Effect of iron catalyst on caffeine oxidation by sono-Fenton technology

Oxidation of waters containing 100.0 mg L-1 of caffeine was conducted by a sono-Fenton treatment employing an ultrasound power of 720W at pH=3.0 and T=25°C. The catalytic action of ferrous ion was studied in a range of [Fe2+]0=0-100.0 mg L-1, using oxidant ratios of [H2O2]0=250.0 mM. The oxidation of caffeine was fitted to second order kinetic model, with the oxidation kinetic constant showing a linear dependence with iron dosage. During oxidation, the water acquired yellow-brown colour, along with an increase of turbidity and aromaticity degree. This is due to byproducts formation of uric acid-derived that has strongly aromatic structures that contain chromophore groups. Iron could give rise to a reaction mechanism with organic matter through the formation of (hydro)peroxo iron complexes. The molar ratio of 1 mol Fe2+: 0.5 mol C8H10N4O2 : 250 mol H2O2 : 720W promotes the formation of coloured species that generate high turbidity in the water.