Comparing the effects of different types of inorganic nanoparticles on 17ß-estradiol adsorption by graphene oxide.

This study compared the effects of five types of inorganic nanoparticles (INPs) on the 17ß-estradiol (E2) adsorption to graphene oxide (GO). The results showed that INPs increased the equilibrium time for the adsorption of E2 to GO. Higher Brunauer-Emmett-Teller (BET) surface area of INPs resulted in lower diffusion rate of E2, and thus the adsorption rate constant (k2) calculated from pseudo-second-order kinetic model negatively correlated with the BET surface area of INPs (p = 0.037). In addition, INPs decreased the adsorption amount of E2 to GO, and the inhibition effects declined in the order of Al2O3 > ZnO > TiO2 > SiO2 > Fe2O3. This is determined by the interactions between GO and INPs. The positively charged ZnO and Al2O3 strongly heteroaggregate with GO via electrostatic attraction, and then significantly inhibited E2 adsorption to GO. In contrast, the homoaggregation of GO was superior to its heteroaggregation with negatively charged SiO2 and TiO2, and then lower inhibition of E2 adsorption to GO was induced. Fe2O3 with less negative charge (-8.48 mV) led to the lowest inhibition effect on E2 adsorption to GO because of its preferable homoaggregation. The results were further confirmed by Derjaguin-Landau-Verwey-Overbeek calculation, transmission electron microscopy, and sedimentation experiments. This study revealed how the properties of INPs influence their effects on the adsorption of E2 by GO, and the findings are critical to understand the behavior and fate of GO and pollutants in natural aquatic environment.