Magnetic nanocomposites of cobalt terephthalate with magnetite:Synthesis and functional characterization

The development of advanced sorbent materials for water purification remains a critical challenge in environmental chemistry. This study presents a novel magnetic nanocomposite combining cobalt (II) 2-aminoterephthalate (Co-TFK-NH?) metal-organic framework with magnetite (Fe?O?) nanoparticles for efficient removal of organic dyes from contaminated water.

The nanocomposite was synthesized through a two-step in situ approach. First, the Co-TFK-NH? framework was prepared solvothermally by reacting 2-aminoterephthalic acid with CoCl?·6H?O in dimethylformamide at 140°C for 72 hours. Subsequently, magnetite nanoparticles were incorporated via controlled alkaline coprecipitation of Fe²?/Fe³? salts (1:2 molar ratio) within the pre-formed MOF matrix. Structural characterization confirmed the successful formation of the hybrid material, with XRD analysis showing characteristic peaks for both crystalline phases (Co-TFK-NH? at 10.75° and 20.05° 2θ; Fe?O? at 30.1° and 35.5° 2θ). FTIR spectroscopy verified the preservation of functional groups, while BET measurements revealed a high specific surface area of 576.4 m²/g and mesoporous structure (0.58 cm³/g pore volume). The composite exhibited superparamagnetic properties enabling rapid magnetic separation (<60 seconds).

Adsorption performance was systematically evaluated using three model dyes: anionic Congo Red (CR) and Tartrazine (TZ), and cationic Methylene Blue (MB). Under optimized conditions (pH 2-10, 5-35°C, initial concentration 1.25-20 mg/L), the material demonstrated exceptional adsorption capacities of 302.7 mg/g (TZ), 119.4 mg/g (MB), and 92.3 mg/g (CR). Kinetic studies revealed pseudo-second-order adsorption behavior (R² > 0.99), while equilibrium data fitted the Langmuir isotherm model, suggesting monolayer chemisorption. The thermodynamic analysis indicated spontaneous (ΔG° = -7.81 to -0.96 kJ/mol) and exothermic (ΔH° = -5.82 to -0.004 kJ/mol) adsorption processes.

Remarkably, the nanocomposite maintained >90% adsorption efficiency after five regeneration cycles and showed excellent performance in high-ionic-strength media (0.723 M artificial seawater). These results demonstrate that the Fe?O?/Co-TFK-NH? nanocomposite combines the advantages of MOF chemistry with magnetic separability, representing a promising solution for wastewater treatment applications. The material's high efficiency, environmental stability, and reusability make it particularly suitable for industrial-scale water purification processes dealing with complex dye mixtures.

Julia D. Bryantseva is a PhD student and research assistant in Analytical Chemistry at the Southern Federal University in Rostov-on-Don. Since obtaining her master’s degree in chemical and environmental sciences in 2021, she has specialized in materials characterization. Her doctoral research focuses on the topic of 'Sorption, Antioxidant and Antibacterial Properties of Metal-Organic Frameworks Based on Metal Terephthalates', investigating innovative functional materials for environmental applications.