The present work is intended to biosynthesize zinc oxide nanoparticles (ZnO NPs) via facile and modern route using aqueous Ziziphus jujuba leaves extract assisted by microwave and explore their photocatalytic degradation of methyl orange anionic dye and methylene blue cationic dye under solar irradiation. The biosynthesized microwave assisted ZnO NPs were characterized and the results showed that ZnO NPs contain hexagonal wurtzite and characterized with a well-defined spherical-like shape with an outstanding band gap (2.70 eV), average particle size of 25 nm and specific surface area of 11.4 m2/g. The photocatalytic degradation of the MO and MB dyes by biosynthesized ZnO NPs under solar irradiation was studied and the results revealed the selective nature of the ZnO NPs for the adsorption and further photocatalytic degradation of the MO dye compared to the MB dye. In addition, the photocatalytic degradation of MO and MB dyes by the ZnO NPs under solar radiation was fitted by the first-order kinetics. Moreover, the photodegradation mechanism proposed that superoxide ions and hydroxyl radicals are the main reactive species.

The green biosynthesis of zinc oxide nanoparticles (GBS ZnO NPs) using Ziziphus jujuba leaves extract assisted by ultrasonic irradiation was reported in this research work. The green biosynthesized ZnO NPs were characterized using different techniques and the results revealed the synthesis of hexagonal wurtzite crystal of GBS ZnO nanoparticles; per the XRD measurement, with average practice size of 90 ± 10 nm; based on both SEM and TEM images, and with specific surface area of 14.23 m2/g; per the nitrogen gas adsorption/desorption isotherms. The antibacterial activity of the prepared GBS ZnO NPs was explored against S. aureus and E. coli bacteria using different evaluation methods; disc diffusion, column (filter), and aqueous solution, and the results showed the effective antibacterial activities against S. aureus and E. coli bacteria, as the inhibition zones were 15 mm and 11 mm for the E. coli and S. aureus, respectively. Moreover, the anticancer activity of the green biosynthesized ZnO NPs was evaluated on two different cancer cells; human colon cancer cell lines (HCT-116) and the human liver cancer (HepG2) cells, and the experiments showed that GBS ZnO NPs had an outstanding cytotoxic effect on both cancer cell lines, as well as dose-dependent behavior, as the viability of the cancer cells decreased by using GBS ZnO NPs at concentrations of 10 and 20 µg/mL. Cell lines (HCT-116) and the human liver cancer (HepG2) cells, and the experiments showed that GBS ZnO NPs had an outstanding cytotoxic effect on both cancer cell lines, as the GBS ZnO NPs enhanced the cytotoxicity mechanism by generating ROS as the nanoparticles interact with cells, lower its cellular defense mechanism, and accordingly cause apoptosis to the cell.

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