β-Cyclodextrin/Fe3O4 Co-Doped Modified Biochar for Adsorptive Removal of Tetracycline from Aqueous Solutions

Tetracycline (TC), one of the most widely used broad-spectrum antibiotics globally, poses significant threats to ecosystems and human health due to its persistent aquatic residues. To address this, β-cyclodextrin/Fe 3 O 4 co-doped modified biochar (β@MHBC) was synthesized from corn straw via co-precipitation and impregnation methods using Fe 2+ /Fe 3+ and β-cyclodextrin (β-CD), respectively. The results of various characterization experiments confirmed the successful incorporation of β-CD and Fe 3 O 4 into pristine biochar (BC), with β@MHBC exhibiting a greater number of oxygen-containing functional groups. Batch adsorption experiments revealed that the optimal pH for TC adsorption on β@MHBC was 4; the divalent metal ions (Ca 2+ and Cu 2+ ) significantly inhibited TC removal efficiency as their concentration increased; and the humic acid (HA) exhibited a biphasic effect (initial enhancement followed by suppression), while oxalic acid (OA) showed negligible interference. The adsorption of TC onto β@MHBC followed the pseudo-second-order kinetics model and the Freundlich isotherm model. The theoretical maximum adsorption capacity fitted by the Langmuir model reached 38.68 mg∙g −1 at 25℃. The increase in temperature promoted the adsorption capacity, indicating that the process was spontaneous and endothermic. The adsorption mechanisms involved hydrogen bonding, coordination complexation, hydrophobic interaction, electrostatic interaction, pore filling, and π-π interaction. After five adsorption–desorption cycles, the TC removal rate by β@MHBC remained at approximately 50%, demonstrating its potential for application in removing TC from water.