Adsorption behavior of 17α-ethinylestradiol onto mesostructured calcium-based metal–organic frameworks adsorbent from water

Abstract

The removal of 17α-ethynylestradiol (EE2), a persistent endocrine-disrupting compound, from aqueous environments was investigated using three calcium-based metal–organic frameworks (Ca-MOFs): Ca-BDC, Ca-BTC, and Ca-MIX. The Ca-MOFs were synthesized and characterized using PXRD, FTIR, BET, and SEM. Batch adsorption experiments were conducted to evaluate the effect of solution pH, temperature, ionic strength, and humic acid concentration on EE2 removal. Kinetic studies were performed at an initial EE2 concentration of 10 µg/L using 50 mg of adsorbent at unadjusted (native) pH, analyzing adsorption over different contact times. Non-linear kinetic models were applied to interpret adsorption behavior. For isotherm studies, EE2 uptake was investigated across a range of initial concentrations (10–200 µg/L) under fixed conditions (50 mg adsorbent, 2 h contact time, native pH). Langmuir and Freundlich isotherm models were employed to describe the equilibrium data. Among the three adsorbents, Ca-MIX exhibited the highest EE2 adsorption capacity (52.03 µg/g), followed by Ca-BDC (35.69 µg/g) and Ca-BTC (19.49 µg/g). Adsorption followed the Langmuir isotherm and pseudo-second-order kinetic models, indicating monolayer chemisorption. Thermodynamic analysis revealed endothermic and spontaneous adsorption. The adsorption mechanism was primarily governed by hydrophobic interactions, electrostatic attraction, and hydrogen bonding. Increased humic acid concentration and extreme pH conditions significantly influenced adsorption behavior. The study demonstrates the potential of Ca-MOFs, especially Ca-MIX, as efficient adsorbents for EE2 removal. These findings contribute valuable insights into designing effective MOF-based adsorbents for water purification applications targeting micropollutants.