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.