Degradation of reactive, acid and basic textile dyes in the presence of ultrasound and rare earths [Lanthanum and Praseodymium]

• Sonochemical degradation of acidic, basic and reactive dyes have been undertaken.
• Degradation of dye molecules followed pseudo-first order reaction.
• The rate constant (k), half life (t1/2) and the sonochemical efficiency (φ) have been calculated.
• Effect of the concentration of dye, pH and the rare earth ion concentration has also been examined.
• Degradation sequence of dyes was examined through LCMS and Raman spectroscopic techniques.

Degradation of five textile dyes, namely Reactive Red 141 (RR 141), Reactive Blue 21 (RB 21), Acid Red 114 (AR 114), Acid Blue 113 (AB 113) and Basic Violet 16 (BV 16) in aqueous solution has been carried out with ultrasound (US) and in combination with rare earth ions (La3+ and Pr3+). Kinetic analysis of the data showed a pseudo-first order degradation reaction for all the dyes. The rate constant (k), half life (t1/2) and the process efficiency (φ) for various processes in degradation of dyes under different experimental conditions have been calculated. The influence of concentrations of dyes (16–40 mg/L), pH (5, 7 and 9) and rare earth ion concentration (4, 12 and 20 mg/L) on the degradation of dyes have also been studied. The degradation percentage increased with increasing rare earth amount and decreased with increasing concentration of dyes. Both horn and bath type sonicators were used at 20 kHz and 250 W for degradation. The sonochemical degradation rate of dyes in the presence of rare earths was related to the type of chromophoric groups in the dye molecule. Degradation sequence of dyes was further examined through LCMS and Raman spectroscopic techniques, which confirmed the sonochemical degradation of dyes to non-toxic end products.