Efficient Laccase Immobilization in MOF/Hydrogel Composites for Enhanced Dye Degradation in Wastewater

Laccase is a class of multicopper oxidases which is widely distributed in plants, fungi, and bacteria, are capable of catalyzing the oxidation of various phenolic and amine compounds. Owing to its high efficiency, environmental friendliness, and renewability, laccase has shown great potential in the treatment of dye-containing wastewater. However, free laccase is highly susceptible to environmental factors, resulting in rapid deactivation, poor stability, and limited reusability, which restrict its practical application. To address these limitations, a gel-based carrier composed of carboxymethyl cellulose (CMC) and polyethyleneimine (PEI) integrated with metal–organic frameworks (MOFs) was constructed for laccase immobilization (denoted as CMC/PEI/MOFs-Lac), achieving efficient enzyme immobilization. Experimental results demonstrated that CMC/PEI/MOFs-Lac exhibited excellent catalytic degradation performance toward malachite green (MG), achieving a degradation efficiency of 100% within 4 h, indicating effective destruction of the dye molecular structure. Further studies revealed that this composite material was also applicable to the degradation of Congo red (CR) and methyl orange (MO). After introducing the mediator ABTS to form a laccase–mediator system (LMS), degradation efficiencies of up to 90% for all three dyes were achieved within 3 h. Notably, the gel matrix–LMS could be synchronously recovered together with the dye solution and reused multiple times for methyl orange degradation. After six consecutive cycles, the degradation efficiency remained above 65.4%. The hydrogel matrix provided a favorable microenvironment for enzyme molecules, significantly enhancing their thermal stability and reusability. Meanwhile, the high specific surface area and porous structure of MOFs promoted substrate adsorption and mass transfer, thereby enhancing the overall catalytic degradation efficiency. This study demonstrates that MOF nanomaterials combined with hydrogels possess significant potential as carriers for the co-immobilization of laccase–mediator systems. Moreover, the efficient and reusable laccase–mediator system offers a new strategy for the application of laccase in wastewater treatment.