| With the development of analysis and detection technology,different kinds of antibiotics in environment matrices have been observed.Ecological risks by residual antibiotics have increasingly attracted great attention.In this study,nano zero valent iron（nZVI）,iron-based bimetallic systems（Ag/Fe,Co/Fe）,sulfide-modified nano zero valent iron（S-nZVI）and modified biochar supported iron-based bimetallic systems were prepared for removal of the most commonly used and widely distributed cephalosporins（cefotaxime and cephalexin）from aqueous solution.The prepared composites were characterized for exploring the material composition,surface morphology and functional information.Degradation products of antibiotics,generated by removing functional groups from the structure of antibiotics,were analyzed by liquid chromatography–mass spectrometry（HPLC-ESI-MS）to investigate the degradation pathway.The following major conclusions are obtained:（1）Modified biochar were prepared by liquid impregnation for removal of cefotaxime（CFX）in solution.The adsorption efficiency,influencing factors and mechanisms of the adsorbent were explored in this study.The results showed that alkali modified biochar（BC-NaOH）exhibited more excellent adsorption than acid and ammonia modified biochar in 30 min（dose:1.6 g/L,cefotaxime initial concentration:16 mg/L,pH:6,T:298K）.The adsorption efficiency of cefotaxime by BC-NaOH was up to 89%and the data fitted the pseudo-second-order kinetic model（R2>0.99）.Thermodynamic studies showed that the adsorption process was spontaneous and exothermic.On the basis of the results of thermodynamics and adsorption influencing factors,the adsorption mechanisms of cefotaxime by BC-NaOH were hydrophobic affinity and electrostatic attraction.（2）Ag/Fe,nZVI and Co/Fe were synthesized by liquid phase reduction method under the absence of air.Biochar supported Co/Fe nanoparticles（Co/Fe/MB）were prepared by immersing biochar and metal-salts first,and then with liquid phase reduction.Biochar supported Ag/Fe nanoparticles（Ag/Fe/MB）were synthesized by a similar above procedure.X-ray diffraction,Fourier transform infrared spectroscopy,scanning electron microscopy,transmission electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the surface morphology,composition and valence electronic information.The results showed that nZVI,Ag/Fe and Co/Fe exhibited severe agglomeration.However,the agglomeration phenomenon of Co/Fe and Ag/Fe particles was greatly reduced by loading particles on the surface of MB.On the other hand,intensity and type of functional groups on the surface of MB were affected by nanoparticles.TEM images of biochar supported nanoparticles showed that the nanoparticles were nearly spherical and the even diameter of the particles was between 30 nm50 nm.（3）Batch experiments were performed for investigating the removal of cefotaxime by Co/Fe/MB.The effects of Co loading,adsorbent dosage,initial solution pH and anions（Cl-,HCO3-and EDTA）on the removal of cefotaxime were investigated.Co/Fe/MB revealed the highest cefotaxime removal efficiency（99%）in100 min under the conditions of pH=5,T=298 K,Co/Fe/MB dosage=0.8 g/L,Co loading=0.4 wt%,cefotaxime=20 mg/L.The removal efficiency was further enhanced in the presence of EDTA and Cl-because of the destruction of passivation layer on iron surface.Additionally,the degradation products and possible degradation pathway of cefotaxime by Co/Fe/MB were analyzed by high performance liquid chromatography-electrospray ionization mass spectrometry.The spectra revealed that the opening and cleavage of theβ-lactam ring was the first step for cefotaxime degradation.Co/Fe/MB composite was found to be an efficient material to remove cefotaxime from the solution.（4）Modified biochar supported Ag/Fe nanoparticles was used to remove cephalexin（CLX）in aqueous solution.More than 86%of CLX was removed by Ag/Fe/MB in 90 min under the simultaneous action of adsorption and reduction（dose:1.5 g/L,CLX initial concentration:20 mg/L,pH:6.15）.Notably,the adsorption was more prevalent than the reduction during the removal of CLX.The removal of CLX was seriously dependent on adsorbate concentration and pH.The presence of citric acid（CA）strongly increased the removal of CLX,where the initial reaction rate was increased by 36 times.Degradation products of CLX,generated by removing functional groups from the structure of CLX,were analyzed by liquid chromatography–mass spectrometry to investigate the degradation pathway.（5）Sulfide-nZVI（S-nZVI）was prepared by post sulfidized method and characterized by X-ray diffraction,transmission electron microscopy and X-ray photoelectron spectroscopy for the surface morphology and valence electronic information.The results showed that the S-nZVI nanoparticles were nearly spherical with an even diameter of 56 nm.Moreover,low density FeS/FeSn formed a discontinuous layer on the surface of nZVI.Sulphur content,Fe2+content and solution pH could affect the removal efficiency of combined pollution（CFX and CLX）.64%of CFX was removed by S-nZVI1/4 in 240 min（dose:0.5 g/L,CFX initial concentration:20 mg/L,pH:8）,while 41%of CLX was removed at the same time.The degradation products of combined pollution were analyzed by HPLC-ESI-MS for investigating the degradation pathway.The degradation of CFX was mainly caused by the ester substitution reaction and the cleavage of theβ-lactam ring.However,the degradation of CLX was mainly caused by the cleavage of the amido bond. |
