An ordered structure nitrogen-doped porous carbon material, a preparation method and application thereof
By adding urea to a chitin nanocrystal solution and controlling the drying conditions, an ordered nitrogen-doped porous carbon material was prepared. This solved the problem of disorder in the self-assembly of chitin nanocrystals, improved the specific surface area and electrochemical performance of the material, and made it suitable for adsorption and capacitor applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HARBIN UNIV OF SCI & TECH
- Filing Date
- 2024-05-23
- Publication Date
- 2026-04-17
AI Technical Summary
Existing technologies make it difficult to achieve ordered structures in nitrogen-doped porous carbon materials through the self-assembly of chitin nanocrystals, resulting in disordered material structures that affect their electrochemical and adsorption properties.
By adding urea to the chitin nanocrystal solution, adjusting the pH to the acidic range, and controlling the drying conditions and carbonization activation process, an ordered nitrogen-doped porous carbon material was prepared. This ensured that the self-assembly behavior of the chitin nanocrystals was not destroyed, and that urea was introduced in situ and formed an ordered structure through the carbonization activation process.
This improved the specific surface area and electrochemical performance of the material, enhanced the electrochemical activity of the capacitor, and strengthened the electrochemical and adsorption properties of the material.
Smart Images
Figure CN118373407B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of nitrogen-doped porous carbon materials, specifically relating to an ordered nitrogen-doped porous carbon material, its preparation method, and its application. Background Technology
[0002] The strong hydrogen bonds within and between chitin molecules make it insoluble in water, dilute acids, dilute alkalis, and common organic solvents. However, treatment of chitin with concentrated acid yields nanoparticles with diameters ranging from a few nanometers to tens of nanometers and lengths from hundreds of nanometers to micrometers. These nanoparticles have high crystallinity and are known as chitin nanocrystals. Chitin nanocrystals are excellent one-dimensional nanomaterials capable of spontaneous self-assembly. Self-assembly refers to the spontaneous organization of basic structural units into a periodic, ordered, and stable structure due to non-covalent interactions.
[0003] The pore structure and specific surface area of carbon materials are key indicators determining their electrochemical and adsorption properties. Existing chitin-based or chitin nanocrystal-based carbon materials are often prepared by blending chitin or chitin nanocrystals with other additives; therefore, the pore structure and specific surface area of these carbon materials are determined by the carbonization and activation processes. No technology or reports have been found regarding the preparation of nitrogen-doped porous carbon materials with ordered structures based on the self-assembly of chitin nanocrystals and the in-situ introduction of a nitrogen source.
[0004] Much research on the self-assembly of nanocrystals has focused on cellulose nanocrystals, attributed to the abundant hydroxyl functional groups on their surface. These functional groups contribute to their high surface potential and strong hydrogen bonding between nanocrystals, facilitating self-assembly. However, chitin nanocrystals have different molecular structures than cellulose nanocrystals, making their self-assembly more difficult. Furthermore, the introduction of doping components has a greater impact on the self-assembly process of chitin nanocrystals, leading to disordered structures in nitrogen-doped carbon materials based on their self-assembly behavior. Summary of the Invention
[0005] The purpose of this invention is to address the technical problem of disordered structure in existing nitrogen-doped porous carbon materials based on chitin nanocrystals, and to provide an ordered nitrogen-doped porous carbon material, its preparation method, and its applications.
[0006] The technical solution of the present invention is as follows:
[0007] One objective of this invention is to provide a method for preparing ordered nitrogen-doped porous carbon materials, the method comprising the following steps:
[0008] S1: Add urea to the chitin nanocrystal solution, adjust the pH to the acidic range, stir and mix well, let stand at room temperature to separate the layers, take the lower layer solution, and dry it under specific temperature and humidity to obtain a chitin nanocrystal / urea composite with an ordered structure.
[0009] S2: Carbonization activation of chitin nanocrystals / urea composites yields ordered nitrogen-doped porous carbon materials.
[0010] Further specifying, the concentration of the chitin nanocrystal solution in S1 is 3–4 wt%.
[0011] Further specifying, the mass ratio of urea to chitin nanocrystals in S1 is (0.01~0.08):1.
[0012] Further specify that the pH in S1 is adjusted to 3.0–5.0.
[0013] Further specified, the stirring speed in S1 is 300-500 rpm, and the time is 20-60 min.
[0014] Further specify that the mixture should be left to stand in S1 for 2-4 days.
[0015] Further specified, S1 is dried at 30-45℃ and 30-40% humidity for 3-7 days.
[0016] Further specify the carbonization and activation process in S2: first, keep it at 200-250℃ under nitrogen protection for 1-3 hours, then soak it in 1M KOH solution for 1-3 hours and dry it, and then keep it at 500-700℃ under nitrogen protection for 2-4 hours.
[0017] The second objective of this invention is to provide an ordered nitrogen-doped porous carbon material prepared by the above method.
[0018] The third objective of this invention is to provide an application of the ordered nitrogen-doped porous carbon material prepared by the above method in the field of adsorption.
[0019] The fourth objective of this invention is to provide an application of the ordered nitrogen-doped porous carbon material prepared by the above method in the field of capacitors.
[0020] The advantages of this invention compared to existing technologies are:
[0021] This invention achieves in-situ composite of chitin nanocrystals and a nitrogen source by controlling the colloidal microenvironment (nanocrystal concentration, nitrogen source addition, pH value, etc.) without disrupting the self-assembly behavior of chitin nanocrystals. A controllable drying process is then used to obtain a structurally ordered chitin nanocrystal / nitrogen source composite material. Subsequently, carbonization and activation processes are employed to prepare an ordered nitrogen-doped porous carbon material based on the self-assembly of chitin nanocrystals. Specific advantages are as follows:
[0022] (1) The self-assembly of chitin nanocrystals is affected by a variety of factors, especially the introduction of various inorganic salts, which often affects or even destroys their self-assembly behavior. This invention achieves in-situ introduction of urea without destroying its self-assembly behavior by controlling parameters such as chitin nanocrystal concentration, urea dosage, and pH value. The advantages of in-situ introduction of urea are reflected in three aspects: in-situ introduction of urea improves the uniformity of the product; in-situ introduction of urea can increase the nitrogen content in the product, and promotes the increase of the proportion of electrochemically active five-membered ring structure pyrrole nitrogen and the decrease of the proportion of electrochemically less active graphite-like nitrogen in the product; in-situ introduction of a specific amount of urea ensures that the system has self-assembly behavior. In addition, when the preparation parameters are too high or too low, the system will not have self-assembly behavior (for example, when the mass ratio of urea to chitin nanocrystals exceeds 0.08:1, the self-assembly behavior of the system disappears).
[0023] (2) After the chitin nanocrystal / urea composite solution was left to stand, the solution with significant self-assembly behavior was taken out. By controlling the drying temperature, drying humidity and drying time, it was ensured that the prepared chitin nanocrystal / urea composite material had an ordered self-assembly structure.
[0024] (3) The ordered structure nitrogen-doped porous carbon material based on chitin nanocrystal self-assembly prepared by carbonization activation process is different from nitrogen-doped porous carbon material without ordered structure under the same conditions. Its feature is that "the introduction of ordered structure increases the specific surface area of carbon material" and improves the electrochemical performance of carbon material. Attached Figure Description
[0025] Figure 1 The morphology of chitin nanocrystals in Example 1;
[0026] Figure 2 The polarized light microscope image shows the lower layer of the chitin nanocrystal / urea solution after standing in Example 1.
[0027] Figure 3 The nitrogen adsorption-desorption curves are for the ordered nitrogen-doped porous carbon material prepared in Example 1.
[0028] Figure 4 Charge-discharge curves of the ordered nitrogen-doped porous carbon material prepared in Example 1 at different current densities;
[0029] Figure 5 XPS spectrum of ordered nitrogen-doped porous carbon material prepared in Example 1;
[0030] Figure 6 XPS spectra of nitrogen in the ordered nitrogen-doped porous carbon material prepared in Example 1;
[0031] Figure 7 The scanning electron microscope morphology of the nitrogen-doped porous carbon material without ordered structure prepared in Comparative Example 1 is shown.
[0032] Figure 8 The scanning electron microscope morphology of the chitin nanocrystal / urea complex in Example 2 is shown.
[0033] Figure 9 The scanning electron microscope (SEM) morphology of the ordered nitrogen-doped porous carbon material prepared in Example 3 is shown. Detailed Implementation
[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.
[0036] Example 1: The preparation method of the ordered nitrogen-doped porous carbon material in this example is carried out according to the following steps:
[0037] (1) Chitosan nanocrystals with a mass concentration of 3% (the morphology of which is shown in the appendix) were subjected to a process. Figure 1 Urea was added to the solution, with a mass ratio of urea to chitin nanocrystals of 0.08:1. The pH was adjusted to 5.0 with HCl, and the mixture was stirred at 300 rpm for 45 min. The mixture was then allowed to stand at room temperature for 3 days to separate into layers. Figure 1 The results show that the initial chitin nanocrystals are in a disordered state.
[0038] (2) Take the lower layer of solution (see attached image for morphology). Figure 2 The chitin nanocrystals / urea composite was dried in a constant temperature and humidity chamber at 35℃ and 30% for 5 days to obtain a structurally ordered chitin nanocrystal / urea composite. Figure 2 The results show that chitin nanocrystals self-assemble into an ordered structure after being left to stand.
[0039] (3) The chitin nanocrystal / urea composite was first treated at 230℃ under nitrogen protection for 2h, then soaked in 1M KOH solution for 2h and dried, and finally treated at 600℃ under nitrogen protection for 3h. It was then washed with deionized water and centrifuged 3 times to obtain ordered nitrogen-doped porous carbon material.
[0040] The nitrogen adsorption-desorption curves of the ordered nitrogen-doped porous carbon material were obtained by testing. Figure 3 Calculations show that the specific surface area reaches 1249 m². 2 ·g -1 , Figure 4 The charge-discharge curves of the material at different current densities show that 1 A·g -1 The specific capacitance reached 268 F·g at the current density. -1 .
[0041] X-ray photoelectron spectroscopy characterization revealed that when the mass ratio of urea to chitin nanocrystals was 0.08:1, the nitrogen atomic percentage reached 7.42%. The pyrrole nitrogen content increased from 59.7% to 67.82% in the porous carbon material prepared without urea, while the graphitic nitrogen content decreased from 6.28% to 4.21%.
[0042] Comparative Example 1: The preparation method of nitrogen-doped porous carbon material without ordered structure is carried out according to the following steps:
[0043] (1) Add a urea solution with a mass concentration of 32.5% to the chitin nanocrystal powder. The mass ratio of urea to chitin nanocrystals is 0.08:1. Mix for 3 min at 1000 rpm using a high-speed mixer.
[0044] (2) The above mixture was placed in a constant temperature and humidity chamber at 35°C and 30% for 5 days to dry, and a disordered chitin nanocrystal / urea composite was obtained.
[0045] (3) The chitin nanocrystal / urea composite was first treated at 230℃ under nitrogen protection for 2 hours, then immersed in 1M KOH solution for 2 hours and dried, and finally treated at 600℃ under nitrogen protection for 3 hours. It was then washed with deionized water and centrifuged three times to obtain nitrogen-doped porous carbon material (this material has no ordered structure). See attached... Figure 7 As shown in the figure, the nitrogen-doped porous carbon material is in the form of irregular particles. No pore structure was found in some areas, while pore structure was found in other areas (but the pore size was uneven and disordered).
[0046] Testing revealed that the specific surface area of the nitrogen-doped porous carbon material without ordered structure reached 1168 m². 2 ·g -1 1A·g -1 The specific capacitance reached 234 F·g at the current density. -1 The comparison revealed that the product prepared by this invention had a 6.8% higher specific surface area and a 14.1% higher specific capacitance.
[0047] Example 2: The preparation method of the ordered structure nitrogen-doped porous carbon material in this example is carried out according to the following steps:
[0048] (1) Add urea to a 4% chitin nanocrystal solution with a mass ratio of 0.02:1. Adjust the pH to 4.0 with HCl. Stir and mix at 500 rpm for 60 min. Let stand at room temperature for 3 days to separate the layers.
[0049] (2) The lower layer solution was placed in a constant temperature and humidity chamber at 30℃ and 35% for 7 days to dry, resulting in a structurally ordered chitin nanocrystal / urea composite; the scanning electron microscope morphology of the chitin nanocrystal / urea composite is shown in the figure. Figure 8 As shown in the figure, the chitin nanocrystal / urea composite exhibits the layered structure characteristic of self-assembly.
[0050] (3) The chitin nanocrystal / urea composite was first treated at 230℃ under nitrogen protection for 2h, then soaked in 1M KOH solution for 2h and dried, and finally treated at 600℃ under nitrogen protection for 3h. It was then washed with deionized water and centrifuged 3 times to obtain ordered nitrogen-doped porous carbon material.
[0051] Testing revealed that the specific surface area of the ordered nitrogen-doped porous carbon material reached 1007 m². 2 ·g -1 1A·g -1 The specific capacitance reached 153 F·g at the current density. -1 .
[0052] Comparative Example 2: The difference between this comparative example and Comparative Example 1 is that the mass ratio of urea to chitin nanocrystals is 0.02:1.
[0053] The comparison revealed that the specific surface area of the product prepared in Example 2 of the present invention was increased by 11.5% and the specific volume was increased by 10.9% compared with Comparative Example 2.
[0054] Example 3: The preparation method of the ordered structure nitrogen-doped porous carbon material in this example is carried out according to the following steps:
[0055] (1) Add urea to a 3% chitin nanocrystal solution with a mass ratio of 0.06:1. Adjust the pH to 5.0 with HCl. Stir and mix at 400 rpm for 30 min. Let stand at room temperature for 3 days to separate the layers.
[0056] (2) The lower layer solution was placed in a constant temperature and humidity chamber at 45℃ and 40% for 3 days to dry, and a chitin nanocrystal / urea composite with an ordered structure was obtained.
[0057] (3) The chitin nanocrystal / urea composite was first treated at 230℃ under nitrogen protection for 2 h, then immersed in 1M KOH solution for 2 h and dried, and finally treated at 600℃ under nitrogen protection for 3 h. It was then washed with deionized water and centrifuged three times to obtain an ordered nitrogen-doped porous carbon material. The scanning electron microscope morphology of the ordered nitrogen-doped porous carbon material is shown below. Figure 9 As shown in the figure, the ordered nitrogen-doped porous carbon material has an ordered oriented pore structure.
[0058] Testing revealed that the specific surface area of the ordered nitrogen-doped porous carbon material reached 1194 m². 2 ·g -1 1A·g -1 The specific capacitance reached 237 F·g at the current density. -1 .
[0059] Comparative Example 3: The difference between this comparative example and Comparative Example 1 is that the mass ratio of urea to chitin nanocrystals is 0.06:1.
[0060] The comparison revealed that the specific surface area of the product prepared in Example 3 of the present invention was increased by 10.9% and the specific capacitance value was increased by 5.1% compared with Comparative Example 3.
[0061] Example 4: The preparation method of the ordered structure nitrogen-doped porous carbon material in this example is carried out according to the following steps:
[0062] (1) Add urea to a 3.5% chitin nanocrystal solution with a mass ratio of 0.04:1. Adjust the pH to 4.0 with HCl. Stir and mix at 350 rpm for 45 min. Let stand at room temperature for 3 days to separate the layers.
[0063] (2) The lower layer solution was placed in a constant temperature and humidity chamber at 40℃ and 35% for 6 days to dry, and a chitin nanocrystal / urea composite with an ordered structure was obtained.
[0064] (3) The chitin nanocrystal / urea composite was first treated at 230℃ under nitrogen protection for 2h, then soaked in 1M KOH solution for 2h and dried, and finally treated at 600℃ under nitrogen protection for 3h. It was then washed with deionized water and centrifuged 3 times to obtain ordered nitrogen-doped porous carbon material.
[0065] Testing revealed that the specific surface area of the ordered nitrogen-doped porous carbon material reached 1102 m². 2 ·g -1 1A·g -1 The specific capacitance reached 203 F·g at the current density. -1 .
[0066] Comparative Example 4: The difference between this comparative example and Comparative Example 1 is that the mass ratio of urea to chitin nanocrystals is 0.04:1.
[0067] The comparison revealed that the specific surface area of the product prepared in Example 4 of the present invention was increased by 12.8% and the specific capacitance value was increased by 29.3% compared with Comparative Example 4.
[0068] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing an ordered nitrogen-doped porous carbon material, characterized in that, The method described: S1: Add urea to the chitin nanocrystal solution, adjust the pH to the acidic range, stir and mix well, let stand at room temperature to separate the layers, take the lower layer solution, and dry it under specific temperature and humidity to obtain a chitin nanocrystal / urea composite with an ordered structure. S2: Carbonization and activation of chitin nanocrystals / urea composites to obtain ordered nitrogen-doped porous carbon materials. The concentration of the chitin nanocrystal solution in S1 is 3-4 wt%; The mass ratio of urea to chitin nanocrystals in S1 is (0.01~0.08):1; Adjust the pH in S1 to 3.0~5.0; Dry in S1 at 30-45℃ and 30-40% humidity for 3-7 days.
2. The method according to claim 1, characterized in that, In S1, the stirring speed is 300~500 rpm, the time is 20~60 min, and it is left to stand for 2-4 days.
3. The method according to claim 1, characterized in that, The carbonization and activation process in S2 is as follows: First, it is kept at 200-250℃ under nitrogen protection for 1-3 hours, then soaked in 1M KOH solution for 1-3 hours and dried, and then kept at 500-700℃ under nitrogen protection for 2-4 hours.
4. The ordered nitrogen-doped porous carbon material prepared by the method according to any one of claims 1-3.
5. The application of the ordered nitrogen-doped porous carbon material of claim 4 in the field of adsorption.
6. The application of the ordered nitrogen-doped porous carbon material of claim 4 in the field of capacitors.
Citation Information
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