Radical Degradation Of Levofloxacin In Aqueous Solution With Fe-Cu Binary Oxide Hollow Sphere For Persulfate Activation

Nowadays,quinolone antibiotics has been widely used in medicine and in veterinary practice.Water pollution with antibiotics has become a serious problem.In the past few years,the processes of heterogeneous activation of peroxymonosulfate/persulfate by transition metal oxide have exhibited potential applications in the removal of antibiotics.These heterogeneous catalytic processes without the aid of external energy are considered to be more promising for large scale water treatment due to its low cost and easy operation.In the present study,the Fe_1.9Cu₄₄ hollow sphere?FCHS?+PS system was constructed for the degradation of levofloxacin?LVF?in aqueous solution.The main objectives were to study the roles of reactive species in FCHS/PS system,indentify the possible degradation pathways of LVF and clarify the degradation mechanism.It helps to provide reference practically in developing advanced oxidation processes?AOPs?for degradation of antibiotics in wastewater treatment.The main conclusions are as follows:?1?The Cu₂O hollow sphere was synthesized by low temperature liquid phase method and iron-loaded.And it was calcined at 600°C in a muffle furnace to prepare the FCHS hollow sphere.SEM,XRD,XPS,FT-IR,TEM and Zeta potential was used to characterize the catalyst.SEM and TEM show that CHS and FCHS are the form of hollow spheres with a particle size of about 0.5-2?m.XRD characterization indicated that the composition of FCHS was CuO,Cu₂O and Fe₂O₃.According to the semi-quantitative analysis of XPS,the Fe???and Fe???ratio in the FCHS composite catalyst was 80.11%,19.89%respectively.And Cu???and Cu?I?were detected to account for 61.67%and 38.33%,respectively.?2?The degradation efficiency of levofloxacin in different heterogeneous catalytic process was studied.Results reveled that fabricated FCHS showed higher catalytic performance than pure CHS.A degradation efficiency of 90%was achieved in 240min.In contrast,only 80%,17.92%,12.48%,and 3.40%degradations of levofloxacin were observed with CHS+PS,FCHS,CHS,and PS,respectively.what's more,FCHS+PS plays a key role in removal of levofloxacin and FCHS has great catalytic performance.?3?The optimal experimental parameters of removing 5 mg/L levofloxacin in the FCHS+PS system were investigated.The optimal catalyst dosage was 0.4 g/L,the PS dosage was 5 mmol/L,and a degradation efficiency of 95%was achieved.The FCHS+PS system shows a good degradation performance in wide pH conditions?3-9?.It was found that the inorganic anions(CO₃^2-,PO₄^3-)have different negative effects on the FCHS+PS system.When 5 mmol/L CO₃^2- and PO₄^3-were present in the reaction system,the degradation efficiency decreased to 70%and 55%,respectively.Moreover,PO₄^3-posed remarkable negative effects on the levofloxacin degradation.?4?In order to distinguish the roles of active radical species in the degradation process,the radical scavengers ethanol?EtOH?and tert-butanol?TBA?were used for quenching SO₄^·-and·OH in this study.It can be summarized that SO₄^·- and ·OH are both in existence and SO₄^·- is the majority.In order to validate the above speculation,the EPR technique was utilized to detect the active radical species in the heterogeneous systems.The classical spin-trapping agent,5,5-dimethylpyrroline-oxide?DMPO?was used to capture the radicals.DMPO-OH and DMPO-SO₄ signals were detected in FCHS+PS systems,agreeing well with the radical quenching studies.In order to evaluate the stability and reusability of FCHS in this study,four successive catalytic degradation experiments were carried out under initial condition?i.e.[FCHS]=0.2 g/L,PS=2 mM,pH=7.0?.The Levofloxacin degradation was not significantly deteriorated in the four successive cycles,revealing the excellent reusability of FCHS.?5?XPS showed that the the synergetic interfacial effect of Fe and Cu on the surface of the catalyst was thought to be the main reason of such specifically catalytic activity for LVF.The existence of·OH and SO₄^·-radicals were evidenced by EPR analysis in the FCHS+PS system.The SO₄^·-could react with H₂O to produce·OH.Besides,The generated Cu???of the catalyst during the PS decomposition would react with H₂O and subsequently regenerated Cu???and also provided·OH.The?Cu???and?Fe???on the surface of FCHS in the reaction system undergo redox reaction and synergistically act on the activation of PS.?6?The levofloxacin degradation intermediates were analyzed by LCMS-IT-TOF.Several compounds were tentatively identified.Based on the current results and previous studies,the levofloxacin proposed degradation pathway is illustrated.Hydroxylation,dehydrogenation,methylation and carboxylation was found to be the way of the degradation.Besides,cleavage,chemical scission or ring-rupturing reactions was found to be another way of the degradation.