Highly Blue-fluorescent Carbon Quantum Dots Obtained from Medlar Seed for Hg(2+) Determination in Real Water Samples.

The carbon quantum dots (CQDs) have been prepared from medlar seeds with pyrolysis method in an oven at 300 °C. UV-vis absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR) spectroscopy, x-ray diffraction (XRD) technique, x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were used in the characterization of CQDs. CQDs, give a strong blue fluorescence under UV lamp (at 365 nm), have a quantum yield of 12.2%. The influence of metal ions such as K, Mg, Ca, Be, Cr, Mn, Ni, Ag, Hg, and Al on the fluorescence properties of the CQDs was investigated by means of emission spectrophotometry. CQDs altering fluorescence characteristics depending on the excitation wavelength show selectivity for Hg ions with outstanding fluorescence quenching among the tested metal ions. Based on these results, a new fluorimetric method has been developed for the determination of Hg in real water samples. The linear range of method is 1.0 to 5.0 mgL. Limit of detection and limit of quantification are 0.26 and 0.79 mgL, respectively. The proposed method has been successfully used in determination of Hg ions in tap, sea, and stream water samples with application of addition-recovery experiments.