<p>In this study, lignin-based carbon quantum dots (CQDs) were prepared by a one-step hydrothermal method using alkaline lignin as the carbon source and then further combined with ZnIn₂S₄ photocatalyst to construct a series of CQDs-X/ZnIn₂S₄ composite photocatalyst. The experimental results indicated that when the loading amount of CQDs was 20&#xa0;mL, the composite material exhibited the best photocatalytic hydrogen production performance. Structural characterization revealed that CQDs with a size of 4–6&#xa0;nm were successfully modified on the surface of flower-like ZnIn₂S₄ photocatalyst microspheres assembled by nanosheets, forming a tight heterostructure. Optical and electrochemical tests confirmed that the introduction of CQDs effectively broadened the light absorption range, adjusted the band structure and significantly promoted the separation and transfer of photogenerated carriers, while reducing the charge recombination rate. In addition, compared with pure ZnIn₂S₄ (48.18 m²·g⁻¹), CQDs-20/ZnIn₂S₄ has a relatively larger specific surface of 79.33 m²·g⁻¹, providing more active sites. This study demonstrated that the composite strategy based on lignin CQDs could significantly enhance the photocatalytic performance of ZnIn₂S₄ photocatalyst, providing an effective approach for the high-value utilization of lignin and solar hydrogen production.</p>