Carbon Quantum Dot-Incorporated Chitosan Hydrogel for Selective Sensing of Hg2+ Ions: Synthesis, Characterization, and Density Functional Theory Calculation

A carbon quantum dot-based chitosan hydrogel was prepared in this work as a fluorescence sensor for the selective sensing of Hg2+ ions. Among the eight tested metal ions, the prepared hydrogel exhibited remarkable sensing selectivity and sensitivity toward Hg2+. The results demonstrated that a prominent fluorescence quenching at 450 nm was observed in the presence of Hg2+ with a linear response range of 0-100.0 nM and an estimated limit of detection of 9.07 nM. The as-prepared hydrogel demonstrates pH-dependent fluorescence intensity and sensitivity. The highest fluorescence intensity and sensitivity were obtained under pH 5.0. The excellent sensing selectivity could be attributed to a strong interaction between the hydrogel film and Hg2+ ions to form complexes, which provokes an effective electron transfer for fluorescence quenching. Results from density functional theory (DFT) calculation confirm that the interaction energies (Delta IE) of the hydrogel with three toxic metal ions (Hg2+, Cd2+, and Pb2+) are in the following order: Hg2+ > Cd2+ > Pb2+.

Automated summary

A carbon quantum dot-based chitosan hydrogel was prepared as a fluorescence sensor for the selective sensing of Hg2+ ions, demonstrating remarkable sensitivity and selectivity. The hydrogel showed the highest fluorescence intensity and sensitivity at pH 5.0, with a linear response range of 0-100.0 nM and a detection limit of 9.07 nM. The excellent sensing selectivity was attributed to the strong interaction between the hydrogel film and Hg2+ ions, with a higher interaction energy compared to Cd2+ and Pb2+ ions according to density functional theory (DFT) calculation.