Preparation method and application of high-yield and high-active-site nitrogen-doped carbon material

Abstract

This invention belongs to the field of water treatment materials technology. More specifically, it relates to a method for preparing a high-yield, high-activity-site nitrogen-doped carbon material and its application. The preparation method of this invention includes: mixing melamine and L-cysteine ​​to obtain a mixture, adding 5-20% by weight of nano-graphene oxide to the mixture, ball milling to obtain a precursor; heating the precursor to 500-700℃ at a rate of 2-5℃ / min under an inert atmosphere, calcining at this temperature for 80-160 min; continuing to heat at a rate of 1-5℃ / min to 900-1200℃, calcining at this temperature for 80-160 min, and then cooling to room temperature in the furnace to obtain the nitrogen-doped carbon material. The mass ratio of melamine to L-cysteine ​​is 1:1; the particle size distribution range of the nano-graphene oxide is 1-200 nm.

Description

Technical Field

[0001] This invention belongs to the field of water treatment materials technology. More specifically, it relates to a method for preparing nitrogen-doped carbon materials with high yield and high active sites, and their applications. Background Technology

[0002] Heterogeneous catalytic ozone oxidation technology is a highly efficient deep oxidation treatment method that has been widely used in drinking water purification, municipal wastewater treatment, and industrial wastewater treatment. This technology promotes ozone decomposition using a heterogeneous ozone catalyst to generate reactive oxygen species, thereby improving ozone utilization efficiency and accelerating the degradation of organic pollutants in water.

[0003] Heterogeneous ozone catalysts mainly fall into two categories: metal-based catalysts and carbon-based catalysts. While metal-based catalysts exhibit high catalytic activity, they suffer from metal ion leaching, potentially posing risks to aquatic environments and human health. Carbon-based catalysts, on the other hand, have received increasing attention in recent years due to their excellent chemical stability, environmental friendliness, and lack of metal leaching risk.

[0004] However, existing carbon-based catalysts suffer from an insufficient number of active sites, resulting in catalytic efficiency that fails to meet practical application requirements. To improve the catalytic performance of carbon-based catalysts, researchers have focused on increasing the number of active sites through modification methods, among which nitrogen doping is an effective modification strategy. The introduction of nitrogen atoms can alter the electronic structure of the carbon material surface, forming new catalytic active centers, thereby improving its catalytic activity for ozone decomposition.

[0005] Currently, the main method for preparing nitrogen-doped carbon materials is a two-step process: first, a carbon support material is prepared, and then the carbon support is subjected to a high-temperature thermal condensation reaction with nitrogen-containing compounds such as melamine to introduce nitrogen doping. However, the above method has the following technical defects: (1) the number of nitrogen doping sites is limited, making it difficult to obtain catalysts with high catalytic activity; (2) the catalyst yield is low, the synthesis cycle is long, which is not conducive to large-scale production; (3) the multi-step synthesis process increases the production cost and operational complexity, limiting its promotion in commercial applications.

[0006] Therefore, developing a nitrogen-doped carbon-based ozone catalyst with abundant nitrogen doping sites, a simple and efficient preparation process, and suitable for large-scale production, as well as its preparation method, is of great significance for promoting the practical application of heterogeneous catalytic ozone oxidation technology. Summary of the Invention

[0007] The technical problem this invention aims to solve is that existing carbon materials for water treatment involve complex preparation processes and produce products with low catalytic activity. To address these challenges, this invention provides a method for preparing nitrogen-doped carbon materials with high yield and high active sites, as well as their applications.

[0008] The purpose of this invention is to provide a method for preparing nitrogen-doped carbon materials with high yield and high active sites.

[0009] Another object of the present invention is to provide an application of nitrogen-doped carbon materials with high yield and high active sites.

[0010] The above-mentioned objective of this invention is achieved through the following technical solution: A method for preparing nitrogen-doped carbon materials with high yield and high active sites, the specific preparation steps include: Ball milling treatment: Melamine and L-cysteine ​​were mixed and then ball-milled to obtain the precursor. Heat shrinkage treatment: Under an inert atmosphere, the precursor was subjected to thermal condensation treatment and then cooled to obtain nitrogen-doped carbon material.

[0011] The beneficial effects of the above technical solution are as follows: The above technical solution uses melamine and L-cysteine ​​as raw materials, and is prepared by a two-step method of ball milling followed by thermal condensation under an inert atmosphere. That is, by selecting raw materials and coupling processes, the preparation process is simplified and the catalytic performance of the product is improved. Specifically, melamine, as a nitrogen-rich precursor, and L-cysteine, as a sulfur- and carbon-containing precursor, are complementary in molecular structure. Ball milling not only achieves microscopic uniform mixing of raw materials, but its mechanical energy may also induce some pre-reactions, increasing the contact area and creating ideal conditions for subsequent thermal condensation. The thermal condensation process is carried out under an inert atmosphere, which allows the nitrogen- and sulfur-containing precursors to be directionally transformed into a stable carbon framework rich in nitrogen and sulfur co-doped active sites through a series of reactions such as condensation, carbonization, and graphitization.

[0012] Furthermore, the mass ratio of melamine to L-cysteine ​​is 1-1.

[0013] The beneficial effects of the above technical solution are as follows: By limiting the ratio of the two raw materials, when the ratio is less than 1:1, an excess of L-cysteine ​​may lead to excessive sulfur doping or the formation of too much amorphous carbon, affecting conductivity and stability. When the ratio is greater than 3:1, an excess of melamine may result in high nitrogen content but incomplete carbon framework development, and excess unreacted melamine may decompose to produce undesirable byproducts. The 1-3:1 range ensures that the two types of molecules can undergo condensation reaction at an optimal molar ratio during thermal condensation, forming a carbon network with suitable nitrogen / sulfur doping concentration and good graphitization. This achieves a stable and highly conductive carbon matrix while ensuring high nitrogen doping to provide abundant catalytic active sites, thereby stabilizing and optimizing the overall catalytic performance of the final material.

[0014] Furthermore, the ball milling process includes: Add zirconia grinding balls at a ball-to-material mass ratio of 1:20-30, and grind for 20-60 minutes at an orbital speed of 300-600 rpm and a rotational speed of 600-1500 rpm.

[0015] Furthermore, the ball milling process also includes: Melamine and L-cysteine ​​are mixed to obtain a mixture, and 5-20% by weight of nano-graphene oxide is added to the mixture. The mixture is then ball-milled to obtain a precursor.

[0016] The beneficial effects of the above technical solution are as follows: In the ball milling process, nano-graphene oxide acts as a two-dimensional dispersed phase. On one hand, it blocks direct contact between melamine and L-cysteine ​​molecules or their aggregates, acting as a "physical isolator" and inhibiting their excessive aggregation and growth during thermal condensation. On the other hand, its abundant oxygen-containing functional groups on its surface may interact with raw material molecules, becoming new reaction sites. At the high temperature of subsequent thermal condensation, the graphene oxide is partially reduced, and its excellent conductivity and mechanical strength, combined with the nitrogen-doped carbon matrix, further enhance the conductivity of the composite material, accelerate electron transport during the catalytic process, and strengthen the mechanical stability of the material, resulting in a synergistic improvement in both catalytic activity and stability.

[0017] Furthermore, the particle size distribution of the nano-graphene oxide ranges from 1 to 200 nm.

[0018] The beneficial effects of the above technical solution are as follows: Graphene oxide sheets with particle sizes in the range of 1-200 nm have extremely high specific surface area and abundant edge sites, enabling them to be more uniformly dispersed in mixtures and form closer and more abundant interfacial contacts with raw material molecules. Excessively large particle sizes (>200 nm) may lead to uneven dispersion and easy stacking, weakening their template and reinforcing effects; excessively small particle sizes (<1 nm), while exhibiting good dispersibility, have extremely high preparation costs and may result in excessive structural damage during high-temperature processing.

[0019] Furthermore, the heat shrinking process includes: Under an inert atmosphere, the precursor is heated to 500-700℃ at a rate of 2-5℃ / min and calcined for 80-160 min. Then, it is heated to 900-1200℃ at a rate of 1-5℃ / min and calcined for 80-160 min. After that, it is cooled to room temperature in the furnace and discharged to obtain nitrogen-doped carbon material.

[0020] The beneficial effects of the above technical solution are as follows: The thermal condensation reaction is carried out using a two-stage stepped heating program. The first stage (500-700℃) is the critical temperature window. Within this range, the raw material molecules mainly undergo deoxygenation, dehydrogenation, and condensation reactions, forming a preliminary carbon framework rich in nitrogen and sulfur heteroatoms. Numerous catalytically active sites, such as pyridine nitrogen and graphitic nitrogen, are generated during this stage. Slow heating (2-5℃ / min) and sufficient holding time (80-160min) ensure the thoroughness and uniformity of this process. The second stage (900-1200℃) is conducted at a higher temperature. Its main function is to promote the graphitization and reconstruction of the carbon framework, eliminate unstable structures, and improve the material's conductivity, chemical stability, and specific surface area. Simultaneously, it ensures the stable existence of the formed nitrogen species within the carbon network. This heat treatment program maximizes the creation and stabilization of highly active nitrogen-doped sites at high temperatures, while simultaneously constructing a highly graphitized carbon support with excellent conductivity, ultimately yielding a catalyst material with both excellent activity and stability.

[0021] An application of a nitrogen-doped carbon material with high yield and high active sites in the catalytic ozone-based advanced treatment of drinking water.

[0022] An application of a high-yield, highly active nitrogen-doped carbon material in the catalytic ozone-based deep treatment of municipal wastewater.

[0023] An application of a high-yield, highly active nitrogen-doped carbon material in the treatment of industrial wastewater from catalytic ozone production.

[0024] The advantages of this invention include: The composite material prepared by this method has a large number of N-doped active sites, which improves the catalytic degradation efficiency of the material.

[0025] Compared with traditional methods, the yield of this invention is significantly increased from tens of milligrams to several grams, which significantly improves the yield of the catalyst and meets the needs of large-scale commercial applications.

[0026] This invention employs ball milling-thermal condensation technology, which simplifies the multi-step preparation process of traditional nitrogen-doped carbon materials, shortens the synthesis cycle, greatly improves production efficiency, and reduces production costs and operational complexity.

[0027] The raw materials used in this invention, melamine and L-cysteine, are environmentally friendly materials. The entire preparation process does not require the use of harmful chemicals, thus reducing the impact on the environment.

[0028] The nitrogen-doped carbon catalyst of the present invention is not only applicable to ozone oxidation water treatment, but also has the potential to be applied to other catalytic fields, such as electrocatalysis and photocatalysis. Attached image description: Figure 1 The X-ray photoelectron spectroscopy (XPS)-C spectrum corresponding to the product of Embodiment 1 of this invention; Figure 2 The X-ray photoelectron spectroscopy (XPS)-O spectrum corresponding to the product of Embodiment 1 of the present invention; Figure 3 The X-ray photoelectron spectroscopy (XPS)-N spectrum corresponding to the product of Embodiment 1 of this invention; Figure 4 The product of Example 1 of this invention is used for the catalytic ozone oxidation and degradation of BZA. Figure 5 The reaction rate constant for the catalytic ozone oxidation of the product in Example 1 of this invention is given. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0030] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0031] Example 1 Ball milling treatment: Melamine and L-cysteine ​​were mixed to obtain a mixture, and 5% of nano-graphene oxide by mass of the mixture was added to the mixture. Zirconia ball milling beads were added at a ball-to-material mass ratio of 1:20. The mixture was ball milled for 20 minutes at an orbital speed of 300 rpm and a rotational speed of 600 rpm. The mixture was then discharged to obtain the precursor. The mass ratio of melamine to L-cysteine ​​is 1:1. The particle size distribution range of the nano-graphene oxide is 1-200 nm; Heat shrinkage treatment: Under an inert atmosphere, the precursor was heated to 500°C at a rate of 2°C / min and calcined at that temperature for 80 min. Then, it was heated to 900°C at a rate of 1°C / min and calcined at that temperature for 80 min. After that, it was cooled to room temperature in the furnace and discharged to obtain nitrogen-doped carbon material. Specifically, argon atmosphere is selected as the inert atmosphere.

[0032] Example 2 Ball milling treatment: Melamine and L-cysteine ​​were mixed to obtain a mixture, and 9% of nano-graphene oxide by mass of the mixture was added to the mixture. Zirconia ball milling beads were added at a ball-to-material mass ratio of 1:22. The mixture was ball milled for 30 minutes at an orbital speed of 400 rpm and a rotational speed of 1000 rpm. The material was then discharged to obtain the precursor. The mass ratio of melamine to L-cysteine ​​is 1:1. The particle size distribution range of the nano-graphene oxide is 1-200 nm; Heat shrinkage treatment: Under an inert atmosphere, the precursor was heated to 600°C at a rate of 3°C / min and calcined for 120 min. Then, it was heated to 1000°C at a rate of 2°C / min and calcined for 120 min. After that, it was cooled to room temperature in the furnace and discharged to obtain nitrogen-doped carbon material. Specifically, argon atmosphere is selected as the inert atmosphere.

[0033] Example 3 Ball milling treatment: Melamine and L-cysteine ​​were mixed to obtain a mixture, and 20% of the mixture mass of nano-graphene oxide was added to the mixture. Zirconia ball milling beads were added at a ball-to-material mass ratio of 1:30. The mixture was ball-milled for 60 minutes at an orbital speed of 600 rpm and a rotational speed of 1500 rpm. The material was then discharged to obtain the precursor. The mass ratio of melamine to L-cysteine ​​is 1:1. The particle size distribution range of the nano-graphene oxide is 1-200 nm; Heat shrinkage treatment: Under an inert atmosphere, the precursor was heated to 700°C at a rate of 5°C / min and calcined for 160 min. Then, it was heated to 1200°C at a rate of 5°C / min and calcined for 160 min. Subsequently, it was cooled to room temperature in the furnace and discharged to obtain nitrogen-doped carbon material. Specifically, argon atmosphere is selected as the inert atmosphere.

[0034] Example 4 The difference between this embodiment and Embodiment 1 is that the particle size distribution range of the nano-graphene oxide is 0.1-200nm, while the other conditions remain unchanged.

[0035] Example 5 The difference between this embodiment and Embodiment 1 is that activated carbon is used instead of graphene oxide, while the other conditions remain unchanged.

[0036] Example 6 The difference between this embodiment and Embodiment 1 is that no graphene oxide was added, while all other conditions remained unchanged.

[0037] The performance of the products obtained in the above embodiments was evaluated using the following specific testing and evaluation methods: The elemental distribution and coordination patterns of the catalyst surface obtained in Example 1 were characterized using X-ray photoelectron spectroscopy (XPS). The instrument used was a Thermo Scientific ESCALAB MK-2. XPS results can identify the active sites and major chemical elements on the catalyst surface, with a scan range of 0-900 eV. The obtained spectra were then deconvolved using XPS PEAK41 software to determine the coordination patterns between different elements.

[0038] like Figure 1-3 As shown in the C and O spectra, this catalyst contains C=C bonds, C–N bonds, –C=O, –COOH, etc.; the N spectrum shows that this catalyst contains quaternary nitrogen, pyrrolic nitrogen, pyridinic nitrogen, and oxidized nitrogen.

[0039] Blank example: To verify the catalytic ozone oxidation activity of the catalyst product obtained in the examples, a 0.25 ppm benzotriazole (BZA) aqueous solution was prepared at room temperature. Ozone gas was continuously introduced in a semi-continuous flow mode to maintain the dissolved ozone concentration in the water at 1.5 mg / L. The catalyst dosage was 0.25 ppm. The degradation of BZA was compared with that of the blank example ozone oxidation system without catalyst. The concentration of BZA was tested after 5 min and 10 min of catalytic oxidation. The relevant test results are shown in Table 1. Table 1: Results of Catalytic Activity Tests The results were fitted to obtain the reaction kinetic constants (kobs) for ozone alone and the ozone + NC system, as shown below. Figure 5 As shown, the ozone + NC system is 13 times more potent than the ozone-only system, demonstrating that NC has excellent catalytic performance in the catalytic oxidation and degradation of BZA by ozone.

[0040] As can be seen from the test results in Table 1, the product obtained by this invention has high catalytic activity.

[0041] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high yield, high active site nitrogen-doped carbon material, characterized by, The specific preparation steps include: Ball milling treatment: Melamine and L-cysteine ​​were mixed and then ball-milled to obtain the precursor. Heat shrinkage treatment: Under an inert atmosphere, the precursor was subjected to thermal condensation treatment and then cooled to obtain nitrogen-doped carbon material.

2. The method for preparing a high-yield, highly active nitrogen-doped carbon material according to claim 1, characterized in that, The mass ratio of melamine to L-cysteine ​​is 1:

1.

3. The method for preparing a high-yield, highly active nitrogen-doped carbon material according to claim 1, characterized in that, The ball milling process includes: Add zirconia grinding balls at a ball-to-material mass ratio of 1:20-30, and grind for 20-60 minutes at an orbital speed of 300-600 rpm and a rotational speed of 600-1500 rpm.

4. A method for preparing a nitrogen-doped carbon material with high yield and high active sites according to any one of claims 1 or 3, characterized in that, The ball milling process also includes: Melamine and L-cysteine ​​are mixed to obtain a mixture, and 5-20% by weight of nano-graphene oxide is added to the mixture. The mixture is then ball-milled to obtain a precursor.

5. The method for preparing a high-yield, highly active nitrogen-doped carbon material according to claim 4, characterized in that, The particle size distribution range of the nano-graphene oxide is 1-200 nm.

6. The method of claim 1, wherein the high yield, high active site nitrogen-doped carbon material is prepared by the steps of: The heat shrinkage process includes: Under an inert atmosphere, the precursor is heated to 500-700℃ at a rate of 2-5℃ / min and calcined for 80-160 min. Then, it is heated to 900-1200℃ at a rate of 1-5℃ / min and calcined for 80-160 min. After that, it is cooled to room temperature in the furnace and discharged to obtain nitrogen-doped carbon material.

7. A high yield, high active site nitrogen-doped carbon material, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. An application of a nitrogen-doped carbon material with high yield and high active sites as described in any one of claims 1-7, characterized in that, It is used in the advanced treatment of drinking water using catalytic ozone.

9. An application of a nitrogen-doped carbon material with high yield and high active sites as described in any one of claims 1-7, characterized in that, It is used in the deep treatment of municipal wastewater using catalytic ozone.

10. Use of a high yield, high active site, nitrogen-doped carbon material according to any one of claims 1 to 7, characterized in that, It is used in the treatment of industrial wastewater reuse in catalytic ozone production.

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