RESUMEN
Simple and green methods of developing nanoparticles (NPs) have attracted the attention of researchers. Literature on utilising leaf extract to prepare cerium oxide (CeO2 NPs) is scarce. The present study synthesised leaf-mediated-CeO2 NPs to produce nanopowders of controllable sizes for further applications. The study is the first to report the optimised parameters (pH 7, 5 g/150 mL concentration of the leaf extract, and 3 h of reaction time) of procuring CeO2 NPs using Melastoma sp. leaf extract as the capping agent with excellent properties. The absorbance of the NPs suspension obtained in this study was recorded at approximately 252 nm with Ultraviolet-Visible (UV-Vis) Spectroscopy. Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Transmission Electron Microscopy (TEM) were also utilised to characterise and confirm the CeO2 NPs prepared. The XRD spectra documented the purity of the NPs at specific diffraction patterns, while TEM revealed the spherical form of the NPs with a particle size of 16 nm. The formation of CeO2 NPs has been confirmed from the FTIR spectra procured, which exhibited a Ce-O peak at 555 nm. Phytochemical screening test and FT-IR analysis of leaf extract revealed the existence of flavonoids, terpenoids, sugars, saponins, quinones, and glycosides. The NPs suspensions of varying concentrations (control, 50, 100, 150, 200, and 250 µg/mL) were prepared and employed for evaluations against Gram-positive and -negative bacteria. Resultantly, CeO2 NPs demonstrated antibacterial activities against both bacteria types. The highest antibacterial activities were recorded against E. coli and K. pneumonia at 1.83 ± 0.137 and 1.83 ± 0.14 mm maximum inhibition zones, respectively, at 250 mg/uL of the NPs.