Terminalia catappa L. mediated cerium oxide nanoparticles for antibacterial activity, seed germination and growth performance of cabbage (Brassica sp.)

Terminalia catappa trees, commonly found in Malaysia, are known for their expansive canopy which provides valuable shade. Despite the scenic appearance of their red and fallen leaves, they are often considered environmental waste. This study reported the green synthesis of novel cerium oxide nanoparticles (NPs) using Terminalia catappa leaf extract as reducing and capping agents to facilitate the development of NPs under various optimisation parameters, such as temperature and precursor concentration. Under optimised conditions of 50°C and a 0.005 M precursor concentration, absorbance bands ranging from 434 nm to 470 nm were observed using Ultraviolet–visible spectroscopy, confirming the successful formation of cerium oxide NPs. The X-Ray diffraction analysis confirmed the NPs’ purity and determined their crystallite size of 4.73 nm using the Scherrer equation. The cerium oxide NPs exhibited antibacterial activity against Escherichia coli and Pseudomonas aeruginosa, while Staphylococcus aureus and Bacillus subtilis showed resistance against the material. The NPs were further assessed for their seed germination effects. The germination percentage of Brassica sp. seeds treated with the materials increased, with the highest germination observed at 40 ppm, showing a 60% increase compared to the control. The application of NPs also significantly influenced the root and shoot growth, with a most notable increase observed at the concentration of 30 ppm, suggesting the potential of cerium oxide NPs as nanofertiliser for Brassica sp. at concentrations below 50 ppm.