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<p>Rapid industrialization has intensified water contamination, necessitating efficient and sustainable remediation technologies. In this study, a dual-confinement strategy was developed for laccase immobilization through adsorption onto nanodiamonds followed by entrapment within a polyvinyl alcohol (PVA)–chitosan hydrogel prepared by the freeze–thaw method and stabilized with citric acid. The resulting hybrid biocatalyst was characterized by TEM, FESEM, XPS, and FTIR, confirming successful fabrication and enzyme immobilization. Compared with free laccase, the immobilized enzyme exhibited markedly improved stability, with the pH operating range broadened from 4.0 to 8.5 and the optimum pH slightly shifted from 5.0 to 4.5. Although both enzyme forms showed maximum activity at 40&#xa0;°C, the immobilized laccase demonstrated superior thermal resistance, retaining 27% of its activity even at 80&#xa0;°C. Kinetic analysis with ABTS showed a reduction in Km from 1.20 to 0.775 mM, indicating improved substrate affinity, whereas Vmax decreased from 1.53 to 0.597 µmol min⁻¹ due to diffusional limitations associated with immobilization. The immobilized laccase also demonstrated strong operational and storage stability, retaining 82% of its initial activity after 10 reuse cycles and 75% activity after more than 90 days of storage. In bisphenol A degradation experiments, the immobilized system achieved 81% removal after 600&#xa0;min, compared with 48% for free laccase, highlighting its promise for water bioremediation.</p>

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Freeze–thaw nanodiamond/PVA-chitosan hydrogel for efficient and stable laccase immobilization: Physicochemical characteristics and water bioremediation

  • 期刊论文

  • 发表日期：

    2026年5月26日

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  • Musab M. Aldhahri,
  • Wedam Alghazzawi,
  • Mustafa Zeyadi,
  • Yaaser Q. Almulaiky

摘要

Rapid industrialization has intensified water contamination, necessitating efficient and sustainable remediation technologies. In this study, a dual-confinement strategy was developed for laccase immobilization through adsorption onto nanodiamonds followed by entrapment within a polyvinyl alcohol (PVA)–chitosan hydrogel prepared by the freeze–thaw method and stabilized with citric acid. The resulting hybrid biocatalyst was characterized by TEM, FESEM, XPS, and FTIR, confirming successful fabrication and enzyme immobilization. Compared with free laccase, the immobilized enzyme exhibited markedly improved stability, with the pH operating range broadened from 4.0 to 8.5 and the optimum pH slightly shifted from 5.0 to 4.5. Although both enzyme forms showed maximum activity at 40 °C, the immobilized laccase demonstrated superior thermal resistance, retaining 27% of its activity even at 80 °C. Kinetic analysis with ABTS showed a reduction in Km from 1.20 to 0.775 mM, indicating improved substrate affinity, whereas Vmax decreased from 1.53 to 0.597 µmol min⁻¹ due to diffusional limitations associated with immobilization. The immobilized laccase also demonstrated strong operational and storage stability, retaining 82% of its initial activity after 10 reuse cycles and 75% activity after more than 90 days of storage. In bisphenol A degradation experiments, the immobilized system achieved 81% removal after 600 min, compared with 48% for free laccase, highlighting its promise for water bioremediation.