The Preparation And Application Of Doped Carbon Quantum Dot Nanomaterials

Carbon quantum dots（CQDs）exhibit some striking features,such as simple and cost-effective synthesis routes,excellent biocompatibility,water solubility,and fluorescence properties.Therefore,CQDs have been widely used in sensors,photocatalysis,biological imaging and other fields.In order to improve the quantum yield of CQDs,nitrogen doping is the most effective strategy.Therefore,this paper explores the preparation,morphology,structure and application of N-doped CQDs,（N,S）co-doped CQDs and（Si,N）co-doped CQDs.Specific research contents are as follows:（1）Nitrogen-doped carbon quantum dots（N-CQDs）were synthesized by hydrothermal method from citric acid（CA）and tetraethylene pentamine（TEPA）.N-CQDs was characterized by X-ray diffraction and infrared spectrum.N-CQDs has good water solubility and light stability.And it is applied to the detection of Fe³⁺.The fluorescent sensor has high sensitivity and specificity of metal ion selection.The detection range of Fe³⁺is 0-540×10^-6mol·L^-1,and the detection limit is as low as 6.377×10^-6 mol·L^-1.It is a valuable Fe³⁺detection tool,which has been successfully applied to the detection of environmental water samples.Moreover,The interaction mechanisms of N-CQDs and bovine serum albumin（BSA）were investigated with the aid of spectroscopic techniques.The results indicated that the native fluorescence intensity of BSA quenched on increasing N-CQDs,and it was a combination of dynamic and static quenching mechanism.N-CQDs altered the micro-environment of tryptophan（Trp）residues in BSA,and N-CQDs changed the hydrophobicity of the micro-environment of the amino acid residues,that was,the conformation of BSA had a slight change.By analyzing the thermodynamic parameters of quenching process,it was found that the interaction force between N-CQDs and BSA was mainly electrostatic attraction,and the reaction was a spontaneous process.（2）In this article,carbon quantum dots（CQDs）were prepared via hydrothermal method from citric acid（CA）and thiosemicarbazone（TSC）.The obtained Nitrogen and sulphur Co-Doped Carbon Quantum Dots（N-S-CQDs）can be applied in a variety of situations,such as both environmental sensor and in cell imaging,is very attractive and promising.N-S-CQDs can be utilized as a reliable fluorescent sensor for ferric ions(Fe³⁺)detection and He La cell imaging.N-S-CQDs have high quantum yiled（at excitation wavelength of 360 nm:34%）.Regards to Fe³⁺detection,the N-S-CQDs show low detection limit(4.039μmol·L^-1)with the detection rage of 0-1780μmol·L^-1,high selectivity when 14kinds of other cationic ions are present and high accuracy to determine the concentration of Fe³⁺in tap water and lake water.Regards to bio-imaging,the N-S-CQDs showing low toxicity,are successfully loaded into cells and emit blue fluorescence in cytoplasm.Furthermore,the N-S-CQDs possess good water dispersibility and excellent photochemical stability,revealing the big potential for practical applications.（3）Si-and N-doped carbon quantum dots（Si-N-CQDs）were prepared from using only citric acid（CA）and（3-Aminopropyl）trimethoxysilane（APTES）.These codoped Si-N-CQDs demonstrated spherical morphology and an average size of～2.54 nm as well as good solubility in water and high quantum yield equal to 14.3%.Fluorescence emission of these Si-N-CQDs was quenched selectively under the presence of Fe³⁺.Based on this property,we developed a very sensitive sensor capable to detect Fe³⁺up to 400μmol·L^-1concentration with a 3.14μmol·L^-1 detection limit.This sensor was used for Fe³⁺detection in real tap and lake water and demonstrated satisfactory recovery equal to 102.3-108.0%and 103.5-108.5%,respectively.Photocatalytic activity of our Si-N-CQDs was demonstrated using methylene blue（MB）organic dye.The degradation rate of MB under visible light irradiation increased 2.7 times under the presence of Si-N-CQDs.The degradation efficiency of MB at the presence of Si-N-CQDs could almost reach up to 88.5%in 60 min.Such excellent performance was attributed to very efficient light absorption of Si-N-CQDs as well as excellent electron transfer and separation of photogenerated charge carriers.