(251u) Synthesis, Purification, and Capillary Electrophoretic Separation of Fluorescent Carbon Nanodots

Fluorescent carbon nanodots (C-dots) have drawn considerable attention in recent years. C-dots are carbon nanoparticles with typical sizes of < 10 nm and have been reported to have excellent characteristics (e.g., low cost, colloidal stability, upconversion photoluminescence, reduced cytotoxicity, very good biocompatibility) that make them promising candidates for a wide range of applications, such as bioimaging, biolabeling, fluorescent ink, photocatalysis, and optoelectronic devices [1]. After the discovery of C-dots [2], much research efforts have focused on developing better synthetic routes to obtain C-dots with relatively high quantum yield (QY). Certainly, numerous synthetic methods have been developed, and fluorescent products with relatively high QY have been reported. However, the purification of the fluorescent products is often neglected and it is difficult to discern if indeed the reported photoluminescence is the result of C-dos or other potential molecular species that can be byproducts of the synthetic route. Therefore, one must ask: are all the photoluminescent species in the synthetic product C-dots? Are the commonly used purification methods good enough to completely isolate the C-dots from potential small fluorescent molecules?

In addressing these questions, we are investigating how the purification process affects the purity of fluorescent C-dots. We have used one of the most commonly reported approaches to synthesize C-dots, namely the hydrothermal treatment of simple molecular precursors. We used citric acid and 1,2-ethylenediamine as the molecular precursors in the production of C-dots. The as-synthesized fluorescent product was purified by the most commonly used purification method reported in the literature; that is the dialysis against pure water [3,4]. The fluorescent products inside the dialysis membrane (retentate) and that outside the membrane (permeate) were collected at different time intervals during the dialysis process that proceeded for several days. The QY of each sample was determined. In addition, the samples were analyzed via capillary electrophoretic (CE) and laser induced fluorescence (LIF). The CE separations showed variation in complexity of retentate and permeate during the dialysis process and the QY was also different. The details of our experiments and findings will be the focus of this presentation.

References

1. Baker, S. N.; Baker, G. A. Angew. Chem., Int. Ed. 2010, 49, 6726-6744.
2. Xu, X. Y.; Ray, R.; Gu, Y. L.; Ploehn, H. J.; Gearheart, L.; Raker, K.; Scrivens, W. A.; J. Am. Chem. Soc. 2004, 126, 12736-12737.
3. Zhu, S.; Meng, Q.; Wang, L.; Zhang, J.; Song, Y.; Jin, H.; Zhang, K.; Sun, H.; Wang, H.; Yang, B. Angew. Chem., Int. Ed. 2013, 52, 3953-3957
4. Zhai, X.; Zhang, P.; Liu, C.; Bai, T.; Li, W.; Dai, L.; Liu, W. Chem. Commun. 2012, 48, 7955-7957.