Recent advances in biological, photocatalytic and adsorption applications of biosynthesized CeO₂ nanoparticles

Cerium oxide nanoparticles (CeO₂-NPs) have garnered significant interest due to their unique properties as well as a wide range of applications in the environmental and biomedical fields. This work examines the recent advances in the production of CeO₂-NPs using various biological agents, including plant extracts and biosources, as sustainable and eco-friendly alternatives to conventional synthetic routes. The formation mechanisms, structural characteristics, and influence of factors on the synthesis of CeO₂-NPs were discussed. We found that most CeO₂-NPs possessed spherical shapes, small particle sizes (10-100 nm), and large surface areas (12-100 m² g^-1). Bio-mediated CeO₂-NPs and their composites had diverse biomedical applications such as antibacterial, antifungal, antioxidant, anticancer, neuroprotective, enzymatic, biosensing, and seed germination activities. Furthermore, CeO₂-based composites, such as ZnO-CeO₂, Ag-doped CeO₂, cellulose/CeO₂, CeO₂/biochar, and Cu/CeO₂, acted as photocatalysts and adsorbents for wastewater treatment applications. The performance of CeO₂ and its composites in the removal of organic pollutants such as dyes, antibiotics, nonsteroidal anti-inflammatory drugs, pesticides, and other organic compounds was evaluated. Remarkably, CeO₂-NPs and their composites exhibited good adsorption capacities of 46-201 mg g^-1 and removal efficiency of up to 99% against heavy metals, dyes, antibiotics, and inorganic contaminants. Finally, this review analyzed the limitations and proposed future research directions for biosynthesized CeO₂-NPs and their composites in biomedical and environmental technologies.