Synergistic removal of tetracycline in water with highly stable Lac immobilized on magnetic metal-organic framework

The arbitrary discharge of tetracycline (TC) residuals has seriously influenced the ecosystem and human health. Laccase (Lac)-based biodegradation technology is considered a more effective way to remove TC due to its high catalytic efficiency and less by-product. Nevertheless, free Lac suffers from poor stability, easy inactivation and difficult recovery, restricting its application. Immobilization of Lac is considered an efficient strategy for addressing these obstacles. In this study, a magnetic metal-organic framework of Fe 3 O 4 @SiO 2 @UiO-66-NH 2 (MMOF) was prepared and used as a carrier to immobilize Lac (Lac@MMOF) for TC degradation. Benefiting from the multiple binding sites, adsorption, and protection effect of MMOF, Lac@MMOF displayed a wider pH application range (2–7) and better thermal (15–85 °C), repeatability, and storage stability than free Lac. Furthermore, owing to the synergism of MOF adsorption and Lac biocatalysis, the removal rate of Lac@MMOF for TC could be up to 98 % at pH = 7 within 1 hr, which was 1.29 and 1.24 times that of free Lac and MMOF, respectively. More importantly, Lac@MMOF could easily be separated from aqueous solution under a magnetic field and maintained good removal performance (80 %) after five cycles. The degradation products were identified by applying LC-MS/MS, and possible degradation mechanisms and pathways were proposed. Finally, the antibacterial activity of intermediate products was evaluated using Escherichia coli , which revealed that the toxicity of TC was reduced effectively by the degradation of Lac@MMOF. Overall, Lac@MMOF is a green alternative for residual antibiotic removal in water.