Green synthesis of Spirulina-based carbon dots for stimulating agricultural plant growth

In this study, photoluminescent carbon quantum dots (CQDs) were synthesized by thermal pyrolysis of the microalgae spirulina without any surface passivating agent. The CQDs showed ~10 nm average size and exhibited blue photoluminescence emission around 450 nm under 340–400 nm excitation wavelength. A quantum yield of 23.5% was attained at 300 °C for 2 h. Thermodynamic and kinetic investigations about pyrolysis reaction showed that CQDs synthesis occurs slowly and non-spontaneously, with a mean activation energy of 192.6 kJ/mol. The final product showed a broad range of solubility, besides being efficient for lentil seed growth when dispersed in 0.05–0.1 mg/mL aqueous solutions. The CQDs reported here may be considered a promising renewable bio-based fertilizer for crop species in the sustainable agriculture field.