Facile and Rapid Synthesis of a Dithiol-Protected
Ag<sub>7</sub> Quantum Cluster
for Selective Adsorption of Cationic Dyes
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Abstract
We report a facile and rapid (less
than 15 min) synthesis of atomically
precise, dithiol-protected, silver quantum cluster, Ag<sub>7</sub>(DMSA)<sub>4</sub> (DMSA: meso-2,3-dimercaptosuccinic acid), through
a modified solid state route. The as-synthesized cluster exhibits
molecular optical absorption features with a prominent λ<sub>max</sub> at ∼500 nm. Composition of the cluster was confirmed
using various spectroscopic and microscopic techniques such as electrospray
ionization mass spectrometry (ESI MS), X-ray photoelectron spectroscopy
(XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy
(FTIR), scanning electron microscopy (SEM), transmission electron
microscopy (TEM), and energy dispersive analysis of X-rays (EDAX).
Clusters supported on neutral alumina have been shown as better adsorbents
for selective adsorption of cationic dyes (over anionic dyes) from
water. This selectivity for cationic dyes was evaluated by zeta potential
(ζ) measurements. The efficiency of clusters for removal of
dyes is very high when compared to nanoparticles (NPs) protected with
ligands (citrate and mercaptosuccinic acid (MSA)) possessing similar
chemical structures as that of DMSA. The higher efficiency of clusters
for the removal of dyes is attributed to their smaller size and large
surface area compared to the NPs in addition to favorable electrostatic
interactions between the clusters and cationic dyes. Adsorption of
dyes (cationic and anionic) was enhanced when dye molecules contain
hydrogen bond forming functional groups. Supported clusters have been
reused up to five cycles without the loss of activity once the adsorbed
dye is extracted using suitable solvents