Immobilization of Laccase by Alkali-Etched Bimetallic CoCu-MOF To Enhance Enzyme Loading and Congo Red Degradation

In this work, the strategy of immobilizing enzymes in bimetallic–organic frameworks was adopted to overcome the disadvantages of free laccases. The surface amino-silanizing of bimetallic CoCu-MOF-H hydrothermally synthesized was performed by (3-Aminopropyl)triethoxysilane (APTES). Then, glutaraldehyde was used as the cross-linking agent, laccase was covalently grafted onto CoCu-MOF-H-APTES to prepare Lac-CoCu-MOF-H-APTE. In addition, CoCu-MOF-OH also was synthesized by alkali etching of CoCu-MOF-H, and Lac-CoCu-MOF-OH-APTES composites were obtained by a similar strategy. The result showed that the relative enzyme activity of Lac-CoCu-MOF-OH-APTES exhibited 264.02% (1.8 times than that of Lac-CoCu-MOF-H-APTES) after six cycles of stability tests, while the free enzyme was almost inactivated. Moreover, the Congo red (CR) removal rate of Lac-CoCu-MOF-OH-APTES exceeded 95% within 1 h and exceeded 89.18% after six cycles at pH 3.5 and 50 °C. This work has the potential to provide a broader application prospect for CR degradation by laccase in the future.