One-pot fabrication of zero-valent iron-embedded activated carbon from rosemary distillation residues for malachite green removal

The current research proposes an innovative strategy for the facile preparation of magnetic activated carbon (MAC) from rosemary distillation residues (RDR). As a magnetic precursor, FeCl3 was impregnated into RDR before KOH was added as an activating agent. One-pot pyrolysis was then conducted to produce zero-valent iron nanoparticles (14.4 wt%) embedded in the activated carbon matrix. Moreover, KOH activation yielded MAC with a large total pore volume of 0.27 cm(3) g(-1), a high specific surface area of 459 m(2) g(-1), and hierarchical porosity. With a large porous system and different polar functional groups, MAC was subsequently investigated for malachite green (MG) removal in aqueous media. At pH 6.0, the adsorption process was consistent with the pseudo-second-order kinetic model and the Langmuir isotherm, with a maximum adsorption capacity of 82.6 mg g(-1). Additionally, MAC demonstrated effective reusability after five consecutive cycles, when MG removal slightly decreased from 96.4 +/- 0.6 to 91.8 +/- 2.3%. Notably, MAC with a strong saturation magnetization of 18.4 emu g(-1) could be conveniently recovered from treated media through magnetic fields. Overall, rosemary distillation residue-derived magnetic activated carbon can be a potential adsorbent for malachite green remediation thanks to its cost-effectiveness, eco-friendliness, and magnetic separability.