Construction of co-immobilized laccase and mediator based on MOFs membrane for enhancing organic pollutants removal

Abstract

Laccase, as an environmentally friendly biocatalyst with high catalytic efficiency and less by-product, has huge potential in the field of biodegradation and attracted extensive attention. However, the substrates range of laccase was limited by its low redox potential. The involvement of redox mediators which are called the laccase-mediator system (LMS) can expand the substrate range of laccase to non-phenolic substances and improve its degradation efficiency. Herein, a co-immobilized method with practical application possibilities of laccase and 2,2-Azino-bis-3-ethylbenzothiazoline-6-sulfonic Acid (ABTS) was developed for the treatment of dyes that could not be directly degraded by laccase in wastewater. An amino-functionalized metal–organic framework (MOF), UiO-66(Zr)–NH2, was grown in situ on polyethylene terephthalate (PET) using a hydrothermal method, and the obtained composites were acted as the carrier of laccase. Laccase was covalently immobilized on the PET/UiO-66(Zr)–NH2, and then ABTS was fixed to the pores of the UiO-66(Zr)–NH2 by adsorption, realizing the co-immobilization of ABTS and laccase, named PET/ABTS@UiO-66(Zr)–NH2/Lac. PET/UiO-66(Zr)–NH2/Lac enhanced the pH stability of free laccase under acidic conditions, and also has a higher affinity for substrate and great recyclability. The resultant lamellar biocatalyst (PET/ABTS@UiO-66(Zr)–NH2/Lac) was used in the degradation of crystal violet (CV), and the CV removal was increased from 8.61% (free laccase) to 58.80% in 24 h. The removal of malachite green (MG), alizarin green (AG), and methyl orange (MO) was up to 64.82%, 61.61%, and 21.12%, respectively. The laccase and ABTS could be recycled synchronously, which avoided the loss of activity of the system. This work provides a navigation reference for the co-immobilization of LMS by MOFs.