Supermagnetically Tuned Halloysite Nanotubes Functionalized with Aminosilane for Covalent Laccase Immobilization

Halloysite nanotubes (HNTs) were tuned with supermagnetic Fe₃O₄ (M-HNTs) and functionalized with γ-aminopropyltriethoxysilane (APTES) (A-M-HNTs). Gluteraldehyde (GTA) was linked to A-M-HNTs (A-M-HNTs-GTA) and explored for covalent laccase immobilization. The structural characterization of M-HNTs, A-M-HNTs, and A-M-HNTs-GTA-immobilized laccase (A-M-HNTs-GTA-Lac) was determined by X-ray photoelectron spectroscopy, field-emission high-resolution transmission electron microscopy, a magnetic property measurement system, and thermogavimetric analyses. A-M-HNTs-GTA-Lac gave 90.20% activity recovery and a loading capability of 84.26 mg/g, with highly improved temperature and storage stabilities. Repeated usage of A-M-HNTs-GTA-Lac revealed a remarkably consistent relative activity of 80.49% until the ninth cycle. The A-M-HNTs-GTA-Lac gave consistent redox-mediated sulfamethoxazole (SMX) degradation up to the eighth cycle. In the presence of guaiacol, A-M-HNTs-GTA-Lac gave elevated SMX degradation compared with 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) and syrinialdehyde. Therefore, the A-M-HNTs can serve as supermagnetic amino-functionalized nanoreactors for biomacromolecule immobilization. The obtained A-M-HNTs-GTA-Lac is an environmentally friendly biocatalyst for effective degradation of micropollutants, such as SMX, and can be easily retrieved from an aqueous solution by a magnet after decontamination of pollutants in water and wastewater.