Highly-efficient removal of norfloxacin with nanoscale zero-valent copper activated persulfate at mild temperature

In this study, mild temperature was applied to enhance norfloxacin (NOR) degradation in nanoscale zero-valent copper (nZVC) activated persulfate (PS) process and the underlying activation mechanism was detailedly elaborated. Results showed that the activation performance of nZVC was far superior than that of micro zero-valent copper (mZVC), and almost complete elimination of 31.32 μM NOR was achieved within only 5 min in the condition of 0.05 g/L nZVC and 1.0 mM PS at 40 °C. The in-situ generated Cu+ was found to be the pivotal active copper species for PS activation and the presence of dissolved oxygen was favorable for its release. Mild temperature not only accelerated the Cu+ release from the nZVC corrision, but provided more opportunity for intermolecular collision to quickly form reactive oxygen species. SO4−∙ and ∙OH played the primary role for NOR destruction, while O2−· and H2O2 served as the mediators for copper cycling. The higher PS concentration favored NOR removal, whereas overdosing nZVC exerted the negative impact. Further increasing reaction temperature significantly accelerated the elimination of NOR in nZVC/PS process. The satisfactory removal of NOR was achieved under the acidic and neutral conditions. The NOR oxidation in the tested process was found to follow four routes and the cleavage of piperazine ring was determined to be the primary one. These encouraging results demonstrated that mild temperature enhanced nZVC/PS process was a promising strategy for the treatment of refractory and non-biodegradable industrial wastewater.