**3.2 Preparation of AgNO3 solution**

Similar to plant extract, the amount of silver salt must be low and precise in order to form stable nanoparticles. If the reaction of silver salt is more or more in bulk, the synthesis of nanoparticles may be hindered. For this purpose, the minimum quantity of reacting material is used for the effective, slow, nucleation of nanoparticles. Because silver nitrate (AgNO3) is very expensive, it is important to

#### **Figure 1.**

*Step-wise process of preparation of leaf extract of* Passiflora foetida *by boiling method for the synthesis of silver nanoparticles [18].*

**99**

**Figure 2.**

*nanoparticles [18].*

*Phytonanofabrication: Methodology and Factors Affecting Biosynthesis of Nanoparticles*

measure it in a very small quantity (1 mM) and therefore a stock of 100 mM aqueous silver nitrate solution (AgNO3) is prepared and used to optimize the synthesis

Nanoparticles are easily synthesized by combining the appropriate concentration of plant extract and silver salt, and in short, 1 mM of silver nitrate (95 ml) is mixed with 5 ml of (diluted) leaf extract and kept at constant stirring in the 250 ml round bottom flask on a magnetic stirrer at room temperature. Later, solutions are allowed to react with each other in order to form nanoparticles. Synthesis of silver nanoparticles is confirmed by a change in the color of the solution from light green to dark brown, detected clearly by the naked eye (visual observation). This noticeable change in color is the primary indicator for the synthesis of Ag nanoparticles. The general optimization method for nanoparticle synthesis is shown in diagram-

Unless, after some time, the mixture does not show any change in color, it would

be due to the acidity of the medium. It has been found in several papers that the alkaline solution is favorable to nanoparticle synthesis. Thus, 0.1 mM of NaOH is therefore used to produce a mixture solution into alkaline. It is vital that either the silver salt or the extract can be applied gradually using a syringe. The release of a moderate volume of extract into silver salt requires the proper synthesis of silver nanoparticles. The complete process of green synthesized silver nanoparticles at

Due to their application intent, colloidal nature of the synthesized silver nanoparticles is a critical aspect to consider. If the silver nanoparticles are not stabilized, they become heavy and will be found at bottom of flask or beaker. This aggregation problems can be resolved by sonicating the silver nanoparticle solution as well as using NaCl salt which hides the charges allowing the particles to clump together to form aggregates. Generally, a peak around 420–460 nm confirms stable silver nanoparticle synthesis, while silver nanoparticle aggregates form a broad peak around 350–525 nm with a decrease in the intensity of the

*General optimization method, criteria, instrument characterization and potential applications of synthesized* 

room temperature is shown in a diagrammatic form in **Figure 3**.

*DOI: http://dx.doi.org/10.5772/intechopen.90918*

of silver nanoparticles.

matic form in **Figure 2**.

**3.4 Nature of silver nanoparticles**

plasmon absorbance [19].

**3.3 Nanoparticle synthesis**

measure it in a very small quantity (1 mM) and therefore a stock of 100 mM aqueous silver nitrate solution (AgNO3) is prepared and used to optimize the synthesis of silver nanoparticles.
