Facilely prepared N-modified carbon quantum dots as microalgal photosynthesis promoters for wastewater treatment

Microalgae-based wastewater treatment integrates wastewater purification with bioenergy recovery, aligning with the principles of the circular bioeconomy. However, the limited utilization of the solar spectrum by microalgae and light attenuation caused by wastewater turbidity constrain microalgal growth. To address these challenges, this study synthesized nitrogen-doped carbon quantum dots (N-CQDs) with down-conversion properties that convert UV light (∼380 nm) from the solar spectrum into blue light (450-475 nm) useable by microalgae, thereby enhancing their solar energy utilization efficiency. Under illumination, N-CQDs significantly enhanced Chlorella sorokiniana growth, photosynthetic pigment accumulation, and nutrient removal efficiency, likely by augmenting microalgal photosynthesis through extracellular light conversion and improved intracellular electron transport. Transcriptomic analysis indicates that N-CQDs enrich pathways related to chlorophyll synthesis and stress resistance. Finally, N-CQDs show great potential in treating real pig farm wastewater, highlighting the role of nanomaterials in enhancing microalgae growth and photosynthesis.