Thioglycolic Acid FTIR Spectra on Ag2S Quantum Dots Interfaces.
Tamara Kondratenko1, Oleg Ovchinnikov1, Irina Grevtseva1
1Department of Optics and Spectroscopy, Voronezh State University, 394018 Voronezh, Russia.
Materials (Basel, Switzerland)
|February 23, 2020
Summary
This study uses FTIR spectroscopy to analyze thioglycolic acid (TGA) passivation on silver sulfide quantum dots (Ag2S QDs). The findings reveal distinct molecular interactions and adsorption forms of TGA, influencing QD luminescence properties and photodegradation.
Area of Science:
- Materials Science
- Spectroscopy
- Nanotechnology
Background:
- Colloidal quantum dots (QDs) exhibit tunable luminescent properties crucial for various applications.
- Passivation of QD surfaces is essential for enhancing stability and controlling optical characteristics.
- Thioglycolic acid (TGA) is a common capping agent used in QD synthesis and functionalization.
Purpose of the Study:
- To investigate the mechanism of colloidal quantum dots (QDs) passivation with thioglycolic acid (TGA) molecules.
- To differentiate passivation features based on varying luminescent properties of Ag2S QDs.
- To understand the molecular interactions between TGA and Ag2S nanocrystals using FTIR spectroscopy.
Main Methods:
- Fourier-transform infrared (FTIR) spectroscopy was employed to analyze the vibrational modes of TGA molecules.
- Density functional theory (DFT) calculations (B3LYP/6-31+G(d)) were used to model TGA vibrational modes, considering anharmonicity.
- Experimental FTIR spectra of Ag2S/TGA QDs with different luminescence types were compared with free TGA spectra.
Main Results:
- The disappearance of the ν(S-H) peak in Ag2S/TGA QDs indicates thiol group interaction with Ag2S surface dangling bonds.
- Emergence of νas(COO-) and νs(COO-) peaks signifies TGA adsorption in its ionic form.
- Distinct shifts in carboxylate peaks (νs(COO-) and νas(COO-)) for exciton luminescence QDs suggest altered TGA molecular symmetry due to passivation.
- Recombination luminescence QDs show smaller shifts, indicating different thiol-TGA interactions with the Ag2S surface.
- FTIR analysis revealed photodegradation of TGA on Ag2S QDs, with non-reversible degradation observed for exciton luminescence QDs, forming a specific acyl radical.
Conclusions:
- FTIR spectroscopy effectively distinguishes between different passivation states of TGA on Ag2S QDs, correlating with luminescence properties.
- The passivation mechanism involves the interaction of TGA's thiol group with the Ag2S surface and adsorption in its ionic carboxylate form.
- Photodegradation pathways of TGA on Ag2S QDs differ based on luminescence type, with exciton luminescence QDs exhibiting irreversible degradation.
Keywords:
Ag2S quantum dotsFTIR spectradimerionic formluminescencephotodegradationthioglycolic acid (TGA)More Related Videos
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