Chitosan-functionalized supermagnetic halloysite nanotubes for covalent laccase immobilization

Halloysite nanotubes (HNTs) were modified with supermagnetic Fe3O4 (M-HNTs) and functionalized with chitosan (CTA) (termed as M-HNTs-CTA). Furthermore, M-HNTs-CTA were cross-linked using glutaraldehyde and applied for covalent laccase immobilization (M-HNTs-CTA-Lac). Facile-synthesized modified HNTs were structurally characterized by scanning electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analyses. M-HNTs-CTA-Lac exhibited 92.74 mg/g of laccase immobilization capacity and 92% of activity recovery. Biochemical properties of M-HNTs-CTA-Lac exhibited higher pH and temperature stabilities, with exceptional reusability capabilities until the 11th cycle. Moreover, M-HNTs-CTA-Lac exhibited 87% of 2,2'-azinobis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS)mediated Direct Red 80 (DR80) decolorization. By the 11th cycle, M-HNTs-CTA-Lac exhibited 33% DR80 decolorization. Therefore, M-HNTs-CTA can function as CTA-modified supermagnetic nonreactors for immobilization of biomacromolecules. The investigated M-HNTs-CTA-Lac are thus biocompatible and environment-friendly biocatalysts for degradation of textile waste, such as DR80, and can be rapidly retrieved from aqueous solution by a magnet after decontamination of environmental pollutants.