Phytogenic Cerium Oxide Nanoparticles as Efficient Antibacterial, Antioxidant, and Photocatalysts for Environmental Remediation

In the present work, CeO2 nanoparticles (NPs) were synthesized greenly using Alexandrian senna leaf extract as a reducing and stabilizing agent. The synthesized nanoparticles were analyzed using several analytical techniques to investigate their physicochemical properties. The average hydrodynamic particle size determined by DLS was 413.9 nm with an average polydispersity index (PDI) of 3.114, and the zeta potential average of the particles was −5.5 mV, showing moderate colloidal stability. The elemental composition of the nanoparticles was verified by energy-dispersive X-ray spectroscopy (EDX), which showed the presence of Ce elements with 72.15% content, O elements with 13.95% content, and C elements with 13.90% content. The antioxidant activity of SA-CeO2 NPs was assessed by the DPPH free radical scavenging assay, which showed a dose-dependent effect, attaining a maximum scavenging efficiency of 75.61% at 100 µg/mL. Antibacterial activity was evaluated for the strains of Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Klebsiella pneumoniae. In addition, the photocatalytic activity of SA-CeO2 NPs was tested for the degradation of methylene blue (MB) dye under sunlight. The degradation efficiency was 88.54% after 180 min of exposure, which is a very high photocatalytic efficiency. The results of the kinetic studies showed that the degradation process was pseudo-first-order, with a rate constant of 0.01344 min−1 (R2 = 0.96298). The results indicate that the green-synthesized CeO2 nanoparticles exhibit promising photocatalytic, antioxidant, and antibacterial properties under the investigated conditions, supporting their potential for further investigation in environmental remediation and related applications.