Colorimetric Detection of Mercury (II) Ions Utilizing Bio-Colloidal Silver Nanoparticles Synthesized Via Microwave-Assisted Method with Matoa Leaf Extract

In this work, bio-colloidal silver nanoparticles (AgNPs) were synthesized using Matoa (Pometia pinnata) leaf extract as a reducing and stabilizing agent under microwave irradiation to promote rapid AgNPs formation. The influence of microwave irradiation powers (360, 540, and 720 W) on the optical, structural, and morphological properties of the synthesized AgNPs was systematically investigated. The AgNPs formation was characterized by yellowish-brown colloids formation with surface plasmon resonant (SPR) bands centered around 430 nm, as detected by UV-Vis spectroscopy. FTIR analysis revealed the presence of C-H and O-H functional groups from polyphenols and flavonoids in Ag+ ion reduction. XRD pattern revealed a face-centered cubic (FCC) crystalline structure of AgNPs, while TEM images showed predominantly quasi-spherical morphology with average diameter of 58–62 nm. The colorimetric sensing performance was examined over Hg2+ concentration ranging from 1–100 ppm. Upon Hg2+ exposure, the AgNPs colloids demonstrated a progressive decrease in SPR intensity along with visible discoloration in the 350–550 nm region. Nanoparticles synthesized at 720 W exhibited the highest sensitivity of AgNPs, which displayed obvious discoloration observed in the range 40–100 ppm of Hg2+ with steepest slope at 8 × 10–4. These findings highlight the potential of microwave-assisted Pometia pinnata-derived AgNPs as a green and eco-friendly approach for the colorimetric sensing of mercury ions.