Iron-crosslinked alginate derived Fe/C composites for atrazine removal from water

Fe/C composite is emerging as a promising nanoscale zero-valent iron (nZVI) based material for wastewater treatment to counteract the limitations of nZVI, while its preparation method, structure-activity relationship, and working mechanisms and conditions still need to be studied. In this study, Fe/C composites derived from iron-crosslinked alginate was successfully achieved via high temperature pyrolysis. Ferric ions were only transformed into Fe₃O₄/γ-Fe₂O₃ at low pyrolysis temperature (≤500 °C), whereas Fe⁰/Fe₃C became the primary Fe species with the formation of graphitic carbon at elevated pyrolysis temperature (≥700 °C). Fe/C composites from higher pyrolysis temperature presented better performance in atrazine (ATZ) removal, and the optimal pyrolysis temperature was 800 °C (Fe/C-800). Batch experiments showed that the removal kinetics of ATZ (10 mg L⁻¹) by Fe/C-800 (0.2 g L⁻¹) followed pseudo-second-order model, and 24-h ATZ removal efficiency maintained at 93.5 ± 1.0% within pH 3–9. The adsorption by the graphitic carbon phase of Fe/C-800 was the principal contributor to the pH-independent superior performance in ATZ removal, and the Langmuir model fitted adsorption capacity was 64.8 mg g⁻¹ at pH 6. Although the carbon-phase adsorbed ATZ was basically unavailable for degradation, Fe⁰/Fe₃C-mediated ATZ degradation contributed to the great reactivity of Fe/C-800 at pH 3. Fe⁰/Fe₃C in Fe/C-800 was more efficient for ATZ degradation than commercial nZVI, and oxidative dealkylation by Fe⁰/Fe₃C mediated Fenton reaction was the predominant ATZ degradation pathway rather than reductive dechlorination. Moreover, the produced ATZ degradation intermediates could be further adsorbed by Fe/C-800, mitigating potential secondary pollution. Thus, iron-crosslinked alginate derived Fe/C composites can be an excellent alternative for nZVI in organics-polluted water treatment with great reactivity and wide pH applicability.