Multi-color Fluorescence Regulation And The Corresponding Applications Of Functionalized Carbon Quantum Dots

Carbon quantum dots?CQDs?are carbon-based novel nanomaterials with a spherical structure with dimensions of 10 nm or less.Since the discovery of carbon quantum dots,carbon quantum dots have become a hot topic for researchers.Carbon quantum dots have the advantages of good chemical stability,high photostability,excellent biocompatibility,low toxicity,and low preparation cost.Therefore,they have broad application prospects in the fields of light-emitting devices?LED?,fluorescence detection,photocatalysis,and biosensing.At present,most of the researches on carbon quantum dots have problems such as insufficient preparation cost,solid state and easy fluorescence quenching.Therefore,in the work of this paper,we aimed at the above bottleneck problem and tried to achieve full-color fluorescence regulation of fluorescent carbon quantum dots through a low-cost synthesis method.The fluorescent CQDs@SiO₂ solid powder was synthesized by reverse microemulsion method,which effectively avoided the fluorescence quenching of carbon quantum dots in the solid state.Fluorescent CQDs@ZIF-8 composites were successfully prepared by the combination of carbon quantum dots and metal organic framework material ZIF-8.The research contents and results are as follows:?1?The tunable luminescence of fluorescent carbon quantum dots was investigated by the preparation of three kinds of systems,and finally the fluorescent carbon quantum dot luminescent materials covering the visible light band were obtained.Firstly,the concentration of the reactant solution and the nitrogen source were changed to prepare different carbon quantum dots by PVA method.The prepared carbon quantum dots gradually shifted red with the increase of the concentration of the reactant solution and the change of the nitrogen source.The method has a small illumination tuning range for carbon quantum dots,and only blue and green carbon quantum dots are prepared.Then,by changing the amount of phosphoric acid and replacing different nitrogen sources,blue,green and yellow fluorescent carbon quantum dots emitting in the wavelength range of 450 nm to 550 nm were obtained by the phosphoric acid method.However,the preparation of full-color carbon quantum dots was still not realized.Finally,orange light and red light carbon quantum dots were obtained by citric acid method with adjusting the ratio of reactants,reactant concentration and reaction temperature.By further adjusting the reaction conditions,fluorescent carbon quantum dots with emission wavelengths from 450 nm to 650 nm were prepared,and the full-color luminescence of carbon quantum dots was realized.The structural characteristics and fluorescence properties of the prepared full-color fluorescent carbon quantum dots were characterized,and the tunable luminescence mechanism of fluorescent carbon quantum dots was further explored.It was preliminarily indicated that the peak position of the fluorescent peaks of carbon quantum dots was attributed to The degree of surface oxidation and the change of carboxyl groups.?2?Full-color luminescent fluorescent CQDs@SiO₂ solid powder was obtained by reverse microemulsion method.The carbon quantum dots were coated with SiO₂,and the full-color luminescent fluorescent CQDs@SiO₂ solid powder was successfully obtained.The abundant hydroxyl groups on the surface of the carbon quantum dots react with ethyl orthosilicate to obtain carbon quantum dots coated with SiO₂.The prepared fluorescent CQDs@SiO₂ solid powder maintains the surface state and environment of the carbon quantum dots,effectively avoiding the aggregation-induced luminescence quenching of the fluorescent carbon quantum dots.The performance of the fluorescent Y-CQDs@SiO₂ solid powder with different amounts of TEOS was characterized.The obtained Y-CQDs@SiO₂ solid powders of various sizes have good dispersibility.Depending on the amount of TEOS added,the prepared phosphors have a wide range of control?18-159 nm?and can be applied in different fields.Finally,LEDs based on fluorescent CQDs@SiO₂ solid powder were prepared using the above-mentioned full-color luminescent fluorescent CQDs@SiO₂ solid powder.By adjusting the content ratio of fluorescent CQDs@SiO₂ solid powders with different colors,a white LED with a CIE value of?0.3497,0.3045?was successfully prepared.?3?ZIF-8 and CQDs@ZIF-8 were successfully prepared by room temperature stirring.The prepared ZIF-8 and CQDs@ZIF-8 are relatively standard rhombohedral dodecahedrons,and the size of the matrix material before and after the incorporation of fluorescent carbon quantum dots is not large.The full-color fluorescence of CQDs@ZIF-8 is achieved,covering almost the entire spectrum of the visible spectrum.Then,CQDs@Eu-ZIF-8 with different dosage ratios was further prepared.The doping of Eu³⁺ions can regulate the size of the framework material.As the Eu³⁺ion content ratio increases,the particle size of CQDs@Eu-ZIF-8 increases from tens of nanometers to several micrometers.At the same time,the luminous intensity of the CQDs@Eu-ZIF-8 blue light band gradually decreases with the increase of the Eu³⁺ion content ratio,and the luminous intensity of the red light band gradually increases.The structural properties and fluorescence properties of CQDs@Eu-ZIF-8 were compared.The 10%CQDs@Eu-ZIF-8 was selected for metal ion detection.The blue band of 10%CQDs@Eu-ZIF-8 has obvious fluorescence quenching in the presence of Fe³⁺ions.The detection range of Fe³⁺ions is 0-8?M,and the detection limit is less than 500 nM.An application demonstration of a fluorescence ratio probe with 10%CQDs@Eu-ZIF-8 as Fe³⁺ion detection was implemented..