Síntese e caracterização de pontos quânticos de carbono obtidos por processos bottom-up

Abstract

This research presents a green synthesis of carbon quantum dots (CQDs) - a class of multifunctional organic nanoparticles, biocompatible and fluorescent emitters, with a wide application area - from Lolium perenne, a plant popularly known as ryegrass. The obtained CQDs were synthesized by three bottom-up process: hydrothermal, microwave and muffle, from different parts of the ryegrass (spikelets and leaves). Ultrapure water (Milli-Q®) was the only solvent used and, different synthetic conditions tested. Six samples were characterized, regarding molecular structure and optical properties, by UV-Vis spectroscopy, molecular fluorescence spectroscopy, infrared spectroscopy (FTIR), Raman spectroscopy and Transmission Electron Microscopy (TEM), as well as qualitative characterizations under ultraviolet light (UV-C). TEM confirmed the presence of nanoparticles with diameters between 5 and 10 nm. FTIR suggested that there are a few nitrogen groups and a possible presence of sulfonated groups, besides different oxygenated groups. Raman spectroscopy indicated that there is a great crystalline character in the nanoparticles, due to the presence of the G band (1600 cm-1), reasserting the presence of sp2 carbon found by FTIR. The samples were fluorescent emission dependent on the excitation wavelength, predominantly in the region between 430 – 470 nm, shown blue color, and quantum yield up to 11%. Preliminary studies have suggested the ability of CQDs to act as fluorescent sensors for the detection of Cr6 + ions in water, as they have fluorescence suppression effects in the presence of low concentrations of the metal.