Synthesis Of Carbon Quantum Dots By Mechanical Ball-milling And Its Application

Carbon quantum dots?CQDs?is a new kind of carbon nanomaterial with small size from 1 to 10 nm.Due to the unique optical properties,excellent biocompatibility,good chemical stability,easy modification and low cost,carbon quantum dots have broad application prospects in sensing,bioimaging,optoelectronics catalysis and photoelectric device.Though the syntheses and application of carbon quantum dots developed rapidly,the practical application and commercialization process has been a difficult problem to be solved urgently.Mechanical ball milling is one of the effective ways to produce nanomaterial.During the ball milling process,a series of non-equilibrium phase transitions and microstructural changes occur during the milling process owe to the high energy effect.The material after repeated grinds will create new interfaces and defects,and also leads to smaller particle size and a greater specific surface area with more excellent properties while achieving a highly homogeneous mixture of components.The operation process is simple and can be mass production.In this paper,a new method for the preparation of fluorescent carbon quantum dots by mechanical ball milling was developed.Then we explored their fluorescence properties,structure,morphology,and they could be applied in ions detection and bioimaging.The main research contents are as follows:In the first part,we report a facile approach to prepare Mg-doped CQDs using microcrystalline cellulose and magnesium by mechanical ball milling.And the influence of reaction time and ratio of reactant on the fluorescence properties of Mg-CQDs were further explored.The TEM results showed Mg-CQDs had uniform size was about 4.8 nm.The XPS,FTIR,X-ray diffraction and Raman results revealed that the Mg-CQDs are amorphous crystals,containing C,H,O,Mg elements,and the surface is rich of hydroxyl,carboxyl groups,which made Mg-CQDs have excellent solubility in water.It was found that the Mg-CQDs had good absorption and emission properties by UV-vis and fluorescence spectroscopy.In addition,it also has excellent photostability and fluorescence intensity and is almost no change even in acid or alkali,high concentration of salt solution.We found that iron ions can quench the Mg–CQDs effectively,while showing great selectivity towards Fe³⁺.Mg–CQDs as Fe³⁺ nano-probe,the detection limit is 0.9 ??/L.In the second part,to prepare CQDs with high photoluminescent and quantum yield,we modified nitrogen?carbamide,PABA,L-glutamine and the so on?during the ball milling process.The performance of CQDs with L-glutamine added is improved greatest.The TEM results showed Mg,N-CQDs had uniform size was about 5.8 nm.The surface is rich of hydroxyl,carboxyl as well as the new introduced amino groups,which made Mg,N-CQDs have excellent solubility in water.Mg,N-CQDs also have excellent resistance to light,strong acid,alkali,high concentration of salt solution and high temperature.The cytotoxicity test showed the Mg,N-CQDs had good biocompatibility.Meanwhile,MCF-7 cells were used as the imaging agents to invest the bioimaging effect of Mg,N-CQDs.The results showed that they could enter the cytoplasm and fully light the cells.Therefore,Mg,N-CQDs could be used as a potential alternative for organic dyes which are photobleach easily or semiconductor quantum dots which have certain biotoxicity in bioimaging.