Examining green and chemical methods for zero-valent iron nanoparticle synthesis in heavy metal adsorption

The increasing concern over heavy metal contamination in water has necessitated the development of sustainable and efficient treatment methods. This study compares two synthesis approaches for zero-valent iron nanoparticles (nZVI) for cadmium, chromium, and arsenic removal: chemical reduction using sodium borohydride and green synthesis utilizing cocoa husk extracts combined with hydrothermal carbonization (HTC). Chemically synthesized nZVI exhibited high initial removal efficiencies (>98%), though desorption effects occurred over time due to particle aging. In contrast, green-synthesized nZVI, stabilized by a carbon matrix, maintained consistent removal efficiencies above 98% for 120 hours under acidic conditions, showcasing superior stability and reactivity. Characterization through SEM, EDS, and XRD confirmed the dual mechanisms of metal removal: reduction and adsorption facilitated by the Fe(0) core and oxide layers. While experimental conditions were optimized for each synthesis method, the findings highlight the promise of green-synthesized nZVI as a sustainable alternative for heavy metal remediation. Future studies should explore adsorption isotherms and long-term applications to further validate the scalability and efficacy of these materials. This study demonstrates the successful green synthesis of zero-valent iron nanoparticles (nZVI) using cocoa husk extracts. Under batch experimental conditions, these particles maintained over 98% removal efficiency of arsenic, cadmium, and chromium for 120 hours, as measured by atomic absorption spectroscopy. • Comparative study of chemical and green nZVI synthesis for heavy metal remediation. • Polyphenols in cocoa husk extracts stabilize nZVI and enhance removal efficiency. • Green nZVI maintains >98% efficiency under varying pH conditions for 120 hours. • Agricultural waste valorization aligns with circular economy and sustainability goals. • Findings support scalable and cost-effective water treatment solutions.