Immobilized laccase on oxygen functionalized nanobiochars through mineral acids treatment for removal of carbamazepine

Biocatalytic treatment with oxidoreductase enzymes, especially laccases are an environmentally benign method for biodegradation of pharmaceutical compounds, such as carbamazepine to less harmful compounds. However, enzymes are required to be immobilized on supports to be reusable and maintain their activity. Functionalization of support prior to immobilization of enzyme is highly important because of biomolecule-support interface on enzyme activity and stability. In this work, the effect of oxidation of nanobiochar, a carbonaceous material produced by biomass pyrolysis, using HCl, H₂SO₄, HNO₃ and their mixtures on immobilization of laccase has been studied. Scanning electron microscopy indicated that the structure of nanobiochars remained intact after oxidation and Fourier transform infrared spectroscopy confirmed the formation of carboxylic groups because of acid treatment. Titration measurements showed that the sample treated with H₂SO₄/HNO₃ (50:50, v/v) had the highest number of carboxylic groups (4.7 mmol/g) and consequently the highest efficiency for laccase immobilization. Additionally, it was observed that the storage, pH and thermal stability of immobilized laccase on functionalized nanobiochar was improved compared to free laccase showing its potential for continuous applications. The reusability tests towards oxidation of 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) showed that the immobilized laccase preserved 70% of the initial activity after 3 cycles. Finally, using immobilized laccase for degradation of carbamazepine exhibited 83% and 86% removal in spiked water and secondary effluent, respectively. - Highlights: • Carboxylic content of nanobiochar was improved by acid treatment. • Immobilized laccase showed higher pH, temperature and storage stability compare to free laccase. • No morphological alteration of nanobiochar was observed during acid treatment. • Nanobiocatalyst maintained 70% of initial activity after 3 cycles.