Green synthesized uncapped Ag colloidal nanoparticles for selective colorimetric sensing of divalent Hg and H2O2

Abstract

The green ecofriendly approach towards crystalline Ag nanoparticles (AgNPs) synthesis using apple (Malus domestica) juice has been demonstrated. The optical properties of synthesized AgNPs were studied by ultraviolet-visible spectroscopy (UV-Vis). The X-ray diffraction (XRD) studies reveals that, the synthesized green AgNPs possess good crystalline nature with face centered cubic lattice structure. Similarly, the Emission Scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) studies reveals that AgNPs has spherical shape with diameter of 60 nm and particle size ranges from 6 to 100 nm. The EDAX studies confirms the impurity free nature of AgNPs. The green synthesized AgNPs possess the surface area of about 5.069 m2/g and cross sectional area of 16.2 Ă2/ molecule. The Ascorbic acid and different proteins of apple juice, reduced silver ions into AgNPs during the synthesis. The color of the as synthesized AgNPs was dark brown and exhibited a Surface Plasmon Resonance (SPR) peak at 527 nm. Upon treating with Hg2+/H2O2, the AgNPs became colorless and the SPR band broadened and blue shifted. AgNPs exhibited remarkable colorimetric as well as spectral changes only toward Hg2+/ H2O2. The limit of detection and sensitivity of the method were 0.2656 ppm and 0.2564 ppm for Hg2+ ions. Similarly, limit of detection and sensitivity of the method was 0.216 ppm (Much less than the Threshold limit value (1 ppm) in drinking water prescribed by WHO) and 0.215 ppm mL−1 for H2O2. The sensitivity of AgNPs towards Hg2+ ions sensing is almost pH independent. Additionally, the colorimetric and naked eye sensing the environmentally toxic metal ion Hg2+ and the biologically important H2O2 using AgNPs has been demonstrated. The present system has been applied for monitoring Hg2+ ions and H2O2 in different water samples and recovery rates in spiked samples were more than 99%.