Removal of 17β-estradiol by few-layered graphene oxide nanosheets from aqueous solutions: External influence and adsorption mechanism

This study demonstrates the use of few-layered graphene oxide nanosheets (GO) as efficient adsorbents for the removal of 17 beta-Estradiol (E2) from aqueous solutions via strong adsorptive interactions. The adsorption performance of GO was investigated by batch adsorption experiments. Further, adsorption experiments were carried out in the presence of other environmental pollutants to understand external influence on the adsorption of E2 by GO. The result indicated that the maximum adsorption capacity (q(m)) of GO for E2 obtained from the Langmuir isotherm was 149.4 mg/g at 298 K and it was the highest values of E2 adsorption compared to that of other adsorbents reported before. Thermodynamic study indicated that the adsorption was a spontaneous process. In addition, the result showed that E2 adsorption on GO was slight affected by the solution pH. The presence of NaCl in the solution facilitated the E2 adsorption and the optimum adsorption capacity was obtained when the NaCl concentration was 0.001 M. Moreover, the effect of background electrolyte divalent cations (Mg2+ and Ca2+) was not similar with the monovalent cations (Na' and K+). While the influence of background electrolyte anions (Cl-, NO3-, SO42-, and PO4(3-)) were not significantly different. The presence of humic acid reduced E2 adsorption on GO at pH 7.0. GO still exhibited excellent adsorption capacity following numerous desorption/adsorption cycles. Besides, both pi-pi interactions and hydrogen bonds might be responsible for the adsorption of E2 onto GO. (C) 2015 Elsevier B.V. All rights reserved.