Competitive adsorption of natural and synthetic estrogens onto sustainable almond-shell and cork residues: kinetics, multi-component isotherms, and mechanism analysis.

This study investigates the competitive removal of three co-existing estrogens, estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2), from aqueous matrices via batch adsorption. Pre- and post-carbonized materials synthesized from industrial almond shell and cork residues were evaluated under multicomponent conditions. Thermal activation via carbonization proved ineffective, whereas raw cork ("in natura," CiN) exhibited the optimal performance. At 25 °C and an adsorbent dosage of 1.0 g/L, CiN achieved a cumulative mean estrogen removal efficiency of 66.1%. The maximum experimental uptake capacities for E1, E2, and EE2 were 3.82, 3.75, and 7.23 mg/g, respectively, yielding a notable combined capacity of 14.79 mg/g. Kinetic profiles were accurately described by the pseudo-second-order (PSO) model, which predicted an equilibrium time of 440 min at 25 °C. The multicomponent Sheindorf-Rebuhn-Sheintuch (SRS) isotherm model successfully simulated the competitive equilibrium data. Operational parameters showed that highly alkaline media (pH ≥ 12) led to a significant decline in uptake capacity due to electrostatic repulsion. Thermodynamic analysis confirmed that the sequestration process is spontaneous ( Δ G 0 < 0 ), exothermic ( Δ H 0 < 0 ), and entropically favorable ( Δ S 0 > 0 ) at the solid-liquid interface. Comprehensive mechanistic evaluation identified a synergistic interplay between physisorption via pore filling and chemisorption governed by p-electron donor-acceptor interactions and hydrogen bonding networks. The superior competitive affinity of the synthetic estrogen (EE2) was successfully rationalized by its higher hydrophobicity and lower activation energy barrier. Overall, this work highlights the viability of sustainable raw cork residues for environmental remediation, demonstrating that surface chemistry can play a more decisive role than texturized porosity in sequestering endocrine-disrupting chemicals.