Adsorption of the harmful hormone ethinyl estradiol inside hydrophobic cavities of CTA⁺ intercalated montmorillonite

Hydrophobic cavities produced by cetyltrimethylammonium cation (CTA⁺) exchanged and trapped in the interlayer space of montmorillonite were used to remove the harmful hormone contaminant ethinyl estradiol (EE2) from water. X-ray diffraction, thermogravimetry/derivative thermogravimetry, elemental analysis (carbon, hydrogen, nitrogen), Fourier transform infrared, scanning electron microscopy/energy dispersive spectroscopy, Brunauer–Emmett–Teller and contact angle analyses showed that the intercalation of 9, 16 and 34 wt% CTA⁺ in the montmorillonite resulted in the d₀₀₁ expansion from 1.37 to 1.58, 2.09 and 2.18 nm, respectively. EE2 adsorption experiments showed that the original clay montmorillonite does not remove EE2 from water whereas the intercalated composites showed high efficiency with adsorption capacities of 4.3, 8.8 and 7.3 mg g⁻¹ for M9CTA⁺, M16CTA⁺ and M34CTA⁺, respectively. Moreover, experiments with montmorillonite simply impregnated with cetyltrimethylammonium bromide showed that the intercalation of CTA⁺ to form the hydrophobic cavity is very important for the adsorption properties. Simple solvent extraction can be used to remove the adsorbed EE2 without significant loss of CTA⁺, which allows the recovery and reuse of the adsorbent for at least five times.