Magnetic Mesoporous γ‑Fe₂O₃ Supports from Meso-MIL-88A via Controlled Oxidation-Reduction Pyrolysis: Enabling...

Enzyme immobilization on solid supports enhances stability and reusability, yet nanoscale carriers such as metal-organic frameworks (MOFs) still face challenges in efficient recovery. While pyrolysis can magnetize Fe-MOFs, conventional methods often compromise either enzyme activity or structural integrity. This study presents a rational two-step oxidation-reduction (O-R) pyrolysis strategy to convert Meso-MIL-88A into a magnetically recyclable, mesoporous biocatalyst support (O-R500). Unlike one-step carbonization, which generates enzyme-incompatible Fe₃O₄, or carbonization-oxidation routes that collapse the framework, our approach first transforms the MOF into a robust α-Fe₂O₃ template while preserving its morphology. Citric acid then acts as a mild, slow-releasing reductant, selectively producing a γ-Fe₂O₃-rich phase without damaging the mesostructure. The resulting O-R500 exhibits well-defined mesopores (∼13 nm), sufficient magnetization (16 emu/g) for rapid separation, and a biocompatible surface that maintains the native conformation of immobilized Candida antarctica lipase B (CalB). In the synthesis of phosphatidyl EPA/DHA, CalB@O-R500 achieved 84.5% incorporation and retained 90.3% activity over five cycles, outperforming nonmagnetic counterparts. This work not only provides a high-performance magnetic biocatalyst but also establishes a generalizable design principle for converting Fe-MOFs into structured, biocompatible, and functionally integrated carriers.