Efficient immobilization of catalase on mesoporous MIL-101 (Cr) and its catalytic activity assay

Enzyme immobilization using metal-organic frameworks (MOFs) as carriers has aroused significant interest owing to the unique pore structure and versatile surface functional groups of MOFs. Catalase (CAT) is an important industrial enzyme that is widely used in the catalytic decomposition of hydrogen peroxide in the fields of food and biological products. In this study, mesoporous MIL-101 (Cr), synthesized through a facile hydrothermal process, was applied for CAT immobilization for the first time. The immobilization capacity of MIL-101 (Cr) for CAT was studied systematically by batch adsorption tests under different adsorption conditions, including the variation of the solution pH, operation temperature, adsorption time, and initial concentration of CAT. Based on these test findings, the optimum adsorption conditions and maximum adsorption capacity were determined. The adsorption kinetics were simulated to further explore the adsorption mechanism, and they suggest that chemical adsorption, rather than physical adsorption, is the main CAT adsorption mechanism. A comparison of Fourier transform infrared (FT-IR) spectra of MIL-101 (Cr) without and with adsorbed CAT reveals the formation of amide bonding between the -NH of CAT and the uncoordinated -CO of MIL-101(Cr). Finally, the stability and activity of the immobilized CAT were assessed, and an improved insensitivity against changes in pH and a prolonged storage time demonstrate the enhanced stability of immobilized CAT by MIL-101 (Cr) carriers. This study demonstrates the application of MOFs as functional supports for the efficient immobilization of versatile enzymes.