New insights into the mechanisms of biomass-derived carbon quantum dots for photocatalytic disinfection

As a potential substitute for photo-disinfection reagents in water treatment, cost-effective and eco-friendly carbon quantum dots (CQDs) have recently attracted significant interest. However, the photo-disinfection mechanism of CQDs remains insufficiently explored. In this study, we focus on two typical nitrogen-containing CQDs (NCQDs) derived from common biomass substrates, namely citric acid and sucrose, to examine their differences in disinfection mechanisms by carefully analyzing their surface chemistry, light absorption/photoluminescence properties, and reactive oxygen species (ROS) generation. Our findings reveal that the photo-disinfection effects of the two NCQDs are driven by different ROS, resulting from their distinct chemical structures. In contrast to citric acid-derived NCQDs, which generate superoxide anions (O₂^•-) that cause self-structural changes and significant disinfection deterioration, sucrose-derived NCQDs are a more stable option for photo-disinfection, as they primarily produce singlet oxygen (¹O₂), which is effective in killing bacteria while exerting minimal impact on the carbon structure. Sucrose-derived NCQDs were also identified as the primary contributors to photo-disinfection in both powdered and membrane-based composites containing graphene oxide. These results highlight the importance of understanding the underlying mechanisms and considering the stability of different CQDs when evaluating their potential for photo-disinfection applications.