The effect of pH on the formation of AgNPs was evaluated by
UV–visible spectroscopic studies and is given in Fig. 3. From the
figure, it is evident that the formation of AgNPs mainly depends on
the pH of the reaction medium. The absorbance value was increased
gradually with increasing of pH range from 4 to 9, suggesting the
rate of formation of AgNPs is high in basic pH than in acidic pH. The
formation of AgNPs occurs rapidly, in neutral and basic pH which
is evident from visual observation and may be due to the ionization
of the phenolic group present in the extract [28]. The slow
rate of formation and aggregation of AgNPs at acidic pH could be
related to electrostatic repulsion of anions present in the solution
[29]. At basic pH range there is a possibility of Ag+ precipitating as
AgOH also. On the basis of the results, it could be concluded that the
optimum condition for the preparation of AgNPs using T. chebula
can be taken as the neutral pH and hence the UV–visible spectroscopic
studies were carried out at various time intervals at
this pH. The effect of reaction time at pH 7 was shown in
Fig. 4. From the figure, it can be observed that the absorbance
of AgNPs increased with increase of reaction time, indicating
more reduction of Ag+ with respect to time. The synthesized
AgNPs are stable for 10 days at 5 ◦C evident from, the max
value