Carbon dots prepared by thermal reactions and selective detections of copper and mercury ions in visible spectrum

Carbon dots (CDots) are characterized by their optical properties including strong absorptions, bright fluorescence emissions, and electron acceptor and donor behaviors in the visible spectrum. In this study, aconitic acid and oligomeric polyethyleneimine were used as precursors to prepare PEI/AA-CDots by vigorous microwave-assisted thermal carbonization. The as-prepared CDots exhibit excitation wavelength-dependent fluorescence with a quantum yield of 44.2% at the excitation wavelength of 380 nm. In addition, the fluorescence in the visible spectrum can be selectively and efficiently quenched by Cu2+ or Hg2+ ions via electron transitions due to the electron donor behaviors of the as-prepared CDots. The detection limits of Cu2+ and Hg2+ ions are 70 and 84 nM, respectively. The quenched fluorescence can be recovered by introducing aspartic acid or L-cysteine into the PEI/AA-CDots-Cu2+ or the PEI/AA-CDots-Hg2+ systems. Furthermore, the as-prepared PEI/AA-CDots can be successfully applied for detecting Cu2+ and Hg2+ ions in real water and can serve as a potential candidate as a probe for detecting these metal ions.