In this study, removal of malachite green (MG), a cationic triphenylmethane dye, by 300 kHz ultrasound was investigated. The effects of operating parameters such as initial dye concentration, ultrasound power and initial pH on the sonochemical degradation were studied. The initial rate of MG degradation and hydrogen peroxide formation as a function of initial concentration were determined. The obtained results show that the degradation rate increases with increasing initial dye concentration up to a plateau. The rate of hydrogen peroxide formation decreases with increasing substrate concentration and reaches a minimum, followed by almost constant production rate for higher MG concentrations. The dominant degradation mechanism is the reaction of substrate with (OH)-O-center dot radicals both at the gas bubble-liquid interface and in the bulk solution. Sonochemical degradation of MG occurs via two competitive processes: N-demethylation and destruction of the conjugated structure. The degradation rate increased proportionally with increasing ultrasonic power, but decreased with the increase of initial pH value from 2 to 7. In the presence of 10 mg/L Fe(II), the initial degradation rate of MG became 2 times larger for initial dye concentration of 5 mg/L and 1.5 times larger for initial substrate concentration of 10 mg/L, respectively. (C) 2012 Elsevier B.V. All rights reserved.