Magnesium oxide nanoparticles MgO NPs were prepared from three samples cumin, pomegranate peels, and coffee using the green synthesis method by adding magnesium salts to their aqueous extracts, and the resulting nano samples were in the form of powder. It was confirmed that the size of samples was less than 100 nm. The X-ray diffraction XRD analysis shows that average crystallite size of samples obtained from cumin, pomegranate peel, and coffee were 21.264, 21.394 and 18.32 nm, respectively. The X-ray pattern also confirmed that the all samples are polycrystalline with face-centered cubic structure (FCC), and the crystallite planes of (111), (200), (220), (311) and (222). The active bonds were also known through Fourier transform infrared (FTIR) to know the chemical properties. It was noted that the infrared spectrum of MgO NPs was in the range of 646.61 cm-1 and 416.33 cm-1. The field emission scanning electron microscopy (FE-SEM) images showed the formation of particles with a regular and sometimes irregular spherical shape, and agglomerations of hexagonal structures. However, they were irregular, with an average diameter of 24.95 nm for sample obtained from the cumin. The average diameter samples obtained from pomegranate peel is 19.68 nm, while the coffee sample showed irregular spherical shapes with an average diameter of 13.89 nm. The energy-dispersive X-ray (EDX) spectrum indicated the presence of magnesium particles and oxygen particles in samples at a high rate. The EDX spectrum also confirmed the presence of impurities, but a very few, and almost negligible. The optical properties were represented by studying both the absorbance and the energy gap as a function of the wavelength in the range of 200 to 1100 nm for all the samples. The energy gapes of 5.7, 5.9 and 5.8 eV were obtained for the cumin, pomegranate peel, and coffee samples, respectively. The antibacterial activity was studied on two types of bacteria, gram-negative and gram-positive. Magnesium oxide particles prepared from cumin and pomegranate peels showed very high effectiveness against gram-positive bacteria, as the bacteria-killing rate reached to 99%. Finally, the activity of cancer cells was studied, and MgO NPs prepared from cumin showed a high effect on cancer cells.
