Solvothermal Synthesis of Functionalized UiO-66/Fe₃O₄@CNCs for Selective Removal of Oxytetracycline

This study reports the design and solvothermal synthesis of a novel ternary nanocomposite named UiO-66/Fe₃O₄@CNCs. The material was developed for the selective adsorption and magnetic recovery of oxytetracycline (OTC) from water. The composite combines three functional components. CNCs derived from Neptunia oleracea serve as a fibrous scaffold. Fe₃O₄ nanoparticles provide magnetic separation, while UiO-66 contributes high surface area and active binding sites as a porous MOF. The Fe₃O₄@CNCs hybrid was prefunctionalized with mercaptoacetic acid to enhance interfacial interactions and promote uniform UiO-66 crystallization, yielding a well-defined core-shell porous architecture. The resulting UiO-66/Fe₃O₄@CNCs composite exhibited a high specific surface area (360.68 ± 1.82 m²/g), mesoporous structure (2-14 nm), and excellent magnetic responsiveness. Under optimized conditions (pH 6, 303 K), the composite demonstrated a maximum OTC adsorption capacity of 48.55 mg/g. Kinetic analysis followed a pseudo-second-order model, confirming chemisorption. Langmuir isotherm fitting (R ² = 0.9932) indicated a monolayer capacity of 110.13 mg/g, with uniform and high-affinity sites. Thermodynamic parameters (ΔG < 0, ΔH = -62.32 kJ/mol, ΔS = -168.06 J/mol·K) confirmed the spontaneous and exothermic nature of the process. The composite also showed high selectivity for OTC compared to other antibiotics. It retained good adsorption performance after several reuse cycles. These findings highlight the potential of UiO-66/Fe₃O₄@CNCs as a sustainable, efficient, and recyclable adsorbent platform for emerging contaminant removal in wastewater treatment.