Degradation of Rhodamine B in water alone or as part of a mixture by advanced oxidation processes

Abstract

Degradation of a dye in water alone or as part of a mixture was studied under different advanced oxidation processes in order to elucidate possible competition or interference between dyes. For this purpose, color degradation of aqueous solutions of Rhodamine B alone or mixed with Indigo Carmine was evaluated under ultrasound, ultraviolet radiation and under their combined effect, in the presence or absence of catalyst, which was either TiO₂ (Degussa P-25) or a mixed catalyst TiO₂-ZrO₂ prepared by sol gel method.

Regardless of the oxidation process used, results suggest that Rhodamine B discoloration was negatively affected by the presence of Indigo Carmine, which was degraded preferentially. Concerning the oxidation processes, synergy was observed for the combined operation of ultrasound and ultraviolet radiation in the presence of TiO₂ catalyst, for both dyes when treated individually, however, for a mixture of dyes synergetic degradation was observed only for Indigo Carmine. It appears that competition exists between individual components in a mixture for the access to catalyst reaction sites and interaction with hydroxyl radicals, and which seem to ease the degradation of some components in detriment of others.

Photosonocatalytic degradation of these dyes was not improved by the presence of mixed TiO₂:ZrO₂ catalysts as compared with Degussa P-25 catalyst. However, for the case of Rodamine B, the yield of decolorized dye converted into mineralized products appears to be enhanced for the mixed catalyst.

Keywords:

• Dye mixture
• sonocatalysis
• Indigo Carmine
• photocatalysis
• photosonocatalysis
• Rhodamine B