γ-Valerolactone/H2O Binary Solvent for One-Pot Preparation and Functional Tailoring of Lignin-Based Carbon Dots

Lignin-based carbon dots (LCDs) have attracted increasing attention, but their limited regulation and the use of harmful chemicals in their preparation have hindered their applications. In this study, we successfully produced LCDs by heating lignin dissolved in a green solvent system, a binary solvent of γ-valerolactone (GVL) and water. Furthermore, we were able to easily regulate the fluorescence properties of the LCDs by adding environmentally friendly chemicals, such as urea and citric acid, to the lignin solution. As a result, the emitting fluorescence of the LCDs was shifted from blue light to yellow, and their fluorescence performances were significantly improved with a maximum relative quantum yield of 33.2%. In addition, we generated LCD-loaded lignin nanoparticles (LNPs) with a size of ∼200 nm in situ via solvent shifting. This simple method of producing LCDs or LCD-loaded LNPs can endow them with versatile functions and wide applications.