Tangyuan-like structure N-doped C shell Fe0 as an efficient catalyst for organic degradation in groundwater: N–Fe synergistic strengthening effect, and activation mechanism.

[Display omitted] • Fe0@NC-0.8–0.6–800 featured high reusability, stability and adaptability. • Fe0@NC-0.8–0.6–800 could effectively treat real groundwater contamination. • N-doped defects improved PS activation through non-radical pathways. • Contribution to four removal paths was studied by quenching and EPR. • Possible Ph degradation pathways in the Fe0@NC-0.8–0.6–800 system was proposed. Zero valent iron (Fe0)-based biochar prepared using Fe salts as the Fe source has low yield and is readily oxidized, which limit its practical applications. In this study, a Tangyuan-like structure N-doped C shell Fe0 composite (Fe0@NC-0.8–0.6–800) was prepared via a "hydrothermal coating-pyrolysis reduction" strategy using glucose, ferroferric oxide (Fe 3 O 4), and urea as raw materials to activate persulfate (PS) for organic contaminant degradation. The results revealed that Fe0@NC-0.8–0.6–800, prepared by pyrolyzing 0.8 g Fe 3 O 4 and 0.6 g urea at 800 °C, removed 100% phenol within 20 min with 0.204 min−1 reaction rate constant (k obs), which was 2.4 times higher than that of Fe0@C-0.8–0-800 without N-doping (0.0866 min−1). The primary Fe0@NC-0.8–0.6–800 facilitation mechanisms include enhanced adsorption capacity, increased number of active sites on the C surface, electron transfer, and Fe2+ regeneration. Moreover, the synergistic effect between Fe0 and N defects (graphitic N and pyridinic N) in Fe0@NC-0.8–0.6–800 is the main reason for promoting non-radical pathway (1O 2) generation. Based on the intermediates detected, five possible phenol degradation pathways were identified. The toxicity of phenol and degradation byproducts was evaluated by ECOSAR program. Through recycling experiments, and application in real groundwater, Fe0@NC-0.8–0.6–800 was found to show promising potential and offers a new strategy for treating organic matter-contaminated groundwater. [ABSTRACT FROM AUTHOR]