Acid-resistant enzyme@MOF nanocomposites with mesoporous silica shells for enzymatic applications in acidic environments.

Zeolitic imidazole frameworks (ZIFs) with tunable pore sizes and high surface areas have recently used as an effective support for immobilizing enzymes. However, the instability in the aqueous acidic environment has limited their practical applications in some cases. In this work, we develop a novel catalase/ZIFs composite with mesoporous silica shell (mSiO2@CAT/ZIFs) via co-precipitation, and controlled self-assembly of silanes. During preparation, the cetyltrimethylammonium bromide induced the formation of the mesostructured silica layer on the outer surface of CAT/ZIFs. The resultant mSiO2@CAT/ZIFs exhibited high activity recovery (92%). Compared with the conventional CAT/ZIFs and free CAT, mSiO2@CAT/ZIFs exhibited excellent acid resistance. For example, after 30 min in acetate buffer solution (pH 3.0), the CAT/ZIFs and free CAT almost lost activity whereas the mSiO2@CAT/ZIFs still retained 35% of original activity. Meanwhile, the thermostability of the mSiO2@CAT/ZIFs was enhanced significantly compared with conventional CAT/ZIFs. In addition, the mSiO2@CAT/ZIFs displayed excellent storage stability, and retained 60% of its initial activity after 15 days storage period. Furthermore, the mSiO2@CAT/ZIFs could maintain 70% of its initial activity after 8 continuous uses, demonstrating superior reusability than the free CAT and CAT/ZIFs. These results demonstrated that the mSiO2@CAT/ZIFs are potential for practical applications even in the acidic environment.