Incorporation of nitrogen-doped carbon dots synthesized from pomelo peels into poly(vinyl alcohol) as highly antioxidant and ultraviolet-blocking food packaging film

Nitrogen-doped carbon dots (CDs) with sizes of 5–12 nm were synthesized via a facile hydrothermal method at 200°C for 12 h, using the albedo portion of pomelo peel waste as the carbon source and urea as the nitrogen dopant. Increasing the amount of urea (0.0–2.0 g) produced CDs with higher nitrogen-doping levels, leading to a blue shift in the absorption spectra, enhanced fluorescence intensity and an increase in zeta potential from −1.41 to −32.1 mV. The average quantum yield of the N-doped CDs was 43% higher than that of the undoped CDs (5.91% versus 4.12%). The effects of the CD types and contents on poly(vinyl alcohol) (PVA)-based films were investigated. A film containing 5% CDs synthesized with the addition of 1.0 g of urea showed a 26% increase in tensile strength, a 13.9% reduction in water swelling, a 26.5% decrease in water vapour transmission rate, and improved thermal stability compared with the pristine PVA film. Furthermore, the film incorporating N-doped CDs exhibited strong antioxidant activity, achieving up to 87% scavenging of 2,2-diphenyl-1-picrylhydrazyl radicals and superior ultraviolet (UV)-shielding performance (approx. 100% for UVB/UVC and >84% for UVA). Consequently, the composite film significantly outperformed commercial polyethylene film in extending the shelf-life of green plums under UV exposure, highlighting its potential as an antioxidant and UV-blocking material for active food packaging.