Kinetics and Mechanism of the Oxidation of Coomassie Brilliant Blue-R Dye by Hypochlorite and Role of Acid Therein

The kinetics of the oxidation of a triphenylmethane dye, Brilliant Blue-R (BB–Na+), in aqueous solution by hypochlorite as a function of pH was investigated. While the degradation of dye obeyed pseudo-first-order kinetics, the oxidation of the dye occurred through two competitive reactions facilitated by [OCl–] and [HOCl]. Both reactions exhibited first-order dependence on [OCl–] and [HOCl], respectively, but the hypochlorous acid initiated reaction was about ten times faster. The relative importance of the two paths rested on the pH-dependent concentrations of hypochlorite and hypochlorous acid. The overall second-order rate constants for the OCl– and HOCl initiated reactions are 1.2±0.2M–1 s–1 and 22.2±1.2M–1 s–1, respectively. The reaction energy parameters were determined as Ea=35.5 kJ mol–1,ΔHt=33.1 kJ mol–1 and ΔSt=–191.9 JK–1 mol–1 for the OCl– driven oxidation; and Ea= 26.8 kJ mol–1, ΔHt=29.3 kJ mol–1 and ΔSt=–204.6 JK–1 mol–1 for the HOCl facilitated reaction. The governing rate law and probable reaction mechanism were elucidated and validated by simulation. The three main oxidation products were 4-(4-ethoxyphenylamino)benzoic acid, 3-[(ethyl-hydroxyamino)methyl]benzene sulfonic acid and 6’-chloro-5’-hydroxybicyclohexylidene-2,5,2’-triene-4,4’-dione.KEYWORDS Brilliant Blue-R, oxidative degradation, hypochlorite, hypochlorous acid, kinetics, simulations.PDF and Supp files attache

Modified carbon fabric electrodes: preparation and electrochemical behavior toward amaranth electrolysis

The final publication is available at Springer via http://dx.doi.org/10.1007/s10800-014-0769-9The electrochemical behavior of non-modified, Pt-modified, and Pt/polyaniline-modified carbon fiber textile electrodes was studied through a series of electrolyses, under potentiostatic conditions, on an amaranth/sulfuric solution in the presence or absence of chloride ion. The morphology of the dispersed Pt, PANI, and PANI/Pt coatings was analyzed by scanning electron microscopy. Scanning electrochemical microscopy confirmed that the textile surface was effectively modified by the electrocatalytic material. Color removal reached values above 90 % in both electroreduction and electrooxidation processes. The amaranth electroreductions carried out with the non-modified electrode showed better charge efficiency than those with the Pt-modified textile electrode. The electrooxidations with Pt-modified textile electrodes showed a significant reduction in electrolysis time. Ultraviolet-visible and Fourier transform infrared with attenuated total reflection spectra enabled the electrochemical behavior of the non-modified and Pt/PANI-modified electrodes to be distinguished.The authors wish to acknowledge to the Spanish Ministerio de Ciencia e Innovacion (contract CTM2011-23583) and Universitat Politecnica de Valencia (Vicerrectorado de Investigacion PAID-06-10 contract 003-233) for the financial support; and as well as Carbongen S. A. (Cocentaina, Spain), who kindly donated the activated carbon fabric. J. Molina is grateful to the Conselleria d'Educacio, Formacio i Ocupacio (Generalitat Valenciana) for the Programa VALi+D Postdoctoral Fellowship. A.I. del Rio is grateful to the Spanish Ministerio de Ciencia y Tecnologia for the FPI fellowship.Fernández Sáez, J.; Del Río García, AI.; Molina Puerto, J.; Bonastre Cano, JA.; Cases Iborra, FJ. (2015). Modified carbon fabric electrodes: preparation and electrochemical behavior toward amaranth electrolysis. 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