New insights on removal mechanism of 17α-estradiol based on adsorption and Fenton-like oxidation by FeNPs/rGO

Wastewater from sewage treatment plants containing 17α-estradiol (αE2) has a high potential to cause environmental and human toxicity. Integration of adsorption and Fenton-like oxidation is one of the potential approaches to enhance αE2 removal. In this study, one-step biosynthesized iron nanoparticles/reduced graphene oxide (FeNPs/rGO) by tea extract was successfully used for αE2 removal. The results showed that the removal of αE2 by FeNPs/rGO increased to 56.1%, being only 25.4% and 45.4% for rGO and FeNPs, respectively, indicating that both adsorption and Fenton-like oxidation enhanced the removal of αE2, where was confirmed by HPLC-UV. To understand the removal mechanism, characterizations, including ESR, SEM, EDS, FTIR and XPS were used to elucidate the specific roles of rGO and FeNPs in the adsorption and oxidation of αE2, and results showed that αE2 was adsorbed as a monolayer on the surface of rGO via π–π bond interactions and that FeNPs underwent reactions with H2O2 to generate ·OH for αE2 degradation. Thereafter, a αE2 degradation pathway was proposed via identification of degradation products (e.g., C18H22O3) by HPLC-MS. Moreover, the removal of αE2 by FeNPs/rGO conformed to the Langmuir isotherm with pseudo-first-order adsorption kinetics and pseudo-second-order degradation kinetics. Based on these evidences, the removal of αE2 by FeNPs/rGO was presented.