Inactivation of Microcystis aeruginosa and degradation of microcystin by urea-derived carbon dots

Harmful algal blooms and microcystin (MC-LR) are threats to fresh aquatic environments and even human health. Herein, the urea-derived carbon dots (UDs) prepared by hydrothermal method have the small size and good fluorescence properties. Compared with nitrate nitrogen and control, UDs (N content: 10 mg/L) could significantly inhibit the growth of Microcystis aeruginosa, with a growth inhibition rate of 78.6 %. Furthermore, UDs could also degrade MC-LR, achieving a degradation rate of 97.7 % after 96 h of illumination. The heteroaggregation between UDs and algae on the surface of algal cells can block the absorption and utilization of light energy by algal cells, thereby reducing the synthesis of chlorophyll. UDs can also serve as a photocatalyst for the generation of free radicals (O-2(-), center dot OH), leading to cell membrane damage and inhibition of algal cell growth. Besides, O-2(-) and center dot OH are capable of attacking the C4-C5 and C6-C7 bonds present in Adda-amino acids, subsequently facilitating the degradation of phycotoxins, ultimately resulting in their decomposition. These findings provide new insights into the application of urea-derived carbon dots in controlling harmful algal blooms and reducing MC-LR.