Microwave Synthesis, Characterization And Properties Of Carbon Nanodots Derived From Amino Acids

With the development of science and technology in recent years,carbon nanomaterials have been extensively studied and their applications can be expanded to many fields such as energy,biomaterials,detection,and environmental protection.As a new type of fluorescent carbon nanomaterials,carbon nanodots are widely reported due to their merits such as easy synthesis,low cost,facile surface-modification,low biotoxicity,and resistance to phtobleaching.Carbon nanodots can be classified into two types in terms of morphology,carbon nanodots with crystalline structure and carbon nanodots without crystalline structure,which have different fluorescent mechanism.Therefore,it is vital to synthesize carbon nanodots with a lattice structure to explain its fluorescent mechanism and expand its application.In this dissertation,we studied the controllable synthesis of nitrogen-doped carbon nanodots with a lattice structure through a microwave-assisted hydrothermal method?which has merits such as high reaction rate,high heating efficiency and highly controllable?using amino acids as sources,and the formation mechanism of carbon nanodots,further promoting the applications in the fields of ion detection,bioimaging and catalyzing the oxygen reduction reaction.In chapter one,we give a introduction of the synthesis,structure,property,and state-of-the art of carbon nanodots?CDs?.We also discuss the purpose and significance of this dissertation.In chapter two,histidine was chosen as the sole carbon source to synthesize nitrogen-doped CDs without further addition of oxidant or passivation agent through a microwave-assisted hydrothermal method.The as-prepared CDs have a blue fluorescence with a quantum yield of 8.9%.By changing the reaction duration,we find out that the CDs experienced a dehydration,condensation,polymerization and carbonization procedure.The as-prepared CDs have phenolic hydroxy group on their surface,which was used to selectively detect the Fe³⁺ions in aqueous solution.The as-prepared CDs were also used as fluorescent agent to label AD293 cells.They can label both the cytoplasm and the nucleus of the AD293 Cells.In chapter three,tyrosine was chosen as the carbon source,and ethanediamine served as the passivation agent.By changing the doze of ethanediamine,the reaction temperature,heating rate and the reaction duration,excitation dependent CDs were acquired through a microwave-assisted hydrothermal method utilizing the shear action of amines.As tyrosine has phenolic hydroxyl group,it can be partly reserved in the CDs.The phenolic hydroxyl group on the CDs can improve the detection limit of Fe³⁺.The limit of detection of Fe³⁺is 0.82nmol×L^-1.The solid CDs have a green fluorescence under 415nm excitation,and it was used as fluorescent agent to label Hela cells.The solid CDs can only label the cytoplasm of the Hela cells.In chapter four,basic amino acid arginine was chosen as the carbon source and glycerol was selected as the passivation agent.By changing the doze of glycerol and the reaction temperature,a highly crystalized nitrogen-doped carbon quantum nanodot?N-CQDs?was prepared using a microwave-assisted hydrothermal strategy.The as-synthesized N-CQDs have an excellent lattice structure?I_D/I_G=0.6?and thus good charge transfer ability.As the N-CQDs have functional groups on their surface,it may reduce the charge transfer among the N-CQDs,so we combined N-CQDs with graphene to improve their domain charge transfer ability.The as-prepared N-CQDs/graphene can be used to catalyze the oxygen reduction reaction?ORR?in the fuel cells.The electron transfer number of N-CQDs/graphene in the ORR was 4,while the electron transfer number of N-CQDs was 2,which demonstrated that N-CQDs/graphene can be used as a metal-free catalyst for the ORR.The as-prepared N-CQDs/graphene has a four electron transfer catalytic property similar to Pt/C,good stability and methanol tolerance property.In the last chapter,we summarize the controllable synthesis and properties of CDs using amino acids as the carbon source as well as their applications in bioimaging,ion detection and electrochemical catalysis.