CN114015441A

CN114015441A - Green solid fluorescent carbon dot and preparation method thereof

Info

Publication number: CN114015441A
Application number: CN202111506661.8A
Authority: CN
Inventors: 王得印; 郭君路; 王育华
Original assignee: Lanzhou University
Current assignee: Lanzhou University
Priority date: 2021-12-10
Filing date: 2021-12-10
Publication date: 2022-02-08
Anticipated expiration: 2041-12-10
Also published as: CN114015441B

Abstract

The invention discloses a green solid fluorescent carbon dot and a preparation method thereof, wherein the fluorescent carbon dot can be excited by ultraviolet light and blue light of 300-500 nm, the emission main peak is 450-650 nm, and the quantum efficiency is 45-75%. The preparation method comprises the steps of taking biuret and trisodium citrate as raw materials, adding the raw materials into deionized water, carrying out ultrasonic stirring, uniformly mixing, placing the mixture into a microwave oven, carrying out microwave heating reaction in the high-fire state of the microwave oven, soaking the softened reaction mixture in deionized water, and drying the softened product in an oven to obtain the green solid fluorescent carbon dots. The preparation method does not need any solid dispersion medium, has wide raw material sources, simple equipment and high synthesis speed, can be prepared in batches, has high luminous intensity of the prepared green light solid carbon dots, has good fluorescence stability, does not need complex modification in the later period, and has good application prospect in the fields of white light LEDs, optical communication and the like.

Description

Green solid fluorescent carbon dot and preparation method thereof

Technical Field

The invention belongs to the technical field of carbon nanodots, and relates to a green solid fluorescent carbon dot and a preparation method thereof.

Background

Carbon dots are a new type of carbon material found in recent years to have excellent optical properties. Compared with the conventional semiconductor quantum dots andthe organic dye and the carbon dots not only keep the advantages of small toxicity, good biocompatibility and the like of the carbon material, but also have the advantages of good stability, photobleaching resistance, easy functionalization, low price, easy large-scale synthesis and the like. Therefore, the carbon dots show good application prospects in the fields of biological imaging, fluorescent labeling, tumor treatment, sensing, photocatalysis, photoelectric devices, energy storage and the like. However, when the carbon dots are aggregated into a solid, the light emitting intensity of the carbon dots can be greatly reduced and even completely quenched due to the pi electron accumulation effect among carbon cores, which greatly limits the application of the carbon dots in the solid state light emitting fields of white light LEDs, optical communication, latent fingerprint development and the like. In order to realize solid-state luminescence of carbon dots, the prior art adopts dispersing the carbon dots in polymer (PMMA, PVA, PVP) or inorganic salt matrix (Ba)₂SO₄, NaSiO₃NaCl), however, this method has problems of uneven distribution of carbon points, poor reproducibility, poor stability, low load ratio, and the like.

Disclosure of Invention

The invention aims to provide a green solid fluorescent carbon dot.

The invention also aims to provide a preparation method of the green solid fluorescent carbon dots, which can prepare carbon dots with uniform distribution, good repeatability, good stability and high load rate.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a green solid fluorescent carbon dot can be excited by ultraviolet light and blue light of 300-500 nm, the main emission peak is 450-650 nm, the optimal emission peak is 520nm, and the quantum efficiency is 45-75%.

The other technical scheme adopted by the invention is as follows: the preparation method of the green solid fluorescent carbon dot specifically comprises the following steps:

1) respectively taking trisodium citrate and biuret according to the mass ratio of 1: 1.25-4, dissolving 1g of trisodium citrate in 8-13 mL of deionized water, taking deionized water, dissolving the trisodium citrate and the biuret in the deionized water, ultrasonically stirring, and uniformly mixing to obtain a reaction solution;

2) placing the reaction solution in a microwave oven, and carrying out microwave heating reaction for 1-2 min in a high-fire state of the microwave oven to obtain a reaction mixture;

3) soaking the softened reaction mixture in deionized water, and pouring out the supernatant to obtain a softened product; and (3) putting the softened product into an oven, and drying at the temperature of 50-80 ℃ for 20-60 min to obtain the green solid fluorescent carbon dots. The green solid fluorescent carbon dots are solid luminescent carbon nanodots.

The preparation method takes trisodium citrate (carbon source) and biuret (nitrogen source) as raw materials, and directly synthesizes the fluorescent carbon dots by a microwave method. The prepared fluorescent carbon dots are functionalized by a large amount of sodium carboxylate, so that carbon cores are not directly contacted, fluorescence resonance energy transfer is inhibited, the carbon dots can still emit light when being in a solid state, and fluorescence quenching caused by aggregation when being in the solid state is overcome.

The preparation method does not need any solid dispersion medium, takes the trisodium citrate and the biuret as raw materials, prepares the green solid fluorescent carbon dots by heating through a microwave method, is economic and quick, has simple operation, and can be prepared in a large scale. The prepared solid luminescent carbon nano-dots have the characteristics of short fluorescence life and high quantum yield, and have good application prospects in the fields of white light LEDs, optical communication and the like.

Drawings

FIG. 1 is a TEM image of a green solid-state fluorescent carbon dot prepared in example 3.

FIG. 2 is an XPS survey of green solid state fluorescent carbon dots from example 3.

FIG. 3 is a graph showing excitation and emission spectra of green solid state fluorescent carbon dots prepared in example 3.

FIG. 4 is a graph of the emission spectra of green solid state fluorescent carbon dots produced in example 3 as a function of excitation wavelength.

FIG. 5 is a graph of the decay of green solid state fluorescent carbon dots produced in example 3.

FIG. 6 is a photoluminescence spectrum of green solid-state fluorescent carbon dots prepared in examples 1 to 4.

Detailed Description

The invention is further illustrated by the following figures and examples.

Example 1

Dissolving 0.5g of trisodium citrate and 1.25g of biuret in 8mL of deionized water, ultrasonically stirring, and uniformly mixing to obtain a reaction solution; placing in a microwave oven, heating with medium-high fire microwave, and reacting for 90s to obtain reaction mixture; the softened reaction mixture was soaked in 10mL of deionized water for 2.5h, the supernatant was decanted to obtain a softened product, which was then dried in an oven at 60 ℃ for 30min to obtain a green solid fluorescent carbon dot (denoted as sample 1). The emission wavelength of sample 1 was 510 nm.

Example 2

Dissolving 0.5g of trisodium citrate and 1.375g of biuret in 8mL of deionized water, ultrasonically stirring, and uniformly mixing to obtain a reaction solution; placing the reaction solution in a microwave oven, and carrying out microwave heating reaction for 90s under a high-fire state to obtain a reaction mixture; the softened reaction mixture was soaked in 10mL of deionized water for 2.5h, the supernatant was decanted to give a softened product, which was dried in an oven at 60 ℃ for 30min to give a solid green fluorescent carbon dot (denoted as sample 2). The emission wavelength of sample 2 was 520 nm.

Example 3

Dissolving 0.5g of trisodium citrate and 1.5g of biuret in 8mL of deionized water, ultrasonically stirring, and uniformly mixing to obtain a reaction solution; placing the reaction solution in a microwave oven, and carrying out microwave heating reaction for 90s in a high-fire state of the microwave oven to obtain a reaction mixture; the softened reaction mixture was soaked in 10mL of deionized water for 2.5h, the supernatant was decanted to give a softened product, which was dried in an oven at 60 ℃ for 30min to give a solid green fluorescent carbon dot (denoted as sample 3). The emission wavelength of sample 3 was 519 nm.

FIG. 1 is a transmission electron microscope image, from which it can be seen that the carbon dots are spheroidal and have good dispersibility without significant agglomeration.

FIG. 2 is an XPS survey of samples prepared in example 3, from which it can be seen that the prepared carbon dots contain the elements carbon, nitrogen, oxygen and sodium, and the composition of which is a typical composition of carbon dots, illustrating the successful preparation of fluorescent carbon dots by the preparation method of the present invention.

An excitation and emission spectrum of the green fluorescent carbon dot prepared in example 3 is shown in fig. 3, and sample 3 has a wide emission range from 450 nm to 600nm, wherein the optimal excitation is 420nm, and the optimal emission is 520 nm.

FIG. 4 is a spectrum diagram of an emission spectrum of a green fluorescent carbon dot obtained in example 3 with a change in excitation wavelength, and it can be seen from the graph that sample 3 exhibits an excitation-independent property, which shows that the green fluorescent carbon dot of the present invention has good spectral stability. When the carbon dots are applied to the aspects of illumination or biological imaging and the like, the carbon dots cannot change color along with the change of the excitation wavelength, and the color drift is prevented from being generated to influence the color purity.

The green fluorescence carbon spot decay map obtained in example 3 shows that the fluorescence lifetime of the sample can be well fitted with a single index, and the fluorescence lifetime of the sample 3 is 13.7ns according to the fitting result, as shown in the graph of FIG. 5. This means that there is only one electron-hole recombination process in the fluorescent carbon dot of the present invention.

Example 4

Dissolving 0.5g of trisodium citrate and 1.75g of biuret in 8mL of deionized water, ultrasonically stirring, and uniformly mixing to obtain a reaction solution; placing the reaction solution in a microwave oven, and carrying out microwave heating reaction for 90s in a high-fire state of the microwave oven to obtain a reaction mixture; the softened reaction mixture was soaked in 10mL of deionized water for 2.5h, the supernatant was decanted to give a softened product, which was dried in an oven at 60 ℃ for 30min to give a solid green fluorescent carbon dot (denoted as sample 4). The emission wavelength of sample 4 was 515 nm.

The photoluminescence spectra of the solid green fluorescent carbon dots prepared in examples 1 to 4 are shown in FIG. 6. As can be seen from the figure, the luminescence peak position of the sample only slightly shifts with the change of the feeding ratio. The green fluorescent carbon dots have good repeatability, and even if the feeding proportion is changed, the emission peak position can still be kept stable in a small range, so that green emission is maintained.

Claims

1. The solid green fluorescent carbon dot is characterized in that the fluorescent carbon dot can be excited by ultraviolet light and blue light of 300-500 nm, the emission main peak is 450-650 nm, and the quantum efficiency is 45-75%.

2. The preparation method of the solid green fluorescent carbon dot of claim 1, which is specifically carried out according to the following steps:

3) soaking the softened reaction mixture in deionized water, pouring out the supernatant, putting the softened product into an oven, and drying to obtain the green solid fluorescent carbon dots.

3. The method for preparing the solid green fluorescent carbon dot according to claim 2, wherein in the step 3), the softened product is placed in an oven and dried at a temperature of 50-80 ℃ for 20-60 min.