Preparation method and application of nitrogen-doped oxygen-rich hierarchical porous carbon

Abstract

The application discloses a preparation method and application of nitrogen-doped oxygen-rich hierarchical porous carbon, and adopts a one-step co-activation method to prepare the nitrogen-doped oxygen-rich hierarchical porous carbon, which is simple in process and low in energy consumption. The structure and surface chemical performance of the prepared nitrogen-doped oxygen-rich hierarchical porous carbon catalyst are easy to control. The prepared TNS-X material has a large specific surface area and a developed pore structure, which is beneficial to exposure of catalytic sites and diffusion of reactants. Through ammonia and water vapor co-activation, efficient doping of nitrogen atoms and oxygen atoms is realized, the number of catalytic sites is increased, and the catalytic activity is improved. The TNS-800 material exhibits high catalytic performance in a peroxymonosulfate (PMS) activation process, and can completely remove organic pollutants such as acetylaminophenol in a short time.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts, and in particular relates to a preparation method of nitrogen-doped oxygen-rich graded porous carbon and application thereof. Background Art

[0002] With the increasing severity of environmental pollution, especially water pollution, how to efficiently and environmentally friendly treat organic pollutants has become a hot topic of global concern. Permonosulfate (PMS) activation technology is widely considered to be an efficient means of treating organic wastewater due to its strong reactivity, high oxidizing ability and wide pH adaptability. Usually, external catalysts or energy are required to activate PMS to produce various types of reactive oxygen species (ROS) (such as SO4 ·- , OH and 1 O2), these ROS can then effectively degrade or mineralize organic pollutants. To date, various methods have been used to activate PMS, including heat treatment, ultraviolet radiation, transition metals, and metal-free carbon catalysts. However, the high energy input required for heat treatment or ultraviolet radiation methods and the inevitable toxic metal leaching of transition metals in PMS systems limit their practical application. Therefore, it is highly desirable to develop a green and metal-free carbon-based catalyst for environmental remediation that can achieve strong activation ability for PMS.

[0003] However, carbon-based catalysts have weak catalytic activity due to the lack of active sites and underdeveloped pore structures. Therefore, it is necessary to adopt some strategies to improve the catalytic performance of carbon catalysts. Incorporating non-metallic (such as nitrogen, oxygen, etc.) heteroatoms into carbon matrices is a feasible strategy. Since carbon and doped heteroatoms have obvious differences in radius and orbital, electronegativity and electron density, heteroatoms can disrupt sp 2 Hybridizing carbon's electron cloud density and spin structure creates active sites such as point defects and effective functional groups, thereby breaking the chemical inertness of the carbon matrix. Nitrogen (N) is the most widely studied heteroatom for improving the properties of carbon materials. However, existing nitrogen-doped porous carbon materials still have some shortcomings during the preparation process.

[0004] The existing nitrogen-doped porous carbon material preparation process usually involves multiple steps, and has the disadvantages of complex preparation process, such as pretreatment, carbonization and activation, etc., and the process is cumbersome and energy consumption is high. For example, the preparation of alkaline carbon catalyst in Patent 1 (CN115364840A) includes three steps of pyrolysis, water vapor activation and ammonia activation, and the total time is 4.5-6.5 hours (excluding heating time). Patent 2 (CN108711518B) prepares nitrogen-oxygen doped materials by a three-step method of hydrothermal synthesis of precursor (8-16 hours), carbonization and ammonia activation (20-120 minutes, excluding heating time). By comparison, it can be seen that both methods require three steps to complete the preparation of the final material, and the process is complicated and time-consuming. In addition, Patent 2 uses a mixture of ammonia and water vapor generated by the decomposition of ammonia water for activation, but because the ammonia decomposition ratio is fixed, it is difficult to accurately control the ratio of ammonia to water vapor, which limits the further optimization of material properties.

[0005] The specific surface area and pore structure of existing nitrogen-doped porous carbon materials are limited. The specific surface area and pore structure of some nitrogen-doped porous carbon materials are not well developed, which limits the exposure of catalytic sites and the diffusion rate of reactants. For example, Zhu et al. (Separation and Purification Technology, 2024, 346, 127456) used lignin particles as carbon precursors and melamine as nitrogen source, formed a uniform suspension by magnetic stirring and calcined to obtain nitrogen-doped porous carbon. However, the specific surface area of ​​the optimal porous carbon obtained was only 308 m 2 / g, and the total pore volume is 0.359cm 3 The small specific surface area and pore volume significantly limit the effective contact between PMS and pollutants and the active sites of the catalyst, thereby hindering the rapid progress of the catalytic reaction.

[0006] The heteroatom doping efficiency in existing nitrogen-doped porous carbon materials is not high. During the doping process, the incorporation amount of nitrogen atoms is often limited, resulting in an insufficient number of catalyst active sites. For example, Wang et al. (Journal of Environmental Chemical Engineering, 2022, 10, 108509) prepared nitrogen-oxygen co-doped activated carbon by a two-step method. First, activated carbon was oxidized by nitric acid to introduce oxygen-containing functional groups, and then nitrogen doping was achieved by ammonia and hydrothermal reaction (12 hours). Although the oxygen-containing functional groups undergo deoxidation reaction during high-temperature pyrolysis, releasing gases such as CO2 or H2O to form unsaturated carbon sites as anchoring sites for nitrogen doping, the nitrogen content of the optimal sample N-OAC-8 finally obtained is only 6.9at%. In addition, the nitrogen doping process causes a certain degree of damage to the carbon skeleton, and its specific surface area and total pore volume decrease by 11.2% and 8.9%, respectively, indicating that there is a trade-off between high nitrogen content and maintaining a good pore structure.

[0007] The existing nitrogen-doped porous carbon material also has the defect of poor catalyst stability, and part of the nitrogen-doped porous carbon material is easy to cause structure damage or active site inactivation in the use process, resulting in poor catalyst stability. This phenomenon may be due to the reconstruction of carbon skeleton and the thermal decomposition of surface functional groups in the high-temperature treatment process, thereby weakening the mechanical strength and chemical stability of the material.

[0008] Therefore, it is an urgent problem to be solved to develop a nitrogen-doped porous carbon technology with simple preparation process, high specific surface area and pore structure, high heteroatom doping efficiency and excellent catalytic performance. SUMMARY

[0009] The present application aims to solve the problems of existing heteroatom-doped porous carbon in preparation process, specific surface area, pore structure, heteroatom doping efficiency and catalyst stability, and provides a nitrogen-doped oxygen-rich hierarchical porous carbon with simple, controllable preparation process, large specific surface area, developed pore structure, high heteroatom doping efficiency and good stability, which can efficiently activate PMS and degrade organic pollutants.

[0010] Specifically, the present application provides a preparation method of nitrogen-doped oxygen-rich hierarchical porous carbon, comprising the following steps:

[0011] Step S1: vacuum drying the gallotannin precursor at 80℃ for 12 hours, and sieving through a standard sieve, and the precursor passing through the sieve is subjected to the next activation treatment;

[0012] Step S2: placing the sieved precursor in a porcelain boat, and placing the porcelain boat in a horizontal tube furnace, and performing programmed temperature rise to a specified temperature under a nitrogen atmosphere;

[0013] Step S3: after reaching the specified temperature, switching the gas source, closing the nitrogen, and simultaneously introducing ammonia and water vapor into the reactor for activation;

[0014] Step S4: after the activation is completed, closing the ammonia and water vapor sources, and simultaneously opening the nitrogen source with a flow rate of 500-150mL / min. Cooling to room temperature under a nitrogen atmosphere to obtain a nitrogen-doped oxygen-rich porous carbon material (TNS-X), wherein TNS-X: T represents tannin, N represents ammonia, S represents water vapor, and X represents the activation temperature.

[0015] Further, the gallotannin in step S1 is 0.2-5g, and the mesh number of the sieve used is 80-200.

[0016] Further, the specified temperature in step S2 is one of 600℃, 700℃, 800℃, 900℃ and 1000℃.

[0017] Further, the temperature rise rate in step S2 is 5℃ / min.

[0018] Furthermore, in step S2, the nitrogen flow rate is 50-150 mL / min.

[0019] Furthermore, the activation duration in step S3 is 60 to 180 minutes, preferably 120 minutes.

[0020] Furthermore, in step S3, the flow ratio of ammonia to water vapor is 1-2:1-2.

[0021] By adjusting the flow rate of ammonia and water vapor, the pore structure and nitrogen and oxygen doping levels of the carbon catalyst can be efficiently and conveniently controlled.

[0022] Furthermore, in step S3, the flow rate of ammonia gas is 50-150 mL / min.

[0023] The present invention also provides an application of the nitrogen-doped oxygen-enriched graded porous carbon prepared by the preparation method as described above, and the prepared nitrogen-doped oxygen-enriched graded porous carbon material is used to catalytically degrade organic pollutants in water.

[0024] Furthermore, nitrogen-doped oxygen-rich graded porous carbon was used to activate peroxymonosulfate (PMS) and then used to catalytically degrade organic pollutants in water.

[0025] The synergistic effect of NH3 and water vapor can optimize the pore structure of porous carbon through the following pathways, and help activate PMS and achieve efficient degradation of difficult-to-degrade organic pollutants.

[0026] (1) NH3 free radical etching: NH3 decomposes at high temperature to generate free radicals such as NH2·, NH·, and H·, which preferentially and selectively etch disordered areas in the carbon skeleton (such as amorphous carbon or defect sites), thereby forming a mesoporous structure (2-50nm). This process effectively avoids the problem of skeleton collapse caused by excessive corrosion in the traditional KOH activation method;

[0027] (2) Water vapor oxidation pore formation: Water vapor reacts with carbon to generate CO and H2, optimizing pore connectivity by selectively removing carbon atoms. For example, water vapor oxidation can remove residual carbon fragments within the pores, significantly improving the permeability of the mesoporous network. The dynamic balance between the two enables the controllable construction of a hierarchical pore structure: micropores provide a high specific surface area, while mesopores promote mass transfer efficiency, and the two synergistically optimize material performance.

[0028] The introduction of heteroatoms is considered to be one of the most effective ways to break the chemical inertness of carbon catalysts, which helps to activate PMS and achieve efficient degradation of difficult-to-degrade organic pollutants. Since the atomic size of nitrogen atoms is similar to that of carbon atoms, nitrogen has been widely introduced into the carbon skeleton. In addition, the electronegativity of nitrogen is higher than that of carbon, so nitrogen doping can effectively regulate the charge distribution and electron density of carbon catalysts. At the same time, water vapor, as an oxidizing gas, introduces rich oxygen-containing functional groups during the activation and pore-forming process. The tannin used in this patent is an oxygen-rich biomass, which further ensures that the carbon material has a high oxygen doping level. The higher oxygen content not only provides key support for the efficient incorporation of nitrogen atoms, but also significantly improves the catalytic performance of carbon materials by regulating electronic structure, optimizing intermediate adsorption energy, and introducing active sites and defects. Ammonia-water vapor synergistic activation achieves the efficient integration of carbon material pore structure (micropore / mesopore synergistic optimization) and nitrogen doping through the dynamic balance of free radical etching and oxidation reaction.

[0029] The present invention provides an efficient and environmentally friendly nitrogen-doped oxygen-rich hierarchical porous carbon material that activates PMS to degrade organic pollutants through a non-radical pathway. The material has high catalytic activity, wide pH adaptability, and excellent reusability, making it suitable for a variety of practical wastewater treatment scenarios. Specifically, the present invention has the following advantages over the prior art:

[0030] 1. Simple and controllable preparation process: This invention uses a one-step co-activation method to prepare nitrogen-doped oxygen-enriched hierarchical porous carbon, which is simple and energy-efficient. Furthermore, this preparation method allows for easily controllable reaction conditions, making the structure and surface chemical properties of the prepared nitrogen-doped oxygen-enriched hierarchical porous carbon catalyst easily tunable.

[0031] 2. Developed specific surface area and pore structure: The prepared TNS-X material has a large specific surface area and a developed pore structure, which is conducive to the exposure of catalytic sites and the diffusion of reactants.

[0032] 3. High heteroatom doping efficiency: Through co-activation of ammonia and steam, efficient doping of nitrogen and oxygen atoms is achieved, which increases the number and activity of catalytic sites.

[0033] 4. Excellent catalytic performance: TNS-800 exhibits highly efficient catalytic performance during the PMS activation process, and can completely remove organic pollutants such as acetaminophen in a short period of time.

[0034] 5. Good recycling performance: TNS-800 can still maintain good catalytic activity after repeated use, and is not prone to structural damage or active site deactivation, indicating that it has excellent regeneration and is suitable for practical applications.

[0035] 6. Highly efficient degradation of various organic pollutants: In addition to acetaminophen (ACT), TNS-800 also shows good degradation ability for a variety of other organic pollutants (such as bisphenol A, tetracycline, sulfadiazine and methyl orange), expanding its scope of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 N2 adsorption-desorption isotherm (left) and corresponding pore size distribution diagram (right) of TNS-800 prepared in Example 1;

[0037] Figure 2 This is the infrared spectrum of TNS-800 prepared in Example 1;

[0038] Figure 3 Figure 1 shows the nitrogen component atomic content (left) and oxygen component atomic content (right) of TNS-800 prepared in Example 1;

[0039] Figure 4 This is the SEM image of TNS-800 prepared in Example 1;

[0040] Figure 5 This is a graph showing the degradation rate of ACT in water catalyzed by the porous carbon materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 at different reaction times;

[0041] Figure 6 Graph showing TOC (total organic carbon, TOC) removal rates of porous carbon materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 at different reaction times;

[0042] Figure 7 This is a test chart of the cycle performance of TNS-800 prepared in Example 1;

[0043] Figure 8 This is a diagram showing the removal effect of bisphenol A, tetracycline, sulfadiazine and methyl orange by the TNS-800 / PMS system composed of TNS-800 and PMS prepared in Example 1. DETAILED DESCRIPTION

[0044] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0045] In the following examples, unless otherwise specified, the raw materials or processing techniques used are conventional commercially available raw materials or conventional processing techniques in the art.

[0046] In the following examples, commercially available gallnut tannin (Shaanxi Haochen Biotechnology Co., Ltd., purity 81±3%) was used as a precursor to prepare nitrogen-doped oxygen-rich hierarchical porous carbon by co-activation with 99.99% high-purity ammonia and water vapor.

[0047] Example 1

[0048] This embodiment provides a method for preparing a nitrogen-doped oxygen-rich hierarchical porous carbon material and its application, comprising the following steps:

[0049] 1. Preparation of nitrogen-doped oxygen-rich hierarchical porous carbon materials:

[0050] Step S1: 2.5 g of gallic tannin precursor was vacuum dried at 80° C. for 12 hours and sieved through a 100-mesh standard sieve. The precursor that passed through the sieve was subjected to the next activation treatment;

[0051] Step S2: placing the screened precursor in a porcelain boat, placing the porcelain boat in a horizontal tube furnace, and heating the temperature to 800°C under a nitrogen atmosphere at a heating rate of 5°C / min and a nitrogen flow rate of 80 mL / min;

[0052] Step S3: After reaching 800°C, the gas source was switched, nitrogen was turned off, and ammonia and water vapor were introduced into the reactor for activation. The activation duration was 120 minutes; the flow rates of ammonia and water vapor were both 75 mL / min;

[0053] Step S4: After activation, the ammonia and water vapor gas sources are turned off, and the nitrogen gas source is turned on at the same time. The mixture is cooled to room temperature under a nitrogen atmosphere with a nitrogen flow rate of 80 mL / min to obtain nitrogen-doped oxygen-rich porous carbon material TNS-800.

[0054] 2. Application of the prepared nitrogen-doped oxygen-rich hierarchical porous carbon material TNS-800 in catalytic degradation of organic pollutants in water:

[0055] 2.1 Application of the prepared nitrogen-doped oxygen-rich hierarchical porous carbon material TNS-800 in catalytic degradation of ACT in water:

[0056] At 25°C, set the shaker speed to 200 r / min, add 100 mL of a 20 mg / L acetaminophen (ACT) solution to the conical flask, then simultaneously add 15 mg of TNS-800 prepared in step 1 as a catalyst (0.15 g / L) and 92 mg of PMS (1.5 mmol / L). The reaction timer is started, and 1 mL of the reaction solution is drawn with a syringe at 2.5, 5, 7.5, 10, 15, 20, 30, 40, 50, and 60 minutes, respectively. After filtering through a 0.22 μm polytetrafluoroethylene filter, 1 mL of chromatography-grade methanol is added to terminate the reaction and the concentration of ACT is measured.

[0057] ACT concentration was determined using a high-performance liquid chromatograph (HPLC1220, Agilent Technologies, Inc., USA) equipped with a C18 reverse-phase column (ZORBAX Eclipse, 5 μm, 4.6 × 250 mm) and a UV-visible detector (SPD-20). Detection conditions were: column temperature 25°C, mobile phase acetonitrile:ultrapure water = 20:80, flow rate 0.8 mL / min, injection volume 10 μL, and detection wavelength 257 nm. The pH of the solution did not require adjustment before the reaction; the initial pH was 3.43.

[0058] ACT removal rate (%) = (C0-C t )×100% / C0

[0059] C0: initial ACT concentration of the reaction (mg / L)

[0060] Ct: ACT concentration at reaction time t (mg / L).

[0061] 2.2 Application of the prepared nitrogen-doped oxygen-rich hierarchical porous carbon material TNS-800 in the catalytic degradation of TOC in water. The specific steps are as follows: Under dark conditions at 25°C, 300 mL of 20 mg / L acetaminophen solution was added to a brown conical flask, along with 45 mg of TNS-800 catalyst (0.15 g / L) and 276 mg of PMS (1.5 mmol / L). The water bath shaker speed was set to 200 r / min. The reaction was timed, and 10 mL of the reaction solution was taken at 10, 20, 30, 40, 50, and 60 minutes, respectively. The samples were filtered through a 0.22 μm polytetrafluoroethylene filter and injected into a TOC analyzer. The samples were automatically detected three times and the average value was taken to calculate the TOC content.

[0062] TOC removal rate (%) = (TOC0-TOC t )×100% / TOC0

[0063] TOC0: initial TOC value of the reaction (mg / L)

[0064] TOC t : TOC value at reaction time t (mg / L).

[0065] The maximum specific surface area, pore structure and active site concentration of TNS-800 prepared in the first step were measured.

[0066] Specific surface area and pore structure analysis: The specific surface area and pore structure of the material were determined by N2 adsorption-desorption isotherms.

[0067] The specific surface area and pore size distribution of TNS-800 were measured by nitrogen adsorption-desorption isotherm experiment, and the instrument used was ASAP2020PLUS physical adsorption instrument produced by Micromeritics Company of the United States. 0.1 g of the prepared nitrogen-doped oxygen-rich hierarchical porous carbon material was weighed into a special quartz tube, liquid nitrogen was used as the adsorption medium, and the adsorption volume of TNS-800 to N2 under different relative pressures (0.0-1.0) at 77 K was tested to obtain the adsorption isotherm of the nitrogen-doped oxygen-rich hierarchical porous carbon material. According to the adsorption isotherm data, the specific surface area of TNS-800 was calculated by the Brunauer-Emmett-Teller (BET) method, the total pore volume was calculated from the adsorption amount at a relative pressure of 0.99 in the nitrogen adsorption isotherm, the micropore volume was calculated according to the Dubinin-Radushkevich equation, and the mesopore volume was obtained by subtracting the micropore volume from the total pore volume. The quenched solid density functional theory model was used to analyze the pore size distribution of TNS-800.

[0068] Elemental analysis and surface chemistry: The elemental composition and surface functional groups of the materials were analyzed by elemental analyzer, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR).

[0069] The elemental composition and content of TNS-800 in this embodiment were determined by elemental analysis and XPS. Elemental analysis tests the composition and content of the whole material, while XPS can only test the elemental composition and content within 10 nm depth of the sample surface, and cannot determine deeper. The elemental composition in the above table is provided by elemental analysis. Elemental analysis: The C, H, N, and O contents of the carbon catalyst were analyzed by VARIO ELcube elemental analyzer (Elementar Company, Germany).

[0070] XPS: This experiment was analyzed by ESCALAB250Xi instrument produced by Thermo Fisher Scientific Company of the United States, and Al Kα ray (hv = 1486.6 eV) was used as the excitation source. The full-spectrum scanning parameters were: beam spot 400 μm, working voltage: 12 kV, lens mode: standard mode, analyzer mode: CAE, pass energy: 100 eV, step length 1 eV; the parameters of narrow-spectrum scanning were the same as those of full-spectrum scanning, but the pass energy was 50 eV, the step length was 0.05 eV, and the scanning times of different elements were at least 5 cycles of signal accumulation. XPSPEAK4.1 peak separation software and origin8.5 were used for peak separation and plotting.

[0071] The infrared testing process is as follows: grind TNS-800 to 200 mesh, mix it with KBr and press it into tablets, and use Nicolet IS50 infrared spectrometer produced by Thermo Fisher Scientific to scan it in the wavelength range of 500 to 4000 cm-1 to obtain the infrared spectrum of TNS-800.

[0072] Microstructure: characterized by SEM.

[0073] Scanning electron microscopy (SEM): A field emission scanning electron microscope Gemini300 from Zeiss Japan was used to observe the surface structure of the material. The test conditions were as follows: the material TNS-800 was placed on a carrier plate, sprayed with gold, and placed in an electron microscope for observation and photography. The electron microscope scanning photos were taken at a magnification of 1000 times, with an acceleration voltage of 0.02 to 30 kV, continuously adjustable in 10 V steps, and a working distance of 8.5 mm.

[0074] After testing and calculation, the maximum specific surface area of ​​TNS-800 prepared in this embodiment is 538m 2 / g, with a well-developed pore structure, of which the mesopore volume is 0.172cm 3 / g, micropore volume 0.289cm 3 / g. It also has a high active site concentration, with a graphitic nitrogen content of 3.90 at.%, and a carbonyl content of 2.29 at.%.

[0075] Figure 1 N2 adsorption-desorption isotherm (left) and corresponding pore size distribution diagram (right) of TNS-800 prepared in this example; Figure 2 This is the infrared spectrum of TNS-800 prepared in this example; Figure 3 Figure 2 shows the nitrogen component atomic content (left) and oxygen component atomic content (right) of TNS-800 prepared in this example; Figure 4 This is the SEM image of TNS-800 prepared in this example.

[0076] Comparative Example 1

[0077] This comparative example also provides a preparation method and application of nitrogen-doped oxygen-rich graded porous carbon materials, with specific reference to Example 1. The difference between this comparative example 1 and Example 1 is step S3: after reaching 800°C, the gas source is switched, the nitrogen is turned off, and pure ammonia is introduced into the reactor at the same time, and the activation duration is 120 minutes; the flow rate of ammonia is 75 mL / min, and the other preparation steps and application steps are the same as Example 1.

[0078] Referring to the test method provided in Example 1, the nitrogen doping amount of the nitrogen-doped oxygen-rich hierarchical porous carbon material prepared in this comparative example is only 4.22 wt.%, and the specific surface area is 406 m 2 / g, and the mesopore volume is only 0.095cm 3 / g.

[0079] Comparative Example 2

[0080] This comparative example also provides a preparation method and application of nitrogen-doped oxygen-rich graded porous carbon materials, with specific reference to Example 1. The difference between this comparative example 1 and Example 1 is step S3: after reaching 800°C, the gas source is switched, the nitrogen is turned off, and pure water vapor is introduced into the reactor at the same time. The activation duration is 120 minutes; the flow rate of water vapor is 75 mL / min, and the other preparation steps and application steps are the same as Example 1.

[0081] Referring to the test method provided in Example 1, the nitrogen-doped oxygen-rich hierarchical porous carbon material prepared in this comparative example has a specific surface area of ​​332 m 2 / g, and the mesopore volume is only 0.062cm 3 / g.

[0082] The TNS-800 catalyst prepared in Example 1 has a graphitic nitrogen content of 3.90 at% and a carbonyl (C=O) content of 2.29 at%. Graphitic nitrogen regulates the electron distribution of carbon-based materials by doping, thereby enhancing the adsorption capacity of PMS and promoting the cleavage of its OO bond. The carbonyl group accelerates the electron transfer between the catalyst and PMS by virtue of its high electron affinity, synergistically activating PMS to generate singlet oxygen ( 1 O2) as the main active oxygen species (ROS); at the same time, the catalyst has a microporous-mesoporous hierarchical pore structure (micropores account for 62.7%), with a specific surface area of ​​538m 2 / g, forming a three-dimensional mass transfer channel, significantly improving the exposure rate of active sites and the efficiency of reactant diffusion. Through the synergistic mechanism of "high active site density-optimized mass transfer path", the PMS activation efficiency of TNS-800 is significantly improved.

[0083] Within 60 minutes, the TNS-800 / PMS system was able to completely remove 20 mg / L of acetaminophen (ACT), with a total organic carbon removal rate of 61.2%. The reaction rate constant reached a maximum of 0.144 min -1 .

[0084] Figure 5 The degradation rate of ACT in water catalyzed by the porous carbon materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 at different reaction times is shown in FIG. Figure 5 It can be seen that the TNS-800 prepared in Example 1 exhibits the best catalytic performance, which is attributed to its significant structural advantages: the largest specific surface area (538m 2 / g), the most developed pore structure (mesopore volume 0.172cm 3 / g, micropore volume 0.289cm3 / g) and the highest active site concentration (graphitic nitrogen content of 3.90 at.%, carbonyl content of 2.29 at.%). This structural feature fully exposes the active sites and significantly reduces mass transfer resistance, resulting in the most outstanding catalytic activity.

[0085] Comparative Example 1 is a nitrogen-oxygen co-doped material. Its performance is limited mainly due to: the nitrogen doping amount is only 4.22 wt.%, resulting in a lower active site density than the embodiment; the pore structure is poor (specific surface area 406 m 2 / g, and the mesopore volume is only 0.095cm 3 / g), resulting in a decrease in the exposure rate and accessibility of the active sites, and a higher mass transfer resistance than that of Example 1, thereby making its catalytic activity weaker than that of Example 1.

[0086] The catalytic performance of Comparative Example 2 (pure oxygen doping) is significantly weaker than that of Example 1 and Comparative Example 1. This is because the sample of Comparative Example 2 is only doped with oxygen atoms, lacks the key graphitic nitrogen active sites, and has the worst pore development (specific surface area 332m 2 / g, mesopore volume 0.062cm 3 / g), which makes it difficult to fully utilize its limited active sites, thus making its catalytic activity the lowest.

[0087] Depend on Figure 5 It can be seen that the TNS-800 prepared in Example 1 has the highest catalytic activity due to its largest specific surface area, the most developed pore structure (largest mesopore volume, largest micropore volume) and the highest number of catalytic active sites (graphitic nitrogen: 3.90at.%; C=O: 2.29at.%). Although Comparative Example 1 is also a nitrogen-oxygen co-doped carbon material, its nitrogen doping amount is only 4.22%, which makes the nitrogen-oxygen co-doped carbon material prepared in Comparative Example 1 insufficient in active sites, and its pore structure is weaker than that of Example 1, with a specific surface area of ​​406m 2 / g, and the mesopore volume is only 0.095cm 3 / g, which is not conducive to the exposure and accessibility of active sites and is also not conducive to mass transfer during the reaction, resulting in weaker catalytic activity than the examples. Comparative Example 2, which is only oxygen-doped and lacks key nitrogen active sites, also has the least developed pore structure, making it difficult to effectively expose its limited active sites. The high mass transfer resistance during the reaction significantly reduces its diffusion efficiency, resulting in the weakest catalytic activity.

[0088] Figure 6The TOC removal rate of the porous carbon material prepared by Example 1, Comparative Example 1, and Comparative Example 2 at different reaction times is shown; Total organic carbon (TOC) is used in the field of environmental water treatment. The removal rate of total organic carbon (TOC) in the available solution represents the mineralization ability of the catalyst in the process of peroxide degradation of organic pollutants in water. The greater the TOC removal rate, the stronger the mineralization ability. As can be seen from the figure, when the reaction time is 60 minutes, Example 1 has the strongest mineralization ability for the organic pollutant acetaminophen (ACT) in water, with a TOC removal rate of 61.2%, followed by Comparative Example 1 (53.8%), and the worst is Comparative Example 2 (48.1%). The mineralization ability of the three samples for ACT is consistent with their degradation removal rate. The embodiment has the most outstanding catalytic performance among the three samples. It can activate potassium peroxymonosulfate (PMS) to produce more reactive oxygen species, achieving more significant degradation and mineralization of ACT.

[0089] Example 2

[0090] In order to evaluate the recycling performance and stability of TNS-800 prepared in Example 1, this example was tested according to the following steps. The single degradation experimental steps of the carbon catalyst are consistent with the ACT degradation experiment in Example 1. After each experiment, the reaction solution was transferred to a centrifuge tube and centrifuged at 7000 rpm for 5 minutes using a centrifuge (HT165, Hunan Xiangyi Laboratory Instrument Development Co., Ltd.) to separate the precipitated carbon catalyst TNS-800. The collected catalyst was rinsed with ultrapure water until neutral, centrifuged again at 7000 rpm for 5 minutes, and the supernatant was discarded, and then dried at 80 ° C for 12 hours. The dried catalyst was used for the next degradation experiment, and the remaining operating steps remained unchanged. The above process was repeated 5 times, and the recycling performance and stability of the catalyst were evaluated by analyzing the changes in the degradation efficiency of ACT.

[0091] Figure 7 This is a test chart of the cycle performance of TNS-800 prepared in Example 1. As can be seen from the figure, as the number of times the TNS-800 in Example 1 is used increases, the removal rate of ACT shows a downward trend, with the values ​​being 100%, 86.4%, 75.4%, 68.2%, and 64.8%, respectively.

[0092] Example 3

[0093] The method of this embodiment refers to that of Example 1. The difference between this embodiment and Example 1 is that acetaminophen (ACT) in Example 1 is replaced by bisphenol A, tetracycline, sulfadiazine and methyl orange respectively. Referring to the method of Example 1, it can be seen that the TNS-800 / PMS system composed of TNS-800 and PMS prepared in Example 1 not only has an excellent degradation effect on ACT, but also shows a broad-spectrum degradation ability for other organic pollutants. Figure 8 , Figure 8 Figure 1 shows the removal efficiency of the TNS-800 / PMS system, composed of TNS-800 and PMS prepared in Example 1, for bisphenol A, tetracycline, sulfadiazine, and methyl orange. Within 60 minutes, the removal rates for bisphenol A, tetracycline, sulfadiazine, and methyl orange were 100%, 85.3%, 87.6%, and 91.8%, respectively, with corresponding total organic carbon (TOC) removal rates of 63.5%, 50.4%, 42.8%, and 43.5%, respectively. This systematic evaluation confirms the material's ability to remove a wide range of organic pollutants in water systems. The TNS-800 / PMS system exhibits significant degradation efficiency for ACT at a pH of 3.43 and demonstrates outstanding versatility in the degradation of bisphenol A, tetracycline, sulfadiazine, and methyl orange. This patent provides a highly efficient metal-free carbon catalyst with great potential for activating PMS in wastewater treatment.

[0094] In summary, the catalyst of the present invention is not only suitable for the degradation of acetaminophen, but can also be expanded to the removal of other organic pollutants, such as bisphenol A (BPA), tetracycline (TC), sulfonamides (SDZ) and methyl orange (MO). The present invention adopts a metal-free catalyst, which reduces the risk of secondary pollution and meets the requirements of sustainable development. These advantages make the catalyst of the present invention have important application potential and practical significance in the field of water treatment.

[0095] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. An application of nitrogen-doped oxygen-rich graded porous carbon, characterized in that: Nitrogen-doped oxygen-rich hierarchical porous carbon activated peroxymonosulfate for catalytic degradation of organic pollutants in water; The preparation of the nitrogen-doped oxygen-rich hierarchical porous carbon comprises the following steps: Step S1: drying the gallic tannin precursor under vacuum at 80° C. for 12 hours and sieving through a standard sieve; the precursor passing through the sieve is subjected to the next activation treatment; Step S2: placing the screened precursor into a porcelain boat, placing the porcelain boat into a horizontal tube furnace, and heating the temperature to a specified temperature under a nitrogen atmosphere; Step S3: After reaching the specified temperature, the gas source is switched, the nitrogen is turned off, and 99.99% pure ammonia and water vapor are introduced into the reactor for activation; Step S4: After activation, the ammonia and water vapor gas sources are turned off, while the nitrogen gas source is turned on, and the mixture is cooled to room temperature under a nitrogen atmosphere to obtain nitrogen-doped oxygen-rich porous carbon; In step S2, the specified temperature is one of 600° C., 700° C., 800° C., 900° C., and 1000° C.; In step S2, the heating rate is 5°C / min; In step S3, the flow ratio of ammonia to water vapor is 1-2:1-2; The ammonia flow rate in step S3 is 50-150 mL / min.

2. The use of nitrogen-doped oxygen-rich graded porous carbon according to claim 1, characterized in that: In step S1, the gallic tannin precursor is 0.2-5 g, and the mesh size of the sieve used is 80-200 meshes.

3. The use of nitrogen-doped oxygen-rich graded porous carbon according to claim 1, characterized in that: The nitrogen flow rate in step S2 is 50-150 mL / min.

4. The use of nitrogen-doped oxygen-rich graded porous carbon according to claim 1, characterized in that: The activation duration in step S3 is 60 to 180 minutes.

5. The use of nitrogen-doped oxygen-rich graded porous carbon according to claim 4, characterized in that: The activation duration in step S3 is 120 minutes.

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