Preparation of magnetic biochar towards efficient tetracycline and hexavalent chromium removal: Harnessing seawater mineral for encapsulating and impregnating nano-iron oxides

A novel magnetic biochar (MB) was developed by combining seawater minerals and potassium ferrate during the pyrolysis of corncob at 400-600 degrees C. The MB pyrolyzed at 600 degrees C (MB600) was optimal for the removal of tetracycline (TC) and hexavalent chromium (Cr(VI)) from aqueous solutions. The process enhanced the biochar with nano magnetic iron species (Fe3O4 and MgFe2O4), increased surface area, and enriched oxygen-containing functional groups for better adsorption. Seawater mineral was instrumental in parceling and dispersing the insitu generated magnetic iron oxides, facilitating formation of nano-sized iron particles. MB600 exhibited adsorption capacities of 570.16 mg/g for TC and 92.34 mg/g for Cr(VI), with high saturation magnetization (40.40 emu/g). The potential adsorption mechanisms for TC and Cr(VI) were driven by hydrogen bonding/ complexation/pi-pi interaction/pore filling and reduction/hydrogen bonding/complexation/electrostatic interaction/pore filling, respectively. This study presents a sustainable method to produce high-efficiency MB from agricultural waste and seawater minerals for pollution control.