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 °C. The MB pyrolyzed at 600 °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 in-situ 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/π-π 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.