Photoreduction of Cr(vi) using hydroxoaluminiumtricarboxymonoamide phthalocyanine adsorbed on TiO2
Hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc) adsorbed at different loadings on TiO2 Degussa P-25 was tested for Cr(vi) photocatalytic reduction under visible irradiation in the presence of 4-chlorophenol (4-CP) as sacrificial donor. A rapid reaction takes place in spite of the presuma...
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| Autores principales: | , |
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2009
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_1474905X_v8_n5_p604_Meichtry http://hdl.handle.net/20.500.12110/paper_1474905X_v8_n5_p604_Meichtry |
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| Sumario: | Hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc) adsorbed at different loadings on TiO2 Degussa P-25 was tested for Cr(vi) photocatalytic reduction under visible irradiation in the presence of 4-chlorophenol (4-CP) as sacrificial donor. A rapid reaction takes place in spite of the presumable aggregation of the dye on the TiO2 surface. The removal of Cr(vi) is fairly negligible under visible-light irradiation, either without photocatalyst or in the presence of bare TiO2. The fast capture of conduction band electrons by Cr(vi), which forms a surface complex with TiO2, inhibits the formation of reactive oxygen species in the reductive pathway. This fact and the easier oxidation of 4-CP as compared to AlTCPc hinder the photobleaching of the dye and make feasible Cr(vi) reduction under visible irradiation. The consumption of Cr(vi) follows a pseudo-first order kinetics; the decay constant depends, in the studied range, on the photocatalyst mass, but it is barely affected by dye loading. The presence of 4-CP is essential, but its concentration has no effect on the Cr(vi) decay rate. Oxidation products of 4-CP, such as hydroquinone, catechol or benzoquinone, are not observed. Direct evidence of the one-electron reduction of Cr(vi) to Cr(v) was obtained by EPR spectroscopy using citric acid as Cr(v) trapping agent. In this case, disappearance of Cr(v) also follows a first order decay, but conduction band electrons do not seem to be involved. The fact that oxidation products of 4-CP are not observed is consistent with the fast dark removal of reaction intermediates by Cr(v), proved by EPR. © The Royal Society of Chemistry and Owner Societies 2009. |
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