The Functionality And Self-exothermic Synthesis Of Carbon Dots And Their Applications In Biochemical And Pharmaceutical Analysis

Carbon dots(CDs),as a new type of photoluminescent(PL)carbon nanomaterials,have been widely applied to cellular imaging,biological and chemical sensing,photoelectric device and analytical fields owing to their superiorities in photostability,tunable PL,good biocompatibility and easy preparation,.In order to satisfy some special applications in different fields,the functionalization of CDs is highly desirable.Currently,element doping and surface modification are the two main functional approaches to change and improve the properties of CDs,however,they are still difficult to meet the different kinds of practical needs.Moreover,to obtain CDs with high quantum yield,a series of methods including hydrothermal synthesis,ultra-sound or microwave-assisted synthesis,laser irradiation,electrochemical etching have been developed.However,all the above methods require a lot of energy supply and are still low yield,which greatly limit their large-scale production and further industrial applications.Therefore,synthesis of CDs at room temperature is very attractive due to its characterized by efficient-energy and simplicity.The conventional room temperature synthesis usually needs chemical cleaving or breaking down of carbonaceous materials to obtain CDs in the presence of a large amount of strong oxidizing agents(concentrated sulfuric acid or nitric acid);or makes the reaction precursors dehydration,condensation,then the carbonization in the presence of concentrated base(concentrated sodium hydroxide)to form CDs.But the CDs prepared at room temperature always suffer from low quantum yield,which is not beneficial for cellular imaging,analytical detection and other applications.In addition,the presence of concentrated acid or alkali not only increases the cost,the difficulty of separation and purification,but also poses a serious threat to the environment,which doesn't meet the requirements of green synthesis and sustainable development.In this thesis,taking the difficulties in functionalization and room temperature synthesis of CDs into consideration,the research is divided into four contents as follows:1.One-pot carbonization synthesis of terbium-doped CDs(Tb-CDs)and the highly selective detection of 2,4,6-trinitrophenol(TNP).The blue PL Tb-CDs,which show excitation wavelength dependent emission property and have a size of about 3 nm,can be prepared through one-pot carbonization method by simply keeping the mixture of terbium(III)nitrate pentahydrate and citric acid.The doping of terbium ions significantly improve the stability of CDs and make them own great salt stability,photostability and oxidation resistance compared with other CDs.In addition,the common metal ions have no influence on the PL of Tb-CDs,therefore,Tb-CDs act as the good fluorescent probe can be used for analytical field.Based on the inner filter effect between TNP and Tb-CDs,TNP can efficiently quench the PL of Tb-CDs.The propose detection method has good repeatability and low relative standard deviation due to the high stability of CDs,which improves the reliability of analytical results and realizes the TNP detection in the complex water samples.2.Two-step hydrothermal synthesis of terbium-modified carbon quantum dots(CQDs-Tb)and the highly selective and sensitive detection of guanosine 3'-diphosphate-5'-diphosphate(pp Gpp).The blue-emissive CQDs are prepared by hydrothermal synthesis;and then terbium(III)ions are coordinated with carboxyl and amine groups in the surface of CQDs at room temperature to form CQDs-Tb.The CQDs-Tb have up to 54.8% of quantum yield and show excitation wavelength independent blue PL emission.The pp Gpp can specificly combine with terbium ions through coordination interaction,making that the terbium ions emit obviously green fluorescence after accepting energy from pp Gpp by antenna effect.Based on this phenomena,we develop a highly selective and sensitive ratiometric fluorescent method for detecting pp Gpp.3.The self-exothermic synthesis of single-layered graphene quantum dots(s-GQDs)and the highly selective detection of aluminium ion.Inspired by traditional hydrothermal synthesis,we introduce the self-exothermic reaction into the synthesis process of CDs to replace external energy supply.The basis of self-catalytic exothermic reaction is that triethylenetetramine(TETA)can quickly prompt the decomposition of hydrogen peroxide(H2O2),during which oxygen is produced and a large amount of heat is released.The as-released heat can make the temperature of the solution increased from room temperature to about 100 oC.Such high temperature can make reaction precursors condensation,then carbonize to form s-GQDs.All of the reactions can be finished in only 5 min.Moreover,the s-GQDs have 2.3% of quantum yield,and rich hydroxyl,anime groups and Schiff base(C=N)structures,which can specifically bind with aluminium ion through coordination and electro-static interaction,producing aggregation-induced emission enhancement effect.4.The self-exothermic synthesis of carbon quantum dots(CQDs)and the selective detection of vitamin B12(VB12).Ethylenediamine(EDA)acting as a catalyst can promote the decomposition of H2O2 to product oxygen and release a lot of heat.The as-released heat is enough to make reaction precursors condensation,and then carbonize to form CQDs.The synthesis can be completed within 15 min,meanwhile,the as-prepared CQDs possess 24.6% of quantum yield,which is greater than other reported CQDs synthesized at room temperature and can efficiently used for cellular imaging and analytical detection.Moreover,the PL of CQDs can be efficiently quenched by VB12 through inner filter effect.Based on this,we construct a selective fluorescence detection method for VB12 detection,and the content of VB12 in VB12 injection has been determined successfully.In conclusion,two kinds of functional CDs with different properties are abtained through direct doping and surface modification with terbium ions.The as-prepared CDs realize the specific detection of explosive TNP and biological active pp Gpp,respectively.Importantly,it is the first time that the self-exothermic reaction replaceing external heating is used for the synthesis of highly PL CDs on the basis of traditional hydrothermal synthesis.The main principle is based on the highly efficient heat release from decomposition of H2O2 catalyzed by organic amine,making the reaction precursors condensation,then carbonizd to form CDs.In addition,the as-obtained CDs can be used for the selective detection of aluminum ions and VB12,respectively,and relize analysis and application in actual samples.Therefore,the self-exothermic synthesis method not only reduces production coast,but also meets green and efficient-energy of sustainable development concept,which provide a new idea for new green synthesis of nanomaterials.