Synthesis of MgO/Fe3O4 nanoparticles embedded activated carbon from biomass for high-efficient adsorption of malachite green

Fe–Mg bimetallic magnetic activated carbons (Fe–Mg BACs) were synthesized using biomass (peanut shells) as precursor combining the activation mechanism of FeCl3 and MgCl2 to realize high adsorption performance on malachite green (MG) toxic dye. It was observed that MgO nanoparticles were formed and aggregated with the Fe3O4 during activation process under CO2 atmosphere, and then formed MgO/Fe3O4 composite nanoparticles on the surface of the carbon basal plane. A large MG adsorption capacity of 4031.96 mg/g was achieved by Fe–Mg15 (activation using 15 g of MgCl2·6H2O and 10 g of FeCl3·6H2O) at 318 K. Fe–Mg15 still possessed superparamagnetic property while the formation of MgO nanoparticles weakened the magnetic property. The best fit of the Pseudo-first-order kinetic and Freundlich isotherm models suggested that a predominant chemisorption occurred. From the thermodynamic analysis, the high affinity of the MgO active site attracted a large number of MG molecules to the solid-liquid interface, indicating that the randomness was promoted and driven by entropy. Interactions between MG dye and Fe–Mg15 including the H-bonding, π-π stacking and the electrostatic attraction triggered considerable adsorption performance. The dominant interaction should be the H-bonding between Mg–OH and N-containing groups in MG. Chemical regeneration method cannot achieve effective removal of adsorbed malachite green, while the adsorptive properties of Fe–Mg BACs can be well regenerated via thermal regeneration method. [Display omitted] •Fe–Mg bimetallic magnetic activated carbons were synthesized for MG removal.•MgO/Fe3O4 composite nanoparticles were formed on the carbon basal plane.•A large MG adsorption capacity of 4031.96 mg/g was achieved at 318 K.•H-bonding interactions between Mg–OH and N atoms of MG was dominant.