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ABSTRACT: Homogeneous aqueous solutions of organochlorine pesticides and chlorophenols, namely, lindane, hexachlorobenzene and 2,4-dichlorophenol
(2,4DCP), undergo effective photodegradation upon photolysis with UV and near visible light in the presence of a characteristic
polyoxometallate catalyst PW12O40
3−. These substrates remained, practically, intact (lindane, HCB) or underwent minor degradation under similar conditions in
absence of catalyst. The main oxidant appears to be OH radicals formed by the reaction of the excited polyoxometallate with
H2O. The system compares with the widely published TiO2. Chlorohydroquinone (ClHQ), hydroquinone (HQ), chlorobenzoquinone (ClBQ), benzoquinone (BQ), 3,5-dichlorocatechol (3,5DCC)
and 4-chlorocatechol (4CC), among others, were identified as the main aromatic intermediates in the photodegradation of 2,4DCP.
Acetic acid was detected as ring cleavage product. In all cases the final photodegradation leads to complete mineralization
of substrates to CO2 and HCl.
Research on Chemical Intermediates 12/1999; 26(3):235-251. · 0.70 Impact Factor
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ABSTRACT: Photolysis of homogeneous solutions of polyoxometalates W10O324−, PW12O403−, and SiW12O404− with near visible and UV light in presence of chlorophenols, leads to complete decomposition of substrates to CO2 and HCl. At the initial stages of photooxidation, decomposition rates, in presence and absence of dioxygen, practically complete with each other. On the contrary, at the final stages of decomposition, the rate in presence of dioxygen is an order of magnitude faster than in absence of dioxygen. The main function of dioxygen seems to be the reoxidation (regeneration) of the catalyst. Several hydroxyl intermediates justify the formation of OH radicals. The hydroxyl aromatic derivatives detected are in accordance with the electrophilicity of OH radicals. Hydroxy butanedioic acid and acetic acid were detected in the three monochlorophenols, prior to mineralization.
Journal of Photochemistry and Photobiology A: Chemistry.
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ABSTRACT: Homogeneous oxygenated aqueous solutions of chlorophenols, undergo photodegradation (λ > 320 nm) to CO2 and Cl− by polyoxometalates W10O4−32, PW12O3−40, and SiW12O4−40. Mineralization takes place, also, in the absence of dioxygen but the process is more than an order of magnitude slower. In presence of dioxygen the effectiveness of these catalysts compares with TiO2 suspension.
Journal of Molecular Catalysis.
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ABSTRACT: Polyoxometalates appear to be effective photocatalysts for a variety of organic pollutants, leading to their decomposition to CO2 and H2O and Cl− in case of chlorinated hydrocarbons. Various aromatic derivatives and chlorinated acetic acids, undergo mineralization upon photolysis with near visible and UV light, in presence of W10O4−32, PW12O3−40, and SiW12O4−40. These catalysts are, at least, as effective as TiO2. The main oxidant appears to be OH radicals formed by the reaction of the excited polyoxometalates with H2O. At the initial stages of photoreaction, dioxygen has a profound effect (up to eighteen times faster) on the photodegradation of chloroacetic acid, whereas, it has minor effect on chlorophenols. On the contrary, at the final stages of photodegradation of chlorophenols, the rates were an order of magnitude faster in presence than in absence of dioxygen. Substitution of WO moiety of SiW12O4−40 for transition metals, namely, [H2OMnIISiW11O39]6− and [H2OCuIISiW11O39]6− reduced, by about an order of magnitude, the effectiveness of the catalyst.
Journal of Molecular Catalysis A: Chemical.
