Electrodes Based on Zeolites Modified with Cobalt and/or Molybdenum for Pesticide Degradation. Part I: Physicochemical Characterization and Efficiency of the Electrodes for O2 Reduction and H2O2 Production

© 2018, Springer Science+Business Media, LLC, part of Springer Nature.With the purpose of obtaining inexpensive electrodes for the degradation of organic pesticides by the electro-Fenton reaction, the required H2O2 being obtained by the 2-electron reduction of dissolved O2, we have prepared glassy carbon electrodes coated with a mixture of graphite with Mo- and/or Co-modified zeolites. Three zeolites were used, Linde type A (ZA), Faujasite (ZY), and MFI (ZSM5), whose maximum possible cation exchange, directly given by the Al/Si ratio, and their hydrophilicity increases in the order ZSM5 < ZY < ZA. The zeolites were modified with Mo and/or Co by the wet impregnation method and characterized by different techniques. The outer surfaces of the three Mo-modified zeolites showed Mo-containing grains (in ZA) or needles (in ZY and ZSM5), which could be largely washed away with hot water. Electrodes were made by depositing on a disc of glassy carbon (GC) a mixture of graphite, zeolite, and a b

Electrodes Based on Zeolites Modified with Cobalt and/or Molybdenum for Pesticide Degradation. Part I: Physicochemical Characterization and Efficiency of the Electrodes for O2 Reduction and H2O2 Production

17 pags., 11 figs., 6 tabs.With the purpose of obtaining inexpensive electrodes for the degradation of organic pesticides by the electro-Fenton reaction, the required HO being obtained by the 2-electron reduction of dissolved O, we have prepared glassy carbon electrodes coated with a mixture of graphite with Mo- and/or Co-modified zeolites. Three zeolites were used, Linde type A (ZA), Faujasite (ZY), and MFI (ZSM5), whose maximum possible cation exchange, directly given by the Al/Si ratio, and their hydrophilicity increases in the order ZSM5 < ZY < ZA. The zeolites were modified with Mo and/or Co by the wet impregnation method and characterized by different techniques. The outer surfaces of the three Mo-modified zeolites showed Mo-containing grains (in ZA) or needles (in ZY and ZSM5), which could be largely washed away with hot water. Electrodes were made by depositing on a disc of glassy carbon (GC) a mixture of graphite, zeolite, and a binder. Quite unexpectedly, the cyclic voltammograms (CVs) of the three Mo-modified zeolites showed at least five pairs of anodic–cathodic peaks, which we assume are due to the presence of the MoO isopolyoxomolybdate anion, proceeding from the impregnating solution, and anchored on the zeolites’ surface. With a rotating ring-disc electrode, the highest efficiency for HO production at − 0.2 V, namely, 12.7%, was obtained with the GC/graphite-(CoMo-exchanged ZA) electrode, but this efficiency decreased with time. On the contrary, the three zeolites modified only with Mo were stable in 4-h electrolyses at − 0.2 V and yielded the highest HO concentrations, which we attribute to the MoO isopolyoxomolybdate anchored on the zeolites. The HO yield was the same for the three Mo-modified zeolites, irrespective of their exchange capacity and hydrophobic/hydrophilic character. [Figure not available: see fulltext.].This work was supported by CONICYT Chile under Grant FONDECYT-1140207 and FONDEQUIP-EQM 160070 and DICYT-USACH grant 021841UZ. FF acknowledges a MECESUP USA 1555 Grant

Atypical antioxidant activity of non-phenolic amino-coumarins

Coumarin compounds have been described as anti-inflammatories, and chemotherapeutic agents as well as antioxidants. However, the origin of the antioxidant activity of non phenolic coumarins remains obscure. In the present report, we demonstrate that non-phenolic 7-dialkyl-aminocoumarins may also have significant antioxidant properties against free radicals derived from 2,2′-azobis(2-amidinopropane) dihydrochloride under aerobic conditions. This atypical behaviour is due to the presence of traces of very reactive hydroxycinnamic acid-type compounds. Changing functional groups at the C-3 and C-4 positions shifts the reactivity of the compounds from peroxyl to alkoxyl free radicals. Kinetic and theoretical studies based on Density Functional Theory support the formation of reactive hydroxycinnamic acid and directly link the antioxidant behaviour of the compounds to hydrogen atom transfer.Fil: Zúñiga Núñez, Daniel. Universidad de Santiago de Chile; ChileFil: Barrias, Pablo. Universidad de Santiago de Chile; ChileFil: Cárdenas Jirón, Gloria. Universidad de Santiago de Chile; ChileFil: Ureta Zañartu, M. Soledad. Universidad de Santiago de Chile; ChileFil: Lopez Alarcón, Camilo. Pontificia Universidad Católica de Chile; ChileFil: Moran Vieyra, Faustino Eduardo. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Borsarelli, Claudio Darío. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Alarcón, Emilio. University of Ottawa; CanadáFil: Aspee, Alexis. University of Ottawa; Canad