Synthesis Of Doped-Graphene Quantum Dots And Their Applications

Graphene, containing a single layer of sp2-hybridized carbon atoms, has fuelled intensiveresearch interest because of its unique two-dimensional (2D) crystalline structure, fascinatingphysical and chemical properties, and potential applications in electronic devices andmolecule sensors. Both theoretical and experimental studies have shown that not only the sizeand shape but also the geometry and chemical nature determine the properties of graphenenanostructures. Graphene nanosheets of less than100nm in size, which are known asgraphene quantum dots (GQDs), are particularly encouraging owing to their outstandingphotoluminescence (PL) properties. It could adjust the electronic band structure of grapheneby hetero atoms into the graphene structure, and then made doped graphene quantum dots bychemical methods. Doping GQDs with heteroatoms can effectively tune their intrinsicproperties, including optical characteristics, surface and local chemical features. Recentlly,theapplication development of heteroatom-doped GQDs remains inchoate, which might beattributed to the limitation in synthesis methods and the difficulties in construction ofeffective GQD-based sensing platform. This paper carried out the work as follows:1、A hydrothermal approach for the cutting of boron-doped graphene (BG) intoboron-doped graphene quantum dots (BGQDs) has been proposed. The transmission electronmicroscopy (TEM) image shows fairly uniform BGQDs with diameters of ca.24nm. Thecorresponding atomic force microscopy (AFM) image reveals a typical topographic height of0.50.8nm, suggesting that most of the BGQDs consist of a single graphene layer. TheBGQDs show a broad UV-vis absorption band with a weak shoulder at295nm, thephotograph shows that BGQDs solution is pale-yellow, transparent and clear under daylightand exhibits blue PL under irradiation by a365nm UV light. Like other luminescent carbonnanoparticles, the BGQDs also exhibit an excitation-dependent PL behaviour. As theexcitation wavelength increases(from310nm to360nm), the emission peak shifts to longerwavelength and its intensity decreases rapidly. The chemically synthesized BGQDs arereadily water-dispersible due to the presence of hydroxyl and carboxylic groups at the surfaceand edges, which is confirmed by Fourier transform infrared (FT-IR) measurement, themagnified FTIR spectrum of BGQDs displays the additional absorption peak fromasymmetric B-O stretching at1410cm-1, confirming the successful preparation of the BGQDs.X-ray photoelectron spectroscopy (XPS) characterizations reveal that the boron atoms havebeen successfully doped into graphene structures with the atomic percentage of3.45%. X-ray diffraction (XRD) the BGQDs show a broader X-ray diffraction (XRD) peak at ca.25°,indicating that the oxidation reaction during the BGQDs preparation process has introducedmore active sites on the surfaces of BGQDs. Raman spectra offer clear evidence of B-dopingin the graphene lattice. The BGQDs exhibit a broader D band, suggesting that theintercalation of B atoms into the conjugated carbon backbone has led to somewhat disorderedstructures. The as-prepared BGQDs solution shows good water solubility, stable opticalperformance and remains homogeneous even after3months at room temperature anyperceptible changes (e.g., aggregation or color change).2、Boron-Doped Graphene Quantum Dots for Selective Glucose Sensing Based on the“Abnormal” Aggregation-Induced Photoluminescence Enhancement. The generation ofboronic acid groups on the BGQDs surfaces facilitates their application as a newphotoluminescence (PL) probe for label free and “turn on” glucose sensing. It is postulatedthat the reaction of the two cis-diol units in glucose with the two boronic acid groups on theBGQDs surfaces creates structurally rigid BGQDs-glucose aggregates, restricting theintramolecular rotations and thus resulting in a great boost in the PL intensity. The presentunusual “aggregation-induced PL increasing” sensing process excludes any saccharide withonly one cis-diol unit, as manifested by the high specificity of BGQDs for fructose, galactoseand mannose. It is believed that the doping of boron can introduce the GQDs a new kind ofsurface state and offer great scientific insights to the PL enhancement mechanism withtreatment of diabetes.