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.
Highlights
Laccase is a multi-copper oxidoreductase, which catalyzes single-electron substrate oxidation using molecular oxygen [1]
We developed a reduction-precipitation based procedure for the magnetization of halloysite nanotubes (HNTs), optimized the chitosan loading on the magnetized HNT surface for enhanced laccase immobilization, studied the biocatalytic properties of the immobilized laccase, and assessed the ability of immobilized laccase to degrade SMX in water
Pristine HNTs were first super-magnetized with the Fe3 O4 NPs
Summary
Laccase is a multi-copper oxidoreductase, which catalyzes single-electron substrate oxidation using molecular oxygen [1]. Enzyme immobilization processes gave us bio-based catalysts with enhanced properties for diverse applications [3,4]. Laccase is a capable biocatalyst for micro-pollutant removal [5]. Enormous population growth has increased the industrial agricultural demands, resulting in increasing micro-pollutant concentrations in the environment. The increased concentration of micro-pollutants in the environment due to constant release, even at trace concentrations (ng/L), from wastewater-treatment plants into water bodies is of great environmental and public health concern [6]. In this study, the pharmaceutical compound and indicator of antibiotic pollution ‘sulfamethoxazole (SMX) was chosen as the target pollutant for immobilized-laccase-based bio-catalytical degradation. SMX is known for its widespread use in human and veterinary medicines, a frequent occurrence in water supplies, and resultant negative health consequences. SMX is known for its widespread use in human and veterinary medicines, a frequent occurrence in water supplies, and resultant negative health consequences. [7]
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