Ultrasound-enhanced nanosized zero-valent copper activation of hydrogen peroxide for the degradation of norfloxacin

Commercial nanosized zero-valent copper (nZVC) was used as hydrogen peroxide (H 2 O 2 ) activator in conjunction with ultrasonic irradiation (US) for the oxidative degradation of norfloxacin (NOR) in this study. Compared with silent degradation system, a significantly enhanced NOR removal was obtained in sono-advanced Fenton process, which involved a synergistic effect between sonolysis and Fenton-like reaction. Almost complete removal of NOR was achieved at 30 min when the operating conditions were 0.25 g/L nZVC and 10 mM H 2 O 2 with ultrasound power of 240 W at 20 kHz. The released Cu + during the nZVC dissolution was the predominant copper species to activate H 2 O 2 and yield hydroxyl radicals ( OH) in US/nZVC/H 2 O 2 system. According to the radical quenching experiments and electron paramagnetic resonance technique, hydroxyl radicals in solution ( OH free ) were verified as the primary reactive species, and superoxide anion radicals ( O 2 − ) were regarded as the mediator for the copper cycling by reduction of Cu 2+ to Cu + . NOR removal efficiencies were improved in various degrees when increased nZVC dosage, ultrasound power, hydrogen-ion amount and H 2 O 2 concentration. Moreover, the inhibitory effect of different inorganic salts on NOR degradation followed the sequence of Na 2 SO 4 > NaNO 3 ≈ no salt > NaCl > NaHCO 3 . Finally, eleven intermediates were identified and five oxidation pathways were proposed, the cleavage of piperazine ring and transformation of quinolone group seemed to be the major pathway.