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 1 O 2 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.