Síntese e caracterização de nanopartículas de semicondutores metálicos do tipo II-VI

Abstract

Inorganic nanomaterials are a class of advanced materials, which have been widespread in both science and nanotechnology. The use of nanomaterials in several areas makes nanoscience an interdisciplinary field. Some challenges, such as the type of synthesis and toxicity control should be explored, mainly because those materials can be controlled at the nanometer level by means of the synthesis variables. In this work, we performed the synthesis of cadmium telluride (CdTe) nanoparticles with the surface capped by a mixture of organic thiol stabilizers such as mercaptopropionic acid (MPA), cysteine (CYS), glutathione (GLU), and biopolymer sodium alginate (ALG). Synthesis were performed by two distinct aqueous methods hydrothermal and reflux and the synthesis parameters such as pH and ratio Cd/Te/stabilizer were fixed based on the literature. The colloidal dispersions obtain present remain stable for at least 3 months (time observed so far). Optical absorption spectra of all mixtures of CdTe - stabilizers presented a red shift with increasing synthesis time, and furthermore, the position of this band was at a wavelength below the bulk CdTe (790 nm). The emission spectra in all cases were intense, with little difference between them. The diameter of the particles, calculated from an empirical equation from the of maximum absorption wavelength, were comparable compared to those obtained by X-ray diffraction (XRD) (Scherrer equation) as well as transmission electron microscopy (TEM). The results from the three techniques agreed very well for CdTe via reflux. However for hydrothermal synthesis it was not possible to determine the diameter of the particles by TEM due to morphology of nanostructured aggregates. The crystal structures as obtained by XRD indicating the incorporation of sulfur atoms in the CdTe structure, in agreement to the literature for this type of synthesis. Infrared spectroscopy confirmed the presence of organic stabilizers on the surface of CdTe. The morfology of samples identified by TEM/HRTEM was different depending on the method of syntesis aggregates for the hydrothermal samples and isolated particles for reflux samples so the mechanisms of nucleation and growth were proposed oriented attachment (OA) and Ostwald ripening (OR) for synthesis CdTe-hydrothermal and reflux, respectively.