Efficient removal of several estrogens in water by Fe-hydrochar composite and related interactive effect mechanism of H2O2 and iron with persistent free radicals from hydrochar of pinewood.

Recently, hydrochar (HC) with existed persistent free radicals (PFRs) has attracted researches' attention for the potential application in heterogeneous Fenton-like reactions, but studies on the interactive effects of H2O2, iron, and HC in removal of organic pollutants are still limited. In this paper, magnetic iron (hydr)oxides immobilized hydrochar composite (Fe/HC) derived from hydrothermal carbon (HTC) of pinewood were synthesized and characterized. The interactive effects of H2O2, iron, and HC in the removal of several estrogens were systematically investigated to understand the removal performance and related mechanism, especially at a pH range close to natural water environment. Batch experiments results showed that estrogens could be efficiently removed over Fe/HC material under a wide pH range of 4-9. Based on the analysis of electron spin resonance, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and electrochemical impedance spectroscopy, mechanism study indicated that the carbon-centered PFRs on the surface of hydrochar can act as electron donors, and transfer the electrons on adsorbed O2 to generate O2- rapidly, while the addition of H2O2 enhanced the transmission ability of electron to produce OH(ads) on the material surface. The iron and hydrochar components contributed to the desirable removal of estrogens via the synergistic effect between catalysis and adsorption. This study provides a promising application for the use of Fe/HC materials on remediation of pollution with trace estrogens in water environment.