Preparation, Characterization And Electrochemical Application Of Graphene Quantum Dots-natural Polysaccharide Composite Materials

A graphene quantum dots(GQDs)-chitosan(CS) composite film was prepared via successive electrodeposition of GQDs and CS on the surface of a glassy carbon electrode(GCE). The strong interactions between GQDs and CS resulted in the formation of a regular and uniform film, which can be applied in the electrochemical chiral recognition of tryptophan(Trp) enantiomers. CS in the composite film provides a chiral microenvironment, meanwhile, GQDs can amplify the electrochemical signals and improve the recognition efficiency. Due to the synergetic effects of GQDs and CS, chiral recognition of Trp enantiomers is achieved successfully. Compared with previous reports utilizing GQDs in photoluminescent research, this work opens a new avenue for broadening the applications of GQDs in electrochemical chiral sensors.GQDs were prepared by pyrolysis of citric acid, and then they were incorporated into β-cyclodextrin(β-CD) via H-bonds between the oxygen-containing groups on GQDs and the hydroxyl groups on β-CD. The nanocomposites of GQDs and β-CD(GQDs/β-CD) were negatively charged due to the ionization of carboxyl groups of GQDs, and therefore they could be effectively electrodeposited onto the surface of GCE. The electrodeposited GQDs/β-CD were optically active due to the introduction of β-CD with well-defined hydrophobic central cavity, meanwhile, GQDs can amplify the electrochemical signals. Finally, the nanocomposities were employed as an electrochemical chiral interface for enantiorecognition of Trp isomers.Nanocomposites of chitosan(CS) and GQDs were prepared via a simple and reliable approach on the basis of electrostatic attraction and H-bondings between CS and GQDs. The nanocomposites of CS and GQDs(GQDs-CS) were characterized by Fourier transform infrared spectroscopy(FT-IR), field-emission scanning electron microscopy(FESEM) and transmission electron microscopy(TEM), exhibiting a well-dispersed status of the GQDs nanofillers in the CS matrix. The GQDs-CS modified GCE is used as the sensing platform for sensitive and simultaneous determination of Zn2+, Cd2+ and Pb2+ for the first time, opening a new avenue to monitor trace heavy metal ions precisely and rapidly.GQDs-CS nanocomposites possess three-dimensional network structure, which can be pyrolyzed to obtain porous carbon material. Thermogravimetric analysis(TGA), Fourier transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS) were adopted for the characterization of the obtained p-C, indicating that the p-C not only remains the three-dimensional network structure from its precursor(GQDs-CS), but also possesses a large specific surface area, excellent electrical conductivity, capacitive behaviors and cycle performance.