Green synthesis of carbon dots (CDs) and their use for selective determination of Pb²

Carbon dots were synthesized from fenugreek seeds through a single step hydrothermal method. The method is simple, fast, pleasant to the environment and cheaper. The CDs were characterized by Fourier Transform Infrared (FTIR), UV-visible spectrophotometer, X-ray diffraction (XRD), High Resolution Transmission electron microscopy (HR-TEM), and fluorescence. The CDs obtained were extremely fluorescent. The fluorescent carbon dots exhibited excitation-dependent behavior with the maximum excitation at 372 nm. The interaction of CDs was studied with different selected cations Al³⁺, Ca²⁺, Cd²⁺, Cr³⁺, Co²⁺, Cu²⁺, Cu⁺, Fe²⁺, Fe³⁺, K⁺, Sn⁴⁺, Na⁺, Ni²⁺, Pb²⁺, Mn²⁺, Zn²⁺, Sr²⁺, (NH₄)₆Mo₇O_24, 4H₂O, Cr⁶⁺, Sb³⁺, Ba²⁺, Li⁺, and Mg²⁺. None of the ions studied showed any effect on its fluorescence intensity except Pb²⁺ which decreased its intensity. A direct relationship was found between Pb²⁺ concentrations and quenching of CDs intensity. Detection limit (DL) and quantification limits (QL) were determined as three and ten times of the standard deviation of the blank for ten number of measurements. DL and QL were found in the order 9.345 μM and 31.15 μM respectively. This linear behavior between quenching and Pb²⁺ concentration is useful for analytical purpose.