Solutions of DB71 dye (C40H23N7Na4O13S4, Aldrich) of different
concentrations were prepared in distilled water.
Then, they were homogenized by stirring until completely
dissolving the dye. The pH of the reaction mixture was adjusted
by adding sulfuric acid and was measured by a pH-meter
(330i WTW 82362, Weilheim). The dye oxidation was
achieved by Fenton’s reagent which was composed of a mixture
of FeSO4.7H2O and H2O2 30% (products Riedel-de
Hae¨ n). The necessary quantities of Fe2+ and H2O2 were added
simultaneously in the dye solution. The experimental device
was constituted of a perfectly agitated reactor in which a volume
(500 ml) of solution was studied. The maximum absorbance
wavelength (kmax) of DB71 was found to be 587 nm.
The kinetics of the oxidation was followed by taking samples
at regular time intervals. The residual concentration of the
dye in the solution at different times of sampling was determined
by UV Visible spectroscopy. COD was determined
(Merck Spectroquant TR320) by a closed reflux colorimetric
method according to Standard Methods for the Examination
of Water and Wastewater (APHA, 1985). The amount of
H2O2 causing enterprise in COD analysis was subtracted from
the amount of COD determined by using the I
3 method (Kang
et al., 1999). The chemical structure of DB71 is shown in Fig 1
(Saien and Soleymani, 2007).