Graphene-like ultrathin nitrogen-doped carbon nanosheets, their preparation methods and applications

Abstract

The present invention discloses graphene-like ultra-thin nitrogen-doped carbon nanosheets and preparation method and application thereof, the graphene-like ultra-thin nitrogen-doped carbon nanosheets are prepared by high-temperature pyrolysis using waste as carbon source and urea as nitrogen source, wherein waste includes any one of glucose, fructose, cellulose, lignin, 5-hydroxymethylfurfural and straw. Meanwhile, the present invention applies the prepared graphene-like ultra-thin nitrogen-doped carbon nanosheets to catalyze 5-hydroxymethylfurfural to be converted into 2,5-furandicarboxylic acid in electrocatalytic reaction, and electrocatalytic conversion effect is better. Compared with prior art, the process of preparing graphene-like ultra-thin nitrogen-doped carbon nanosheets by the present invention is simple and convenient, and the required raw material sources for preparation are extensive, low in price, and environmentally friendly, can be mass-produced, and the graphene-like ultra-thin nitrogen-doped carbon nanosheets prepared by the present invention are thin in thickness, and electrocatalytic conversion effect is good, and economic benefit is high, with wide application prospects and large market potential.

Description

Technical Field

[0001] This invention relates to the field of catalytic synthesis, and more particularly to graphene-like ultrathin nitrogen-doped carbon nanosheets, their preparation methods, and applications. Background Technology

[0002] 2,5-Furfurandicarboxylic acid (FDCA) is a novel bio-based monomer with a wide range of applications. It shares similar structure and reactivity with the traditional petroleum-based monomer terephthalic acid (PTA), making it a potentially environmentally friendly alternative to PTA in the production of polyesters, polyamides, and other novel bio-based polymers. Compared to traditional industrial FDCA production processes, the route using typical biomass solid wastes such as agricultural and forestry waste, organic household waste, and livestock manure as raw materials for the catalytic oxidation of FDCA with 5-hydroxymethylfurfural (HMF) is a promising and readily industrial-scale FDCA synthesis pathway with abundant raw material sources. Currently existing conversion pathways primarily utilize catalytic systems composed of high temperature, high pressure, noble metal catalysts, and organic solvents, which still have significant room for improvement in terms of reaction conditions, energy consumption, life-cycle environmental emissions, and techno-economic efficiency. Therefore, developing a green, environmentally friendly, low-energy-consumption, and highly efficient selective oxidation system for the conversion of HMF into FDCA is a hot topic of research worldwide.

[0003] Electrocatalytic oxidation of HMF to FDCA is a method that uses water as a medium and utilizes the thermodynamically more favorable 5-hydroxymethylfurfural oxidation reaction (HMFOR) to replace the oxygen evolution reaction, achieving the oxidative conversion of FDCA under mild conditions. Its coupling with the cathodic reduction hydrogen evolution reaction can significantly improve energy utilization efficiency and economic benefits, providing a strategy to effectively improve energy utilization and co-produce high-value-added chemicals and hydrogen energy. The most crucial aspect of the electrocatalytic oxidation of HMF to FDCA is the selection of the catalyst. Carbon materials possess excellent physicochemical properties and stability under different conditions. Currently, various carbon materials with different microstructures and morphologies, such as activated carbon, mesoporous carbon, and graphene, have been used in high-value conversion processes of biomass. In recent years, many researchers have developed nitrogen-doped carbon nanosheets with excellent performance as energy storage devices or catalysts; however, most reported graphene-like ultrathin nitrogen-doped carbon nanosheets contain metals to enhance their performance. Another Chinese patent discloses a method for preparing two-dimensional nitrogen-doped hierarchical porous carbon nanosheets, including the following steps: carbonizing a nitrogen-containing organometallic framework at a carbonization temperature of 910–2000 °C in a gas atmosphere, followed by cooling to obtain two-dimensional nitrogen-doped hierarchical porous carbon nanosheets. This method uses zinc ions as the metal ion to prepare a nitrogen-containing metal-organic framework, and it can produce two-dimensional porous nitrogen-doped carbon nanosheets without a template. However, this synthesis method involves two steps: carbonization and activation, making the process complex. Furthermore, the precursor sources are relatively difficult to obtain, resulting in high costs. Another Chinese patent discloses a nitrogen-phosphorus co-doped carbon nanosheet method using p-phenylenediamine, terephthalaldehyde, and DOPO flame retardant as raw materials. These are organic reagents, which are environmentally polluting and unsuitable for large-scale production. Currently, there is no invention that uses simple, low-value, and pollution-free raw materials to prepare metal-free ultrathin nitrogen-doped carbon nanosheets for the electrocatalytic conversion of HMF to FDCA.

[0004] Therefore, how to provide graphene-like ultrathin nitrogen-doped carbon nanosheets that are very thin and can effectively catalyze the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid in electrocatalytic reactions is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method for preparing metal-free ultrathin nitrogen-doped carbon nanosheets using simple, low-value and pollution-free raw materials. The method utilizes waste materials to prepare graphene-like ultrathin nitrogen-doped carbon nanosheets, so that the prepared graphene-like ultrathin nitrogen-doped carbon nanosheets are free of metal doping, can be mass-produced, and can be effectively catalyzed in electrocatalytic reactions to convert 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid.

[0006] To achieve the above objectives, the present invention provides a method for preparing graphene-like ultrathin nitrogen-doped carbon nanosheets, the method comprising:

[0007] S1. Crush the waste material to obtain powder;

[0008] S2. The obtained powder is dissolved in a urea aqueous solution, and then stirred and dried to obtain pretreated powder.

[0009] S3. Pyrolyze the obtained pretreated powder to obtain a black solid;

[0010] S4. The obtained black solid is dispersed in water and then subjected to ultrasonication, filtration and drying to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets.

[0011] In the first aspect, the waste includes any one of glucose, fructose, cellulose, lignin, 5-hydroxymethylfurfural, and straw.

[0012] In the first aspect, the step of dissolving the obtained powder in a urea aqueous solution and then sequentially stirring and drying to obtain pretreated powder specifically includes: the mass ratio of the powder to the urea aqueous solution is 0.5-1.5:15-30; the concentration of the urea aqueous solution is 0.15-0.35 g / mL; the stirring speed is 300-500 rpm; the stirring time is 45-90 minutes; the drying temperature is 45-90°C; and the drying time is 10-18 hours.

[0013] In the first aspect, the pyrolysis of the obtained pretreated powder to obtain a black solid specifically includes: placing the obtained pretreated powder into a tube furnace, continuously introducing argon gas into the tube furnace at a flow rate of 80-120 mL / min, simultaneously raising the temperature to 300-900°C at a rate of 1-5°C / min, and holding the temperature for pyrolysis for 45-90 minutes to obtain a black solid.

[0014] In the first aspect, the step of dispersing the obtained black solid in water and sequentially subjecting it to ultrasonication, filtration, and drying to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets specifically includes: the ultrasonic power of the ultrasonication is 200-300W, the ultrasonication time is 45-90 minutes; the pore size of the filter membrane used for filtration is 0.22-0.8 micrometers; the drying temperature is 45-60℃, and the drying time is 10-18 hours.

[0015] In the first aspect, the step of crushing the waste to obtain powder specifically includes crushing the waste in at least one of the following ways: ball milling, grinding, or crushing with a crusher.

[0016] This invention also provides the application of graphene-like ultrathin nitrogen-doped carbon nanosheets, in which porous nickel foam-supported graphene-like ultrathin nitrogen-doped carbon nanosheets are used as working electrodes to electrocatalyze the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, wherein the graphene-like ultrathin nitrogen-doped carbon nanosheets are the graphene-like ultrathin nitrogen-doped carbon nanosheets described in claim 7.

[0017] Compared with existing technologies, this invention has the following advantages due to the adoption of the above technical solutions: 1) This invention uses waste as the main raw material, which effectively reduces the pollution of the environment by waste, and can achieve energy conservation, emission reduction and green low carbon. At the same time, waste has a wide range of sources, low price and high economic benefits; 2) Using waste as carbon source and urea as nitrogen source, after high-temperature pyrolysis, it is dispersed in water and then subjected to ultrasonic, filtration and drying treatment to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets. This process is simple and convenient and can be prepared on a large scale; 3) The prepared graphene-like ultrathin nitrogen-doped carbon nanosheets can catalyze the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid in electrocatalytic reaction, and the electrocatalytic activity is high and the electrocatalytic conversion effect is good. 2,5-furandicarboxylic acid can be used as a chemical intermediate to produce corrosion-resistant polymer plastics and pharmaceutical intermediates, which further improves the value of waste and improves economic benefits; 4) The graphene-like ultrathin nitrogen-doped carbon nanosheets prepared by this invention are very thin, up to 1.5 nm. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The linear sweep voltammetric curve of the graphene-like ultrathin nitrogen-doped carbon nanosheets used as the working electrode in Example 1 of this invention, supported by porous nickel foam, is shown in the electrocatalytic process.

[0020] Figure 2 The linear sweep voltammetry curve of the graphene-like ultrathin nitrogen-doped carbon nanosheets used as the working electrode in Example 2 of this invention, supported by porous nickel foam, is shown in the electrocatalytic process.

[0021] Figure 3 The linear sweep voltammetric curve of the graphene-like ultrathin nitrogen-doped carbon nanosheets used as the working electrode in Example 5 of this invention, supported by porous nickel foam, is shown.

[0022] Figure 4 This is the Raman diagram of the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 1 of this invention;

[0023] Figure 5 This is the Raman diagram of the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 2 of this invention;

[0024] Figure 6 This is the Raman diagram of the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 5 of this invention;

[0025] Figure 7 This is an XPS image of the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 1 of this invention;

[0026] Figure 8 This is an XPS image of the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 2 of this invention;

[0027] Figure 9 This is an XPS image of the graphene-like ultrathin nitrogen-doped carbon nanosheet in Example 5 of this invention;

[0028] Figure 10 This is a TEM image of the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 5 of this invention;

[0029] Figure 11 This is a TEM mapping image of the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 5 of this invention.

[0030] Figure 12 These are the XRD patterns of graphene-like ultrathin nitrogen-doped carbon nanosheets in Examples 1 to 5 of this invention;

[0031] Figure 13 This is the AFM image of the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 5 of this invention. Detailed Implementation

[0032] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this specification are within the scope of protection of this invention.

[0033] Example 1

[0034] This embodiment provides a method for preparing graphene-like ultrathin nitrogen-doped carbon nanosheets, specifically including: S1, crushing waste materials to obtain powder; S2, dissolving the obtained powder in a urea aqueous solution, and then sequentially stirring and drying to obtain pretreated powder; S3, pyrolyzing the obtained pretreated powder to obtain a black solid; S4, dispersing the obtained black solid in water, and then sequentially ultrasonicating, filtering, and drying to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets.

[0035] Compared with the prior art, the preparation method of graphene-like ultrathin nitrogen-doped carbon nanosheets provided in Embodiment 1 of the present invention has the following advantages: 1) The present invention uses waste as the main raw material, which effectively reduces the pollution of the environment by waste, and can achieve energy conservation, emission reduction and green low carbon. At the same time, waste is widely available, inexpensive and economically efficient; 2) Using waste as carbon source and urea as nitrogen source, after high-temperature pyrolysis, the nanosheets are dispersed in water and then subjected to ultrasonication, filtration and drying to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets. The process is simple and convenient and can be prepared on a large scale; 3) The prepared graphene-like ultrathin nitrogen-doped carbon nanosheets can catalyze the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid in electrocatalytic reaction, and have high electrocatalytic activity and good electrocatalytic conversion effect. 2,5-furandicarboxylic acid can be used as a chemical intermediate to produce corrosion-resistant polymer plastics and pharmaceutical intermediates, further improving the value of waste and improving economic efficiency; 4) The graphene-like ultrathin nitrogen-doped carbon nanosheets prepared by the present invention are very thin, up to 1.5 nm.

[0036] In some possible implementations, the waste includes any one of glucose, fructose, cellulose, lignin, 5-hydroxymethylfurfural, and straw; the step of dissolving the obtained powder in a urea aqueous solution, and then sequentially stirring and drying to obtain pretreated powder specifically includes: the mass ratio of the powder to the urea aqueous solution is 0.5–1.5:15–30; the concentration of the urea aqueous solution is 0.15–0.35 g / mL; and the stirring speed is 300–500 rpm. The stirring time is 45-90 minutes, the drying temperature is 45-90℃, and the drying time is 10-18 hours. The process of pyrolyzing the pretreated powder to obtain a black solid specifically includes: placing the pretreated powder into a tube furnace, continuously introducing argon gas into the tube furnace at a flow rate of 80-120 mL / min, simultaneously raising the temperature to 300-900℃ at a rate of 1-5℃ / min, and holding the temperature for pyrolysis for 45-90 minutes to obtain a black solid.

[0037] Specifically, graphene-like ultrathin nitrogen-doped carbon nanosheets are prepared by high-temperature pyrolysis using waste materials such as glucose, fructose, cellulose, lignin, 5-hydroxymethylfurfural, and straw as carbon sources and urea as a nitrogen source. Waste materials such as glucose, fructose, cellulose, lignin, 5-hydroxymethylfurfural, and straw are widely available, contain no metal additives, and are inexpensive. Urea is also inexpensive, and the preparation method is simple and convenient, making the preparation of graphene-like ultrathin nitrogen-doped carbon nanosheets more economical.

[0038] In some possible implementations, the step of dispersing the obtained black solid in water and sequentially subjecting it to ultrasonication, filtration, and drying to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets specifically includes: the ultrasonic power of the ultrasonication being 200–300 W, the ultrasonication time being 45–90 minutes; the pore size of the filter membrane being filtered being 0.22–0.8 micrometers; the drying temperature being 45–60°C, and the drying time being 10–18 hours.

[0039] Specifically, the black solid obtained by high-temperature pyrolysis in a tube furnace is graphene-like ultrathin nitrogen-doped carbon nanosheets, but it still contains some unreacted residues. By dispersing the black solid in water and ultrasonically cleaning it, the residues on the graphene-like ultrathin nitrogen-doped carbon nanosheets are removed. The residues are then filtered out to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets.

[0040] In some possible implementations, the process of crushing the waste to obtain powder specifically includes crushing the waste in at least one of the following ways: ball milling, grinding, or crushing.

[0041] Specifically, waste materials such as glucose, fructose, cellulose, lignin, 5-hydroxymethylfurfural, and straw may not be fine powders, but may be clumped or still in their original state like straw. In this case, they need to be crushed to form the required powder. During the crushing process, at least one of the following methods can be selected: ball milling, grinding, or crushing. For example, crushing can be performed first, followed by two ball millings or two grindings, with each ball milling or grinding session lasting 20 minutes.

[0042] Example 2

[0043] This invention provides graphene-like ultrathin nitrogen-doped carbon nanosheets, prepared by the method described in Example 1. Those skilled in the art will understand that these graphene-like ultrathin nitrogen-doped carbon nanosheets are obtained by pulverizing any one of the following waste materials: glucose, fructose, cellulose, lignin, 5-hydroxymethylfurfural, and straw. The obtained powder is dissolved in a urea aqueous solution, stirred and dried, and then pyrolyzed at 300–900°C under an argon atmosphere to obtain a black solid. The obtained black solid is then dispersed in water to wash away unreacted substances. The solid is then filtered, collected, and dried to obtain the final product. This method ensures that the graphene-like ultrathin nitrogen-doped carbon nanosheets are free of metal dopant and possess the advantage of effectively catalyzing the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid in electrocatalytic reactions. It should be noted that the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 2 are prepared according to the method described in Example 1. Therefore, the performance principle of these graphene-like ultrathin nitrogen-doped carbon nanosheets will not be elaborated here; for details not described herein, please refer to Example 1.

[0044] Example 3

[0045] Embodiment 3 of this invention provides an application of graphene-like ultrathin nitrogen-doped carbon nanosheets, specifically including: using porous nickel foam-supported graphene-like ultrathin nitrogen-doped carbon nanosheets as a working electrode to electrocatalyze the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. The graphene-like ultrathin nitrogen-doped carbon nanosheets are the same as those described in Embodiment 2. It should be noted that the graphene-like ultrathin nitrogen-doped carbon nanosheets in Embodiment 2 were prepared according to the preparation method described in Embodiment 1.

[0046] Compared with the prior art, the method for preparing graphene-like ultrathin nitrogen-doped carbon nanosheets provided in Embodiment 1 of the present invention has the following advantages: When the graphene-like ultrathin nitrogen-doped carbon nanosheets prepared by the present invention are applied to electrocatalytic reactions, they can effectively catalyze the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, with good electrocatalytic activity and good catalytic conversion effect, and the yield of 2,5-furandicarboxylic acid can reach 80.47%.

[0047] To further illustrate the technical solution of this application and support the technical problem to be solved by this application, specific examples of the preparation method are given below, such as Examples 1 to 6.

[0048] Example 1

[0049] Grind 10g of glucose waste twice, 20 minutes each time, to obtain glucose powder;

[0050] 1g of the obtained glucose powder was dissolved in 20mL of urea aqueous solution with a concentration of 0.25g / mL, stirred at 400 rpm for 60 minutes, and then dried at 80℃ for 16 hours to obtain pretreated glucose powder.

[0051] The pretreated glucose powder was placed in a tube furnace, and argon gas was continuously introduced into the tube furnace at a flow rate of 100 mL / min. At the same time, the temperature was increased to 900℃ at a rate of 1℃ / min and held at that temperature for 60 minutes to obtain a black solid.

[0052] The obtained black solid was dispersed in water and sonicated for 60 minutes at an ultrasonic power of 250W. The solid was then filtered through a 0.45-micron pore size filter membrane and collected. The collected solid was then dried at 50°C for 16 hours to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets.

[0053] Example 2

[0054] Grind 10g of fructose waste twice, 20 minutes each time, to obtain fructose powder;

[0055] 1g of the obtained fructose powder was dissolved in 20mL of urea aqueous solution with a concentration of 0.25g / mL, stirred at 400 rpm for 60 minutes, and then dried at 80℃ for 16 hours to obtain pretreated fructose powder.

[0056] The pretreated fructose powder was placed in a tube furnace, and argon gas was continuously introduced into the tube furnace at a flow rate of 100 mL / min. At the same time, the temperature was increased to 900℃ at a rate of 1℃ / min and held at that temperature for 60 minutes to obtain a black solid.

[0057] The obtained black solid was dispersed in water and sonicated for 60 minutes at an ultrasonic power of 250W. The solid was then filtered through a 0.45-micron pore size filter membrane and collected. The collected solid was then dried at 50°C for 16 hours to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets.

[0058] Example 3

[0059] 10g of lignin waste was ground twice, 20 minutes each time, to obtain lignin powder;

[0060] 1g of the obtained lignin powder was dissolved in 20mL of urea aqueous solution with a concentration of 0.25g / mL, stirred at 400 rpm for 60 minutes, and then dried at 80℃ for 16 hours to obtain pretreated lignin powder.

[0061] The pretreated lignin powder was placed in a tube furnace, and argon gas was continuously introduced into the tube furnace at a flow rate of 100 mL / min. At the same time, the temperature was increased to 300℃ at a rate of 1℃ / min and held at the temperature for 60 minutes to obtain a black solid.

[0062] The obtained black solid was dispersed in water and sonicated for 60 minutes at an ultrasonic power of 250W. The solid was then filtered through a 0.45-micron pore size filter membrane and collected. The collected solid was then dried at 50°C for 16 hours to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets.

[0063] Example 4

[0064] Grind 10g of cellulose waste twice, 20 minutes each time, to obtain cellulose powder;

[0065] 1g of the obtained cellulose powder was dissolved in 20mL of urea aqueous solution with a concentration of 0.25g / mL, stirred at 400 rpm for 60 minutes, and then dried at 80℃ for 16 hours to obtain pretreated cellulose powder.

[0066] The pretreated cellulose powder was placed in a tube furnace, and argon gas was continuously introduced into the tube furnace at a flow rate of 100 mL / min. At the same time, the temperature was increased to 600℃ at a rate of 1℃ / min and held at the temperature for 60 minutes to obtain a black solid.

[0067] The obtained black solid was dispersed in water and sonicated for 60 minutes at an ultrasonic power of 250W. The solid was then filtered through a 0.45-micron pore size filter membrane and collected. The collected solid was then dried at 50°C for 16 hours to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets.

[0068] Example 5

[0069] 10g of 5-hydroxymethylfurfural waste was ground twice, 20 minutes each time, to obtain 5-hydroxymethylfurfural powder;

[0070] 1g of the obtained 5-hydroxymethylfurfural powder was dissolved in 20mL of urea aqueous solution with a concentration of 0.25g / mL, stirred at 400 rpm for 60 minutes, and then dried at 80℃ for 16 hours to obtain pretreated 5-hydroxymethylfurfural powder.

[0071] The pretreated 5-hydroxymethylfurfural powder was placed in a tube furnace, and argon gas was continuously introduced into the tube furnace at a flow rate of 100 mL / min. At the same time, the temperature was increased to 900℃ at a rate of 1℃ / min and held at the temperature for 60 minutes to obtain a black solid.

[0072] The obtained black solid was dispersed in water and sonicated for 60 minutes at an ultrasonic power of 250W. The solid was then filtered through a 0.45-micron pore size filter membrane and collected. The collected solid was then dried at 50°C for 16 hours to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets.

[0073] Example 6

[0074] Grind 10g of straw waste twice, 20 minutes each time, to obtain straw powder;

[0075] 1g of the obtained straw powder was dissolved in 20mL of urea aqueous solution with a concentration of 0.25g / mL, stirred at 400 rpm for 60 minutes, and then dried at 80℃ for 16 hours to obtain pretreated straw powder.

[0076] The pretreated straw powder was placed in a tube furnace, and argon gas was continuously introduced into the tube furnace at a flow rate of 100 mL / min. At the same time, the temperature was increased to 900℃ at a rate of 1℃ / min and held at that temperature for 60 minutes to obtain a black solid.

[0077] The obtained black solid was dispersed in water and sonicated for 60 minutes at an ultrasonic power of 250W. The solid was then filtered through a 0.45-micron pore size filter membrane and collected. The collected solid was then dried at 50°C for 16 hours to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets.

[0078] The applications and performance tests of the graphene-like ultrathin nitrogen-doped carbon nanosheets prepared by Examples 1-6 are as follows:

[0079] Application in electrocatalytic reactions: Graphene-like ultrathin nitrogen-doped carbon nanosheets prepared in Examples 1-6 were obtained using conventional methods by loading porous nickel foam onto these nanosheets. These nanosheets were labeled as Application Examples 1-6 in sequence. Electrocatalytic reaction tests were then conducted. The test steps were as follows: a three-electrode system was used for catalytic oxidation in an H-type electrolytic cell. The porous nickel foam-loaded graphene-like ultrathin nitrogen-doped carbon nanosheets were used as the working electrode, Hg / HgO as the reference electrode, and platinum wire as the counter electrode. In the cathodic electrolysis chamber, 10 mL of a 1 mol / L potassium hydroxide aqueous solution was used as the cathodic electrolyte. In the anodic electrolysis chamber, 12.6 mg of 5-hydroxymethylfurfural was dissolved in 10 mL of a 1 mol / L potassium hydroxide aqueous solution as the anodic electrolyte. An electrocatalytic reactor was constructed using the aforementioned working electrode, reference electrode, counter electrode, cathode electrolyte, and anolyte. The anolyte was then continuously stirred at 400 rpm in the anolyte chamber. During stirring, a constant voltage was applied to the electrocatalytic reactor. For example, the constant voltage applied to the electrocatalytic reactors using Application Examples 1-4 as working electrodes was 1.458 V, and for example, the constant voltage applied to the electrocatalytic reactors using Application Examples 5-6 as working electrodes was 1.373 V. After applying the constant voltage, an electrocatalytic reaction occurred in the electrocatalytic reactor. The reaction continued until the anolyte turned reddish-brown. Then, the voltage was stopped and stirring was ceased. The anolyte after the electrocatalytic reaction was collected, and the content of 2,5-furandicarboxylic acid produced was detected by high-performance liquid chromatography (HPLC). The yield of 2,5-furandicarboxylic acid in the electrocatalytic reaction was obtained, and the results are shown in Table 1.

[0080] Table 1. Yield of 2,5-furandicarboxylic acid in the electrocatalytic reaction.

[0081] Example Yield of 2,5-furandicarboxylic acid Example 1 77.23％ Example 2 78.09％ Example 3 53.59％ Example 4 46.63％ Example 5 80.47％ Example 6 75.73％

[0082] As shown in Table 1, the graphene-like ultrathin nitrogen-doped carbon nanosheets prepared from waste materials and loaded onto porous nickel foam as the working electrode in this invention exhibit a yield of 46.63%–80.47% for the electrocatalytic conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. Specifically, Example 5, using graphene-like ultrathin nitrogen-doped carbon nanosheets prepared from 5-hydroxymethylfurfural and loaded onto porous nickel foam as the working electrode, achieved the highest yield of 2,5-furandicarboxylic acid at 80.47%. Example 2, using graphene-like ultrathin nitrogen-doped carbon nanosheets prepared from fructose and loaded onto porous nickel foam as the working electrode, yielded 78.09% of 2,5-furandicarboxylic acid. Example 1, using graphene-like ultrathin nitrogen-doped carbon nanosheets prepared from glucose and loaded onto porous nickel foam as the working electrode, achieved a yield of 77.23% of 2,5-furandicarboxylic acid.

[0083] Linear scanning voltammetry (LCVFC) testing during the electrocatalytic process: Ultrathin nitrogen-doped carbon nanosheets similar to graphene, prepared in Examples 1-2 and 5 using porous nickel foam as the loading agent were obtained. The electrocatalytic reaction was then tested. The testing steps were as follows: a three-electrode system was used for catalytic oxidation in an H-type electrolytic cell; the ultrathin nitrogen-doped carbon nanosheets were used as the working electrode, Hg / HgO as the reference electrode, and platinum wire as the counter electrode. In the cathode electrolysis chamber, 10 mL of a 1 mol / L potassium hydroxide aqueous solution was used as the cathode electrolyte. In the anolyte electrolysis chamber, the reaction was controlled by whether or not 5-hydroxymethylfurfural was added to the 1 mol / L potassium hydroxide aqueous solution. Examples 1-2, Example 5, and Comparative Examples 1-2 and Comparative Example 5 are provided. In Examples 1-2 and Example 5, 12.6 mg of 5-hydroxymethylfurfural was dissolved in 10 mL of a 1 mol / L potassium hydroxide aqueous solution as the anolyte. In Comparative Examples 1-2 and Example 5, a 1 mol / L potassium hydroxide aqueous solution was used as the anolyte. An electrocatalytic reactor was constructed using the aforementioned working electrode, reference electrode, counter electrode, cathode electrolyte, and anolyte. The anolyte was then continuously stirred at 400 rpm in the anolyte chamber. During stirring, a constant voltage from 1.2 to 1.55 V was applied to the electrocatalytic reactor. The current variation with voltage was measured and recorded, and a linear sweep voltammetric curve of the electrocatalytic process was plotted. The results are shown in [Figure number missing]. Figures 1 to 3 .

[0084] Raman characterization: The graphene-like ultrathin nitrogen-doped carbon nanosheets prepared in Examples 1-2 and Example 5 were characterized using Raman spectroscopy. The characterization results are shown in the figure. Figures 4-6 .

[0085] XPS characterization: The graphene-like ultrathin nitrogen-doped carbon nanosheets prepared in Examples 1-2 and Example 5 were characterized using X-ray photoelectron spectroscopy. The characterization results are shown in [Figure 1]. Figures 7-9 .

[0086] TEM characterization: The graphene-like ultrathin nitrogen-doped carbon nanosheets prepared in Example 5 were characterized using transmission electron microscopy. The characterization results are shown in [Figure number missing]. Figures 10-11 .

[0087] XRD characterization: The graphene-like ultrathin nitrogen-doped carbon nanosheets prepared in Examples 1-5 were characterized using X-ray diffraction analysis. The characterization results are shown in the figure. Figure 12 .

[0088] AFM characterization: The graphene-like ultrathin nitrogen-doped carbon nanosheets prepared in Example 5 were characterized using atomic force microscopy. The characterization results are shown in [Figure number missing]. Figure 13 .

[0089] Through the Figures 1 to 3 The linear sweep voltammetry analysis shows that when the maximum current peak occurs in Example 5, the corresponding constant voltage applied is less than that applied when the maximum current peak occurs in Examples 1 and 2. Furthermore, the maximum current peak of Example 5 is greater than that of Examples 1 and 2. This indicates that Example 5 consumes less energy in the electrocatalytic reaction than Examples 1 and 2, and that the electrocatalytic activity of Example 5 is higher than that of Examples 1 and 2.

[0090] Through the Figures 4-6 Raman plot analysis shows that Examples 1-2 and Example 5 are all at 1580cm. -1 Nearby and 1350cm -1 Characteristic peaks of graphene were detected nearby, indicating that graphene was successfully prepared in the graphene-like ultrathin nitrogen-doped carbon nanosheets of Examples 1-2 and 5.

[0091] Through the Figures 7-9 XPS plot analysis shows that the graphene in the graphene-like ultrathin nitrogen-doped carbon nanosheets prepared in Examples 1-2 and Example 5 contains three elements: C, N, and O. The N1s plot shows that the peak value near 400 eV in Example 5 is higher than that in Examples 1-2, indicating that the graphene N doping amount in the graphene-like ultrathin nitrogen-doped carbon nanosheets in Example 5 is higher than that in the graphene-like ultrathin nitrogen-doped carbon nanosheets in Examples 1-2.

[0092] Through the Figures 10-11 TEM image analysis shows that the graphene-like ultrathin nitrogen-doped carbon nanosheets prepared in Example 5 are thin sheets containing graphene sheet structures, and N atoms were successfully doped.

[0093] Through the Figure 12XRD analysis revealed an asymmetric peak (002) and a weak peak (100) on the spectrum. The appearance of these two characteristic peaks is consistent with the structural characteristics of graphene crystals, indicating that the graphene synthesis in the graphene-like ultrathin nitrogen-doped carbon nanosheets prepared in Examples 1-5 was good.

[0094] Through the Figure 13 AFM plot analysis shows that the graphene-like ultrathin nitrogen-doped carbon nanosheets prepared by 5-hydroxymethylfurfural in Example 5 are very thin, with a thickness of only 1.5 nm.

[0095] In summary, this invention utilizes waste materials such as glucose, fructose, cellulose, lignin, 5-hydroxymethylfurfural, and straw to prepare graphene-like ultrathin nitrogen-doped carbon nanosheets. The preparation method is simple, consumes little energy, and can be mass-produced. The resulting graphene-like ultrathin nitrogen-doped carbon nanosheets do not contain metal atoms, are thin, and successfully doped with nitrogen atoms. In the electrocatalytic reaction, they exhibit good conversion rates of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid.

[0096] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. The application of graphene-like ultrathin nitrogen-doped carbon nanosheets, characterized by: A graphene-like ultrathin nitrogen-doped carbon nanosheet is used as the working electrode to electrocatalyze the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. The preparation method of the graphene-like ultrathin nitrogen-doped carbon nanosheet includes: S1. Crush the waste material to obtain powder; S2. The obtained powder is dissolved in a urea aqueous solution, and then stirred and dried to obtain pretreated powder. S3. Pyrolyze the obtained pretreated powder to obtain a black solid; S4. The obtained black solid is dispersed in water and then subjected to ultrasonication, filtration and drying to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets. The process of pyrolyzing the pretreated powder to obtain a black solid specifically includes: placing the pretreated powder into a tube furnace, continuously introducing argon gas into the tube furnace at a flow rate of 80-120 mL / min, simultaneously raising the temperature to 300-900℃ at a rate of 1-5℃ / min, and holding the temperature for pyrolysis for 45-90 minutes to obtain a black solid. The process of dispersing the obtained black solid in water and sequentially subjecting it to ultrasonication, filtration, and drying to obtain graphene-like ultrathin nitrogen-doped carbon nanosheets specifically includes: the ultrasonic power of the ultrasonication is 200~300W, the ultrasonication time is 45~90 minutes; the pore size of the filter membrane is 0.22~0.8 micrometers; the drying temperature is 45~60℃, and the drying time is 10~18 hours.

2. The application of the graphene-like ultrathin nitrogen-doped carbon nanosheets as described in claim 1, characterized in that: The waste includes any one of glucose, fructose, cellulose, lignin, 5-hydroxymethylfurfural, and straw.

3. The application of the graphene-like ultrathin nitrogen-doped carbon nanosheets as described in claim 2, characterized in that, The process of dissolving the obtained powder in a urea aqueous solution and then sequentially stirring and drying to obtain pretreated powder specifically includes: The mass ratio of the powder to the urea aqueous solution is 0.5~1.5:15~30; the concentration of the urea aqueous solution is 0.15~0.35g / mL; the stirring speed is 300~500 rpm; the stirring time is 45~90 minutes; the drying temperature is 45~90℃; and the drying time is 10~18 hours.

4. The application of the graphene-like ultrathin nitrogen-doped carbon nanosheets as described in claim 3, characterized in that, The process of crushing waste to obtain powder specifically includes: The waste is crushed in at least one of the following ways: ball milling, grinding, or crushing.

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