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

The sono-catalytic 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 degrees C) in the presence of Co₃O₄/TiO₂ and Pt/TiO₂ nano-catalysts. About 90% of EDTA (C_o = 5 10^-3) M) was oxidized during ultrasonic treatment at 40 degrees 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 (E_a = 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. (authors)