Assessing the efficiency and reusability of zirconium-based MOF-biochar composite for the removal of Pb (II) and Cd (II) in single and multi-ionic systems

Recent studies have highlighted the promising properties of metal-organic frameworks (MOF) and biochar composites as cost effective adsorbents. Although MOF-biochar composites have shown significant potential for contaminant removal in aquatic environments, further research is needed for their scalable performance in removing a wide range of emerging contaminants from wastewater. In this paper, we introduce a novel UiO67-biochar composite (MBC) for the first time, synthesised via an in-situ solvothermal method, as an innovative solution for removing heavy metals from water. The composite was characterised by various analytical techniques (SEM, TEM, XRD, FTIR, XPS, BET, and TGA) and the results demonstrated that the specific surface area of the composite (≈540 m²/g) elevated 28 times compared to the unmodified biochar (≈20 m²/g). The adsorption tests indicate remarkable adsorption capacity and removal efficiency in the range of 121.1 mg/g and 90.8 % as well as 59.7 mg/g and 89.5 % for Pb (II) and Cd (II), respectively, which sustained under impacts of co-existing ions. Kinetic studies demonstrated that the experimental data for both heavy metal ions were best described by the Pseudo-second order kinetic model, inferring that chemical interactions mainly control adsorption. The formulated material showed promising stability (retained crystallinity confirmed by XRD analysis) over reusability tests with approximately 87 % removal efficiency. The ion exchange, surface complexation, and electrostatic interactions were the main adsorption mechanisms of the heavy metal ions on the MBC composite. The formulated composite proposed in this study offers scalable, sustainable, and affordable material to treat heavy metal-polluted water and wastewater.