Preparation And Application Of Functionalized Fluorescent Carbon Dots

Carbon dot is a kind of nano-material with the dimension below 10 nm.It has attracted the attention of many researchers due to their excellent physical and optical properties.Up to date,diverse carbon dots have been developed and used in many fields,like a fluorescent sensor for the detection of pollutants,the bioimaging in medical field and the optoelectronic materials in energy field.But carbon dot still has some problems including low stability and single synthetic method.To address these bottleneck,some strategies were developed in this paper.Firstly,the solvothermal method is used to prepare ionic fluorescent carbon dots and apply them to the selective detection of metal ions.Secondly,the solvothermal method was used to prepare chiral fluorescent carbon dots,and a chiral fluorescent sensor based on carbon dots was constructed for the identification of non-aromatic amino alcohol enantiomers.Finally,the microwave-assisted method was used to prepare chiral fluorescent carbon dots and their optical properties were studied.The specific research contents are as follows:(1)To improve the stability in acidic or basic aqueous solutions,two ionic fluorescent carbon dots CDs-2 and CDs-3 were synthesized by solvothermal method,in which citric acid and 4-(aminomethyl)pyridine were used as the carbon source and the reaction precursor,respectively.Studies have found that protic solvents(such as ethanol,water and N,N-dimethylformamide)will significantly affect the fluorescence emission intensity of carbon dots.Because of the presence of pyridine cations,carbon dots have good fluorescence stability in solutions with p H=2?11.In addition,when Cu²⁺and Fe²⁺are present in the solution,the carbon dots will undergo fluorescence quenching.The PL quenching of CDs-2 for Fe²⁺and Cu²⁺is only 29%and 66%,respectively.Differently,the PL quenching of CDs-3 for Fe²⁺and Cu²⁺can be achieved with the values of 95%and 93%,respectively.Therefore,this study also tried to be used for the selective detection of specific metal ions.(2)A simple method was carried out to synthesize a chiral ionic carbon dot(S,S)-C-dots-1 by two steps.4-Pyridinemethaneamine was chosen as the amine precursor to react with citric acid followed by direct linkage to1,1'-((1S,2S)-cyclohexane-1,2-diyl)bis(3-(2-bromoethyl)urea),generating a pyridinium cation.Studies have found that with the participation of copper ions,carbon dots can be used to identify non-aromatic amino alcohol enantiomers.It is found that(S,S)-C-dots-1 has clear discrimination toward different configurations of nonaromatic amino alcohols in the presence of Cu(II).When(R)-isomer is added to the(S,S)-C-dots-1+Cu(II)solution,it shows much higher fluorescent intensity than(S)-isomer.The values of recognition efficiency are 2.9 and2.3 for 2-aminobutan-1-ol and 2-aminopropan-1-ol,respectively.(3)Different with the solvothermal method,a chiral carbon dot(S,S)-CHA-CD was synthesized by microwave-assisted method,in which citric acid and(1S,2S)-1,2-cyclohexanediamine were used as carbon source and a chiral modifier,respectively.The prepared carbon dots emit blue fluorescence under the irradiation of ultraviolet light and are independent on the excitation wavelength.When the excitation wavelength is in the range of 320-390 nm and 400-470 nm,the maximum emission wavelength of(S,S)-CHA-CD remains at 455 nm and 525 nm,respectively.Through further research,it is found that the prepared carbon dots still have chiral optical activity.Therefore,the preparation method can be applied to the preparation of chiral carbon dot materials.