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 (αE 2 ) 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 αE 2 removal. In this study, one-step biosynthesized iron nanoparticles/reduced graphene oxide (FeNPs/rGO) by tea extract was successfully used for αE 2 removal. The results showed that the removal of αE 2 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 αE 2 , 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 αE 2 , and results showed that αE 2 was adsorbed as a monolayer on the surface of rGO via π–π bond interactions and that FeNPs underwent reactions with H 2 O 2 to generate ·OH for αE 2 degradation. Thereafter, a αE 2 degradation pathway was proposed via identification of degradation products (e.g., C 18 H 22 O 3 ) by HPLC-MS. Moreover, the removal of αE 2 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 αE 2 by FeNPs/rGO was presented.