Research On The Performance And Mechanism Of Chloramphenicol Removal In Water By Micro Sulfidated Zero Valent Iron

With the progress of society and rapid economic development,water resources have become an increasingly scarce resource,and water pollution has become more and more serious.As a new type of organic pollutant,antibiotics pose a potential threat to the natural environment and human health.The pollution problems it causes are becoming more and more severe.Exploring an effective antibiotic removal method are becoming a hot research topic in the environmental field.Zero-valent iron(ZVI)has the advantages of abundant reserves,low price,strong reduction,and environmental friendliness.It plays an important role in groundwater remediation and surface water pollution treatment.However,the exposure of zero-valent iron to the air forms a dense oxide film on the surface,and its electronic selectivity is poor.The narrow applicable pH range also inhibits its reactivity to a certain extent.The sulfide modification of zero-valent iron can improve these deficiencies.In addition,oxygen is also an important influencing factor.Groundwater is mainly an anaerobic environment,and surface water is an aerobic environment.Studying the reaction effects under different oxygen conditions also has important guiding significance for practical applications.In this study,chloramphenicol(CAP)was selected as the target antibiotic pollutant,and sulfur compounds were used to modify ZVI.The performance and mechanism of CAP removal under anaerobic and aerobic conditions were explored.In this study,wet sulfide modification method was used to modify pristine micro zero-valent iron with sodium sulfide to prepare micro sulfidated zero-valent iron(S-ZVI)materials,and S-ZVI materials with different S/Fe molar ratios were prepared by controlling the sodium sulfide content.The results showed that sulfidation could significantly enhance the removal of CAP by ZVI.Scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray energy dispersive spectroscopy(EDS).X-ray photoelectron spectroscopy(XPS)and X-ray diffraction(XRD)were used to study the surface morphology,chemical composition and composition structure of ZVI before and after sulfidation.Compared with ZVI,it is found that the surface of S-ZVI was loose and porous,and the roughness significantly increased.The S element was introduced on the surface of the material and was loaded on the ZVI surface in the form of FeSx.In addition,the surface morphology of S-ZVI materials prepared under different S/Fe molar ratios also had certain differences.This study first explored the performance of S-ZVI materials with different S/Fe molar ratios on CAP.When the S/Fe molar ratio of S-ZVI was 0.028,the removal efficiency of CAP was the highest.And when the S/Fe molar ratio was too high or too low,it would reduce the reactivity of S-ZVI.Then the research systematically studied the CAP removal performances of ZVI and S-ZVI(S/Fe=0.028)under anaerobic and aerobic conditions respectively.The results showed that under anaerobic conditions,the removal rate of CAP by S-ZVI was more than 90%,which was significantly higher than that of aerobic conditions.Compared with the ZVI system,the removal rate of CAP by S-ZVI was increased by 20%?50%;that is to say,sulfidation increased the reactivity of ZVI.In addition,this research systematically explored the influences of various influencing factors(such as initial pH,S-ZVI dosage,initial CAP concentration,reaction temperature,ionic strength,etc.)on the CAP removal.The results showed that ZVI was more susceptible to corrosion at lower pH,which was beneficial to the removal of CAP by S-ZVI.Due to the limited reactive sites of S-ZVI,the removal rate of CAP decreased with increasing initial concentration.With the increase of S-ZVI dosage,the removal rate of CAP increased.Increasing the reaction temperature accelerated the molecular motion to elevate the reaction rate.The increase in ionic strength played different effects under aerobic and anaerobic conditions.For aerobic conditions,due to the intervention of oxygen,the mechanisms of oxidative degradation and reductive degradation were discussed.By analyzing the solution in the reaction system under aerobic conditions by liquid chromatography-mass spectrometry(HPLC-MS/MS),it was found that the degradation process of CAP was mainly due to the reduction of ZVI.Mass spectrometry analysis further confirmed the three reduction products,namely CAP-O,CAP-20 and CAP-20-C1.The process of CAP removal by S-ZVI was to first reduce 2 oxygen atoms on the nitro(-NO2)group on the CAP molecule,and then remove 1 chlorine atom.By measuring the TOC value of the solution before and after the reaction,it was found that the CAP mineralization rate was only about 10%.In addition,the quenching experiments of hydroxyl radicals and sulfate radicals showed that no hydroxyl radicals and sulfate radicals were produced during the reaction,and there was no such oxidative degradation process related to these free radicals.