Colorimetric Discrimination of Pd2+ and Hg2+ Ions in Solvent and Solid-Film State Using Organic Acid-Assisted Green Synthesized Silver Nanoparticles

In this study, a colorimetric discrimination of Pd2+ and Hg2+ ions in the solvent and solid film states in one silver nanoparticles (AgNPs) sensing system is presented. First, silver nanoparticles were prepared by reducing AgNO3 with sodium borohydride in the presence of chitosan and different organic acids, including acetic acid, propanedioic acid, and citric acid. The addition of different organic acids allowed for the surface plasmon resonance (SPR) intensity and size distribution of AgNPs to be adjusted. Chitosan acts as a stabilizer and complexing agent, endowing AgNPs excellent film-forming properties. Then, the chitosan-stabilized AgNPs in the solvent and solid-film state are used to detect metal ions. In the presence of Hg2+ and Pd2+ ions, the color of the AgNP solution changed rapidly from pale yellow to colorless and light brown, respectively. The characteristic SPR peaks of the AgNPs also disappeared completely, and the solid films of AgNPs with a yellowish-brown color also change rapidly to colorless and dark brown with the addition of Hg2+ and Pd2+ ions, respectively. The discrimination of Hg2+ and Pd2+ ions can be clearly observed in both the solvent and the solid film state. However, the addition of other metal ions cannot change the color of the AgNPs.