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 FeO@SiO@UiO-66-NH (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.