Photoinduced reduction of chromium(VI) by iron aminopolycarboxylate complex (FeNTA)

O. ABIDA; G. MAILHOT; H. MESTANKOVA; M. LITTER; M. BOLTE

Photochemical and Photobiological Sciences

ROYAL SOC CHEMISTRY

Año: 2010 vol. 9 p. 823 - 829

1474-905X

Chromium(VI) reduction photoinduced by iron(III) nitrilotriacetate (FeNTA) was investigated under monochromatic excitation. 313 nm was used as the irradiation wavelength in order to minimize the absorption of the light by chromium(VI): 91% of the photons were absorbed by FeNTA at pH = 7.0. Quantum yields of FeNTA and chromium(VI) disappearance and iron(II) formation were measured at pH’s 2.0, 4.0 and 7.0. In all the cases, chromium(VI) reduction follows a first order kinetics with a maximum of efficiency at pH = 2.0. The observed rate constant is proportional to FeNTA concentrations up to a maximum for FeNTA concentration equal to 6.0×10-4 mol.L-1. The effect of oxygen was also investigated. If there is no large pH effect and no effect of oxygen on the quantum yields of chromium(VI) and FeNTA disappearance, the pH strongly influences the nature of the reduced chromium species. At pH = 2.0, only chromium(III) was detected whereas at pH = 4.0 and 7.0 no chromium(III) resulting from chromium(VI) reduction was observed. Chromium(V) is supposed to be formed and stabilized by the chelating groups of NTA or NTA photoproducts.