Sonocatalytic oxidation of EDTA in aqueous solutions over noble metal-free Co3O4/TiO2 catalyst

Abstract

The sonocatalytic degradation of EDTA in aqueous solution was studied under ultrasound irradiation (345 kHz, 73 W, acoustic power 0.20 W·mL−1, Ar and Ar/O2 saturating gases, T = 20–50 °C) in the presence of Co3O4/TiO2 and Pt/TiO2 nanocatalysts. About 90% of EDTA (C0 = 5 10-3 M) was oxidized during ultrasonic treatment at 40 °C in the presence of the Co3O4/TiO2 catalyst and Ar/O2 gas mixture. By contrast, Pt/TiO2 catalyst exhibited much lower sonocatalytic activity in this system. Suggested mechanism of EDTA oxidation in the presence of Co3O4/TiO2 catalyst involved the generation of oxidizing radicals by acoustic cavitation and Co(II)-Co(III) redox process. Quite low apparent activation energy of the sonocatalytic process (Ea = 19 kJ mol−1) was attributed to diffusion of reagents in the vicinity of the active sites of catalyst. Sonocatalytic degradation of EDTA is accompanied by formation of iminodiacetic acid, formic acid, oxalic acid, glycolic acid and acetic acid as intermediate products in an agreement with radical-driven mechanism.