Kinetic and mechanistic analysis of azo dyes decolorization by ZVI-assisted Fenton systems: pH-dependent shift in the contributions of reductive and oxidative transformation pathways

The chemical decolorization of the azo-dye Acid Black 1 (AB1) by ZVI-assisted Fenton systems was investigated for assessing the relative importance of reductive and oxidative pathways. To this end, system evolution was followed by UV–vis, HPLC, CG–MS, TOC and toxicity measurements. The effects of reaction conditions including initial pH, oxidants (O2 and H2O2) concentrations, ZVI loading, and the presence of SO42− were studied. Mechanistic issues were addressed by following H2O2, Fe(II), Fe(III) and pH profiles, as well as by performing experiments in the presence of iron-complexing agents (o-phenanthroline and EDTA) or reactive species scavengers (2-propanol and DMSO). Results show that AB1 reduction occurs through heterogeneous processes with moderate to low pH dependent rates, whereas AB1 oxidation is ruled by the Fenton reaction with significantly pH dependent rates. Mechanistic studies demonstrated that AB1 decolorization in ZVI-assisted Fenton systems involves both oxidative and reductive pathways, whose relative contributions significantly change as the initial pH is raised from 3 to 5. In acidic media, AB1 is mostly transformed by oxidative pathways linked to H2O2 consumption. In contrast, in circumneutral media, a rather inefficient H2O2 consumption leads to similar contributions of oxidative and reductive AB1 transformation pathways. A detailed analysis of the pH dependence of the key reactions involved suggests that the overall system behavior is ruled by a shift in the oxidation mechanism of Fe(II) species, as a consequence of the development of a thigh corrosion layer onto ZVI particles at circumneutral pH values.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Kinetic and mechanistic analysis of azo dyes decolorization by ZVI-assisted Fenton systems: pH-dependent shift in the contributions of reductive and oxidative transformation pathways

The chemical decolorization of the azo-dye Acid Black 1 (AB1) by ZVI-assisted Fenton systems was investigated for assessing the relative importance of reductive and oxidative pathways. To this end, system evolution was followed by UV–vis, HPLC, CG–MS, TOC and toxicity measurements. The effects of reaction conditions including initial pH, oxidants (O2 and H2O2) concentrations, ZVI loading, and the presence of SO42− were studied. Mechanistic issues were addressed by following H2O2, Fe(II), Fe(III) and pH profiles, as well as by performing experiments in the presence of iron-complexing agents (o-phenanthroline and EDTA) or reactive species scavengers (2-propanol and DMSO). Results show that AB1 reduction occurs through heterogeneous processes with moderate to low pH dependent rates, whereas AB1 oxidation is ruled by the Fenton reaction with significantly pH dependent rates. Mechanistic studies demonstrated that AB1 decolorization in ZVI-assisted Fenton systems involves both oxidative and reductive pathways, whose relative contributions significantly change as the initial pH is raised from 3 to 5. In acidic media, AB1 is mostly transformed by oxidative pathways linked to H2O2 consumption. In contrast, in circumneutral media, a rather inefficient H2O2 consumption leads to similar contributions of oxidative and reductive AB1 transformation pathways. A detailed analysis of the pH dependence of the key reactions involved suggests that the overall system behavior is ruled by a shift in the oxidation mechanism of Fe(II) species, as a consequence of the development of a thigh corrosion layer onto ZVI particles at circumneutral pH values.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Kinetic and mechanistic analysis of azo dyes decolorization by ZVI-assisted Fenton systems: pH-dependent shift in the contributions of reductive and oxidative transformation pathways

The chemical decolorization of the azo-dye Acid Black 1 (AB1) by ZVI-assisted Fenton systems was investigated for assessing the relative importance of reductive and oxidative pathways. To this end, system evolution was followed by UV–vis, HPLC, CG–MS, TOC and toxicity measurements. The effects of reaction conditions including initial pH, oxidants (O2 and H2O2) concentrations, ZVI loading, and the presence of SO42− were studied. Mechanistic issues were addressed by following H2O2, Fe(II), Fe(III) and pH profiles, as well as by performing experiments in the presence of iron-complexing agents (o-phenanthroline and EDTA) or reactive species scavengers (2-propanol and DMSO). Results show that AB1 reduction occurs through heterogeneous processes with moderate to low pH dependent rates, whereas AB1 oxidation is ruled by the Fenton reaction with significantly pH dependent rates. Mechanistic studies demonstrated that AB1 decolorization in ZVI-assisted Fenton systems involves both oxidative and reductive pathways, whose relative contributions significantly change as the initial pH is raised from 3 to 5. In acidic media, AB1 is mostly transformed by oxidative pathways linked to H2O2 consumption. In contrast, in circumneutral media, a rather inefficient H2O2 consumption leads to similar contributions of oxidative and reductive AB1 transformation pathways. A detailed analysis of the pH dependence of the key reactions involved suggests that the overall system behavior is ruled by a shift in the oxidation mechanism of Fe(II) species, as a consequence of the development of a thigh corrosion layer onto ZVI particles at circumneutral pH values.Fil: Donadelli, Jorge Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Carlos, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Arques, Antonio. Universidad Politécnica de Valencia; EspañaFil: Garcia Einschlag, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Planificación de una unidad didáctica : el estudio del movimiento

In this study we attempt to apply an outline of Teaching Units for the study of Cinematics at Secondary Level. Having analysed the teaching problems indicated by teachers, the scientific contents involved and the methodological problems, a sequence of learning contents is established from a creative construction perspective

EEM-PARAFAC as a convenient methodology to study fluorescent emerging pollutants degradation: (fluoro)quinolones oxidation in different water matrices

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Enhancement of Iron-Based Photo-Driven Processes by the Presence of Catechol Moieties

Photo-induced Advanced Oxidation Processes (AOPs) using H2O2 or S2O82- as radical precursors were assessed for the abatement of six different contaminants of emerging concern (CECs). In order to increase the efficiency of these AOPs at a wider pH range, the catechol organic functional compound was studied as a potential assistant in photo-driven iron-based processes. Different salinity regimes were also studied (in terms of Cl- concentration), namely low salt water (1 g center dot L-1) or a salt-water (30 g center dot L-1) matrix. Results obtained revealed that the presence of catechol could efficiently assist the photo-Fenton system and partly promote the photo-induced S2O82- system, which was highly dependent on salinity. Regarding the behavior of individual CECs, the photo-Fenton reaction was able to enhance the degradation of all six CECs, meanwhile the S2O82--based process showed a moderate enhancement for acetaminophen, amoxicillin or clofibric acid. Finally, a response-surface methodology was employed to determine the effect of pH and catechol concentration on the different photo-driven processes. Catechol was removed during the degradation process. According to the results obtained, the presence of catechol in organic macromolecules can bring some advantages in water treatment for either freshwater (wastewater) or seawater (maritime or aquaculture industry)

Effect of Salinity on UVA-Vis Light Driven Photo-Fenton Process at Acidic and Circumneutral pH

In the present work, the treatment of a mixture of six emerging pollutants (acetamiprid, acetaminophen, caffeine, amoxicillin, clofibric acid and carbamazepine) by means of photo-Fenton process has been studied, using simulated sunlight as an irradiation source. Removal of these pollutants has been investigated in three different aqueous matrices distinguished by the amount of chlorides (distilled water, 1 g L-1 of NaCl and 30 g L-1 of NaCl) at a pH of 2.8 and 5.0. Interestingly, the presence of 1 g L-1 was able to slightly accelerate the pollutants removal at pH = 5, although the reverse was true at pH = 2.8. This is attributed to the pH-dependent interference of chlorides on photo-Fenton process, that is more acute in an acidic medium. As a matter of fact, the fastest reaction was obtained at pH = 3.5, in agreement with literature results. Monitoring of hydrogen peroxide consumption and iron in solution indicates that interference with chlorides is due to changes in the interaction between iron and the peroxide, rather than a scavenging effect of chloride for hydroxyl radicals. Experiments were also carried out with real seawater and showed higher inhibition than in the NaCl experiments, probably due to the effect of different dissolved salts present in natural water

Urban biowaste-derived sensitizing materials for caffeine photodegradation

[EN] Caffeine-photosensitized degradation has been studied in the presence of bio-based materials derived from urban biowaste after aerobic aging. A peculiar fraction (namely bio-based substances (BBSs)), soluble in all the pH range, has been used as photosensitizing agent. Several caffeine photodegradation tests have been performed, and positive results have been obtained in the presence of BBSs and H2O2, without and with additional Fe(II) (photo-Fenton-like process). Moreover, hybrid magnetite-BBS nanoparticles have been synthesized and characterized, in order to improve the sensitizer recovery and reuse after the caffeine degradation. In the presence of such nanoparticles and H2O2 and Fe(II), the complete caffeine degradation has been attained in very short time. Both homogeneous and heterogeneous processes were run at pH = 5, milder condition compared to the classic photo-Fenton process.This work was performed with the financial support for academic interchange by the Marie Sklodowska-Curie Research and Innovation Staff Exchange project funded by the European Commission H2020-MSCA-RISE-2014 within the framework of the research project MAT4TREAT (project number 645551). Compagnia di San Paolo and University of Torino are gratefully acknowledged for funding Project Torino_call2014_L2_126 through BBando per il finanziamento di progetti di ricerca di Ateneo – anno 2014 (Project acronym: Microbusters). Additionally, authors would like to acknowledge Dr. Flavio R. Sives (La Plata, Argentina) for magnetization measurements.Prevot, AB.; Baino, F.; Fabbri, D.; Franzoso, F.; Magnacca, G.; Nistico, R.; Arques Sanz, A. (2017). Urban biowaste-derived sensitizing materials for caffeine photodegradation. Environmental Science and Pollution Research. 24(14):12599-12607. https://doi.org/10.1007/s11356-016-7763S1259912607241