Sustainable and efficient activated carbon/Mg-Cr LDH/modified chitosan composite for synergistic remediation of β-Estradiol and Chrysoidine: Kinetics, isotherms, and reusability.

Global water quality faces relentless challenges due to pervasive contamination from domestic, agricultural, and industrial activities. Among these, biosorption has emerged as a promising and eco-friendly solution for wastewater treatment. A composite adsorbent comprising activated carbon, Mg/Cr-layered double hydroxide (LDH), and modified chitosan was synthesized and characterized for eliminating β-Estradiol (β-Estra) and Chrysoidine (Chrys) from wastewater. FTIR and XPS analyses confirmed the successful incorporation and functionalization, revealing key interactions like the formation of a Schiff base and extensive hydrogen bonding. XRD, N₂-BET, and SEM analyses showed that the composite possesses a heterogeneous, porous structure with a bimodal pore size distribution, combining the amorphous nature of activated carbon with the layered structure of the LDH. Adsorption experiments demonstrated high efficiencies, with the process being significantly influenced by contaminant concentration, adsorbent dosage, and pH. Optimal removals of 25.9 mg.g-1 and 29.43 mg.g-1 achieved for β-Estra and Chrys, respectively, at the composite's point of zero charge (pHpzc 7.8). Kinetic studies indicated the process was well-defined by a pseudo-2nd-order (PSO) model (R2 > 0.9995-0.9997), suggesting the chemisorption is the rate-limiting step. The elimination process follows the Freundlich isotherm model, confirming the heterogeneous nature of the composite's surface. Finally, the composite exhibited excellent reusability, retaining its capacity after five cycles with the capability of using green solvent for regeneration. These results lessen the gap between the sustainability and reusability of bisorbents during biosorption of organic pollutants, and highlight the composite's potential as a stable, efficient, and sustainable material for the bioremediation of diverse organic pollutants in wastewater.