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.

Pristine and manganese ferrite modified biochars for copper ion adsorption: Type-wide comparison.

This study synthesized nine biochars from different feedstocks and chemically modified their surfaces using MnFe2O4 precipitation at pH 11 (MnFe2O4-biochars). The maximum adsorption quantities (qmax) of Cu(II) at pH 6 and 25 °C for pristine biochars based on Langmuir model ranged 10.4-23.6 mg/g and for MnFe2O4-biochars, 32.7-43.1 mg/g, with enhancement from 65.6% (bamboo biochar) to 246% (white popinac biochar). Type-wide comparison shows no correlation between surface area of pristine or MnFe2O4-biochars on the adsorption performance. Conversely, the carboxyl groups on the nine biochar surfaces have contributed to Cu(II) adsorption. The type-dependence for qmax of different MnFe2O4-biochars becomes insignificant, confirming the role of biochars being principally an oxide carrier instead of an adsorbent.