Synthesis Of Highly Luminescent Carbon Quantum Dots And Their Applications

Compared with conventional semiconductor quantum dots and fluorescent dyes, the carbon quantum dots exhibit unique properties such as high fluorescent stability, good biocompatibility, tunable emission, small size and up-conversion fluorescence performance. Based on its unique optical and electrical properties, carbon quantum dots and their composites have been widely applied in many fields, such as catalysis, detection, bioimaging and so on. In this paper, we mainly explored the optical property of CQDs synthesized by the microwave and hydrothermal method, the prepared amino functional CQDs were used for photocatalyst design and heavy metal ion detection.The prepared carbon quantum dots are amorphous carbon structure without complete and continuous crystal structure. The CQDs synthesized by hydrothermal method were well distributed among a narrow range between 2-3 nm without apparent agglomeration. The size of the carbon dots, quantum yields and fluorescence properties prepared by hydrothermal method were superior to microwave method. Carbon dots have strong absorption ability in the ultraviolet area, the absorption band can be extended to the visible light region. CQDs surface contains abundant hydrophilic groups such as hydroxyl and carboxyl, so the CQDs have good water solubility and biocompatibility.The emission wavelength, emission peak intensity and emitting light colors were of a typical wavelength-dependent PL feature. Whether CQDs or N-CQDs have upconversion fluorescence performance. Excited by long-wavelength light?700-900 nm?, it can emit light shorter than the excitation wavelength?350-500 nm?. At the process of amination, the functional groups on the surface of CQDs react with nitrogen source generate the amide and alcohols, such as-OH, NH-R and-CONH, these reduce the nonradiative recombination, the fluorescence properties of N-CQDs are better than the CQDs.Strong oxidizing ions interfer the recombining of electrons and holes, it can promote nonradiative electron-hole recombination annihilation through the effective electron transfer. Weak oxidizing ions interact with some defects and functional group on the surface of the carbon dots, the fluorescence intensity is enhanced. We further explored the use of CQDs as a novel sensing probe for label-free sensitive and selective detection of Fe³⁺, which is based on the fluorescence quenching due to the complex formed by CQDs and Fe³⁺. Based on such excellent upconversion fluorescence performance, the CQDs/Ti O₂ composite photocatalyst were designed and synthesized, it can use a wide spectrum of sunlight?extend to visible light? to photodegrade MB efficiently. Finally, an explanation of such photocatalyst's mechanism.