Water-Resistant, Luminescent Reversible, and pH-Responsive Holocellulose Films Decorated by Carbon Quantum Dots from <i>Camellia oleifera</i> Shells
Abstract
Abstract Lignocellulosic residues, particularly those with a high hemicellulose content, represent a hitherto underutilized resource for the production of functional materials. Camellia oleifera shells (COS) have been identified as a potentially valuable feedstock for the production of value-added materials. In this study, carbon quantum dots (CQDs) were synthesized efficiently from COS holocellulose (COSH) by a microwave-assisted method using urea and malic acid as auxiliary reagents. The obtained carbon quantum dots (CQDs) exhibited uniform particle sizes (3–5 nm), clear lattice fringes, and abundant surface functional groups, together contributing to pronounced pH-dependent fluorescence behavior. Meanwhile, the preparation of biodegradable regenerated COSH films (rCF) involved the dissolution and regeneration of COSH in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). The incorporation of 2 wt % ascorbic acid during the dissolution process has been shown to effectively mitigate thermo-oxidative degradation, thereby facilitating the regeneration of films that exhibit enhanced crystallinity, a more compact structure, and augmented mechanical strength (up to 92.19 MPa). The anchoring of CQDs onto rCF resulted in the fabrication of a flexible and fully biodegradable pH-responsive composite film. The resulting CQD-loaded regenerated COSH film (C-rCF) exhibited rapid, reversible, and visually distinguishable fluorescence changes over a pH range of 3–11. This study provides an efficient and environmentally friendly route for converting agricultural waste into functional holocellulose-based materials, offering a basis for the development of a biodegradable fluorescent composite film.