Synthesis of Carbon Quantum Dots from Novel Carbon Sources of Black Tea and Detection of pb2+ Ions

Carbon based quantum dots (CQDs) have found their applications in various areas due to their unique properties such as photoluminescence (PL) properties, good water solubility and biocompatibility, high chemical stability, low toxicity, environmental friendliness and light bleaching resistance. Herein, a novel functional sensing platform based on bright green fluorescent nitrogen-doped carbon quantum dots (N-CQDs) was prepared for the detection of a variety of ions. Using black tea as a new carbon source, ethylenediamine as nitrogen source and surface modifier, nitrogen doped carbon quantum dots (N-CQDs) with low crystallinity, spherical and uniformly dispersed graphite structure were prepared. Its diameter distribution is between 1.0 and 3.0 nm. Unlike the other transition metal ions such as Al 3+ , Cu 2+ , Cd 2+ , Hg 2+ , Ni 2+ , Fe 2+ , Zn 2+ , and Ag + , as well as the main group metal ions such as Na + , K + , Mg 2+ , Ca 2+ , and Ba2+ , the addition of Pb2+ to the aqueous solution of the as prepared CQDs leads to the significant quenching of the fluorescence centered at 450 nm. Such quantitative quenching effect was used to develop a CQDs sensor that is able to detect the trace amount of Pb2+ in the aqueous solution. The sensor exhibits a detection limit of 13.3 nmol/L for Pb 2+ , and the quenching efficiency reaches 70.2%. The quenching mechanism was also discussed. The results in the present work indicate the Pb 2+ sensor developed from the tea based CQDs may find broad application in the real time monitoring of water quality and other environmental samples.