Removal of tetracycline from water using immobilized laccase on polyvinyl alcohol-gum Arabic hydrogel nanocomposites

• Polyvinyl alcohol-gum Arabic hydrogel (nano)composite synthesized as enzyme carrier • Immobilization of laccase onto the hydrogel nano-carrier enhanced its efficiency in TC removal up to 83% • Nano-filler in the hydrogel reduced the pore size and increased TC removal through sorption and Fenton-like degradation • Immobilized laccase exhibited superior stability and reusability over six cycles This study explored the synthesis of the hydrogel nanocomposite based on gum Arabic (GA) and polyvinyl alcohol (PVA) reinforced with Fe 2 O 3 nanoparticles incorporated onto nanocellulose (NC-Fe). The water absorbencies of the hydrogels varied from 33.1 to 217.1 g/g, depending on Fe/NC and cross-linker content, as well as PVA molecular weight. The SEM images of the hydrogels revealed that the presence of Fe/NC led to smaller pores in the hydrogel matrix (i.e., pore size range of 6.9-50 µm in hydrogel nanocomposite vs. 8.3-63.3 μm in the pristine hydrogel). The immobilization of a metagenomic laccase (PersiLac3) onto the hydrogels provided an efficient, innovative, and multi-functional system for the removal of the antibiotic tetracycline (TC) from water. Immobilizing PersiLac3 on both the pristine hydrogel (PVA-GA-hydrogel) and the hydrogel nanocomposite (PVA-GA-hydrogel/NC-Fe) remarkably boosted its performance in TC removal compared to the free enzyme. At an initial TC concentration of 500 mg/L, the maximum removal reached 83%, 67%, and 38% for PersiLac3@PVA-GA-hydrogel/NC-Fe, PersiLac3@PVA-GA-hydrogel, and the free PersiLac3, respectively, within 60 min. Moreover, the TC removal performance of the neat hydrogels (48% for PVA-GA-hydrogel/NC-Fe and 17% for PVA-GA-hydrogel) suggested that the antibiotic was eliminated through the combined processes of adsorption by the hydrogels and enzymatic degradation by PersiLac3. Addition of NC-Fe in the hydrogel played a bi-functional role in TC removal: it reduced the pore size, thereby increasing TC sorption by the hydrogel, and it acted as a Fenton-like catalyst in TC degradation. Finally, the immobilized enzyme demonstrated superior stability in harsh environments compared to the free enzyme, removing 70% of TC after six consecutive runs. This is the first report on the potential application of the bio-based PVA–GA/Fe–NC hydrogel as a robust, reusable, and eco-friendly carrier for metagenomic laccase in antibiotic degradation, offering a novel strategy for sustainable water treatment.