Pontos quânticos de carbono incorporados à mantas nanofibrosas poliméricas

Abstract

This work presents the development and characterization of polymeric nanofibrous mats made of polystyrene in its crystal (PS) and expanded (EPS) forms, functionalized with carbon quantum dots (CQDs) for potential application in sensors. The CQDs were synthesized from citric acid through thermal carbonization. In this method, citric acid is carbonized and poured into solvents or solvent mixtures. Ethanol and two ethanol–chloroform mixtures (50% v/v and 5% v/v) were used. The CQDs were evaluated based on their optical absorption and emission properties. A shift in the ab- sorption of the samples produced with the 50% v/v ethanol–chloroform mixture was observed. As for the emission, no difference in the wavelength was noted. This absorption shift resulted in lower Stokes shift values. The fibers containing carbon quantum dots were produced using the Solution Blow Spinning (SBS) technique, resulting in fibrous mats with average diameters (XC) ranging from 1.75 to 1.44 μm. Regarding the Raman spectroscopy results, the fibers exhibited typical cha- racteristics of PS and EPS, suggesting that the technique did not affect the chemical structure of the polymers used. Micrographs showed fibers with varied orientations and surface morphology featuring porosity and roughness, which may indicate potential application in sensors. The pre- sence of CQDs led to a reduction in the (XC) values and in the dispersion of diameters (FWHM), suggesting greater dimensional uniformity of the fibers. Fluorescence microscopy confirmed the presence of CQDs. Impedance analysis showed that the nanofibrous mats exhibit predominantly capacitive behavior, with dielectric differences between PS and EPS. In PS, the addition of CQDs increased the real dielectric constant (ε’), especially in sample PS-2. In EPS, although the pure material presented higher capacitance, the CQDs modified the mechanisms of interfacial polariza- tion and dielectric relaxation, with sample EPS-2 standing out at high frequencies. Additionally, the use of recycled EPS as a polymer matrix reinforces the project’s sustainability approach by promoting reuse and adding value to low-cost waste materials. Thus, the nanocomposites develo- ped in this study show promise for application in capacitive sensors, combining favorable dielectric performance, fluorescence properties, and environmental relevance.