Synergy of dielectric barrier discharge plasma and magnetically separable MOF-derived Co@C composite for the improved degradation of norfloxacin antibiotic in water

Abstract

Norfloxacin (NOR) is a highly toxic fluoroquinolone antibiotic, which is continuously discharged into aquatic environment. Due to its poor biodegradability, NOR is difficult to be removed and has exerted a serious impact on environmental risk. In this paper, a coaxial double dielectric barrier discharge (DBD) device was designed and built, then was synergic with cobalt-carbon (Co@C) composites for the improved degradation of NOR in wastewater with high degradation efficiency. The Co@C composite, a porous carbon material, was synthesized by calcination of Co-metal organic frameworks (Co-MOFs), and was further characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface analyzer, Fourier transform infrared spectrometry and vibrating sample magnetometer. The combination of DBD with Co@C system has an obvious synergistic effect for the removal of NOR. The degradation rate could reach to 84.7% and the treatment time was in 15 min, which were 14.1% higher and 10 min shorter than those of solo DBD system. The synergistic factor was estimated to be 1.12, and the energy yield of process could reach to the maximum of 7.6 mg/kWh. The effects of discharge voltage, pH, NOR initial concentration and Co@C dosage on the degradation rate of NOR have been explored in detail. The experimental results indicated that the system of DBD coupled with Co@C for NOR degradation was appropriate in a wide initial pH from 3.0 to 11.0. Moreover, Co@C could be reused several times and convenient to be magnetically recycled. Furthermore, it was proved that O3, •OH and H2O2 were the main reactive oxygen species during the catalytic decomposition reactions of NOR, and the generated O3 in DBD system could be converted into •OH under the synergic catalysis of Co@C, further promoting degradation efficiencies for NOR. Finally, main intermediate products of NOR degradation were analyzed by liquid chromatography-mass spectrometry, and possible degradation mechanism and pathways were speculated.