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.

Graphical abstractWe 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 full-size imageDownload as PowerPoint slide