The adsorption of endocrine-disrupting compounds (EDCs) on carbon nanotubes: effects of algal extracellular organic matter (EOM)

Carbon nanotubes (CNTs) have been considered as a promising adsorbent material for the removal of endocrine-disrupting compounds (EDCs) in recent years. Their adsorption affinities could be affected by aquatic chemistry parameters, such as algal extracellular organic matter (EOM), in the real aquatic system. However, little is known about the effects of EOM on the adsorption of different steric-structured EDCs on different functionalized CNTs. In this study, the effects of EOM on the adsorption of a butterfly-structured bisphenol A (BPA) and planar 17α-ethinyl estradiol (EE2) to graphitized multiwalled carbon nanotube (G-MWCNTs) and hydroxylated multiwalled carbon nanotube (OH-MWCNTs) were examined. Further, the mechanisms controlling the effects of EOM were discussed. The results indicated that EOM could inhibit the adsorption of BPA and EE2 to MWCNTs. This could be attributed to the decreased available sorption sites and reduced hydrophobicity of MWCNTs after the adsorption of EOM. The surface properties and molecular size of MWCNTs and EOM could affect the inhibition effects on adsorption behavior. Furthermore, the steric structure of EDCs could further affect the inhibition effects on their adsorption to MWCNTs. Compared with the more hydrophobic molecule, i.e., EE2, BPA showed better negative correlation between the adsorption affinity values (log Kd) and the polarity ((O+N)/C) of MWCNTs after the adsorption of EOM. This is likely because of the advantage of its unique butterfly structure. The findings of the present study may have significant implications for the environmental fate assessment of EDCs and CNTs.