Preparation Of Doped Graphene Quantum Dots And Their Application As Fluorescence Sensors

In recent years,graphene quantum dots（GQDs）have been used as fluorescence sensors to detect various substances.However,the biggest disadvantage of graphene quantum dots as fluorescence sensing is the low quantum yield and non-specificity,which largely limits the application of graphene quantum dots as fluorescence sensing in practical life.Doping other atoms in graphene quantum dots can effectively change the functional group structure,increase the specific binding,chemical activity,electronic structure and quantum yield,so that graphene quantum dots have better photoluminescence properties.In this article,by studying the co-doping of metal elements and non-metal elements,the doped graphene quantum dots with better quantum yield and fluorescence performance were obtained.,the selective analysis is studied by using fluorescence properties of metal ions,and has carried on the exploration,in cell imaging experiments show that it has potential application in the field of fluorescent sensor specific research content is as follows:（1）Black boron and nitrogen doped graphene quantum dots（BN-GQDs）solid powder was synthesized by one-step hydrothermal method using citric acid and urea as the precursors.Its morphology and structure were characterized by transmission electron microscopy（TEM）,and its crystal structure was analyzed by high resolution transmission electron microscopy（HRTEM）and X-ray diffraction（XRD）.Then,the composition and chemical bond information of the element were analyzed by Fourier Transform infrared spectrometer（FTIR）and X-ray photoelectron spectrometer（XPS）.Finally,the optical properties of the element were discussed.The results show that the size of BN-GQDs is3.9-9.5 nm,with good crystal structure and lattice spacing of 0.232 nm.The maximum excitation and emission wavelengths are 345 nm and 434 nm respectively,and the quantum yield and fluorescence lifetime are 20.12%and 7.005 ns,respectively.（2）We first doped Mn,B,N metal elements and non-metal elements into graphene quantum dots.The morphology and fluorescence properties of the synthesized Mn-BN-GQDs and BN-GQDs were compared,and the doping mechanism was further explored.Then,Mn-BN-GQDs was used as fluorescence sensor to detect and analyze Fe³⁺and the quenching mechanism was analyzed.Finally,Mn-BN-GQDs was explored in biocompatibility and cell fluorescence.The results show that the size of Mn-BN-GQDs decreases by 2.4-3 nm compared with BN-GQDs,the fluorescence intensity increases significantly,the quantum yield increases from 20.12%to 30.52%,and the fluorescence lifetime increases from 7.005 ns to 7.444 ns.The linear range of 10μM-100μM and 100μM-800μM was 0.78μM and 9.08μM,respectively.The optimal p H value of the detection is 7,which has low cytotoxicity and good biocompatibility,and shows good fluorescence effect in living cells.（3）A light green nitrogen and sulfur doped graphene quantum dots（NS-GQDs）solid powder was synthesized by using citric acid as carbon source and thiourea as nitrogen and sulfur atom doped precursor.The product was characterized by TEM,and further characterized by XRD and HRTEM in order to explore its crystal structure.Finally,in order to explore whether N and S elements are doped into GQDs,XPS and FTIR were used to test and analyze its functional groups and chemical bond types,and finally its optical properties were characterized and analyzed.The results show that the size of NS-GQDs is2.94-8.31 nm,the crystal structure is good,the lattice spacing is 0.32 nm,the maximum excitation and emission wavelengths are 336 nm and 434 nm,the quantum yield and fluorescence lifetime are 13.33%and 7.062 ns,respectively.（4）After the synthesis of NS-GQDs,the experiment doped the metal element Mn into graphene quantum dots（GQDs）for the first time,analyzed the morphology,quantum yield,fluorescence intensity and other changes between the two,and studied the doping mechanism,and analyzed the crystal structure,element composition and chemical bond information of Mn-NS-GQDs.Finally,the sensitivity of Mn-NS-GQDs to Co²⁺was tested and the interference of other ions on the experiment was explored.The results showed that compared with NS-GQDs,the size of Mn-NS-GQDs decreased by 2.19-2.56 nm,the fluorescence intensity increased significantly,the quantum yield increased from 13.33%to30.16%,and the fluorescence lifetime increased from 7.062 ns to 7.416 ns.The detection of Co²⁺has a good linearity in the range of 10-160μM,and the detection limit is 0.86μM.The optimal p H value was 7.In a word,this article synthesized four kinds of doped graphene quantum dots by one-step hydrothermal synthesis method.Then,the morphology changes of Mn²⁺metal ions and non-metal elements co-doped in GQDs were explored,and the changes of fluorescence properties and quantum yield were tested and analyzed.Then,Mn-BN-GQDs and Mn-NS-GQDs were used as fluorescence sensors to detect Fe³⁺and Co²⁺respectively by using their good optical properties.Two kinds of rapid,simple and selective fluorescence sensors have been obtained,which have good application prospects for environmental protection and human health detection.At the same time,Mn-BN-GQDs as a fluorescence sensor has good biocompatibility and cell fluorescence,which has a potential development prospect in cell imaging.