The pH of solution plays a crucial role in the synthesis of Ag NPs
[33]. The effect of pH on the synthesis of Ag NPs was studied by
carrying out reactions at different pH (pH 4, 6, 8, 10 and 12) using
0.1% LBG and 1 mM Ag NO3. At acidic pH (pH 4 and 6), no surface
plasmon peak was observed in the visible region which is a characteristic
for Ag NPs. This suggests that acidic pH is not favorable for
the Ag NPs synthesis. As seen in Fig. 6, an increase in the intensity
of surface plasmon peak was observed under alkaline conditions
(pH 8, 10 and 12) due to the increased formation of Ag NPs. Yellowish
color appears at pH 8 which gradually changes to dark yellow
at pH 10 and further brown at pH 12. However at pH 12, agglomeration
of Ag NPs was observed whereas no agglomeration was
observed at pH 10. This indicates poor stability of Ag NPs at extreme alkaline pH. These observations are well in agreement with the
earlier reports