Modified Nanoscale Zero-Valent Iron For Enhanced Removal Of Antibiotic Florfenicol

The large-scale use including abuse of antibiotics is receiving significant attention in recent years,and they cannot be effectively removed by the traditional treatment methods in wastewater treatment plants.Nanoscale zero-valent iron（nZVI）has been widely applied to the environmental remediation of heavy metals and organic contaminants,due to its large surface area,high reactivity,wide range of sources and easy preparation.However,the mobility of nZVI can be reduced cuasing its tendency to aggregate in the water,and the side reaction with water will generate iron oxides covered in the surface of Fe⁰,thus slowing down the reaction rate.In this study,florfenicol（FF）was selected as the target compound,and the modification of nZVI was used to improving the reaction activity and prolonging reactive lifetime.Sulfied-modified nZVI（S-nZVI）was synthesized with one-step method that reducing dissolved iron in the presence of sodium dithionite.The introduce of sulfur could effectively inhibit the aggregation of nZVI,resulting in the increasing surface area,from 10.2 m² g^-1（nZVI）to 62.5 m² g^-1（S-n ZVI）.No obvious removal of FF was observed by unsulfidized nZVI.S-nZVI degraded FF,having a surface area normalized reaction rate constant(k_SA)of 3.1×10^-4 L m^-2 min^-1,was 48 times of that of nZVI,and the t_1/2/2 also decresed from 1730 min for nZVI to 38 min for S-nZVI.The effects of the S/Fe molar ratio,initial FF concentration,initial pH,temperature,and water composition on the removal of FF by S-nZVI,and on the formation of reaction products,were systematically investigated.Both dechlorination and defluorination were observed.High removal efficiencies of FF by S-n ZVI were achieved in groundwater,river water,seawater,and wastewater.The reactivity of S-n ZVI was relatively unaffected by the presence of both dissolved ions and organic matter in the waters tested.Bamboo wood derived biochar（BC）was prepared via pyrolysis process at 380℃,having a large surface area and extraordinary adsorption properties for heavy metals and organic pollutants.p BC1 and pBC2 were obtained by using phosphoric acid to functionalize BC with different time.Phosphoric acid not only removed the mineral impurities on BC surface,but also introduced-OH,-COOH,-P=OOH and other functional groups to improve the adsorption capacity of BC.The adsorption capacity of pBC1 and pBC2(0.5 g L^-1)was 115.7 mg g^-11 and 85.2 mg g^-1 respectively,and the adsorption removal rate of FF in 10 min was up to 90%and 75%respectively.Phosphorus was introduced during the fabrication of biochar-supported and sulfide-modified nanoscale zero-valent iron（p BC2-S-nZVI）,which addressed some important issues of nZVI（i.e.easy aggregation,deactivation,and loss due to side reaction with water）.Enhanced removal of FF by S-nZVI was achieved after the support of BC that was pretreated by H₃PO₄,which provided phosphorus group with strong affinity toward Fe²⁺to favor the precipitation and subsequent reduction of Fe²⁺onto the surface of BC.Participation of phosphorus group during the nanohybrids preparation,good support of particles by pBC2,and higher reactivity of the nanohyrbids were confirmed by FTIR spectra,SEM images,and XRD and XPS spectra,respectively.The kinetics of FF dechlorination by pBC2-S-n ZVI were pseudo-first-order with respect to S-nZVI.The k_SA of FF removal by S-nZVI,BC-S-nZVI,and pBC2-S-nZVI were very close,suggested that the reaction was controlled by the active surface area.The reactive lifetime of pBC2-S-nZVI was assessed by consecutive experiments.The pBC2-S-nZVI nanohybrids was sensitive with oxygen and was not reactive in the presence of oxygen.