Maryam Juma Yaseen Simply because you need to prepare the precursor Cu(OH)2 for decomposition to Cu2O and subsequent reduction to Cu0. Note that in water or any oxygen containing environment (e.g. air) your 'copper' will be coated with a layer of oxide that would need removing before any subsequent processing. I assume you're using ESCA/XPS to chemically characterize your surface chemistries.

Sodium hydroxide is added during copper nanoparticle synthesis to create a basic pH environment, which facilitates the reduction of copper ions and stabilizes the nanoparticles. This basic medium helps prevent aggregation and ensures uniform dispersion of the nanoparticles.

The pH drops to acidic instead of staying basic because of certain compounds in the plant extract. Some plants have acidic substances that react with sodium hydroxide or release acids during the process. These reactions can reduce the basicity of the mixture. To keep the pH stable, it is important to balance the amount of plant extract and sodium hydroxide properly.

Thank you all for the valuable answers, adding the base to the reaction medium has increased the acidity of the reaction of the medium despite the fact that the beginning of the reaction was neutral

The question is, if you add an acid to the medium, do we expect the opposite, increasing the alkalinity of the medium and showing a neutral and alkaline medium for the plant.