Probing the food packaging applications of green carbon quantum dots

Abstract

Carbon quantum dots (CQDs) have emerged as promising nanomaterials due to their low toxicity, high aqueous solubility, high electrical conductivity, and remarkable fluorescence properties. Their tunable emission, high intensity, biocompatibility, and ability to enhance mechanical, thermal, barrier, antioxidant, and antimicrobial properties make CQDs ideal for diverse applications, including innovative food packaging. This study explores the green synthesis of CQDs from agricultural waste fibres, namely jute, coconut husk, banana, and water hyacinth, designated as CQD1, CQD2, CQD3, and CQD4, respectively. The CQDs were embedded into a polyvinyl alcohol (PVA) matrix to fabricate composite films S1, S2, S3, and S4, which were extensively characterized for their physicochemical and functional properties. Mechanical analysis revealed significant improvements in the tensile strength and elongation at break of all composite films, particularly for the S4 film, which increased to 1.72 ± 0.002 MPa and 223.8 ± 0.535 %, respectively, compared to the pure PVA film (1.00 ± 0.007 Mpa and 111.70 ± 0.433 %). Water barrier properties were enhanced, with the S4 film exhibiting the lowest swelling index (47.28 ± 0.022 %) and solubility (30.52 ± 0.042 %) compared to pure PVA (77.89 ± 0.058 % and 65.76 ± 0.045 %, respectively). Gas barrier properties were significantly improved, with the S1 film reducing oxygen permeability (OP) by 36.44 % (2.18 ± 0.023 cm³ m⁻¹ 24 h⁻¹ atm⁻¹) and the S4 film exhibiting the lowest water vapor transmission rate (WVTR) of 95.11 ± 0.029 g m⁻² h⁻¹. The UV-blocking efficacy of all films exceeded 89 %, with S4 achieving 92.55 %. Antimicrobial assays demonstrated that S1 and S2 effectively inhibited Bacillus cereus and Salmonella typhi. Additionally, all films exhibited biofilm inhibitory activity, with S4 showing 100 % inhibition against Escherichia coli and Staphylococcus aureus. In food packaging evaluations, the S3 and S4 films extended the shelf life of plums and bananas by up to 15 and 6 days, respectively, by reducing spoilage. Cytotoxicity studies using the MTT assay revealed that S3 and S4 films had IC₅₀ values of 279.5 μg/mL and 260.35 μg/mL, respectively, indicating low cytotoxicity and excellent biocompatibility. These findings highlight the potential of CQDs derived from agricultural waste fibres as sustainable additives with multifunctional properties, making them promising materials for active food packaging applications.