CN110790267A - Preparation method of nitrogen-doped graphene - Google Patents
Preparation method of nitrogen-doped graphene Download PDFInfo
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- CN110790267A CN110790267A CN201911066884.XA CN201911066884A CN110790267A CN 110790267 A CN110790267 A CN 110790267A CN 201911066884 A CN201911066884 A CN 201911066884A CN 110790267 A CN110790267 A CN 110790267A
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Abstract
The invention discloses a preparation method of nitrogen-doped graphene, which comprises the following steps: adding graphite powder and sodium nitrate into concentrated sulfuric acid to form a first reaction system; adding potassium permanganate into the first reaction system, heating to a first preset temperature, and stirring for a first preset time to form a second reaction system; adding deionized water into the second reaction system, heating to a second preset temperature, and stirring for a second preset time to obtain a third reaction system; diluting the third reaction system with deionized water and adding H2O2Obtaining a fourth reaction system; standing the fourth reaction system until layering occurs, and washing the precipitate; dialyzing the product to be neutral, and drying the dialyzed product to obtain graphite oxide; dispersing graphite oxide in deionized water, adding urea or ammonium salt, uniformly mixing, freeze-drying, and quickly heating the obtained product in a high-temperature tube furnace and slowly cooling to obtain the nitrogen-doped graphene. The preparation method has the characteristics of high efficiency and environmental friendliness.
Description
Technical Field
The invention belongs to the technical field of material preparation, and particularly relates to a preparation method of nitrogen-doped graphene.
Background
In recent years, research on the preparation and application of graphene with a two-dimensional layered structure has been attracting attention. The preparation of the graphene material is a precondition for the application research of the graphene material, and researchers have developed the technologies of chemical vapor deposition, solvothermal technology, liquid phase stripping technology and the like to synthesize the high-quality graphene material so as to meet the current research requirements. At present, the structure and performance of graphene can be effectively regulated and controlled by modifying the graphene in the modes of chemical modification, surface functionalization, chemical doping and the like, and the application field of the graphene is further expanded. For example, when a carbon atom in the crystal structure of graphene is replaced with a nitrogen atom, nitrogen-doped graphene is formed. The nitrogen doping can improve the dispersion performance of the graphene, increase the surface active site of the graphene, regulate and control the electronic structure of the graphene, and improve the carrier density, so that the graphene has wide application prospects in the aspects of catalysis, supercapacitors, lithium ion batteries and the like.
The preparation method of the nitrogen-doped graphene reported in the prior art mainly comprises the following steps: chemical Vapor Deposition (CVD), arc discharge, NH3Or N2Plasma method, solvothermal method, high-temperature annealing of nitrogen-containing molecules, graphite oxide, and the like. The chemical vapor deposition method mainly uses carbon-containing and nitrogen-containing micromolecules as raw materials, uses transition metal as a substrate, realizes rearrangement and deposition of carbon atoms and nitrogen atoms at high temperature, and finally forms the nitrogen-doped graphene. In the method, a transition metal catalyst such as nickel, copper and the like is one of the key factors for preparing the nitrogen-doped carbon material. However, the transition metal material particles can be embedded into the gaps of the graphene layers and are difficult to remove, and the research on the catalytic performance of the nitrogen-doped graphene can be influenced. In addition, the nitrogen sources such as ammonia gas or pyridine and the like used in the preparation process are toxic and harmful chemicals which need special treatment, thereby greatly limiting the application of the chemical vapor deposition method. Other synthesis methods, such as arc discharge method and plasma method, require special equipment, and the preparation conditions are harsh, so that large-scale production is difficult. In order to simplify the synthesis equipment and eliminate the influence of the transition metal substrate, it is necessary to develop a simple, fast and catalyst-free preparation method.
Disclosure of Invention
The invention aims to provide a preparation method of nitrogen-doped graphene.
The invention provides a preparation method of nitrogen-doped graphene, which comprises the following steps:
sequentially adding graphite powder and sodium nitrate into concentrated sulfuric acid to form a first reaction system; adding potassium permanganate into the first reaction system under the stirring state, heating to a first preset temperature, and continuously stirring for a first preset time to form a second reaction system; adding deionized water into the second reaction system, heating to a second preset temperature, and continuously stirring for a second preset time to obtain a third reaction system; diluting the third reaction system with deionized water and adding H thereto2O2Until no bubble exists, obtaining a fourth reaction system; standing the fourth reaction system until layering occurs, removing supernatant, and washing the lower precipitate; putting the obtained product into a dialysis bag, dialyzing to be neutral, and drying the dialyzed product to obtain graphite oxide;
dispersing graphite oxide in deionized water, adding urea or ammonium salt, and freeze-drying after mixing uniformly; heating the obtained product to 700-1000 ℃, preserving heat for 15-25 min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
Optionally, the mass ratio of the graphite oxide to the urea or the ammonium salt is 1: 0.5-50.
Optionally, the ammonium salt is any one of ammonium chloride, ammonium sulfate, ammonium carbonate, ammonium bicarbonate and ammonium citrate.
Optionally, the graphite oxide is uniformly dispersed in the deionized water in an ultrasonic dispersion manner.
Optionally, the mass ratio of the graphite powder to the sodium nitrate is 1: 0.4-0.6;
the dosage of the concentrated sulfuric acid is as follows: each gram of graphite powder corresponds to 8mL-12mL of concentrated sulfuric acid.
Optionally, the first reaction system is placed in an ice-water bath at 0-5 ℃.
Optionally, the adding amount of the potassium permanganate is 2.5-3.5 times of the graphite powder, and the temperature is controlled below 5 ℃ in the process of adding the potassium permanganate.
Optionally, the first predetermined temperature is 30-40 ℃, and the first predetermined time is 25-35 min.
Optionally, the amount of deionized water added to the second reaction system is: adding 80-120 mL of deionized water into each gram of graphite powder;
the second preset temperature is 90-100 ℃, and the second preset time is 0.5-1 h.
Optionally, transferring the precipitate to a centrifugal device, and centrifugally washing the precipitate with hydrochloric acid solution and deionized water respectively; drying the dialysis product at 50-70 ℃.
The invention has the beneficial effects that: according to the invention, the nitrogen-doped graphene is prepared by adopting a rapid expansion method and taking graphite oxide and urea or ammonium salt as raw materials, wherein the raw materials for preparation are cheap and easy to obtain and have low toxicity. In addition, a metal catalyst is not needed in the preparation process, and the defect that metal material particles are embedded into gaps of the graphene layer and are difficult to remove in the prior art is overcome. The preparation method of the invention has the characteristics of rapidness and environmental friendliness. In addition, the nitrogen-doped graphene material prepared by the method has the advantages of large specific surface area, more catalytic active sites and better stability.
Other features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments thereof, which proceeds with reference to the accompanying drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.
Fig. 1 is an X-ray diffraction spectrum of the nitrogen-doped graphene provided by the invention.
Fig. 2a and 2b are SEM images of the nitrogen-doped graphene provided by the present invention at different magnifications, respectively.
Fig. 3 is a TEM image of nitrogen-doped graphene provided by the present invention.
Fig. 4 is a Raman spectrum of the nitrogen-doped graphene provided by the present invention.
Fig. 5 is an EDS spectrum analysis diagram of the nitrogen-doped graphene provided by the present invention.
Fig. 6 and 7 are XPS spectra of the nitrogen-doped graphene provided by the present invention.
Detailed Description
Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that: the relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.
The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.
Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate.
In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.
The embodiment of the invention provides a preparation method of nitrogen-doped graphene. The preparation method comprises the following steps:
step S1, preparing graphite oxide:
and S1.1, sequentially adding graphite powder and sodium nitrate into concentrated sulfuric acid in sequence to form a first reaction system. The mass ratio of the graphite powder to the sodium nitrate can be controlled to be, for example, 1: 0.4-0.6. The dosage of concentrated sulfuric acid can be controlled as follows: each gram of graphite powder needs 8mL-12mL of concentrated sulfuric acid.
It should be noted that the temperature of the concentrated sulfuric acid in this step should be relatively low, i.e. cold concentrated sulfuric acid is used. For example, concentrated sulfuric acid may be placed in an ice-water bath environment at 0-5 ℃ in advance. The container for holding concentrated sulfuric acid may be, for example, a round-bottomed flask, but other containers known to those skilled in the art may be used, and the present invention is not limited thereto. At this time, the first reaction system was also formed under the ice-water bath condition of 0 to 5 ℃.
In addition, according to the preparation method of the invention, the graphite powder is natural flake graphite powder. The natural crystalline flake graphite powder is natural crystalline graphite, has a fish scale-like appearance, belongs to a hexagonal system, and has good high temperature resistance, conductivity, lubrication, plasticity, acid and alkali resistance and other properties.
Step S1.2, after the first reaction system is formed, adding potassium permanganate into the first reaction system in a stirring state, heating to a first preset temperature, and continuously stirring for a first preset time to form a second reaction system.
In the step S1.2, the adding amount of potassium permanganate is 2.5 to 3.5 times of the mass of the graphite powder in the step. It should be noted that in the present invention, the quality of graphite powder is used as a standard to measure the usage amount of potassium permanganate. For example, when the graphite powder is used in an amount of 1g in the preparation of the first reaction system, the amount of potassium permanganate to be added is preferably controlled to be 2.5g to 3.5g in the preparation of the second reaction system. Furthermore, the temperature of the potassium permanganate needs to be controlled below 5 ℃ during the addition process, so as to prevent the temperature from rising to initiate other reactions. In addition, when the potassium permanganate is added to the first reaction system, it is preferable to use a batch addition method so that the potassium permanganate and the first reaction system can sufficiently react. For example, potassium permanganate can be added in 3 times, and the operation can be flexibly adjusted by a person skilled in the art according to specific situations, and is not limited.
In the step S1.2, the first preset temperature can be controlled to be 30-40 ℃, and the first preset time can be controlled to be 25-35 min. Of course, one skilled in the art can make reasonable adjustments to specific temperature and time parameters as desired.
And S1.3, adding deionized water into the second reaction system, heating to a second preset temperature, and continuously stirring for a second preset time to obtain a third reaction system. Wherein, the amount of deionized water added into the second reaction system can be controlled as follows: 80-120 mL of deionized water is correspondingly added into each gram of graphite powder.
In the present invention, the amount of deionized water is measured by using the amount of graphite powder as a standard. For example, when the amount of graphite powder used in the preparation of the first reaction system is 1g, the amount of deionized water to be added is preferably controlled to 80mL to 120mL, and so on, to adjust the appropriate amount of deionized water to be added in the preparation of the third reaction system.
In the step S1.3, the second preset temperature is controlled to be 90-100 ℃, and the second preset time is controlled to be 0.5-1 h. Of course, one skilled in the art can make reasonable adjustments to specific temperature and time parameters as desired.
Step S1.4, diluting the third reaction system by using deionized water, and adding H into the third reaction system2O2Until no bubble exists, obtaining a fourth reaction system; the fourth reaction system was allowed to stand until the separation occurred, at which time the supernatant was removed and the precipitate of the lower layer was subjected to a washing treatment. In this step, the amount of the deionized water is not limited, and those skilled in the art can appropriately dilute the third reaction system according to actual needs.
In this step S1.4, optionally, the precipitate is transferred to a centrifugal device, for example, the centrifugal device may adopt a centrifugal tube, and then the precipitate is centrifugally washed by hydrochloric acid solution and deionized water, respectively, so as to completely remove impurities, so that the obtained product is purer, and the mixing of unnecessary impurities is reduced. The hydrochloric acid solution is prepared by uniformly mixing hydrochloric acid and deionized water, and the volume ratio of the hydrochloric acid to the deionized water is controlled to be 1: 10.
And S1.5, putting the product obtained in the step S1.4 into a dialysis bag, dialyzing to be neutral, and drying the dialyzed product to obtain the graphite oxide.
In the present step S1.5, optionally, the dialysis product is placed in a vacuum drying oven and dried at 50 ℃ to 70 ℃. It should be noted that the drying temperature is not too high, otherwise the product is liable to be agglomerated, which is not favorable for the implementation of the subsequent steps.
Step S2, preparing nitrogen-doped graphene:
firstly, dispersing graphite oxide in deionized water, adding urea or ammonium salt, and after uniformly mixing, carrying out freeze drying treatment; heating the obtained product to 700-1000 ℃, preserving heat for 15-25 min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
In step S2, if urea is used, the mass ratio of graphite oxide to urea is 1: 0.5-50. If ammonium salt is adopted, the mass ratio of the graphite oxide to the ammonium salt is 1: 0.5-50. The graphite oxide may be uniformly dispersed in deionized water by ultrasonic dispersion, for example, to form a dispersion. The ammonium salt may be any one of ammonium chloride, ammonium sulfate, ammonium carbonate, ammonium bicarbonate, and ammonium citrate, for example. Of course, other ammonium salts known to those skilled in the art may be used, and the present invention is not limited thereto.
In step S2, the freeze-drying process may be performed using, for example, a vacuum freeze-drying apparatus. After the freeze drying treatment is finished, placing a product obtained after the freeze drying treatment in a crucible with a cover, then placing the crucible into one end of a tube furnace, heating the tube furnace to 700-1000 ℃ under the protection of inert atmosphere, then moving the crucible to a high temperature region, preserving heat for 15-25 min, and then slowly cooling to room temperature.
The preparation method provided by the invention is simple, easy to operate and very suitable for popularization and use in industrial production. According to the invention, the nitrogen-doped graphene is prepared by adopting a rapid expansion method and taking graphite oxide and urea or graphite oxide and ammonium salt as raw materials, wherein the raw materials for preparation are cheap and easy to obtain and have low toxicity. In addition, a metal catalyst is not needed in the preparation process, and the defect that metal material particles are embedded into gaps of the graphene layer and are difficult to remove in the prior art is overcome. The preparation method of the invention has the characteristics of rapidness and environmental friendliness. In addition, the nitrogen-doped graphene material prepared by the method has the advantages of large specific surface area, more catalytic active sites and better stability.
Fig. 1 is an X-ray diffraction pattern (XRD) of the nitrogen-doped graphene of the present invention. Referring to fig. 1, the XRD spectrum shows that a broad diffraction peak, which is a characteristic diffraction peak of the (002) crystal plane of graphene, appears around 26 °. This indicates that the prepared material is indeed a graphene material.
Fig. 2a and fig. 2b are SEM images of the nitrogen-doped graphene provided by the present invention at different magnifications, respectively. Fig. 3 is a TEM image of nitrogen-doped graphene provided by the present invention. Fig. 4 is a Raman spectrum of the nitrogen-doped graphene provided by the present invention. According to SEM images and TEM images, the micro-morphology of the prepared nitrogen-doped graphene presents a random porous structure, and the lamella of the nitrogen-doped graphene is almost transparent. Moreover, due to the action of a large amount of gas generated in the thermal decomposition process and an ice template in the freeze drying process, pore channels and folds exist among the graphene sheet layers, and the graphene sheet layers are greatly exposed on the surface of the graphene, so that the subsequent application research is facilitated. Also, in the Raman spectrum shown in FIG. 4, it is located at 1384.8cm-1And 1617.2cm-1Respectively assigned to the D peak and the G peak of the graphene structure. This indicates that the basic skeleton of graphene is maintained, but that there are more defects in its lattice. This is mainly because the six-membered ring structure in graphene is destroyed due to decomposition of oxygen-containing functional groups and breakage of dangling bonds during the high-temperature reaction.
In order to further confirm the specific composition of the nitrogen-doped graphene prepared by the present invention, the inventors of the present invention also performed corresponding analysis on the elements of the prepared nitrogen-doped graphene through the energy spectrum and XPS attached to the scanning electron microscope, and the analysis structure can be shown in table 1.
Table 1 XPS analysis results of nitrogen-doped graphene materials
| Element(s) | Atom% |
| C K | 85.57 |
| N K | 7.72 |
| O K | 6.71 |
As shown in fig. 5, there are distinct characteristic peaks of carbon and nitrogen elements. From the XPS results shown in table 1, it can be seen that the nitrogen content is 7.72% (atomic percentage content).
In addition, as shown in fig. 6 and 7, from the fitting spectrum of N1s with high resolution, it can be seen that the nitrogen element in the nitrogen-doped graphene has pyridine type, pyrrole type, graphite type and oxidation type, wherein pyridine type nitrogen is taken as the main component, which fully indicates that nitrogen atoms are doped into the crystal lattice of graphene and form a C — N covalent bond.
According to the method, the graphite oxide and the urea/ammonium salt are used as raw materials to prepare the nitrogen-doped graphene, so that the preparation steps are simplified, the cheap and easily obtained urea or ammonium salt is used for replacing ammonia gas as a nitrogen source, and the limitations of methods such as a Chemical Vapor Deposition (CVD) method and the like are avoided. The method accelerates the practical application possibility of the nitrogen-doped graphene. Meanwhile, no metal catalyst is added in the whole preparation process, so that the pollution of the nitrogen-doped graphene is completely eliminated, and a foundation is laid for subsequent application research. In addition, the content of nitrogen atoms in the graphene crystal lattice and the configuration of nitrogen elements can be regulated and controlled by regulating and controlling the raw material proportion, the reaction temperature and the reaction time in the whole preparation process. The nitrogen-doped atomic percentage can reach 8.05 percent at most.
The production method of the present invention is described in detail below with reference to a plurality of specific examples.
Example 1
Sequentially adding 1g of natural crystalline flake graphite powder and 0.4g of sodium nitrate into 8mL of cold concentrated sulfuric acid to form a first reaction system, and placing the first reaction system in an ice-water bath at 0 ℃; adding 2.5g of potassium permanganate into the first reaction system under the stirring state, heating to 30 ℃, continuing stirring for 25min to form a second reaction system, wherein the temperature is required to be controlled below 5 ℃ in the process of adding the potassium permanganate, and the potassium permanganate can be added in two times; adding 80mL of deionized water into the second reaction system, heating to 90 ℃, and continuously stirring for 0.5h to obtain a third reaction system; diluting the third reaction system with deionized water and adding H thereto2O2And until no bubble exists, obtaining a fourth reaction system, standing the fourth reaction system until layering is generated, removing the supernatant, then centrifugally washing the precipitate on the lower layer, transferring the precipitate into a centrifuge tube, and centrifugally washing the precipitate by using a hydrochloric acid solution and deionized water respectively, wherein the hydrochloric acid solution is prepared by uniformly mixing hydrochloric acid and deionized water, and the volume ratio of the hydrochloric acid to the deionized water is controlled to be 1: 10; putting the obtained product into a dialysis bag for dialysis until the product is neutral, and then putting the dialysis product into a vacuum drying oven for drying at 50 ℃ to obtain graphite oxide;
uniformly dispersing 0.1g of graphite oxide in deionized water by adopting an ultrasonic mode, adding 0.05g of urea, fully dissolving the urea in a dispersion liquid after ultrasonic treatment, and then placing the dispersion liquid in a vacuum freeze-drying device for freeze-drying; and placing the obtained product in a crucible with a cover, then placing the crucible into one end of a tube furnace, heating the tube furnace to 700 ℃ under the protection of inert atmosphere, then moving the crucible to a high-temperature region, preserving heat for 15min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
Example 2
Sequentially adding 1g of natural crystalline flake graphite powder and 0.4g of sodium nitrate into 8mL of cold concentrated sulfuric acid to form a first reaction system, and placing the first reaction system in an ice-water bath at 0 ℃; 2.5g of potassium permanganate was added to the first reaction system under stirring and heated toContinuously stirring for 25min at 30 ℃ to form a second reaction system, wherein the temperature is required to be controlled below 5 ℃ in the process of adding the potassium permanganate, and the potassium permanganate can be added in two times; adding 80mL of deionized water into the second reaction system, heating to 90 ℃, and continuously stirring for 0.5h to obtain a third reaction system; diluting the third reaction system with deionized water and adding H thereto2O2And until no bubble exists, obtaining a fourth reaction system, standing the fourth reaction system until layering is generated, removing the supernatant, then centrifugally washing the precipitate on the lower layer, transferring the precipitate into a centrifuge tube, and centrifugally washing the precipitate by using a hydrochloric acid solution and deionized water respectively, wherein the hydrochloric acid solution is prepared by uniformly mixing hydrochloric acid and deionized water, and the volume ratio of the hydrochloric acid to the deionized water is controlled to be 1: 10; putting the obtained product into a dialysis bag for dialysis until the product is neutral, and then putting the dialysis product into a vacuum drying oven for drying at 50 ℃ to obtain graphite oxide;
uniformly dispersing 0.1g of graphite oxide in deionized water by adopting an ultrasonic mode, adding 0.1g of ammonium chloride, fully dissolving the ammonium chloride in a dispersion liquid after ultrasonic treatment, and then placing the dispersion liquid in a vacuum freeze-drying device for freeze-drying; and placing the obtained product in a crucible with a cover, then placing the crucible into one end of a tube furnace, heating the tube furnace to 750 ℃ under the protection of inert atmosphere, then moving the crucible to a high-temperature region, preserving heat for 18min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
Example 3
Sequentially adding 1g of natural crystalline flake graphite powder and 0.5g of sodium nitrate into 10mL of cold concentrated sulfuric acid to form a first reaction system, and placing the first reaction system in an ice-water bath at 3 ℃; adding 3g of potassium permanganate into the first reaction system under the stirring state, heating to 35 ℃, continuing stirring for 30min to form a second reaction system, wherein the temperature is required to be controlled below 5 ℃ in the process of adding the potassium permanganate, and the potassium permanganate can be added in three times; adding 100mL of deionized water into the second reaction system, heating to 95 ℃, and continuously stirring for 1h to obtain a third reaction system; for miningDiluting the third reaction system with ionized water and adding H thereto2O2And until no bubble exists, obtaining a fourth reaction system, standing the fourth reaction system until layering is generated, removing the supernatant, then centrifugally washing the precipitate on the lower layer, transferring the precipitate into a centrifuge tube, and centrifugally washing the precipitate by using a hydrochloric acid solution and deionized water respectively, wherein the hydrochloric acid solution is prepared by uniformly mixing hydrochloric acid and deionized water, and the volume ratio of the hydrochloric acid to the deionized water is controlled to be 1: 10; putting the obtained product into a dialysis bag for dialysis until the product is neutral, and then putting the dialysis product into a vacuum drying oven for drying at 65 ℃ to obtain graphite oxide;
uniformly dispersing 0.1g of graphite oxide in deionized water by adopting an ultrasonic mode, adding 1g of ammonium sulfate, fully dissolving the ammonium sulfate in a dispersion liquid after ultrasonic treatment, and then placing the dispersion liquid in a vacuum freeze drying device for freeze drying; and placing the obtained product in a crucible with a cover, then placing the crucible into one end of a tube furnace, heating the tube furnace to 800 ℃ under the protection of inert atmosphere, then moving the crucible to a high-temperature region, preserving heat for 20min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
Example 4
Sequentially adding 1g of natural crystalline flake graphite powder and 0.5g of sodium nitrate into 10mL of cold concentrated sulfuric acid to form a first reaction system, and placing the first reaction system in an ice-water bath at 3 ℃; adding 3g of potassium permanganate into the first reaction system under the stirring state, heating to 35 ℃, continuing stirring for 30min to form a second reaction system, wherein the temperature is required to be controlled below 5 ℃ in the process of adding the potassium permanganate, and the potassium permanganate can be added in three times; adding 100mL of deionized water into the second reaction system, heating to 95 ℃, and continuously stirring for 1h to obtain a third reaction system; diluting the third reaction system with deionized water and adding H thereto2O2Obtaining a fourth reaction system until no bubbles exist, standing the fourth reaction system until layering is generated, removing the supernatant, performing centrifugal washing on the precipitate at the lower layer, and transferring the precipitate to a centrifugal washing machineAnd in the core tube, centrifugally washing the precipitate by respectively using hydrochloric acid solution and deionized water, wherein the hydrochloric acid solution is prepared by uniformly mixing hydrochloric acid and deionized water, and the volume ratio of the hydrochloric acid to the deionized water is controlled to be 1: 10; putting the obtained product into a dialysis bag for dialysis until the product is neutral, and then putting the dialysis product into a vacuum drying oven for drying at 65 ℃ to obtain graphite oxide;
uniformly dispersing 0.1g of graphite oxide in deionized water by adopting an ultrasonic mode, adding 2g of ammonium carbonate into the deionized water, fully dissolving the ammonium carbonate in a dispersion liquid after ultrasonic treatment, and then placing the dispersion liquid in a vacuum freeze-drying device for freeze-drying; and placing the obtained product in a crucible with a cover, then placing the crucible into one end of a tubular furnace, heating the tubular furnace to 850 ℃ under the protection of inert atmosphere, then moving the crucible to a high-temperature region, preserving heat for 22min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
Example 5
Sequentially adding 1g of natural crystalline flake graphite powder and 0.5g of sodium nitrate into 10mL of cold concentrated sulfuric acid to form a first reaction system, and placing the first reaction system in an ice-water bath at 3 ℃; adding 3g of potassium permanganate into the first reaction system under the stirring state, heating to 35 ℃, continuing stirring for 30min to form a second reaction system, wherein the temperature is required to be controlled below 5 ℃ in the process of adding the potassium permanganate, and the potassium permanganate can be added in two times; adding 100mL of deionized water into the second reaction system, heating to 95 ℃, and continuously stirring for 1h to obtain a third reaction system; diluting the third reaction system with deionized water and adding H thereto2O2And until no bubble exists, obtaining a fourth reaction system, standing the fourth reaction system until layering is generated, removing the supernatant, then centrifugally washing the precipitate on the lower layer, transferring the precipitate into a centrifuge tube, and centrifugally washing the precipitate by using a hydrochloric acid solution and deionized water respectively, wherein the hydrochloric acid solution is prepared by uniformly mixing hydrochloric acid and deionized water, and the volume ratio of the hydrochloric acid to the deionized water is controlled to be 1: 10; placing the obtained product in a dialysis bag, dialyzing to neutrality, and placing the dialyzed product in a containerDrying in a vacuum drying oven at 60 deg.C to obtain graphite oxide;
uniformly dispersing 0.1g of graphite oxide in deionized water by adopting an ultrasonic mode, adding 2.5g of ammonium bicarbonate, fully dissolving the ammonium bicarbonate in a dispersion liquid after ultrasonic treatment, and then placing the dispersion liquid in a vacuum freeze-drying device for freeze-drying; and placing the obtained product in a crucible with a cover, then placing the crucible into one end of a tube furnace, heating the tube furnace to 900 ℃ under the protection of inert atmosphere, then moving the crucible to a high-temperature region, preserving heat for 25min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
Example 6
Sequentially adding 1g of natural crystalline flake graphite powder and 0.5g of sodium nitrate into 10mL of cold concentrated sulfuric acid to form a first reaction system, and placing the first reaction system in an ice-water bath at 3 ℃; adding 3g of potassium permanganate into the first reaction system under the stirring state, heating to 35 ℃, continuing stirring for 30min to form a second reaction system, wherein the temperature is required to be controlled below 5 ℃ in the process of adding the potassium permanganate, and the potassium permanganate can be added in two times; adding 100mL of deionized water into the second reaction system, heating to 95 ℃, and continuously stirring for 1h to obtain a third reaction system; diluting the third reaction system with deionized water and adding H thereto2O2And until no bubble exists, obtaining a fourth reaction system, standing the fourth reaction system until layering is generated, removing the supernatant, then centrifugally washing the precipitate on the lower layer, transferring the precipitate into a centrifuge tube, and centrifugally washing the precipitate by using a hydrochloric acid solution and deionized water respectively, wherein the hydrochloric acid solution is prepared by uniformly mixing hydrochloric acid and deionized water, and the volume ratio of the hydrochloric acid to the deionized water is controlled to be 1: 10; putting the obtained product into a dialysis bag for dialysis until the product is neutral, and then putting the dialysis product into a vacuum drying oven for drying at the temperature of 60 ℃ to obtain graphite oxide;
uniformly dispersing 0.1g of graphite oxide in deionized water by adopting an ultrasonic mode, adding 3g of ammonium citrate into the deionized water, fully dissolving the ammonium citrate in a dispersion liquid after ultrasonic treatment, and then placing the dispersion liquid in a vacuum freeze drying device for freeze drying; and placing the obtained product in a crucible with a cover, then placing the crucible into one end of a tubular furnace, heating the tubular furnace to 950 ℃ under the protection of inert atmosphere, then moving the crucible to a high-temperature region, preserving heat for 15min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
Example 7
Sequentially adding 1g of natural crystalline flake graphite powder and 0.6g of sodium nitrate into 12mL of cold concentrated sulfuric acid to form a first reaction system, and placing the first reaction system in an ice-water bath at 5 ℃; adding 3.5g of potassium permanganate into the first reaction system under the stirring state, heating to 40 ℃, continuing stirring for 35min to form a second reaction system, wherein the temperature is required to be controlled below 5 ℃ in the process of adding the potassium permanganate, and the potassium permanganate can be added in three times; adding 120mL of deionized water into the second reaction system, heating to 100 ℃, and continuously stirring for 1h to obtain a third reaction system; diluting the third reaction system with deionized water and adding H thereto2O2And until no bubble exists, obtaining a fourth reaction system, standing the fourth reaction system until layering is generated, removing the supernatant, then centrifugally washing the precipitate on the lower layer, transferring the precipitate into a centrifuge tube, and centrifugally washing the precipitate by using a hydrochloric acid solution and deionized water respectively, wherein the hydrochloric acid solution is prepared by uniformly mixing hydrochloric acid and deionized water, and the volume ratio of the hydrochloric acid to the deionized water is controlled to be 1: 10; putting the obtained product into a dialysis bag for dialysis until the product is neutral, and then putting the dialysis product into a vacuum drying oven for drying at 70 ℃ to obtain graphite oxide;
uniformly dispersing 0.1g of graphite oxide in deionized water by adopting an ultrasonic mode, adding 4g of ammonium sulfate, fully dissolving the ammonium sulfate in a dispersion liquid after ultrasonic treatment, and then placing the dispersion liquid in a vacuum freeze drying device for freeze drying; and placing the obtained product in a crucible with a cover, then placing the crucible into one end of a tube furnace, heating the tube furnace to 800 ℃ under the protection of inert atmosphere, then moving the crucible to a high-temperature region, preserving heat for 20min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
Example 8
Sequentially adding 1g of natural crystalline flake graphite powder and 0.6g of sodium nitrate into 12mL of cold concentrated sulfuric acid to form a first reaction system, and placing the first reaction system in an ice-water bath at 5 ℃; adding 3.5g of potassium permanganate into the first reaction system under the stirring state, heating to 40 ℃, continuing stirring for 35min to form a second reaction system, wherein the temperature is required to be controlled below 5 ℃ in the process of adding the potassium permanganate, and the potassium permanganate can be added in three times; adding 120mL of deionized water into the second reaction system, heating to 100 ℃, and continuously stirring for 1h to obtain a third reaction system; diluting the third reaction system with deionized water and adding H thereto2O2And until no bubble exists, obtaining a fourth reaction system, standing the fourth reaction system until layering is generated, removing the supernatant, then centrifugally washing the precipitate on the lower layer, transferring the precipitate into a centrifuge tube, and centrifugally washing the precipitate by using a hydrochloric acid solution and deionized water respectively, wherein the hydrochloric acid solution is prepared by uniformly mixing hydrochloric acid and deionized water, and the volume ratio of the hydrochloric acid to the deionized water is controlled to be 1: 10; putting the obtained product into a dialysis bag for dialysis until the product is neutral, and then putting the dialysis product into a vacuum drying oven for drying at 70 ℃ to obtain graphite oxide;
uniformly dispersing 0.1g of graphite oxide in deionized water by adopting an ultrasonic mode, adding 5g of urea into the deionized water, fully dissolving the urea in a dispersion liquid after ultrasonic treatment, and then placing the dispersion liquid in a vacuum freeze-drying device for freeze-drying; and placing the obtained product in a crucible with a cover, then placing the crucible into one end of a tube furnace, heating the tube furnace to 1000 ℃ under the protection of inert atmosphere, then moving the crucible to a high-temperature region, preserving heat for 20min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
According to the invention, the nitrogen-doped graphene material is prepared by adopting a rapid thermal expansion method, the preparation process is less in time consumption and lower in cost, and large-scale production can be realized. No metal catalyst is used in the preparation process. The nitrogen source is urea or ammonium salt, and the materials are cheap, easy to obtain, low in toxicity and simple in treatment process.
Although some specific embodiments of the present invention have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustrative purposes only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that modifications may be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.
Claims (10)
1. A preparation method of nitrogen-doped graphene is characterized by comprising the following steps:
sequentially adding graphite powder and sodium nitrate into concentrated sulfuric acid to form a first reaction system; adding potassium permanganate into the first reaction system under the stirring state, heating to a first preset temperature, and continuously stirring for a first preset time to form a second reaction system; adding deionized water into the second reaction system, heating to a second preset temperature, and continuously stirring for a second preset time to obtain a third reaction system; diluting the third reaction system with deionized water and adding H thereto2O2Until no bubble exists, obtaining a fourth reaction system; standing the fourth reaction system until layering occurs, removing supernatant, and washing the lower precipitate; putting the obtained product into a dialysis bag, dialyzing to be neutral, and drying the dialyzed product to obtain graphite oxide;
dispersing graphite oxide in deionized water, adding urea or ammonium salt, and freeze-drying after mixing uniformly; heating the obtained product to 700-1000 ℃, preserving heat for 15-25 min, and then cooling to room temperature to obtain the nitrogen-doped graphene.
2. The method of claim 1, wherein: the mass ratio of the graphite oxide to the urea or the ammonium salt is 1: 0.5-50.
3. The method of claim 1, wherein: the ammonium salt is any one of ammonium chloride, ammonium sulfate, ammonium carbonate, ammonium bicarbonate and ammonium citrate.
4. The method of claim 1, wherein: and the graphite oxide is uniformly dispersed in the deionized water in an ultrasonic dispersion mode.
5. The method of claim 1, wherein: the mass ratio of the graphite powder to the sodium nitrate is 1: 0.4-0.6;
the dosage of the concentrated sulfuric acid is as follows: each gram of graphite powder corresponds to 8mL-12mL of concentrated sulfuric acid.
6. The method of claim 1, wherein: the first reaction system is placed in an ice-water bath at the temperature of 0-5 ℃.
7. The preparation method of claim 1, wherein the addition amount of the potassium permanganate is 2.5-3.5 times of the mass of the graphite powder, and the temperature is controlled to be below 5 ℃ during the addition of the potassium permanganate.
8. The method of claim 1, wherein the first predetermined temperature is 30-40 ℃ and the first predetermined time is 25-35 min.
9. The preparation method according to claim 1, wherein the amount of deionized water added to the second reaction system is: adding 80-120 mL of deionized water into each gram of graphite powder;
the second preset temperature is 90-100 ℃, and the second preset time is 0.5-1 h.
10. The method according to claim 1, wherein the precipitate is transferred to a centrifugal device, and the precipitate is centrifugally washed with a hydrochloric acid solution and deionized water, respectively;
drying the dialysis product at 50-70 ℃.
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