Chitosan-Grafted Halloysite Nanotubes-Fe3O4 Composite for Laccase-Immobilization and Sulfamethoxazole-Degradation

Abstract

A surface-engineered nano-support for enzyme laccase-immobilization was designed by grafting the surface of halloysite nanotubes (HNTs) with Fe3O4 nanoparticles and chitosan. Herein, HNTs were magnetized (HNTs-M) by a cost-effective reduction-precipitation method. The synthesized HNTs-M were grafted with 0.25%, 0.5%, 1%, and 2% chitosan (HNTs-M-chitosan), respectively. Synthesized HNTs-M-chitosan (0.25%), HNTs-M-chitosan (0.5%), HNTs-M-chitosan (1%) and HNTs-M-chitosan (2%) were linked with glutaraldehyde (GTA) for laccase immobilization. Among these formulations, HNTs-M-chitosan (1%) exhibited the highest laccase immobilization with 95.13% activity recovery and 100.12 mg/g of laccase loading. The optimized material was characterized thoroughly by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM) analysis. The immobilized laccase (HNTs-M-chitosan (1%)-GTA-Laccase) exhibited higher pH, temperature, and storage stabilities. The HNTs-M-chitosan (1%)-GTA-Laccase possesses excellent reusability capabilities. At the end of 10 cycles of the reusability experiment, HNTs-M-chitosan (1%)-GTA-Laccase retained 59.88% of its initial activity. The immobilized laccase was utilized for redox-mediated degradation of sulfamethoxazole (SMX), resulting in 41%, 59%, and 62% degradation of SMX in the presence of 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), guaiacol (GUA), and syringaldehyde (SA), respectively. Repeated SMX degradation (57.10% after the sixth cycle) confirmed the potential of HNTs-M-chitosan (1%)-GTA-Laccase for environmental pollutant degradation. Thus, we successfully designed chitosan-based, rapidly separable super-magnetic nanotubes for efficacious enhancement of laccase biocatalysis, which can be applied as nano-supports for other enzymes.

Thiolation of Chitosan Loaded over Super-Magnetic Halloysite Nanotubes for Enhanced Laccase Immobilization

“…The tubes seemed to be broadened, possibly due to the coatings of the CTs. Similar observations for chitosan modified HNTs was seen in an earlier report [ 13 , 14 ]. The SEM morphologies gave an idea of the significant modification of the plane surface of the HNTs.…”

“…First, the HNTs were tuned with Fe 3 O 4 NPs by the coprecipitation method [ 13 ]. Second, Fe 3 O 4 NP-modified HNTs (HNTs-Fe 3 O 4 ) were functionalized with the chitosan (CTs) (HNTs-Fe 3 O 4 -CTs) [ 14 ]. Finally, in the third step, NH 2 functional groups of HNTs-Fe 3 O 4 -CTs were thiolated (-SH) by NHS-ester reaction (HNTs-Fe 3 O 4 -CTs).…”

“…These include: easy and low-cost availability, structural morphology in the form of nanotubes, nanotubular lumen, and an extremely modifiable surface [ 12 ]. The surface modifications of HNTs are the main key to developing them into a comprehensive nanosupport for laccase immobilization [ 13 , 14 ]. The surface modification of HNTs with Fe 3 O 4 nanoparticles (NPs) makes HNTs super-magnetic.…”

“…As CTs is a ubiquitous biopolymer used for enzyme immobilization due to having the surface amino (-NH 2 ) functional group. In our previous research, modification of the HNT surface with Fe 3 O 4 and CTs proved to be excellent for laccase immobilization [ 13 , 14 , 18 ]. In these studies, the immobilization of “laccase” and “CTs and Fe 3 O 4 modified HNTs” was carried out by glutaraldehyde cross-linking.…”

α-Cellulose Fibers of Paper-Waste Origin Surface-Modified with Fe3O4 and Thiolated-Chitosan for Efficacious Immobilization of Laccase

“…Hence, the detailed activity recovery and laccase loading capacity data provided the information about immobilization behavior of α-Cellulose-Fe3O4-CTNs-SH. The significant laccase loading obtained by α-Cellulose-Fe3O4-CTNs-SH was quite high among the recently reported materials [33,46,[54][55][56][57][58][59][60][61]. Thus, the developed α-cellulose based material has significant potential to look like an enzyme immobilization material.…”