Study On The Preparation And Properties Of Asphalt-based Graphene Quantum Dots

The new carbon materials graphene quantum dots?GQDs?has excellent optical,chemical and electrical properties due to its unique structure,which has a potential application prospect in fluorescence probe,biological imaging and surfactant etc.At present,it is still a great challenge to prepare these carbon materials at low cost and large scale.Deoiled Asphalt?DOA?,which is rich in resin and asphaltene,has a rich structure of polycyclic aromatic hydrocarbons.GQDs with excellent properties could be prepared by simple chemical oxidation from DOA.Therefore,a series of new asphaltene-derived GQDs were prepared in this study.Then their fluorescence properties,surface properties and application in cell imaging,detection of heavy metals and the properties of oil-water emulsion were discussed.The carboxyl-type graphene quantum dots?GQDs?were prepared by chemical oxidation using DOA as raw material and concentrated nitric acid and concentrated sulfuric acid as oxidant.Multiple analysis methods were used to characterize the structure of GQDs.The results show that DOA can be transformed into graphene quantum dots by mild oxidation,and they are much smaller and thinner than most reported GQDs.The asphalt-GQDs possess a variety of functional groups such as carboxyl,hydroxyl,and nitro groups.They present such excellent fluorescence properties as stable ability to retain strong green fluorescence within a relative broad excitation range in a bio-suitable pH range of 4–7,high photoluminescence quantum yield of 18%.The amide-type graphene quantum dots?GQDs?were synthesized by carboxyl-type GQDs and a series of amines,respectively tetraethylenepentamine,octylamine,dodecylamine,octadecylamine.It was found that compared with carboxyl-type GQDs,the fluorescence intensity of amide-type GQDs increases greatly,and the fluorescence intensity increases with the increase of reaction time and amine dosage.The emission peak positions shifted blue,and the more the electron donating group,the more pronounced the blue shift.The fluorescence spectra of carboxyl-type GQDs were treated by deconvolution,The results show that all PL spectra of the prepared GQDs can be well deconvolved into two Gauss components,which show that the fluorescence spectrum can be obtained by the interaction of two kinds of controlled states.The results show that the two control states are in accord with the theoretical model of eigenstates and edge/surface states.The eigenstates affect the fluorescence of the UV excitation region,and the edge/surface states determine the fluorescence states of the visible excitation region.Fluorescence probe imaging test were performed on carboxyl-type GQDs.After incubating HeLa cells with GQDs at different concentrations from 20 to 200?g mL–1 for24 h,all of the cell survival rates were over 90%.Cell imaging indicated the GQDs were endocytosed into HeLa cells,which can be used as fluorescent probes.Water-soluble amide-type GQDs was used to detect heavy metals,Linear fitting of the GQDs fluorescence intensity and Hg²⁺concentration was obtained,I=-1093.4 C+-699051,R²=0.9588,the detection limit is 100nmol/L.Carboxyl-type GQDs and amide-type GQDs have the ability to reduce interfacial tension and can act as an stabilizing agent at the oil-water interface.The stable mechanism could be interpreted as that GQDs spreading on the oil-water interface,on the one hand reduce interfacial tension,on the other hand the nano particles at the interface form a compact protective layer to enhance the interface strength.