Graphene oxide dispersed mesoporous ZIF-8-encapsulated laccase for removal of toluidine blue with multiple enhanced stability.

Abstract

The extensive use and discharge of toluidine blue have caused serious problems to the water environment. As a green biocatalyst, laccase has the ability to decolorize the dyes, but it is limited by poor reusability and low stability. Metal-organic frameworks (MOFs) are a good platform for enzyme immobilization. However, due to the weak dispersion of MOFs, the enzyme activity is inevitably inhibited. Herein, we proposed to use graphene oxide (GO) as the dispersion medium of mesoporous ZIF-8 to construct MZIF-8/GO bi-carrier for laccase (FL) immobilization. On account of the narrower bandgap energy of FL@MZIF-8/GO (4.07eV) than that of FL@MZIF-8 (4.69eV), electron transport was enhanced which later increased the catalytic activity of the immobilized enzyme. Meanwhile, the improved hydrophilicity characterized by contact angle and full infiltration time further promoted the efficiency of the enzymatic reaction. Benefiting from such regulatory effects of GO, the composite showed excellent storage stability and reusability, as well as multifaceted enhancements including pH, thermal, and solvent adaptation. On the basis of the characterized synergistic effect of adsorption and degradation, FL@MZIF-8/GO was successfully applied to the degradation of toluidine blue (TB) with a removal rate of 94.8%. Even in actual treated wastewater, the highest removal rate still reached more than 80%. Based on the inner mechanism analysis and the universality study, this material is expected to be widely used in the degradation of pollutants in real water under complex environmental conditions.