Selective Interactions of Al(III) with Plasmonic AgNPs by Colorimetric, Kinetic, and Thermodynamic Studies

In this paper, we report a simple, novel, and highly selective plasmonic nanoparticles (NPs)-based colorimetric nanoprobe for the detection of Al­(III) ions in aqueous solution. 5-Hydroxy indole-2-carboxylic acid (5H-I2CA) was utilized as a reducing as well as capping agent for the preparation of silver nanoparticles (5H-I2CA@AgNPs). The interaction between Al­(III) and AgNPs was determined by UV–vis absorption spectroscopy, high-resolution transmission electron microscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, and dynamic light scattering techniques. The absorption values (A 452–410) of the 5H-I2CA@AgNPs solution exhibited a linear correlation with Al­(III) ion concentrations within the linear range of 0.1–50 nM. An outstanding selectivity toward Al­(III) was demonstrated by the proposed nanoprobe in the presence of interfering cations. Kinetics was used to study the selectivity of nanoprobe, which indicated second-order kinetics, and the rate constant was very high. The activation energies of Al­(III) were found to be the lowest compared to those of other interfering ions. The results of kinetics and thermodynamic study of Al­(III) were compared to those of four other competing ions. The thermodynamic data reveal that the interaction best suited for Al­(III) ion compared to other metal ions (Al­(III) > Co­(II) > Hg­(II) > Cr­(III) ≅ Cr­(VI)). The lower detection limit of the proposed nanoprobe for Al­(III) is 1 nM. The present method also holds practical applicability for real water samples.