Continuous Filtration of Multimetal-Contaminated River Water and Groundwater Using Antioxidants Preserved Redox-Sensitive Nanocomposites: Ultrahigh Reactivity and Self-Sedimentation Possibility

Antioxidant coating is emerging as a new technique to preserve the reactivity of redox-sensitive nanocomposites. Current work extends potential environmental applications of antioxidants in preserving Fe⁰-biochar nanocomposites further and highlights the remediation of multimetal-contaminated river water and groundwater. Nanocomposites were prepared via a liquid-phase iron reduction in the presence of almond shell biochar surfaces, followed by its interaction with antioxidants extracted from almond skin. Antioxidant coating resulted in the generation of an iron-carbonyl shell on the composite surface, preserving the redox state of Fe⁰ nanoparticles. Synthesized composites were explored for the removal of both cationic and anionic metallic species from river water and groundwater in batch and continuous column modes. Synthesized nanocomposites have shown efficient contaminant removal capacities (AsO₂^–, 167.9 mg/g; Cd²⁺, 134.1 mg/g; CrO₄^2–, 118.7 mg/g; and Ni²⁺, 130.2 mg/g) in a monometallic system and ultrahigh total metal sorption capacities, i.e., 695, 802, and 770 mg/g, respectively, in 0.01 M NaNO₃, river water, and groundwater samples, contaminated with multimetallic species. In addition, continuous column separation of all metals (>1,50,000 L/kg), no secondary release of contaminants, suspension stability in river water, and self-settling possibility after contaminant sorption justify their large-scale environmental applicability.