Preparação e caracterização de pontos de carbono a partir de diferentes métodos e precursores de baixa massa molar e suas aplicações como sensores para íons metálicos

Abstract

Carbon dots (CDs) are nanoparticles with a diameter around 2-10 nm, and normally have different oxygenated groups on their surface. These nanomaterials present interesting properties such as proper solubility in water, possibility of functionalization with different compounds, resistance to photodegradation, low toxicity, and interesting optical properties, such as fluorescence. Due to their photoluminescent properties, CDs have emerged as sensors for the detection of different substances, using the fluorescence quenching phenomenon. In the first section of this work, twelve samples of CDs were prepared using different bottom-up strategies: hydrothermal carbonization in an autoclave (AC), microwave-assisted reaction (MW) and reflux heating (RH). The results showed that the nanomaterials obtained by AC presented a higher value of fluorescence quantum yield (QY) when compared with the nanoparticles obtained by the MW and RH methods. The nanoparticles obtained by the AC method showed fluorescence emissions in the blue/green region of the spectrum and had an average size between 1.2 and 2.2 nm. In addition, CDs prepared in an autoclave were studied as sensors for the detection of metal ions, showing selectivity and sensitivity in the detection of Fe3+ ions, with a limit of detection (LOD) = 0.89 µmol.L-1 . In the second section of this work, twenty samples of CDs were prepared using different combinations of different low molecular mass precursors as carbon and nitrogen sources. Among these nanoparticles, six obtained a QY value greater than 15%, and the two that presented the highest QY values were prepared using ammonium citrate as a nitrogen source. In general, the fluorescence curves of the CDs showed emissions in the blue/green region of the spectrum, except for the sample prepared with maleic acid and P-phenylenediamine, which showed emissions in the yellow region of the spectrum. In addition, CDs with QY values equal to or greater than 5% were studied as possible fluorescent nanosensors, and four samples were sensitive and selective to Fe3+ ions, with LOD equal to 0.44 µmol.L-1, 3, 92 µmol.L-1, 0.55 µmol.L-1 and 0.58 µmol.L-1. Furthermore, the nanoparticles used as sensors were obtained with an environmentally friendly strategy, and the CD-based photoluminescence method is simple, has a short response time and has a low cost.