One-pot microwave-assisted synthesis of fluorescent carbon dots from tomato industry residues with antioxidant and antibacterial activities

Barata, Patrícia; Costa, Alexandra; Martins, Sónia; Semedo, Magda; Prata, José Virgílio

http://hdl.handle.net/10400.21/21970

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Abstract(s)

Tomato waste (TW) was employed as a sustainable source for the synthesis of fluorescent carbon dots (CDs) via a microwave-assisted hydrothermal carbonization (Mw-HTC) method, aiming at its valorization. Several amines were used as nitrogen additives to enhance the fluorescence quantum yield (QY) of CDs, and a set of reaction conditions, including additive/TW mass ratio (0.04–0.32), dwell time (15–60 min), and temperature (200–230 °C) of the HTC process, were scrutinized. The structural analysis of the tomato waste carbon dots (TWCDs) was undertaken by FTIR and 1H NMR techniques, revealing their most relevant features. In solid state, transmission electron microscopy (TEM) analysis showed the presence of nearly spherical nanoparticles with an average lateral size of 8.1 nm. Likewise, the topographical assessment by atomic force microscopy (AFM) also indicated particles’ heights between 3 and 10 nm. Their photophysical properties, revealed by UV–Vis, steady-state, and time-resolved fluorescence spectroscopies, are fully discussed. Higher photoluminescent quantum yields (up to 0.08) were attained when the biomass residues were mixed with organic aliphatic amines during the Mw-HTC process. Emission tunability is a characteristic feature of these CDs, which display an intensity average fluorescence lifetime of 8 ns. The new TWCDs demonstrated good antioxidant properties by the ABTS radical cation method (75% inhibition at TWCDs’ concentration of 5 mg/mL), which proved to be related to the dwell time used in the CDs synthesis. Moreover, the synthesized TWCDs suppressed the growth of Escherichia coli and Staphylococcus aureus at concentrations higher than 2000 μg/mL, encouraging future antibacterial applications.

Keywords

Carbon dots Tomato waste Valorization Hydrothermal carbonization Microwave-assisted synthesis Fluorescence Antioxidant capacity Antibacterial activity

URI

http://hdl.handle.net/10400.21/21970

Citation

Barata, P. D., Costa, A. I., Martins, S., Semedo, M. C., Antunes, B. G. & Prata, J. V. (2025). One-pot microwave-assisted synthesis of fluorescent carbon dots from tomato industry residues with antioxidant and antibacterial activities. Biomass, 5(2), 1-19. https://doi.org/10.3390/biomass5020035