Photocatalytic degradation of a mixture of two anionic dyes: Procion Red MX-5B and Remazol Black 5 (RB5)

The photocatalytic degradation of a mixture of two anionic dyes, Remazol Black (RB5) and Red Procion MX-5B in presence of TiO2 Degussa P-25 was investigated using wavelength higher than 290 nm. UV-vis spectroscopy was employed to monitor the amount of each dye in the mixture and to compare the degradation of both dyes individually and mixed. The adsorption equilibrium of each dye, the influence of pH and the initial concentration of dyes on the kinetics of discoloration and mineralization were performed and compared to their kinetics when they are individually degraded. Although no complex was put in evidence between these two coloring agents using spectroscopy UV-vis, an important modification of the RB5 adsorption is noted in the mixture. However, the presence of RB5 has no effect on the MX-5B adsorption. This difference of behaviour can be explained by considering the modification of pH by increasing the initial concentration of MX-5B in the mixture. Above 15 mu mol/L, both anionic dyes are in competition for the same site. Even if the adsorption of RB5 is modified, the disappearance rate of both dyes individually or mixed are similar at low concentration of dyes. At high concentration their disappearance rates in the mixture decrease in agreement with the number of available site. Besides the study of the discoloration, we studied the evolution of Total Organic Carbon (TOC), the formation of NH4+, NO3-, SO42- of both dyes during their individual or mixed photocatalytic degradation are compared. The results suggest that the mechanisms of degradation are modified in the mixture. (C) 2010 Elsevier B.V. All rights reserved.