Sonocatalytic degradation of oxalic acid in the presence of oxygen and Pt/TiO2

• Oxidation of oxalic acid is enhanced under 360 kHz ultrasound, Pt/TiO2 and oxygen.
• OH radicals formed by sonolysis contribute to catalytic activity enhancement.
• High frequency ultrasound leads to the highest oxalic acid degradation rate increase.
• 360 kHz ultrasonic irradiation drastically reduces the average catalyst aggregate size.

In order to treat aqueous effluents containing organic pollutants, several techniques can be considered depending on the organic compound concentration. Sonochemistry appears to be a promising solution to answer water remediation issue. In fact, when submitted into a liquid, ultrasound can induce the nucleation, growth, and violent collapse of vapor/gas filled bubbles. However, despite the extreme local conditions observed during acoustic cavitation, using ultrasound alone is efficient only at low concentration in organic pollutants. In the present study, 0.05 M oxalic acid degradation kinetics were followed at 40 °C under various conditions, in presence or not of Pt/TiO2 catalyst under silent conditions or ultrasound at 20 and 360 kHz. Experiments were achieved under controlled atmosphere and comparison between argon, Ar/O2 (20 vol% O2) and pure O2 conditions was performed. Oxidation rate increase of oxalic acid was measured under Ar/O2 atmosphere in presence of Pt/TiO2 catalyst due to strong dispersion effect of both low and high ultrasonic frequency and formation of chemically active species by sonolysis. High frequency ultrasonic irradiation under Ar/O2 atmosphere gives the highest kinetic increase compared to silent conditions with oxalic acid degradation rate around 13 μmol min−1 at 40 °C with 2 g L−1 of 3 wt% Pt on P25 TiO2 catalyst.