The influence of precursors on optical properties of carbon nanodots synthesized via hydrothermal carbonization technique

Carbon nanodots (CDs) have drawn much attention due to their potential applications in optoelectronic devices, bioimaging, biosensor, and hole transporting materials for a perovskite solar cell. In this work, CDs were synthesized from natural mono- or disaccharide precursors (glucose, fructose, and sucrose) via a hydrothermal carbonization technique with the addition of ethanol or acetone. Structural and morphology of CDs were investigated using transmission electron microscopy and selected area electron diffraction. The average particle size of CDs was in the range 4.86-9.99 nm. The optical properties of CDs were characterized by UV-Visible spectroscopy and Fluorescence spectroscopy. The absorbance intensity of CDs increased with increasing precursor concentration. In the present work, the influences of precursors with addition of acetone on the optical properties of CDs were investigated and discussed the possible reason. The results revealed the improvement on the absorbance of CDs synthesized using a sucrose precursor. Additionally, the CDs showed the shifted fluorescence peaks when excited at different excitation wavelengths, indicating the excitation wavelength-dependent emission properties of CDs. FTIR spectra show that the CDs surface containing double bonded oxygen functional groups (C=O) formed during the hydrothermal carbonization of fructose and sucrose precursor, which is not found in glucose-derived CDs. Oxidation, reduction potentials and band gaps of CDs were also analyzed using the cyclic voltammograms (CV). The as-prepared CDs in diluted ethanol presented slightly difference of the HOMO and LUMO energy when compared with the CDs synthesized in diluted acetone.