CN114015441B

CN114015441B - Green solid fluorescent carbon dot and preparation method thereof

Info

Publication number: CN114015441B
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: 2023-09-26
Anticipated expiration: 2041-12-10
Also published as: CN114015441A

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 with the wavelength of 300-500 nm and blue light, and has an emission main peak of 450-650 nm and a quantum efficiency of 45-75%. The 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 a high-fire state of the microwave oven, soaking and softening the reaction mixture by the deionized water, and placing the softened product into an oven for drying 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 prepare in batches, has high light intensity of the prepared green light solid carbon dots, has good fluorescence stability, does not need later complex modification, 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 novel carbon material with excellent optical properties discovered in recent years. Compared with the traditional semiconductor quantum dot and organic dye, the carbon dot not only maintains the advantages of low toxicity, good biocompatibility and the like of the carbon material, but also has the advantages of good stability, photo-bleaching resistance, easiness in functionalization, low cost, easiness in large-scale synthesis and the like. Therefore, the carbon dots have good application prospects in the fields of biological imaging, fluorescent marking, tumor treatment, sensing, photocatalysis, photoelectric devices, energy storage and the like. However, when the carbon dots are aggregated into a solid, due to pi electron accumulation effect among carbon nuclei, the luminous intensity of the carbon dots can be greatly reduced and even completely quenched, which greatly limits the application of the carbon dots in the solid-state luminous fields such as white light LEDs, optical communication, development of latent fingerprints and the like. In order to realize solid state light emission of carbon dots, the prior art adopts carbonThe dots are dispersed in a polymer (PMMA, PVA, PVP) or inorganic salt matrix (Ba ₂ SO ₄ , NaSiO ₃ NaCl), however, this method has problems such as uneven distribution of carbon dots, poor reproducibility, poor stability, and low loading rate.

Disclosure of Invention

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

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

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

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

1) Taking trisodium citrate and biuret according to a mass ratio of 1:1.25-4, respectively, taking deionized water according to a proportion that 1g trisodium citrate is dissolved in 8-13 mL deionized water, dissolving trisodium citrate and biuret in the deionized water, and carrying out ultrasonic stirring and uniform 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 under the high fire state of the microwave oven to obtain a reaction mixture;

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

The preparation method takes trisodium citrate (carbon source) and biuret (nitrogen source) as raw materials, and directly synthesizes 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 in direct contact, fluorescence resonance energy transfer is inhibited, the carbon dots can still emit light in a solid state, and fluorescence quenching caused by aggregation in the solid state is overcome.

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

Drawings

FIG. 1 is a transmission electron microscope image of green solid state fluorescent carbon dots produced in example 3.

FIG. 2 is an XPS survey of the solid state fluorescence carbon dots of example 3.

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

FIG. 4 is a graph showing the emission spectrum of the 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 the 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 described below with reference to the drawings and examples.

Example 1

Dissolving 0.5g of trisodium citrate and 1.25g of biuret in 8mL of deionized water, and stirring by ultrasonic waves, and uniformly mixing to obtain a reaction solution; placing the mixture in a microwave oven to perform high-fire microwave heating reaction for 90s to obtain a reaction mixture; the softened reaction mixture was soaked in 10mL of deionized water for 2.5 hours, the supernatant was removed to obtain a softened product, and the softened product was dried in an oven at 60 ℃ for 30 minutes to obtain a green solid fluorescent carbon dot (designated as sample 1). The emission wavelength of sample 1 was 510nm.

Example 2

Dissolving 0.5g of trisodium citrate and 1.375g of biuret in 8mL of deionized water, and stirring by ultrasonic waves, 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 to obtain a reaction mixture; the softened reaction mixture was soaked in 10mL of deionized water for 2.5 hours, the supernatant was removed to obtain a softened product, and the softened product was dried in an oven at 60 ℃ for 30 minutes to obtain a solid green fluorescent carbon dot (denoted as sample 2). Sample 2 emitted a wavelength of 520nm.

Example 3

Dissolving 0.5g of trisodium citrate and 1.5g of biuret in 8mL of deionized water, and stirring by ultrasonic waves, 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 2.5 hours, the supernatant was removed to obtain a softened product, and the softened product was dried in an oven at 60 ℃ for 30 minutes to obtain a solid green fluorescent carbon dot (denoted as sample 3). Sample 3 emitted a wavelength of 519 nm.

In the transmission electron microscope image shown in fig. 1, it can be seen that the carbon dots are sphere-like and have good dispersibility and no obvious agglomeration phenomenon.

FIG. 2 is a full spectrum of XPS of the sample prepared in example 3, from which it can be seen that the carbon dots prepared contain carbon, nitrogen, oxygen, and sodium elements, whose composition is typical of carbon dots, illustrating that the preparation method of the present invention successfully prepared fluorescent carbon dots.

Example 3 a plot of the excitation and emission spectra of the green fluorescent carbon dots is produced, as can be seen in figure 3, from which sample 3 has a broad emission in the range 450 to 600nm with an optimum excitation of 420nm and an optimum emission at 520nm.

FIG. 4 is a graph showing the emission spectrum of the green fluorescent carbon dots prepared in example 3 according to the change of the excitation wavelength, and it can be found from the graph that the sample 3 shows the property of independent excitation, which indicates that the green fluorescent carbon dots have good spectral stability. When the carbon dots are applied to illumination, biological imaging and other aspects, the color change can not occur along with the change of the excitation wavelength, and the color drift is avoided, so that the color purity is prevented from being influenced.

The decay pattern of the green fluorescent carbon dots prepared in example 3, as shown in the graph of fig. 5, can be better fit with a single index, and the fluorescent lifetime of sample 3 is 13.7ns from the fitting result. This means that there is only one electron-hole recombination process in the fluorescent carbon dots of the present invention.

Example 4

Dissolving 0.5g of trisodium citrate and 1.75g of biuret in 8mL of deionized water, and stirring by ultrasonic waves, 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 2.5 hours, the supernatant was removed to obtain a softened product, and the softened product was dried in an oven at 60 ℃ for 30 minutes to obtain a solid green fluorescent carbon dot (denoted as sample 4). Sample 4 emitted a wavelength of 515 nm.

Photoluminescence spectra of 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 is slightly shifted with the change of the feeding ratio. The green fluorescence carbon dot repeatability of the invention is good, and even if the feeding proportion is changed, the emission peak position can still be kept stable in a small range, and green emission is maintained.

Claims

1. The preparation method of the solid green fluorescent carbon dot is characterized by comprising the following steps of:

3) Soaking the softened reaction mixture with deionized water, pouring out supernatant, putting the softened product into an oven, and drying at 50-80 ℃ for 20-60 min to obtain a green solid fluorescent carbon dot;

the fluorescent carbon dot can be excited by ultraviolet light of 300-500 nm and blue light, and has a main emission peak of 450-650 nm and a quantum efficiency of 45-75%.