Investigation into the Reactivity of Unsupported and Supported Ag7 and Ag8 Clusters with Toxic Metal Ions

We report the chemical interactions of unsupported and alumina-supported Ag-7 and Ag-8 clusters protected with MSA (mercaptosuccinic acid) with heavy metal ions Hg(II), Cd(II), and Pb(II) in water at different concentrations. The investigation was carried out to determine the feasibility of this interesting new class of materials called quantum clusters for water purification. These systems were studied using various spectroscopic and microscopic techniques such as ultraviolet visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, dynamic light scattering, zeta potential measurements, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy and in detail by X-ray photoelectron spectroscopy. We observed that the metal ions interact with both the silver atoms of the clusters and the functional groups of the capping agent (MSA). The mercuric ions were reduced to metallic mercury by both supported and unsupported clusters, due to the feasibility of the redox reaction, whereas no reduction was observed for Cd(II) and Pb (II). As a result of the interaction, the luminescence of the cluster is lost which can be used to sense Hg(II). At lower concentrations, the metal ions were chemically bonded to the carboxylate groups of MSA. Absence of reduction of Hg(II) at lower concentration is due to the chemical affinity of the ligands and the lower silver content per cluster compared to the number of carboxylate groups.