MOF-biochar nanocomposite for sustainable remediation of contaminated soil

Abstract

Soil contamination by heavy metals represents a critical environmental risk. Innovative and sustainable remediation strategies are urgently needed to address this global challenge. Biochar, derived from biomass pyrolysis, has gained attention as an eco-friendly material for heavy metal adsorption. However, its adsorption performance is highly dependent on the pyrolysis conditions and can be further enhanced through functionalization. In this study, wheat straw biochar was optimized for enhanced porosity, carbon content, and structural stability and further functionalized by incorporating metal–organic frameworks (MOFs) to create a high-performance nanocomposite. Three MOFs—ZIF-8, UiO-66, and MIL-100(Fe)—were evaluated for their Cu^2⁺ and Pb^2⁺ adsorption capacities. MIL-100(Fe) emerged as the most effective due to its high pore volume and iron-active sites. Coating biochar with MIL-100(Fe) increased its surface area sixfold, achieving 419 m²∙g⁻¹, and doubled its sorption capacity for heavy metals in soil (142 mmol·kg⁻¹ for Cu^2⁺ and 156 mmol·kg⁻¹ for Pb^2⁺). Advanced characterization techniques, including XAFS, XRD, and SEM–EDX, revealed that the sorption mechanisms were dominated by complexation and cation exchange, with the nanocomposite demonstrating superior metal immobilization compared to neat biochar. These findings highlight the potential of the nanocomposite as an effective amendment for reducing heavy metal toxicity in soils.