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International Journal of Photoenergy
Volume 3, Issue 4, Pages 181-186
http://dx.doi.org/10.1155/S1110662X0100023X

Photoredox reactions of environmental chromium

Faculty of Chemistry, Jagiellonian University, Ingardena 3, Kraków 30-060, Poland

Copyright © 2001 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The role of direct photochemical reactions of Cr(VI) and Cr(III) species in the environmental degradation of organic matter was investigated by means of Cr(VI)/alcohol and Cr(III)/EDTA model systems under conditions mimicking the environmental ones. Photoreduction of Cr(VI) proceeds through reductive quenching of chromate(VI) excited within UV-A by an alcohol molecule. Although HCrO4 is more susceptible to the quenching than the CrO42 ion, and oxygen favours the reverse reaction, the reduction can be easy noticeable at air-saturated natural waters. Photoredox behaviour of [crEDTA(L)]n- is more complex: it is initiated also by photoreduction, Cr(III) hv Cr(II), which at alkaline medium and a large excess of O2 over Cr(II) is followed by the Cr(II) Cr(VI) oxidation. Both the photoreductions are accompanied by oxidation of organic matter. Due to the substitutional lability of the [crEDTA(L)]n- complexes the conditions can be adjusted under which the Cr(VI)/Cr(III) forms are able to mediate the O2 oxidation of organic matter in the environmental photocatalytic cycle.