A silver nanoparticle-based colorimetric detection of Fe²⁺

Silver nanoparticles (AgNPs) can be developed into materials for the detection of metals in the environment. The detection was carried out based on the color change AgNP colloids after reacted with metal ions, known as a colorimetric method. In this study, silver nanoparticles were obtained through biosynthesis using the aqueous extract of Diospyros discolor Willd. (Bisbul) leaves which was mixed with 1 mM of AgNO3 precursor. The characterization results using a UV-Vis spectrophotometer showed a peak in the range of 300500 nm which is the typical absorption spectrum of silver nanoparticles. Formation of AgNPs was also indicated by the solution color change from yellow to brown. After 24 hours of reaction, the formed AgNPs were tested as indicator solutions for 6 metal ions, namely Pb²⁺, Zn²⁺, Co²⁺, Mg²⁺, Mn²⁺, and Fe²⁺, at 1000 mg/L. The specific visual colour change was observed only when AgNPs solution was added into Fe²⁺ ion solution. Further testing was carried out to detect the presence of Fe²⁺ ions at 0; 0,1; 1; 10; 100; 500; and 1000 mg/L. The results showed a solution discoloration ranging from brownish to greenish. The change in solution color after AgNPs were added into Fe²⁺ solution was caused by AgNPs unique optical properties in the visible wavelength. Silver nanoparticles also tend to have an affinity with Fe²⁺ and showed larger size based on the PSA (Particles Size Analyzer) and TEM (Transmission Electron Microscope) characterizations. The results showed that the AgNPs tend to agglomerate after the addition of a higher concentration of Fe²⁺. This detection method has the potency to be developed and enhanced to detect the presence of Fe²⁺ metal ions in the environment.