In this study, fluorescent carbon quantum dots (CQDs) are prepared using a one-step pyrolysis from tobacco wastewater. The TEM, UV-vis, XPS, FT-IR and PL techniques are employed to characterize the morphology, elementary composition and optical properties of these CQDs. It is found
that the CQDs in ethanol solution can achieve strongly the blue light emission under the UV irradiation and the fluorescence quantum yield (QY) can reach up to 51.7%. Most importantly, we find that the CQDs can be applied for selective detection of Ferric(III) ions in solutions via photoluminescence
(PL) measurement. The sensitivity of the detection can reach up to 0.1 M. The analysis of the electronic energy structure suggests that the quenching of the PL emission by the presence of Ferric(III) ions is attributed to the surface functional groups attached to the CQDs, which can interact
with metal ions so that the electrons in the excited state of the CQDs are transferred into the unoccupied orbits of Ferric(III) ions. A corresponding physical mechanism is proposed to gain a understanding about how the presence of the Ferric(III) ions can affect the PL emission from CQDs.
