PHOTOCATALYTIC DEGRADATION OF PATENT BLUE V BY SUPPORTED TiO₂: KINETICS, MINERALIZATION, AND REACTION PATHWAY

Abstract

The photocatalytic degradation of patent blue V (sodium salt of [4-(α-(4-diethylaminophenyl)-5-hydroxy-2, 4-disulfophenyl-methylidene)-2, 5-cyclohexadien-1-ylidene] diethylammonium hydroxide) in aqueous solutions has been investigated by using TiO₂-coated nonwoven fibers as the photocatalyst. Before the study began, adsorption in the dark was done, and the effect of the initial concentration of dye in the solution was determined. The mineralization was monitored by chemical oxygen demand (COD), and the HPLC-MS method was used to identify reaction intermediates. The experimental results show that adsorption is an important parameter, controlling the apparent kinetic constant of degradation. The rate of fading was favored by a high concentration of dye in the solution with respect to the Langmuir-Hinshelwood model. The COD abatement was slower than the discoloration of the solution; this indicates that the dye was not directly mineralized, but transformed to intermediate photoproducts. These intermediate photoproducts lead to other cycles of degradation, to the point of total mineralization. Several by-products were detected and identified by HPLC-MS. On the basis of these findings, we propose a probable degradation pathway as critical for assessing the suitability of detoxification procedures for the degradation of particular contaminant classes.

Keywords:

• Mineralization
• Patent blue V
• Photocatalysis
• Reaction pathway
• Supported TiO₂

Acknowledgments

The authors would like to gratefully thank Mr. J. Dussaud from Ahlstrom Research & Services (France) for generously supplying the photocatalyst used in the work reported here.