Tailoring La ₂ O ₃ Nanomaterials Through Doping and Coating for Improved Photocatalytic Degradation, Catalytic Reduction, and Other Biological Applications

Abstract This research introduces a novel green synthesis approach for fabricating multifunctional lanthanum oxide nanoparticles (La 2 O 3 ), including undoped, Cd‐doped (Cd‐La 2 O 3 ), and Ag‐coated (La 2 O 3 ‐Ag) variants, using Cymbopogon citratus (lemongrass) leaf extract as a natural reducing and stabilizing agent. The synthesized nanoparticles were systematically characterized using advanced analytical techniques. UV–visible spectroscopy (UV–vis) revealed bandgap energies of 4.35, 3.25, and 3.75 eV for La 2 O 3 , Cd‐La 2 O 3 , and La 2 O 3 ‐Ag nanoparticles, respectively, enabling enhanced optical and photocatalytic properties. X‐ray diffraction (XRD) confirmed their crystalline nature with an average crystallite size of 18–22 nm. Scanning electron microscopy (SEM) and high‐resolution transmission electron microscopy (HRTEM) images showcased distinct rod and spherical shape structures ranging from 20–50 nm. Energy‐dispersive X‐ray (EDAX) verified the high purity and elemental composition. The nanoparticles demonstrated exceptional photocatalytic efficiency, achieving 92.43% degradation of methylene blue under UV light and 89.68% conversion of 4‐nitrophenol (4‐NP) to 4‐aminophenol (4‐AP). Additionally, nanoparticles demonstrated remarkable antibacterial activity against the Gram‐positive and Gram‐negative bacteria, outperforming ampicillin. The inhibition zones exceeded 18 ± 2 mm by disc diffusion assay. Antioxidant assays revealed superior free radical scavenging (ROS) ability compared to ascorbic acid, reducing DPPH radicals by 70 ± 5% at 1000 µg/mL. Hemolytic analysis indicated minimal cytotoxicity at higher concentrations, underscoring their biocompatibility. This study highlights the novelty and multifunctionality of La 2 O 3 nanoparticles, demonstrating their potential for advanced environmental remediation and biomedical applications.