Preparation of lignin-based full-color carbon quantum dots and their multifunctionalization with waterborne polyurethanes.

Lignin is an excellent choice for energy transition and high-value utilization due to its low cost, non-toxicity, renewability, and widespread availability. However, its complex structure has hindered its development. Waterborne polyurethane (WPU) uses water as a dispersion medium, making it safer for humans and the environment, but it also has some drawbacks. In this study, we prepared multicolored photoluminescent carbon quantum dots (CQDs) with a range of wavelengths, using lignin. We successfully created panchromatic CQDs by additive mixing. Red-shifting of the emission wavelengths was attributed to the synergistic effects of the sp2 conjugate size and the carbonyl group, amide. Solid-state luminescence based on full-color CQDs was successfully achieved, and most importantly, the application of full-color CQDs in light-emitting diodes (LEDs) was realized; On the other hand, the embedding of multicolor CQDs in WPU not only makes WPU luminescent, but also improves the water-resistance and mechanical properties of WPUs dramatically based on hydrogen-bonding interactions between the functional groups on the surface of the CQDs and the urethane. We investigated the UV and strong blue light shielding ability of WPU/Y-CQDs films, which significantly improved due to the unique absorption peaks of Y-CQDs in the UV region and the strong blue light region. This work provides a reference for the high-value utilization of biomass materials and shows the direction for the multifunctional application of WPU.