Preparation,Characterization Of Carbon Quantum Dots And Their Applications In Plant Imaging

Carbon quantum dots(CQDs)are a new kind of zero-dimensional material with the carbon skeleton structure,and its size are lower than 10 nm(smaller or close to the Poule radius of exciton)so that CQDs can emit bright fluorescence excited by the ultraviolet light due to its quasi-split energy level.The CQDs has been widely applied in the bio & chemical sensing fields due to the good fluorescence,good water solubility and biocompatibility,and high chemical stability.According to the type and molecular size of the reactants,the synthetic methods of CQDs can be divided into the top-down synthesis and bottom-up synthesis.Specific experimental methods include carbonization,calcination,pyrolysis,hydrothermal,solvothermal,chemical oxidation,erosion,electrochemistry,ultrasound processing and microwave assist methods.Among these CQDs synthesis methods,the microwave method is one of the fastest and simplest methods,whereas other synthesis methods mostly involve complex reactions and severe synthesis conditions.It is difficult to control the molecular weight during the process of generating CQDs.Therefore,the size and the surface groups of CQDs are different when the synthesis methods of CQDs are different.We can control the size and properties of the CQDs through purification grogress in order to expand the application of CQDs.In this paper,we studied the structure and properties of CQDs synthesized by the microwave assist method,and then used organic solvents to purify CQDs in order to overcome the drawback of that most CQDs only excited under UV.The CQDs were applied in plant imaging research for the practical application of CQDs.This woke was funded by National Natural Science Foundation of China(No.61575150).The main research contents and results of this paper are as follows:(1)CQDs were synthesized by the microwave assisted method,in which citric acid used as carbon source,ammonia,urea and thiourea used as nitrogen source,respectively.The effects of reaction time and raw material ratio on the fluorescence properties of CQDs were studied in detailed.The results show that the CQDs were more suitable for long-wavelength light excitation(430 nm).The structures and morphologies of carbon quanta were characterized by the infrared,X-ray photoelectron spectroscopy and transmission electron microscopy.The results showed that the CQDs were spherical particles with 5 nm and the surface groups of CQDs are-COOH,-NH2,-OH,et.al.(2)Ethanol,acetone and ethyl acetate were used as solvent to purify the synthesized CQDs,respectively.The effects of different organic solvents on the fluorescence properties of CQDs were studied.The results showed that the CQDs with ethanol purification had the best fluorescence performance,the quantum yield reached 24.3%,and the optimal excitation wavelength was up to 460 nm.(3)The CQDs solutions were used to cultivate melon and rice seedlings to study the transport of CQDs in plants.Through the study of plant cell imaging,we can see that CQDs have good biocompatibility and it can be absorbed by the plant roots,and then transported to the leaves.The accumulation of CQDs increases with time in culture over a period of time.