| In this study,four typical quinolone antibiotics with high detection rate in water environment were treated as the analyzed target compound including norfloxacin,ciprofloxacin,lomefloxacin and sparfloxacin,and their solid photocatalytic degradation mechanism was studied.The research work is summarized as follows.Firstly,a high-performance liquid chromatography tandem mass spectrometry method（HPLC-MS/MS）was established and validated for the analysis of four kinds of quinolone antibiotics.They were separated on a Sharpsil-H C18column（2.1×100 mm,3μm）and quantified with a tandem mass spectrometry.The results indicated that the four quinolone antibiotics showed good linear relationship from 0.01 to 10μg·m L-1,and the correlation coefficients R2were all above 0.9943.Recoveries achieved at spiking levels of 0.05μg·m L-1,0.2μg·m L-1and 1.0μg·m L-1were between 93.4%and 105.2%.The relative standard deviation（RSD）was less than 5%.The limits of detection（LOD）were from 2 to 7 ng·m L-1.The developed method can be performed to analyze actual samples.Secondly,three kind photocatalysts of Bi VO4、Bi VO4/Si O2and Bi VO4/Si O2/RGO were prepared by the simple solvothermal method,and the preparation technology of Bi VO4/Si O2/RGO composite photocatalyst was optimized,and the effects of different graphene oxide doping amount,p H value of precursor solution,reaction temperature and reaction time on the morphology,crystal structure and optical properties of the composites were investigated.The results showed that the prepared Bi VO4/Si O2/RGO photocatalyst has a good crystal structure,Lower band gap（2.33 e V）and low photoluminescence（PL）intensity with the dosage of 1%graphene oxide,precursor solution p H value of 5,solvothermal reaction temperature of 180℃and the solvothermal reaction time of 4h.And the used of characterization measures include the field-emission scanning electron microscope（FE-SEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,BET specific surface area analyzer and ultraviolet visible diffuse reflectance spectrum（UV-vis）technologies.Thirdly,photocatalytic degradation of four quinolone antibiotics at 10μg·m L-1by visible light was used to evaluate the activity of the three photocatalytic materials.The results showed that the degradation rates of norfloxacin were 71.6%,64.5%and 99.1%for Bi VO4,Bi VO4/Si O2and Bi VO4/Si O2/RGO,respectively.The degradation rates of ciprofloxacin were 70.6%,69.5%and 98.3%.The degradation rates of lomefloxacin were 28.6%,30.9%and 91.3%,respectively.The degradation rates of sparfloxacin were 73.6%,68.9%and 99.6%,respectively.Obviously,the composite photocatalyst Bi VO4/Si O2/RGO has the highest catalytic activity.Finally,the solutions of norfloxacin,ciprofloxacin,lomefloxacin and sparfloxacin were analyzed by high performance liquid chromatography-mass spectrometry（HPLC-MS）after 0 min,30 min and 120 min photocatalytic degradation.The degradation mechanism was deduced by measuring the degradation product composition,and the degradation path was simulated.The results of mass spectrometry analysis showed that there were two degradation routes of norfloxacin under irradiation of visible light,one was the intermediate product of m/z 336,334and 322 through the degradation of piperazine ring,the other was the substitution of quinolinone ring,and the m/z 233 product was formed by further cleavage under light irradiation.The photocatalytic degradation of ciprofloxacin was achieved mainly by the cleavage of piperazine ring,the degradation products of m/z 334,306,291 and 263 were detected.The degradation process of lomefloxacin was carried out simultaneously with the breakage of piperazine ring and hydroxyl radical attack,the intermediate products detected in the solution were m/z 350,348 and m/z 326,respectively.The degradation of sparfloxacin was due to the degradation of the fluorine atom on the quinolinone ring by hydroxyl radical attack to produce the product with the mass to charge ratio of 391,and the cyclopropane cracking on the quinolinone ring under the action of photocatalysis,that was,the cleavage of C-N bond to produce the product of m/z 352.As the photocatalysis proceeds,the two products of m/z 294 and 256 were finally formed by cleavage of the piperazine ring. |
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