Mineralization of organic pollutants by anodic oxidation using reactive electrochemical membrane synthesized from carbothermal reduction of TiO2

Reactive Electrochemical Membrane (REM) prepared from carbothermal reduction of TiO2 is used for the mineralization of biorefractory pollutants during filtration operation. The mixture of Ti4O7 and Ti5O9 Magnéli phases ensures the high reactivity of the membrane for organic compound oxidation through •OH mediated oxidation and direct electron transfer. In cross-flow filtration mode, convection-enhanced mass transport of pollutants can be achieved from the high membrane permeability (3300 LMH bar-1). Mineralization efficiency of oxalic acid, paracetamol and phenol was assessed as regards to current density, transmembrane pressure and feed concentration. Unprecedented high removal rates of total organic carbon and mineralization current efficiency were achieved after a single passage through the REM, e.g. 47 g m-2 h-1 - 72% and 6.7 g m-2 h-1 - 47% for oxalic acid and paracetamol, respectively, at 15 mA cm-2. However, two mechanisms have to be considered for optimization of the process. When the TOC flux is too high with respect to the current density, aromatic compounds polymerize in the REM layer where only direct electron transfer occurs. This phenomenon decreases the oxidation efficiency and/or increases REM fouling. Besides, O2 bubbles sweeping at high permeate flux promotes O2 gas generation, with adverse effect on oxidation efficiency

Formulation d'insecticides en poudre par adsorption des huiles essentielles de Xylopia aethiopica et de Ocimum gratissimum sur des argiles camerounaises modifiées

En Afrique sud- saharienne, plusieurs méthodes de protection des stocks alimentaires sont utilisées ; parmi elles, les insecticides synthétiques qui représentent un risque réel pour la santé humaine. Pour apporter une alternative à ces insecticides chimiques potentiellement dangereux, le présent travail a pour objectif de développer des bio-insecticides en formulant des poudres par adsorption d huiles essentielles sur des argiles. Deux argiles naturelles du Cameroun ont été utilisées comme adsorbants des composés terpéniques des huiles essentielles de Xylopia aethiopica et Ocimum gratissimum pour la préparation d insecticides. Dans le but d améliorer leur capacité d adsorption, ces argiles ont été traitées par la soude et l acide sulfurique. Elles ont également été modifiées par des solutions de polycations d aluminium ou de fer de rapport molaire varié ainsi que par des cations d alkylammoniums. Une bentonite commerciale a été utilisée comme référence dans le suivi des modifications. Ces différentes matrices ont été caractérisées avant et après modifications par diffraction des rayons X, adsorption-désorption d azote, spectroscopie infra rouge à transformée de Fourier, analyses thermogravimétriques et différentielles, et photométrie de flamme. Il ressort de la caractérisation que l échantillon de Wak est majoritairement constitué de kaolinite, et celui de Maroua de montmorillonite. Le traitement par l acide sulfurique et par les polycations métalliques entraînent une augmentation de la surface spécifique des argiles, tandis que la soude et les cations d alkylammoniums la réduisent fortement. La surface spécifique de la montmorillonite passe de 82 m .g-1 à 4,5 m .g-1 après traitement au céthyl triméthyl ammonium (CTMA). Les diffractogrammes montrent une augmentation de la distance interfoliaire des argiles étudiées après modification aux cations alkylammoniums. La distance interfoliaire augmente de 5,5 Å et de 10,6 Å respectivement pour la montmorillonite et la bentonite traitée par le CTMA. Les argiles de type smectite après modifications aux polycations métalliques, présentent en revanche un étalement du pic caractéristique de l espace interfoliaire. Les cations alkylammoniums entraînent donc une intercalation effective des molécules de CTMA et phényl triméthyl ammonium (PTMA) entre les feuillets de montmorillonite et de bentonite tandis que les polycations métalliques entraînent une exfoliation du matériau argileux. Les argiles-alkylammoniums présentent les plus grandes capacités d adsorption des composés terpéniques malgré les plus faibles surfaces spécifiques. Ainsi, face aux composés terpéniques, la capacité d adsorption des argiles ne dépend pas uniquement de la surface spécifique mais également de l espacement interfoliaire de l adsorbant ainsi que de l affinité des molécules d adsorbât vis-à-vis de l adsorbant. Des tests insecticides ont montré que les formulations à base de la Mont-CTMA présentent une toxicité plus stable que celle préparée à partir de l argile brute (Mont-Na). La formulation Mont-Na-HE perd la totalité de son activité insecticide au bout de 30 jours de conservation dans les boîtes ouvertes. La formulation Mont-CTMA-HE par contre n en perd qu environ 60% dans les mêmes conditions. La rémanence de la formulation varie avec l adsorbant utilisé ; car l effet insecticide de l huile essentielle d O. gratissimum persiste pendant 107 jours lorsqu elle est fixée sur la Mont-CTMA, tandis que fixée sur l argile brute, elle perd son activité au bout de 45 jours. Ces résultats nous permettent d affirmer que les argiles modifiées augmentent la durée de l effet insecticide des huiles essentielles et peuvent être utilisées pour une application industrielle dans la production des bio-insecticides.In sub-Saharan Africa, several methods to protect food stocks are used ; amongst them are synthetic insecticides. These synthetic insecticides pose high real risk to human health. This study aims at providing an alternative to the dangerous synthetic chemical insecticides, by developing bioinsecticides formulating powders through adsorption of essential oils on Cameroonian clays. Two natural clays collected in Cameroon were used as adsorbents of terpene compounds of Xylopia aethiopica and Ocimum gratissimum essential oils, for the preparation of insecticides. The clay fractions were obtained from soil aggregates by sedimentation. In order to improve their adsorption capacity, these clays were treated with sodium hydroxide and sulfuric acid. They were also modified with solutions of aluminum, iron polycations with molar ratio varied and alkylammoniums cations. A commercial bentonite was used as reference for these modifications. These different adsorbents materials were characterized before and after modifications by X-ray diffraction, nitrogen adsorption-desorption, infrared Fourier transform spectroscopy, thermal analysis, and flame photometry. According to the characterizations of the clay materials, Wak sample contained more kaolinite clay, while Maroua sample contained more montmorillonite clay. The sulfuric acid and metallic polycations caused an increase in the specific surface of clays, while sodium hydroxyl and alkylammoniums cations greatly reduced the SBET. For example, the Mont-Na+ SBET decreased from 82 m . g-1 to 4.5 m .g-1 after treatment with cetyl trimethyl ammonium (CTMA). Diffractogrammes showed spacing of smectites interlayer (montmorillonite and bentonite) after treatments with alkylammoniums cations at 5.5 Å and 10.6 Å respectively, for the interlayer space of Mont- CTMA and Bentonite- CTMA clays. After treatments with metallics polycations, smectite clays show a broadening of characteristic peak. Alkylammoniums cations led to an effective insertion of CTMA molecules and phenyl trimethyl ammonium (PTMA) between the interfoliar space of montmorillonite and bentonite while the metal polycations led to an exfoliation of the same clays. The interreticular spacings of kaolinite remain unchanged after any treatments. The kinetic model of pseudo second order is applicable to the adsorption of terpenic compounds by clays. Finding also showed that spread is not the only limiting factor in the process of adsorption of terpene compounds. Alkylammoniums-clays have the largest adsorption capacities of terpene compounds despite the lower specific surface they present. All this allows us to maintain that in the presence of terpenic compounds, the adsorption capacity of clays depends not only on the SBET but more on the interlayer spacing of the adsorbent and on the affinity of the adsorbate molecules toward the adsorbent. Concerning bioassays, it appears that the formulations made with Mont- CTMA presented a more stable toxicity than Mont-Na. Mont-Na-EO formulation loses all its insecticidal activity after 30 days of storage in the open boxes ; while Mont-CTMA- EO formulation only loses about 60% under the same conditions. Moreover, the Mont-Na-EO loses 50% of its insecticidal power (LD50) after 6 days ; while Mont-CTMA- EO loses the same quantity after 16 days when stored in open boxes. The remnance effect of the formulations based on essential oil varied with the adsorbent used. Because the insecticidal effect of O. gratissimum essential oil persisted during 107 days when it is adsorbed on Mont-CTMA, when adsorbed on Mont-Na, it loses all its activity for about 45 days. These results allow us to assert that modified clays increase the duration of the insecticidal effect of essential oils and can be used for industrial application in the production of bio-insecticides based on essential oils.MONTPELLIER-Ecole Nat.Chimie (341722204) / SudocSudocFranceF

Dynamic cross-flow electro-Fenton process coupled to anodic oxidation for wastewater treatment: application to the degradation of acetaminophen

In this work, we present an integrated dynamic cross-flow electro-Fenton (DCF-EF) system for the treatment of the pharmaceutical, acetaminophen (paracetamol), in aqueous medium. A carbonaceous electrocatalytic membrane was used as cathode, allowing the continuous production of H2O2 during EF in dynamic filtration mode. The transmembrane pressure (TMP) and current were the two driving forces of the system, whose influence strongly affected the global efficiency. It was found that H2O2 production from the electrochemical reduction of dissolved O2 was favoured at higher TMP values as a consequence of an increase of the O2 partial pressure, and higher H2O2 amounts entailed an increase in the efficiency of the process. Current also had a positive effect on H2O2 production and acetaminophen degradation and mineralization efficiencies up to an optimal value. Complete degradation of the drug and 44% mineralization were achieved under optimal conditions (2.0 bar and 100 mA). On the other hand, the results pointed out that the use of a Ti4O7 rod as counter electrode (anode) had an important contribution to the mineralization of the acetaminophen’s solutions owing to the formation of hydroxyl radicals (OH) on its surface, which highlighted the oxidative power of this anode material. The oxidation mechanisms involved during the process were assessed by electrochemical measurements with both electrodes (carbon membrane and Ti4O7 rod), and a degradation pathway for paracetamol oxidation was proposed based on the identification of the main aromatic and aliphatic degradation by-products. This DCF-EF process is presented as a potential alternative for water treatment and reuse in which the integration of membrane and electrochemical technologies brings together separation science and advanced oxidation

Efficiency of plasma elaborated sub-stoichiometric titanium oxide (Ti4O7) ceramic electrode for advanced electrochemical degradation of paracetamol in different electrolyte media

This paper investigates the behavior of conductive Ti4O7 ceramic anode in different electrolytes during the degradation of the anti-inflammatory drug paracetamol (PCM) by advanced electrochemical oxidation processes mainly anodic oxidation with generation of H2O2 (AO-H2O2) and electro-Fenton (EF). Regardless of the medium, better degradation and mineralization efficiency was always observed with EF compared to AO-H2O2. The degradation of PCM was carried out by hydroxyl radical (OH) produced on the anode surface from water oxidation and mediated oxidation in the solution from oxidant species generated at the anode such as sulfate radicals and active chlorine species depending on the supporting electrolytes used, as well as OH generated homogeneously in the solution by electrochemically assisted Fenton’s reaction. Faster degradation was observed in Cl− compared to other media, but the solution was poorly mineralized. Highest total organic (TOC) removal efficiency with excellent degradation rate was attained in SO42− with either process, thus remain the best medium for advanced electrochemical wastewater treatment. Comparative studies with dimensional stable anode (DSA) and boron-doped diamond anode (BDD) showed similar trend of degradation and TOC removal efficiency with DSA anode achieving low mineralization power compared to Ti4O7 anode, whereas BDD showed slightly better efficiency than Ti4O7 in all electrolytes studied. The analysis of concentration of generated active chlorine species, especially ClO−, during AO-H2O2 decreased in the order: DSA > Ti4O7 > BDD. Therefore, the Ti4O7 electrode was found to be a promising anode material for an efficient treatment of PCM in SO42−, NO3− and ClO4− media but less effective in Cl− medium

Electro-oxidation of organic pollutants by reactive electrochemical membranes

Electro-oxidation processes are promising options for the removal of organic pollutants from water. The major appeal of these technologies is the possibility to avoid the addition of chemical reagents. However, a major limitation is associated with slow mass transfer that reduces the efficiency and hinders the potential for large-scale application of these technologies. Therefore, improving the reactor configuration is currently one of the most important areas for research and development. The recent development of a reactive electrochemical membrane (REM) as a flow-through electrode has proven to be a breakthrough innovation, leading to both high electrochemically active surface area and convection-enhanced mass transport of pollutants. This review summarizes the current state of the art on REMs for the electro-oxidation of organic compounds by anodic oxidation. Specific focuses on the electroactive surface area, mass transport, reactivity, fouling and stability of REMs are included. Recent advances in the development of sub-stoichiometric titanium oxide REMs as anodes have been made. These electrodes possess high electrical conductivity, reactivity (generation of •OH), chemical/electrochemical stability, and suitable pore structure that allows for efficient mass transport. Further development of REMs strongly relies on the development of materials with suitable physico-chemical characteristics that produce electrodes with efficient mass transport properties, high electroactive surface area, high reactivity and long-term stability

Electrochemical abatement of analgesic antipyretic 4‐aminophenazone using conductive boron‐doped diamond and sub‐stoichiometric titanium oxide anodes: kinetics, mineralization and toxicity assessment

The oxidation ability of two prominent eco‐friendly electrochemical advanced oxidation processes (EAOPs), namely anodic oxidation with H2O2 generation (AO‐H2O2) and electro‐Fenton (EF) for complete abatement of acidic solution of 4‐aminophenazone (4‐APZ) has been investigated using conductive boron‐doped diamond (BDD) and sub‐stoichiometric titanium oxide (Ti4O7) anodes and carbon‐felt cathode. The higher performance of EF compared to AO‐H2O2 with either anode was demonstrated. In all trials, 4‐APZ was completely destroyed, following pseudo first‐order kinetics with the rate constant values increasing with applied current and higher values attained with BDD compared to Ti4O7 anode at similar conditions. The absolute rate constant for the reaction between 4‐APZ and hydroxyl radicals was found to be 3.9±0.2×109 L mol−1 s−1. Complete mineralization could be attained with BDD anode, whereas Ti4O7 anode only showed excellent mineralization up to 94 % TOC removal. Therefore, Ti4O7 anode can constitutes a promising anode material thanks to its lower manufacturing cost. Inorganic ions like NO3− and HCO3− at concentration up to 25 mM has no effect on mineralization efficiency during AO‐H2O2, but the presence of Cl− even at lower concentration of 10 mM significantly reduced the TOC removal efficiency. The toxicity of the solution sharply increased at initial stage of treatment, corresponding to the formation of cyclic by‐products but their conversion to carboxylic acids due to longer treatment time involved a sharp toxicity decrease, thus ensuring overall detoxification

Les membranes électrochimiquement réactives : des matériaux d'électrode multifonctionnels pour le traitement de la pollution bioréfractaire

International audienc

Efficient strategies for biorefractory pollutants mineralization using ceramic and carbon electrochemical materials

International audienc

Anodic and cathodic materials designed as Reactive Electrochemical Membranes for the treatment of pharmaceuticals in waste water

International audienc

Reactive electrochemical membranes for the treatment of biorefractory pollutants in waste water

Sydney, Australi