Synthesis And Characterization Of Graphene Quantum Dots And Their Application In The Sensing

Graphene quantum dots(GQDs),as a new kind of quantum dots,have attracted increasing attention in nanoscience and nanotechnology.Due to their pronounced quantum confinement and edge effects,GQDs exhibit numerous novel chemical/physical properties.Among these remarkable properties,the most inspiring ones are their excellent solubility and biocompatibility which makes them fascinating for applications in bioimaging,sensing and drug delivery.However,the development of GQDs is still in its initial stage,and more work should be done to investigate their properties and to broaden their applications.In this paper,we covered a wide range of work,involving the synthesis,characterization of the structure and properties,as well as the novel sensing application of GQDs.Specifically,there were four aspects introducing in detail in the following paragraphs.In the first chapter,we summarized the recent advances in the synthesis,chemical and physical properties of GQDs along with their applications.In the second chapter,we fabricated the GQDs by acidic oxidation method using GO as precursor.Through a simple dialysis technique,we found that blue-photoluminescent GQDs(b-GQDs)and green-photoluminescent GQDs(g-GQDs)can be successfully separated.Although the transmission electron microscopy(TEM)and atomic force microscopy(AFM)images show their similar morphology,the results of X-ray photoelectron spectroscopy(XPS),fourier-transform infrared(FTIR)and Raman measurements reveal their distinct structures and different origins from GO.In addition,the characterization of PL emission,PL excitation(PLE)and time-resolved photoluminescence(TRPL)spectroscopy also show the two GQDs have different luminescence mechanism which is related to their distinct structure.More interestingly,the g-GQDs exhibit higher peroxidase-like catalytic activity and can be used to detect H2O2 with the detection limit of 87 nM.Combining with its low cytotoxicity,the g-GQDs may have tremendous potential for applications in biosensing field.In the third chapter,we prepared blue photoluminescent GQDs by hydrothermal method.Based on the mechanism that the fluorescence of GQDs can be regulated by metal ions,we developed a GQDs-based fluorescence "turn on" sensor for the detection of AA in the presence of Cu2+.The experimental results show that the detection process is ultrafast and can be completed within 5 min.The detection limit of the sensor is as low as 94 nM,which is comparable to or even better than other reported assays.In addition,this sensing system also shows good selectivity for detecting AA in the presence of different physiological molecules and inorganic ions.Finally,the proposed sensing system was successfully applied to assay AA in real samples with satisfactory results.In the fourth chapter,we also explored the bottom-up methods for preparing GQDs.Using citric acid(CA)and ethanediamine(EA)as the carbon source and nitrogen source,we synthesized the N-doped GQDs(N-GQDs)through the combination of hydrothermal and solvethermal methods.As compared with the carbon dots frabricated by hydrothermal methods,the N-GQDs produced by the two-step method show a higher degree of carbonization.The yield of the N-GQDs is as high as 10.5%,which can provide a novel strategy to prepare GQDs in large scale.In a word,GQDs were studied from several aspects in this paper.We believe that these studies play important roles in developing new preparation methods,understanding the structure and PL properties of GQDs as well as broadening their applications in sensing.