Iron-based Materials For Nonradical Degradation Of Endocrine Disrupting Chemicals

Endocrine Disrupting Chemicals（EDCs）are a class of compounds that are capable of interfering with the metabolism of biological endocrine system through binding to hormone receptors.Due to their low concentration and difficult biodegradation,EDCs cannot be completely removed by current sewage treatment plants,resulting in a widespread presence of EDCs in the surface water,endangering the health of human and ecology.Advanced oxidation processes（AOPs）is an effective technology for EDCs treatment via generation of strongly oxidative hydroxyl radicals（·OH）as active sites.However,the strongly oxidative·OH is also easily to be used by widespread natural organic matters and inorganic anions,resulting a decease of the efficiency of EDCs treatment.Herein,a non-radical oxidation system based on high-valent iron-oxo species was established to overcome the problem of low selectivity of traditional AOPs for EDCs.Iron complex activated by oxidants is a common pathway to obtain high-valent iron-oxo species.However,the current iron complexes have poor stability and are easy to deactive,resulting in low efficiency of pollutant degradation process.Therefore,in the second chapter,a robust iron（III）complex bearing across-bridgedcyclamligand（Fe-cyclam,cyclam=4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane）was prepared.The purity and structure of Fe-cyclam were analyzed by C/H/N Element analyzer and Electrospray Ionization Mass Spectrometry.A homogeneous Fe-cyclam/H₂O₂system was constructed using H₂O₂as the oxidant,and its catalytic oxidation ability was preliminarily tested using rhodamine B（Rh B）as a model substrate.In the third chapter,the Fe-cyclam/H₂O₂catalytic system was applied to selective degradation of environmental estrogens.The catalytic mechanism of this system was revealed,and the application potential of this system in the treatment of environmental pollutants was discussed.In order to solve with the problem of difficult reuse of homogeneous catalyst and improve the application potential of high-valent iron-oxo species based oxidation system in the environment,a magnetic chitosan chelated Fe catalyst（FC900）was prepared in the fourth chapter.A heterogeneous Fe chitosan/peroxymonosulfate（PMS）catalytic system using PMS as oxidant was constructed.This system was easily recovered,and a model EDCs bisphenol A（BPA）was used to test the degradation ability of Fe chitosan/PMS system.Main results are as follows:（1）The Fe-cyclam complex was successfully synthesized,and the complex remained stable for a long time in a solution of p H 2-7.Fe-cyclam/H₂O₂system could effectively degrade Rh B.10μM Fe-cyclam was capable of continuously degradating Rh B and the removal efficiency of Rh B reached 95.7%after 240 mins’reaction.At the same iron concentration loading,the removal efficiency of Rh B by Fenton reaction was only 43.7%.When the catalyst concentration was 50μM,the removal efficiency of Rh B by the two systems were equivalent,and the removal efficiency could reach more than 95%after 60 mins’reaction.Moreover,Fe-cyclam/H₂O₂system was also capable of degrading the dyes including acid red 88,acid orange II,reactive red 24 and neutral red,and had the ability to degrade dyes in a wide p H range（2-7）.In addition,comparing with the Fenton system,the Fe-cyclam/H₂O₂system had greater anti-interference ability.The addition of natural organic matters showed minor effect on the degradation of Rh B,and the removal efficiency of Rh B were still higher than 93%.（2）Fe-cyclam/H₂O₂system was able to degrade a variety of EDCs,and had excellent selectivity for 17β-estradiol,estriol and 17α-estradiol,with a removal efficiency of 93%,94%,and 98%after 90 mins’reaction,respectively.After treatment,the estrogenic activity of reaction solution significantly decreased（>95%）.Quenching experiments,Electron Paramagnetic Resonance（EPR）determination experiments and Nitro-Blue Tetrazolium（NBT）reduction experiments excluded the possibility of·OH and superoxide anion（O₂^-·）as active species.The ultra-low temperature（77.15 K）EPR directly captured the signal of high-valent iron（V）-oxo species.These evidences proved that the degradation of EDCs by Fe-cyclam/H₂O₂system was a high-valent iron（V）-oxo species dominated process rather than a radical controlled degradation process.In addition,after three cycles of degradation experiments,the removal efficiency of 17β-estradiol was still more than90%.Moreover,the Fe-cyclam still had catalytic ability more than three days of continuous operation,indicating the excellent stability of Fe-cyclam complex.（3）A magnetic chitosan chelated Fe catalyst was successfully prepared.Using PMS as oxidant,a FC900/PMS catalytic system was constructed.The removal efficiency of BPA by FC900/PMS reached97.8%after 40 mins’reaction,and the degradation rate was 9.2 times higher than that of commercial nano ferroferric oxide.The mineralization efficiency of BPA was higher than 70%,and the estrogenic activity of BPA was decreased more than 97%.The degradation rate of BPA was accelerated by decreasing p H,increasing FC900 dosages and concentration of PMS.NO₃^-,SO₄^2-,H₂PO₄^-,and humic acid showed insignificant effect on the degradation of BPA,while Cl^-significantly promoted the degradation of BPA.Quenching experiments,EPR determination experiments,NBT reduction experiments and PMSO probe experiments confirmed that the degradation of BPA by FC900/PMS system is a nonradical-dominated reaction,and the dominated active species were singlet oxygen and high-valent iron-oxo species.