Preparation And Performance Study Of Fluorescent Carbon Nanomaterials

As an emerging fluorescent nanomaterial,carbon dots(CDs)attract more and more researchers' attention because of their unique properties,such as small particle size,good water solubility,good resistance to bleach and low toxicity.Optical lighting,ion detection,photocatalyst and other fields have potential application value.So far,most of the researches on CDs are the fluorescent performance in liquid state and that the prepared emission wavelengths are mainly concentrated in short-wavelength bands of blue and green.There is still few studies about the solid-state fluorescent performance and long-wavelength emission of CDs.For the existing problems of CDs in the current stage,this paper mainly studies the preparation of CDs composites and multi-light color CDs.At the same time,the properties and luminescent mechanism of the prepared materials are discussed,which lay the foundation on the development of CDs and the application of new fields.The main contents are as follows:1.A one-step thermal cracking method was used to prepare a CDs emitting yellow-green light,and then three solid-state CDs composite materials with fluorescent properties were prepared by simple compounding.First citric acid and urea were used as raw materials,and CDs emitting yellow-green luminescence were prepared at 200 ? by one-step thermal cracking method.The CDs have a graphite-like structure with particle diameter about 4 nm,and the surface is rich in functional groups,such as-OH,-NH,-COOH and so on.By testing luminescence,it is found that CDs have a strong emission at 518 nm with three excitations at 293 nm,362 nm,and 464 nm.And CDs show high fluorescent intensity,high quantum yield(58%),and good fluorescent stability.At the same time,three composite materials: carbon dot-silica,carbon dot-resin,carbon dot-silica aerogel composites were prepared by a simple one-step composite with ethyl silicate,acrylic resin,silica aerogel and prepared CDs.Optical testing of these three composite materials show that they all have good fluorescent properties and achieve the goal of fluorescent solid CDs.Compared to the CDs,their emission peaks are almost unchanged,which are 510 nm,508 nm,and 515 nm,respectively.Through the stability testing of composite materials,the results are found that the three CD composites have excellent resistance to light and heat stability.Based on this characteristic,we used carbon dot-silica composite and polydimethylsiloxane to prepare a LED device that can emit light in the entire visible light range,which also reflects the great applicable value in terms of optical illumination.In addition,we explored the formation of new chemical bonds when CDs are combined with the three raw materials,and the raw materials act as dispersed medium,to prevent agglomeration between the CDs and avoid fluorescence quenching.In the end composite materials have fluorescence.2.Multi-light color CDs,having an emission peak in the range of 490 nm to 650 nm,were prepared by solvothermal method.The color regulation was achieved by regulating the concentration of the raw material citrazinic acid,acetamide in the solvent N-N dimethylformamide and the reaction temperature.It's easier to produce long-wavelength-emitting CDs with the higher concentration and the higher reaction temperature.Three CDs(emission of 530 nm,585 nm and 650 nm)were selected as the research objects,and their structural characterization and optical tests were carried out.In terms of structure,they are all spherical,evenly distributed and exist in the form of graphitic carbon.The particle sizes of the green,orange,and red CDs are 1.94±0.53 nm,3.07±0.74 nm,and 4.45±0.86 nm,respectively.As the particle size increases,the emission wavelength gradually shifts to red.The surfaces are rich in functional groups such as-OH,-COOH,C=O,-NH and so on,and the content of functional groups are different.The relative contents of-COOH and C=O on the surfaces of green,orange and red CDs are gradually increased.In terms of optics,the fluorescence of the three light-colored CDs are not excited by ultraviolet light.The fluorescent emissions are relatively pure,and the higher fluorescent quantum yields are 56.9 %,37.5 %,24.8 %,respectively.The study has potential applications for CDs in new optical lighting applications.