Green rGO/FeNPs nanocomposites activated peroxydisulfate for the removal of mixed 17β-estradiol and estriol.

Reduced graphene oxide/iron nanoparticles (rGO/FeNPs) synthesized by the chemical method have been used in Fenton oxidation of organic contaminants, yet little is known about biosynthesized rGO/FeNPs using green tea extract (GT) as how to activate persulfate in sulfate radical-based advanced oxidation processes. In this study, rGO/FeNPs were used to activate peroxydisulfate (PDS) for 17β-estradiol (βE) and estriol (E) removal. The rGO/FeNPs-PDS system removed 83.6% of βE and 62.5% of E within 240 min, which was confirmed by a combination of adsorption and degradation via both radical and non-radical pathways. Four main reactive species in βE and E degradation were observed, i.e., hydroxyl radical (·OH), sulfate radical (SO), singlet oxygen (O) and electron transfer, with the respective contributions of ·OH (32.9 and 34.7%), SO (16.1 and 19.7%), O (12.2 and 14.1%) and electron transfer (8.0 and 7.2%). Analysis of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), Electron Paramagnetic Resonance (EPR) and electrochemical measurements all indicated that beside the well-known role of Fe, CO from rGO through the generation of ·OH, SO, O and electron transfer, as well as GT through electron transfer also participated in the activation of PDS. Finally, the degradation pathways of βE/E were proposed. Overall, this study provides a new insight into the biosynthesis of rGO/FeNPs to activate PDS for the oxidation of mixed emerging contaminants.