CN111518542A

CN111518542A - Synthesis method and application of zinc-doped carbon dots with high quantum yield

Info

Publication number: CN111518542A
Application number: CN202010469539.7A
Authority: CN
Inventors: 马凡怡; 张昀; 郭紫琼; 刘路; 王瑞娇; 刘绣华; 王登科
Original assignee: Henan University
Current assignee: Henan University
Priority date: 2020-05-28
Filing date: 2020-05-28
Publication date: 2020-08-11
Anticipated expiration: 2040-05-28
Also published as: CN111518542B

Abstract

The invention belongs to the field of biomedicine, and particularly relates to a synthetic method of zinc-doped carbon dots with high quantum yield and application thereof. The method comprises the following steps: (1) synthesis of a precursor: adding trisodium citrate and zinc chloride into water, magnetically stirring for 5h under the conditions of pH4-6 and water bath, then adding absolute ethyl alcohol, centrifugally collecting precipitates, cleaning for 2-4 times, then dissolving the precipitates in water, and freeze-drying to obtain a precursor zinc citrate complex TC-Zn; (2) and (2) calcining the precursor prepared in the step (1) at the temperature of 100-400 ℃ for 0.5-24 h respectively to obtain the zinc-doped carbon dots. The invention inspects the influence of the calcination time and the calcination temperature on the fluorescence intensity of two zinc-doped carbon dots and determines the optimal calcination process of Zn @ C-A and Zn @ C-B. The preparation method has simple process and high yield, and is suitable for industrial production.

Description

Synthesis method and application of zinc-doped carbon dots with high quantum yield

Technical Field

The invention belongs to the field of biomedicine, and particularly relates to a synthetic method of zinc-doped carbon dots with high quantum yield and application thereof.

Background

Since carbon dot Carbonates (CDs) were first discovered and reported in 2004, due to their special size effect, compared with common carbon materials such as activated carbon and graphite, they have many unique characteristics, such as good water solubility, biocompatibility, light stability, electrochemiluminescence, highly tunable photoluminescence, etc., which make them an emerging research hotspot in various fields such as biomedicine, chemical sensors, catalysis, and optoelectronics. However, because the CDs are easy to aggregate due to special particle size, and obvious fluorescence quenching is caused, the CDs are not fluorescent in solid and can only show fluorescence in solution, which limits the application of the CDs in the fields of photoelectron, photocatalysis and the like. With the continuous and deep research on CDs, more and more CDs doped with various kinds of chemical heteroatoms are invented by a chemical heteroatom doping method so as to improve the fluorescence efficiency and the electron transport performance. Some of them show excitation-dependent fluorescence emission with tunable emission, some with pH-dependent fluorescence emission, and some CDs with up-converted fluorescence. Common non-metal doping elements are nitrogen, boron, silicon, sulfur, phosphorus, etc., co-doped with nitrogen and sulfur, and although the quantum yield of CDs can be significantly increased by doping or surface passivation techniques, the quantum yield of most CDs does not exceed 50%. The low quantum yield of CDs remains a difficult point that is currently urgently needed to solve, compared to the quantum yield of more than 80% that is common for conventional semiconductor quantum dots. Compared with the CDs doped with non-metals, the doping efficiency is generally low due to the fact that metal ions have a certain quenching effect on the CDs, and therefore research on the CDs doped with metals is just started.

It is found that the structure and band gap of the doped carbon dots can be adjusted by doping CDs with metal atoms, the optical performance is improved, and various new functions are obtained, such as Cu, Gd (III), Ni, Eu (III) and α -Bi₂O₃、TiO₂、Cu-Al₂O₃And the like. However, the heavy metal atom doping not only increases the toxicity of the CDs and limits the application of the CDs in the biological and medical fields, but also increases the production cost of the CDs and has certain pollution to the environment. Therefore, it is a hot spot of current research to research a metal-doped CDs with high fluorescence efficiency and low toxicity. Ideally the doping metal atoms should be environmentally friendly and should not cause any toxic side effects to the doped CDs, and such metals are commonly found in: calcium, iron, zinc, and the like. Wherein zinc is one of essential dietary trace metals in physiological and biochemical functions of human body. Zinc deficiency affects the immune system, resulting in developmental retardation, loss of appetite, rough skin, hypogonadism, mental fatigue, recurrent infections, etc. Moreover, compared with the fluorescence quenching effect of calcium and iron ions on CDs, zinc ions can significantly increase the fluorescence intensity of CDs. In addition, the conventional preparation method of CDs is a solvothermal method, which requires a large amount of energy consumption, low yield and cumbersome processing procedure in subsequent processing, so that metal-doped CDs are limited to laboratory research.

Disclosure of Invention

The invention provides a synthesis method and application of zinc-doped carbon dots with high quantum yield, which improve the quantum yield of Zn metal carbon dots and unexpectedly obtain two zinc-doped carbon dots with strong stability, high luminous intensity and good fluorescence effect in aqueous solution and solid.

The technical scheme of the invention is realized as follows:

a method for synthesizing zinc-doped carbon dots with high quantum yield comprises the following steps:

(1) synthesis of a precursor: adding trisodium citrate and zinc chloride into water, magnetically stirring for 5h under the conditions of pH4-6 and water bath, then adding absolute ethyl alcohol, centrifugally collecting precipitates, cleaning for 2-4 times, then dissolving the precipitates in water, and freeze-drying to obtain a precursor zinc citrate complex TC-Zn;

(2) and (2) calcining the precursor prepared in the step (1) at the temperature of 100-400 ℃ for 2-4 h respectively to obtain the zinc-doped carbon dots.

In the step (1), the molar ratio of trisodium citrate to zinc chloride is 1: (0.6-1), and the addition amount of the absolute ethyl alcohol is 3-4 times of the volume of the reaction system.

And (2) freezing and drying at the water bath temperature of 0-100 ℃ in the step (1).

The zinc-doped carbon dots with high quantum yield synthesized by the method are Zn @ C-A or Zn @ C-B; . The solid fluorescence intensity of Zn @ C-A is strongest, and the aqueous solution fluorescence intensity of Zn @ C-B is strongest. The Zn @ C-A and the Zn @ C-B obtained by the method form a plurality of holes, wherein the holes formed by the Zn @ C-B are more and larger; zn @ C-A and Zn @ C-B are mainly composed of C, O and Zn elements, O, Zn and Na are uniformly distributed, C can emit bright spots, both form sphere-like carbon quantum dots, and zinc is uniformly distributed in the carbon dots, wherein the diameter of Zn @ C-B is smaller than that of Zn @ C-A. Acute toxicity studies show that both Zn @ C-A and Zn @ C-B are nontoxic.

The zinc-doped carbon point Zn @ C-A with the high quantum yield is obtained by calcining the precursor at the temperature of 200-230 ℃.

The zinc-doped carbon point Zn @ C-B with high quantum yield is obtained by calcining the precursor at 230-260 ℃.

The application of the zinc-doped carbon dot Zn @ C-A with high quantum yield in preparing fluorescent dye, printing and marking color developing reagents.

The high quantum yield zinc-doped carbon dot Zn @ C-B is applied to preparation of a fluorescent probe for cell imaging.

The invention has the following beneficial effects:

1. the invention firstly adopts a response surface method to optimize the synthesis process of a precursor TC-Zn, and synthesizes Zn @ C-A with strong solid fluorescence and Zn @ C-B with strong fluorescence in an aqueous solution for the first time through calcination at different temperatures. The influence of the calcination time and the calcination temperature on the fluorescence intensity of two zinc-doped carbon points is examined, and the optimal calcination process of Zn @ C-A and Zn @ C-B is determined. The preparation method has simple process and high yield, and is suitable for industrial production.

2. According to the invention, a zinc-doped carbon dot with solid fluorescence, quantum yield up to 71.50% and low toxicity is synthesized by directly calcining at low temperature by taking a metal zinc trisodium citrate complex as a precursor as shown in figure 18. By structural representation, the fluorescence luminescence mechanism of the doped carbon dots doped with zinc is explained, and as shown in FIG. 15, the maximum excitation wavelengths of Zn @ C-A and Zn @ C-B are 450 nm; lays a foundation for further development and utilization of the novel carbon dots.

3. The Zn @ C-A and the Zn @ C-B prepared by the method are shown in figure 16, can stably exist in an aqueous solution or a 0.1mol/L NaCl solution for 24 hours, and the existence of NaCl has a stabilizing effect on the fluorescence intensity of the two. Zn @ C-B is used as a fluorescent probe and can be applied to the aspect of biological cell marking, the luminous intensity of Zn @ C-A is high as shown in figure 20, the toxicity is low, and the Zn @ C-A can be used as fluorescent ink for fluorescent marking; zn @ C-B has low toxicity, can survive 90% of cells after being incubated for 24 hours at 600 mu g/mL, has high luminous intensity, and can be used as a cell probe for cell fluorescence imaging.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a graph showing the results of single factor examination of fluorescence values of the samples in example 1.

FIG. 2 is a graph showing interaction of various factors in example 1.

FIG. 3 is a graph of the sun (A), UV (B), solid fluorescence (C) and aqueous solution fluorescence (D) of Zn @ C at different calcination temperatures for example 1.

FIG. 4 is a graph of the sun (A), UV (B), solid fluorescence (C) and aqueous solution fluorescence (D) of Zn @ C-A for different calcination times for example 1.

FIG. 5 is a graph of Zn @ C-B sunlight (A), ultraviolet light (B), aqueous solution fluorescence (C), and aqueous solution fluorescence measurements (D) for different calcination times for example 1.

FIG. 6 shows the elemental analysis charts of TC-Zn (A), Zn @ C-A (B) and Zn @ C-B (C) obtained in example 1 by scanning electron microscopy, transmission electron microscopy and EDX.

FIG. 7 is a distribution diagram of Zn @ C-A elements obtained in example 1.

FIG. 8 is an IR spectrum of trisodium citrate, TC-Zn, Zn @ C-A, and Zn @ C-B obtained in example 1.

FIG. 9 is an XRD pattern of TC-Zn and Zn @ C obtained in example 1.

FIG. 10 shows XPS survey spectra (D) and C1 s, O1 s of TC-Zn (A), Zn @ C-A (B), and Zn @ C-B (C) obtained in example 1.

FIG. 11 is a nuclear magnetic diagram of TC-Zn (A), Zn @ C-A (B), and Zn @ C-B (C) obtained in example 1; FIG. 12 is a schematic diagram of TC-Zn and Zn @ C structures obtained in example 1.

FIG. 13 is a thermogravimetric analysis of TC-Zn obtained in example 1.

FIG. 14 is a graph of UV-VIS absorption spectra of Zn @ C obtained in example 1 at different calcination temperatures.

FIG. 15 is a graph showing fluorescence spectra of Zn @ C-A and Zn @ C-B obtained in example 1 at different excitation wavelengths.

FIG. 16 shows the effect of different pH values on the fluorescence intensity of Zn @ C-A (A) and Zn @ C-B (B) obtained in example 1;

FIG. 17 shows the effect of different anions (A) and different residence times (B) on the fluorescence intensity of Zn @ C-A, Zn @ C-B obtained in example 1.

FIG. 18 shows the solid fluorescence quantum yield of Zn @ C-A obtained in example 1.

FIG. 19 shows the fluorescence lifetime of the Zn @ C-A solid obtained in example 1 and the fluorescence lifetime of the aqueous solution.

FIG. 20 is a graph of the written daylight pattern (A) and the fluorescence pattern (B) under a 365nm lamp of Zn @ C-A obtained in example 1.

FIG. 21 shows cytotoxicity of Zn @ C-B MTT method obtained in example 1 at various concentrations.

FIG. 22 is a heliogram (A) and a fluorescence plot (B) of Zn @ C-B MCF-7 cells obtained in example 1.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

Example 1

The synthesis method of the zinc-doped carbon dots with high quantum yield of the embodiment comprises the following steps:

1. optimized synthesis of precursor zinc citrate complex TC-Zn

Adding trisodium citrate and zinc chloride into 20 mL of water, adjusting the pH value to a proper value, carrying out water bath reaction for a certain time at a certain temperature, adding 4 times of absolute ethyl alcohol after the reaction is finished, centrifuging at 4000 rpm for 2min, washing the precipitate for 3 times by using 80% ethyl alcohol, removing free zinc ions and unreacted substances, dissolving the precipitate in a proper amount of water, carrying out freeze drying to obtain a white fluffy powdery sample, namely the zinc citrate complex TC-Zn, and inspecting the yield, the zinc content and the solubility of the TC-Zn.

According to the central combined test design principle of the BBD, the experimental result is optimized and simulated by using a response surface method on the basis of a single-factor test result (shown in figure 1). The proportion of trisodium citrate to zinc chloride, pH value, reaction concentration and reaction time are selected to be 4 factors, and the factors are shown in table 1:

TABLE 1 Experimental factors and levels

The experiment was designed using a four-factor three-level response surface analysis method, and the specific experimental design is shown in table 2:

TABLE 2 response surface analysis test design and results

The results are analyzed as shown in table 3:

TABLE 3 ANOVA TABLE

Note: indicates a very significant difference (P < 0.01); indicates significant difference (P < 0.05); n indicates no significant difference (P > 0.05)

The result chart of the response surface method is shown in figure 2, and the synthesis process of the precursor TC-Zn is optimized:

the fluorescence value of the precursor TC-Zn calcined at the temperature of 200-290 ℃ for 0.5-8 hours is taken as an index, and the synthesis process of the precursor TC-Zn is preferably selected as shown in figures 3-5. The optimal synthesis process conditions obtained by Design-Expert 8.0 are as follows: the ratio of trisodium citrate to zinc chloride is 1: 0.8, controlling the reaction pH at 5.0 and magnetically stirring for 5 h. Under the condition, the regression model predicts that the fluorescence theoretical value can reach 475. The TC-Zn obtained by the method is smooth and spherical in appearance, and as shown in FIG. 7, Zn @ C-A mainly comprises C, O and Zn elements.

2. Preparation of Zn @ C doped carbon dots

And (3) calcining the prepared precursor TC-Zn in a tube furnace at 210 ℃ and 260 ℃ for 2 h respectively to obtain zinc-doped carbon points Zn @ C-A and Zn @ C-B correspondingly, wherein the reaction process is shown in figure 12. The solid fluorescence intensity of Zn @ C-A is strongest, and the aqueous solution fluorescence intensity of Zn @ C-B is strongest.

The Zn @ C-A and the Zn @ C-B obtained by the method form a plurality of holes as shown in figure 6, wherein the holes formed by the Zn @ C-B are more and larger; zn @ C-A and Zn @ C-B are mainly composed of C, O and Zn elements, as shown in FIG. 12, the products O, Zn and Na of the present application are uniformly distributed, and C can emit bright spots as shown in FIG. 22. Both form sphere-like carbon quantum dots, and zinc is uniformly distributed in the carbon dots, wherein the diameter of Zn @ C-B is smaller than that of Zn @ C-A.

A comparison of the individual bond contents of the carbons in TC-Zn and Zn @ C is shown in Table 4:

TABLE 4 comparison of the respective bond contents of the carbons in TC-Zn and Zn @ C

The TC-Zn prepared according to the example 1 is smooth and spherical in appearance, after calcination, Zn @ C-A forms a plurality of holes, Zn @ C-B forms more and larger holes, the holes and the holes form spheroidal carbon quantum dots, zinc is uniformly distributed in the carbon dots (an element distribution diagram is shown in figure 7), and the element distribution diagram is obviously different from a transmission electron microscope of the TC-Zn raw material shown in figure 6. Wherein the diameter of Zn @ C-B is smaller than that of Zn @ C-A.

EDX, transmission electron, scanning electron, infrared, XRD, X-ray photoelectron, nuclear magnetic H1, thermogravimetry, and ultraviolet-visible absorption spectra (fig. 8-11, fig. 13-14) with Zn @ C-a and Zn @ C-B illustrate the formation of zinc-doped carbon dots. The solid fluorescence yield of Zn @ C-A is as high as 71.50% as shown in FIG. 18 by detection, the specific analysis is shown in Table 5, the fluorescence quantum yield of Zn @ C-B aqueous solution is higher than that of the common carbon point, and the yield of Zn @ C-B is shown in Table 6.

TABLE 5 Zinc content and yield of TC-Zn, Zn @ C-A and Zn @ C-B (n = 3)

TABLE 6 Zn @ C-B Quantum yields

Examples of the effects of the invention

Effect example 1: acute toxicity test

Kunming mouse, male and female half, clean grade. All mice are fed normally, after adaptive feeding for one week, Kunming mice with the weight of 18-22 g are randomly grouped, and the mice are respectively divided into 5 dose groups and 1 control group (10 mice in each group and half of males and females) by adopting an oral administration mode. The administration was performed by gavage with increasing doses of 200, 400, 600, 800 and 1000 mg/kg Body Weight (BW), and the same amount of physiological saline was administered to the control group, followed by 14 days of observation after administration. As a result, none of the mice died, and no adverse reaction was observed in the mice. The result is shown in FIG. 21, and it can be seen that Zn @ C-A and Zn @ C-B have no acute toxicity, so that Zn @ C-A and Zn @ C-B have low toxicity, which indicates that Zn @ C-A and Zn @ C-B can be used as potential bioluminescent probes.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A method for synthesizing zinc-doped carbon dots with high quantum yield is characterized by comprising the following steps:

(2) and (2) calcining the precursor prepared in the step (1) at the temperature of 100-400 ℃ for 0.5-24 h respectively to obtain the zinc-doped carbon dots.

2. The method for synthesizing high quantum yield zinc-doped carbon dots according to claim 1, characterized in that: in the step (1), the molar ratio of trisodium citrate to zinc chloride is 1: (0.6-1), and the addition amount of the absolute ethyl alcohol is 3-4 times of the volume of the reaction system.

3. The method for synthesizing high quantum yield zinc-doped carbon dots according to claim 1, characterized in that: the temperature of the water bath in the step (1) is 0-100 ℃, and the frozen and dried water bath is reserved.

4. High quantum yield zinc doped carbon dots synthesized by the method of any one of claims 1 to 3, characterized in that: the zinc-doped carbon dots are Zn @ C-A or Zn @ C-B.

5. The high quantum yield zinc-doped carbon dot of claim 4, characterized in that: the Zn @ C-A is obtained by calcining the precursor at the temperature of 100-230 ℃.

6. The high quantum yield zinc-doped carbon dot of claim 4, characterized in that: the Zn @ C-B is obtained by calcining the precursor at the temperature of 230-400 ℃.

7. Use of the high quantum yield zinc doped carbon dot Zn @ C-a as defined in claim 4 for the preparation of fluorescent dyes, printing, labelling chromogenic reagents.

8. Use of the high quantum yield zinc doped carbon dot Zn @ C-B as claimed in claim 4 for the preparation of a fluorescent probe for cell imaging.