In recent years, lignin has attracted substantial attention from researchers because of its diverse sources, low cost, and renewability. The effective functionalization and enhanced value‐added utilization of lignin have successfully addressed the challenges associated with biomass resource waste, low utilization rate, high material cost, and underwhelming performance in energy, environmental protection, and medical applications. The emergence of lignin carbon quantum dots (LCQDs) has opened new avenues for the development and utilization of lignin by offering exciting opportunities for their applications. LCQDs possess unique characteristics such as fluorescence properties, size effect, surface effect, and interface effects, which are promising for applications in many fields. This paper provides a comprehensive overview of the structure and applications of lignin with a specific focus on the preparation method of LCQDs as well as their various applications in drug delivery systems, electrode material fabrication, and antibacterial agent development. Furthermore, this study offers valuable insights into the prospects of LCQDs and aims to contribute to their functional development. Finally, the challenges associated with leveraging the fluorescence properties of LCQDs are discussed, along with potential directions for future research.

Oxygen delignification presents high efficiency but causes damage to cellulose, therefore leading to an undesired loss in pulp strength. The effect of ionic liquid pretreatment of [BMIM][HSO₄] and [TEA][HSO₄] on oxygen delignification of the eucalyptus kraft pulp was investigated at 10% IL loading and 10% pulp consistency, after which composition analysis, pulp and fiber characterizations, and the mechanism of lignin degradation were carried out. A possible dual effect of enhancing delignification and protecting fibers from oxidation damage occurred simultaneously. The proposed [TEA][HSO₄] pretreatment facilitated lignin removal in oxygen delignification and provided fibers with improved DP, fiber length and width, and curl index, resulting in the enhanced physical strength of pulp. Particularly, its folding endurance improved by 110%. An unusual brightness reduction was identified, followed by detailed characterization on the pulps and extracted lignin with FTIR, UV, XPS, and HSQC. It was proposed that [TEA][HSO₄] catalyzed the cleavage of β-O-4 bonds in lignin during the oxygen delignification, with the formation of Hibbert’s ketones and quinonoid compounds. The decomposed lignin dissolved and migrated to the fiber surface, where they facilitated the access of the oxidation agent and protected the fiber framework from oxidation damage. Therefore, it was concluded that ionic liquid pretreatment has a dual effect on oxygen delignification.