Preparation method of nitrogen-doped juncus roemerianus spherical carbon material

Abstract

The invention relates to a preparation method of a nitrogen-doped juncus roemerianus spherical carbon material, which comprises the following steps: (1) drying juncus roemerianus in the sun, peeling, pulling cores, chopping, puffing, and crushing to obtain puffed juncus roemerianus powder; (2) adding the puffed juncus roemerianus powder into an acidic solution, mixing and stirring, putting into a closed hydrothermal kettle, carrying out hydrothermal activation reaction, cooling to room temperature, carrying out centrifugal separation, and washing to be neutral, so as to obtain a prefabricated juncus roemerianus carbon carrier; and (3) mixing the prefabricated juncus roemerianus carbon carrier, an organic nitrogen source or the nitrogen-doped prepolymer and a shaping agent, performing protective calcination in an inert atmosphere, soaking in an acid solution, performing suction filtration and washing until the pH value of supernatant liquid is neutral, and drying to obtain the nitrogen-doped juncus roemerianus spherical carbon material. The carbon material obtained through the method is stable in spherical morphology characteristic, controllable in specific surface area and pore size distribution, simple in process, environmentally friendly, rich in raw material source, low in cost and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to a method for preparing carbon materials, specifically a method for preparing nitrogen-doped rush spherical carbon materials. Background Technology

[0002] Carbon materials are key materials in energy, catalysis, and environmental fields, and their performance is highly dependent on their microstructure and chemical composition. Carbon nanospheres are an important type of carbon nanomaterial, widely used in energy storage, catalysis, and adsorption due to their unique spherical structure, high specific surface area, and tunable pore structure. Controlling the morphology of carbon materials and heteroatom doping are two core strategies for improving their performance. Nitrogen doping can effectively alter the electron-donating properties, surface polarity, and chemical stability of carbon materials, thereby significantly enhancing their catalytic activity and charge transport capabilities in electrochemical reactions. Simultaneously, constructing a spherical morphology helps to obtain higher packing density, good fluidity, and structural stability, making them ideal as electrode materials or catalyst supports, with potential advantages in separation adsorption, electrochemistry, and catalytic support engineering.

[0003] As a natural biomass material, rush pith possesses a unique interconnected pore structure, theoretically making it an ideal porous carbon precursor. However, existing technologies for directly carbonizing rush pith typically yield irregular blocky or fibrous carbon with uncontrollable morphology, limited specific surface area, and difficulty in achieving effective nitrogen doping. Current technological approaches face significant challenges in directly converting fibrous raw materials like rush pith into spherical carbon materials with uniform morphology and good dispersion. CN 118976525A discloses a method for preparing a porous nitrogen-doped carbon-supported noble metal catalyst, but its support preparation process is complex, and the carbon source remains limited to non-renewable petrochemical products. CN103787303A discloses a method for in-situ conversion of natural biomass to prepare porous carbon with hierarchical pore network structure, and CN 109485042A discloses a method for preparing activated carbon material based on the interconnected porous structure of Tetrapanax papyriferus / Juncus effusus. However, the preparation methods disclosed by both methods synthesize activated carbon materials with porous network structure, and do not involve the regulation of the morphology and structural properties of activated carbon by nitrogen doping.

[0004] In summary, there is an urgent need to develop a method that can use natural, low-cost rush pith as raw material and achieve spherical morphology construction and efficient nitrogen doping in one step through a simple and environmentally friendly process. This is crucial for obtaining high-performance, low-cost advanced carbon materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for preparing nitrogen-doped rush spherical carbon materials with stable spherical morphology, controllable specific surface area and pore size distribution, simple process, environmentally friendly, abundant raw material sources, low cost, and suitable for large-scale production.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: A method for preparing nitrogen-doped rush spherical carbon material, comprising the following steps: (1) Dry the rush pith, remove the skin and core, chop it, puff it up, and then pulverize it to obtain puffed rush pith powder. (2) Add the puffed rush powder obtained in step (1) to an acidic solution, mix and stir, place in a sealed hydrothermal reactor, carry out hydrothermal activation reaction, cool to room temperature, centrifuge and wash until neutral to obtain pre-made rush carbon carrier. (3) After mixing the pre-made rush carbon carrier, organic nitrogen source or nitrogen-doped prepolymer obtained in step (2) with the plasticizer, the mixture is calcined under an inert atmosphere, then soaked in an acidic solution, filtered and washed until the pH of the supernatant is neutral, and dried to obtain nitrogen-doped rush spherical carbon material.

[0007] The inventive concept and principle of obtaining spherical carbon materials in this invention are analyzed as follows: In the method of this invention, the core mechanism for forming carbon nanospheres with uniform morphology may mainly come from the structural characteristics of expanded rush pith after expansion treatment and the combined effect of subsequent hydrothermal treatment and nitrogen doping treatment: 1) Self-assembly and surface interaction: that is, carbon precursor molecules or nanounits spontaneously aggregate and assemble into spherical structures with lower energy through intermolecular forces, hydrogen bonds or hydrophobic interactions; because rush pith contains a certain amount of sugar (such as glucose or sucrose), rush pith first undergoes a series of decomposition phenomena in the expansion reaction of step (1) and the hydrothermal activation reaction of step (2), and then the oligosaccharide molecules undergo dehydration to cause cross-linking reaction, forming small molecules or polymers. Therefore, the formation and growth of carbon nanospheres may conform to Lamer model; or in step (1) other macromolecules are formed, and then the formed nucleus is in the solution in step (2). The aromatic polymer generated by glucose polymerization grows isotropically through π-π stacking and other effects to form a crystal nucleus. The crystal nucleus continuously absorbs surrounding small molecules and grows, thereby self-assembling into carbon nanospheres; 2) Nitrogen doping mainly promotes the formation of spherical nanostructures of carbon materials through multiple synergistic mechanisms. Its main role comes from the fact that nitrogen-containing precursors can self-assemble into spherical micelles in solution as self-templates; the crosslinking points provided by nitrogen atoms can stabilize the initial morphology and inhibit structural collapse during carbonization; at the same time, the surface charge effect can prevent particle aggregation, ultimately leading to a more thermodynamically stable and morphologically regular spherical structure. In summary, the entire formation process of carbon nanospheres prepared by the method of the present invention is greatly affected by reaction kinetics. By precisely controlling parameters such as temperature and time, the structure and morphology of the final product can be regulated to prepare monodisperse carbon nanospheres of uniform size.

[0008] Preferably, in step (1), the puffing temperature is 110–150 °C (more preferably 110–140 °C), the feeding speed is 0.01–0.10 m / s (more preferably 0.02–0.08 m / s), and the screw rotation speed is 120–200 r / min (more preferably 140–180 r / min). The puffing of rush pith is an instantaneous process in which the internal moisture of the material undergoes "flash evaporation" under the combined action of high temperature, high pressure, and high shear force. Inside the extruder, the material undergoes a series of processes: conditioning → extrusion, heating and pressurization → instantaneous release. Conditioning involves mixing and homogenizing the material with water derived from the molecular structure of rush pith, preparing it for subsequent reactions. Extrusion and heating / pressurization occur when the material is compressed under the propulsion and shearing action of the screw, rapidly heating it due to mechanical energy and external heating, creating a high-temperature, high-pressure state where the water is superheated but not boiling. Instantaneous release occurs when the material is extruded through the die under high pressure, causing the pressure to drop sharply to atmospheric pressure. The superheated water vaporizes instantly (flash evaporation), generating tremendous expansion force, thus destroying the dense structure of the material and forming a porous, puffed structure. This process simultaneously achieves physical restructuring of the material and potential chemical changes such as partial starch gelatinization. Since the puffing effect is highly dependent on the precise control of process parameters, these parameters are interrelated and jointly determine the "quality" and "quantity" of the puffing process. A twin-screw extruder is preferred.

[0009] Preferably, in step (1), the material is pulverized to pass through a 100-mesh sieve. This ensures that the particle size of the pulverized rush is less than 150 μm. At this particle size, the rush has a large specific surface area, its fiber structure is destroyed, its crystallinity is reduced, and its mass transfer efficiency is improved, thus achieving material homogenization.

[0010] Preferably, in step (2), the mass-to-volume ratio of the rush pith powder to the acidic solution is 1:1 to 20 (more preferably 1:5 to 20). A suitable amount of acid can disrupt the crystal structure of lignocellulose in the rush pith, hydrolyzing the macromolecular polymers (polysaccharides) into usable small molecule monomers (monosaccharides), and further chemically transforming them into a looser, more porous form.

[0011] Preferably, in step (2), the concentration of the acidic solution is 0.1–2.0 mol / L (more preferably 1.0–2.0 mol / L). An acid of suitable concentration breaks glycosidic bonds, "disassembling" biomass macromolecules into fermentable sugars and platform chemicals, while simultaneously achieving an optimal balance between saccharification efficiency and sugar degradation loss.

[0012] Preferably, in step (2), the solute in the acidic solution includes one or more of formic acid, acetic acid, hydrochloric acid, nitric acid or sulfuric acid.

[0013] Preferably, in step (2), the mixing and stirring time is 2 to 4 hours.

[0014] Preferably, in step (2), the volume of the acidic solution is equivalent to 10-60% (more preferably 30-50%) of the volume of the sealed hydrothermal reactor.

[0015] Preferably, in step (2), the temperature of the hydrothermal activation reaction is 80–200 °C, and the time is 1–6 h. The core of acid hydrothermal activation is to maximize the "deconstruction" of lignin by precisely controlling parameters such as temperature, time, and acid concentration, generating condensed lignin with a more complex structure, larger molecular weight, and greater hydrophobicity, and breaking through the fiber structure, removing most of the hemicellulose, destroying the cellulose crystallization zone, greatly increasing the specific surface area and porosity, and making it more loose and fluffy.

[0016] Preferably, in step (3), the mass ratio of the pre-prepared rush pith carbon carrier, organic nitrogen source or nitrogen-doped prepolymer to the plasticizer is 1:1 to 10:1 to 10 (more preferably 1:1 to 8:1 to 8, and even more preferably 1:1 to 4:1 to 4). The organic nitrogen source can be directly or first prepared as a nitrogen-doped prepolymer before being mixed and calcined with other raw materials. In the controllable synthesis of spherical nitrogen-doped carbon nanomaterials, the synergistic regulation of the pre-prepared rush pith carbon carrier, organic nitrogen source or nitrogen-doped prepolymer, and plasticizer is the key to achieving material structure design and performance optimization. The carbon support forms the basic framework of the material, and its dosage directly affects the integrity and yield of the spherical structure. The nitrogen source introduces catalytic active sites through doping, and its dosage needs to be precisely balanced. Too little nitrogen results in insufficient activity, while too much nitrogen may damage the carbon framework. The plasticizer guides the formation of regular spherical and porous structures, and its dosage directly regulates the pore size distribution and specific surface area. The three work together to form an ordered porous structure, with the plasticizer guiding the formation of an ordered porous structure, the carbon support precisely replicating and supporting this structure, and the nitrogen source achieving efficient doping without damaging the framework. Together, they determine the final morphology, pore structure, and surface chemical properties of the material. Any imbalance in the proportion of any component will break this delicate balance, leading to morphological collapse, pore blockage, or a reduction in active sites.

[0017] Preferably, in step (3), the shaping agent includes one or more of MgCl2, CaCl2, KOH, or ZnCl2. The shaping agent reacts with the pre-made rush pith carbon carrier, nitrogen source, or nitrogen-doped prepolymer at high temperature, and through etching, pore formation, etc., greatly expands the specific surface area, controls the pore size distribution, and forms a rich pore structure.

[0018] Preferably, in step (3), the protective calcination refers to: heating to 200–800 °C (more preferably 300–600 °C) at a rate of 1–10 °C / min (more preferably 4–10 °C / min), followed by protective calcination for 2–10 h (more preferably 3–6 h). The calcination process is a crucial thermochemical transformation stage for the formation of nitrogen-doped rush carbon nanospheres. Precise control of temperature and heating rate is key to regulating the composition and properties of nitrogen-doped rush carbon nanospheres. During calcination, the organic components of rush first undergo pyrolysis and carbonization, non-carbon elements escape in the form of volatile small molecules, and the remaining carbon atoms are reconstructed to form sp... 2 The material exhibits a hybrid graphitic carbon skeleton. Simultaneously, the nitrogen source undergoes a complex evolution: some nitrogen-containing groups are embedded into the carbon skeleton as dopants, forming active sites such as pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen; while unstable nitrogen species are lost due to thermal decomposition. Accompanying the above reactions, the escape of volatiles creates abundant micropores and mesopores in the material, while the graphitization rearrangement and shrinkage of the carbon skeleton at high temperatures may also lead to the collapse of some pores. This series of transformations collectively determines the final carbon skeleton structure, nitrogen doping state, and porous characteristics of the material.

[0019] Preferably, in step (3), the inert atmosphere includes one or more of nitrogen, argon, or helium. The inert atmosphere used in the method of this invention is a high-purity atmosphere with a purity ≥ 99.999%.

[0020] Preferably, in step (3), the concentration of the acidic solution is 0.1–2.0 mol / L (more preferably 1.0–2.0 mol / L). Acid washing of carbon nanospheres is a multifunctional refining process, mainly used to remove metals and amorphous carbon, improve dispersibility, and at a suitable concentration, it is more beneficial to finely control the structure of nitrogen-doped rush pith carbon nanospheres by etching and pore formation.

[0021] Preferably, in step (3), the solute in the acidic solution includes one or more of formic acid, acetic acid, hydrochloric acid, nitric acid or sulfuric acid.

[0022] Preferably, in step (3), the immersion treatment is carried out at a temperature of 20–60 °C (more preferably 30–50 °C) for 1–10 h (more preferably 2–6 h) for a duration of 1–10 h. Immersion at suitable temperature and time is beneficial for the deep purification of carbon nanospheres. Mild acid treatment can create nanoscale depressions on the surface of carbon nanospheres, further increasing the specific surface area of ​​the spheres. This is beneficial for the construction of catalytic active centers as carriers for various catalysts, and can also remove unstable doping configurations, thus achieving "refinement" of the surface chemical composition of the material.

[0023] Preferably, in step (3), the nitrogen-doped prepolymer is prepared by placing an organic nitrogen source in an air atmosphere and calcining it with oxygen.

[0024] Preferably, the temperature of the aerobic calcination is 300–800 °C (more preferably 300–600 °C), and the time is 1–4 h (more preferably 1–3 h). Oxygen promotes crosslinking but accelerates nitrogen oxidation loss, and the degree of crosslinking of the prepolymer needs to be moderate to avoid melt collapse or insufficient pore structure during calcination. Therefore, it is necessary to control the appropriate temperature and time to obtain a suitable nitrogen-doped prepolymer.

[0025] Preferably, the organic nitrogen source includes one or more of urea, 2,2'-bipyridine, melamine, amino acids, imidazole, dicyandiamide, or 3-amino-1,2,4-triazole. Selecting a suitable nitrogen source is a crucial step in preparing high-performance nitrogen-doped rush carbon nanospheres, directly affecting the final nitrogen content, nitrogen species type, pore structure, and application performance of the carbon nanospheres.

[0026] The beneficial effects of the method of the present invention are as follows: (1) The nitrogen-doped rush spherical carbon material obtained by the method of the present invention has stable spherical morphology, with a particle size mainly of 100-200 nm and a specific surface area >600 m². 2 / g, pore volume > 3 cm³ 3 / g, the pore size distribution is mainly 3-10 nm, the average pore size is about 6 nm, and the specific surface area and pore size distribution are controllable; the nitrogen-doped rush spherical carbon material obtained by the method of the present invention has broad application prospects in separation adsorption, electrochemistry, catalytic support engineering and other fields. (2) The method of the present invention is simple, environmentally friendly, and has abundant raw material sources and low cost, making it suitable for large-scale production. Attached Figure Description

[0027] Figure 1 These are SEM images of the nitrogen-doped rush spherical carbon material obtained in Example 1 of this invention at different scales (wherein) Figure 1 (a) is the SEM image at a scale bar of 500 nm. Figure 1 (b) is the SEM image at a scale bar of 100 nm. Figure 2 These are TEM images of the nitrogen-doped rush spherical carbon material obtained in Example 1 of this invention at different scales (wherein) Figure 2 (a) is the TEM image at a scale bar of 200 nm. Figure 2 (b) is the TEM image at a scale bar of 10 nm. Figure 3 This is a particle size distribution diagram of the nitrogen-doped rush spherical carbon material obtained in Example 1 of the present invention; Figure 4 This is the XRD pattern of the nitrogen-doped rush spherical carbon material obtained in Example 1 of this invention; Figure 5This is the Raman spectrum of the nitrogen-doped rush spherical carbon material obtained in Example 1 of this invention; Figure 6 These are XPS spectra of different elements in the nitrogen-doped rush spherical carbon material obtained in Example 1 of this invention (wherein) Figure 6 (a) is the XPS full spectrum. Figure 6 (b) is the C 1s spectrum. Figure 6 (c) is the N 1s spectrum. Figure 6 (d) is the O1s spectrum. Figure 7 This is a nitrogen adsorption-desorption curve of the nitrogen-doped rush spherical carbon material obtained in Example 1 of the present invention; Figure 8 This is a pore size distribution diagram of the nitrogen-doped rush spherical carbon material obtained in Example 1 of the present invention; Figure 9 These are SEM images of the nitrogen-doped rush tubular carbon material obtained in Comparative Example 1 of this invention at different scales (wherein) Figure 9 (a) is the SEM image at a scale bar of 50 µm. Figure 9 (b) is the SEM image at a scale bar of 2 µm. Figure 10 These are SEM images of the nitrogen-doped rush cauliflower-like carbon material obtained in Comparative Example 2 of this invention at different scales (wherein) Figure 10 (a) is the SEM image at a scale bar of 500 nm. Figure 10 (b) is the SEM image at a scale bar of 100 nm. Figure 11 These are SEM images of the nitrogen-doped rush spherical and cauliflower-like hybrid carbon material obtained in Comparative Example 3 of this invention at different scales (wherein) Figure 11 (a) is the SEM image at a scale bar of 500 nm. Figure 11 (b) is the SEM image at a scale bar of 100 nm. Figure 12 These are SEM images of the nitrogen-doped irregular spherical carbon material from Juncus effusus obtained in Comparative Example 4 of this invention at different scales (wherein) Figure 12 (a) is the SEM image at a scale bar of 500 nm. Figure 12 (b) is the SEM image at a scale bar of 100 nm. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0029] The inert atmospheres used in the embodiments and comparative examples of this invention are all high-purity atmospheres with a purity of ≥99.999%; the raw materials or chemical reagents used in the embodiments and comparative examples of this invention, unless otherwise specified, are obtained through conventional commercial channels.

[0030] For the preparation method of nitrogen-doped prepolymer, refer to Example 1. 3-Amino-1,2,4-triazole was placed in an air atmosphere and calcined at 300°C for 2 hours to obtain a nitrogen-doped prepolymer.

[0031] For the preparation method of nitrogen-doped prepolymer, refer to Example 2. 2,2'-bipyridine was placed in an air atmosphere and calcined at 500°C for 2 hours to obtain a nitrogen-doped prepolymer.

[0032] For the preparation method of nitrogen-doped prepolymer, refer to Example 3. Urea was placed in an air atmosphere and calcined at 300°C for 2 hours to obtain a nitrogen-doped prepolymer.

[0033] Example 1: A method for preparing nitrogen-doped rush spherical carbon materials (1) The harvested rush pith is dried, peeled, cored, chopped, and placed in an extruder. It is then extruded at 110 ℃, with a feeding speed of 0.05 m / s and a screw speed of 150 r / min. After extrusion, it is pulverized to pass through a 100-mesh sieve to obtain extruded rush pith powder. (2) Add 4.0 g of puffed rush powder obtained in step (1) to 20.0 mL of 1.0 mol / L nitric acid solution, mix and stir for 2 h, place in a 50 mL sealed hydrothermal reactor, carry out hydrothermal activation reaction at 100 °C for 2 h, cool to room temperature, centrifuge and wash until neutral to obtain pre-prepared rush carbon carrier. (3) After mixing 1.0 g of pre-made rush carbon carrier obtained in step (2), 2.0 g of nitrogen-doped prepolymer obtained in Example 1 and 2.0 g of ZnCl2, the mixture was heated to 300 °C at a rate of 10 °C / min under a high-purity nitrogen atmosphere and then calcined for 3 h. The mixture was then placed in a 1.0 mol / L hydrochloric acid solution and soaked at 40 °C for 5 h. The mixture was then filtered and washed until the pH of the supernatant was neutral and dried to obtain nitrogen-doped rush spherical carbon material.

[0034] like Figure 1 As shown in (a) and (b), the nitrogen-doped rush spherical carbon material obtained in the embodiments of the present invention exhibits a neat spherical distribution with an average particle size of approximately 167 nm. The spheres have clear outlines and a small number of neatly distributed depressions on their surfaces. Figure 2 As shown in (a) and (b), the nitrogen-doped rush spherical carbon materials obtained in the embodiments of the present invention have a neat morphology and uniform structure, smooth and neat spherical surfaces, obvious stacking of spherical carbon materials, and clear gaps between spheres; as Figure 3 As shown, the particle size of the nitrogen-doped rush spherical carbon material obtained in the embodiments of the present invention exhibits a normal distribution, with an average particle size of approximately 154.25 ± 4.5 nm.

[0035] like Figure 4 As shown, the nitrogen-doped rush spherical carbon material obtained in the embodiments of the present invention is in 2 θ The presence of two broad diffraction peaks in the (002) and (101) planes of amorphous carbon at angles of 23° and 43° indicates the generation of numerous defect structures, making it suitable as an ideal support for catalysts.

[0036] like Figure 5 As shown, the nitrogen-doped rush spherical carbon material obtained in the embodiments of the present invention exhibits a thickness of ~1340 cm⁻¹. -1 sp 3 Type disordered carbon-related D bands and ~1580 cm -1 sp 2 Hybrid carbon-related G bands, their I D / I G The ratio of D-band intensity to G-band intensity is around 1.11, indicating that it has a large number of defects and disorder, which can provide ideal adsorption sites for loading other catalytically active molecules, making it suitable as an ideal support for catalysts.

[0037] like Figure 6 As shown in (a), the full spectrum reveals the characteristic peaks of C, N, and O in the nitrogen-doped rush spherical carbon material obtained in the embodiments of the present invention; as Figure 6 As shown in (b), the high-resolution spectrum of C1S can be deconvolved into three peaks located at 284.8 eV, 286.2 eV, and 288.8 eV, attached to CC, CN, and CO, respectively; Figure 6 As shown in (c), the high-resolution spectrum of N 1s can be deconvoluted into four characteristic peaks: pyridine-N (398.4 eV), pyrrole-N (399.5 eV), graphite-N (400.9 eV), and oxide-N (404.1 eV). It contains abundant pyridine (pyrrole) nitrogen functional groups that can interact with other coordinating ions to regulate the electronic structure and jointly construct the catalytic active center; such as Figure 6 As shown in (d), the high-resolution spectrum of O 1s can be deconvolved into two main peaks at 532.1 eV and 533.4 eV, corresponding to CO and C=O respectively. This indicates that there is still a certain amount of oxygen in the nitrogen-doped Juncus effusus spherical carbon material. This may be because a small amount of CO and C=O were not completely condensed and carbonized during the processing of Juncus effusus.

[0038] like Figure 7 , 8As shown, the adsorption-desorption curves of the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention exhibit a type I curve, indicating the presence of micropores and mesopores in the material. The sharp increase in nitrogen adsorption at relatively low pressure indicates the presence of micropores, and the hysteresis loop in the range of P / P0 = 0.8 to 1.0 indicates the presence of mesopores in the material. The nitrogen adsorption-desorption test also shows that the pore volume of the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention is 3.34 cm³. 3 / g, pore size distribution is mainly 3-10 nm, average pore size is about 6 nm, and specific surface area is 639.64 m². 2 / g.

[0039] Example 2: A method for preparing nitrogen-doped rush spherical carbon materials (1) The harvested rush pith is dried, peeled, cored, chopped, and placed in an extruder. It is then extruded at 120 °C, with a feeding speed of 0.05 m / s and a screw speed of 180 r / min. After extrusion, it is pulverized to pass through a 100-mesh sieve to obtain extruded rush pith powder. (2) Add 2.5 g of puffed rush powder obtained in step (1) to 25.0 mL of 1.0 mol / L acetic acid solution, mix and stir for 4 h, place in a 50 mL closed hydrothermal reactor, carry out hydrothermal activation reaction at 200 °C for 4 h, cool to room temperature, centrifuge and wash until neutral to obtain pre-prepared rush carbon carrier. (3) After mixing the 2.0 g pre-made rush carbon carrier obtained in step (2), the 4.0 g nitrogen-doped prepolymer obtained in Example 1, and 2.0 g MgCl2, the mixture was heated to 600 °C at a rate of 5 °C / min under a high-purity nitrogen atmosphere and then calcined for 3 h. The mixture was then placed in a 1.0 mol / L hydrochloric acid solution and soaked at 50 °C for 3 h. The mixture was then filtered and washed until the pH of the supernatant was neutral and dried to obtain nitrogen-doped rush spherical carbon material.

[0040] Upon testing, the nitrogen-doped rush spherical carbon material obtained in the embodiments of the present invention exhibits a neat spherical distribution with an average particle size of approximately 174 nm. The spheres have clear outlines and a small number of neatly distributed depressions on their surfaces.

[0041] Testing revealed that the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention exhibited a high performance at 2... θ The presence of two broad diffraction peaks in the (002) and (101) planes of amorphous carbon at angles of 23° and 43° indicates the generation of numerous defect structures, making it suitable as an ideal support for catalysts.

[0042] Testing revealed that the adsorption-desorption curves of the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention exhibited Type I curves, indicating the presence of micropores and mesopores in the material. The sharp increase in nitrogen adsorption at relatively low pressure indicates the presence of micropores, while the hysteresis loop within the P / P0 range of 0.8 to 1.0 indicates the presence of mesopores. The nitrogen adsorption-desorption test also showed that the pore volume of the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention is 3.22 cm³. 3 / g, pore size distribution is mainly 3-10nm, average pore size is about 6nm, specific surface area is 621.38 m² / g. 2 / g.

[0043] Example 3: A method for preparing nitrogen-doped rush spherical carbon materials (1) Same as step (1) in Example 1; (2) Add 2.0 g of puffed rush powder obtained in step (1) to 40.0 mL of 2.0 mol / L sulfuric acid solution, mix and stir for 3 h, place in 100 mL of closed hydrothermal reactor, carry out hydrothermal activation reaction at 200 °C for 6 h, cool to room temperature, centrifuge and wash until neutral to obtain pre-prepared rush carbon carrier; (3) After mixing 1.0 g of pre-made rush carbon carrier obtained in step (2), 1.0 g of nitrogen-doped prepolymer obtained in Example 2 and 2.0 g of KOH, the mixture was heated to 500 °C at a rate of 8 °C / min under a high-purity nitrogen atmosphere and then calcined for 4 h. The mixture was then placed in a 2.0 mol / L hydrochloric acid solution and soaked at 40 °C for 4 h. The mixture was then filtered and washed until the pH of the supernatant was neutral and dried to obtain nitrogen-doped rush spherical carbon material.

[0044] Upon testing, the nitrogen-doped rush spherical carbon material obtained in the embodiments of the present invention exhibits a neat spherical distribution with an average particle size of approximately 162 nm. The spherical surface has a clear outline and a small number of neatly distributed depressions.

[0045] Testing revealed that the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention exhibited a high performance at 2... θ The presence of two broad diffraction peaks in the (002) and (101) planes of amorphous carbon at angles of 23° and 43° indicates the generation of numerous defect structures, making it suitable as an ideal support for catalysts.

[0046] Testing revealed that the adsorption-desorption curves of the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention exhibited Type I curves, indicating the presence of micropores and mesopores in the material. The sharp increase in nitrogen adsorption at relatively low pressure indicates the presence of micropores, while the hysteresis loop within the P / P0 range of 0.8 to 1.0 indicates the presence of mesopores. The nitrogen adsorption-desorption test also showed that the pore volume of the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention is 3.41 cm³.3 / g, pore size distribution is mainly 3-10nm, average pore size is about 6nm, and specific surface area is 643.45 m². 2 / g.

[0047] Example 4: A method for preparing nitrogen-doped rush spherical carbon materials (1) Same as step (1) in Example 1; (2) Add 4.0 g of puffed rush powder obtained in step (1) to 20.0 mL of 1.0 mol / L nitric acid solution, mix and stir for 2 h, place in a 50 mL sealed hydrothermal reactor, carry out hydrothermal activation reaction at 120 °C for 2 h, cool to room temperature, centrifuge and wash until neutral to obtain pre-prepared rush carbon carrier. (3) After mixing 1.0 g of pre-made rush carbon carrier obtained in step (2), 2.0 g of nitrogen-doped prepolymer obtained in Reference Example 3 and 2.0 g of ZnCl2, the mixture was heated to 400 °C at a rate of 10 °C / min under a high-purity nitrogen atmosphere and then calcined for 5 h. The mixture was then placed in a 1.5 mol / L hydrochloric acid solution and soaked at 45 °C for 5 h. The mixture was then filtered and washed until the pH of the supernatant was neutral and dried to obtain nitrogen-doped rush spherical carbon material.

[0048] Upon testing, the nitrogen-doped rush spherical carbon material obtained in the embodiments of the present invention exhibits a neat spherical distribution with an average particle size of approximately 169 nm. The spheres have clear outlines and a small number of neatly distributed depressions on their surfaces.

[0049] Testing revealed that the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention exhibited a high performance at 2... θ The presence of two broad diffraction peaks in the (002) and (101) planes of amorphous carbon at angles of 23° and 43° indicates the generation of numerous defect structures, making it suitable as an ideal support for catalysts.

[0050] Testing revealed that the adsorption-desorption curves of the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention exhibited Type I curves, indicating the presence of micropores and mesopores in the material. The sharp increase in nitrogen adsorption at relatively low pressure indicates the presence of micropores, while the hysteresis loop within the P / P0 range of 0.8 to 1.0 indicates the presence of mesopores. The nitrogen adsorption-desorption test also showed that the pore volume of the nitrogen-doped rush spherical carbon material obtained in this embodiment of the invention is 3.30 cm³. 3 / g, pore size distribution is mainly 3-10nm, average pore size is about 6nm, and specific surface area is 636.27 m². 2 / g.

[0051] Comparative Example 1 The only difference between this comparative example and Example 1 is that in step (1), the harvested rush is dried, peeled, cored, chopped, and crushed to obtain rush powder; step (2) is deleted; in step (3), 1.0 g of pre-made rush carbon carrier is replaced with 1.0 g of rush powder obtained in step (1), and nitrogen-doped rush tubular carbon material is finally obtained. The rest is the same as in Example 1.

[0052] like Figure 9 As shown in (a) and (b), the nitrogen-doped rush carbon material obtained in the comparative example of the present invention has an irregular hollow tubular structure with a diameter of about 2 to 3 µm. The tube wall has irregular rough protrusions, and the tube opening has an irregular cross-section. This indicates that the lack of expansion process and hydrothermal activation conditions in the preparation process has a significant impact on the control of the spherical morphology of nitrogen-doped rush carbon material.

[0053] Comparative Example 2 The only difference between this comparative example and Example 1 is that step (2) is deleted; in step (3), 1.0 g of pre-made rush carbon carrier is replaced with 1.0 g of puffed rush powder obtained in step (1), and nitrogen-doped rush cauliflower-shaped carbon material is finally obtained. The rest is the same as in Example 1.

[0054] like Figure 10 As shown in (a) and (b), the nitrogen-doped rush carbon material obtained in the comparative example of the present invention has a cauliflower-shaped layered structure with an average particle size of about 320 nm and a petal thickness of about 1 to 3 nm; indicating that the lack of hydrothermal activation conditions during the preparation process has a significant impact on the control of the spherical morphology of the nitrogen-doped rush carbon material.

[0055] Comparative Example 3 The only difference between this comparative example and Example 1 is that in step (3), the 2.0 g nitrogen-doped prepolymer and 2.0 g ZnCl2 obtained in Example 1 are replaced with 4.0 g ZnCl2, ultimately yielding a nitrogen-doped bulrush-shaped and cauliflower-shaped hybrid carbon material. The rest is the same as in Example 1.

[0056] like Figure 11 As shown in (a) and (b), the nitrogen-doped rush carbon material obtained in the comparative example of the present invention has a mixed structure of spherical and cauliflower-shaped structures. The average particle size of the carbon nanospheres is about 170 nm, the average particle size of the cauliflower-shaped structure is about 320 nm, and the thickness of the cauliflower petals is about 1-3 nm. This indicates that the synergistic effect of the organic nitrogen source or nitrogen-doped prepolymer and the plasticizer has a significant impact on the control of the spherical morphology of the nitrogen-doped rush carbon material.

[0057] Comparative Example 4 The only difference between this comparative example and Example 1 is that in step (3), the 2.0 g nitrogen-doped prepolymer and 2.0 g ZnCl2 obtained in Example 1 are replaced with 4.0 g nitrogen-doped prepolymer obtained in Example 1, ultimately yielding nitrogen-doped Juncus effusus irregular spherical carbon material. The rest is the same as in Example 1.

[0058] like Figure 12 As shown in (a) and (b), the nitrogen-doped rush carbon material obtained in the comparative example of the present invention has an irregular spherical structure with an unclear spherical surface outline, an average particle size of about 170 nm, and very few neat depressions on the spherical surface; indicating that the synergistic effect of organic nitrogen source or nitrogen doping prepolymer and plasticizer has a significant impact on the control of spherical morphology of nitrogen-doped rush carbon material.

Claims

1. A method for preparing nitrogen-doped rush spherical carbon material, characterized in that, Includes the following steps: (1) Dry the rush pith, remove the skin and core, chop it, puff it up, and then crush it to obtain puffed rush pith powder. (2) Add the puffed rush powder obtained in step (1) to an acidic solution, mix and stir, place in a sealed hydrothermal reactor, carry out hydrothermal activation reaction, cool to room temperature, centrifuge and wash until neutral to obtain pre-made rush carbon carrier. (3) After mixing the pre-made rush carbon carrier, organic nitrogen source or nitrogen-doped prepolymer obtained in step (2) with the plasticizer, the mixture is calcined under an inert atmosphere, then soaked in an acidic solution, filtered and washed until the pH of the supernatant is neutral, and dried to obtain nitrogen-doped rush spherical carbon material.

2. The method for preparing nitrogen-doped rush spherical carbon material according to claim 1, characterized in that: In step (1), the puffing temperature is 110-150 ℃, the feeding speed is 0.01-0.10 m / s, and the screw rotation speed is 120-200 r / min; the crushing is passed through a 100-mesh sieve.

3. The method for preparing nitrogen-doped rush spherical carbon material according to claim 1 or 2, characterized in that: In step (2), the mass-to-volume ratio of the rush pith powder to the acidic solution (g / mL) is 1:1 to 20; the concentration of the acidic solution is 0.1 to 2.0 mol / L; the solute in the acidic solution includes one or more of formic acid, acetic acid, hydrochloric acid, nitric acid, or sulfuric acid; the mixing and stirring time is 2 to 4 hours; the volume of the acidic solution is equivalent to 10 to 60% of the volume of the sealed hydrothermal reactor; the temperature of the hydrothermal activation reaction is 80 to 200 °C, and the time is 1 to 6 hours.

4. The method for preparing nitrogen-doped rush spherical carbon material according to claim 1 or 2, characterized in that: In step (3), the mass ratio of the pre-made rush pith carbon carrier, organic nitrogen source or nitrogen-doped prepolymer to the plasticizer is 1:1 to 10:1 to 10; the plasticizer includes one or more of MgCl2, CaCl2, KOH or ZnCl2; the protective calcination refers to: heating to 200 to 800 ℃ at a rate of 1 to 10 ℃ / min and then performing protective calcination for 2 to 10 h; the inert atmosphere includes one or more of nitrogen, argon or helium; the concentration of the acidic solution is 0.1 to 2.0 mol / L; the solute in the acidic solution includes one or more of formic acid, acetic acid, hydrochloric acid, nitric acid or sulfuric acid; the immersion treatment temperature is 20 to 60 ℃ and the time is 1 to 10 h; the nitrogen-doped prepolymer is prepared by: placing the organic nitrogen source in an air atmosphere and performing aerobic calcination; the aerobic calcination temperature is 300 to 800 ℃ and the time is 1 to 4 h. h; The organic nitrogen source includes one or more of urea, 2,2'-bipyridine, melamine, amino acids, imidazole, dicyandiamide, or 3-amino-1,2,4-triazole.

5. The method for preparing nitrogen-doped rush spherical carbon material according to claim 3, characterized in that: In step (3), the mass ratio of the pre-made rush pith carbon carrier, organic nitrogen source or nitrogen-doped prepolymer to the plasticizer is 1:1 to 10:1 to 10; the plasticizer includes one or more of MgCl2, CaCl2, KOH or ZnCl2; the protective calcination refers to: heating to 200 to 800 ℃ at a rate of 1 to 10 ℃ / min and then performing protective calcination for 2 to 10 h; the inert atmosphere includes one or more of nitrogen, argon or helium; the concentration of the acidic solution is 0.1 to 2.0 mol / L; the solute in the acidic solution includes one or more of formic acid, acetic acid, hydrochloric acid, nitric acid or sulfuric acid; the immersion treatment temperature is 20 to 60 ℃ and the time is 1 to 10 h; the nitrogen-doped prepolymer is prepared by: placing the organic nitrogen source in an air atmosphere and performing aerobic calcination; the aerobic calcination temperature is 300 to 800 ℃ and the time is 1 to 4 h. h; The organic nitrogen source includes one or more of urea, 2,2'-bipyridine, melamine, amino acids, imidazole, dicyandiamide, or 3-amino-1,2,4-triazole.

Images