Formation Of Single-Layered Graphene Quantum Dots Based On Layered Confinement Effects And Their Optical Sensing Application

Graphene quantum dots (GQDs) have received much research attention due to their unique optical/electrical/magnetic features. However, the correlation between the structure and fluorescence origin of GQDs remains not fully understood yet, because controlled synthesis and accurate structure determination of GQDs is still a great challenge. Layered double hydroxides (LDHs) represent one kind of layered materials with tunable interlayer space and variable interlayer guests. The confined space of the 2D interlayer galleries of LDH hosts leads to substantial improvements in the luminescence properties of the fluorophore ensemble and disperse the fluorescence guest. The structure observation and optical sensing of grapheme quantum dots based on the confinement effects of LDHs have been discussed as follows:(1) The single-layered GQDs are successfully obtained by hydrothermal treatment of intercalated citrate in the confined space of the 2D interlayer galleries of layered double hydroxides (LDHs). The composition and structure of the S-GQDs are characterized by different spectroscopy techniques including NMR, X-ray photoelectron spectroscopy (XPS) and mass spectrometry. The distinct molecular structures of the single-layered GQDs (S-GQDs) reveal that the blue photoluminescence of GQDs derives from the rigid ?-conjugate plane structure, and it is consistent with the theoretical calculation. This work will open the door towards quantitative understanding of the structure-property effect of GQDs.(2) An optical sensor of graphene quantum dots and layered double hydroxides composite (GQD-LDHs) with high selectivity has been obtained based on the confinement effects from the LDHs nanoreactors and sensing performance of graphene quantum dots (GQDs). The mechanism showed the LDHs with two dimension (2D) confined space provided a stable microenvironment and acted as the disperse matrix to control the distribution of intercalated GQDs. LDHs confinement effects decreased ·OH diffusion rate, or even annihilated ·OH during the diffusion process into the LDH interlayer galleries. As a result, the interference was eliminated and selective detection of nitrogen dioxide (NO2) was improved. It was found that the fluorescence of GQD-LDHs could be linearly quenched by NO2 in a broad range from 0.1 to 10 uM and the limit of the detection was estimated to be as low as 90 nM. Furthermore, a rapid and portable indicating paper sensor coated with GQD-LDHs for visual detection of NO2 gas was successfully developed. This success of our work provides a new method to markedly enhance the selectivity of sensors by taking advantage of confinement effects in the inorganic nanoreactors.