CN113247885A

CN113247885A - Preparation method of nitrogen-doped graphene, graphene and application

Info

Publication number: CN113247885A
Application number: CN202110637397.5A
Authority: CN
Inventors: 杨荣华
Original assignee: Shaoxing Yiyan Technology Development Co ltd
Current assignee: Shaoxing Yiyan Technology Development Co ltd
Priority date: 2021-06-08
Filing date: 2021-06-08
Publication date: 2021-08-13

Abstract

The invention discloses a preparation method of nitrogen-doped graphene. Comprising cleaning and annealing of the catalyst substrate: cleaning the catalyst substrate, drying after cleaning, and annealing after drying; taking ionic liquid as a carbon source, taking the annealed catalyst substrate as a substrate, coating the ionic liquid on the catalyst substrate, and pyrolyzing and carbonizing the ionic liquid on the catalyst substrate at high temperature under the atmosphere of hydrogen and inert gas to prepare nitrogen-doped graphene; transferring nitrogen-doped graphene: coating PMMA anisole solution on the surface of nitrogen-doped graphene, removing impurities on the back of a substrate, and adding FeCl₃And (5) soaking and etching the substrate in the solution to remove the substrate, so as to obtain the graphene PMMA complex. Repeatedly soaking and washingWashing the composite body, removing impurities, and then soaking in an organic solvent to dissolve and remove PMMA, thereby obtaining the nitrogen-doped graphene independent film. The invention also discloses nitrogen-doped graphene and application of the nitrogen-doped graphene. Highly graphitic nitrogen-doped graphene with few defects can be obtained.

Description

Preparation method of nitrogen-doped graphene, graphene and application

Technical Field

The invention relates to the field of graphene, in particular to a preparation method of graphene and the graphene prepared by the method.

Background

Graphene is a complete two-dimensional lattice structure material with carbon atoms bonded by covalent bonds, shows unique physicochemical properties such as a large specific surface area, high mechanical strength, excellent chemical stability and the like, and these extraordinary characteristics make graphene have a wide application prospect in many fields such as electronic devices, energy storage and conversion, biotechnology and the like. However, graphene is a zero band gap material, and its conductivity cannot be fully controlled as with conventional semiconductors, and they are too "metallized" for many electronic applications to be designed. Therefore, it is necessary to find a method for changing the fermi level of graphene and manipulating the electronic and optical properties of graphene.

Doping with heteroatoms is a convenient way to adjust the physical/chemical properties of graphene among many. Among the many heteroatoms, nitrogen atoms show attractive properties. This is due to the fact that the nitrogen atom has a radius comparable to that of the carbon atom and contains five valence electrons available to form strong covalent bonds, easily doping into the graphene lattice. For the moment, among all possible C-N configurations of graphene (i.e. pyridine nitrogen, pyrrole nitrogen, graphite nitrogen and nitrogen oxide), graphitized N-doping (i.e. substitutional N-doping) is the only bonding type that leads to N-type doping, moving the graphene fermi level above the dirac point, the local density of states near the fermi level is suppressed, which leads to the opening of the band gap of the nitrogen-doped graphite structure. In addition, the graphitized N doping is beneficial to maintaining the periodic honeycomb lattice structure of the graphene, so that the nitrogen-doped graphene maintains high carrier mobility, and the conductivity is remarkably increased, thereby promoting the application of the nitrogen-doped graphene in the fields of transparent conductive materials, electrons, silicon-valley electronic devices and the like. To date, several conventional methods have been proposed to synthesize nitrogen-doped graphene. Geng et al in NH₃Thermal annealing is performed on Graphene Oxide (GO) in the atmosphere, so that nitrogen doping can be realized. Li et al by arc discharge method with NH₃And the He gas mixture is used as a nitrogen source, and the nitrogen-doped graphene is synthesized. However, although the nitrogen-doped graphene is obtained by the methods, the method also has the problem that the content of graphitized nitrogen is low, and the structural integrity of the graphene is damaged due to the existence of a large amount of pyridine nitrogen and pyrrole nitrogen, so that the electrical property of the nitrogen-doped graphene is greatly reduced.

Many attempts have been made by scientists to increase the nitrogen content of graphite. The wei et al firstly substitute-dope the graphene, and the nitrogen-doped graphene shows an n-type behavior, so that the electrical property of the graphene can be effectively adjusted. Zhao et al synthesized graphene mainly doped with graphite nitrogen with a small defect density, and considered that such doping is a promising method for obtaining high-quality graphene thin films with high carrier concentration. Liu et al synthesized highly graphitized N-doped graphene materials, which showed strong electron-hole asymmetry in spacer scattering, thus showing transport properties. However, on one hand, the methods relate to oxygen-assisted etching, the process is complex, and the doped N content is low; on the other hand, due to the CVD method, parameters are not easy to control due to the existence of the gaseous precursor, and the performance of the obtained nitrogen-doped graphene is unstable. Therefore, it is of great importance to explore a simple synthetic method for preparing the high-graphite nitrogen-doped graphene with a complete structure.

Disclosure of Invention

Therefore, the technical problem to be solved by the present invention is to provide a method for preparing nitrogen-doped graphene.

Another technical problem to be solved by the present invention is to provide the nitrogen-doped graphene.

Another technical problem to be solved by the present invention is to provide an application of the nitrogen-doped graphene.

The technical scheme of the invention is that the preparation method of the nitrogen-doped graphene comprises the following steps:

cleaning and annealing the catalyst substrate, namely selecting one of a copper foil, a nickel foil, a platinum foil, a semiconductor silicon wafer or a sapphire wafer as the catalyst substrate, cleaning the catalyst substrate, drying after cleaning, and annealing after drying;

(2) generation of nitrogen-doped graphene: taking ionic liquid as a carbon source, taking the annealed catalyst substrate as a substrate, coating the ionic liquid on the catalyst substrate, and pyrolyzing and carbonizing the ionic liquid on the catalyst substrate at high temperature under the atmosphere of hydrogen and inert gas to prepare nitrogen-doped graphene;

(3) transferring nitrogen-doped graphene: dissolving polymethyl methacrylate (PMMA) in anisole to prepare PMMA anisole solution, coating the PMMA anisole solution on the surface of the nitrogen-doped graphene obtained in the step (2),vacuum drying, cooling to room temperature, protecting the nitrogen-doped graphene with a PMMA coating, removing impurities on the back of the substrate, and adding pre-prepared FeCl₃And (3) soaking and etching the substrate in the solution to remove the substrate, so that the nitrogen-doped graphene is transferred to the PMMA protective layer to obtain the nitrogen-doped graphene PMMA complex.

Preparing FeCl3 solution by adding FeCl₃·6H₂Putting O powder into a weighing bottle, adding distilled water, and stirring until FeCl is obtained₃·6H₂The O powder was completely dissolved.

(4) Stripping the nitrogen-doped graphene and the PMMA coating: and (4) repeatedly soaking and washing the graphene PMMA complex obtained in the step (3) in distilled water to remove impurities, and then soaking in an organic solvent to dissolve and remove PMMA, so as to obtain the nitrogen-doped graphene independent film.

According to the preparation method of nitrogen-doped graphene, the cleaning in the step (1) is preferably performed by sequentially cleaning with a dilute hydrochloric acid solution, distilled water, acetone, ethanol and distilled water. The concentration of the dilute hydrochloric acid solution is 15-30 wt%.

Further, step (1) cleaning and annealing: selecting a catalyst substrate with the thickness of 15-35 mu m, cleaning, removing water from the catalyst substrate after cleaning, and then carrying out annealing treatment; the annealing treatment is that under the atmosphere of hydrogen and inert gas, the temperature is raised from room temperature to 1000-1100 ℃ at the temperature raising rate of 10-20 ℃/min, the heating is stopped after the temperature is maintained for 10-20min, and the catalyst substrate is naturally cooled to the room temperature; the catalyst substrate is selected from one of copper foil, nickel foil, platinum foil, semiconductor silicon wafer and sapphire wafer.

Further, the step (2) is that the nitrogen-doped graphene is generated: preparing nitrogen-doped graphene by taking the ionic liquid as a liquid carbon source and the annealed catalyst substrate as a substrate; taking 10-100 mu L of ionic liquid on the annealed catalyst substrate, and spin-coating under high-speed rotation. And (3) heating the spin-coated catalyst substrate from room temperature to 950-1050 ℃ at the heating rate of 10-20 ℃/min under the atmosphere of hydrogen and inert gas, keeping the temperature for 10-20min, stopping heating, and naturally cooling to room temperature to obtain the nitrogen-doped graphene.

Further, step (3) nitrogen-doped grapheneThe transfer of (2): dissolving polymethyl methacrylate (PMMA) in anisole according to the concentration of 30-50mg/mL, and heating until the PMMA is completely dissolved to prepare PMMA anisole solution; dripping 10-30 mu L of PMMA solution on the surface of the graphene obtained in the step (2), spin-coating at high speed, placing the spin-coated sample in a vacuum oven at the temperature of 100-140 ℃, vacuumizing and drying for 10-20min, and then cooling to room temperature; removing impurities on the back of the substrate, and adding prepared FeCl of 1-5g/mL₃In the solution, keeping the surface coated with the PMMA protective layer facing upwards, soaking for 8-16 hours, and etching to remove the substrate; and transferring the nitrogen-doped graphene to a PMMA film to obtain the graphene PMMA complex.

Further, stripping the nitrogen-doped graphene from the PMMA coating in the step (4): and repeatedly soaking and washing the obtained graphene PMMA complex in distilled water to remove impurities, then soaking the film in acetone to dissolve and remove PMMA to obtain the nitrogen-doped graphene independent film, then taking out the film, putting the film into a container filled with acetone, and drying the film for later use.

According to the preparation method of nitrogen-doped graphene, preferably, the ionic liquid in the step (2) is one or more than one; the ionic liquid is obtained by combining cation and anion, wherein the cation is as follows: 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-R₃radical-2-R₂radical-3-R₁Radical imidazolium cation (R)₃Radical, R₂Radical, -R₁The radicals being alkyl or hydrogen atoms, R₃Radical, R₂Radical, -R₁The groups may be the same or different), pyridinium cations, pyrazolinium cations, pyrroliinium cations, imidazolinium cations, quaternary ammonium cations, quaternary phosphonium cations; the anion is selected from: dicyandiamide anions, tricyanomethane anions, sulfite monoester anions, sulfate monoester anions, difluosulfonylimide anions (FSI), bistrifluoromethanesulfonylimide anions (TFSI), bisoxalato borate anions (BOB), fluoride anions, chloride anions, bromide anions, iodide anions, tetrachloroaluminate ions, tetrafluoroborate ions, hexafluorophosphate ions, carboxylate ions, sulfonate ions, fluorosulfonic acid heels,nitrate ion, trifluoromethylsulfonate ion, amino acid radical ion, nitrate ion. The structural formula of each cation composing the ionic liquid is as follows:

the structural formula of each anion forming the ionic liquid is as follows:

for example, the following three ionic liquids may be composed:

according to the preparation method of the nitrogen-doped graphene, preferably, the coating method in the step (2) is high-speed rotation coating, and the rotation speed of the high-speed rotation is 2000-4000 rpm/min; the spin coating time in the step (2) is 0.2-2 min; the coating method in the step (3) is high-speed rotation coating, and the rotation speed of the high-speed rotation is 2000-4000 rpm/min; the spin coating time in the step (3) is 0.2-2 min.

According to the preparation method of nitrogen-doped graphene, the flow rate of the hydrogen in the step (2) is preferably 40-80mL/min, and the flow rate of the inert gas is 250-350 mL/min.

And (3) adding an organic solvent into the ionic liquid in the step (2) and then spin-coating the ionic liquid on the catalyst substrate.

The ionic liquid may or may not contain an organic solvent. When the organic solvent is added, the organic solvent may be one or more. Preferably, the organic solvent is selected from: ACN (acetonitrile), DMF (N, N-dimethylformamide), diethyl ether, dichloromethane, ethanol, NMP (N-methylpyrrolidone).

The invention also provides the nitrogen-doped graphene prepared by the preparation method of the nitrogen-doped graphene, wherein the nitrogen content in the nitrogen-doped graphene is more than 6%, and the nitrogen content in the nitrogen is more than 60%. The thickness of the nitrogen-doped graphene is larger than 0.33 nm and smaller than 10 nm.

Most of the C atoms in the nitrogen-doped graphene are arranged in a conjugated honeycomb lattice; the percentage of N element in the graphene is more than 6%; the nitrogen atoms in the graphene are mainly in the form of graphite nitrogen, and account for more than 60% of the total nitrogen.

The invention also provides application of the nitrogen-doped graphene in the field of batteries.

The invention also provides application of the nitrogen-doped graphene in semiconductor materials.

The invention also provides application of the nitrogen-doped graphene in the aspect of electronic components.

The invention also provides application of the nitrogen-doped graphene to an LED (light emitting diode) material.

As energy storage (lithium battery) application, the N atoms of the pyridine are introduced into the graphene structure, so that defects are increased, the adsorption capacity of the NG on lithium ions is enhanced, the insertion of the lithium ions in an electrode is enhanced, and the charge and discharge capacity is increased.

The graphene oxide semiconductor material is applied as a semiconductor material (a graphene field effect transistor), the content of high graphitized N (all graphitized N) is high, and the complete crystal structure of graphene is protected, so that the transistor has high carrier mobility; the dirac point is shifted to-24V, exhibiting a significant n-type transmission characteristic.

Applied in the novel display field (transparent electrodes in smart windows), has excellent transmissivity (93% at 550 nm); good conductivity (sheet resistance of 1.1 K.OMEGA./sq).

The catalyst is used as electrocatalysis, and the NG can be used as a cathode catalyst in a fuel cell system to replace a rare noble metal platinum-based catalyst to carry out metal-free catalytic oxygen reduction reaction, so that the cost is reduced, and the catalyst has higher catalytic stability and durability. The NG has stronger CO resistance, can resist CO generated in the use process of the fuel cell and prolong the service life of the cell

Used as a sensor, has high electron state density and provides more active sites. The larger specific surface area, the more analyzable molecules are loaded.

The super capacitor and the 3D nitrogen-doped porous graphene structure increase the specific surface area of an electrode material, accelerate ion migration, and enable the super capacitor (8800W kg is high)^-1At a power density of 29Wh kg, it still remains^-1Energy density) cycle length (96.6% of the initial capacitance remains after 20,000 cycles).

In the aspect of photocatalysis, high charge and spin density of nitrogen atoms, nitrogen doping can promote the formation of an active region. NG as adsorption center to anchor and activate CO₂Molecules, even directly, participate in photocatalytic reactions. The catalyst can replace noble metal catalyst to reduce cost.

High graphitized N content (all graphitized N) for electronic devices, protecting the complete crystal structure of graphene with high carrier mobility (13,000 cm)²V^-1s^-1)NG film cluster growth, reduced charge scattering, and improved high conductivity (1.62X 10)⁷S/m); adjustable work function and high stability, so that the Nc-G film becomes a promising material for realizing novel quantum phenomena in future high-speed chips.

Flexible electronics

Indium Tin Oxide (ITO), a conventional material for transparent conductive coatings, is expensive due to the rare earth element indium, and in addition, ITO is very brittle and easily broken, which makes it difficult to develop in the field of flexible electronics. Graphene has very high conductivity and very high transmittance (97.7%), and is a transparent conductive material with excellent performance due to excellent mechanical flexibility of graphene. Bae et al prepared graphene thin films with dimensions as high as 30inch by a roll-to-roll method and used for manufacturing transparent electrodes, and showed that the electrodes had good light transmittance and could be easily bent without changing the properties.

Lithium battery

Wu, a highly promising potential in the battery field due to its high specific surface area, excellent capacitive behavior and electrochemical properties^[10]The three-dimensional graphene/carbon nanotube porous aerogel material is applied to a sulfur simple substance carrier and interlayer integrated anode of a lithium-sulfur battery to obtain a lithium-sulfur battery III and a super capacitor with high volume energy density (1615Ah/L) and excellent cycling stability (under the condition of high current density of 2C, the battery can stably cycle for 500 circles, and the capacity is hardly attenuated)

The specific surface area of the graphene is 2630m²G, inherent capacitance of 21 mu F/cm²The graphene solves the problems that electrolyte on the surface of an electrode cannot be infiltrated and an electric double layer cannot be formed due to the fact that the electrolyte cannot enter a microporous structure of active carbon of an electrode material, and the like, and when the current density of the graphene electrode super capacitor prepared by Liu and the like is 1A/g, the energy density reaches 85.6Wh/kg in a room temperature environment, and when the temperature is increased to 80 ℃, the energy density can be increased to 136 Wh/kg.

Composite material and coating

As an additive in the polymer, graphene has a huge specific surface area and excellent mechanical, chemical and electronic properties, so that the working temperature and mechanical strength of the polymer can be improved, the hygroscopicity of the polymer is reduced, the antistatic capability of the polymer is provided, and the like, Gao et al prepare graphene conductive ink, print electrodes with different shapes by an ink-jet printing method, and the resistance of the electrodes is only 0.81 +/-0.2 k omega/sq.

Fifth, the sensor

Graphene sp²The hybridized special 2D crystal structure and large specific surface area, each atom of the graphene is a feasible target of a reactant, so that the environmental change can be sensitively perceived, and a sensor prepared by the graphene is usually prepared by the surface of a graphene materialThe adsorption performance is improved, and the graphene has better sensitivity in daily application due to lower resistivity than the traditional material. Yang et al have shown a novel little conformal graphite alkene electrode of 3D for super sensitive and tunable flexible capacitive pressure sensor, because the roughness of electrode can improve capacitive touch sensor's performance effectively, through controllable little conformal structure sensitivity regulation, the sensor of building has high sensitivity, quick response speed, low detection limit.

Sixthly, electrocatalysis

Graphene materials have attracted considerable attention for their high electrical conductivity, high surface area, catalytic properties, and excellent thermal stability for use in energy storage and energy conversion devices, and noble metal particles deposited on graphene can improve their properties by increasing the electrocatalytic activity. Bae et al prepared a nanosheet composite with electrochemical catalytic properties by depositing platinum on polydopamine coated graphene and showed outstanding performance.

Seventhly, aerospace

3D graphene foam, wherein randomly oriented graphene sheets are chemically cross-linked by covalent bonds mainly at the edges, showing the same mechanical properties at room temperature, including almost completely reversible superelastic behavior up to 90% strain, unchanged Young's modulus, Poisson's ratio close to zero and good cyclic stability, Chen et al developed a novel three-dimensional graphene material that can maintain good stability and high elasticity in the range from 4K (about-269 deg.C) deep low temperature to 1273K (about 1000 deg.C). The novel space sponge has good application prospect in the fields of production and experiments under extreme conditions, aerospace equipment manufacturing and the like.

Eight, integrated circuit

Graphene has extensive application in the field of integrated circuits with good heat-dissipating ability, and class et al increase a graphite alkene layer in three-dimensional chip and solve the heat dissipation problem, add graphite alkene superficial layer after, graphite alkene layer can improve better, and graphite alkene layer can provide good heat dissipation interface, will scatter fast.

Advantageous effects

We firstly propose that the ionic liquid is used as a liquid precursor, a copper foil, a nickel foil, a platinum foil, a semiconductor silicon wafer and a sapphire wafer are used as substrates, and Ar/H is performed₂And under the mixed gas, the one-step preparation of the high-graphite nitrogen-doped graphene with a complete structure is realized. ILs represent an environmentally friendly alternative to organic solvents, whose combination of liquid and negligible vapor pressure represents nearly ideal precursor performance, greatly simplifying the process compared to solid, especially vapor phase, educts. In addition, the ionic liquid is combined with nitrogen atoms, can be directly used as a carbon source and a nitrogen source, and can directly transfer the nitrogen atom structure to graphene through reaction, so that the defect caused by secondary doping is avoided, and the nitrogen content is more controllable. By the method, highly graphitic nitrogen-doped graphene with few defects can be obtained, the nitrogen content is 7.27%, and the graphitized N content accounts for about 70%. By fabricating field effect transistors, nitrogen-doped graphene exhibits typical n-type transport behavior. Resistivity measured using four probe resistance was 1.13 x10^-5Omega.m. The work of the people provides a new idea for preparing high-quality graphite nitrogen-doped graphene with a complete structure, provides a simple and efficient preparation method, and enables the graphene to play an irreplaceable role in various fields.

Drawings

FIG. 1 is a Si/SiO₂A substrate loaded with nitrogen-doped graphene film.

FIG. 2 is a schematic diagram of a paper reticle.

FIG. 3 reticle mounting schematic.

Fig. 4 is a schematic view of a field effect transistor.

FIG. 5 is an SEM image of nitrogen-doped graphene (NG) prepared using EMIM-dca as a precursor.

FIG. 6 is an EDS (SEM equipment) elemental map of the preparation of NG (samples were vacuum dried at 100 ℃ before testing) using EMIM-dca (vacuum dried at 100 ℃) as precursor.

FIG. 7 is a TEM image of NG prepared using EMIM-dca as a precursor.

FIG. 8 is a Raman diagram of the preparation of NG using EMIM-dca as a precursor.

FIG. 9 is an XPS chart showing NG production using EMIM-dca as a precursor

FIG. 10 TGA and DSC plots of EMIM-dca tested at a ramp rate of 10 deg.C/min from room temperature to 1000 deg.C under nitrogen atmosphere.

FIG. 11 is a FT-IR spectrum of a solid product prepared by EMIM-dca pyrolysis at different temperatures (after scraping the solid sample off the Cu substrate with a spatula).

FIG. 12 is a Raman plot of NG prepared with EMIM-tcm and BMIM-tcm as precursors, respectively.

FIG. 13 is a graph showing the preparation of NG I from EMIM-dca, EMIM-tcm and BMIM-tcm as precursors_2D/I_GAnd I_D/I_GFigure (a).

FIGS. 14a-14c are XPS spectra of NG prepared from EMIM-tcm and BMIM-tcm precursors, respectively.

FIG. 15 is a graph of the pyridine-N, pyrrole-N and graphite-N contents for the preparation of NG using EMIM-dca, EMIM-tcm and BMIM-tcm as precursors, respectively.

FIG. 16 is an XPS spectrum of NG prepared from EMIM-dca as a precursor, held at 950 ℃ and 1050 ℃ for 15min and 1000 ℃ for 10min and 20min, respectively.

FIG. 17 is an SEM and TEM image of NG prepared at different growth temperatures and times with EMIM-dca as the precursor.

FIG. 18 shows the source-drain current (I) of an FET for preparing NG using EMIM-dca as a precursor_ds) -back gate voltage (V)_g) Graph is shown. Illustration is shown: the fermi level position of NG.

FIG. 19 is a graph of sheet resistance versus temperature for NG prepared using EMIM-dca as a precursor. Illustration is shown: measurement of ln (R) and T of NG sheet resistance in the range of 100 to 300 ℃ by four-probe resistance method^-1Graph is shown.

FIG. 20 is an XPS survey and C1s survey of NG prepared using EMIM-dca as a precursor.

FIG. 21 is an EDS (SEM kit) spectrum of the preparation of NG using EMIM-dca (vacuum dried at 100 ℃) as precursor (NG samples were vacuum dried at 100 ℃ before testing).

FIG. 22 is an EDS (SEM arm) spectrum of an NG prepared from EMIM-dca (not vacuum dried at 100 ℃) as a precursor (NG samples were not vacuum dried at 100 ℃) prior to testing.

FIG. 23 is an AFM plot of NG prepared with EMIM-dca as precursor and the corresponding height profile plot (top) along the marked line in the AFM plot; digital photographic images of clear NG floating on distilled water (bottom) after removal of the copper foil.

FIG. 24 is an SEM image of NG prepared with EMIM-tcm (top) and BMIM-tcm (bottom) precursors, respectively.

FIG. 25 is a TEM image of NG prepared with EMIM-tcm (top) and BMIM-tcm (bottom) precursors, respectively.

FIG. 26 is a graph of the contact angle of EMIM-dca with a copper foil substrate.

FIG. 27 is a graph of the contact angle of EMIM-tcm with a copper foil substrate.

Fig. 28 is a Raman diagram of the preparation of N-doped porous carbon material using PAN as a precursor.

Fig. 29 is an XPS full spectrum and an N1s spectrum of an N-doped porous carbon material prepared using PAN as a precursor.

Fig. 30 is an SEM image of PAN as a precursor for preparing an N-doped porous carbon material.

Fig. 31 is an EDS elemental map of the synthesis of an N-doped porous carbon material using PAN as a precursor.

FIG. 32 is an XPS plot of NG prepared from EMIM-dca as a precursor at 950 deg.C and 1050 deg.C for 15min (left) and 1000 deg.C for 10min and 20min (right), respectively.

FIG. 33 is a Raman diagram of NG prepared by using EMIM-dca as a precursor and maintaining the temperature at 950 ℃ and 1050 ℃ for 15min and 1000 ℃ for 10min and 20min, respectively.

FIG. 34 is a TEM image of NG prepared with EMIM-dca (ACN dilution).

FIG. 35 is an AFM picture of 1 preparation of NG using EMIM-dca (ACN dilution).

FIG. 36 is a digital photographic image (left) of a clear NG floating on distilled water after removing copper foil from NG prepared with EMIM-dca (diluted ACN and EMIM-dca/ACN: 35. mu.L: 2000. mu.L). NG film (PMMA removed) to Si/SiO₂Optical image on substrate (right).

FIG. 37 is a [ BMIM ]]BF₄SEM images of N, B double doped graphene (NBG) were prepared for the precursors.

FIG. 38 is a [ BMIM ]]BF₄XPS plots of N, B double doped graphene (NBG) were prepared for the precursors.

FIG. 39 is a [ BMIM ]]BF₄Preparation of N, B double doping for precursorsRaman plot of graphene (NBG).

FIG. 40 is a [ BMIM ]]BF₄EDS (SEM outfitted) elemental maps of N, B double doped graphene (NBG) were prepared for the precursors.

FIG. 41 is a [ BMIM ]]BF₄EDS (SEM equipped) spectra of N, B double doped graphene (NBG) were prepared for the precursors.

Detailed Description

Example 1

Cleaning and annealing copper foil

1. Cleaning of copper foil

Copper foil (purchased from Alfa Aesar; model 10950; thickness 25 μm) was cut into 1cm by 1cm and washed with 25 wt% hydrochloric acid, distilled water, acetone, ethanol, and distilled water in this order. The method comprises the following specific steps: (1) weighing 5g of 36 wt% concentrated hydrochloric acid, putting the concentrated hydrochloric acid into a 25mL beaker, adding 2.2g of distilled water for dilution, immersing the cut copper foil into the beaker, slightly stirring the copper foil by using a glass rod every 2min, and continuously cleaning the copper foil for 15 min; (2) clamping the copper foil with tweezers, and soaking in 25ml beaker containing 10g distilled water for 15min, wherein the distilled water is replaced every 5min for 3 times; (3) clamping the copper foil in the step (2) by using a pair of tweezers, and sequentially placing the copper foil into 25mL beakers containing 10g of acetone and 10g of ethanol for sequentially soaking for 15 min; (4) then clamping the copper foil with tweezers, putting the copper foil into a 25mL beaker filled with 10g of distilled water, and repeating the operation in the step (2); (5) finally, the copper foil is lightly clamped by using a pair of tweezers and is placed on the dust-free paper to remove the moisture on the surface of the copper foil.

2. Annealing of copper foil

Loading the cleaned copper foil on a quartz boat, placing in a tube furnace (OTF-1200X, product of Onhui Fei crystal materials technology Co., Ltd., model number) with H2 and Ar flow rates of 60mL/min and 300mL/min respectively, heating from room temperature to 1050 deg.C at a heating rate of 15 deg.C/min, holding for 15min, stopping heating, and naturally cooling the copper foil to room temperature.

Generation of di, N-doped graphene

And preparing the nitrogen-doped graphene by taking the ionic liquid as a liquid carbon source and the annealed copper foil as a substrate. The preparation process comprises the following steps: placing the annealed copper foil on a flexible glue homogenizer (Riboke science instrument of Jiangsu)Ltd, model EZ6), 30 μ L of ionic liquid 1-ethyl-3-methylimidazolium dicyanamide (EMIM-dca) was drawn up onto a copper foil with a pipette and spin-coated for 1min at 3000 rpm/min. Lightly clamping the spin-coated copper foil with tweezers, loading on quartz boat, placing in tube furnace (Onhua Kagaku Crystal Material technology Co., Ltd., model OTF-1200X), and maintaining H₂And Ar flow rate is respectively 60mL/min and 300mL/min, the temperature is increased from room temperature to 1000 ℃ at the temperature increase rate of 15 ℃/min, the heating is stopped after the temperature is maintained for 15min, and the nitrogen-doped graphene is prepared by naturally cooling to the room temperature.

Transfer of nitrogen-doped graphene

1. Preparing polymethyl methacrylate (PMMA) solution

Weighing 40mg of PMMA solid in a round-bottom flask by using an analytical balance, adding 1mL of anisole, then placing the round-bottom flask in a water bath kettle at 50 ℃, and heating until PMMA is completely dissolved to prepare PMMA anisole solution.

2. Preparation of FeCl₃Solution: 2.703g FeCl was weighed out with an analytical balance₃6H2O powder in a weighing bottle, 10mL distilled water was added and stirred with a glass rod to FeCl 3.6H₂Completely dissolving O powder to prepare FeCl₃And (3) solution.

3. Preparation of nitrogen-doped graphene film

(1) Graphene film layer protection: and (3) placing the nitrogen-doped graphene grown on the copper foil substrate prepared in the second step on a carrying table of a smart spin coater (model EZ6, instruments of Ribogaku, Jiangsu), and sucking 20 mu LPMMA solution by using a pipette gun to drop on the surface of the graphene. Spin-coating at 3000rpm/min for 1min, lightly clamping the spin-coated sample with tweezers, vacuum-drying at 120 deg.C for 15min, and cooling to room temperature.

(2) Stripping graphene from a copper substrate: first, the back surface of the copper foil (the surface on which graphene is not grown) was lightly rubbed with sandpaper to remove all impurities on the back surface. Then put into the prepared FeCl₃In the solution (note that the side coated with the PMMA protective layer was kept facing up), the copper foil was etched away by soaking for 12 hours. At this time, the copper foil is FeCl₃The solution is completely dissolved, and the nitrogen is doped with the grapheneAnd transferring the graphene film to a PMMA film, wherein a light gray film-shaped substance is floated in the solution, and the substance is PMMA-loaded nitrogen-doped graphene. Next, the light gray film-like material was taken out, and soaked in a 25mL beaker containing 10mL of distilled water for 10min for washing, and repeated 3 times to remove FeCl₃And (3) waiting for impurities, taking out the light gray film-shaped substance, putting the light gray film-shaped substance into a weighing bottle containing 10mL of acetone, soaking for 2 days to dissolve and remove PMMA to obtain the nitrogen-doped graphene independent film, then taking out the nitrogen-doped graphene independent film by using a glass plate, putting the nitrogen-doped graphene independent film into a 5mL sample bottle containing about 1mL of acetone, finally putting the sample bottle into an oven at 60 ℃ for drying for about half an hour, cooling to room temperature, and storing for later use.

Manufacture and performance test of field effect transistor

1. Fabrication of field effect transistors

(1) Transfer of nitrogen-doped graphene to Si/SiO₂Substrate

Taking out the PMMA-loaded nitrogen-doped graphene film soaked in the distilled water, and cutting the PMMA-loaded nitrogen-doped graphene film into Si/SiO films with the length and the width of 20mm and 10mm respectively₂On a substrate (a paraelectric electronic technology single-polishing silicon dioxide wafer; model P/100; thickness 625 +/-20 mu m), keeping the graphene film surface continuously spread on the substrate and attached to the center of the substrate, then placing the substrate in a vacuum oven at 120 ℃ for vacuumizing and drying for 30min, after cooling, placing the substrate in a weighing bottle containing 10mL of acetone for soaking for 2 days to dissolve and remove PMMA, and then using tweezers to dissolve Si/SiO₂And taking out the substrate loaded with the nitrogen-doped graphene film, drying the film in a 60 ℃ oven for about 10min, cooling the film to room temperature, and storing the film for later use. The prepared sample is shown in FIG. 1.

(2) Preparing a mask: cutting the copy paper into square paper sheets with the length and the width of 1cm respectively, and cutting the paper sheets into I-shaped patterns shown in the figure 2 to obtain the required mask plate.

(3) Spraying gold: covering a mask on the Si/SiO prepared in the step (1)₂The substrate is loaded with nitrogen-doped graphene film, and the mask plate is fixed by folding a transparent adhesive tape from the back to the surface along the arrow direction in FIG. 3 (note that the adhesive tape can not cover Si/SiO in FIG. 3)₂Part), the fixed sample is shown in fig. 3. Then, the exposed nitrogen is doped with graphene by a scraperThe thin film (the hatched portion in fig. 3) was scraped off, followed by vacuum gold spraying for 60 seconds using a hitachi ion sputtering apparatus (hitachi scientific instruments ltd., model MC1000), and then the mask was removed to obtain the desired field effect transistor, as shown in fig. 4.

2. Electrical Performance testing

The field effect transistor samples shown in fig. 4 above were tested for electrical performance using a gishy semiconductor characterization system (tex, usa, model 4200-SCS). The test conditions are shown in the table below.

FIG. 5 is an SEM image of nitrogen-doped graphene (NG) prepared using EMIM-dca as a precursor. The figure shows a clean, uniform, smooth surface, the white line reflecting the effect of wrinkling in the NG sample (left). The NG samples were clearly seen to have clear wrinkles and folded edges, indicating that the samples were thin, 6-8 layers (right).

FIG. 6 is an EDS (SEM equipment) elemental map of the preparation of NG (samples were vacuum dried at 100 ℃ before testing) using EMIM-dca (vacuum dried at 100 ℃) as precursor. The EDS elemental map showed a uniform distribution of C, N elements in the NG sample. FIG. 6 shows C-K on the left and N-K on the right.

FIG. 7 TEM image of NG prepared with EMIM-dca as precursor.

FIG. 8 is a Raman diagram of the preparation of NG using EMIM-dca as a precursor. In the figure, I_D/I_G0.36, indicating that the NG sample had fewer defects. I is_2D/I_GThe number of the layers is 0.5, which indicates that the number of the sample layers is 6-8.

FIG. 9 is an XPS plot of NG prepared using EMIM-dca as a precursor. The NG samples were predominantly two N species, pyridine-N and graphite-N, with graphite-N being the predominant species, accounting for 92% of the total N content.

FIG. 10 TGA and DSC plots of EMIM-dca tested at a ramp rate of 10 deg.C/min from room temperature to 1000 deg.C under nitrogen atmosphere. EMIM-dca starts the reaction at higher temperatures around 300 ℃, which is consistent with DSC profiles, at low temperatures (decomposition temperature of ionic liquids is 500 ℃), presumably the alkyl chain of the cation breaks, the heterocycle opens and decomposes, then cross-linking polymerization occurs between the in situ formed fragments, the cationic cyano groups undergo trimerization to form triazine ring intermediates, which may be a key step in the formation of graphene.

FIG. 11 is a FT-IR spectrum of a solid product prepared by EMIM-dca pyrolysis at different temperatures (after scraping the solid sample off the Cu substrate with a spatula). FIG. 11 shows that the spectrum of EMIM-dca-300 (the lowermost curve) clearly shows 1000-^-1The C ═ N and C — N bonds appeared with a broad shoulder appearance, and the peak intensity disappeared as the temperature increased to 1000 ℃, indicating that the C ═ N and C — N bonds were involved in the bonding during the reaction. The curves of FIG. 11 represent RT, 1000 ℃, 500 ℃ and 300 ℃ from top to bottom.

At 2200-^-1A characteristic signal of CN was detected, and as the temperature was increased to 1000 ℃, the CN peak signal disappeared, indicating that the reaction related to the substance formed was a cycloaddition reaction of cyanide.

The N-H telescopic belt appears at 3300cm^-1Here, as the temperature was increased to 1000 ℃ the N-H peak did not disappear, indicating that an amino group had been formed.

FIG. 12 is a Raman plot of NG prepared with EMIM-tcm and BMIM-tcm as precursors, respectively. The upper curve represents EMIM-tcm and the lower curve represents BMIM-tcm. Preparation of NG I with EMIM-tcm and BMIM-tcm as precursors_D/I_G1.08 and 0.97, respectively, indicate that the NG sample is highly defective. No significant 2D peak was observed, indicating that the number of sample layers was 8-10 thick. In summary, the change of the cations in the ionic liquid has little influence on the defects and the number of layers of the NG sample.

FIG. 13 preparation of NG I with EMIM-dca, EMIM-tcm and BMIM-tcm as precursors, respectively_2D/I_GAnd I_D/I_GFigure (a). Preparation of NG I with EMIM-dca, EMIM-tcm and BMIM-tcm as precursors_2D/I_G0.5, 0.35 and 0.3, respectively, indicate that the number of NG layers prepared by EMIM-dca is relatively thin, about 6, and that the number of NG layers prepared by EMIM-tcm and BMIM-tcm is relatively thick, about 8. Preparation of NG I with EMIM-dca, EMIM-tcm and BMIM-tcm as precursors_D/I_G0.36, 1.08, 0.97, respectively, indicating EMIM-tcm and BMIM-tcAnd the NG defect is large when m is precursor preparation.

In summary, the change of anions in the ionic liquid has a large influence on NG defects and the number of layers.

FIGS. 14a-14c are XPS spectra of NG prepared from EMIM-tcm and BMIM-tcm precursors, respectively. Both the EMIM-tcm and BMIM-tcm precursors were used to prepare NG samples containing C, N, O elements. The NG sample prepared by using EMIM-tcm as a precursor contains three N, pyridine-N, pyrrole-N and graphite-N contents which are respectively 16%, 38% and 46% of the total N content, wherein the pyrrole-N and the graphite-N are more. NG samples prepared using BMIM-tcm as the precursor contained three N, pyridine-N, pyrrole-N and graphite-N contents of 29%, 62% and 9% of the total N content, respectively, with a higher pyrrole-N content.

In summary, the change in cation in the ionic liquid has an effect on the N content.

FIG. 15 is a graph of the pyridine-N, pyrrole-N and graphite-N contents for the preparation of NG using EMIM-dca, EMIM-tcm and BMIM-tcm as precursors, respectively. The contents of pyridine-N, pyrrole-N and graphite-N for preparing NG by taking EMIM-dca as a precursor respectively account for 8 percent, 0 percent and 92 percent of the total N content, wherein the graphite-N is the most. The pyridine-N, pyrrole-N and graphite-N contents of NG prepared by taking EMIM-tcm as a precursor are respectively 16%, 38% and 46% of the total N content, wherein the pyrrole-N and graphite-N are more. The pyridine-N, pyrrole-N and graphite-N contents for preparing NG by taking BMIM-tcm as a precursor are respectively 29 percent, 62 percent and 9 percent of the total N content, wherein the pyrrole-N is more.

In summary, the change of the anion in the ionic liquid has a large influence on the N type and the N content.

FIG. 16 is an XPS spectrum of NG prepared from EMIM-dca as a precursor, held at 950 ℃ and 1050 ℃ for 15min and 1000 ℃ for 10min and 20min, respectively. The preparation of NG samples with EMIM-dca as precursor, maintained at 950 ℃ and 1050 ℃ for 15min, respectively, was predominantly pyrrole-N and predominantly graphitic-N at 1000 ℃, probably due to destruction of the C-N bond structure of graphene and elimination of nitrogen atoms inherent in the graphitic N structure when the growth temperature was too hot, and the reduction of the content of pyridine-N at 1050 ℃ compared to 950 ℃, confirms that pyrrole-N has higher thermal stability than either pyridine-N or graphitic-N.

The preparation of NG samples mainly comprises pyrrole-N at 1000 ℃ for 10min and 20min by taking EMIM-dca as a precursor, and mainly comprises graphite-N at 15min, which shows that 15min is more favorable for maintaining the crystal structure of NG.

FIG. 17 is an SEM and TEM image of NG prepared at different growth temperatures and times with EMIM-dca as the precursor. SEM and TEM images of NG prepared at 1000 c, 950 c and 1050 c for 15min showed significant folding and surface non-uniformity on the sample surface.

SEM and TEM images of NG prepared at 10min and 20min compared to 15min at 1000 c showed that the sample surface was not uniform and had significant folding.

In summary, EMIM-dca as a precursor, the retention of 950 ℃ and 1050 ℃ for 15min and 1000 ℃ for 10min and 20min is not good for the formation of high quality NG.

FIG. 18 shows the source-drain current (I) of an FET for preparing NG using EMIM-dca as a precursor_ds) -back gate voltage (V)_g) Graph is shown. Illustration is shown: the fermi level position of NG. The Ids-Vg curve of an N-doped graphene FET exhibits typical N-type transport characteristics, with electrons acting as the dominant carriers, V of an N-doped graphene Field Effect Transistor (FET)_DiracAt about-14V.

Fermi level E of NG in inset compared to pristine graphene_FMoving upward, the N-type transmission characteristics of N-doped graphene Field Effect Transistors (FETs) were confirmed.

FIG. 19 is a graph of sheet resistance versus temperature for NG prepared using EMIM-dca as the precursor. Illustration is shown: measurement of ln (R) and T of NG sheet resistance in the range of 100 to 300 ℃ by four-probe resistance method^-1Graph is shown.

The NG sheet resistance significantly increased upon cooling from room temperature to 80K, demonstrating the semiconducting properties of NG.

According to ln (R) and T in the inset^-1The graph can be used to estimate the effective band gap (Eg) of the NG thin film by using R (T). varies.. exp (Eg/2kBT), and the Eg is 0.31 eV.

FIG. 20 is an XPS survey and C1s survey of NG prepared using EMIM-dca as a precursor. NG was prepared using EMIM-dca as a precursor, and the sample contained C, N, O elements. Peaks at 284.7eV and 285.3eV in the NG sample correspond to the peaks, respectivelyIn sp²-C and N-sp²C, and sp²more-C, indicating that most of the C atoms in NG are arranged in the honeycomb lattice.

FIG. 21 is an EDS (SEM kit) spectrum of the preparation of NG using EMIM-dca (vacuum dried at 100 ℃) as precursor (NG samples were vacuum dried at 100 ℃ before testing). In the case of NG prepared using EMIM-dca (vacuum dried at 100 ℃ C.) as a precursor (NG samples were vacuum dried at 100 ℃ C. before testing), the NG samples contained C, N, O elements in addition to Cu.

FIG. 22 is an EDS (SEM arm) spectrum of an NG prepared from EMIM-dca (not vacuum dried at 100 ℃) as a precursor (NG samples were not vacuum dried at 100 ℃) prior to testing. NG was prepared using EMIM-dca (not vacuum dried at 100 ℃) (NG samples not vacuum dried at 100 ℃) as a precursor, which had C, N, O elements in addition to Cu in the NG samples and the O content was elevated compared to fig. 21, indicating that vacuum drying was useful for reducing the O content in the NG samples.

FIG. 23 is an AFM plot of NG prepared with EMIM-dca as precursor and the corresponding height profile plot (top) along the marked line in the AFM plot; digital photographic images of clear NG floating on distilled water (bottom) after removal of the copper foil. In the graph, a1-a3 shows that the thicknesses of different positions in the NG sample are 4.733nm,6.365nm and 4.372nm respectively, and the thickness of single-layer NG is about 1nm, so that it can be concluded that the NG sample is 4-7 layers, indicating that the sample thickness is not uniform. After removing the copper foil, the NG size of floating on distilled water was about 1cm²And the transparency is good, and the NG film has darker color, which shows that the transparency is related to the number of layers, and the thicker the number of layers, the darker the color.

FIG. 24 is an SEM image of NG prepared with EMIM-tcm (top) and BMIM-tcm (bottom) precursors, respectively. SEM images of NG prepared using EMIM-tcm (top) and BMIM-tcm (bottom) as precursors show that the samples show significant folding and surface non-uniformity.

FIG. 25 is a TEM image of NG prepared with EMIM-tcm (top) and BMIM-tcm (bottom) precursors, respectively. TEM images of NG prepared using EMIM-tcm (top) and BMIM-tcm (bottom) as precursors show that the samples are thicker, 8-10 layers, and no significant interlayer spacing is seen.

FIG. 26 is a graph of the contact angle of EMIM-dca with a copper foil substrate. The contact angle of EMIM-dca with the copper foil substrate was 55 deg..

FIG. 27 is a graph of the contact angle of EMIM-tcm with a copper foil substrate. The contact angle of EMIM-tcm with the copper foil substrate was 63 deg., and EMIM-dca showed better contact and adsorption performance with the copper foil substrate than that of FIG. 26.

Fig. 28 is a Raman diagram of the preparation of N-doped porous carbon material using PAN as a precursor. To contrast with NG prepared with ionic liquids, we used Polyacrylonitrile (PAN), which also has a cyano group, as a precursor, and dissolved 100mg PAN in 2mg DMF to form a solution, with a Cu foil as a substrate, and no 2D peak was observed in the Raman plot of the prepared sample under the same growth conditions, indicating that PAN was not converted to graphene.

Fig. 29 is an XPS full spectrum and an N1s spectrum of an N-doped porous carbon material prepared using PAN as a precursor. The XPS survey showed C, N, O elements in the sample. The XPS N1s plot shows three nitrogen configurations, pyridine-N, pyrrole-N and graphite-N, with pyrrole-N predominating.

Fig. 30 is an SEM image of PAN as a precursor for preparing an N-doped porous carbon material. SEM images further demonstrate that the samples prepared with PAN as a precursor are nitrogen-doped porous carbon materials.

Fig. 31 is an EDS elemental map of the synthesis of an N-doped porous carbon material using PAN as a precursor. The EDS elemental map indicates that the N element is uniformly distributed and the C element is not uniformly distributed in the sample, presumably related to the porous carbon material formed, demonstrating the uniqueness of NG production using ionic liquids as precursors.

FIG. 32 is an XPS plot of NG prepared from EMIM-dca as a precursor at 950 deg.C and 1050 deg.C for 15min (left) and 1000 deg.C for 10min and 20min (right), respectively. Taking EMIM-dca as a precursor, NG samples prepared by respectively keeping at 950 ℃ and 1050 ℃ for 15min (left) and 1000 ℃ for 10min and 20min (right) mainly contain C, N, O element, and the peak intensity has no obvious change, which shows that the influence of 950 ℃ and 1050 ℃ for 15min and 1000 ℃ for 10min and 20min on the content of C, N, O element in the prepared NG is small.

FIG. 33 is a Raman diagram of NG prepared by using EMIM-dca as a precursor and maintaining the temperature at 950 ℃ and 1050 ℃ for 15min and 1000 ℃ for 10min and 20min, respectively. NG was prepared by holding at 950 ℃ and 1050 ℃ for 15min, respectively, and the Raman image of the sample showed broad peak shapes of D and G, and large defects, and no 2D peak was observed.

NG was prepared at 1000 ℃ for 10min and 20min, respectively, and the Raman image of the sample showed a broad peak shape for D and G, with large defects, and no significant 2D peak was observed, indicating that the sample was too thick. In summary, EMIM-dca as a precursor, 950 ℃ and 1050 ℃ for 15min and 1000 ℃ for 10min and 20min are not conducive to the formation of high quality NG.

FIG. 34 is a TEM image of NG prepared with EMIM-dca (ACN dilution). Compared with the prior undiluted ionic liquid for preparing NG, the diluted ionic liquid for preparing NG has thinner layer number, and obvious interlayer spacing can be seen.

Comparing the upper and lower figures, it can be seen that the number of synthesized NG layers was changed from about 5 to 3 by controlling the ratio of ionic liquid to organic solvent, indicating that dilution with ACN was effective for preparing thin NG layers.

FIG. 35 is an AFM picture of 1 preparation of NG using EMIM-dca (ACN dilution). EMIM-dca/ACN: 35 μ L of: 1000. mu.L (upper), 35. mu.L: 2000. mu.L (bottom). Compared with the prior undiluted ionic liquid for preparing NG, the diluted ionic liquid for preparing NG has smoother and more uniform surface.

Comparing the upper and lower figures, it can be seen that controlling the ratio of ionic liquid to organic solvent, the number of synthesized NG layers was changed from 4 to 3, indicating that dilution with ACN was effective for preparing thin NG layers.

FIG. 36 is a digital photographic image (left) of a clear NG floating on distilled water after removing copper foil from NG prepared with EMIM-dca (diluted ACN and EMIM-dca/ACN: 35. mu.L: 2000. mu.L). NG film (PMMA removed) to Si/SiO₂Optical image on substrate (right). After removing the copper foil, the NG size of floating on distilled water was about 1cm²And the transparency is better, and the transparency of the NG film is related to the number of layers, which shows that the number of layers is less. The thickness uniformity is shown in the right panel, indicating that the NG film surface is smooth and uniform.

Example 2

Adding 35 mu l of ionic liquid EMIM-dca into a weighing bottle, adding 1000 mu l of Acetonitrile (ACN) solvent, fully stirring and uniformly dissolving to obtain an ACN solution of EMIM-dca, taking 30 mu l of the solution, and preparing the nitrogen-doped graphene independent film by the same process as in example 1. The rest is the same as example 1.

Example 3

Adding 35 mu l of ionic liquid EMIM-dca into a weighing bottle, adding 2000 mu l of CAN solvent, fully stirring and dissolving uniformly to prepare the CAN solution of EMIM-dca, taking 30 mu l of the solution, and preparing the nitrogen-doped graphene independent film by the same process in the embodiment 1. The rest is the same as example 1.

Examples 2 and 3 are diluted ionic liquids, and the results are shown in fig. 34, fig. 35 and fig. 36.

Example 4

And under the same condition, replacing EMIM-dca (1-ethyl-3-methylimidazole dicyanomethane salt) with EMIM-tcm (1-ethyl-3-methylimidazole tricyanomethane salt) to prepare the nitrogen-doped graphene independent film. The rest is the same as example 1.

Example 5

Under the same condition, an ionic liquid BMIM-tcm is used for replacing EMIM-dca to prepare the nitrogen-doped graphene independent film. The rest is the same as example 1.

Example 6

Under the same conditions as in example 1, with [ BMIM ]]BF₄N, B double doped graphene (NBG) was prepared for the precursor. The rest is the same as example 1. The results are shown in FIGS. 37-41.

The overall morphology of NBG is shown in the SEM image of fig. 37, where the transparent and wrinkled sheet-like structure of graphene can be seen, and the white line is further enlarged, and the morphology of the gauze-like wrinkles can be clearly seen, which is typical of graphene.

In fig. 38, the XPS total spectrum result confirms that the N and B double-doped graphene is successfully realized, the content of the N element is 6.16%, the content of the B element is 6.72%, and a small O peak appears in the spectrum, and it is analyzed that the peak appears probably due to the fact that the ionic liquid is not vacuum-dried during the spin coating process and is not vacuum-dried after the NBG preparation is completed, and moisture in the air is absorbed; the peaks at 284.5eV, 285.5eV, 286.5eV in the NBG sample correspond to the sp of graphite-like²C、N-sp²C and N-sp³C; the NBG sample contains three main N types, namely graphite N, pyrrole N and pyridine N27%, 42% and 31% of the total N content; peaks at 187.5eV and 190.5eV in the NBG sample correspond to C-B and B-N bonds.

In FIG. 39, I_D/I_G0.95, indicating that the sample defects were large, presumably due to structural distortion caused by increased hetero-atom interference. The wide 2D wave band indicates that the number of the prepared doped graphene layers is 8-10 layers.

In fig. 40, the EDS elemental map indicates that C, N, B elements were uniformly distributed in the NBG sample, demonstrating that N, B doping was successfully achieved.

In FIG. 41, [ BMIM ]]BF₄NBG was prepared for the precursor, and the sample contained C, B, N, O and other elements in addition to Cu.

Comparative example

In order to contrast with the preparation of NG with ionic liquids, we used Polyacrylonitrile (PAN) as a precursor, which also has cyano groups, to prepare nitrogen-doped graphene, with the following specific steps:

2 ml of N, N-Dimethylformamide (DMF) was weighed out, poured into a weighing flask, and 100mg of polyacrylonitrile powder (molecular weight 150000) was added and stirred at room temperature until dissolved.

Samples were prepared under the same growth conditions as in example 1, using a Cu foil as a substrate. The results are shown in FIGS. 28-31.

Claims

1. A preparation method of nitrogen-doped graphene is characterized by comprising the following steps: the method comprises the following steps:

(1) cleaning and annealing of the catalyst substrate: selecting one of a copper foil, a nickel foil, a platinum foil, a semiconductor silicon wafer or a sapphire wafer as a catalyst substrate, cleaning the catalyst substrate, drying after cleaning, and annealing after drying;

(3) transferring nitrogen-doped graphene: dissolving polymethyl methacrylate (PMMA)Dissolving into anisole to prepare PMMA anisole solution, coating the PMMA anisole solution on the surface of the nitrogen-doped graphene obtained in the step (2), drying in vacuum, cooling to room temperature, protecting the nitrogen-doped graphene with a PMMA coating, removing impurities on the back of the substrate, and adding FeCl prepared in advance₃Soaking and etching the substrate in the solution to remove the substrate, so that the nitrogen-doped graphene is transferred to the PMMA protective layer to obtain a nitrogen-doped graphene PMMA complex;

2. The method for preparing nitrogen-doped graphene according to claim 1, wherein the method comprises the following steps: the cleaning in the step (1) is sequentially performed by dilute hydrochloric acid solution, distilled water, acetone, ethanol and distilled water.

3. The method for preparing nitrogen-doped graphene according to claim 1, wherein the method comprises the following steps: the ionic liquid in the step (2) is one or a mixture of more than one; the ionic liquid is obtained by combining cation and anion, wherein the cation is as follows: 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-R₃radical-2-R₂radical-3-R₁Imidazolium cations, pyridinium cations, pyrazolinium cations, pyrrolinium cations, imidazolinium cations, quaternary ammonium cations, quaternary phosphonium cations; the anion is selected from: dicyandiamide anion, tricyanomethane anion, sulfite monoester anion, sulfate monoester anion, difluosulfonylimide anion (FSI), bistrifluoromethanesulfonylimide anion (TFSI), bisoxalato borate anion (BOB), fluoride anion, chloride anion, bromide anion, iodide anion, tetrachloroaluminate ion, tetrafluoroborate ion, hexafluorophosphate ion, carboxylate ion, sulfonate ion, fluorosulfonate ion, nitrate ion, trifluoromethylsulfonate ion, amino acidRoot ion, nitrate ion.

4. The method for preparing nitrogen-doped graphene according to claim 1, wherein the method comprises the following steps: the coating method in the step (2) is high-speed rotation coating, and the rotation speed of the high-speed rotation is 2000-4000 rpm/min; the spin coating time in the step (2) is 0.2-2 min; the coating method in the step (3) is high-speed rotation coating, and the rotation speed of the high-speed rotation is 2000-4000 rpm/min; the spin coating time in the step (3) is 0.2-2 min.

5. The method for preparing nitrogen-doped graphene according to claim 1, wherein the method comprises the following steps: the flow rate of the hydrogen in the step (2) is 40-80mL/min, and the flow rate of the inert gas is 250-350 mL/min.

6. The method for preparing nitrogen-doped graphene according to claim 1, wherein the method comprises the following steps: and (3) adding an organic solvent into the ionic liquid in the step (2) and then spin-coating the ionic liquid on the catalyst substrate.

7. The nitrogen-doped graphene prepared by the preparation method of nitrogen-doped graphene according to claim 1, wherein the preparation method comprises the following steps: the nitrogen content of the nitrogen-doped graphene is more than 6%, and the nitrogen content of the graphite is more than 60% in the nitrogen. The thickness of the nitrogen-doped graphene is larger than 0.33 nm and smaller than 10 nm.

8. The application of the nitrogen-doped graphene in the field of batteries according to claim 7.

9. Use of a nitrogen-doped graphene according to claim 7 in a semiconductor material.

10. The application of the nitrogen-doped graphene in electronic components and parts according to claim 7.

11. Use of a nitrogen-doped graphene according to claim 7 in an LED (light emitting diode) material.