Marc Cretin

A highly active based graphene cathode for the electro-fenton reaction

Reduced Graphene Oxide (rGO) was coated on Carbon Felt (CF) in order to design a novel cathode applied in the Electro-Fenton (EF) reaction for decontamination of wastewater polluted with Persistent Organic Pollutants (POPs). The new cathode was fabricated by an electrophoretic deposition of Graphene Oxide (GO) followed by its electrochemical reduction at a current density of −1.5 mA cm−2 for 10 min. The modified electrode and GO were characterized by SEM, AFM, XRD and XPS, showing the presence of rGO after optimization of the electrochemical conditions of synthesis. Electrode modification has improved the CF electrochemical properties as proved by the decrease of the charge-transfer resistance (Rct) determined by electrochemical impedance spectroscopy (EIS) and the increase of the CV response (2.5 times) of the FeIII/FeII couple used as a redox probe. Degradation of Acid Orange 7 (AO7), a model pollutant molecule, was monitored by UV-Vis spectrophotometry at the selected single wavelength λ = 485 nm. The results show that the degradation kinetics were 2 times higher on the graphene modified cathode compared to raw carbon felt proving the efficiency of this modification process.

A hierarchical CoFe-layered double hydroxide modified carbon-felt cathode for heterogeneous electro-Fenton process

Hierarchical CoFe-layered double hydroxide (CoFe–LDH) was grown on carbon felt (CF) as a heterogeneous catalyst by in situ solvothermal growth. The CoFe–LDH/CF serves as a cathode as well as a Fe2+ (catalyst) source in the electro-Fenton (EF) process. A combined structural and electrochemical characterization revealed highly ordered and well crystallized CoFe–LDH anisotropically grown on a CF substrate with highly dense urchin-like structures that were highly stable at circumneutral pH. EF experiments with the CoFe–LDH/CF cathode showed excellent mineralization of Acid Orange II (AO7) over a wide pH range (2–7.1). The mineralization of AO7 with CoFe–LDH/CF was by both homogeneous and surface-catalyzed processes at low acidic pH, whereas only the surface-catalyzed process occurs at circumneutral pH due to the stability of the LDH as well as precipitation of the catalyst. Higher mineralization was achieved with CoFe–LDH/CF compared to homogeneous EF with raw CF using the Fe2+/Co2+ catalyst at all pH values studied and the TOC removal with the CoFe–LDH/CF cathode was at least 1.7 and 3.5 times higher than that with the homogeneous system with Fe2+/Co2+ at pH 5.83 and 7.1, respectively. The enhanced performance observed with CoFe–LDH/CF was ascribed to (i) the surface-catalyzed reaction occurring at the surface of the cathode which can expand the working pH window, avoiding the precipitation of iron sludge as pH increases, (ii) enhanced generation of H2O2 due to the improved electroactive surface area of the cathode and (iii) the co-catalyst effect of the Co2+ in the LDH that can promote regeneration and additional production of Fe2+ and the hydroxyl radical, respectively. The CoFe–LDH/CF cathode exhibited relatively good reusability as the TOC removal after 2 h was still above 60% after 7 cycles of degradation, indicating that the prepared CoFe–LDH/CF is a promising cathode for the removal of organic pollutants by EF technology.

Sub-stoichiometric titanium oxide (Ti4O7) as a suitable ceramic anode for electrooxidation of organic pollutants: A case study of kinetics, mineralization and toxicity assessment of amoxicillin.

Electrochemical degradation of aqueous solutions containing antibiotic amoxicillin (AMX) has been extensively studied in an undivided electrolytic cell using a sub-stoichiometric titanium oxide (Ti4O7) anode, elaborated by plasma deposition. Oxidative degradation of AMX by hydroxyl radicals was assessed as a function of applied current and was found to follow pseudo-first order kinetics. The use of carbon-felt cathode enhanced oxidation capacity of the process due to the generation of H2O2. Comparative studies at low current intensity using dimensional stable anode (DSA) and Pt anodes led to the lower mineralization efficiencies compared to Ti4O7 anode: 36 and 41% TOC removal for DSA and Pt respectively compared to 69% for Ti4O7 anode. Besides, the use of boron doped diamond (BDD) anode under similar operating conditions allowed reaching higher mineralization (94%) efficiency. Although Ti4O7 anode provides a lesser mineralization rate compared to BDD, it exhibits better performance compared to the classical anodes Pt and DSA and can constitutes an alternative to BDD anode for a cost effective electro-oxidation process. Moreover several aromatic and aliphatic oxidation reaction intermediates and inorganic end-products were identified and a plausible mineralization pathway of AMX involving these intermediates was proposed.

Fabrication of free-standing electrospun carbon nanofibers as efficient electrode materials for bioelectrocatalysis

Electrospun carbon nanofibers (CNFs) were prepared by electrospinning of a polyacrylonitrile solution followed by convenient stabilization and carbonization thermal treatments. By observations of scanning electron microscopy, a mat of interlaced continuous submicronic fibers was detected. Characterization by Raman spectroscopy demonstrated the successful preparation of a carbon material and the influence of the heating-treatment temperature on the structure of the resulting CNFs. The novelty of the approach relies in the easy handling of the resulting electrospun mat electrode that does not require addition of any polymer binder or conductive material. This is the first time that electrospun conductive fibers are envisaged as electrode supports for redox enzymes immobilization applied to bioelectrocatalytic O2reduction. The most interesting thing is the remarkable benefit effect of the CNFs on the electrical performances of the electrode which can ascribe to high loading of active enzymes and fast kinetics at the electrode surface. The remarkably intensified current density (∼1 mA cm−2) achieved at the enzymatic CNFs bioelectrode is probably due to the unique nanostructure and surface properties of these nanomaterials that make them promising candidates as enzymatic cathodes in biofuel cell devices.

Elaboration and properties of TiO2–ZnAl2O4 ultrafiltration membranes deposited on cordierite support

The preparation and characterization of porous ceramic multilayer ultrafiltration (UF) membranes is described. The fist step consisted to prepare high-quality macroporous supports in cordierite (2MgO, 2Al2O3, 5SiO2). The microporous interlayer was then prepared by slip casting from Zirconia commercial powder suspension, and finally the active UF top layer was obtained by sol–gel route using TiO2 and ZnAl2O4 mixed sols. The water permeability of this membrane is 6.3 l h−1 m−2 bar−1, its thickness is 1.2 μm, the pore diameter of the active layer is centred on 4 nm and the cutoff is 3000 Da. The filtration tests performed with NaCl and Na2SO4 solution show the electric interactions govern the rejection rates of the solutes. The efficiency of the membrane is quite good for the elimination of methylene blue and of salts which contain Cr(III), Pb(II), Cd(II).

NASICON structure for alkaline ion recognition

Abstract Crystallized fast-alkaline conductors have promising properties for ion electrochemical sensors. Their conductivity at room temperature is very high (about 10−4–10−3 S cm−1). The selectivity effect of such membranes is based on the calibration of conductive sites in the structure. NASICON materials are good examples from this point of view. Suitable cationic substitutions allow to adjust the size of the conduction sites and then to improve the selectivity effect. Recent experimental results on Na + and Li+ membranes are shown in this field.

Elaboration and properties of TiO2–ZnAl2O4 ultrafiltration membranes

Abstract New ceramic ultrafiltration membranes with a pore size diameter in the range of 6 nm have been prepared by sol gel route using TiO 2 and ZnAl 2 O 4 mixed sols. The main characteristics of the membranes are given and their filtering properties discussed by taking into account of the electrophoretic behavior of powder suspension elaborated with the different sols used for the membrane preparation. As for other membrane materials, the salt rejection rate depends mainly on the surface charge of the material which is correlated to the ζ potential.

Design of a novel fuel cell-Fenton system: a smart approach to zero energy depollution

A model azo dye pollutant, Acid Orange 7 (AO7), was removed efficiently from an aqueous medium by a smart eco-friendly Fuel Cell-Fenton (FC-Fenton) system without any external power supply. In this approach, AO7 was degraded by an electro-Fenton process at a designed cathode (Carbon Felt (CF)/porous Carbon (pC)) supplied by direct clean electrical energy from abiotic glucose oxidation at a CF/gold anode (CF@Au). The highly active cathode was fabricated by an attractive route combining Atomic Layer Deposition (ALD) of ZnO on commercial carbon felts (CFs) followed by subsequent solvothermal conversion of the metal oxide to a metal organic framework (here ZIF-8). The as-prepared composite material was further calcined at high temperature under a controlled atmosphere. A pC-based support with high specific surface area and nitrogen as a dopant was thus obtained, enhancing both conductivity and electrocatalytic properties toward H2O2 production from oxygen reduction. Degradation kinetics of AO7 (0.1 mM initial concentration) at the CF@pC cathode was monitored by UV-vis spectrophotometry and High-Performance Liquid Chromatography (HPLC) to prove the efficiency of the composite material for the degradation of such a bio-refractory model molecule. Benefitting from the H2O2 production rate (9.2 mg L−1 h−1) by the pC layer, AO7 (35.0 mg L−1) was degraded by the electro-Fenton process in acidic medium (pH = 3) with removal efficiency reaching 90% in 10 h. The durability of the system was extended for more than 2 months with an average power output of 170 mW m−2, confirming this abiotic FC-Fenton system as a promising, green, future technology for both environmental and energy-related areas, including membrane-coupled reactor systems.

Studies of Phosphonic Acids Containing a π-Conjugated Ferrocenyl Unit Grafted on Metal Oxides − Mössbauer and Electrochemical Behaviour

The modification of metal oxide surfaces by π-conjugated ferrocene units has been performed. A phosphonic acid functionality was used to covalently anchor the π-conjugated ferrocene moiety to SnO2 and TiO2 particles. The covalent attachment and the monolayer coverage at the surface of the particles were confirmed by solid-state MAS 31P NMR spectroscopy, microanalysis and electronic microscopy (EDX). The properties of the ferrocene-modified oxides were analysed by cyclic voltammetry, which confirmed the electroactivity of the material, and 57Fe Mossbauer spectrometry, which provided information about the oxidation state and environment of the iron atoms. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Electrodeposition of functionalized Pyrrole (N-[3-(dimethylpyridyl-2-yl)aminopropyl], N-(3-aminopropyl), N-(3-acetamidopropyl) and N-(2-cyanoethyl)) on Stainless Steel gauze for membrane preparation

The preparation of dense membranes for ion separation by the electropolymerization of functionalized pyrrole has been carried out using pyrrole monomers with complexing groups such as amino and bis pyridine. The synthesis conditions of polymer films depend mainly on the applied potential and electrolyte composition; for polymer films derived from pyrrole monomers bearing amino groups, the film synthesis has been achieved only in acid solution. The main results obtained for the electropolymerization of N-(2-cyanoethyl)pyrrole, N-(3-aminopropyl)pyrrole, N-(3-acetamidopropyl)pyrrole and N-[3-(dimethylpyridyl-2-yl)aminopropyl]pyrrole are compared and the experimental conditions for membrane preparation discussed. The thickness and the morphology of the supported conducting polymer membrane prepared at a constant potential depend on the precursor monomer used. The duration of electrolysis should be sufficient to cover the metallic support, particularly for the N-[3-(dimethylpyridyl-2-yl)aminopropyl]pyrrole polymer membrane.