Biochar-Fe3O4 nanosheet composite activated by manganous chloride for high-efficient antimony removal: Morphology modulation and temperature-dependence

The pollutant removal performance of iron-loaded biochar synthesized through one-pot pyrolysis is limited by its defect characteristics. Herein, the manganous chloride (MnCl₂) was employed to improve this process through being added to the precursors of cottonwood sawdust immersed by ferric trichloride (FeCl₃) solution, before subjecting to one-pot pyrolysis at 500°C (FMBC500) and 800°C (FMBC800). It was found that MnCl₂ effectively activated the composites, and the activation effect was significantly influenced by the pyrolysis temperature. At 500°C, MnCl₂ notably increased the porosity of the carbon skeleton while co-activation with FeCl₃ at 800°C notably enlarged the pores. The MnCl₂ activation helped preserve the Fe₃O₄ during pyrolysis at 800°C by preventing its reduction in a more reducing atmosphere, which is essential for solid–liquid separation of the composite. The morphology of Fe₃O₄ was altered due to the MnCl₂ activation and pyrolysis temperature: FMBC800 loaded Fe₃O₄ nanosheet with 4.40 mmol·g⁻¹ of Fe, whereas FMBC500 contained Fe₃O₄ sphere with 2.25 mmol·g⁻¹ of Fe. This modification produced a biochar-Fe₃O₄ nanosheet composite at 800°C. MnCl₂ modification significantly improved the removal performance of the composites, particularly FMBC800, which exhibited the highest Sb(Ⅲ)/Sb(Ⅴ) adsorption amount at 157.83/57.32 mg·g⁻¹. The loaded Fe-O bonds played a crucial role in the oxidation and adsorption of Sb ions. This study presents a viable strategy for optimizing the functionalities of iron-loaded biochar by adjusting the pyrolysis temperature and incorporating a modified reagent.