Adsorption And Heterogeneous Fenton Degradation Of Environmental Antibiotics On Iron Oxides

Although the discovery and use of antibiotics is a major revolution in human history,the presence of residual pharmaceuticals in the natural system has caused serious environmental problems in recent years.Hematite and goethite are abundant and important hydrous iron oxides in soils.This study investigated the adsorption behaviors and mechanisms of three different kinds of antibiotics,oxytetracyline?OTC?,streptomycin?STR?and sulfamerazine?SMR?,on the surface of hematite and goethite and analyzed the similarities and differences of them.Meanwhile,this study also investigated the oxidation degradation activities of goethite and modified goethite as heterogeneous Fenton catalysts for OTC.We studied the adsorption behaviors and mechanisms of three different kinds of antibiotics on hematite and goethite as a function of pH,ionic strength,as well as competing compounds EDTA and PO₄^3-.The results indicated that the adsorption capacities of three antibiotics followed OTC>STR>SMR,and the adsorption behaviors of three antibiotics were pH-dependent,moreover,sensitive degree of antibiotics for ionic strength were not identical.There were great differences among the interactions between three antibiotics and iron oxides.The inner-sphere surface complex and electrostatic interaction played key roles on the adsorption of OTC onto hematite.And the adsorption of STR was mainly controlled by electrostatic interaction.Simultaneously,the adsorption of SMR onto hematite was driven by the hydrophobic interaction.For goethite,expect the above,the dissolved Fe³⁺could increase adsorption capacities of three antibiotics through formation of cation bridging between goethite and antibiotics at pH=2.In addition,hydroxyl groups on goethite surface also played an important role on the adsorption of antibiotics.Goethite-catalyzed heterogeneous Fenton system also had excellent activity for the degradation of OTC.The oxidation degradation reactions mainly occurred on the surface of the goethite and had association with adsorption process.Goethite heterogeneous Fenton system obtained the highest OTC degradation rate in the neutral condition and overcome the straight working pH value of 2.0-3.5 of traditional homegeneous Fenton systems.Moreover,experiments had confirmed that?OH was major active group.The presence of HA and ascorbate could promote the efficient Fe???/Fe???cycle to accelerate OTC degradation.Compared with goethite,Ce³⁺substituted goethite Ce_0.2Fe_0.8OOH can significantly enhance degradation rate and mineralization efficiency of OTC.In this system,the presence of Ce³⁺could greatly promote the Fe³⁺/Fe²⁺and Ce⁴⁺/Ce³⁺cycle on the catalyst surface and decomposition of H₂O₂.