Statistical modeling and optimization of dexamethasone adsorption from aqueous solution by Fe3O4@NH2-MIL88B nanorods: Isotherm, Kinetics, and Thermodynamic

Abstract

The presence of pharmaceutical compounds in the environment poses a significant threat to human and aquatic animal health. Dexamethasone (DEX), a synthetic steroid hormone with endocrine-disrupting effects, is one such compound that needs to be effectively removed before discharging into the environment. This research presents a novel approach utilizing magnetically recyclable Fe3O4@NH2-MIL88B NRs as an efficient adsorbent for the treatment of DEX from aqueous solutions. The synthesized adsorbent was characterized by X-ray diffraction (XRD), scanning microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), diffuse reflectance spectra (DRS), and Fourier transform infrared spectroscopy (FTIR). Response surface methodology based on central composite design (RSM-CCD) was employed to optimize DEX removal efficiency by determining the optimal conditions, including pH, adsorbent dose, time, and DEX concentration. Under the optimized conditions (pH: 5.53, adsorbent dose: 0.185 g/L, time: 16.068 min, and DEX concentration: 33.491 mg/L), Fe3O4@NH2-MIL88B NRs revealed remarkable DEX adsorption efficiency of 91 ± 1.34% and adsorption capacity of 180.01 mg/g. The Langmuir isotherm and pseudo-second-order kinetic model were found to fit well with the experimental data, indicating a monolayer and chemical adsorption process. Thermodynamic analysis revealed that the adsorption process was spontaneous and endothermic. The study also investigated the inhibitory effect of background ions on DEX removal by Fe3O4@NH2-MIL88B NRs. Magnesium exhibited superior competitive ability with dexamethasone to occupy the active sites of the adsorbent compared to other background ions. The reuse of the adsorbent over ten consecutive cycles resulted in a 39.46% decrease in removal efficiency. The Fe3O4@NH2-MIL88B NRs are surrounded by abundant amounts of functional groups and π-electrons bands that can play a key role in the adsorption and separation of DEX from aqueous environments. The promising results obtained under real conditions highlight the potential of Fe3O4@NH2-MIL88B NRs as a practical and efficient adsorbent for the removal of DEX and other similar corticosteroids from aqueous solutions.