Starch-based biopolymer films with nitrogen-doped carbon quantum dots for enhanced barrier functions via surface microarchitectures

This study presents the development of multifunctional starch-based biopolymer films reinforced with nitrogen-doped carbon quantum dots (N-CQDs), synthesized via a hydrothermal method, and exhibiting a high quantum yield (∼70 %). N-CQDs were incorporated into the starch matrix at varying concentrations (0.1–1.0 wt%), significantly influencing the structural, morphological, and functional properties of the films. Comprehensive analyses confirmed successful nitrogen doping, uniform dispersion, and strong interfacial interactions with the polymer network. TEM revealed well-dispersed spherical N-CQDs with a mean diameter of 5.2 nm, whereas XRD indicated their role as nucleation agents that promote crystallinity through starch retrogradation. Cross-sectional SEM imaging further demonstrated the formation of dense and tortuous microarchitectures. This structural reorganization resulted in a significant enhancement of the barrier function, as evidenced by an approximately 70 % reduction in water vapor permeability and decreased water solubility, thereby improving long-term stability. The films also exhibited outstanding ultraviolet (UV) shielding, blocking over 84 % of UV-B and 88 % of UV-A radiation while maintaining visible transparency. Mechanically, the N-CQDs induced a brittle-to-ductile transition, improving the flexibility by up to 35 % without compromising the tensile integrity. Overall, these findings highlight the potential of N-CQDs as multifunctional nanofillers for the development of biodegradable films with superior barrier, optical, and mechanical properties for sustainable packaging applications.