**5. Biosynthesis of copper oxide (CuO) nanoparticles**

The parameters of plant extracts such as phytochemicals, metal salt concentration, temperature and pH control the rate of formation of nanoparticles as well as their stability and yield [59]. Extracts of plant leaves are considered a good source for metal and metal oxide NPs synthesis. Additionally, plant leaf extracts play a greater role as reducing and stabilizing agents of the biosynthesis process, the phytochemical composition of plant leaf extract is also an important factor in the synthesis of CuO NPs [60]. Green synthesis of Cu NPs can reduce the use of many hazardous chemical substances; many methods use L-ascorbic acid as a reducing agent in synthesis, and the synthesized Cu NPs were highly stable (**Table 1**) [61].
