Green Synthesized Unmodified Silver Nanoparticles as Reproducible Dual Sensor for Mercuric Ions and Catalyst to Abate Environmental Pollutants

The present study involves the green synthesis of unmodified silver nanoparticles using the aqueous leaf extract of Mimosa diplotricha (AgNP-MD). This work highlights the reliable optical and electrochemical sensing of Hg2+ ion (5-45 mu M) by AgNP-MD with high selectivity. Optical sensing was easily identified by the color change of AgNP-MD to colorless upon effective interaction of metal nanoparticles with mercuric ions, which is in accordance with the decrement in surface plasmon resonance (SPR) of nanoparticles. Electrochemical voltammetric sensing was performed using a platinum electrode modified with AgNP-MD (AgNP-MD-Pt). The limit of detection (LOD) of the developed green sensor for mercuric ions was calculated from differential pulse voltammetry (DPV) analysis as 1.46 mu M. The applicability of unmodified AgNP-MD towards Hg2+ ions was inspected for the collected real water samples. Ultraviolet-visible (UV-vis) spectrophotometer, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), zeta potential, and dynamic light scattering (DLS) techniques were used to characterize the synthesized AgNP-MD and AgNP-MD-Hg2+ complexation. Moreover, the catalytic potential of green synthesized AgNP-MD towards the reduction of methyl orange and methylene blue was also evaluated. Both the degradations were fast, completed within few minutes, and followed pseudo-first-order kinetics with good regression coefficients. To the best of our knowledge, this is the first report on the synthesis of AgNP-MD using MD extract and its multifunctional applications including the fields of sensors and catalysis.