Method for preparing nitrogen-doped graphene

Abstract

The invention relates to the field of nitrogen-doped graphene preparation, in particular to a preparation method. The preparation method comprises the following steps: taking a graphite flake material as a working electrode, taking one of a platinum sheet, a gold sheet and a graphite foil as a counter electrode, and performing electrochemical oxidation stripping on the graphite flake material in an electrolyte environment; after stripping is completed, the electrolyte is filtered and separated, and a solid product is subjected to cleaning, filtering, centrifugal separation and vacuum drying to obtain high-quality nitrogen-doped graphene; the electrolyte comprises an electrolyte and a nitrogen source additive; the electrolyte is methane sulfonate or sulfamate; the nitrogen source additive is a water-soluble nitrogen-containing compound and is electrolyzed to generate nitrogen-containing free radicals. According to the method, the graphite foil can be converted into the nitrogen-doped graphene in one step, the prepared nitrogen-doped graphene is low in oxidation degree, the electrolytic stripping rate in the preparation process is high, no harmful gas is generated, the energy loss is low, the process is simple and convenient, the cost is low, and the repeated utilization rate of the solution is high.

Description

Technical Field

[0001] The invention belongs to the field of nitrogen-doped graphene preparation, and particularly relates to a method for preparing nitrogen-doped graphene. Background Art

[0002] Graphene has excellent optical, electrical and mechanical properties, and has important application prospects in materials science, micro-nano processing, energy, biomedicine and drug delivery. Studies have shown that the physical, optical, electrical and structural properties of graphene can be modified by doping with heteroatoms such as nitrogen. It is worth noting that the chemical doping of graphene produces a band gap, and it behaves like an n-type semiconductor. Due to the interaction between the p orbital of graphene and the lone pair of nitrogen electrons, the electrocatalytic activity of graphene is significantly increased. In order to improve the interaction between graphene and hydrogen atoms, the introduction of heteroatoms such as nitrogen is an effective method. Recently, some theoretical and experimental studies have shown that nitrided graphene is also a potential hydrogen storage material. Nitrogen-doped graphene is widely used in lithium-ion batteries, supercapacitors, graphene-based catalysts, electrocatalytic oxygen reduction reactions, dye-sensitized solar cell counter electrodes and other fields, showing good performance.

[0003] To date, many synthesis methods, including chemical vapor deposition (CVD), thermal annealing, pyrolysis, arc discharge, plasma treatment, N2H4 treatment, hydrothermal method, solvothermal method, microwave-assisted hydrothermal method, wet chemical synthesis, microwave treatment, flame treatment, supercritical reaction method and freeze-drying assisted thermal treatment, have been used to prepare N-doped graphene. Graphene sheets doped with N atoms will produce three common bond configurations in the lattice, including pyridinic N, graphitic N and pyrrolic N. Among them, pyridinic N and pyrrolic N are the most discussed. Literature (Journal of Materials Chemistry, 2011, 21 (22): 8038-8044.) reported that in the presence of ammonia, hydrogen and ethylene were thermally CVD-synthesized on copper foil monolayer graphene doped with pure pyridinic N. This pyridinic N doping in carbon materials is generally considered to be the reason for the enhanced ORR (oxygen reduction reaction) activity. However, since it is necessary to use high-purity ethylene, hydrogen and ammonia as gas sources to react at a high temperature of 900°C on pure copper, the energy loss is large, the tail gas is difficult to remove, and it is easy to cause environmental pollution. Document (Physical Chemistry Chemical Physics, 2010, 12 (38): 12055-12059.) et al. oxidize graphite into graphene oxide by a chemical method, and then pass argon, hydrogen and ammonia methods in a tubular furnace filled with graphene oxide at high temperature, so that graphene oxide is modified to synthesize N-doped graphene, and the resulting material shows higher electrochemical activity than Pt in methanol oxidation. The results show that compared with the original graphene, N-doping can indeed improve the performance of graphene. However, its synthesis method is complicated, the synthetic raw materials are expensive, and the synthesis process is accompanied by the use of strong acids, strong bases and strong oxidants, which will cause greater pollution to the environment.

[0004] In summary, the prior art has the technical problems of complex steps for preparing nitrogen-doped graphene from graphite, harsh preparation conditions, generation of harmful gases and large energy loss. Summary of the invention

[0005] The invention aims to solve the problems that the preparation process of preparing graphite into nitrogen-doped graphene is simple and the conditions are mild, no harmful gas is generated and the energy loss is low.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a method for preparing nitrogen-doped graphene, which comprises the following steps: using a graphite sheet material as a working electrode and using a platinum sheet, a gold sheet, or a graphite foil as a counter electrode, electrochemically oxidizing and exfoliating the graphite sheet material in an electrolyte environment; after the exfoliation is completed, filtering and separating the electrolyte, washing, filtering, centrifuging, and vacuum drying the solid product to obtain high-quality nitrogen-doped graphene;

[0007] Wherein, the electrolyte comprises an electrolyte and a nitrogen source additive;

[0008] Wherein, the electrolyte is methane sulfonate or amino sulfonate;

[0009] The nitrogen source additive is a water-soluble nitrogen-containing compound and its electrolysis generates nitrogen-containing free radicals. The beneficial effects of the present invention are that the method provided by the present invention can realize the one-step conversion of graphite foil into nitrogen-doped graphene, the obtained nitrogen-doped graphene has a low degree of oxidation, the electrolytic stripping process of the preparation process is fast, no harmful gas is generated, the energy loss is low, the process is simple, the cost is low, and the solution reuse rate is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A scanning electron microscope (SEM) image of nitrogen-doped graphene prepared in Example 1;

[0011] Figure 2 Transmission electron microscope (TEM) image of nitrogen-doped graphene prepared in Example 1;

[0012] Figure 3 The Raman spectrum (Raman) of the nitrogen-doped graphene prepared in Example 1;

[0013] Figure 4 X-ray photoelectron spectroscopy (XPS) diagram of nitrogen-doped graphene prepared in Example 1;

[0014] Figure 5 An atomic force microscope (AFM) image of nitrogen-doped graphene prepared in Example 1;

[0015] Figure 6 This is a layer number analysis diagram of the graphene prepared in Example 1. DETAILED DESCRIPTION

[0016] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0017] The first aspect of the present invention provides a method for preparing nitrogen-doped graphene, which comprises the following steps: using a graphite sheet material as a working electrode and using one of a platinum sheet, a gold sheet, and a graphite foil as a counter electrode, electrochemically oxidizing and exfoliating the graphite sheet material in an electrolyte environment; after the exfoliation is completed, filtering and separating the electrolyte, washing, filtering, centrifuging, and vacuum drying the solid product to obtain high-quality nitrogen-doped graphene;

[0018] Wherein, the electrolyte comprises an electrolyte and a nitrogen source additive;

[0019] Wherein, the electrolyte is methane sulfonate or amino sulfonate;

[0020] The nitrogen source additive is a water-soluble compound and its electrolysis generates nitrogen-containing free radicals.

[0021] In the present invention, the inventors found that the anions in the electrolyte will be intercalated into the graphite foil under the condition of electric polarization, expanding the interlamellar spacing, guiding water molecules and nitrogen source additives to insert into the layers, and generating nitrogen-containing free radicals under the action of positive potential; the nitrogen-containing free radicals bind to the interlamellar spacing of the graphite foil to achieve the nitridation process. During the continuous electrolysis process, the gas generated by the oxidation between the layers promotes the peeling of the graphene layers, and finally nitrogen-doped graphene is obtained.

[0022] In the present invention, when methanesulfonic acid is selected as the electrolyte, adding a sulfur-containing nitrogen source additive is likely to produce a gas with a rotten egg smell (H2S), and the prepared nitrogen-doped graphene has a high degree of oxidation. In the planar structure of nitrogen-doped graphene, a high content of oxygen atoms will affect the electronic structure of nitrogen-doped graphene, and thus affect its physical, optical, electrical and structural properties; compared with methanesulfonate, the nitrogen-doped graphene obtained by using aminosulfonate as the electrolyte has a higher nitrogen content, but the stripping efficiency is slightly lower.

[0023] According to the present invention, the nitrogen source additive is selected from at least one of thiourea, urea, thioacetamide, formamidine acetate, glycine, L-cysteine, L-arginine, ammonium carbonate, ammonium nitrate, 4-pyridinemethanol and 4-pyridinecarboxylic acid.

[0024] According to the present invention, the methane sulfonate is potassium methane sulfonate or sodium methane sulfonate.

[0025] According to the present invention, the aminosulfonate is one of potassium aminosulfonate, sodium aminosulfonate and ammonium aminosulfonate.

[0026] According to the present invention, the electrochemical stripping time is 0.5-2h.

[0027] According to the present invention, the thickness of the graphite flake material is 0.1 mm-3 mm.

[0028] According to the present invention, the concentration of the electrolyte in the electrolyte is 0.1M-3M.

[0029] According to the present invention, the concentration of the nitrogen source additive in the electrolyte is 0.01M-2M.

[0030] According to the present invention, during the electrochemical stripping process, the positive potential applied to the working electrode is 6-13V.

[0031] According to the present invention, the cleaning is ultrasonic cleaning, the ultrasonic power operating frequency is 35-52kHz; the ultrasonic time is 10-30min; and the ultrasonic temperature is 0-30°C.

[0032] According to the present invention, the centrifugal speed of the centrifugal separation is 8000-12000 r / min; the centrifugal time is 5-15 min.

[0033] According to the present invention, the vacuum drying temperature is 50-80°C; the vacuum drying time is 24-72h.

[0034] In the present invention, the nitrogen content of the nitrogen-doped graphene prepared by the method provided by the present invention is 1-8 atomic%. The inventors found that if the nitrogen content is too low, the catalytic effect on the reaction is poor; if the nitrogen content is too high, hydroxyl radicals continue to attack graphite during the preparation process, resulting in a high degree of oxidation of the nitrogen-doped graphene.

[0035] In the present invention, the nitrogen content is the percentage of nitrogen atoms in all atoms.

[0036] Test Method

[0037] The C / O atomic ratio of nitrogen-doped graphene was measured by X-ray photoelectron spectroscopy.

[0038] The number of nitrogen-doped graphene layers is measured using an atomic force microscope, and the number of layers is calculated as follows: nitrogen-doped graphene thickness / theoretical single-layer thickness = number of layers.

[0039] The technical scheme of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments implemented by ordinary technicians in this field without making creative improvements belong to the protection scope of the present invention.

[0040] Embodiment 1:

[0041] Weigh 1.3420g potassium methanesulfonate and dissolve it in 100mL water to prepare a 0.1M potassium methanesulfonate electrolyte. Take 30mL of the electrolyte and 0.2284g of thiourea in an electrolytic cell. The concentration of thiourea is 0.1M. A 1.5cm*2.5cm*0.1mm graphite foil is used as the working electrode, and a platinum electrode is used as the counter electrode. The two electrodes are 3cm apart. A positive potential of 10V is applied to the working electrode, and the graphite foil is electrochemically oxidized and exfoliated using a two-electrode system.

[0042] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35kHz, the time is 1.5h, the temperature is 25°C, and the nitrogen-doped graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at 70°C for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 4.55atomic%.

[0043] The prepared nitrogen-doped graphene was tested by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (Raman) methods. Figure 1 This is an SEM image of nitrogen-doped graphene prepared by electrochemistry. From the image, we can see that the grooves are uneven, the folds are large, and the transparency is high, which indicates that nitrogen-doped graphene is prepared with a small number of graphene layers. Figure 2 This is a TEM image of nitrogen-doped graphene, which shows high transparency and few layers. Figure 3 This is the Raman image of nitrogen-doped graphene. It can be seen from the figure that with the increase of nitrogen content, the G peak in the figure will undergo a more obvious blue shift, which also reflects that the prepared graphene contains nitrogen doping; Figure 4 Shown is an XPS image of nitrogen-doped graphene, in which the N bond configurations include pyrrolic nitrogen, pyridinic nitrogen, and graphitic nitrogen, and the N bond configuration is mainly pyrrolic nitrogen. Figure 5 This is an AFM image of nitrogen-doped graphene. It can be seen from the figure that the prepared graphene sheets are large in size, with an average sheet thickness of 0.42nm, which is consistent with the thickness of nitrogen-doped graphene sheets. Figure 6 The number of layers of nitrogen-doped graphene was analyzed. The number of layers of 100 sheets of nitrogen-doped graphene was counted, and the number of single-layer graphene can reach 14%. And the yield of three-layer and less graphene can reach 70%.

[0044] Embodiment 2:

[0045] Weigh 1.3420g potassium methanesulfonate and dissolve it in 100mL water to prepare a 0.1M potassium methanesulfonate electrolyte. Take 30mL of the electrolyte and 0.2252g of glycine in an electrolytic cell, the glycine concentration is 0.1M, use a 1.5cm*2.5cm*0.1mm graphite foil as the working electrode, a platinum electrode as the counter electrode, the two electrodes are 3cm apart, apply a positive potential of 10V to the working electrode, and use a two-electrode system to electrochemically intercalate and exfoliate the graphite foil.

[0046] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35kHz, the time is 1.5h, the temperature is 25℃, the nitrogen-doped graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at 70℃ for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 1.12atomic%.

[0047] Embodiment 3:

[0048] Weigh 1.3420g potassium methanesulfonate and dissolve it in 100mL water to prepare a 0.1M potassium methanesulfonate electrolyte. Take 30mL of the electrolyte and 0.3125g of formamidine acetate in an electrolytic cell. The concentration of formamidine acetate is 0.1M. A 1.5cm*2.5cm*0.1mm graphite foil is used as the working electrode, and a platinum electrode is used as the counter electrode. The two electrodes are separated by 3cm. A positive potential of 10V is applied to the working electrode, and the graphite foil is electrochemically intercalated and exfoliated using a double electrode system.

[0049] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, the temperature is 25℃, and the nitrogen-doped graphene is repeatedly rinsed, filtered, and centrifuged using anhydrous ethanol and water. The centrifugal speed is 10000r / min, and vacuum drying is performed at a temperature of 70℃ for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 1.80atomic%.

[0050] Embodiment 4:

[0051] Weigh 1.3420g potassium methanesulfonate and dissolve it in 100mL water to prepare a 0.1M potassium methanesulfonate electrolyte. Take 30mL of the electrolyte and 0.3244g of 4-pyridinemethanol in an electrolytic cell. The concentration of 4-pyridinemethanol is 0.1M. A 1.5cm*2.5cm*0.1mm graphite foil is used as the working electrode, and a platinum sheet electrode is used as the counter electrode. The two electrodes are separated by 3cm. A positive potential of 10V is applied to the working electrode, and the graphite foil is electrochemically oxidized and exfoliated using a two-electrode system.

[0052] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, the temperature is 25℃, and the nitrogen-doped graphene is repeatedly rinsed, filtered, and centrifuged using anhydrous ethanol and water. The centrifugal speed is 10000r / min, and vacuum drying is performed at a temperature of 70℃ for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 1.48atomic%.

[0053] Embodiment 5:

[0054] Weigh 1.3420g potassium methanesulfonate and dissolve it in 100mL water to prepare a 0.1M potassium methanesulfonate electrolyte. Take 30mL of the electrolyte and 0.2883g of ammonium carbonate in an electrolytic cell. The concentration of ammonium carbonate is 0.1M. A 1.5cm*2.5cm*0.1mm graphite foil is used as the working electrode, and a platinum electrode is used as the counter electrode. The two electrodes are separated by 3cm. A positive potential of 10V is applied to the working electrode, and the graphite foil is electrochemically oxidized and stripped using a two-electrode system.

[0055] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, the temperature is 25℃, and the nitrogen-doped graphene is repeatedly rinsed, filtered, and centrifuged using anhydrous ethanol and water. The centrifugal speed is 10000r / min, and vacuum drying is performed at a temperature of 70℃ for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 4.68atomic%.

[0056] Embodiment 6:

[0057] Weigh 1.1809g of sodium methanesulfonate and dissolve it in 100mL of water to prepare a 0.1M sodium methanesulfonate electrolyte. Take 30ml of the electrolyte and 0.2284g of thiourea in an electrolytic cell. The concentration of thiourea is 0.1M. A 1.5cm*2.5cm*0.1mm graphite foil is used as the working electrode, and a platinum electrode is used as the counter electrode. The two electrodes are 3cm apart. A positive potential of 10V is applied to the working electrode, and the graphite foil is electrochemically oxidized and exfoliated using a two-electrode system.

[0058] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, and the produced graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at a temperature of 70°C for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 4.52atomic%.

[0059] Embodiment 7:

[0060] Weigh 1.1809g of sodium methanesulfonate and dissolve it in 100ml of water to prepare a 0.1M sodium methanesulfonate electrolyte. Take 30ml of the electrolyte and 0.2252g of glycine in an electrolytic cell, the glycine concentration is 0.1M, use a 1.5cm*2.5cm*0.1mm graphite foil as the working electrode, a platinum electrode as the counter electrode, the two electrodes are 3cm apart, apply a positive potential of 10V to the working electrode, and use a two-electrode system to electrochemically oxidize and exfoliate the graphite foil.

[0061] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, and the produced graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at a temperature of 70°C for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 1.10atomic%.

[0062] Embodiment 8:

[0063] Weigh 1.1809g of sodium methanesulfonate and dissolve it in 100mL of water to prepare a 0.1M sodium methanesulfonate electrolyte. Take 30mL of the electrolyte and 0.3125g of formamidine acetate in an electrolytic cell. The concentration of formamidine acetate is 0.1M. A 1.5cm*2.5cm*0.1mm graphite foil is used as the working electrode, and a platinum electrode is used as the counter electrode. The two electrodes are separated by 3cm. A positive potential of 10V is applied to the working electrode, and the graphite foil is electrochemically oxidized and stripped using a two-electrode system.

[0064] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, and the produced graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at a temperature of 70°C for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 1.46atomic%.

[0065] Embodiment 9:

[0066] Weigh 1.1908g of sodium aminosulfonate and dissolve it in 100mL of water to prepare a 0.1M aminosulfonic acid electrolyte. Take 30mL of the electrolyte and 0.2252g of glycine in an electrolytic cell, the glycine concentration is 0.1M, use a 1.5cm*2.5cm*0.1mm graphite foil as the working electrode, a platinum electrode as the counter electrode, the two electrodes are 3cm apart, apply a positive potential of 10V to the working electrode, and use a two-electrode system to electrochemically oxidize and exfoliate the graphite foil.

[0067] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, and the produced graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at a temperature of 70°C for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 1.68atomic%.

[0068] Embodiment 10:

[0069] Weigh 1.3518g of potassium sulfamate and dissolve it in 100mL of water to prepare a 0.1M potassium sulfamate electrolyte. Take 30mL of the electrolyte and 0.2284g of thiourea in an electrolytic cell. The concentration of thiourea is 0.1M. A 1.5cm*2.5cm*0.1mm graphite foil is used as the working electrode, and a platinum electrode is used as the counter electrode. The two electrodes are 3cm apart. A positive potential of 10V is applied to the working electrode, and the graphite foil is electrochemically oxidized and stripped using a two-electrode system.

[0070] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, and the produced graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at a temperature of 70°C for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 4.93atomic%.

[0071] Embodiment 11:

[0072] Weigh 1.1908g of sodium sulfamate and dissolve it in 100mL of water to prepare a 0.1M sodium sulfamate electrolyte. Take 30mL of the electrolyte and 0.3125g of formamidine acetate in an electrolytic cell. The concentration of formamidine acetate is 0.1M. A 1.5cm*2.5cm*0.1mm graphite foil is used as the working electrode, and a platinum electrode is used as the counter electrode. The two electrodes are separated by 3cm. A positive potential of 10V is applied to the working electrode, and the graphite foil is electrochemically oxidized and stripped using a double electrode system.

[0073] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, and the produced graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at a temperature of 70°C for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 2.30atomic%.

[0074] Embodiment 12:

[0075] Weigh 1.3420g potassium methanesulfonate and dissolve it in 100mL water to prepare a 0.1M potassium methanesulfonate electrolyte. Take 30mL of the electrolyte and 0.1802g of urea in an electrolytic cell, the concentration of urea is 0.1M, use a 1.5cm*2.5cm*0.1mm graphite foil as the working electrode, a platinum electrode as the counter electrode, the two electrodes are 3cm apart, a positive potential of 10V is applied to the working electrode, and the graphite foil is electrochemically oxidized and stripped using a two-electrode system.

[0076] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, and the produced graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at 70℃ for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 4.36atomic%, and the C / O atomic ratio is 3.48.

[0077] Embodiment 13:

[0078] Weigh 22.8240g of ammonium sulfamate and dissolve it in 100mL of water to prepare a 2M ammonium sulfamate electrolyte. Take 30mL of the electrolyte and 5.4054g of urea in an electrolytic cell, the concentration of urea is 3M, use a 1.5cm*2.5cm*0.1mm graphite foil as the working electrode, a platinum electrode as the counter electrode, the two electrodes are 3cm apart, apply a positive potential of 10V to the working electrode, and use a two-electrode system to electrochemically oxidize and exfoliate the graphite foil.

[0079] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, and the produced graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at 70℃ for 24h to obtain high-quality nitrogen-doped graphene. The nitrogen content in the obtained nitrogen-doped graphene is 7.89atomic%.

[0080] Embodiment 14:

[0081] Nitrogen-doped graphene was prepared according to the preparation method of Example 1, except that a positive potential of 8 V was applied to the working electrode, and the nitrogen content in the obtained nitrogen-doped graphene was 4.38 atomic %.

[0082] Embodiment 15:

[0083] Nitrogen-doped graphene was prepared according to the preparation method of Example 11, except that a graphite foil of 1.5 cm*2.5 cm*2.0 mm was used as a working electrode, and the nitrogen content in the obtained nitrogen-doped graphene was 3.86 atomic %.

[0084] Comparative Example 1

[0085] The electrochemical system consists of pure graphite as anode and Pt electrode as cathode material. The electrodes are placed vertically and parallel to each other. The electrode parts are immersed in an ionic electrolyte aqueous solution. 0.5M sulfuric acid (H2SO4) is used as the electrolyte solution and 2.5g urea (Aldrich grade) is added to H2SO4 as a nitrogen precursor. The nitrogen content in the obtained nitrogen-doped graphene is 0.48 atomic%.

[0086] Comparative Example 2

[0087] Graphite was used as the anode, a Pt sheet (12 mm long and 10 mm wide) was used as the counter electrode, and a 3M glycine and ammonia solution (25-28%) was used as the electrolyte. A DC power supply (LW10J2, Shanghai Liyou Electric Co., Ltd.) was used to apply a static potential of 10 V to the two electrodes. After 12 hours of electrolysis, the stripped product was ultrasonically treated for 1 hour, then collected by filtration and thoroughly washed with water and ethanol. The washing cycle was repeated six times, and the final precipitate was dispersed in 100 mL of deionized water. After 24 hours of precipitation, large / thick graphite sheets were completely precipitated at the bottom of the bottle. The supernatant was filtered through a glass fiber filter membrane (Waterson, GF / C) under vacuum, and then vacuum dried overnight at 50°C to obtain a nitrogen-doped graphene sample. The nitrogen content in the obtained nitrogen-doped graphene was 6.05 atomic%.

[0088] Comparative Example 3

[0089] Use a pipette to take 0.652 mL of methanesulfonic acid and dissolve it in 100 mL of water to prepare a 0.1 M methanesulfonic acid electrolyte. Take 30 mL of the electrolyte and 0.1802 g of urea in an electrolytic cell. The concentration of urea is 0.1 M. A 1.5 cm*2.5 cm*0.1 mm graphite foil is used as the working electrode, and a platinum electrode is used as the counter electrode. The two electrodes are 3 cm apart. A positive potential of 10 V is applied to the working electrode, and the graphite foil is electrochemically oxidized and stripped using a double electrode system.

[0090] The graphite foil is completely peeled off, and finally a suspension of nitrogen-doped graphene is obtained in the electrolytic cell. The obtained nitrogen-doped graphene suspension is filtered and separated, and then the separated solid is ultrasonically washed, the ultrasonic power operating frequency is 35KHz, the time is 1.5h, and the produced graphene is repeatedly rinsed, filtered, and centrifuged with anhydrous ethanol and water, the centrifugal speed is 10000r / min, and vacuum dried at a temperature of 70℃ for 24h to obtain high-quality nitrogen-doped graphene. The C / O atomic ratio is 5.33 and the nitrogen content is 1.30% atomic.

[0091] Table 1 shows the stripping time and nitrogen doping content of nitrogen-doped graphene prepared in Examples 1-15 and Comparative Examples 1-3.

[0092] Table 1

[0093] serial number Stripping time Nitrogen doping content Example 1 45min 4.55 atomic% Example 2 28min 1.12 atomic% Example 3 19min 1.80 atomic% Example 4 60min 1.48 atomic% Example 5 86min 4.68 atomic% Example 6 46min 4.52 atomic% Example 7 30min 1.10 atomic% Example 8 19min 1.46 atomic% Example 9 35min 1.68 atomic% Example 10 58min 4.93 atomic% Embodiment 11 24min 2.30 atomic% Example 12 64min 4.36 atomic% Example 13 83min 7.89 atomic% Embodiment 14 56min 4.38 atomic% Embodiment 15 115min 4.99 atomic% Comparative Example 1 - 0.48 atomic% Comparative Example 2 600min 6.05 atomic% Comparative Example 3 20min 1.30 atomic%

[0094] Table 2 shows the nitrogen doping content and C / O atomic ratio of Example 12 and Comparative Example 3.

[0095] Table 2

[0096] serial number Nitrogen doping content C / O atomic ratio Example 12 4.36 atomic% 3.48 Comparative Example 3 1.30 atomic% 5.53

[0097] It can be seen from Examples 1-15 and Comparative Examples that the preparation method of the present invention is used to electrochemically strip graphite foil in aqueous solutions of nitrogen source additives such as potassium methanesulfonate, sodium methanesulfonate, aminosulfonic acid electrolyte and thiourea, urea, thioacetamide, formamidine acetate, glycine, L-cysteine, L-arginine, ammonium carbonate, ammonium nitrate, 4-pyridinemethanol and 4-pyridinecarboxylic acid, thereby preparing nitrogen-doped graphene.

[0098] Comparative Example 1 adopts a method of electrolyzing graphite in an electrolyte under acidic conditions (0.5M sulfuric acid) and containing 2.5g of urea (Aldrich grade) as a nitrogen precursor. The nitrogen content of the prepared nitrogen-doped graphene is 0.48 atomic%, which is much lower than the nitrogen-doped graphene prepared by the method provided by the present invention. The acidic conditions are highly corrosive to the equipment.

[0099] Comparative Example 2 uses high-concentration ammonia water and glycine as electrolytes to electrolyze graphite to prepare nitrogen-doped graphene. The disadvantages are: 1. Under concentrated alkaline conditions, strict requirements are placed on experimental equipment; 2. During the electrolysis process, harmful gases such as ammonia will be produced; 3. Under alkaline conditions, the quality of the prepared nitrogen-doped graphene is relatively low.

[0100] In Comparative Example 3, methanesulfonic acid is selected as the electrolyte, and the nitrogen content of the obtained nitrogen-doped graphene is not high. During the electrolysis process, a gas with a rotten egg smell (H2S) is generated, and the degree of oxidation of the obtained nitrogen-doped graphene is relatively high.

[0101] This method realizes the one-step conversion of graphite foil into nitrogen-doped graphene, and the nitrogen in the nitrogen-doped graphene has a bond configuration dominated by pyrrolic nitrogen, and the electrolytic stripping process is fast, with little environmental pollution, simple process, low cost, large product sheet size, and high solution reuse rate. The production of high-quality nitrogen-doped graphene with low cost and environmental protection plays an important role in the fields of lithium-ion batteries, supercapacitors, electrocatalytic reactions, preparation of nitrogen-doped graphene-based catalysts, and electrodes for dye-sensitized solar cells.

[0102] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing nitrogen-doped graphene, characterized in that: The method comprises the following steps: using a graphite sheet material as a working electrode and using one of a platinum sheet, a gold sheet and a graphite foil as a counter electrode, and electrochemically oxidizing and exfoliating the graphite sheet material in an electrolyte environment; After the stripping is completed, the electrolyte is filtered and separated, and the solid product is washed, filtered, centrifuged, and vacuum dried to obtain high-quality nitrogen-doped graphene; Wherein, the electrolyte comprises an electrolyte and a nitrogen source additive; Wherein, the electrolyte is methane sulfonate or amino sulfonate; The nitrogen source additive is a water-soluble compound and its electrolysis generates nitrogen-containing free radicals.

2. The method according to claim 1, characterized in that The nitrogen source additive is selected from at least one of thiourea, urea, thioacetamide, formamidine acetate, glycine, L-cysteine, L-arginine, ammonium carbonate, ammonium nitrate, 4-pyridinemethanol and 4-pyridinecarboxylic acid; Wherein, the methane sulfonate is potassium methane sulfonate or sodium methane sulfonate. Wherein, the aminosulfonate is one of sodium aminosulfonate, potassium aminosulfonate and ammonium aminosulfonate.

3. The method according to claim 1, characterized in that: The electrochemical stripping time is 0.5-2h.

4. The method according to claim 1, characterized in that: The thickness of the graphite flake material is 0.1 mm-3 mm.

5. The method according to claim 1, characterized in that The concentration of the electrolyte in the electrolyte solution is 0.1M-3M.

6. The method according to claim 1, characterized in that The concentration of the nitrogen source additive in the electrolyte is 0.01M-2M.

7. The method according to claim 1, characterized in that During the electrochemical stripping process, the positive potential applied to the working electrode is 6-13V.

8. The method according to claim 1, characterized in that: The cleaning is ultrasonic cleaning, the ultrasonic power operating frequency is 35-52KHz; the ultrasonic time is 10-30min; the ultrasonic temperature is 0-30°C.

9. The method according to claim 1, characterized in that: The centrifugal speed of the centrifugal separation is 8000-12000 r / min; the centrifugal time is 5-15 min.

10. The method according to claim 1, characterized in that The vacuum drying temperature is 50-80°C; the vacuum drying time is 24-72h.

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