Removal Of 17?-ethynylestradiol (EE2) From Aqueous Solutions By Fe-Mn Binary Oxides: Adsorption And Oxidation

After heavy metal pollution estrogen pollution and water eutrophication,estrogens pollution has been the third generation of water pollutants,and becomes a significant problem which influences human survival and development.Recently,an integrated material named Fe-Mn binary oxide?FMBO?was synthesized and proved to be highly efficient for heavy metal removal.However its application and theory in organic treatment remains further studied,in addition the governance of estrogen by FMBO has not been reported yet.So this paper firstly synthesized Fe-Mn binary oxide with 17?-ethynylestradiol?EE2?as the target pollutant,and systematicly discussed the adsorption and oxidation characteristic of EE2 removal by FMBO.By using Scanning electron microscopy?SEM?,X-ray diffractometry?XRD?,X-ray photoelectron spectroscopy?XPS?and Fourier transform infrared spectroscopy?FTIR?to measure its performance parameters,and through the establishment of the removal kinetics,isotherm and thermocynamic models of EE2 by FMBO as well as the identification of the reaction intermediates at different reaction times by Gas chromatograph-mass spectrometer?GC-MS?,the adsorption and oxidation reaction mechanism of Fe-Mn binary oxides for EE2 removal were studied comprehensively.The major results are as follows:The surface area of FMBO was 318.29 m²/g which was apparently improved compared with FeOOH and MnO₂,its zero charge points was partial acid.The SEM results showed that FMBO was composed of uneven size of spherical particles and presented a rough and porous surface structure.XRD showed that the FMBO appeared an amorphous phase morphology and successfully composited iron and manganese oxide,its chemical composition was mainly Fe₂O₃,?-MnO₂,MnFe₂O₄.XPS analysis proved Fe³⁺was the main iron valence state and manganese valence state was composed of+3 and+4 in FMBO.FTIR results indicated the existence of the characteristics peaks of iron and manganese oxide groups such as Fe-OH and Mn-OH and other activity peaks of hydroxyl groups,which provided it strong removal ability.The effects of the reaction time,adsorbent dosage,pH,ionic strength and the coexistent solute for EE2 removal by FMBO were investigated and results showed the removal progress was fast and with a considerable adsorption capacity.The reaction was close to equilibrium at 15 min and it released Mn²⁺accompanying the adsorption process.With the increase of adsorbent dosage the removal percentage of EE2increased while the adsorption quantity was remarkably reduced.In a wide pH range from 5 to 7,the removal percentage remained a high level more than 90%,and the maximum removal rate was 96.51%at pH 6.As the ionic strength rised,the removal percentage of EE2 wad firstly increased and then decreased.And the inhibition effect of conexist anion or cation ions in the solution was PO₄^3->CO₃^2->Cl^-?SO₄^2-,Mn²⁺>Fe³⁺>Ca²⁺>Mg²⁺>Na⁺respectively.The kinetic results displayed that the adsorption of EE2 by FMBO followed pseudo-second-order kinetic model in acidic conditions and was controlled by external diffusion and particle diffusion.Moreover Freundlich isotherm model appeared to fit the isotherm data better and the adsorption capacity enhanced with the rising of temperature with the maximum adsorption quantity of 178.21 mg/g.Thermodynamic analysis found that?G⁰<0,?H⁰>0,?S⁰>0,showed the adsorption was spontaneous endothermic,and belonged to the entropy driven process.The FTIR and XPS results revealved that EE2 was adsorbed by hydrogen bond association reaction between phenolic hydroxyl or alcohol hydroxyl in EE2 and Fe-OH or Mn-OH in the surface of FMBO,iron oxides only existed adsorption effect while manganese oxide existed adsorption and oxidation effect.GC-MS was applied to identity the reaction intermediates at different time,it was shown that the degradation products still mostly retained the core ring structure of estrogens,but the estrogen activity of the intermediate significantly decreased.Above all,the results suggested the Fe-Mn binary oxides would be a promising adsorbent for the removal of estrogenic pollutants.