Adsorption of 17β-estradiol by multi-walled carbon nanotubes in natural waters with or without aquatic colloids

Abstract

The adsorption of 17β-estradiol (E2) by multi-walled carbon nanotubes (MWCNTs) was investigated under environmentally relevant conditions. Six different surface water samples were collected in different areas of China. The effects of aquatic colloids on E2 adsorption by MWCNTs were estimated by separating the colloids using cross-flow filtration. The results show that, in the absence of aquatic colloids, the distribution coefficient (Kd) for E2 adsorption by MWCNTs shows strong correlation with the zeta potential of the MWCNTs and the fluorescence intensities of the water samples, indicating that the binding between dissolved organic matter and E2 and the increasing negative charges of MWCNTs inhibits the E2 adsorption by MWCNTs. In the presence of aquatic colloids, the Kd values for E2 adsorption by MWCNTs are negatively affected by various factors simultaneously, including the colloid content, the intensities of two typical fluorescence peaks, total organic carbon content, conductivity, and zeta potential of MWCNTs. The binding of aquatic colloids and MWCNTs, which was shown using transmission electron microscopy images, may inhibit or promote E2 adsorption by blocking or providing the adsorption sites for E2. These two effects may counteract and result in different effects of various aquatic colloids on E2 adsorption by MWCNTs.