Sonocatalytic degradation of oxalic acid in the presence of oxygenand Pt/TiO₂

In order to treat aqueous effluents containing organic pollutants, several techniques can be considereddepending on the organic compound concentration. Sonochemistry appears to be a promising solutionto answer water remediation issue. In fact, when submitted into a liquid, ultrasound can induce thenucleation, growth, and violent collapse of vapor/gas filled bubbles. However, despite the extreme localconditions 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 at40°C under various conditions, in presence or not of Pt/TiO₂ catalyst under silent conditions or ultrasoundat 20 and 360 kHz. Experiments were achieved under controlled atmosphere and comparison betweenargon, Ar/O₂(20 vol% O₂) and pure O₂ conditions was performed. Oxidation rate increase of oxalic acidwas measured under Ar/O₂ atmosphere in presence of Pt/TiO₂ catalyst due to strong dispersion effectof both low and high ultrasonic frequency and formation of chemically active species by sonolysis. Highfrequency ultrasonic irradiation under Ar/O₂ atmosphere gives the highest kinetic increase compared tosilent 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.