Manganese ferrite modified agricultural waste-derived biochars for copper ions adsorption

Biochar is an eco-friendly, low-cost, and carbon-rich material. This study synthesized the biochars from three agricultural wastes, pinecone, white popinac, and sugarcane bagasse, and then modified them by manganese ferrite (MnFe₂O₄) co-precipitation. These biochars were applied as adsorbents for the removal of Cu(II) ions from water. All three different MnFe₂O₄-biochars have similar adsorption performances: rapid adsorption kinetics with equilibrium being reached within 5 hr of contact and significantly enhanced adsorption capacities of Cu(II) ions from water. The principal adsorption mechanisms were identified as complexation reactions, contributed by the carboxyl and hydroxyl groups by pristine biochars and by the Mn-O and Fe-O groups for all three MnFe₂O₄-biochars. The MnFe₂O₄-biochars can be reused for three cycles, with the maximum adsorption capacities of Cu(II) of the regenerated biochars declining with the loss of precipitated MnFe₂O₄.