Zirconium-based MOF-808 loaded magnetic biochar derived from biomass: Magnetic nanocomposite characterization and adsorption performance

This study presents the synthesis of the novel zirconium-based MOF-808-loaded magnetic biochar. The MOF-808 (Zr) was synthesized employing solvothermal techniques and embedded on the CoFe₂O₄ loaded biochar derived from pistachio shell biochar (PSB) through a wet impregnation technique, resulting in the magnetic nanocomposite (PSB/CoFe₂O₄/MOF-808 (Zr)). The fabricated materials were characterized using Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Mapping (EDS-Map), and Vibrating Sample Magnetometer (VSM) techniques. Adsorptive performance was evaluated through methylene blue (MB) uptake. The maximum MB adsorption efficiencies were 97.78, 98.45, and 99.43 % in pH of 10, 25 °C, 10 mg/L of MB, 2.5, 1.5, and 1 g/L of adsorbent dose and 60, 60, and 80 min of contact time, for PSB, PSB/CoFe₂O₄, and PSB/CoFe₂O4/MOF-808 (Zr), respectively. The pseudo-second-order (PSO) and Langmuir models outperformed other models in fitting with adsorption experimental data. Thermodynamic evaluations demonstrated that MB adsorption was exothermic and spontaneous. The results also showed that co-existing K⁺, Ca²⁺, and Na⁺ cations decreased the MB adsorption efficiency. Additionally, all adsorbents retained reasonable adsorption performance, achieving over 70 % efficiency after seven adsorption-desorption cycles. Electrostatic attractions, n-π, π-π, and H-bonding interactions were identified as the dominant mechanisms driving the MB adsorption process. High surface area, abundant functional groups, fast kinetics, and acceptable reusability of the PSB/CoFe₂O₄/MOF-808 (Zr) demonstrated its potential as a promising adsorbent for practical wastewater applications.