Caffeine oxidation by sono-Fenton treatment

Oxidation of waters containing caffeine was conducted by a sono-Fenton treatment employing an ultrasound power of 720 W at pH=3.0 and T=25°C. The catalytic action of ferrous ion was studied in a range of [Fe]=0-100.0 mg/L and oxidant concentrations between [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, obtaining removals of 98% when dosing 485 mol H2O2/mol C8H10N4O2. During the oxidation, the water acquired a strong brown colour at the same time as there was a strong increase in turbidity and degree of aromaticity. The interaction of (hydro)peroxo-iron complexes with the byproducts of caffeine degradation (1,3,7-trimethyluric acid, theobromine, paraxanthine, theophylline) generated supramolecular structures, being 116 mol H2O2/mol C8H10N4O2, the relationship that induced colour and aromaticity, while the formation of turbidity was favoured by using 29 and 116 mol H2O2/mol C8H10N4O2.