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Fe 3 O 4 nanoparticles supported on graphene (Fe 3 O 4 /graphene) and Printex carbon (Fe 3 O 4 /Printex) are reported as promising catalysts for oxygen reduction reaction (ORR) to H 2 O 2 in alkaline medium. The catalysts were synthesized by a simple precipitation method using NaBH 4 as reducing agent to favor the formation of the magnetite phase. The structure and morphology of the catalysts was evaluated by x-ray diffraction, transmission electron microscopy and small angle electron diffraction. The electrocatalytic activity towards ORR was investigated by means of cyclic and linear voltammetries in 1 mol L −1 KOH. The linear polarization curves highlighted the synergetic effect between the oxide and the carbon supports. Analysis of the polarization curves showed that electro-catalytic activity of the materials towards oxygen reduction expressed by the current density at −0.3 V vs SCE increases from Printex (0.29 mA cm −2 ) < Fe 3 O 4 /Printex (0.38 mA cm −2 ) < graphene (0.85 mA cm −2 ) < Fe 3 O 4 /graphene (1.12 mA cm −2 ). The number of exchanged electrons was close to 2.7 for both catalysts, and the % H 2 O 2 electro-generated above 60% in the −0.2 to −0.7 V ( vs SCE) potential range. Furthermore, both Fe 3 O 4 /graphene and Fe 3 O 4 /Printex catalysts show excellent durability. [ABSTRACT FROM AUTHOR]

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 5 h 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. [ABSTRACT FROM AUTHOR]

Amaranth dye is used widely in the processing of paper, textiles, foods, cosmetics, beverages and medicines, and effluents contaminated with this compound are discharged daily into the environment. Recent studies have shown that azo dyes, especially those such as amaranth dye that have been classified as endocrine disruptors, may cause adverse effects to animal and human health. This paper describes the application of electrochemical oxidation (with a boron-doped diamond BDD thin-film anode) coupled with ultrasound sonolysis (20 kHz and 523 W cm −2 ) to the removal of amaranth dye from dilute alkaline solution. The electrochemical and sonoelectrochemical processes (ECh and SECh, respectively) were carried out at constant current density (10 to 50 mA cm −2 ) in a single compartment cylindrical cell. Sonolysis was virtually less useful for the decolorization and degradation of amaranth dye, whilst ECh and SECh were more effective in degrading the dye with almost complete removal (90 - 95%) attained after 90 min of experiment at an applied current density of 50 mA cm −2 . Degradation of the dye followed pseudo first-order kinetics in both processes, but the rate of reaction was faster with the SECh treatment confirming a synergistic effect between the cavitation process and the electrochemical system. Additionally, at low applied current densities (10 and 25 mA cm −2 ), SECh was considerably more effective than ECh for the amaranth dye mineralization. Although at 35 and 50 mA cm −2 , the two processes showed the respective removal of total organic carbon values: (i) 85% for the ECh and 90% for the SECh at 35 mA cm −2 ; (ii) 96% for the ECh and 98% for the SECh at 50 mA cm −2 . It is concluded that SECh presented the most favorable results for the decontamination of wastewaters containing azo dye compounds. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effluents containing azo food dye amaranth (AM) represent an environmental hazard. [•] Electrodegradation of AM achieved using a modified gas diffusion electrode (MGDE). [•] Decolorization and mineralization of AM was maximal in presence of 0.15mM Fe2+. [•] Energy consumption for removal of total organic carbon was minimal with 0.15mM Fe2+. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen peroxide (H2O2) is a commonly used oxidant with a wide variety of applications in, for example, organic synthesis and wastewater treatment. This paper describes the development of catalysts for the electrogeneration of H2O2 in acidic medium using gas diffusion electrodes (GDE). Initial experiments were performed using rotating ring-disk electrodes modified with microporous layers of Printex 6L carbon containing various amounts of cobalt (II) phthalocyanine (CoPc) in order to evaluate catalytic activities. The results showed that the current efficiency for the formation of H2O2 increased from 69.7% for Printex 6L carbon without catalyst to 81.5% when using Printex 6L carbon with CoPc, and this was accompanied by a decrease in the number of electrons involved in the oxygen reduction reaction from 2.6 to 2.3. Based on these findings, modified GDEs were constructed containing 3.0, 5.0 and 10.0% of CoPc on Printex 6L carbon. The concentration of H2O2 that formed after 90min electrolysis with the GDE modified with Printex 6L carbon alone was 176mgL−1, while the GDE with 5.0% CoPc on carbon produced 331mgL−1 of H2O2, i.e. an increase in yield of 89.1% relative to Printex 6L carbon. Additionally, using GDE s modified with CoPc on carbon, the potential at which H2O2 formation attained its maximum value shifted to less negative values in comparison with electrodes without catalyst. It is concluded that CoPc is an appropriate catalyst for efficient electrogeneration of H2O2. [Copyright &y& Elsevier]

• Fe 3 O 4 nanoparticles were used as a heterogeneous catalyst. • The dye was degraded by photo electro-Fenton and solar Photoelectro-Fenton process. • Fe2+ ions were used as a catalyst for the electrodegradation process. • The dye was significantly removed by solar Photoelectro-Fenton process. • Fe 3 O 4 nanoparticles were reused for 8 consecutive cycles of degradation. This work describes the study of sunset yellow (SY) dye degradation based on the heterogeneous electro-Fenton (EF) process, where Fe 3 O 4 NPs were used as heterogeneous catalysts. The electrochemical system used was an undivided electrochemical cell with single compartment and a gas diffusion electrode (GDE) was used as a working electrode. The SY dye samples were analyzed by UV–vis spectrophotometry, high performance liquid chromatography (HPLC) and total organic carbon (TOC). Fe 3 O 4 NPs were synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N 2 -physisorption analysis. For the Photoelectro-Fenton (PEF) process, the concentration decay of SY dye was 80 and 99 % in the presence of 0.1 mol L−1 Na 2 SO 4 and 0.13 mol L−1 NaCl respectively. The results of TOC removal, showed that ∼50 % of mineralization was achieved at 90 min. For the solar Photoelectro-Fenton process (SPEF) there was high catalytic yield, i.e., 98.7 % of color removal, 100 % of concentration decay and 71 % of TOC removal at 90 min. of electrolysis. The Fe 3 O 4 NPs stability was confirmed after eight consecutive degradation cycles, showing that there is no loss of catalytic activity at the end of the last cycle. The results obtained by XRD analysis showed that there was no structural alteration in the crystallography of the NPs after 5 h of degradation in both electrolytes. There was no dissolution of Fe2+ ions at the end of electrolysis when the SY dye was subjected to the degradation by EF, PEF and SPEF processes. [ABSTRACT FROM AUTHOR]

This work developed efficient heterogeneous catalysts for the methylene blue (MB) dye degradation under photo-Fenton-like conditions. The material was modified to incorporate Fe(III) into ZnO, creating Fe/ZnO strucuture, and applied as heterogeneous catalysts at various pH levels. SEM analysis revealed an agglomerated and plate-like morphology of the synthesized catalysts. The enhanced structure facilitated a removal efficiency of 96.2% for MB dye when employing the photo-Fenton-based process using 5.0% Fe/ZnO catalyst. The high removal efficiency is attributed to the synergy between ≡Fe(III) and ≡Zn(II), which promotes the generation of photoradical species through the Fenton effect. Real water matrices served as a source of MB dye contamination, exhibiting minimal interference and achieving ∼100 % of removal. Scavenger studies indicate that •OH and e⁻ are the primary contributors to the high MB dye degradation efficiency. Additionally, the by-products formed after photo-Fenton process exhibit minimal toxicity towards Lactuca sativa L. No Fe(II) ions were leached at the end of the process. Eight cycles of degradation did not cause significant spectral changes in the FTIR analysis, as well as in the XRD patterns, indicating the material efficient and stable structure. [Display omitted] • Fe/ZnO structure was applied as heterogeneous catalysts to produce active species for the MB removal. • ≡Fe(III) and ≡ Zn(II) promoted high generation of radical in photo-Fenton-like process. • The 5.0 % Fe/ZnO catalyst maintained a high removal rate after eight cycles of reuse. • Lactuca sativa L. germination tests showed no toxicity in the water generated after the degradation process. • No Fe(II) ions were leached after the photo-Fenton-like process. [ABSTRACT FROM AUTHOR]

Highlights: [•] The iron (II) phthalocyanine was used as modifier in the GDE for H2O2 generation. [•] At 90min the GDE generated 240mgL−1 of H2O2. [•] The most generation consumption 165kWh for kg of H2O2. [ABSTRACT FROM AUTHOR]

The catalytic performance of modified hydroxyapatite nanoparticles, Ca 10-x Fe x-y W y (PO 4) 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 Ca 4 FeII 1·92 W 0·08 FeIII 4 (PO 4) 6 (OH) 2 was combined with UVC radiation and electrogenerated H 2 O 2 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. [Display omitted] • New modified hydroxyapatite nanoparticles as catalysts to produce.●OH in the MB, FG dyes and NOR degradation; • High recyclability of the heterogeneous catalyst was verified due to magnetic properties. • MB, FG dyes and NOR reached high degradation rate by Photo-Electro-Fenton process using GDE. • Acute and chronic theoretical toxicological was evaluated to NOR. • The by-product identification study resulted in low toxicity compounds. [ABSTRACT FROM AUTHOR]