High green-emission carbon dots and its optical properties: Microwave power effect

Abstract

The nature of carbon quantum dot (CD) luminescence is still broadly investigated based on different CD synthesis processes. This study aims at investigating the effect of microwave power on optical characteristics of CDs using microwave radiation techniques. CDs are synthesized with citric acid as a source of carbon and urea as a passivation agent. CDs have been successfully synthesized, and an increase in the CD burn-off percentage was observed with an increase in the microwave power. The TEM test results show that the dimensions of the CDs resulted are in the range of 3.4–9.5 nm with an average size of 6 nm at 450 W. The results of the FTIR functional group structural analysis show that a CD has N—H and O—H stretching bonds. According to the results of UV–Vis analysis, the CDs have absorption peaks at 335 nm and 407 nm, which indicates a π → π* electronic transition from the C=C bond and an n → π* transition from the C=O bond. Using the Tauc-plot method, the CD energy bandgap values were found to be 2.47 eV, 2.51 eV, 2.51 eV, 2.52 eV, and 2.53 eV at CD 300, CD 450, CD 600, CD 850, and CD 1000, respectively. The optical multichannel analyzer test results show that the peak emission waves produced by CDs are 536 nm and 532 nm with the strongest bright green light at CD 1000. Time-resolved photoluminescence testing shows that the CD decay time generally ranges from 5 ns. Overall, an increase in the microwave power causes an increase in the percentage of burn-off, energy bandgap, absorption intensity, and CD emission intensity.

Optical properties and photoactivity of carbon nanodots synthesized from olive solid wastes at different carbonization temperatures

“…The bandgap for the synthesized CNDs (CD300-CD600) has been estimated as shown in Fig.S6† and the results are 2.77, 2.65, 2.51, and 2.46 eV, respectively. The values of the energy bandgap for the synthesized CNDs from 2.46 to 2.77 eV are in the visible region and are consistent with other studies showing C-dots with values in the range of 1.5-3.5 eV 4,62. The carbon dots synthesized from carbonized olive solid wastes at 300 C (named CD300) show the highest energy bandgap of 2.77 eV, and this high value compared to the other CNDs (CD400, CD500, and CD600) could be attributed to the existence of oxygenated groups such as C]O, C-O-C,…”

“…Light exposure can generate electrons and holes during photocatalysis. 61 CNDs with an energy bandgap between 1.5–3.5 eV 62 are considered semiconductors with high visible-light absorption and excellent light-trapping ability, generating electron–hole pairs that are needed for photocatalysis and the degradation of organic dyes.…”

Broad-Spectrum Antibacterial Activity of Synthesized Carbon Nanodots from d-Glucose

“…This value matches well with other semiconducting CNDs as reported in previous research. 57 The higher value of bandgap for R300 could be attributed to the highest electron withdrawing charge capacity gained due to the presence of oxygen groups such as C=O, C−O−C, and C−OH on the surface. 58 Furthermore, the CNDs synthesized in the presence of NH 4 OH (named RA300) presented a lower band gap (of about 0.25 eV, see Figure 6c).…”

A Novel Surfactant Sensitized Fluorescent Sensor for Co(II) Based on Nitrogen Doped Carbon Quantum Dots

“…The reason might be that the reaction time was too short or the microwave power was too low, which resulted in a decrease in the N-CDs crystal number and insufficient crystal nucleus growth. If the reaction time was too long or the microwave power was too high, N-CDs might easily produce large particles, which would also lead to the uneven particle size of N-CDs, resulting in a decrease in the Φ of N-CDs [28].…”