Sonophotocatalytic degradation of Rhodamine B using a novel reactor geometry: Effect of operating conditions

In this work, the decoloration of azo dye in aqueous solution by an ultrasound-assisted photocatalytic oxidation (US/UV/TiO2) process was addressed. Rhodamine B (RhB) (basic violet 10), as the model compound, was decolorized completely within a few minutes in the US/UV/TiO2 system. A more remarkable synergistic effect was observed on the RhB decolorization by US/UV/TiO2 process, at low ultrasound frequency, than that observed in the case of individual process such as sonolytic (US), photolytic (UV) or photocatalytic oxidation (UV/TiO2). The effects of various operating conditions such as initial dye concentration, TiO2 concentration, hydrogen peroxide (H2O2) concentration, ultrasound power and temperature were investigated. In addition, the effects of the presence of radical scavenger tert-butyl-alcohol and the carbon tetrachloride (CCl4) on the decolorization rate were also studied. Sonophotocatalytic decolorization of RhB was strongly influenced by the initial substrate concentration, acoustic power, temperature and catalyst concentration. It was also found that the dye decolorization was enhanced with increasing CCl4 concentrations due to the formation of oxidant chlorine species. RhB decolorization increased slightly with increasing the H2O2 concentration, with an optimum level reached at H2O2 concentration of 1 mmol/L. The rate of dye decolorization was inhibited by the presence of low concentration of tert-butyl-alcohol. If the sonophotocatalysis is carried out in the presence of high tert-butyl-alcohol concentration, a very little RhB decolorization occurs. At low ultrasound frequency, the results indicated that total chemical oxygen demand (COD) removal was obtained in the tested RhB solutions when applying US/UV/TiO2 system, signifying its great potential for the treatment of wastewaters contaminated with Rhodamine B.

► The potential application of the sonophotocatalytic process has been evaluated.
► The decolorization of Rhodamine B depends on the operating conditions.
► A novel sonophotocatalytic reactor configuration has been evaluated at low ultrasound frequency.
► The presence of CCl4 increases the decolorization percentage.