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.