Removal of norfloxacin by surface Fenton system (MnFe2O4/H2O2): Kinetics, mechanism and degradation pathway

Abstract

Magnetic MnFe2O4 particles were prepared by sol-gel method and used to activate H2O2 for norfloxacin removal from water. The results of hydrodynamic particle size distribution and Zeta potential analyses show that the particle size ranged from 100 nm to 500 nm, and Zeta potential from −76 mV to −25 mV at pHintial = 7.0. The MnFe2O4/H2O2 system was able to remove 90.6% of norfloxacin at neutral pH, and the spent material can be reused in multiple cycles of operations. Fluorescence detection and DMPO capture analyses indicated that OH was the main free radicals, which played a primary role in degradation of norfloxacin. The valence variations of Mn and Fe were analyzed by XPS, and the results showed that coupled transformations of Mn2+/Mn3+ and Fe2+/Fe3+ were involved in generation of OH. Moreover, the removal rate in the MnFe2O4/H2O2 system showed a positive correlation with the adsorption efficiency of NOR by MnFe2O4. Eight degradation intermediates were detected by LC-QToF-MS/MS, and consequently, three degradation pathways were proposed, including defluorination, piperazinyl ring opening, and quinolone transformation. Further analyses of F−, NH4+, NO3− and NO2− before and after the reaction showed that defluorination process was the main degradation pathway. The MnFe2O4/H2O2 system may offer an efficient alterative for degradation of emerging persistent contaminants.