| Florfenicol(FF)is a new type of chloramphenicol broad-spectrum antimicrobial agent,which plays an important role in disease control and treatment of livestock and poultry.It is not only a bioaccumulative persistent compound but also can migrate in a long distance.The residual FF in the environment will pose long-term potential harm to human health and ecological environment.Therefore,it is of great theoretical significance and practical value to develop the degradation methods forremoving FF from environment.SO4·-,generally can be generated by persulfate(PS)or peroxymonosulfate(PMS)through activation has many excellent characteristics,such as owning a relatively higher redox potential and stability than OH,degrading contaminants selectively and can fully or partially mineralizing organic compounds.Previous studies focused on degrading contaminants by SO4·-in homogeneous systems,and up to now,no report related to the destruction of FF via SO4·-based heterogeneous system and the underlying mechanism was published.In this paper,the feasibility of employing Fe3O4 activated PS to degrade FF was assessed.Fe3O4 nanoparticles were fabricated using a facile one-step routine and its role as a heterogeneous activator towards PS was systematically investigated.The possible mechanisms involved in the FF degradation were investigated through deter-mination of degradation pathway.The main contents in this thesis were listed below:1.Preparation and Characterization of Fe3O4In this paper,Fe3O4 nanoparticles were successfully prepared by thermal reduction.Scanning electron microscopy(SEM),X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS)were used to complexly characterize the crystalline structure,composition and morphology of Fe3O4.The characterization results were as follows:SEM results showed that the Fe3O4 particle owned the average particle size of 62 nm.XRD test results showed that the material peak pattern was consistent with the standard Fe3O4 sample(JCPDS:19-0629)pattern,indicating the product was pure Fe3O4.XPS results showed that the typical double peaks of Fe corresponded to peaks of Fe2p3/2 and Fe2p1/2,respectively.The difference between two peaks was approximately 14 eV,which was the typical characteristic of Fe3O4.2.The mechanism of florfenicol degradation by Fe3O4 activated PSThe influencing factorshh the PS activated by the prepared Fe3O4 nanoparticles for the the removal of FF were studied.Experimental results are follows:(1)At room temperature and pH 7.0,with initial concentration of FF of 15 ?M,the removal rate in 90 minutes may reach 90%(PS/Fe3O4 of 5 mM/1.0 g L'1).TOC contents were reduced by 22.4%and 49.5%in 90 minutes and 240 minutes respectively.Increasing the reaction temperature could promote the reaction rate.However,the presence of chloride ions and bicarbonate ions reduced the reaction rate and natural organic substances also possessed negative impacts on degradation.The crystallinity of Fe3O4 after the reaction was slightly reduced.However,the structure and composition of Fe3O4 did not change showing the well stability of the material.After 3 cycles of utilization,the degradation rate was still kept at 34%in 120 min.(2)During FF degradation with Fe3O4 activated PS method,SO4·-and HO· were found to be coexisted in the reaction solution and SO4·-was indentified as the main active radical.Total of six intermediates were detected during the reaction and two possible degradation pathways were tentatively proposed.In the first pathway,chlorine substitution happened on the benzene ring and produced the N-trichloroacetylfluoronicladamide.In the second pathway,hydrolyzation and dechlorination happened at the fluorine site.After hydroxylation,one hydroxyl group and one chloro group were removed and form an aldehyde group via oxidation,which at last resulted in product of methylphenyl sulfone.3.Degradation of florfenicol homologues by Fe3O4 activated PSIn this paper,the degradation of structural related compounds of FF(chloramphenicol and thiamphenicol)by Fe3O4 activated PS were compared and the respective degradation pathways were studied.The experimental results showed that the degradation rates of three compounds within 120 min were in the order of thiamphenicol>chloramphenicol>FF.The possible explaination for this may because chloramphenicol contains a nitrate group and FF contains a fluoro group and a nitro froup in their molecules respectively which reduced their degradation rate.The degradation pathway of chloramphenicol contained two steps.In the first step,chloramphenicol gradually lost two chlorine groups,one hydroxyl group,one acetyl group and one butyl group,which was then oxidized into enzaldehyde at last.In the second step,chloramphenicol was eventually oxidized into 2,3-dimethyl-1-butanol by removing one nitrobenzene and two chlorine groups.The degradation pathway of thiamphenicol was mainly focused on the removal of methylphenyl-sulfone froup which was followed by the removal of a hydroxyl group and a propionyl group and finally produced DL-2-amino-3-methyl-1-butanol by oxidation. |
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