Fast Orange Peel-Mediated Synthesis of Silver Nanoparticles and Use as Visual Colorimetric Sensor in the Selective Detection of Mercury(II) Ions

This paper presents the green synthesis of silver nanoparticles (AgNPs) using orange (Citrus sinensis) peel extract. The effects of different factors such as silver ion concentration, reaction time, temperature, pH, and extract quantity on the AgNPs synthesis were studied, enabling us to determine optimum synthesis conditions. We characterized the AgNPs with different techniques: UV–Visible Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), FTIR, and XRD. The AgNPs showed yellowish brown to golden brown colors and a surface plasmon resonance (SPR) absorption band around a wavelength of 420 nm. FESEM images showed polydisperse AgNPs having an average size of about 55 nm. The XRD profile of the synthesized nanoparticles showed peaks that are characteristic of silver while the FTIR spectrum highlighted the functional groups associated with reducing silver ions and stabilizing the AgNPs. With the selected optimum conditions, the AgNPs were formed in less than 1 min. This is the fastest reaction time so far reported and is significantly shorter than in earlier reports. The AgNPs colloid solution was applied as nanosensor in the visual colorimetric detection of mercury(II) ions in water. The golden brown AgNPs colloid solution turned colorless and the characteristic SPR absorption band disappeared when mercury(II) ions were added to the solution. While the AgNPs show good sensitivity and selectivity for the colorimetric detection of mercury(II) ions with a detection limit of 1.24 × 10⁻⁶ mol/L (0.25 ppm), we also demonstrated the suitability of the method for detecting mercury(II) ions in drinking water.