Adsorption of estrogen contaminants (17β-estradiol and 17α-ethynylestradiol) by graphene nanosheets from water: Effects of graphene characteristics and solution chemistry

In this research, adsorption of two estrogens, namely, 17β-estradiol (E2) and 17α-ethynylestradiol (EE2), by graphene nanosheets with different reduction degrees (rGOs) were investigated; and the effects of solution chemistry, such as natural organic matter (NOM), pH and ionic strength (IS), on the E2 and EE2 adsorption behaviors were also examined. Results indicated that adsorption abilities of estrogens increased with increasing the reduction degree of rGOs; the π-π stacking interaction could be considered as a predominant interaction to the enhanced adsorption capacities of rGOs. Among the solution chemistry, NOM exhibited the significant influence on estrogens adsorption, which suggested that once released into water environments, graphene materials will adsorb estrogens but with a lower adsorption ability than that in ultrapure water due to the ubiquitous presence of NOM in aquatic environments. Besides, estrogens adsorption on rGOs was pH-dependent, but the influence of acid rain would be insignificant due to slight change in low pH range. However, IS within the typical range in natural waters did not exhibit significant influence on the uptake of estrogens by rGOs. Above findings of this work might have significant implications for the fate and transport of estrogens with graphene materials in the environment.