Fluorescent Probe for Detection of Hg2+ and S2- Based on N-Doped Ti3C2 MXene Quantum Dots

A novel fluorescent "on-off-on" method for the detection of Hg2+ and S2- was developed based on N-doped Ti3C2 MXene quantum dots N-Ti3C2 MQDs and complexation. The prepared N-Ti3C2 MQDs emitted blue fluorescence lambda(em)=440 nm) with a fluorescence quantum yield of 15.7%. Hg2+ can selectively coordinate with functional groups of -NH2, -COOH, and -OH on the surface of N-Ti3C2 MQDs through electrostatic interaction, resulting in fluorescent quenching of the N-Ti3C2 MQDs system. After the addition of S2-, HgS precipitation is formed due to the strong binding force between S2- and Hg2+, leading to the fluorescent recovery of the N-Ti3C2 MQDs. Based on this principle, a fluorescent "on-off-on" sensing method was constructed to quantitatively detect Hg2+ and S2-. The fluorescenty of the N-Ti3C2 MQDs probe is proportional to Hg2+ and S2- concentrations in the range of 0.02-200 mu mol/L and 0.07-150 mu mol/L, with a detection limit of 10 nmol/L and 30 nmol/L S/N=3), respectively. This proposed method has the advantages of low cost, simple operation, high sensitivity, and good selectivity, which has been used for the determination of Hg2+ and S2- in real water samples.