Single-Atom Iron Sites Enable Enhanced Arsenic Removal From Water Through Synergistic Adsorption-Oxidation

Iron (Fe)-based adsorbents represent a transformative approach for arsenic (As) decontamination, yet achieving atomic-level control of Fe species for efficient As(III) adsorption-oxidation remains a formidable challenge. This study introduces single-atom Fe-decorated nitrogen-rich porous biochar (SAFeC), a breakthrough material with dual As(III) adsorption-oxidation capabilities. SAFeC achieves unprecedented performance, with an adsorption capacity of 237.5 mg g^-1 and 56.9% of the immobilized As species existing as As(V), while exhibiting excellent environmental robustness and recyclability. Fe atoms in SAFeC display outstanding chemical reactivity toward As(III) (39833.54 mg (g·Fe)^-1). Atomic-scale characterization and theoretical calculations reveal that SAFeC captures As(III) from water through monodentate inner-sphere complexation, precipitation, hydrogen bonding, and electrostatic attraction. The complementary synergy between support and single-atom Fe facilitates the activation of molecular oxygen, generating ¹O₂ as the primary oxidant for As(III) transformation. This study not only underscores the exceptional efficacy of single-atom Fe active sites in the advanced purification of As(III) but also paves the way for the development of next-generation environmental remediation materials to tackle global As contamination challenges.