Graphitic Carbon Nitride-Reinforced Chitosan/Ca²⁺-Alginate Nanocomposite Films with Multifunctional Properties for Sustainable Packaging

This study presents the synthesis and characterization of Ca 2 + -cross-linked alginate (ALG), chitosan (CHT), and g-C 3 N 4 -based ternary composites for multifunctional applications. The electrostatic interactions between ALG and CHT, combined with the ionic interaction of Ca 2+ with ALG, significantly enhanced the composite properties. Furthermore, incorporation of g-C 3 N 4 into the ALG/CHT matrix resulted in a uniform dispersion in the ALG/g-C 3 N 4 /CHT composite, as confirmed by morphological analysis, due to strong hydrogen bonding among the components. The resulting composite exhibited improved water vapor barrier, mechanical strength, and antimicrobial activity. Specifically, the ALG/g-C 3 N 4 /CHT composite (with g-C 3 N 4 loading 1.33%) achieved a tensile strength of 88.4 MPa and a Young’s modulus of 1.6 GPa, representing increases of 19.4 and 100.6% over pure ALG and CHT films, respectively. The UV shielding performance of the ALG/g-C 3 N 4 /CHT composite film was exceptional, providing exceptional UV protection across the entire UV spectrum (100–400 nm), with blocking efficiencies of 97.9% (UV-A), 98.2% (UV-B), and 99.7% (UV-C). Additionally, water vapor permeability of the ALG/g-C 3 N 4 /CHT composite film decreased by 79 and 92% compared to those of CHT and ALG films. The composite also demonstrated high antibacterial activity against Staphylococcus aureus (97.7%) and Escherichia coli (98.2%), along with a radical scavenging activity of 61%. These outstanding multifunctional properties highlight the potential of this ternary composite as a sustainable alternative to conventional petroleum-based packaging materials.