Continuous flow catalysis with a biomimetic copper(II) complex covalently immobilized on graphite felt

International audienceThe catecholase activity of a copper(II) complex coordinated by a tripodal pyrazole-based ligand was investigated in continuous flow catalysis. The covalent immobilization of the complex on the surface was achieved by a two steps method. First, the porous graphite felt support is functionalized by electrochemical reduction of 4-carboxymethyl-benzenediazonium salts. Second, the complex is covalently immobilized by esterification reaction between the COOH-containing linker and a primary alcohol group present on the C6 chain of the ligand. The two steps of the immobilization process were optimized by using nitro-containing molecules and cyclic voltammetry analyses. The copper complex exhibits higher catecholase activity in continuous flow catalysis than in solution with a 50 times lower amount of catalyst, underlining the advantages of the flow procedure. The presence of H2O2 is detected after catalysis, showing that the four-electron reduction of dioxygen to water does not occur unlike the natural enzyme

Impact of nature and length of linker on the catecholase activity of a covalently immobilized copper(II) complex in continuous flow catalysis

International audienceThe catecholase activity of four immobilized mononuclear copper(II) catalysts with chains of different nature and length used as linkers is studied in continuous flow catalysis. The graphite felt support was first derivatized by cathodic reduction of 4-carboxymethyl-benzenediazonium salts. Complexes with different chains were then covalently immobilized on the functionalized porous support by esterification reaction. The successful achievement of the immobilization process is attested by the presence of the CuII/I reversible system in cyclic voltammetry. Volume concentrations around 10−8 mol cm−3 of immobilized catalysts are estimated by integration of the redox peak. Comparison of the catecholase activity of the immobilized complexes allows to conclude on the effect of the chain nature and length. First, high chain length positively influences the catalytic activity. Second, the presence of oxygen atoms in the linker significantly enhances the catecholase activity of the catalyst. A possible explanation is the chain hydrophilicity, making easier the access of the catalytic center by H2O molecules

Combined electrochemical and biological treatment for pesticide degradation - Application to phosmet

International audienceThe aim of this study was to determine the feasibility of coupling an electrochemical process with a biological treatment in order to degrade phosmet, an organophosphorous pesticide. The absence of biodegradability of phosmet by Pseudomonas fluorescens and activated sludge was verified in our operational conditions. So, a conventional biological treatment is not appropriate for phosmet polluted effluents. Electrochemical behavior of phosmet was studied by cyclic voltammetry and the feasibility of an electrochemical pretreatment was thus demonstrated. Preliminary results with activated sludge showed a diminution of 26% for COD (chemical oxygen demand) measured when the electrolyzed solution was used as the sole carbon and nitrogen sources. When glucose and ammonium were added as supplementary carbon and nitrogen sources, the COD diminution reached 34% after 79 h of culture. This study demonstrates the feasibility of an electrochemical pre-treatment prior to biotreatment

Electrocatalytic reduction of metronidazole using titanocene/Nafion®-modified graphite felt electrode

International audienceThe main objective of this study was to examine the feasibility of an electrocatalytic reduction on titanocene/Nafion®-modified graphite felt electrode, as pretreatment, before a biological treatment, for the degradation of metronidazole, a nitro biorecalcitrant pollutant. A titanium complex, know as an effective catalyst in the reduction of nitro groups, was immobilized on the electrode surface by encapsulation into a Nafion® film. The different operating conditions used to prepare the modified electrode, i. e. the initial concentrations of catalyst and Nafion® and the sonication time, were optimized and the modification of the electrode was highlighted by cyclic voltammetry and electronic scanning microscopy coupled with energy dispersive spectroscopy analysis. The results show a good stability and reproducibility of the modified electrode. Flow heterogeneous catalytic reduction of metronidazole was then carried out with the titanocene/Nafion®-modified graphite felt as working electrode. The HPLC analysis underlined the total reduction of metronidazole after 1 hour and the evolution of the biological oxygen demand to chemical oxygen demand ratio showed a significant increase of biodegradability from 0.06 before pretreatment to 0.35 ± 0.05 after electrolysis on the modified graphite felt electrode. The comparison of both homogeneous and heterogeneous reactions underlined the interest of the immobilization process that led to a higher stability of the catalyst, giving rise to a higher turnover number and an improvement of biodegradability. The stability of the modified electrode was investigated after electrolysis by cyclic voltammetry and successive electrolyses

Direct electrochemical oxidation of a pesticide, 2,4-dichlorophenoxyacetic acid, at the surface of a graphite felt electrode: Biodegradability improvement

International audiencePesticides' biorecalcitrance can be related to the presence of a complex aromatic chains or of specific bonds, such as halogenated bonds, which are the most widespread. In order to treat this pollution at its source, namely in the case of highly concentrated solutions, selective processes, such as electrochemical processes, can appear especially relevant to avoid the possible generation of toxic degradation products and to improve biodegradability in view of a subsequent biological mineralization. 2,4-D was found to be electroactive in oxidation, but not in reduction, and the absence of hydroxyl radicals formation during the electrochemical step was demonstrated, showing that the pretreatment can be considered as a "direct" electrochemical process instead of an advanced electrochemical oxidation process. The presence of several degradation products in the oxidized effluent showed that the pretreatment was not as selective as expected. However, the relevance of the proposed combined process was confirmed since the overall mineralization yield was close to 93%

Combined process for removal of tetracycline antibiotic - Coupling pre-treatment with a nickel-modified graphite felt electrode and a biological treatment.

International audienceBiodegradability improvement of tetracycline-contg. solns. after an electrochem. pre-treatment was examd. Cyclic voltammetry with a nickel electrode revealed a significant electrochem. activity of tetracycline, in both oxidn. and redn. Electrochem. treatment was therefore performed in a home-made flow cell using a nickel-modified graphite felt electrode as the working electrode. Optimal conditions, namely 100 mg l-1 initial tetracycline, above 0.45 V potential, and between 1 and 6 mL min-1 flow rate, led to a more than 99% conversion yield of tetracycline in oxidn. in alk. conditions, after only a single pass through the percolation cell. However, total org. carbon (TOC) analyses revealed a low mineralization level, i.e., always below 31%, underscoring the importance of a combined electrochem. and biol. treatment. This was confirmed by the favorable trends of the COD/TOC ratio, decreasing from 2.7 to 1.9, and the av. oxidn. state, increasing from 0.044 to 1.15, before and after oxidn. pretreatment at 0.7 V and 3 mL min-1 flow rate. Electrolyzed solns. appeared biodegradable, since BOD5/COD increased from 0 to 0.46 for untreated and pretreated TC at 0.7 V/SCE. Biol. treatment showed only biosorption for non-pretreated tetracycline, while after 11.5 days of culture, the mineralization of solns. electrolyzed in oxidn. was 54%, leading to a 69% overall TOC decrease during the combined process

Reductive dehalogenation of 1,3-dichloropropane by a [Ni(tetramethylcyclam)]Br2-Nafion modified electrode

International audienceDechlorination reaction of 1,3-dichloropropane, a contaminant solvent, was investigated by electrochemical reduction in aqueous medium using a Ni(tmc)Br2 complex, known as effective catalyst in dehalogenation reactions. The catalytic activity of the complex was first investigated by cyclic voltammetry and flow homogeneous redox catalysis using a graphite felt as working electrode. A total degradation of 1,3-dichloropropane was obtained after 5 h of electrolysis with a substrate/catalyst ratio of 2.3. The concentration of chloride ions determined by ion chromatography analysis showed a dechlorination yield of 98%. The complex was then immobilized on the graphite felt electrode in a Nafion® film. Flow heterogeneous catalytic reduction of 1,3-dichloropropane was then carried out with the [Ni(tmc)]Br2-modified Nafion® electrode. GC analyses underlined the total degradation of the substrate in only 3.5 h with a substrate/catalyst ratio of 100. A dechlorination yield of 80% was obtained, as seen with ion chromatography analyses of chloride ion. Comparison of both homogeneous and heterogeneous reactions highlighted the interest of the [Ni(tmc)]Br2-modified Nafion® electrode that led to a higher stability of the catalyst with a turnover number of 180 and a higher current efficiency

Combined process for 2,4-Dichlorophenoxyacetic acid treatment-Coupling of an electrochemical system with a biological treatment

International audienceA coupled process was studied for the removal of a chlorinated pesticide: 2,4-Dichlorophenoxyacetic acid (2,4-D). A home-made electrochemical flow cell was used for the pre-treatment and a biological treatment was then carried out using activated sludge supplied by a local wastewater treatment plant. 2,4-D was used as a target compound for the study. Several parameters were monitored during the biological treatment, like dissolved organic carbon (DOC), the target compound and the major by-product. Pretreatment led to a quick decrease of DOC during the biological process, since a 66% mineralization yield was measured after the second day, and 79% after the seventh day of culture. After two days of treatment, HPLC results revealed a total degradation of Chlorohydroquinone, the major by-product. The electrochemical pretreatment shortened the length of the biological treatment, since DOC measurements showed that in the case of non-pretreated 2,4-D, no mineralization was observed before day 7. These promising results should be subsequently confirmed on commercial 2,4-D-containing solutions and then on real effluents

Indirect electroreduction as pretreatment to enhance biodegradability of metronidazole.

International audienceThe removal of metronidazole, a biorecalcitrant antibiotic, by coupling an electrochemical reduction with a biological treatment was examined. Electroreduction was performed in a home-made flow cell at -1.2V/SCE on graphite felt. After only one pass through the cell, analysis of the electrolyzed solution showed a total degradation of metronidazole. The biodegradability estimated from the BOD5/COD ratio increased from 0.07 to 0.2, namely below the value usually considered as the limit of biodegradability (0.4). In order to improve these results, indirect electrolysis of metronidazole was performed with a titanium complex known to reduce selectively nitro compounds into amine. The catalytic activity of the titanium complex towards electroreduction of metronidazole was shown by cyclic voltammetry analyses. Indirect electrolysis led to an improvement of the biodegradability from 0.07 to 0.42. To confirm the interest of indirect electroreduction to improve the electrochemical pretreatment, biological treatment was then carried out on activated sludge after direct and indirect electrolyses; different parameters were followed during the culture such as pH, TOC and metronidazole concentration. Both electrochemical processes led to a more efficient biodegradation of metronidazole compared with the single biological treatment, leading to an overall mineralization yield for the coupling process of 85%