Fabrication of valine-functionalized graphene quantum dots and its use as a novel optical probe for sensitive and selective detection of Hg2 +

• We first reported a facile synthesis of valine-functionalized graphene quantum dots.
• The graphene quantum dots offer a better fluorescence intensity and photostability.
• The introduction of valine groups greatly improves fluorescent response to Hg2 +.
• The proposed method provides the advantage of sensitivity, selectivity and stability.
• The study can also be used for design of functionalized graphene quantum dots.

The functionalization of graphene quantum dots has become a powerful method to modulate its chemical, electronic and optical properties for various applications. In the study, we reported a facile synthesis of valine-functionalized graphene quantum dots (Val-GQDs) and its use as a novel fluorescent probe for optical detection of Hg2 +. Herein, Val-GQDs was synthesized by the thermal pyrolysis of citric acid and valine. The resulting Val-GQDs has an average size of 3 nm and the edge of graphene sheets contains the rich of hydrophilic groups, leading to a high water-solubility. Compared to the GQDs prepared by thermal pyrolysis of citric acid, Val-GQDs exhibits a stronger fluorescence (> 10-fold) and better photostability (> 4-fold). Interestingly, the existence of valine moieties in the Val-GQDs results in a more sensitive fluorescent response to Hg2 +. The fluorescent signal will linearly decrease with the increase of Hg2 + concentration in the range from 0.8 nM to 1 μM with the correlation coefficient of 0.992. The detection limit is 0.4 nM (S/N = 3), which the sensitivity is > 14-fold that of GQDs. The analytical method provides the prominent advantage of sensitivity, selectivity and stability. It has been successfully applied in the optical detection of Hg2 + in real water samples. The study also provides a promising approach for the design and synthesis of functionalized GQDs to meet the needs of further applications in sensing and catalysis.

We reported a facile synthesis of valine-functionalized graphene quantum dots by pyrolysis of citric acid and valine. The as-prepared valine-functionalized graphene quantum dots offer an excellent optical property and was successfully used to the detection of Hg2 + by fluorescence method with good rapidity, sensitivity and selectivity.Figure optionsDownload as PowerPoint slide