The Preparation Of Carbon Quantum Dots And Their Complexes,Luminescent Properties And Application Research

Carbon nanomaterials such as fullerenes,carbon nanotubes and graphene have made great progress in the fields of materials science and life sciences.Recently,researchers are focus on carbon nanomaterials with luminescence properties to further expand the scope of carbon nanomaterials application.As a new type of carbon nanomaterial,carbon quantum dots(abbreviated as CQDs)not only have luminescent properties and small size characteristics similar to those of conventional quantum dots,but also have the advantages of adjustable wavelength of light emission,good water solubility,and low biological toxicity,which give promising opportunities in the light-emitting diodes,bioimaging,sensors,photocatalysis and fields.Therefore,it is particularly important for development of carbon dots with multi-color-emitted,high luminous efficiency,and simple synthesis method characteristics.Compared with CQDs in the form of liquids,which can only be used in bioimaging,solid-luminescence CQDs has a wide range of application prospects.However,such studies are relatively rare.Herein,in this paper reports we report the synthesis of several new kinds of CQDs and investigation of their luminescence properties.Additionally,a series of representative CQDs are used to study their solid-state behaviors.The detailed research works and conclusions are as follows:1.CQDs with good water solubility and excellent fluorescence properties were successfully prepared by a one-step hydrothermal method by using ethylenediamine as a nitrogen source and citric acid as a carbon source,respectively.Fluorescence and phosphorescence,UV-Vis absorption,FTIR and electron microscopy were utilized to discusse the effects of different synthesis temperatures and reaction times on the optical performance of synthesized CQDs.The results show that the synthesized CQDs has an average particle diameter of 4.8 nm,the emission peak locates at 450 nm under the excitation of 365 nm.the synthesized CQDs owns a quantum efficiency reached up to 80%and exhibits excitation wavelength independent fluorescence characteristics.The further studies show that the groups such as-OH,-COOH and-NH2 facilitate the dehydration and carbonization between molecules and promote the formation of CQDs.At the same time,these hydrophilic groups favor to the enhancement of its water solubility and quantum efficiency.2.Multi-color-emitted blue,green and red CQDs were successfully prepared by a solvothermal method by using o-phenylenediamine,m-phenylenediamine and p-phenylenediamine as nitrogen sources,citric acid as a carbon source and ethanol as solvent.The factors of temperature,reaction time and reaction pH values on the optical properties of synthesized CQDs were detailed discussed.The experimental results show that the red,green and blue carbon with emission peaks located at 445,535 and 615 nm can be obtained.The red CQDs quantum efficiency is as high as 25.3%and presents reversible discoloration characteristics in acid and alkali.Using the unique property of the color of the carbon dots solution,which has a reversible change,we make it a simple qualitative acid-base indicator.By using the relationship between the fluorescence intensity and the pH value of the carbon dots,we can make it into a pH meter for the quantitative determination of the pH value of the solution.3.BaSO4 and Al(OH)3 were chosen to achieve blue and green fluorescence CQDs-based composite materials by using the electrostatic assembly interaction,and all of the samples showed the green room temperature phosphorescence,Moreover,the solid composites still retain their green room temperature phosphorescence properties.The results show that blue fluorescence emission peak of the synthesized CQDs@BaSO4 composite material is 450 nm and the room temperature phosphorescence emission peak is 520 nm under and remove of 365 nm excitation,respectively.The average phosphorescence lifetime is 251 ms.The synthesized green CQDs emission peak located at 505 nm.After the coating of urea(UG),UG-CQDs composite exhibits fluorescence peak around 510 nm.In order to further improve the stability of the solid CQDs luminescent material,Al(OH)3 was used to coat UG-CQDs.This composite(UG-CQDs@ Al(OH)3)owns a fluorescence peak around 503 nm under the excitation of 365 nm.The room temperature phosphorescence emission peaks of UG-CQDs and UG-CQDs@ Al(OH)3 both locate at 510 nm,and the average room-temperature phosphorescent lifetimes are determined to be 808 and 300 ms,respectively.Studies also show that the obtained room temperature phosphorescent carbon dot composites have excellent resistance to acid and alkali solution properties and excellent thermal stability.Finally,the obtained carbon composites were successfully applied to anti-counterfeiting stamps.The obtained carbon composites have potential applications in anti-counterfeiting,information storage and white light-emitting-diode fields.