Ultrasound-assisted degradation of methyl orange in a micro reactor

In this study, an aqueous solution containing methyl orange (MO) was indirectly sonicated in a polydimethylsiloxane/glass micro reactor using a 200 kHz transducer. A removal efficiency (RE) of about 9% was observed in 90 min when 5 mg L−1 MO solution was circulated at a flow rate of 0.76 mL min−1 at pH 2 and 20 °C. While a lower RE was observed with an increase in solution temperature, an increase in MO concentration, flow rate and acoustic power led to an increase in RE. The addition of 100 mg L−1 of CCl4 increased RE by 4% under similar experimental conditions. The mechanism of MO degradation involved sonochemically generated oxidising radicals, which was confirmed by the formation of H2O2 during sonolysis of water and reduction in RE with the addition of a radical scavenger.