Influência da cinética de secagem na obtenção de pontos de carbono a partir da casca da banana prata (Musa acuminata Cavendish).

Abstract

Quantum dots are nanoscale materials with remarkable electronic and optical properties. However, a portion of them is synthesized from toxic materials, which limits their usage. Carbon dots emerge as substitutes since they can be obtained from carbonaceous materials, which are not only abundant but also inexpensive. An alternative source for obtaining carbon dots is the peel of the chunkey banana (Musa acuminate Cavendish), which contributes to the environment with the disposal of approximately 36 million tons per year, while having almost negligible reutilization, resulting in ecological imbalance. In light of this, with the aim of repurposing this residual biomass and consequently reducing environmental impact, the objective of this study was to assess the influence of drying kinetics on the production of carbon dots from chunkey banana peels. The process was conducted at a fixed temperature of 60°C, varying the drying time between 6, 12, and 24 hours. After drying, the samples underwent grinding, sieving, and the synthesis of carbon dots through hydrothermal reaction and muffle furnace carbonization. This was followed by centrifugation, filtration, and, ultimately, analyses including comparison, using both white LED and ultraviolet black light incidence, as well as characterization through spectroscopies and microscopy. The drying kinetics curves indicated the presence of 88% moisture and that the second period of the decreasing rate was predominant for all three drying times. In the evaluation through comparison, the samples progressed to lighter tones, with those obtained via hydrothermal synthesis doing so subtly, and those via carbonization doing so abruptly. Additionally, all samples exhibited photoluminescence. In the characterization analysis, absorption spectroscopy indicated significant differences between synthesis routes, but minimal differences regarding drying time. Emission spectroscopy pointed to a shift in the emission curve when exposed to different excitation wavelengths, with significant influence from both synthesis routes and drying time. Fourier-transform infrared spectroscopy led to the conclusion that the samples possess similar functional groups adhered to their surfaces. Finally, transmission electron microscopy exhibited globular points at scales close to 5 nm, which align with the morphology of carbon dots.