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Ruiz G.T.,Institute Investigaciones Fisicoquimicas Teoricas y Aplicadas | Juliarena M.P.,Institute Fisica Arroyo Seco IFAS | Ferraudi G.,University of Notre Dame | Lappin A.G.,University of Notre Dame | And 2 more authors.
Polyhedron | Year: 2012

We have explored in this work the photo- and thermally-induced degradations of water soluble lignin in aqueous homogeneous media. Coordination complexes, Al(III) phthalocyaninetetrasulfonate ([Al III(tspc)] 3- and tspc 6- = phthalocyaninetetrasulfonate) and Co III/II dimethylglyoximate (dimethylglyoximate = DMG -) were used as catalysts of degrading processes with different mechanisms. The photodegradation was induced with visible light, λ exc ≥ 470 nm, and [Al III(tspc)] 3- as the photosensitizer of the ( 3Σ g -)O 2 to ( 1Δ g)O 2 conversion. ( 1Δ g)O 2 was the primary active species of the degrading process. [Co(DMG) 2(SO 3) 2] 3- and [Co(DMG) 2Cl 2] - in the presence and absence of SO 3 2- were used as catalysts of the thermal lignin degrading process. Differences in the mechanisms of the photo and thermally induced processes lead to some diversity of products. Adducts formed in solutions containing [Al III(tspc)] 3- and lignin have the absorption spectrum of phthalocyanine oligomers and could be located in pockets of the lignin. Under a steady state irradiation, the attack of lignin by ( 1Δ g)O 2 was followed by changes in the spectrum of the solution and by the formation of various products. The participation of O 2 ·- radicals in the mechanism photodegrading process was investigated with the pulse radiolysis technique. Different lignin radicals were produced when pulse radiolytically generated O 2 ·- and N 3 · radicals reacted with lignin. The Co III/II dimethylglyoximate catalyzed lignin degrading process was investigated in the presence and absence of SO 3 2-. Although the presence SO 3 2- in the medium is not essential, it accelerates the degrading process. This observation shows the participation of inorganic S(V) radicals, e.g., SO 3 ·-, as active species in the mechanism when SO 3 2- is present. Moreover, the pulse radiolysis experiments demonstrate that O 2 ·- can be an active species when SO 3 2- is absent. © 2012 Elsevier Ltd. All rights reserved. Source

Nichela D.A.,National University of La Plata | Nichela D.A.,National University of Comahue | Berkovic A.M.,National University of La Plata | Berkovic A.M.,Institute Fisica Arroyo Seco IFAS | And 3 more authors.
Chemical Engineering Journal | Year: 2013

Nitrobenzene (NBE) degradation in Fenton-like systems using copper(II) as catalyst was investigated and compared with the trends observed in iron(III)-based systems. UV-vis spectroscopy, HPLC and TOC measurements were used to characterize the evolution of the reaction mixtures. Kinetic profiles were analyzed under a wide range of experimental conditions in order to assess the effects of the reaction temperature, initial concentrations and working pH. For both Cu(II)-based and Fe(III)-based systems, treatment times decreased with increasing oxidant and catalyst concentrations, but augmented with increasing NBE concentration. However, significant differences were observed for Cu(II)-based systems: higher activation energy above room temperature, broader pH range of activity with an optimal pH of about 6.2, absence of 1,3-dinitrobenzene among the reaction products and important reductions in the TOC levels even in the absence of irradiation. © 2013 Elsevier B.V.. Source

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