Visual and Spectrophotometric Detection of Iodide Ion by Pyridine based Silver Nanoprobe and DFT Analysis

Abstract

Introduction: A novel chemosensor has been developed utilizing a newly synthesized pyridine-carboxaldehyde thiosemicarbazone silver nanoprobe (PT-AgNP) for detecting and quantifying iodide ions in aqueous media, both visually and spectrophotometrically using a UV-Vis spectrophotometer. Method: Notably, this sensor demonstrates remarkable selectivity for I- ions, effectively distinguishing them from other common anions such as AcO-, Br-, Cl-, CN-, and F-. The PTAgNP solution undergoes a rapid color change from yellow to black, providing a clear visual indication of the presence of iodide ions. This color transition is directly proportional to the concentration of iodide ions, as indicated by the reduction in the intensity of the surface plasmon resonance band due to nanoparticle aggregation. A linear correlation is observed between the change in intensity and the concentration of iodide ions within the range of 10 to 50 nM, with a detection limit of 8.8 nM. The stability of the PT-AgNP complex is evaluated through experimental methods such as UV-Vis spectroscopy, zeta potential analysis, and powder X-ray diffraction (PXRD), complemented by theoretical calculations using density functional theory (DFT) with Gaussian 09W software. Results: Theoretical investigations reveal that the silver ion (Ag+) and the imine bond of pyridine carboxaldehyde act as potential nucleophilic targets, consistent with the observed morphological color change from yellow to black upon PT-AgNP complexation with iodide ions. Conclusion: Furthermore, DFT calculations indicate a higher HOMO-LUMO energy gap in the pyridine molecule compared to the PT-AgNP complex, suggesting its enhanced sensitivity and reactivity towards iodide ions.