Activation Of Persulfate By Nanoscale Zero-valent Iron Loaded Biochar For The Removal Of 17b-estradiol

17β-estradiol（E2）is an environmental endocrine disruptor that can cause great harm to the environment in small doses.Advanced oxidation processes can effectively remove organic matter in the environment,and zero-valent iron loaded biochar can be used to catalyze advanced oxidation based on persulfate.In this work,the porosity,graphitization and iron doping of biochar were realized simultaneously by the pyrolysis of biomass and potassium ferrate（K₂FeO₄）,then the iron-doped graphitized biochar was reduced to synthesize nanoscale zero-valent iron loaded porous graphitized biochar（n ZVI/PGBC）.Subsequently,the structure and physicochemical properties of the material were analyzed by scanning electron microscopy（SEM）,specific surface area and aperture analysis,X-ray diffraction（XRD）,Raman spectroscopy（Raman）,Fourier transform infrared spectroscopy（FTIR）,and X-ray photoelectron spectroscopy.The analysis results showed that n ZVI/PGBC successfully formed nano-scale zero-valent iron,and the specific surface area of the biochar increased,the degree of graphitization improved,and the oxygen-containing functional groups on the surface of the biochar increased significantly compared with the original biochar.E2 removal experiments illustrated that n ZVI/PGBC（100 mg/L）could completely remove E2（3 mg/L）within 45 min by activating sodium persulfate（PS,400 mg/L）.The E2removal efficiency of n ZVI/PGBC was obviously superior to that of pristine biochar（BC）,iron-doped graphitized biochar（Fe/GBC）,nanoscale zero-valent iron（n ZVI）and porous graphitized biochar（PGBC）.The removal efficiency could be affected by reaction conditions,including reaction temperature,acidity,dosage of catalyst and oxidant and water matrix.Quenching experiments and electron spin resonance（ESR）demonstrated that SO₄^-·and HO·were both responsible for E2 degradation.This study indicated that Fe⁰and Fe²⁺were the main catalytic active substances,while the catalytic ability of PGBC was not obvious.The reaction mechanism was proposed,that is,PS was activated to form radicals by electrons provided by the redox reaction between Fe²⁺and Fe³⁺,and PGBC acted as the carrier of n ZVI,the adsorbent of E2 and the mediator of electron-transfer,then E2 adsorbed on the surface of biochar was oxidized and degraded by SO₄^-·and HO·.This study demonstrates that n ZVI/PGBC can be used as an effective activator for PS to remove organic pollutants in water.