Cellulose Nanofiber/Polyvinyl Alcohol-Based pH-Responsive Films Containing Anthocyanin and Carbon Dots

Environment-responsive fluorescent materials have been widely studied in the determination and utilization of different environmental factors. Particularly, it is still challenging to develop multifunctional environment-friendly pH-responsive fluorescent materials based on biomass and renewable polymers. In this study, a pH-responsive intelligent color-changing fluorescent film based on cellulose nanofibers (CNFs)/polyvinyl alcohol (PVA) incorporated with anthocyanin (Ant) extracted from the Lycium ruthenicum fruit and amino-functionalized carbon dots (CO-CDs) was prepared. Due to the influence of Ant and CO-CDs, the mechanical properties, oxidation resistance, and UV resistance are obviously promoted. Under different pH conditions, the composite film exhibits obvious pH-dependent color change and fluorescence color change. Its fluorescence intensity ratio (F550/F450) varies linearly with pH at 1–6 and 6–13. Thereby, qualitative and quantitative perception of environmental pH change can be realized by using the composite film. In food trial, with the extension of shrimp storage time, both the visual color and fluorescence emission color of the film change evidently. The film can delay deterioration. The Ant/CO-CDs/CNF-PVA film, as a pH-responsive smart color-changing fluorescent film, has a potential application value in the fields of intelligent packaging, agriculture, and pH sensing.