CN111117610A

CN111117610A - Method for efficiently preparing water-soluble blue fluorescent carbon nanoparticles

Info

Publication number: CN111117610A
Application number: CN201911317989.8A
Authority: CN
Inventors: 周兴平; 柳絮萦; 马琛敖
Original assignee: Donghua University
Current assignee: Donghua University; National Dong Hwa University
Priority date: 2019-12-19
Filing date: 2019-12-19
Publication date: 2020-05-08

Abstract

The invention relates to a method for efficiently preparing water-soluble blue fluorescent carbon nano-particles. The method comprises the following steps: mixing citric acid monohydrate with ethylenediamine, calcining, cooling, purifying and drying. The method prepares the water-soluble blue fluorescent carbon dots with high fluorescence quantum yield and high yield.

Description

Method for efficiently preparing water-soluble blue fluorescent carbon nanoparticles

Technical Field

The invention belongs to the field of carbon nano-material preparation, and particularly relates to a method for efficiently preparing water-soluble blue fluorescent carbon nano-particles.

Background

The carbon dots not only keep the advantages of low biotoxicity, good biocompatibility and the like of the carbon-based material, but also have the excellent characteristics of light stability, adjustable light-emitting range, excellent water solubility, no light wink, no light flicker, light bleaching resistance, easy functionalization, abundant and cheap raw material sources, easy large-scale synthesis and the like. Moreover, the carbon dots have great potential in the fields of application, including ion detection, cell imaging and the like, are good choices for replacing quantum dots and traditional markers, and have wide application prospects.

However, due to the limitation of the prior art means, the preparation and synthesis of carbon dots enter the bottleneck period, and the large-scale, simple, environment-friendly and high-efficiency mass production of fluorescent carbon dots is still an important research direction.

Since 2004, carbon dots with photoluminescence effect are reported to have been developed for fourteen years, and the synthesis method is complicated, and can be mainly classified into three categories: "Top-down" (Top-down synthetic route), "Bottom-up" (Bottom-up synthetic route), and surface modification (surface treatment and functional).

The top-down method mainly adopts nano diamond, carbon nano tube, graphite, carbon dust and the like as raw materials, and nano carbon particles are peeled off from a larger carbon skeleton. The fluorescent carbon dot particles prepared in the way are uniform, but the quantum yield is generally low, and the energy consumption is huge.

The bottom-up method mainly uses carbonization to make macromolecular organic substances into small molecules. Generally, the fluorescent carbon nanoparticles are prepared by using citric acid, carbohydrate, polymer and other raw materials, and the surface of the micromolecular carbon particles is modified or passivated to obtain the fluorescent carbon nanoparticles with higher fluorescence quantum yield. The carbon dots obtained by the method have high fluorescence quantum yield, but have the phenomenon of serious nanoparticle agglomeration. Chinese patent CN109181689A discloses that citric acid, hexadecylamine and urea are mixed according to the mass ratio of 1:1:1-1:5:3, calcined at 120-220 ℃ for 5min-8h, dissolved in an organic solvent, filtered, dried and extracted to obtain the hydrophobic nitrogen-doped fluorescent carbon dots.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for efficiently preparing water-soluble blue fluorescent carbon nano particles so as to overcome the defects of low preparation yield and low quantum yield of carbon dots in the prior art.

The invention discloses a method for efficiently preparing water-soluble blue fluorescent carbon nano particles, which comprises the following steps:

mixing citric acid monohydrate and ethylenediamine, calcining, cooling, purifying and drying to obtain the water-soluble blue fluorescent carbon nano-particles, wherein the ratio of the citric acid monohydrate to the ethylenediamine is 1-2g:0.2mL-0.8 mL.

The calcination temperature is 130-170 ℃, and the calcination time is 10-30 min.

The calcination is as follows: fully mixing citric acid monohydrate and ethylenediamine in a nickel crucible, wrapping the crucible with tin foil paper to prevent a large amount of ethylenediamine from volatilizing, and putting the crucible in an oven at 130-170 ℃ for heating for 10-30 min.

The centrifugation speed is 8000-10000r/min, and the centrifugation time is 10 min.

The purification is carried out by adopting a microporous filter membrane with the pore diameter of 0.22 micron.

The invention provides a water-soluble blue fluorescent carbon nanoparticle prepared by the method.

The invention also provides application of the water-soluble blue fluorescent carbon nano-particles prepared by the method.

The invention adopts ethylenediamine as nitrogen doping agent, has high amino content and more activity compared with hexadecylamine, has fluorescence quantum yield of more than 90 percent, adopts solid phase pyrolysis method, has easy operation process, simple reactant materials, no need of any additive, activator, solvent and the like, is green, safe and pollution-free, has high atom utilization rate and yield, and accords with the green chemical principle.

Advantageous effects

According to the invention, citric acid is used as a carbon source, ethylenediamine is used as a nitrogen dopant, and the water-soluble blue fluorescent carbon dots with high fluorescent quantum yield and high yield are prepared by a solid phase pyrolysis method, wherein the quantum yield is up to more than 90%, and the yield is up to more than 80%. The preparation method has the advantages of simple preparation process, good product performance, rich raw materials and extremely low cost, and is suitable for large-scale, simple, environment-friendly and mass production. Therefore, the fluorescent carbon dots prepared by the method have a high practical prospect.

Drawings

FIG. 1 is a schematic diagram of a process for preparing a water-soluble fluorescent carbon dot and an excitation process;

FIG. 2 is a three-dimensional fluorescence spectrum of carbon dots (CA-EDA-CDs) according to the present invention;

FIG. 3 is a UV-fluorescence composite spectrogram for determining fluorescence quantum yield of a product in example 1;

FIG. 4 is a graph of the change in fluorescence intensity of the carbon spot (sample A) with time within 100 minutes as measured by the fluorometer in example 3;

FIG. 5 is a graph showing the change of fluorescence intensity with time of the carbon spot in example 3 after being continuously excited for 9 hours under a 350nm xenon lamp, and a graph showing the change of intensity of the carbon spot in example 3 on the right.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

The main reagent used was citric acid monohydrate (99.0%, 500g), purchased from national pharmaceutical group chemical agents, ltd; ethylenediamine (99.0%, 500ml), purchased from national pharmaceutical group chemical agents, ltd; quinine sulfate (25g, 99%), available from national drug group chemical agents, ltd.

Example 1

In order to study the fluorescence quantum yield of the fluorescent carbon dots, 1g of citric acid monohydrate solid and 0.5ml of ethylenediamine liquid are weighed and fully mixed in a nickel crucible by using citric acid monohydrate as a carbon source and ethylenediamine as a nitrogen dopant, the crucible is wrapped by tinfoil paper to prevent a large amount of ethylenediamine from volatilizing, and the mixture is placed in an oven at 150 ℃ for 20min to obtain a carbon dot crude product. Slightly cooling the synthesized carbon dots (CA-EDA-CDs), adding 10ml of deionized water for dissolving, after the synthesized product is fully dissolved, centrifuging at a high speed by using a centrifuge at a rotating speed of 10000r/min for 10min, and taking supernatant; filtering and purifying the centrifuged carbon dot (CA-EDA-CDs) supernatant solution through a 0.22 micron microporous filter membrane to obtain a carbon dot solution; freeze drying to obtain carbon dot solid powder, and irradiating with ultraviolet lamp to obtain blue powder.

Diluting the purified sample solution until the ultraviolet absorbance is lower than 0.05, and detecting the fluorescence intensity of the solution to obtain a fluorescence map of the carbon dot solution;

the simplest and most direct parameter for measuring the fluorescence intensity of the fluorescent substance is the fluorescence quantum yield, and the fluorescence quantum yield is also used for quantitatively analyzing the fluorescence intensity of the nitrogen-doped fluorescent carbon dots in the experiment. Taking quinine sulfate as a standard reference substance, measuring the absorbance of a quinine sulfate standard solution at the same excitation wavelength (350nm), and recording the fluorescence emission peak area (the fluorescence spectrophotometer software automatically calculates S3). The quantum yield was then calculated according to the following formula:

wherein QY is quantum yield, FA is fluorescence emission peak area, Ab is absorbance under excitation wavelength, η is refractive index of solution, subscript sm is sample, and st is reference substance.

The default refractive index of the aqueous carbon dot solution and the aqueous quinine sulfate solution are the same. Dissolving a small amount of quinine sulfate in sulfuric acid with the concentration of 0.01M to prepare a standard quinine sulfate solution (C)_{Quinine sulfate}＝2×10^-6mol/L) as reference substance. Then measuring the absorbances of the fluorescent carbon dot aqueous solution and the quinine sulfate solution at corresponding excitation wavelengths, respectively using deionized water to dilute the carbon dot aqueous solution and 0.01M sulfuric acid solution to dilute the quinine sulfate solution until the absorbances of the two solutions are less than 0.05 (the absorbance is less than 0.05, and the influence caused by the self-absorption of the solutions can be prevented) at the corresponding excitation wavelengths, respectively measuring a fluorescence emission spectrum obtained by the quinine sulfate under the excitation condition of 350nm and a fluorescence carbon dot fluorescence spectrum obtained by the fluorescent carbon dots under the optimal excitation wavelength, calculating the area of the half-peak height of the fluorescence emission spectrum and the fluorescence carbon dot fluorescence spectrum, substituting the areas into the formula, and calculating the quantum yield which is higher than 80% and can reach 92.5% at most (see table 1).

TABLE 1 statistical tables of quantum yields of samples and references

As can be seen from the 3D image of FIG. 2 and the contour lines of the fluorescence spectra of the bottom layer EX and EM, when the excitation wavelength is 330nm, the corresponding emission wavelength is about 445nm, where the fluorescence intensity is strongest, corresponding to the sharp point in the 3D image. As can be seen from FIG. 3, the blue carbon dot has only one ultraviolet absorption peak, and the maximum absorption peak is at about 330 nm; when the carbon spot was de-excited with excitation light at 330nm, it was seen that there was one and only one fluorescence emission peak, with the maximum emission peak position at about 450nm, which corresponds to the blue carbon spot observed.

Example 2

The procedure of example 1 was repeated except that "0.5 ml of ethylenediamine liquid" in example 1 was changed to "0.2 ml of ethylenediamine liquid", and "20 min heating in an oven at 150 ℃ was changed to" 10min heating in an oven at 150 ℃, so that a carbon dot solution was obtained, and the carbon dot solution was lyophilized into powder by a low-temperature lyophilizer. The final mass of the weighed powder was 0.9826g, and the sum of the masses of the reactants before the reaction was 1.2g, giving a product yield of 80% or more.

Example 3

The carbon dot powder in example 2 is taken for light stability study, the nitrogen-doped fluorescent carbon dots have unique and excellent light stability, and the light stability of the carbon dots can be simply detected through the Time Scan function of an F-4500 fluorescence spectrophotometer. The fluorescence spectrophotometer can only measure the fluorescence spectrum continuously excited for 100 minutes at most, the light stability for a longer time is not determined, so that the nitrogen-doped fluorescent carbon point is placed under a 350nm xenon lamp for continuous illumination, the fluorescence curve of the nitrogen-doped fluorescent carbon point is measured every 30min and is irradiated for 9 hours, and a graph of the change of the fluorescence intensity along with the excitation time is drawn, as shown in figures 4 and 5, the nitrogen-doped fluorescent carbon point prepared by the invention has better photobleaching resistance.

The solid phase pyrolysis method adopted by the invention has the advantages of simple operation steps, environmental protection, safety and no pollution, and the fluorescence quantum yield is up to more than 90 percent, so that the method is suitable for synthesizing carbon dots with stable optical properties and excellent performance in a large scale.

Claims

1. A method for efficiently preparing water-soluble blue fluorescent carbon nanoparticles, comprising:

2. The method according to claim 1, wherein the calcination temperature is 130-170 ℃ and the calcination time is 10-30 min.

3. The method as claimed in claim 1, wherein the centrifugation speed is 8000-10000r/min, and the centrifugation time is 10 min.

4. A water-soluble blue fluorescent carbon nanoparticle prepared according to the method of claim 1.

5. Use of the water-soluble blue fluorescent carbon nanoparticles prepared by the method of claim 1.