Facile ionic-liquid-assisted electrochemical synthesis of size-controlled carbon quantum dots by tuning applied voltages

Carbon quantum dots (CQDs) were prepared by electrochemical ablation of graphite rods in a mixture of water and ionic liquid as electrolyte. Size-controlled CQDs were achieved by changing the voltages applied to the electrodes and the forming mechanism is also discussed in this paper. Monodisperse and spherical CQDs with sizes of 2.9, 4.4 and 6.6 nm were obtained at voltages of 9, 15 and 30 V, respectively. The obtained aqueous solution of CQDs exhibited dependence of excitation-wavelength on size in photoluminescence spectra, and these phenomenona might be caused by the surface energy traps from passivation of the ionic liquid. The UV-vis absorption spectra of CQDs with similar shape and different intensities may be caused by the change of size.