Silica-encapsulated CdTe/MPA quantum dots: microstructural, thermal, and chemical stability characterization

In this paper, we describe the synthesis of silica-encapsulated CdTe/MPA quantum dot (QD) nanocomposites (CdTe/MPA@SiO2) at room temperature starting from water-soluble CdTe QDs capped with 3-mercaptopropionic acid (MPA) as surface ligand (CdTe/MPA), followed by their encapsulation with a thin layer of silica using the sol-gel process. The objective of this work was to evaluate the microstructural, thermal, and chemical properties of the encapsulated material as a way to evaluate these characteristics for possible applications in different technological areas. Transmission electron microscopy results proved that CdTe QDs (2.5 nm in size) were inside the SiO2 nanoparticles, and the spherical CdTe/MPA@SiO2 nanocomposite with a 69-nm thick shell. The photoluminescence intensity was evaluated as a function of pH in the range of 2-12. The CdTe/MPA@SiO2 nanocomposite showed better chemical stability and greater intensity of photoluminescence in the pH 2-12 range than CdTe/MPA. In addition, the CdTe/MPA@SiO2 nanocomposites showed good heat stability up to 125 degrees C. The changes in their optical properties were also evaluated by means of photoluminescence spectroscopy. The materials were also characterized by diffuse reflectance spectroscopy, X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis.