Synthesis Of Alkali Lignin/Polyethyleneimine Carbon Dots And Its Application In Analysis And Detection

Carbon dots?CDs?is a new type of fluorescent nanocarbon material that can stably emit light.It's a particle size of less than 10 nm with a quasi-spherical structure.Compared to conventional semiconductor quantum dots,it has no heavy metal contamination and low biological cytotoxicity.It is an environment-friendly material that can be functionalized by chemical modification.The particle size of the carbon dots is smaller compared to organic dyes,which facilitates cell imaging,labeling and detection by intramolecular encapsulation.Due to the current high-cost preparation of carbon dots,complicated operation,difficult purification,low fluorescence efficiency,strong acid or strong oxidant and some other problems,and the biomass material,alkali lignin?AL?,and polyethyleneimine?PEI?are used as carbon source,meanwhile,polyethyleneimine is applied as a surface deactivator,and a high fluorescence efficiency AL/PEI-CDs is simply and efficiently prepared by one-step hydrothermal method in the presence of hydrogen peroxide,and fluorescence properties,chemical structure,crystal structure,surface microstructure and pH sensitivity of the samples were studied respectively.Through the study of the quenching of metal ions,amino acids and dyes,it was found that the obtained fluorescent carbon dots have highly selective quenching to sunset yellow at the same time the mechanism was further studied.Then,regarding the application research of carbon dots analysis and detection in the study,based on the dynamic imide bond,AL/PEI-CDs were immobilized in the matrix of dialdehyde cellulose nanocrystals?DA-CNCs?to construct a new type of nanocellulo-based fluorescent probe,which is expected to expand the efficient,green conversion and functional utilization of forest resources.The main contents and results of this paper are as follows:?1?Alkali lignin?AL?and Polyethylenimine?PEI?were used as carbon sources.PEI was used not only as a carbon source but also as a surface passivator.Under the oxidation of H₂O₂,it was green by one step hydrothermal method.Efficient preparation of high fluorescence,long life and polyethylenimine carbon dots?AL/PEI-CDs?.The effects of alkali lignin/PEI mass ratio,hydrothermal temperature and hydrothermal time on the fluorescence intensity of carbon dots were investigated.The optimal reaction conditions were determined.The sensitivity and stability of AL/PEI-CDs to pH were also investigated.Ultraviolet spectrophotometer?UV-vis?,fluorescence spectrophotometer,atomic force microscope?AFM?,high resolution transmission electon microscopy?HRTEM?,Fourier infrared spectrometer?Fourier?The optical properties,morphology,chemical structure and crystal structure of AL/PEI-CDs were characterized by transform infrared spectroscopy?FTIR?and X-ray diffractometer?XRD?.The results showed that the fluorescence quantum yield?QY?of the synthesized AL/PEI-CDs was25.53%,fluorescence under the condition of alkali lignin/PEI mass ratio of 1:12,hydrothermal temperature of 190°C and hydrothermal time of 12h.The life is 5.06 ns,the surface is rich in amino and hydroxyl groups,and the particle size is uniform,water-soluble and good stability.The corresponding emission peak is 405 nm at the optimal excitation wavelength of ex=313 nm.Bright blue light is emitted under the UV lamp.The carbon dots prepared in this study may have good application prospects in ion monitoring and cell metabolic process monitoring proton sensors.?2?Exploring the application of AL/PEI-CDs in analysis and detection,as well as the reaction of various common heavy metal ions,amino acids and dyes with AL/PEI-CDs,the results show that AL/PEI-CDs has good selectivity for sunset yellow.In addition,the mechanism of fluorescence quenching is explained by studying the effects of buffer system pH,reaction time and temperature on quenching conditions.The sunset yellow concentration has a good linear relationship with AL/PEI-CDs in the range of 0.1×10^-61×10^-44 mol/L.The linear regression equation is:log??I₀/I=0.0113x+0.0277,R²=0.9989?.?3?Preparation of dialdehyde cellulose nanocrystals by sodium periodate oxidation method,dynamic imine bond combines AL/PEI-CDs with Dialdehyde cellulose nanocrystals,fixes fluorescent carbon dots on the surface of Dialdehyde cellulose nanocrystals,and synthesizes new fluorescent carbon dots Composite material.The results of FTIR and XPS showed that the surface aldehyde group?-CHO?of DA-CNCs reacted successfully with the amino group?-NH₂?of AL/PEI-CDs to form an imine bond?C=N?.This research is expected to be applied to be simple and effective.Ion detection,separation and catalyst fields.