Effects of salt and pH on sonophotocatalytic degradation of azo dye reactive black 5

The effects of salt and pH on the sonophotocatalytic degradation of azo dye Reactive Black 5 (RB5) were investigated. The applied frequency was 35 kHz, and 254nm UVC lamps and TiO₂ were used. At salt concentrations of 0, 50, 500, and 5000 mg/L, salt acted as an inhibitor or a OH radical scavenger under neutral pH condition and there was no significant difference in the removal trends for salt-added conditions. Under acidic condition, adsorption of RB5 on the surface of TiO₂ was observed before the start of the sonophotocatalytic process and it was revealed that adsorption of RB5, negatively charged dye anions, could be enhanced under acidic condition because the charge of the TiO₂ surface was changed from negative to positive at a pH of 6.6. This enhancement under acidic condition was observed during the entire operation time. In the comparison of the pH and salt effects, the enhancement by acidic pH control was larger than the inhibition by the effect of salt as a radical scavenger.