Preparation And Properties Of Full-color-emission Carbon Quantum Dots

Carbon quantum dots（CQDs）have been attracted increasing great attention from researchers at home and abroad due to the unique properties,such as the excellent water solubility,good optical stability and biocompatibility,low cost and toxicity,easy functionalization and so on.However,there are still many challenges in CQDs research,including the lack of a clear explanation of the structure and fluorescence source,broad fluorescence emission peak and relatively low quantum yield in long wavelengths emission,which still limit the further application.In this work,CQDs were synthesized by a one-step solvent method.Firstly,the effects of carbon source,reaction temperature and p H value on the luminescence properties of CQDs were studied.What’s more,the luminescence mechanism of CQDs was discussed based on the structure and performance analysis results of full-color CQDs synthesized by different solvents.Finally,to expand application areas,the electrochemical properties were further explored by combining it with electrode materials.The main research contents and results are as follows:（1）The CQDs with different luminescent properties were obtained by using three phenylenediamines isomers as carbon source and phosphorus acid as auxiliary acid,by a one-step hydrothermal method.In addition,the effect of reaction temperature and ambient p H on the performance of CQDs are systematically researched in the hydrothermal process.The results show that the CQDs exhibited a dual emission behavior and excellent luminescent properties.Furthermore,it can be included that the tunable optical properties of CQDs can be achieved due to the higher temperature and the smaller p H,which will promote the long wavelength emission.（2）The full-color-emission CQDs were successfully obtained by a simple one-step solvent engineering strategy,utilizing the m-phenylenediamines as carbon source and phosphorus acid as auxiliary acid.Then,the luminescence mechanism is elucidated in detail.The results show that these CQDs can emit bright and stable light under a UV light.Moreover,the redshifted emission of the CQDs samples are ascribed to the synergistic effect of the contents of sp²-hybridized domains,surface C=O and the pyridinic N but not the particle size.（3）Ni S-CQDs（CTAB）were rationally designed and successfully synthesized using the nickel sulfide（Ni S）nanocrystals decorated with green fluorescent CQDs obtained in（2）and the hexadecyl trimethyl ammonium bromide（CTAB）as the adjuvant,by a hydrothermal method.As supercapacitor electrode material,the resulting nonomaterials of Ni S-CQDs（CTAB）exhibited a high specific capacitance of 1956 F/g at a current density of 1 A g^-1 and a remarkable rate capability of 57%at 8 A g^-1,much higher than that of the Ni S,Ni S-CQDs and Ni S（CTAB）samples.The enhanced electrochemical performance of Ni S-CQDs（CTAB）eletrode should be ascribed to the synergistic effect with the introduction of CQDs and CTAB as a bridge.