivative products were monitored employing stir bar sorptive extraction (SBSE), using liquid and thermal desorption, combined with gas chromatography coupled with ion trap mass spectrometry (GC-IT-MS) technology. GC-IT-MS enabled the proposal of the lambda-cyhalothrin chemical transformation pathway and the full identification of twelve derivative products. Among them, only 3-phenoxybenzaldehyde is reported as a degradation product of lambda-cyhalothrin, and this compound is an environmental pollutant with endocrine disrupting activity.
This work presents the electrochemical treatment of wastewater of biodiesel production, using DSA based on IrO2 and Nb2O5. The anode was prepared by modified Pechini method and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), in order to evaluate structural and morphological properties and by electrochemical impedance spectroscopy, cyclic voltammetry and accelerated stability test to investigate the electrochemical behavior. The SEM image shows the typical mud-cracked layer. By the XRD measurements, the oxides onto the support were crystallized as tetragonal IrO2 and hexagonal Nb2O5. The amount of glycerin and methanol in the wastewater were 1.60 and 0.31% (w/w), respectively. The electrochemical treatment of the wastewater was evaluated by electrolysis at different current densities and time. The total organic carbon (TOC) and UV-Vis spectra were performed during the electrolysis. The UV-Vis spectra obtained during the electrolysis at 100 and 150 mA cm-2, shows the disappearance of an absorption band at 264 nm and the appearance of one at 290 nm, which the absorption increases as current and the time of the electrolysis increases. The electrochemical treatment with the proposed DSA leads to 80% of removal of TOC by electrolysis at 150 mA cm-2 during the first 6 hours of the electrochemical treatment.
We have studied the treatment of Reactive Black 5 (RP5) and Blue 19 (RA19), which are respectively azo and anthraquinone textile dyes, by electrochemical oxidation using a non commercial boron doped diamond electrode supported on titanium metallic with a relation between B and C equal to 15,000 ppm. Pt was used as counter electrode and Ag/AgCl(sat) was the reference electrode. The variables investigated to optimize the degradation were support electrolyte concentration (0.05, 0.1 and 0.2 mol L-1 of K2SO4), temperature (25, 35 and 45 ºC) and pH (2.5 and 10) by applying a current density of 75 mA cm-2. Total decolorization was observed in all electrochemical conditions studied. The highest rates of mineralization and chromatographic area removal were attained at high support electrolyte concentration due to the increase of conductivity, which caused more generation of hydroxyl radicals. RP5 was degraded at lower electrolysis time than RA19 with smaller requirement of electric charge. The mineralization rate increased in acid medium and at higher temperature since the increase in temperature favors the generation reactions of persulfate. These conditions led to the highest levels of current efficiencies and lower energy consumed.
The pyrethroids, their metabolites and by-products have been recognized as toxic to environment and human health. Despite several studies about esfenvalerate toxicity and its detection in water and sediments, information about its degradation products is still scanty. In this work, esfenvalerate degradation products were obtained by chemical oxidation with hydrogen peroxide and their structure was elucidated using a procedure known as stir bar sorptive extraction (SBSE) probe desorption gas chromatography-ion trap mass spectrometry (GC-IT-MS) analysis. This procedure consists of the thermal desorption of analytes extracted from a SBSE stir bar introduced by a probe into a gas chromatograph (GC) coupled to an ion trap mass spectrometry (IT-MS) system. Based on IT-MS data, a degradation pathway of esfenvalerate is proposed with ten products of chemical oxidation of esfenvalerate that are fully identified. Among these compounds, 3-phenoxybenzoic acid and 3-phenoxybenzaldehyde were detected, reported as being environmental metabolites of some pyrethroids, with endocrine-disrupting activity.
Diuron (DR) and hexazinone (HX) are potent herbicides worldwide consolidated in agricultural practices. In Brazil, their mixed formulation has been intensively applied to cultures of sugar cane crops. However, when detected in agricultural watersheds, these compounds are potentially toxic to aquatic organisms and may be potentially carcinogenic. Advanced oxidation processes (AOP) is an alternative treatment of DR/HX in aqueous environment. In this study, we evaluate the H2O2/UV simultaneous degradation and photolysis process of DR/HX using central composite design. The HX and DR initial concentrations were close to 7 and 20 mg L-1, respectively. In the system, the planning showed that the H2O2 concentration has bigger influence than pH. The optimum degradation conditions (7 mmol L-1 of H2O2 and pH 2.8) provide a total organic carbon removing of 96.4% while the photolysis process only 17.2%. Since neither of the herbicides were detected after 2 min of reaction, it was not possible to differ kinetics degradation process of DR and HX during the process. After the treatment, the toxicity was tested using Vibrio fischeri bioluminescent bacteria and showed a decrease when H2O2/UV is applied. Degradation H2O2/UV was successfully employed, showing excellent performance due to increased mineralization.
Diuron (DR) e hexazinona (HX) são agrotóxicos da classe dos herbicidas muito utilizados na agricultura, sendo que no Brasil, a sua formulação mista é utilizada principalmente na cultura de cana-de-açúcar. Esses compostos são tóxicos aos organismos aquáticos, sendo potencialmente cancerígenos. Os processos oxidativos avançados (AOP) são uma alternativa para o tratamento de DR/HX em ambientes aquosos. Neste estudo, avaliou-se a degradação simultânea de DR/HX via H2O2/UV e fotólise direta utilizando um planejamento experimental do tipo composto central. As concentrações iniciais de HX e DR foram 7 e 20 mg L-1, respectivamente. No sistema, o planejamento indicou que a concentração de H2O2 tem maior influência do que o pH. As condições ótimas de degradação (7 mmol L-1 de H2O2 e pH 2,8) proporcionaram uma remoção de carbono orgânico total de 96,4%, enquanto que o processo de fotólise direta removeu apenas 17,2%. Análises cromatográficas indicaram a remoção completa dos dois agrotóxicos a partir de 2 min de reação, o que impossibilitou a diferenciação da cinética de degradação entre DR e HX. Após o tratamento, a toxicidade foi testada utilizando bactérias Vibrio fischeri bioluminescentes, com uma diminuição com a utilização de H2O2/UV. A degradação via H2O2/UV foi empregada com sucesso, mostrando excelente desempenho devido ao aumento da taxa de mineralização.
The increasing occurrence of antibiotics and their metabolites in surface and ground waters is causing a significant impact on the environment and needing of developing novel treatments for the complete removal of such contaminants. This paper presents the study of the electrogeneration of hydrogen peroxide (H2O2) in acidic medium and the degradation of the analgesic dipyrone in an electrochemical flow reactor using a gas diffusion electrode (GDE) modified with 5.0% cobalt (II) phthalocyanine (CoPc) and pressurized with O2. The highest yield of H2O2 (133 mg L-1) was achieved after 90 min of electrolysis at an applied potential of -2.1 V (vs. Pt//Ag/AgCl/KCl s) and the best results for degradation of dipyrone were obtained under electro-Fenton conditions, where the total organic carbon (TOC) was reduced 62.8% after 90 min of reaction and 49.1 kW h of energy was consumed per kg of dipyrone degraded.
A crescente ocorrência de antibióticos e seus metabólitos estão cada vez maiores em águas superficiais e subterrâneas, causando impactos significativos no meio ambiente e necessitando de desenvolvimento de novos tratamentos para a remoção completa de tais contaminantes. Este trabalho apresenta o estudo da eletrogeração de peróxido de hidrogênio (H2O2) em meio ácido e a degradação do analgésico dipirona em um reator de fluxo eletroquímico usando um eletrodo de difusão gasosa (GDE) modificado com 5,0% ftalocianina de cobalto (II) (CoPc) e pressurizado com O2. A maior produção de H2O2 alcançada foi de 133 mg L-1 a um potencial aplicado de -2,1 V (vs. Pt//Ag/AgCl/KCl s) e os melhores resultados para a degradação da dipirona foram obtidos sob condições eletro-Fenton, em que o carbono orgânico total (TOC) foi reduzido 62,8% após 90 min de reação e 49,1 kW h de energia foi consumida por kg de dipirona degradada.
A simple procedure based on stir bar sorptive extraction and high-performance liquid chromatography-ultraviolet/photodiode array detection (SBSE/LC-UV/PAD) to determine intermediates and by-products of esfenvalerate is described. The influence of organic modifier, ionic strength, extraction time, temperature and pH were simultaneously evaluated by using a factorial experimental design. The utilization of different organic solvents and desorption times were also investigated to establish the optimal conditions for SBSE liquid desorption. Among the ten different peaks (intermediates and by-products) detected after degradation of esfenvalerate, eight (including 3-phenoxybenzoic acid and 3-phenoxybenzaldehyde) were successfully extracted by SBSE under the optimized conditions.
The use of activated carbon powder (ACP), red mud and oxidation with chlorine to remove mefenamic acid in water are described, aimed at their application as a complement to sewage treatment processes in Brazil. A study on the behavior of mefenamic acid in water was performed by evaluating its dissolution for different concentrations and times. Subsequently, the optimal conditions for removal of mefenamic acid were investigated using ACP adsorption at different pH and concentrations, and red mud adsorption using different pH. The utilization of different pH and times was also investigated to establish the ideal conditions for chemical oxidation of the drug. Among the different conditions studied, the best condition for drug removal by ACP and red mud were 100% and 96%, respectively, while the best condition for chemical oxidation occurred using solutions with pH 6 and 7 and reaction times of 30 and 60 minutes.
This work reports the development of GDE for electrogeneration of H2O2 and their application in the degradation process of Reactive Blue 19 dye. GDE produced by carbon black with 20% polytetrafluoroethylene generated up to 500 mg L-1 of H2O2 through the electrolysis of acidic medium at -0.8 V vs Ag/AgCl. Reactive Blue 19 dye was degraded most efficiently with H2O2 electrogenerated in the presence of Fe(II) ions, leading to removal of 95% of the original color and 39% of TOC at -0.8 V vs Ag/AgCl.
Tebuthiuron (TBH) is a herbicide widely used in different cultures and known for its toxic effects. Electrochemical methods are promising for removing pollutants such as pesticides. This study showed the degradation of TBH using a DSA® anode operated at current densities of 50 to 200 mA cm-2. Removal presented pseudo-first order kinetics while high-pressure liquid chromatography (UV detection) showed two peaks, ascribed to degradation intermediates. The maximum percentage of total organic carbon removed was 12.9%. Ion chromatography revealed that higher concentrations of nitrate and nitrite ions formed with increasing current density.
The construction and application of a biomimetic sensor for determination of 4-methylbenzylidene camphor (4-MBC), an ultraviolet (UV) radiation protector, are described. The sensor was prepared by modifying a carbon paste electrode with iron(III) phthalocyanine chloride (FePcCl). Amperometric measurements carried out with the sensor under an applied potential of 0.0 V vs. Ag|AgCl in a mixture of tetrahydrofuran and 0.1 mol L-1 H2SO4 solution (30:70 volume ratio) showed a linear response range from 1.8×10-4 to 9.0×10-4 mol L-1. A detailed selectivity investigation for other nine UV filters was also performed. A sensor response mechanism was proposed and the results for 4-MBC quantification in commercial sunscreens and in water from swimming pools and rivers are presented.
A construção e a aplicação de um sensor biomimético para a determinação de 4-metilbenzilideno cânfora (4-MBC), um protetor de radiação ultravioleta (UV), são descritas. O sensor foi preparado pela modificação de um eletrodo de pasta de carbono com um complexo de cloreto de ferro(III) com ftalocianina, FePcCl. As medidas amperométricas conduzidas com o sensor, sob um potencial aplicado de 0,0 V vs. Ag|AgCl em uma mistura de tetraidrofurano e 0,1 mol L-1 H2SO4 (30:70 em volume), mostraram uma resposta linear no intervalo de 1,8×10-4 to 9,0×10-4 mol L-1. Uma investigação detalhada da seletividade da resposta frente a outros nove filtros UV também foi realizada. Um mecanismo de resposta do sensor foi proposto e os resultados para a quantificação de 4-MBC em protetores solares comerciais e em águas de piscinas e de rios são apresentados.
This paper reports a study of electrochemical degradation of the chloramphenicol antibiotic in aqueous medium using a flow-by reactor with DSA® anode. The process efficiency was monitored by chloramphenicol concentration analysis with liquid chromatography (HPLC) during the experiments. Analysis of Total Organic Carbon (TOC) was performed to estimate the degradation degree and Ion Chromatography (IC) was performed to determinate inorganic ions formed during the eletrochemical degradation process. In electrochemical flow-by reactor, 52% of chloramphenicol was degraded, with 12% TOC reduction. IC analysis showed the production of chloride ions (25 mg L-1), nitrate ions (6 mg L-1) and nitrite ions (4.5 mg L-1).
The study of the electrochemical degradation of the ranitidine was developed using an electrochemical reactor with a gas diffusion electrode (GDE) as cathode. The electrolysis experiments was performed at constant current (1 < A < 10) and flow rate of 200 L h-1. The process of drug degradation, chemical/electrochemical and electro-Fenton ways, using electrochemical reactor showed best efficiency at current values of > 4 A. The process reached a production of 630 mg L-1 of the H2O2 at 7 A. The ranitidine concentrations was reduced in 99.9% (HPLC) and chemical oxygen demand (COD) was reduced in 86.7% by electro-Fenton.
This paper describes a degradation study of the anti-inflammatory sodium diclofenac in aqueous medium using an electro-chemical flow reactor with a gas diffusion electrode as cathode. Two degradation processes were compared: by H2O2 electro-generated and H2O2 electro-generated/Fe(II). Concentration of sodium diclofenac was determined during the experiments by HPLC. The changes in chemical oxigen demand (COD) were also evaluated. Under the specific reaction conditions, 350 mg L-1 of H2O2 was electro-generated and 99.2% of sodium diclofenac was degradated, with 27.4% COD reduction. At the same conditions, but using Fe(II), drug degradation was 99.4% and the COD reduction was 63.2%.