Amino-functionalized MOF immobilized laccase for enhancing enzyme activity stability and degrading Congo red

Laccase is attracting the attention of environmental engineers in the direction of wastewater treatment because of its high efficiency and environmental friendliness. However, free laccase has the problems of poor stability and difficult recovery. In this study, amino-modified and silanized MOF materials were synthesized by hydrothermal method, and laccase molecules were immobilized with glutaraldehyde as a cross-linking agent. The enzyme-loading capacity of the amino-functionalized modified Cu-MOF increased by 27.98% to 128.48 mg/g compared with that of the control group. The modified Cu-MOF material provided excellent protection to laccase molecules in various environments. The enzyme activity of Lac-Cu-MOF-NH2 reached 2.57 times that of the free enzyme at pH 3.5. Moreover, Lac-Cu-MOF-NH2 achieved 95% removal of Congo red (CR) at pH 3.5, 50 °C, whereas CR degradation by free laccase was only 11.52%. The degradation rate of Lac-Cu-MOF-NH2 still reached 84.63% after six cycles. Thus, Lac-Cu-MOF-NH2 significantly improved CR-degradation efficiency by establishing a synergistic effect between adsorption and laccase degradation. A new strategy is proposed for the industrial application of laccase in the field of wastewater treatment.