## 3 Results
### Optimization of AgNPs Synthesis
#### 3.2.3 The Influence of pH on AgNPs Synthesis  
The initial pH of the _T. erecta_ aqueous extract was determined, with the obtained value being 5. In order to determine the optimum pH required for the reactions between the components of the extract and the silver nitrate solution, 1 mL of extract was taken and adjusted to a pH value of 2 using a solution of 0.1 M HCl, and to a pH of 8 with a 0.1 M NaOH solution. Then, 1 mL of the extract was added to another vial without changing its  
Figure 3: The influence of different plant extract:AgNO\({}_{3}\) ratios (1:9, 5:5 and 9:1) on AgNPs-H\({}_{2}\)O formation.  
Figure 2: The influence of different AgNO\({}_{3}\) concentrations (1 mM, 3 mM, 5 mM, and 10 mM) on AgNPs-EtOH formation.  
pH. A total of 9 mL of 3 mM AgNO\({}_{3}\) were added, the mixtures were stirred for one hour, then the absorption spectra for each of the three mixtures, corresponding to pH values of 2, 5, and 8, were recorded. The UV-Vis spectra obtained for the three samples are presented in Figure 5.  
The spectra show that at pH 2 and 5, AgNPs synthesis is suppressed. On the other hand, at pH 8, a well-r demonstrating the formation of AgNPs-H\({}_{2}\)O. It should be noted that, in the 400-500 nm range, the spectra of the AgNO\({}_{3}\) solution and of the plant extract do not display peaks. Therefore, the extract brought to a pH of 8 was further used for the actual synthesis.  
Considering the three samples with different pH values, and after recording their corresponding spectra, it was observed that in this case as well, the pH value at which the peak corresponding to the formation of AgNPs was obtained (420 nm) was also 8 (Figure 6).  
Figure 4: The influence of different plant extract:AgNO\({}_{3}\) ratios (1:9, 5:5 and 9:1) on AgNPs-EtOH formation.  
Figure 5: The influence of pH (2, 5, and 8) on AgNPs-H\({}_{2}\)O formation.  
3.2.4. The Influence of Temperature on AgNPs Synthesis  
In order to optimize even further the reaction conditions, the samples with the reaction mixture consisting of _T. eercta_ extract brought to a pH of 8 and of 3 mM AgNO\({}_{3}\) solution (1:9 ratio) were stirred for one hour at different temperatures: 20 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, 60 \({}^{\circ}\)C, and 80 \({}^{\circ}\)C, respectively. The absorption spectra recorded for the four samples are presented in Figure 7.  
The measured absorbance increases with temperature, reaching the highest value of absorbance at 80 \({}^{\circ}\)C. However, given that satisfactory results were obtained at 40 \({}^{\circ}\)C, that this temperature is easier to reach, and that the temperature is low enough that the active components of the plant extract do not deteriorate excessively, this value was chosen as the optimal one for the AgNPs-H\({}_{2}\)O synthesis.  
Figure 6: The influence of pH (2, 5, and 8) on AgNPs-EtOH formation.  
Figure 7: The influence of temperature (20 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, 60 \({}^{\circ}\)C, and 80 \({}^{\circ}\)C) on AgNPs-H\({}_{2}\)O formation.  
Regarding AgNPs-EtOH formation, an increase in absorbance was observed on the recorded absorption spectra, which is directly proportional to the temperature increase and a maximum absorbance was obtained when the sample was heated up to 80 \({}^{\circ}\)C. However, given the same considerations as in the first case, the temperature of 40 \({}^{\circ}\)C was chosen for the actual AgNPs synthesis (Figure 8).