Synthesis And Properties Of Novel Green Fluorescent Carbon Dots And Their Optical Thin Films

Fluorescent carbon quantum dots which also can be called carbon dots(CDs)have attracted attention due to their low costs,water solubility,low toxicity,surface modification flexibility,good biocompatibility,and high photostability.CDs have potential applications in bioimaging,drug delivery,fluorescent pattern,sensors,photocatalysis optoelectronic devices and optical thin films.Various synthesis methods have been developed to prepare CDs,including hydrothermal route,solvothermal route,pyrolysis method,microwave-assisted synthesis and electron-beam irradiation.On the other hand,different precursors,including natural products or synthetic chemicals such as citric acid,o-phenylenediamine and urea etc.,have been widely explored for CDs with different size,structure,morphologies,luminescence,and surface groups.However,a majority of carbon dots show blue emission,limiting their applications in multi-color required fields,such as colorful detection and imaging,white LED,etc.Thus,long wavelength luminescent carbon dots,such as green or red luminescent carbon dots,are one of the key problems to be solved in this field.In addition,it is still a challenge to introduce long-wavelength luminescent carbon dots into photonic crystals to construct optical films with double optical response properties.In this paper,a novel green fluorescent carbon dots was developed,its application in metal ion sensing and solvation effect was studied.And on that basis,the fluorescence photonic crystal gel film was prepared by combining the green carbon dots with the photonic crystal film.The response of the film to different temperatures and solvents was studied,and then the two-mode optical detection mechanism was explored.The following main results were obtained through a series of characterization and testing:(1)A novel green fluorescent carbon was prepared by one-step solvent heating method and its properties were studied.In this part,sodium lignosulfonate and p-phenylenediamine were first used as carbon,nitrogen and sulfur sources,and then movel green fluorescence carbon dots was prepared by one-step solvent thermal method.The carbon dots was evenly distributed in particle size,and its size was about 2 nm.The carbon dots also has good optical stability and solubility in water.The carbon dots can show the bright green under 365 nm UV lamp irradiation,and when there are many kinds of metal ions,the aqueous solution of carbon dots has obvious fluorescence quenching effect on iron ion or silver ion,indicating that it has strong selectivity to these two kinds of ions.The fluorescence intensity showed a good linear relationship with the concentration of iron/silver ion solution(between 100 mol/L and 1000 mol/L),and the detection limits were 1.7 ?M and 11.6 ?M,respectively.In addition,the carbon dots could be used for the detection of iron ion concentration in actual water samples and the imaging of Hela cells.It was found that the carbon dots were emitting green fluorescence in water and acid organic solvents,while blue fluorescence was emitting in alcohol and amide organic solvents,and further applied to the detection of the above mixed polar solvents.Based on the above results,the luminescence mechanism of green fluorescent carbon dots was studied: functional groups on the surface of carbon dots played a crucial role.(2)In the second part,through the template synthesis method,the photonic crystal with the green fluorescent carbon dots were combined to prepare fluorescent photonic crystal gel film,and the performance of film was studied.In the first place,the opal photonic structure photonic crystal thin film was prepared by vertical deposition method and used as template.Hydroxyethyl methacrylate(HEMA),acrylic acid and NIPAM were used as monomers,and the mixed aqueous solution of acrylic modified carbon dots and initiator 1173 was filled into the above template.Then the hydrogel/opal template composite structure was formed by UV curing.Finally,the fluorescence photonic crystal gel film was obtained by selective etching.The prepared fluorescence photonic hydrogels reflect the versatility and have two optical characteristics:(1)reflection-based structure color;(2)luminescence characteristics based on fluorescence.At the same time,different temperatures and solvents can be detected by using these two optical characteristics.In terms of solvent detection,when the ethanol accounted for the proportion of larger and the concentration is between 0 to 25%,the fluorescence intensity of fluorescence photonic crystal hydrogel is higher,when the ethanol concentration reached 25%,fluorescence intensity will be decreased with the increase of ethanol concentration.When the concentration of ethanol increased from 0 to 45%,the reflection wavelength of fluorescence photonic crystal gel film is gradually red shift,and the ethanol concentration with reflection wavelength of fluorescence photonic crystal gel film has good linear relationship;in terms of temperature response,with the increase of temperature,the reflection spectrum of fluorescence photonic crystal gel film has a blue shift trend,and its fluorescence intensity gradually decreases.