Magnetic Iron Oxide–Silica Nanohybrids for Targeted Remediation of Cadmium in Agricultural Soil: Mechanistic Insights and Field-Scale Feasibility

Cadmium contamination in agricultural soils severely threatens food safety and ecosystem health, demanding innovative remediation strategies. This study investigates iron oxide–silica nanohybrids (Fe₃O₄@SiO₂ NPs) for targeted Cd immobilization, leveraging their high surface area, magnetic recyclability, and compatibility with plant–soil systems. The NPs were synthesized via sol–gel co-precipitation (confirmed by XRD/TEM) and functionalized with carboxyl groups to enhance Cd adsorption. Contaminated soil (45 mg/kg Cd) was treated with NPs (0.1–1.0 wt%), and Cd bioavailability was assessed using sequential extraction (BCR method), revealing a 70% reduction in plant-available Cd at 0.5 wt% NP dosage. X-ray absorption spectroscopy (XAS) demonstrated Cd sequestration via surface complexation, while FTIR confirmed NP–soil binding mechanisms. The NPs improved soil microstructure (SEM-EDS), increasing porosity by 25% and water retention by 15%, which mitigated compaction stress. Lettuce (Lactuca sativa) grown in NP-amended soil showed 60% lower Cd accumulation in edible tissues, alongside enhanced biomass (30% increase). Microbial diversity (16S rRNA sequencing) revealed that NP-treated soils retained Proteobacteria dominance (25% higher abundance), critical for nutrient cycling. The NPs were magnetically recovered with 92% efficiency, enabling reuse. These results highlight Fe₃O₄@SiO₂ NPs as a sustainable, scalable solution for Cd remediation, combining high efficiency with minimal ecological disruption. Future work will optimize field-scale NP deployment and long-term soil health monitoring, addressing gaps in nano-agriculture regulatory frameworks.