A Novel Mesoporous Hydroxyapatite–Cobalt Oxide Composite: Synergistic Catalyst for Efficient Methylene Blue Degradation and Reusability in Wastewater Remediation

ABSTRACT This study aims to develop an efficient catalyst for methylene blue (MB) degradation by preparing cobalt oxide–incorporated hydroxyapatite (HAp–CoO) as a support for horseradish peroxidase (HRP) immobilization. The synthesized composite was characterized using FTIR, XRD, SEM, and BET analyses, which revealed a mesoporous structure ideal for enzyme immobilization. The immobilization process achieved an 86% yield of HRP on HAp–CoO at an optimal pH of 7.0. The immobilized HRP exhibited significant thermal stability, maintaining robust activity across a broader temperature range (40°C–50°C) compared to its free form. Kinetic analysis revealed an increase in the Michaelis–Menten constant ( K m ) from 3.74 (free HRP) to 6.12 mM (HAp–CoO@HRP), indicating a slight reduction in substrate affinity, while the maximum reaction velocity ( V max ) remained consistent, demonstrating preserved catalytic efficiency. The inhibition constant ( K i ) showed minimal change, reflecting consistent resistance to competitive inhibition. Catalytic efficiency was evaluated for MB degradation with HAp–CoO@HRP achieving up to 92% degradation at 50 mg/L. HAp–CoO@HRP maintained 79% efficiency after five reusability cycles and retained 85% of its activity after 28 days of storage at 4°C. These findings highlight HAp–CoO@HRP as a robust and effective catalyst for dye bioremediation, offering significant potential in wastewater treatment.