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Effect of thioglycolic acid molecules on luminescence properties of $$\hbox {Ag}_2$$Ag2S quantum dots
摘要： For monoclinic Ag2S nanocrystals (quantum dots, Ag2S/TGA QDs), the correlation between their luminescence properties and aspects of their passivation by thioglycolic acid (TGA) molecules is considered. The features of quantum confinement effect in the QDs absorption and photoluminescence spectra are analyzed for Ag2S QDs with an average size of 1.7–3.1 nm. We show that, in various conditions of passivation of QDs interfaces, the luminescence mechanism of Ag2S/TGA QDs is switched from recombination luminescence in the 870–1000 nm region to exciton luminescence with a band maximum at 620 nm. By means of FTIR spectra, two major types of interactions between TGA molecules and Ag2S QDs, arising due to changing the [Ag+]:[S2?] ratio from 1:0.9 to 1:1.43, are determined. Exciton luminescence (620 nm) occurs in case of using TGA as the sulfur source in Ag2S crystallization and the interface passivation agent, with [Ag+]:[S2?] = 1:1. The analysis of the FTIR spectra indicates bonding of TGA with the Ag2S surface by both thiol and carboxylic groups in this case. With increasing the sulfur concentration in the synthesis of Ag2S/TGA QDs, the exciton luminescence is suppressed. The employment of Na2S as the sulfur source in Ag2S crystallization with TGA acting as the surface passivation agent promotes the formation of recombination centers for IR luminescence. In this case, analysis of the FTIR spectra indicates passivation of Ag2S QDs by TGA molecules due to adsorption of thiol groups. It is found that the photodegradation or IR luminescence of Ag2S/TGA QDs upon exposure to exciting radiation is due to the photolysis of Ag2S nanocrystals with formation of luminescence quenching centers as well as due to photodestruction of TGA molecules.
关键词： Size dependence,Thioglycolic acid,Interaction mechanism,FTIR spectra,Trap state luminescence,Silver sulfide,Luminescence properties
更新于2025-09-23 15:19:57
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Thioglycolic Acid FTIR Spectra on Ag2S Quantum Dots Interfaces
摘要： 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 Ag2S/TGA QDs with exciton and recombination luminescence are differ from each other and B “freeB” TGA molecules. The ν(S ? H) TGA peak (2559 cm?1) disappears in FTIR spectra of Ag2S/TGA QD samples. This fact indicates the interactions between TGA thiol group and dangling bonds of Ag2S nanocrystals. Ag2S QDs passivation with TGA molecules leads to emergence νas(COO?) (1584 cm?1) and νs(COO?) (1387 cm?1) peaks. It indicates TGA adsorption in ionic form. For Ag2S/TGA QDs with exciton luminescence we observed (a) significant low-frequency shift of νs(COO?) peak from 1388 cm?1 to 1359 cm?1 and high-frequency shift of νas(COO?) peak from 1567 cm?1 to 1581 cm?1; (b) change in the ratio of intensities of νas(COO?) and νs(COO?) vibrations. This feature is caused by the change in the symmetry of TGA molecules due to passivation of Ag2S quantum dots.For Ag2S/TGA QDs with recombination luminescence, the insignificant high-frequency shift of 7–10 cm?1 for νas (COO?) at 1567 cm?1 and low-frequency shift of 3–5 cm?1 for νs (COO?) at 1388 cm?1, probably caused by the interaction of thiol with Ag2S 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 Ag2S QDs. In the case of Ag2S QDs with exciton luminescence, the degradation process is non-reversible. It is accompanied by TGA photodegradation with the formation of α-thiol-substituted acyl radical (S-CH2-CO?) TGA.
关键词： photodegradation,FTIR spectra,thioglycolic acid (TGA),dimer,luminescence,Ag2S quantum dots,ionic form
更新于2025-09-23 15:19:57
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Detection of lead Using Thioglycolic Acid Capped ZnSe and ZnSe@ZnS core-shell Quantum Dots
摘要： Herein, we proffer a sensitive and selective sensor using ZnSe and ZnSe@ZnS quantum dots (QDs), for detection of toxic metal ions at nm level. It has been found that the TGA capped ZnSe and ZnSe@ZnS QDs were apparently sensitive to Pb2+ ions as perceptible from their fluorescence quenching measurements. However, in case of few common heavy metal ions such as Zn2+, Co2+, Fe2+, , Mg2+, Cu2+, Ni2+ and Cd2+ ions, negligible quenching compared to Pb2+ ions was noted. Hence, we have successfully detected Pb2+ ions in aqueous solutions based on the photoluminescence (PL) spectroscopy. The observed linearity range was from 10 NM to 100 nM for both Pb2+ ions. An alternative QD based sensor for the spectroscopic detection, and concentration quantification of Pb2+ ions is proposed.
关键词： Metal ions,Photoluminescence,Thioglycolic acid,Quantum dots,Core-shell QDs
更新于2025-09-12 10:27:22
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Detection of theophylline using molecularly imprinted polymers based on thioglycolic acid-modified CdTe quantum dots
摘要： Molecularly imprinted polymers (MIPs) and quantum dots (QDs) have been widely employed to fabricate highly sensitive and selective sensor. Here, we developed a fluorescence nanosensor based on thioglycolic acid-modified CdTe QDs that is coated with molecularly imprinted polymers for the specific detection of theophylline (THP). Initially, water-soluble thioglycolic acid-modified CdTe QDs were synthesized by refluxing method. Then, MIPs-coated QDs (MIPs-QDs) composite was produced by sol–gel process using THP as a template. Therefore, the selectivity of the molecular imprinting technique and advantages of QDs were combined. The prepared QDs and the MIPs-QDs were characterized using X-ray diffraction technique, transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, and fluorescence spectrometry. Finally, this sensing system was successfully used to detect THP in human plasma samples with recoveries of 90% to 108%. A very good linear relationship was observed between the decreasing in the fluorescence intensity of MIPs-QDs and increasing the THP concentration within concentration range of 0.14–3.05 μmol L?1, with a correlation coefficient of 0.9992 and detection limit of 0.07 μmol L?1.
关键词： Molecularly imprinted polymers,Thioglycolic acid-modified CdTe QDs,Theophylline
更新于2025-09-11 14:15:04