Chitosan–halloysite hybrid-nanotubes: Horseradish peroxidase immobilization and applications in phenol removal

Chitosan–halloysite hybrid-nanotubes were synthesized through the assembly of chitosan onto halloysite, a natural nanotubular aluminosilicate. Nitrogen adsorption–desorption measurement, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy analysis were employed to elucidate the structure of the hybrid-nanotubes. The results indicated that the hybrid-nanotubes could form three-dimensional (3D) nanocomposites with hierarchically porous structure. As-prepared structure showed excellent capacity for horseradish peroxidase (HRP) immobilization through cross-linking by glutaraldehyde. The maximum enzyme loading reached as large as 21.5 mg/g, higher than 3.1 mg/g of raw halloysite. After 35 days storage, the immobilized HRP did not undergo any activity loss while the free HRP only retained 27% of its original activity. Phenol removal efficiency by the immobilized HRP was also explored. The result showed the immobilized HRP exhibited overall high removal efficiency for phenol from wastewater.