Abstract:

Nitrogen and sulfur co-doped blue fluorescent carbon dots （NS-CDs） for detection of copper ion in real samples were prepared by the hydrothermal method using citric acid as the carbon source. The structure， composition and optical properties of NS-CDs were characterized by high-resolution transmission electron microscopy， X-ray diffraction， infrared absorption spectroscopy， X-ray photoelectron spectroscopy， and fluorescence spectroscopy. The results show that the NS-CDs have amorphous carbon structure， high dispersibility， and its particle size is in the range of 0.6～2.2 nm. There are carboxyl， hydroxyl and amide functional groups on NS-CDs′ surfaces. The C， N， O and S element contents of NS-CDs are 54.01%， 24.49%， 19.39% and 2.11%， respectively. NS-CDs show good fluorescence stability for the irradiation by ultraviolet light， pH value， and ionic strength， and the fluorescence quantum yield is 25%. Cu²⁺ could interact with the functional groups on NS-CDs， resulting in the aggregation/network structure and causing quenching of fluorescence intensity. A fluorescence analysis method is established to detect Cu²⁺ with linear ranges of 0~10， 10~50 and 50~100 μmol/L， respectively. The detection limit is achieved as 41 nmol/L （S/N=3）， which meets the Chinese guidelines for Cu²⁺ in soil in Environmental Quality Standard for Soils. The method is successfully applied in detection of Cu²⁺ in soil samples with recoveries of 104.9%~105.6%. The copper ion concentration is 2.55 μmol/L. The method is rapid， sensitive and highly selective for detection of Cu²⁺.

Key words: Carbon dots, Fluorescence quenching, Copper ions, Detection