Green synthesis and multifunctional evaluation of Zr, Bi, and Mo‑doped CeO₂ nanoparticles and their chitosan‑encapsulated variants

The simultaneous removal of organic dyes and microbial contaminants from water requires multifunctional materials that combine photocatalytic, antibacterial, and biocompatible properties. However, existing single-function systems have not fully addressed this challenge. In this study, zirconium (Zr), bismuth (Bi), and molybdenum (Mo)-doped cerium oxide nanoparticles (CeO 2 NPs) were synthesized via a sustainable route using Otacanthus azureus leaf extract as a bioreductant. Subsequently, chitosan was used to encapsulate the nanoparticles to enhance their stability and improve their performance. The solution-based synthesis yielded mesoporous nanostructures with reduced crystallinity upon chitosan encapsulation compared to non-encapsulated NPs, as evidenced by the PXRD, BET, and SEM-EDX analyses. Antioxidant assays showed significant improvement in radical scavenging activity of encapsulated NPs (CEDCNP) (4–24% across 62.5–1000 µg/ml) compared to non-encapsulated NPs (NEDCNP) (2–10%). CEDCNP demonstrated superior degradation of Rhodamine B dye (up to 92% at pH 2) under optimized conditions. Adsorption isotherm modeling (Langmuir, Temkin, and Freundlich) and Monte Carlo simulations revealed favorable monolayer adsorption, strong binding affinity, and thermodynamic feasibility. Biological evaluations highlighted the enhanced antibacterial efficacy of CEDCNPs, with MIC values of 25 mg/ml against Vibrio cholerae and Listeria monocytogenes, outperforming NEDCNPs. Antibiofilm assays confirmed reduced exopolysaccharide production and suppression of microbial aggregation. Hemocompatibility studies indicated negligible hemolysis in RBCs treated with CEDCNPs (0–25 mg/ml), whereas NEDCNPs induced slight hemoglobin release. NEDCNPs exhibited stronger anti-inflammatory activity (83.13% at 400 mg/ml) than CEDCNPs (77.05% at 800 mg/ml). GC-MS analysis of the O. azureus leaf extract revealed 11 major bioactive compounds with antioxidant, antimicrobial, antibiofilm, anti-inflammatory, and membrane-protective activities, underscoring its dual role as a reservoir of natural therapeutics and a sustainable platform for nanomaterial synthesis. Overall, this study provides evidence that green synthesis, strategic doping, and chitosan encapsulation improve the physicochemical, catalytic, antioxidant, and antimicrobial properties of CeO 2 NPs. These multifunctional nanomaterials show potential as eco-friendly, cost-effective candidates for wastewater remediation and biomedical applications where oxidative stress control, microbial resistance, and safety are critical.