Facile synthesis of two ionized fluorescent carbon dots and selective detection toward Fe2+ and Cu2+

In this paper, facile synthesis of two ionized carbon dots (CDs-2 and CDs-3) is reported, in which different ionic pairs are formed at the surface of carbon core. Different with CDs-3, it is clear to observe the accumulational carbon core in TEM of CDs-2 due to the linkage of dibromine alkyl. Compared with naked CDs in the absence of ionic pair, the maximum emission wavelength undergoes a red-shift of nearly 60 nm. And protic solvents (water, ethanol and N,N’-dimethyl formamide) have apparent effect on the emission intensity of CDs-2 and CDs-3. The time-resolved average lifetimes of CDs-2 and CDs-3 are calculated as 56.34 ns and 54.50 ns, respectively. Furthermore, they both have much better fluorescent stability in the solution with pH ranging from 2 to 11 due to presence of imidazolium cation. It is interesting to see that CDs-2 and CDs-3 have much different responses towards Cu2+ and Fe2+. The CDs-3 solution generates clear fluorescence quenching when treated with Fe2+. In brief, we believe that these findings can inspire more research development in the synthesis and further application of functional CDs.