Hydrogen peroxide (H2O2) is a versatile oxidizing agent that is synthesized commercially by the reduction of oxygen in organic medium. Electrochemical technology employing a modified gas diffusion ...electrode (MGDE) offers a viable alternative for the industrial-scale synthesis of the oxidant. Addition of 1% (w/w) of tert-butyl-anthraquinone (TBAQ) to carbon black deposited in the form of a microporous layer onto the disk of a rotating ring-disk electrode produced an increase in the ring current, which is directly related to H2O2 formation, and presented an efficiency of H2O2 generation of 89.6% compared with 76.6% for carbon black alone. No significant changes were detected in the number of electrons transferred in the presence of the catalyst suggesting an electrochemical/chemical mechanism for H2O2 formation. Analogous improvements in the generation of H2O2 were obtained with MGDEs comprising TBAQ on carbon black. The highest concentrations of H2O2 (301mgL−1) were produced at the fastest rate (5.9mgL−1min−1) with the lowest energy consumption (6.0kWhkg−1) when a potential of −1.0V vs SCE was applied to a MGDE containing 1.0% of TBAQ on carbon black. It is concluded that the application of MGDEs comprising TBAQ on carbon black support offers considerable advantages in the electrogeneration of H2O2.
A comparative study of two different conductive carbon-black pigments, Vulcan XC-72 R and Printex L6, for the electrogeneration of hydrogen peroxide (H
2O
2) by reducing dissolved oxygen in an ...alkaline solution was performed. The materials were physically characterized by X-ray diffraction (XRD), Fourier transform infrared attenuated total reflection (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). XRD shows the presence of SO
2 and ATR-FTIR technique indicates a difference in NO and SO
2 functional groups between the two carbon pigments. XPS indicated presence of SO and NO and more oxygenated acid species on Printex L6. A rotating ring-disk electrode was used for electrochemical analysis of the oxygen reduction reaction (ORR). The results showed that the Printex L6 was better than Vulcan XC-72 R for H
2O
2 production. Results also indicate that the number of electrons transferred in the ORR for Printex L6 and Vulcan XC-72 R were 2.2 and 2.9, respectively, while the percentages of H
2O
2 formed were 88% and 51%. Scanning electrochemistry microscopy images confirmed the higher amount of H
2O
2 formed in the Printex L6 pigment. Printex L6 was shown to be a more promising for H
2O
2 production than Vulcan XC-72 R, while the latter was shown to have more potential for fuel cells.
► Electrochemical advanced oxidation process was studied using BDD based anodes with different boron concentrations. ► The difference between the non-active and active anodes for organics ...degradation. ► The influence of morphologic and structural properties of BDD electrodes on the RO-16 dye degradation.
Boron-doped diamond (BDD) films grown on the titanium substrate were used to study the electrochemical degradation of Reactive Orange (RO) 16 Dye. The films were produced by hot filament chemical vapor deposition (HFCVD) technique using two different boron concentrations. The growth parameters were controlled to obtain heavily doped diamond films. They were named as E1 and E2 electrodes, with acceptor concentrations of 4.0 and 8.0
×
10
21
atoms
cm
−3, respectively. The boron levels were evaluated from Mott–Schottky plots also corroborated by Raman's spectra, which characterized the film quality as well as its physical property. Scanning Electron Microscopy showed well-defined microcrystalline grain morphologies with crystal orientation mixtures of (1
1
1) and (1
0
0). The electrode efficiencies were studied from the advanced oxidation process (AOP) to degrade electrochemically the Reactive Orange 16 azo-dye (RO16). The results were analyzed by UV/VIS spectroscopy, total organic carbon (TOC) and high-performance liquid chromatography (HPLC) techniques. From UV/VIS spectra the highest doped electrode (E2) showed the best efficiency for both, the aromaticity reduction and the azo group fracture. These tendencies were confirmed by the TOC and chromatographic measurements. Besides, the results showed a direct relationship among the BDD morphology, physical property, and its performance during the degradation process.
•The treatment with boron-doped diamond anodes is able to completely degrade imazapyr.•The wastewater toxicity can be reduced by electrochemical treatment.•The major degradation intermediates are ...detected and identified by LC–MS/MS analyses.•Formic, acetic and butyric acids are the main non aromatic by-products.
In this work we have studied the treatment of imazapyr by electrochemical oxidation with boron-doped diamond anode. Electrochemical degradation experiments were performed in a one-compartment cell containing 0.45L of commercial formulations of herbicide in the pH range 3.0–10.0 by applying a density current between 10 and 150mAcm−2 and in the temperature range 25–45°C. The maximum current efficiencies were obtained at lower current densities since the electrochemical system is under mass transfer control. The mineralization rate increased in acid medium and at higher temperatures. The treatment was able to completely degrade imazapyr in the range 4.6–100.0mgL−1, although the current charge required rises along with the increasing initial concentration of the herbicide. Toxicity analysis with the bioluminescent bacterium Vibrio fischeri showed that at higher pollutant concentrations the toxicity was reduced after the electrochemical treatment. To clarify the reaction pathway for imazapyr mineralization by OH radicals, LC–MS/MS analyses we performed together with a theoretical study. Ions analysis showed the formation of high levels of ammonium in the cathode. The main final products of the electrochemical oxidation of imazapyr with diamond thin film electrodes are formic, acetic and butyric acids.
The inefficiency of conventional water treatment methods in the treatment of recalcitrant herbicides has led to the search for new, efficient and eco-friendly mechanisms for degrading these organic ...pollutants. Electrochemical advanced oxidation processes (EAOP) have emerged as a promising alternative due to their high degree of efficiency in degrading organic pollutants. This work investigates the removal of Tebuthiuron (TBH) in synthetic and real wastewater using different EAOPs in a flow-by reactor. The degradation/mineralization experiments were performed using boron-doped diamond electrode as anode and gas-diffusion electrode (GDE) as cathode for the in situ electrogeneration of hydrogen peroxide (H2O2). For the analysis conducted in synthetic medium, TBH degradation was found to fit well in a pseudo-first-order kinetic reaction with increasing k1 values according to the following order of efficiency: anodic oxidation (AO, 3.1 × 10−5 s−1) < AO with H2O2 generation (AO-H2O2, 4.8 × 10−5 s−1) < electro-Fenton (EF, 5.9 × 10−5 s−1) < AO-H2O2/UVC (2.6 × 10−4 s−1) < photoelectro-Fenton (PEF, 3.2 × 10−4 s−1). AO-H2O2/UVC and PEF processes presented the highest rates of mineralization and similar energy consumption per order (~ 45 kWh m−3 order−1). The degradation experiment conducted using real urban wastewater yielded a 1.7-fold decrease in TBH degradation kinetics compared to the synthetic medium; this difference was attributed to the presence of inorganic ions and natural organic matter in real wastewater which tended to affect the electrochemical system efficiency. The findings of this study are of great interest and confirm the viability of electrochemical techniques for treating complex effluents contaminated by herbicides.
Methane fed TiO2/RuO2/PTFE gas diffusion electrodes (GDEs) have been used for the electrosynthesis of methanol in 0.1molL−1 of Na2SO4 supporting electrolyte. By-products such as formaldehyde and ...formic acid are usually also formed during electrolyses, with the latter formed at a similar rate as that of methanol. In this study, V2O5 was added to the composition of the GDE to improve its selectivity for methanol. TiO2/RuO2/V2O5 powder hot-pressed with PTFE resulted in a GDE suitable for oxidative electrosynthesis with simultaneous oxygen evolution. By feeding the TiO2/RuO2/V2O5/PTFE GDE with methane, it was possible to enhance its selectivity for methanol at low values of current density. Furthermore, the formation of formic acid and formaldehyde was suppressed, allowing for higher current efficiencies. The addition of 5.6% of V2O5 increased the electrode's current efficiency to 57% at 2.0V, which is 2-fold higher than the efficiency achieved in the absence of vanadium oxide.
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.
In the search for greener treatment technologies, this work studies the coupling of a wind turbine energy supply with an electrolytic cell (CWTEC device) for the remediation of wastewater polluted ...with pesticide 2,4-dichlorophenoxyacetic acid (2,4-D). The discontinuous and unforeseeable supply of energy is the main challenge inspiring this new proposal, which aims at reducing the environmental impact of electrolytic treatment by using a green energy supply. The results obtained using the coupled technologies are compared with those obtained by powering the electrolyser with a traditional power supply with a similar current intensity. The mineralisation of wastewater can be accomplished independently of how the electrolytic cell is powered, although differences in performance are clearly observed in the total organic carbon (TOC) and 2,4-D decays. These changes can be explained in terms of the changing profile of the current intensity, which influences the concentrations of the oxidants produced and thereby the mediated electrolytic process.
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•This work presents a wind-powered electrochemical cell for the removal of 2,4-D.•The complete mineralisation of 2,4-D is achieved in the wind-powered system.•Charge applied to reach complete mineralisation does not depend on the power source.•Mediated oxidation is favoured in the wind-powered device.
In this work, four bench-scale plants containing soil spiked with four herbicides (2,4-Dichlorophenoxyacetic acid (2,4-D), oxyfluorfen, chlorsulfuron and atrazine) undergo treatment consisting of an ...electrokinetic soil flushing (EKSF). Results clearly demonstrate that efficiency of EKSF depends on the chemical characteristic of the pesticide used. The amount of pesticide collected in the anode well is more significant than that collected in the cathode wells, indicating that the electromigration is much more important than drainage by electro-osmotic flux for this application. After 15 d of treatment, the 2,4-D is the pesticide most efficiently removed (95% of removal), while chlorsulfuron is the pesticide more resilient to the treatment. Additionally, volatilization was found to be a process of the major significance in the application of electrokinetic techniques to soil polluted with herbicides and because of that it should always be taken into account in the future design of full-scale processes.
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•EKSF can remediate soils polluted with ionic and non-ionic herbicides.•Herbicides can be mobilized towards the electrodes by electromigration.•Herbicides can be transported towards the cathode by electroosmotic dragging.•Volatilization has a great importance and should be accounted in large processes.•After 15 d long treatment, more than 80% of pesticide is removed.
•9% SnNi/C 6:1 was the best choice for H2O2 electrogeneration among all materials.•9% SnNi/C 6:1 transferred 2.2 electrons and had a H2O2 percentage efficiency of 88%.•X-ray diffraction analysis ...identified a phase for 9% SnNi/C 6:1 (Ni3Sn4).•Ni3Sn4 is a structure tolerant of defects that can increase oxygen diffusion.
This work describes both the preparation and the characterization of nanostructured materials based on tin and nickel. Composite materials of SnNi/C were prepared by the polymeric precursor method and were supported on Vulcan XC-72R, which is a high surface area carbon, for a comparative study. Three proportions on carbon were evaluated: 6%, 9% and 13%. Binary materials were prepared varying the atomic ratios of Sn and Ni at 6:1, 3:1, 1:1, 1:3 and 1:6 for each percentage composition tested. The materials were characterized by X-ray diffraction to determine the mean crystallites sizes of the important phases for the catalytic process, such as Ni3Sn, Ni3Sn2 and Ni3Sn4, and by energy dispersive spectroscopy (EDS) measurements to determine the percentage composition of the material with highest catalytic activity. The results showed that the binary material prepared with 9% metal load at a ratio of 6:1 Sn:Ni was the best material for H2O2 electrogeneration. This material showed the highest ring current, which was a consequence of the highest amount of H2O2 production having a ring current higher than that obtained for the ORR for Vulcan carbon. The best electrocatalyst transferred 2.2 electrons in the ORR with an 88% yield of H2O2, while the Vulcan carbon, which is the reference material for the 2-electron transfer reaction, produced just a 63% yield of H2O2. Thus, based on these results, 9% Sn:Ni (6:1) is a promising material to be used in H2O2 electrogeneration and in AOPs. This result is likely due to the presence of acid oxygen-containing species on carbon and to the large defect concentration in Ni3Sn4 lattice parameters, which increase oxygen diffusion and promote H2O2 production.
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