Removal of natural and synthetic endocrine disrupting estrogens by multi-walled carbon nanotubes (MWCNT) as adsorbent: Kinetic and mechanistic evaluation

Environmental persistence of endocrine disrupting chemicals/estrogens (EDCs) in water bodies has garnered global attention due to their possible disruptive effects in an intact organism, or its progeny, subsequent to endocrine function even at nanogram levels. Removal of two EDCs viz., natural [estriol (E3)] and synthetic [17 alpha-ethynylestradiol (EE2)] reported to be present in water bodies was studied by adsorption using multi-walled carbon nanotubes (MWCNT) as adsorbent employing agitated non-flow batch sorption experiments. MWCNT showed good potential for removal of both natural and synthetic estrogens from aqueous phase at relatively lower concentrations. EDC-MWCNT sorption system was found to depend on the aqueous phase sorbate concentration and pH. The intraparticle diffusion plot revealed the complex nature of sorption mechanism between EDC-MWCNT involving both boundary layer and intra-particle diffusions. Equilibrium data showed relatively good fit with pseudo second-order kinetic model especially at lower concentrations. EDCs sorption onto nanotubes was found to be controlled by film diffusion process. Linear Langmuir's isotherm model showed good fit with the sorption data. Relatively good EDCs sorption was observed at neutral redox conditions. Cyclic voltametry was performed on virgin and estrogen sorbed MWCNT to study the sorption behavior. Estrogens concentration was estimated quantitatively by direct competitive immuno-enzymatic colorimetric (EIA) method. (C) 2011 Elsevier B.V. All rights reserved.