3.1. Effect of initial pH on the biosynthesis of silver nanoparticles
The initial pH value of the aqueous AgNO3 solutions was an important parameter in the synthesis of silver nanoparticles using mango peel extract. It was observed that the color of AgNO3 solutions changed from light brown yellow to dark brown when the initial pH of solution was increased. The color change would be an indication of silver bioreduction mediated by mango peel extract and the subsequent formation of silver nanoparticles after 15 min of the reactions. UV–vis absorption spectroscopy is a main tool to analyze the noble metal nanoparticles formation, whichdepends on surface plasmon resonance (SPR). The optical absorption spectrum of metal nanoparticles is dominated by the SPR,depending upon the particle size, shape, state of aggregation and the surrounding dielectric medium (Mulvaney, 1996). The UV–vis spectra obtained from solutions at differentinitial pH after the reaction show characteristic absorption bands of silver nanoparticles at around 412.0–434.0 nm. It is known that an absorption band appears at about 400–440 nm because of the surface plasmon resonance in Ag nanoparticles