Microwave Assisted Phytosynthesised Silver Nanoparticles for the Sensing of Toxic Mercuric Ions and as Catalyst for the Treatment of Environmental Pollutants

Abstract

Silver nanoparticles (AgNP) were prepared using the fresh leaf extract of Coleus amboinicus (CA) as both the capping and reducing agent through a microwave-assisted method. The phytosynthesized AgNP with CA (AgNP-CA) demonstrated highly selective optical and electrochemical sensing capabilities for mercuric ions. The AgNP-CA and complexation AgNP-CA with Hg²⁺ ions (AgNP-CA-Hg²⁺) were characterized using UV-vis spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared (FTIR), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM), zeta potential, and dynamic light scattering (DLS) techniques. The effective complexation of AgNP-CA with Hg²⁺ ions resulted in visually observable colour changes, confirmed by UV-vis spectroscopy. The green-fabricated electrochemical AgNP-CA modified platinum electrode (AgNP-CA-Pt) sensor exhibited a limit of detection (LOD) of 0.8524 µM using the differential pulse voltammetry (DPV) method. The catalytic potential of AgNP-CA for the reduction of toxic organic dyes, Congo Red and Safranin, using NaBH₄ was also examined. The catalytic reductions were completed within a few minutes and followed a pseudo-first-order kinetics model. The linear relationship between catalyst concentration and reduction rates was experimentally determined. This eco-friendly approach to AgNP-CA synthesis and its applications is a useful tool for monitoring and managing environmental pollution.