Síntese e caracterização de soluções coloidais de pontos quânticos de ZnS, In2S3 E Zn-In-S estabilizados com carboximetilcelulose para potencial aplicação em nanofotocatálise

Abstract

Since the end of the 20th century, nanotechnology has been seen as a revolutionary area. As a result, countless possibilities of this science are being explored for the advancement of human life. In the environmental field, efforts have been made to modify current legislation to introduce these new and promising technologies that can be a solution to several problems related to air, water and soil pollution. With this in mind, the work includes a synthesis of fluorescent colloidal nanostructures of ZnS QDs doped with indium by a sustainable route for environmental application in photocatalysis. The synthesis parameters, the effect of indium doping, the functionalization with stabilizers and biomolecules on the morphological and optical characteristics of the QDs are essential for evaluating the possibility of their application. The techniques used for chemical, morphological, structural and optical characterization will be: transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDX) and selected area electron diffraction (SAED), dynamic light scattering (DLS), zeta potential (ZP), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV- Vis) and photoluminescence spectroscopy (PL). Thus, this synthesis is a complex multidisciplinary problem involving chemistry, physics, materials engineering, among others. The analyzed system of three different elements associated with a biopolymer verified different forbidden bands of 4.04 eV for ZnS, 3.4 eV for In2S3, 3.27 eV for Zn-In-S in the theoretical proportion 1-2-4 and 3.17 eV for Zn-In-S in the theoretical proportion 1-4-20. Regarding the maximum wavelength of photoluminescence for these 4 systems we had 424 nm, 450 nm, 355 nm and 380 nm, respectively, with the ZnS QDs having the highest intensity. Regarding the sizes, the colloids were between 24 nm and 188 nm with a negative surface charge representing the CMC involving the quantum dots, while the size of the quantum dots was between 2.4 nm and 3.3 nm. Regarding the applications, two types of dyes were analyzed, methylene blue (MB), cationic, and methyl orange (MO), anionic, in the ZnS and In2S3 quantum dots. For the ZnS system, different pHs of 3, 5 and 7 were evaluated, with the greatest efficiency being at pH 5 for both dyes, being 65% degradation for MB and 72% for MO. In the Zn-In-S and In2S3 systems, when adding the quantum dots to the MB solution, a decrease in absorbance resulting from the interaction of indium with the dye was observed, which was not observed for MO. During the photocatalysis test, a decrease in intensity associated with a blue-shift of the solution, characterized by dye demethylation, was also observed. Thus, the quantum dots synthesized by green synthesis proved to be promising for environmental application since, in addition to having low toxicity potential, they are capable of degrading two of the dyes most commonly used in industry.