- Novel integrated carbon particle based three dimensional anodes for the electrochemical degradation of reactive dyes
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Three-dimensional carbon bed electrochemical reactors have been recently applied for the degradation of several organic pollutants. However, the carbon particles in such reactors slowly undergo attrition. We fabricated a novel flow-through three-dimensional anode using granular activated carbon (GAC) particles and polyvinylidene fluoride (PVDF) binder that potentially avoids such attrition. Optimization of the composition of GAC and PVDF with respect to mechanical integrity and electrical conductivity is reported. The anodes were tested in the electro oxidation of the reactive dyes: Reactive Orange-16 (RO-16), Reactive Red-2 (RR-2), and Reactive Blue-4 (RB-4). A tentative mechanism of dye degradation was proposed based on the observed role of the supporting electrolyte and the cyclic voltammetric, UV-vis, FT-IR and GC-MS data. The decolorization efficiencies were 75 ± 3, 81 ± 5 and 88 ± 4% for RB-4, RO-16 and RR-2, respectively. The integrated 3-D anodes are advantageous because of the absence of carbon attrition, which is otherwise found when a bed of GAC is used in the electrochemical reactors.
- Misra, Rohit,Neti, Nageswara Nao,Dionysiou, Dionysios D.,Tandekar, Mahendra,Kanade, Gajanan S.
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- Kinetics and mechanism of aliphatic amine oxidation by aqueous (batho)2CuII
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The kinetics of oxidation of a large series of aliphatic amines by the "high-potential" oxidant (batho)2CuII (batho = 2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolinedisulfonate) was studied under pseudo-first-order conditions (excess amine) in water or in 30% aqueous methanol (v/v) at 25 °C over the pH range 7-11. The oxidations follow bell-shaped pH-rate profiles, with the low-pH leg reflecting the fact that only the free amine base is subject to oxidation and the high-pH leg representing conversion of (batho)2CuII to an ineffective oxidant at high pH. The latter is thought to be (batho)CuII(OH2)OH on the basis of the observed effect of [batho] on rate at high pH, and curve fitting of the rate data yielded estimates of the unitless Keq values governing this conversion. The variation in rate with degree of N-substitution and other structure-reactivity trends (such as the effect of ring size and the non-rate-retarding effect of 2,4,6-trimethyl substitution on PhCH2NR2) support a mechanism involving initial outer-sphere one-electron transfer, followed by proton transfer to the solvent, and then a rapid second one-electron oxidation to give imine/iminium product. Inner-sphere coordination of chelating amines shuts down the redox reaction, presumably as a consequence of displacement of the batho ligand(s) needed for high oxidant strength. Deuterium kinetic isotope effect (DKIE) measurements (i) comparing PhCD2N(CD3)2 vs PhCH2N(CH3)2 (intermolecular DKIE) and (ii) determining N-dealkylation preference in the case of PhCH2N(CH3)CD2Ph (intramolecular DKIE) suggest that the initial electron transfer is mainly rate-limiting. A rate comparison between erythro and threo diastereomers of 1,2-diphenyl-2-piperidinoethanol indicates a stereoelectronic preference for one-electron oxidation at nitrogen when held antiperiplanar to a β-hydroxyl. Stoichiometry studies using an excess of the Cu(II) oxidant reveal regioselective and chemoselective factors governing the overall amine-to-iminium oxidations.
- Wang, Fengjiang,Sayre, Lawrence M.
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p. 248 - 255
(2007/10/02)
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