Ion-specific effects on the sonochemical degradation of Naphthol Blue Black: from inorganic salts to natural water matrices

This study investigates the effects of inorganic salts and natural water matrices on the high-frequency sonochemical degradation of Naphthol Blue Black (NBB). Experiments were conducted at 585 kHz and 3.58 W/cm 2 using initial NBB concentrations of 5 mg/L (8.11 × 10 −6 M) and 30 mg/L (4.87 × 10 −5 M). NaCl, KNO 3 , Na 2 SO 4 , and NaHCO 3 were evaluated over broad concentration ranges and compared with bicarbonate-rich Ca–Mg mineral water and seawater. The response depended strongly on ion identity and pollutant loading. Chloride produced the most persistent enhancement, nitrate showed a more modest positive trend, sulfate displayed an optimum-type response, and bicarbonate shifted from promotion at low concentration and low NBB loading to pronounced inhibition at higher concentrations. Both natural matrices enhanced NBB removal relative to ultrapure water, with seawater showing the greatest improvement. The observed trends are consistent with combined contributions from pollutant accessibility to the bubble–liquid interface, ion-dependent radical chemistry, and changes in the cavitation environment. These findings demonstrate the importance of realistic water chemistry when evaluating high-frequency sonochemical treatment of saline and mineralized waters.