Metal–organic framework modified biochar nanocomposite for sustainable stabilization of heavy metals in contaminated soils

Soil pollution with heavy metals from anthropogenic activities poses serious threats to the environment and human health. Although biochar-based sorbents are widely used as soil amendments due to their high porosity and sorption capacity, their ability to firmly immobilize metals and prevent their re-release or re-mobilization under changing environmental conditions remains limited. To address this challenge, biochar produced from wheat straw (BC) was functionalized with the metal–organic framework (MOF) MIL-100(Fe) via hydrothermal synthesis (BC@MIL) to enhance its capacity for heavy metal removal. Structural analysis confirmed uniform MIL-100(Fe) nanoparticle distribution on biochar surfaces, boosting surface area sixfold. Pot experiments in both unpolluted and metal-contaminated soil revealed that BC@MIL facilitated the transformation of Cu, Pb, Zn, and Cd from acid exchangeable fraction to oxidizable and residual fractions. The risk assessment code decreased, and the reduced partition index increased for all heavy metals with sorbent application, indicating an increase in their fixation strength in soils. X-ray diffraction analysis showed that the sorbents effectively stabilized Pb, Cu and Zn in contaminated soils through precipitation processes. In all cases, BC@MIL showed greater efficiency in the stabilization of heavy metals compared to BC. Overall, the study highlights the potential of MOF-modified biochar as an advanced soil amendment for sustainable remediation of heavy metal-contaminated soils.