Lipase Immobilization over Hierarchically Carbonized Macro-MIL-88A for Biodiesel Production

Macroporous metal–organic frameworks (MOFs) exhibit immense promise as carriers for immobilizing macromolecules, notably lipases. Nevertheless, their minute particle dimensions pose challenges in the recycling process, thereby significantly constraining their widespread practical utilization. To address this limitation, this study explores the potential of incorporating magnetic substances during the carbonization process, especially focusing on the use of magnetically carbonized Macro-MIL-88A for lipase immobilization and biodiesel production. The effects of different carbonation temperatures on macroporous MIL-88A and microporous MIL-88A were investigated. Our findings revealed that the carbonization temperature influenced the preservation of the 3D structure and the generation of magnetite. Carbonized Macro-MIL-88A (Macro-Fe₃O₄-C) at 500 °C exhibited superior specific activity and enhanced activity recovery. Lipase immobilized on Macro-Fe₃O₄-C (Macro-Fe₃O₄-C-TLL) demonstrated higher methanol tolerance during the biodiesel production process compared to Micro-Fe₃O₄-C. The reduced reusability of Macro-Fe₃O₄-C-TLL was attributed to the adsorption of the by-product glycerol. We further investigated pre- and posthydrophobic modifications on Macro-Fe₃O₄-C and found that post-PDMS modification maintained both high enzyme loading and good reusability of the immobilized lipase during biodiesel production. This study presents a promising method to enhance the reusability of immobilized large molecules by incorporating magnetite via a straightforward carbonization process.