Thioglycolic Acid FTIR Spectra on Ag(2)S Quantum Dots Interfaces

The mechanism features of colloidal quantum dots (QDs) passivation with thioglycolic acid molecules (TGA) for cases of different luminescent properties is considered using FTIR. This problem is considered based on FTIR spectra analysis for various ionic forms of TGA. Experimental TGA molecules FTIR spectra is interpreted, basing on the data on modeling of TGA vibrational modes, realized in the framework of density functional method (DFT /B3LYP/6-31+G(d)) taking into account the vibrations anharmonicity of every functional group. This approach provides a significant improvement in the agreement between the experimental and calculated data. FTIR spectra of Ag [Formula: see text] S/TGA QDs with exciton and recombination luminescence are differ from each other and B “freeB” TGA molecules. The [Formula: see text] TGA peak (2559 cm [Formula: see text]) disappears in FTIR spectra of Ag [Formula: see text] S/TGA QD samples. This fact indicates the interactions between TGA thiol group and dangling bonds of Ag [Formula: see text] S nanocrystals. Ag [Formula: see text] S QDs passivation with TGA molecules leads to emergence [Formula: see text] (COO [Formula: see text]) (1584 cm [Formula: see text]) and [Formula: see text] (COO [Formula: see text]) (1387 cm [Formula: see text]) peaks. It indicates TGA adsorption in ionic form. For Ag [Formula: see text] S/TGA QDs with exciton luminescence we observed (a) significant low-frequency shift of [Formula: see text] (COO [Formula: see text]) peak from 1388 cm [Formula: see text] to 1359 cm [Formula: see text] and high-frequency shift of [Formula: see text] (COO [Formula: see text]) peak from 1567 cm [Formula: see text] to 1581 cm [Formula: see text]; (b) change in the ratio of intensities of [Formula: see text] (COO [Formula: see text]) and [Formula: see text] (COO [Formula: see text]) vibrations. This feature is caused by the change in the symmetry of TGA molecules due to passivation of Ag [Formula: see text] S quantum dots.For Ag [Formula: see text] S/TGA QDs with recombination luminescence, the insignificant high-frequency shift of 7–10 cm [Formula: see text] for [Formula: see text] (COO [Formula: see text]) at 1567 cm [Formula: see text] and low-frequency shift of 3–5 cm [Formula: see text] for [Formula: see text] (COO [Formula: see text]) at 1388 cm [Formula: see text] , probably caused by the interaction of thiol with Ag [Formula: see text] S surface is observed. Using FTIR spectra, it was found that IR luminescence photodegradation is also accompanied by changes in the thioglycolic acid molecules, which capped Ag [Formula: see text] S QDs. In the case of Ag [Formula: see text] S QDs with exciton luminescence, the degradation process is non-reversible. It is accompanied by TGA photodegradation with the formation of [Formula: see text]-thiol-substituted acyl radical (S-CH [Formula: see text]-CO [Formula: see text]) TGA.