Integrative engineering of biomass-derived CQDs for enhancing photosynthesis of microalgae coupled with bioethanol production.

Carbon quantum dots (CQDs), a novel type of fluorescent carbon-based nanomaterial, hold a promising potential for enhancing photosynthetic efficiency in microalgae. However, the potential of green biomass-derived CQDs for improving photosynthetic efficiency in microalgae has not yet been fully explored, and their mechanism remains insufficiently understood. In this study, CQDs synthesized from S. alterniflora via a green hydrothermal method were used to cultivate marine microalgae (Chlorella vulgaris and Dunaliella salina), and the incompletely utilized biomass of S. alterniflora can be further employed for bioethanol production. The results showed that CQDs significantly improved the microalgae's resilience to UV radiation and enhanced photosynthesis through improved energy capture, electron transfer, and energy transmission, leading to a 28.82% increase in Chlorella vulgaris biomass and a 20.03% increase in Dunaliella salina. Meanwhile, Lipid accumulation increased by 8.84% and 5.97%, while carbohydrate content increased by 6.09% and 9.79%. Transcriptomic analysis also revealed notable expression changes in genes related to photosynthesis and other metabolic pathways. Additionally, the cellulose-rich residues of S. alterniflora after hydrothermal treatment exhibited high saccharification efficiency with ethanol production increasing by 6.47%. This research holds considerable significance for advancing the application of biomass-derived carbon quantum dots in the carbon fixation of microalgae and for resource utilization of the invasive plant species S. alterniflora.