The effect of hydrothermal temperature and time of urea-doping on the optical properties of lemongrass-based carbon dots

CDs sourced from spiced lemongrass have been produced by hydrothermal method at hydrothermal temperatures of 120 ℃, 140 ℃, 160 ℃ and 180 ℃. The addition of urea as a nitrogen source was carried out in the synthesis of carbon nanoparticles at a hydrothermal temperature of 180 ℃ for two hours and three hours to see the effect on the optical properties of the CDs. The addition of urea gave a different effect on the two CDs. But the energy band gap (Eg) of the two becomes narrower. For two hours of hydrothermal duration, the addition of urea showed a significant increase in absorbance, but a decrease in fluorescence intensity, whereas for three hours, it resulted in an increase in fluorescence intensity. The results of measuring the size distribution of carbon nanoparticles showed a peak value of 52.32 nm. Functional group analysis using the FTIR spectrometer showed that the carbon nanoparticles consisted of C=C, C-O, O-H, 𝐶-N-𝐶 bonds. Urbach energy (Eu) increases with increasing hydrothermal synthesis temperature at 2 hours and 3 hours. The decrease and increase in the Urbach energy (Eu) is caused by the increasing regularity of the hydrothermal temperature as a result of the synthesis time so that the structure of the CDs becomes more stable and homogeneous.