Adsorption kinetics of 17α-ethinyl estradiol and bisphenol A on carbon nanomaterials. II. Concentration-dependence
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Carbon nanomaterials (CNMs) have attracted a great deal of research interest for their potential environmental applications because of their unique properties. Adsorption of organic chemicals on CNMs was reported to be important in controlling their environmental risks. However, the kinetics of the adsorption is hardly investigated in literature. The objective of this work was, therefore, to quantitatively describe the sorption kinetics of 17 α-ethinyl estradiol (EE2) and bisphenol A (BPA) on CNMs as compared to activated carbon (AC).
Materials and methods
Batch adsorption/desorption (kinetic) experiments were conducted, and different kinetic models were used to process experimental data and obtain kinetic parameters.
Results and discussion
CNM adsorption kinetics could be described well using the improved pseudo second order kinetics model, and negative relationships were observed between the equilibrium solid-phase concentration and the modified rate constant (k2a*). The rearrangement of CNM aggregates after adsorbing high concentrations of adsorbates could be the reason of decreased adsorption rate with increasing EE2 or BPA loading on CNMs. The diffusion-controlled kinetic process seems not important for the adsorption of EE2 and BPA on CNMs; whereas, their adsorption on AC appears to be diffusion controlled, as indicated by a linear relationship between solid-phase concentration and t0.5.
Single-walled carbon nanotubes adsorb large amounts of EE2 and BPA fast and retain them strongly. These results suggest that single-walled carbon nanotubes have potential for applications in the treatment and purification of water contaminated by the chemicals.