Green synthesis of carbon quantum dots from Phragmites communis and its protective effect on Artemia salina under copper stress

Carbon quantum dots (CQD) and Nitrogen-doped CQDs (N-CQDs) were synthesized through a one-step hydrothermal process, utilizing reed leaves and urea as carbon and nitrogen sources, respectively. The maximum excitation wavelength of CQDs and N2-CQDs was 325 nm, and the corresponding emission wavelength was 407 nm and 406 nm, respectively. Synthetic CQDs have excellent fluorescence properties, while N-doping enhances the fluorescence intensity and stability of CQDs. Next, the adsorption effect of N2-CQDs on various metal ions was also studied using the fluorescence quenching method. The results showed that N2-CQDs have a significant capacity for adsorption of Cu2+ ions. The following quantitative analysis indicated that the Cu2+ concentration showed an excellent linear relationship between 0 ~ 500 µmol/L and the limit of detection (LOD) was 0.074 µmol/L. The N2-CQDs at 0-200 µg/mL have no deleterious effects on the viability of HeLa cells and the survival rate of Artemia nauplii. Finally, the agarose gel containing N2-CQDs was constructed, and its absorption behavior of Cu2+ in artificial seawater was evaluated. The results showed that this N2-CQDs-based gel was able to efficiently remove Cu2+ from seawater, leading to a higher survival rate of the nauplii under 10 and 50 mg/L Cu2+ stress. Our results collectively provide a cost-effective method for removing heavy metal ions from seawater and mitigating their harmful effects on sea animals.