Sonolytic degradation of naphthol blue black at 1700 kHz: Effects of salts, complex matrices and persulfate

In the present work, the effect of salts (NaCl and Na2SO4), complex matrices (natural water and seawater) and persulfate ions on the sonochemical degradation of an acidic diazo dye, naphthol blue black (NBB), in water at 1700 kHz was clarified. Additionally, the influence of initial dye concentration and liquid temperature on the extent of NBB sonolytic removal was investigated. It was found that the NBB degradation rate increased with increasing the initial substrate concentration in the range 3–15 mg L−1. Significant enhancements in the NBB degradation rates were observed at high liquid temperatures: 96.5% of NBB was removed at 65 °C after 45 min of sonication while only 51% was reached at 25 °C. The presence of salts (NaCl or Na2SO4) has a beneficial effect on NBB degradation. The degradation rate of NBB in the presence of 0.5 and 1 M NaCl was 3–6 times higher than that obtained without salt. Interestingly, faster degradation rates of NBB were observed in complex matrices. The complete destruction of NBB required 40 min in seawater and 60 min in natural water instead of 210 min in distilled water. The addition of persulfate (PS) ions improved substantially the sonochemical degradation of NBB through the ultrasonic (US) generation of sulfate radical (SO4–), which is more efficient toward the degradation of NBB. The system US/PS resulted in 100% NBB removal within only 60 min of ultrasonic treatment.