CN108821261B

CN108821261B - Nitrogen-doped carbon nanoring and preparation method and application thereof

Info

Publication number: CN108821261B
Application number: CN201810243998.6A
Authority: CN
Inventors: 徐泉; 苏日古
Original assignee: China University of Petroleum Beijing
Current assignee: China University of Petroleum Beijing
Priority date: 2018-03-23
Filing date: 2018-03-23
Publication date: 2020-08-28
Anticipated expiration: 2038-03-23
Also published as: CN108821261A

Abstract

The invention provides a nitrogen-doped carbon nanoring and a preparation method and application thereof, wherein the preparation method comprises the following steps: mixing a carbon source and a nitrogen source to obtain a precursor mixture; directly heating the precursor mixture, and reacting at a temperature capable of melting a nitrogen source in the precursor mixture to obtain the nitrogen-doped carbon nanoring; the nitrogen source is urea, and the carbon source is sodium citrate. The method for preparing the nitrogen-doped high-photoluminescence carbon nano-ring only needs one-step reaction without high pressure, has ultra-fast reaction speed, few byproducts and intermediate products, little raw material consumption, arbitrary proportion, low cost and high fluorescence quantum yield, and the obtained carbon nano-ring has high luminous intensity and is successfully applied to Fe³⁺And in addition, the pH value in the solution can be identified, and the method has wide application prospect in water treatment.

Description

Nitrogen-doped carbon nanoring and preparation method and application thereof

Technical Field

The invention relates to a nitrogen-doped carbon nanoring and a preparation method and application thereof, belonging to the field of nano materials.

Background

Carbon is the basis of all known lives on the earth and plays a significant role in the development of modern science and technology. Numerous compounds of carbon are indispensable in daily life, and products range from nylon and gasoline, perfume and plastics to shoe polish, nasal drops, explosives and the like, and are widely diversified. Carbon has various electron orbital characteristics (sp, sp)²And sp³) Therefore, many substances with peculiar structures and properties, such as carbon nanotubes, fullerene, nanodiamond, graphene oxide and the like, can be formed.

In recent years, research on nano carbon materials is being conducted vigorously, and fluorescent carbon nanorings are used as a novel carbon nanomaterial, and due to the excellent optical properties and low-toxicity characteristics, the carbon nanorings become an environment-friendly nanomaterial with the greatest application prospect, have the characteristics of excellent luminescence property, stable luminescence, easiness in functionalization and industrialization, low toxicity, easiness in preparation and excellent biocompatibility, can be widely applied to the fields of environmental monitoring, biological imaging, cell detection, photoelectrocatalysis and the like, and have important application values.

In recent years, researchers have made a lot of researches on the preparation and application of carbon nanomaterials with high fluorescence properties, and the synthesis methods of carbon nanomaterials are mainly classified into "top-down" and "bottom-up" methods. The carbon source for preparing the carbon nano material is very wide, and can be a carbon simple substance or a carbon compound. However, the preparation of carbon nanomaterials is usually carried out under harsh conditions such as pressurization and microwave, and these conditions limit the popularization and application of carbon nanomaterials. In addition, the carbon nano-materials obtained by adopting different raw materials as carbon sources and different synthesis methods have greatly different fluorescence effects, and some of the carbon nano-materials even have no fluorescence. In order to obtain the carbon nano material with high luminous intensity and widen the application of the carbon nano material in the fields of biomedicine and the like, a great exploration space is still provided for simply preparing the fluorescent carbon nano material with good water solubility and high luminous intensity.

Disclosure of Invention

In view of the actual needs, the main object of the present invention is to provide a method for preparing nitrogen-doped carbon nanorings, so that carbon nanorings with high luminous intensity can be conveniently and rapidly obtained.

Another object of the present invention is to provide a nitrogen-doped carbon nanoring obtained by the above production method.

Still another object of the present invention is to provide applications of the nitrogen-doped carbon nanoring.

To achieve the above objects, in one aspect, the present invention provides a method for preparing nitrogen-doped carbon nanorings, comprising: mixing a carbon source and a nitrogen source to obtain a precursor mixture; directly heating the precursor mixture, and reacting at a temperature capable of melting a nitrogen source in the precursor mixture to obtain the nitrogen-doped carbon nanoring; the nitrogen source is urea, and the carbon source is sodium citrate.

The preparation method is a direct heating method, is very simple and convenient, avoids the harsh conditions of pressurization, microwave and the like adopted in the conventional synthesis of carbon nano materials, and can synthesize the nitrogen-doped carbon nano ring with high fluorescence intensity in one step.

Regarding the dosage of the sodium citrate and the urea, the nitrogen-doped carbon nano-ring product with the fluorescent effect can be obtained regardless of the mass ratio of the sodium citrate to the urea.

Further preferably, the mass ratio of the sodium citrate to the urea is 1:0.1 to 1:16, such as 1:0.1, 1:0.25, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, etc. The ratio of the sodium citrate to the urea is 1:4, the experiment of the invention shows that when the mass ratio of the sodium citrate to the urea is 1:4, a peak value appears in the fluorescence intensity and the quantum yield, and when the mass ratio of the sodium citrate to the urea is below 1:4, the fluorescence intensity is not obviously increased; above 1:4, there is also no significant, i.e., slight, but less significant, decrease in fluorescence intensity.

Preferably, the mass of the sodium citrate in the precursor solution is 0.25g, and the mass of the urea is 0.25-4 g, preferably 1 g. That is, the mass ratio of the sodium citrate to the urea is 1:1 to 1:16, for example, 1:1, 1:2.5, 1:4 or 1:8, preferably 1: 4. If the preferred mass ratio of the sodium citrate to the urea is 1:4, the fluorescence quantum yield can reach 20.9%.

As described above, the reaction temperature in the present invention may be a temperature at which urea in the solid precursor mixture is melted, and the nitrogen-doped carbon nanorings having fluorescent properties can be synthesized by the reaction at this temperature. Preferably, the reaction temperature is 140 to 240 ℃ (e.g., 140 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃, 185 ℃, 195 ℃, 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃ and the like), and the nitrogen-doped carbon nanoring with fluorescence performance can be synthesized in the temperature range.

The reaction time is not limited in the present invention, and the nitrogen-doped carbon nanorings having fluorescent properties can be produced as long as the reaction occurs, and is preferably 1min or more, for example, 1min, 5min, 30min, 1h, 2h, or the like, and preferably 1h or more.

The above direct heating method of the present invention can be performed in a conventional manner, for example, placing a carbon source and a nitrogen source in a crucible, mixing them to obtain a precursor mixture, covering the crucible containing the precursor mixture with a lid, and placing the crucible in a heating device for direct heating, wherein the heating device is a device commonly used in the art, and the heating device is not particularly limited as long as it can heat up, and the present invention is not limited to a conventional oven or a muffle furnace.

In the above production method, preferably, the grinding may be performed before the precursor mixture is directly heated. So that the materials are mixed uniformly.

In the above preparation method, preferably, it further comprises a separation step, and more preferably, the separation step comprises:

and naturally cooling the reacted material (preferably to room temperature), adding water into the cooled material, filtering by using a retention membrane to obtain a filtrate, and freeze-drying the filtrate to obtain the nitrogen-doped carbon nanorings.

The room temperature is 20-30 ℃.

The molecular weight cut-off of the cut-off membrane provided by the invention is any one of 3kDa, 5kDa, 10kDa or 30kDa or a combination of at least two of the two.

The present invention is not particularly limited in the form of filtration, and may be carried out in a laboratory using a cylindrical membrane separation filter, but this does not exclude the present invention from carrying out the filtration operation in other ways.

In the above preparation method, the freeze-drying is carried out under vacuum at-50 deg.C to-45 deg.C, preferably for 24 h.

The preparation method of the nitrogen-doped carbon nanoring is a direct heating method, and preferably comprises the following steps:

(1) weighing a carbon source and a nitrogen source, and placing the carbon source and the nitrogen source in a crucible for mixing to obtain a precursor mixture;

(2) placing the obtained precursor mixture in heating equipment to react and synthesize a nitrogen-doped carbon nanoring, and then naturally cooling to room temperature to obtain a solid-phase product;

(3) adding deionized water into the obtained solid-phase product to dissolve and separate the product to obtain a clear solution;

(4) condensing and freeze-drying the obtained clear solution to obtain the nitrogen-doped carbon nano-ring;

in the step (1), the carbon source is sodium citrate, the nitrogen source is urea, and the mass ratio of the sodium citrate to the nitrogen source is 1:4 (for example, the mass of the sodium citrate is 0.25g, and the mass of the urea is 1 g). In this way, relative fluorescence quantum yields of greater than 20% can be achieved.

The preparation method has the advantages that the preparation method is simple, the raw materials can be in any proportion (the raw materials can be in any proportion in the place which is different from other synthesized nano materials and is particularly outstanding), the required reaction time is short (the product can be obtained as long as the melting point of urea reaches the melting point of sodium citrate is added), the initial product can be obtained after the reaction is carried out for 1-5 min under the condition that the reaction temperature reaches, the obtained nitrogen-doped carbon nano-ring has high fluorescence intensity (the dilute solution shows strong yellow-green fluorescence under the irradiation of an ultraviolet lamp), and the fluorescence is stable (the good fluorescence effect can be kept after the nitrogen-doped carbon nano-ring is placed for more than 1 month).

In another aspect, the present invention provides a nitrogen-doped carbon nanoring prepared by the above preparation method. Preferably, the nitrogen-doped carbon nanoring has an element content of 50 to 60% of C, 15 to 20% of N, and 20 to 30% of O, such as 55.35% of C, 18.20% of N, and 26.45% of O, as analyzed by XPS.

As described above, the nitrogen-doped carbon nanoring obtained by the invention has high fluorescence intensity and stable fluorescence.

In another aspect, the invention provides an application of the nitrogen-doped carbon nanoring as an acid-base recognition agent for recognizing the pH of an aqueous solution. The invention discovers that the nitrogen-doped carbon nanoring is yellow-green under the irradiation condition of 365nm of a portable ultraviolet lamp after being added into the aqueous solution with the pH value less than 11, and blue under the irradiation condition of 365nm of the ultraviolet lamp after being added into the aqueous solution with the pH value more than 11. Accordingly, the nitrogen-doped carbon nanoring can be used as an acid-base recognition agent for recognizing whether the pH of the aqueous solution is more than 11 or less than 11 according to the property.

In another aspect, the invention provides the nitrogen-doped carbon nanorings as a detection reagent for detecting Fe³⁺The concentration of the ions. Specifically, when the aqueous solution containing the nitrogen-doped carbon nanorings does not contain ferric ions, the aqueous solution exhibits yellow-green light under 365nm ultraviolet lamp irradiation and has high fluorescence intensity, but once the ferric ions are added to the aqueous solution, the aqueous solution is subjected to ultraviolet lamp irradiation with increasing concentrationThe color of the synthesized nitrogen-doped carbon nanoring is lighter and lighter until the color disappears under 365nm irradiation, and the experiment of the invention shows that the synthesized nitrogen-doped carbon nanoring can detect Fe in aqueous solution³⁺Ions.

In another aspect, the present invention provides the use of the nitrogen-doped carbon nanorings as an adsorbent for adsorbing PM particles in air. Experiments of the invention show that the adsorption effect of the nitrogen-doped carbon nanoring is far higher than that of activated carbon, and can reach more than 2 times.

In summary, the present invention provides a method for preparing nitrogen-doped carbon nanorings, and nitrogen-doped carbon nanorings prepared by the method, and applications thereof, wherein the method for preparing nitrogen-doped highly photoluminescent carbon nanorings only requires one step of reaction, high pressure is not required, the reaction speed is very high, and byproducts and intermediate products are few (the products separated after the reaction are nitrogen-doped carbon nanorings except for unreacted insoluble solids), the raw materials are few in dosage, the arbitrary proportion, the cost is low, the fluorescence quantum yield is high, the obtained carbon nanorings have high luminous intensity, and the method can be successfully applied to Fe³⁺And in addition, the pH value in the solution can be identified, and the method has wide application prospect in water treatment.

Drawings

Fig. 1 is a transmission electron microscope image of a nitrogen-doped carbon nanoring prepared in example 1 of the present invention.

FIG. 2 is a fluorescence spectrum of a nitrogen-doped carbon nanoring prepared in example 1 of the present invention.

Fig. 3 is an excitation and emission pattern of the nitrogen-doped carbon nanoring prepared in example 1 of the present invention.

Fig. 4 is an ultraviolet-visible absorption diagram of the nitrogen-doped carbon nanoring prepared in example 1 of the present invention.

Fig. 5 is an XPS analysis diagram of nitrogen-doped carbon nanorings prepared in example 1 of the present invention.

FIG. 6 shows the fluorescence intensity variation and Fe of the N-doped carbon nanoring fabricated in example 1 of the present invention³⁺The corresponding linear relationship of the solution concentration.

Fig. 7 is a graph comparing adsorption effects of the nitrogen-doped carbon nanorings prepared in example 1 of the present invention and activated carbon.

Detailed Description

For a more clear understanding of the technical features, objects and advantages of the present invention, reference is now made to the following detailed description taken in conjunction with the accompanying specific embodiments, and the technical solutions of the present invention are described, it being understood that these examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention. In the examples, each raw reagent material is commercially available, and the experimental method not specifying the specific conditions is a conventional method and a conventional condition well known in the art, or a condition recommended by an instrument manufacturer.

Example 1

(a) Taking 0.25g of sodium citrate and urea with different masses, and grinding in a mortar to obtain a precursor mixture;

(b) transferring the ground precursor mixture into a crucible and covering the crucible with a cover; placing the crucible in an oven, heating to 200 ℃ and reacting for 30 min;

(c) several groups of samples added with urea with different masses are compared and analyzed, namely the mass of the urea is 0.25 g; 0.50 g; 1.0 g; 1.25 g; 1.5 g;

(d) naturally cooling the reacted mixture to room temperature, namely 20-30 ℃, so as to obtain an initial reaction product;

(e) adding 20g of pure water into the initial reaction product for dissolving to obtain a suspension;

(f) filtering the suspension by using a 3kDa cut-off cylindrical membrane separation filter, collecting filtrate, determining the fluorescence quantum yield of urea with different masses, and optimally adding urea with different masses to obtain the optimal addition amount of 1.0 g; freeze drying to obtain the nitrogen-doped carbon nanorings with high fluorescence yield.

Fig. 1 is a transmission electron micrograph of the nitrogen-doped carbon nanoring prepared in this example, and the lattice spacing thereof measured from fig. 1 was about 0.36nm, and had a distinct ring structure.

Example 2

(a) 1.0g of urea and sodium citrate with different mass are put into a mortar to be ground to obtain a precursor mixture;

(b) transferring the ground precursor mixture into a crucible and covering the crucible with a cover; placing the crucible in an oven, heating to 200 ℃, and reacting for 30 min;

(c) several groups of samples added with sodium citrate with different mass are compared and analyzed, namely the mass of the sodium citrate is 0.05 g; 0.10 g; 0.25 g; 0.50 g; 1.0g, etc.;

(f) filtering the suspension by using a 3kDa cut-off cylindrical membrane separation filter, collecting filtrate, determining the fluorescence quantum yield of sodium citrate with different masses, and optimally adding sodium citrate with different masses to obtain the optimal addition amount of 0.25 g; freeze drying to obtain the nitrogen-doped carbon nanorings with high fluorescence yield.

Fig. 2 is a fluorescence spectrum of the nitrogen-doped carbon nanoring prepared in this example, and it can be seen from fig. 2 that the obtained fluorescence spectrum has an excitation-dependent characteristic.

Example 3

(a) Putting 0.25g of sodium citrate and 1.0g of urea in a mortar for grinding to obtain a precursor mixture;

(b) transferring the ground precursor mixture into a crucible and covering the crucible with a cover; placing the crucible in an oven to be heated to 200 ℃;

(c) carrying out comparative analysis on a plurality of groups of samples with different reaction times, namely the reaction time is 1 min; 5 min; 15 min; 30 min; 1 h; 2h, and the like.

(f) filtering the suspension with a 3kDa cylindrical membrane separation filter, collecting the filtrate, determining the fluorescence quantum yield of different reaction times, and obtaining a product with a fluorescence effect within 1min of extremely short reaction time; the optimal reaction time can be obtained when the reaction time is 1 h; freeze drying to obtain the nitrogen-doped carbon nanorings with high fluorescence yield.

Fig. 3 is an excitation and emission diagram of the nitrogen-doped carbon nanoring prepared in the embodiment, and it can be seen from fig. 3 that the strongest fluorescence intensity can be obtained when the excitation wavelength is 410nm, and the peak position of the fluorescence emission spectrum is 535 nm.

Example 4

(b) transferring the ground precursor mixture into a crucible and covering the crucible with a cover; placing the crucible in an oven to react for 1 hour;

(c) carrying out comparative analysis on a plurality of groups of samples with different reaction temperatures, namely the reaction temperature is 145 ℃; 165 ℃; 185 ℃ of temperature; 205 deg.C; 225 ℃ and the like.

(f) filtering the suspension by using a cylindrical membrane separation filter with the molecular weight cutoff of 3kDa, collecting filtrate, and determining the fluorescence quantum yield at different reaction temperatures; optimizing the reaction temperature may result in an optimum reaction temperature of 185 ℃; freeze drying to obtain the nitrogen-doped carbon nanorings with high fluorescence yield.

Fig. 4 is an ultraviolet-visible absorption diagram of the nitrogen-doped carbon nanoring prepared in the present embodiment, and it can be seen from fig. 4 that the carbon nanoring has a better absorption performance around 410 nm.

Fig. 5 is an XPS elemental composition and content analysis result of the nitrogen-doped carbon nanorings prepared in this example, and it can be seen from fig. 5 that the nitrogen-doped carbon nanorings obtained in this example are mainly composed of three elements, C (55.35%), N (18.20%), and O (26.45%).

Example 5

(b) transferring the ground precursor mixture into a crucible and covering the crucible with a cover; placing the crucible in an oven, heating to 185 ℃ and reacting for 1 hour;

(c) naturally cooling the reacted mixture to room temperature, namely 20-30 ℃, so as to obtain an initial reaction product;

(d) adding 20g of pure water into the initial reaction product for dissolving to obtain a suspension;

(e) filtering the suspension by using a cylindrical membrane separation filter with the molecular weight cutoff of 3kDa, and collecting filtrate;

(f) the filtrate is placed in a glass bottle and is placed normally at room temperature, the fluorescence quantum yield is measured after the filtrate is placed for different time (namely 1 day, 5 days, 10 days, 15 days, 25 days and 30 days), the original fluorescence quantum yield can be kept after the filtrate is placed for 30 days, and the obtained filtrate, namely the nitrogen-doped carbon nanoring, has particularly stable optical properties.

Within the range of pH 1-11, the nitrogen-doped carbon nanoring prepared by the embodiment shows yellow-green color without obvious change of the luminescent color, but when the alkalinity is too strong, the bonds between the original elements of the nitrogen-doped carbon nanoring are destroyed, the yellow-green color is obviously weakened until the yellow-green color disappears and becomes blue to be dominant, and the change of the luminescent color can be used as a strong alkaline environment in the identification solution, namely the pH is more than 11.

Detecting part

Example 6

The nitrogen-doped carbon nanorings of the invention are successfully used for Fe³⁺Detection of (3). 2.5. mu.L of the carbon nanoring was diluted to 1mL with deionized water, and after excitation with light having a wavelength of 410nm, the luminescence intensity at 530nm was recorded as initial intensity F0. Adding Fe-containing solution to the solution³⁺The luminescence intensity was measured after 5min and designated as F1. Δ F is Fe³⁺The expression of (a) is F0-F1. The excitation slit width and emission slit width were 5nm and 5nm, respectively. FIG. 6 is the carbon nanoring pair Fe³⁺Experimental results of sensitivity of (2). Different Fe³⁺Luminescence intensity of carbon nanorings at concentration (0, 1, 25, 50, 100, 150, 200 μ M). Luminous intensity dependent on Fe³ ⁺The increase in concentration decreased significantly. FIG. 7 shows the attenuation of luminescence intensity versus Fe³⁺The relationship of concentration. When Fe³⁺Concentration is 1-200 mu M), the two are in strong linear relation, and the correlation coefficient is 0.9984. According to the three-time standard deviation method, the detection limit is 10 nmol/L.

Particle adsorption applications

Example 7

The nitrogen-doped carbon nanorings of the present invention are successfully used for adsorption of PM particles. A small adsorption device is adopted, after a glass tube in the middle of the device is weighed, smoke is introduced from one end of the inverted round-bottom flask until the round-bottom flask is filled with the smoke, the other end of the round-bottom flask is connected with an air pump, and a circulating pump is turned on to perform smoke adsorption test operation after the round-bottom flask is ready.

Fig. 7 shows that the nitrogen-doped carbon nanoring solid powder prepared in example 1 of the present invention is applied to PM particle adsorption equipment, and comparative analysis is performed on adsorption performance of the nitrogen-doped carbon nanoring and activated carbon, which shows that the adsorption effect of the doped carbon nanoring is much higher than that of activated carbon, and can be up to 2 times or more.

Finally, the description is as follows: although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover any modifications or equivalents as may fall within the scope of the invention.

Claims

1. A method of preparing nitrogen-doped carbon nanorings, comprising: mixing a carbon source and a nitrogen source to obtain a precursor mixture; directly heating the precursor mixture to avoid pressurization, and reacting at a temperature capable of melting a nitrogen source in the precursor mixture to obtain the nitrogen-doped carbon nanoring; the nitrogen source is urea, and the carbon source is sodium citrate.

2. The production method according to claim 1, wherein the precursor mixture is ground before being directly heated.

3. The method of claim 1, wherein the mass ratio of the sodium citrate to the urea is 1:0.1 to 1: 16.

4. The production method according to claim 3, wherein the mass ratio of the sodium citrate to the urea is 1: 4.

5. The method according to claim 1, wherein the reaction temperature is 140 to 240 ℃.

6. The method according to claim 2, wherein the reaction temperature is 140 to 240 ℃.

7. The method according to claim 3, wherein the reaction temperature is 140 to 240 ℃.

8. The method according to claim 4, wherein the reaction temperature is 140 to 240 ℃.

9. The production method according to any one of claims 1 to 8, wherein the reaction time is 1min or more.

10. The production method according to claim 9, wherein the reaction time is 1 hour or more.

11. The production method according to any one of claims 1 to 8 and 10, wherein the production method further comprises a separation step.

12. The production method according to claim 11, wherein the separating step includes:

and naturally cooling the reacted material, adding water into the cooled material, filtering by adopting a interception membrane to obtain filtrate, and freeze-drying the filtrate to obtain the nitrogen-doped carbon nanorings.

13. The method of claim 9, wherein the method further comprises a separation step.

14. The method of manufacturing of claim 13, wherein the separating step comprises:

15. The production method according to claim 12 or 14, wherein the cut-off membrane has a molecular weight cut-off of any one of 3kDa, 5kDa, 10kDa, or 30kDa, or a combination of at least two thereof.

16. The method according to claim 12 or 14, wherein the freeze-drying is performed under vacuum at-50 ℃ to-45 ℃.

17. The method of claim 15, wherein the freeze-drying is performed under vacuum at-50 ℃ to-45 ℃.

18. A nitrogen-doped carbon nanoring produced by the production method according to any one of claims 1 to 17.

19. The nitrogen-doped carbon nanoring of claim 18, wherein the nitrogen-doped carbon nanoring has an element content of 50 to 60% of C, 15 to 20% of N, and 20 to 30% of O, as analyzed by XPS.

20. Use of the nitrogen-doped carbon nanoring of claim 18 or 19 as an acid-base recognition agent for recognizing the pH of an aqueous solution.

21. The nitrogen-doped carbon nanoring of claim 18 or 19 as a detection reagent for detecting Fe³⁺Application of ion concentration.

22. Use of the nitrogen-doped carbon nanorings of claim 18 or 19 as an adsorbent for adsorbing PM particles in air.