Degradation Of Norfloxacin By Prussian Blue Modified Ceria Heterogeneous Fenton-like System

In recent years,the overuse of antibiotics has posed a potential threat to human health and ecosystem balance.It has become one of the research hotspots in the field of environmental science for developing proficient and fast treatment technologies to remove such refractory organics efficiently.As a typical class of fluoroquinolone antibiotics,norfloxacin（NOR）,which belongs to one of widely used antibacterial agents,has been frequently detected in the environmental waters.Besides,NOR was difficult to be biodegraded in traditional municipal waste water treatment plants due to its persistent biological toxicity and oxidation-refractory properties.Fenton and Fenton-like processes,as newly fast devoloping treatment technologies in advanced oxidation processes,which can produce highly active free radicals to removal refractory organic pollutants.Based on the construction of prussian blue modified ceria（PB/CeO₂）heterogeneous Fenton-like system,the influence factors and Fenton-like catalytic mechanisms towards the degradation of NOR were investigated.In this work,the preparation methods of PB/CeO₂ heterogeneous Fenton-like catalysts were explored,and the morphologies and structural characteristics of catalysts synthesized were studied.The degradation efficiencies and reaction mechanisms of NOR were researched and analyzed.The photocatalytic performances,optical constructions and Fenton-like reaction mechanisms of PB/CeO₂ were investigated for the first time.The molecule of NOR were calculated by guassian09 software to deduce the reactive sites.The degradation intermediates were detected by LC-MS/MS to analyze the possible degradation pathways.The results showed that:（1）The crystal structure of CeO₂ was affected by the two different doping methods of PB.Among them,physical doping didn’t change the morphology and structure of CeO₂ obviously,but the lattice distortion of CeO₂ occurred in the chemical doping process,which increased the lattice spacing and specific surface area.X-ray photoelectron spectroscopy results showed that Ce atoms could be partially replaced by Fe in the doping process,which promoted the formation of oxygen vacancies.Moreover,the Ce³⁺content of chemically supported catalyst was higher than that of physically supported catalyst.（2）NOR could be effectively removed by PB/CeO₂ heterogeneous Fenton-like catalyst in fresh water.The effects of multiple parameters on the degradation of NOR were investigated.The results showed that the concentration of catalyst,the doping amount of PB,the concentration of H₂O₂and the reaction temperature promoted the degradation of NOR.PB/CeO₂composite showed well catalytic adaptability and stability at the wide p H value range of 2-9,with the low dissolution content of iron.Fourier transform infrared spectroscopy indicated that the functional group structures of PB/CeO₂ remained stable before and after the reaction.In addition,free radical quenching experiments and electron spin resonance characterization results demonstrated that·OH was the main active species in the Fenton-like reaction.（3）The photocatalytic degradation experiments of PB/CeO₂ showed that there was an excellent synergistic photocatalysis between PB and CeO₂.Under the irradiation of UV,the degradation rate of NOR was significantly improved,and the mineralization degree of pollutants was also observably facilitated.The UV-vis DRS spectra confirmed that PB/CeO₂ exhibited strong absorption in the near-ultraviolet region.Meanwhile,photoluminescence spectroscopy indicated that PB/CeO₂ possessed superior efficiency of electron-hole separation.The electron paramagnetic resonance further revealed that oxygen vacancies enhancing Fenton-like photocatalytic oxidation was the main reaction mechanism.（4）Based on the density functional theory（DFT）,the frontier orbitals and charge distribution characteristics of NOR were calculated and analyzed.The results indicated that piperazine ring and fluorine atom were the main electron-donating groups and reaction sites,which could be attacked by electrophilic reagents easily.Two main degradation pathways of NOR were inferred:the fragmentation of piperazine ring and defluorination.