Preparation method and application of nitrogen-doped oxygen-enriched graded porous carbon

Abstract

The invention discloses a preparation method and application of nitrogen-doped oxygen-enriched graded porous carbon, the nitrogen-doped oxygen-enriched graded porous carbon is prepared by adopting a one-step co-activation method, the process is simple, and the energy consumption is low. The structure and surface chemical properties of the prepared nitrogen-doped oxygen-enriched graded porous carbon catalyst are easy to regulate and control. The prepared TNS-X material has a relatively large specific surface area and a developed pore structure, and is beneficial to exposure of catalytic sites and diffusion of reactants. Through co-activation of ammonia gas and water vapor, 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 shows efficient catalytic performance in the peroxymonosulfate (PMS) activation process, and can completely remove acetaminophen and other organic pollutants in a short time.

Description

Technical Field

[0001] The invention belongs to the field of catalysts, and in particular relates to a preparation method and application of nitrogen-doped oxygen-rich graded porous carbon. 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 regarded as an efficient means of treating organic wastewater due to its strong reactivity, high oxidation capacity 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), and then these ROS can effectively degrade or mineralize organic pollutants. So far, a variety of methods have been used to activate PMS, including thermal treatment, ultraviolet radiation, transition metals, metal-free carbon catalysts, etc. However, the high energy input required for thermal treatment or ultraviolet radiation methods and the inevitable toxic metal leaching of transition metals in PMS systems limit their practical applications. Therefore, it is very desirable to develop a green and metal-free carbon-based catalyst for environmental remediation to 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, some strategies are needed to improve the catalytic performance of carbon catalysts. Incorporating non-metallic (such as nitrogen, oxygen, etc.) heteroatoms into the carbon matrix is ​​a feasible strategy. Since carbon and doped heteroatoms have obvious differences in radius and orbital, electronegativity and electron density, heteroatoms can disrupt the sp 2 The electron cloud density and spin structure of hybrid carbon produce active sites such as point defects and effective functional groups, thus 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 in 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 ammonia decomposition to produce a mixed gas of ammonia and water vapor for activation, but due to the fixed ratio of ammonia decomposition, 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, and 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 is only 308 m 2 / g, and the total pore volume is 0.359cm 3 / g. 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 amount of nitrogen atoms incorporated 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 reactions 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 obtained was 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 decreased 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] Existing nitrogen-doped porous carbon materials also have the disadvantage of poor catalyst stability. Some nitrogen-doped porous carbon materials are prone to structural damage or active site deactivation during use, resulting in poor catalyst stability. This phenomenon may be due to the reconstruction of the carbon skeleton and the thermal decomposition of surface functional groups during high-temperature treatment, which weakens the mechanical strength and chemical stability of the material.

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

[0009] The present invention aims to solve the problems existing in the existing heteroatom-doped porous carbon in terms of preparation process, specific surface area, pore structure, heteroatom doping efficiency and catalyst stability, and provide a nitrogen-doped oxygen-enriched graded porous carbon with a simple and controllable preparation process, a large specific surface area, a developed pore structure, high heteroatom doping efficiency and good stability, so as to efficiently activate PMS and degrade organic pollutants.

[0010] Specifically, the present invention provides a method for preparing nitrogen-doped oxygen-rich graded porous carbon, comprising the following steps:

[0011] Step S1: drying the gallic tannin precursor under vacuum at 80° C. 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 screened precursor in a porcelain boat, placing the porcelain boat in a horizontal tube furnace, and performing a programmed temperature increase to a specified temperature under a nitrogen atmosphere;

[0013] Step S3: After reaching the specified temperature, switch the gas source, turn off the nitrogen, and introduce ammonia and water vapor into the reactor for activation;

[0014] Step S4: After activation, turn off the ammonia and water vapor sources, and turn on the nitrogen source at a flow rate of 500-150 mL / min. Cool to room temperature under a nitrogen atmosphere to obtain a nitrogen-doped oxygen-rich porous carbon material (TNS-X), where T represents tannin, N represents ammonia, S represents water vapor, and X represents activation temperature.

[0015] Furthermore, in step S1, the gallic tannin is 0.2-5 g, and the mesh size of the sieve used is 80-200 meshes.

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

[0017] Furthermore, the heating rate in step S2 is 5° C. / 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-rich graded porous carbon prepared by the preparation method as described above, and the prepared nitrogen-doped oxygen-rich graded porous carbon material is used for catalytic degradation of organic pollutants in water.

[0024] Furthermore, nitrogen-doped oxygen-rich graded porous carbon was used to activate permonosulfate (PMS) and then used to catalyze the degradation of 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 cleavage free radical etching: NH3 cleaves 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) Pore formation by steam oxidation: Water vapor reacts with carbon to generate CO and H2, optimizing pore connectivity by selectively removing carbon atoms. For example, steam oxidation can remove residual carbon fragments in the pores and significantly improve the connectivity 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 work together to 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. Nitrogen has been widely introduced into the carbon skeleton because the atomic size of nitrogen atoms is similar to that of carbon atoms. In addition, nitrogen has a higher electronegativity than 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 abundant 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 level of oxygen doping. The high 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 efficient integration of carbon material pore structure (micropore / mesopore synergistic optimization) and nitrogen doping through a dynamic balance between free radical etching and oxidation reactions.

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

[0030] 1. The preparation process is simple and controllable: The present invention adopts a one-step co-activation method to prepare nitrogen-doped oxygen-enriched hierarchical porous carbon, which has a simple process and low energy consumption. At the same time, the reaction conditions of this preparation method are easy to control, and the structure and surface chemical properties of the prepared nitrogen-doped oxygen-enriched hierarchical porous carbon catalyst are easy to regulate.

[0031] 2. Specific surface area and well-developed pore structure: The prepared TNS-X material has a large specific surface area and a well-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 atoms and oxygen atoms is achieved, which increases the number and activity of catalytic sites.

[0033] 4. Excellent catalytic performance: TNS-800 exhibits efficient catalytic performance during the PMS activation process and can completely remove organic pollutants such as acetaminophen in a short 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 many 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 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 The degradation rate diagram 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 The TOC (total organic carbon, TOC) removal rate diagram of the 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 diagram 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 in conjunction with 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, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0046] In the following examples, commercially available gallic 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 of high-purity ammonia 99.99% 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, and 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, switch the gas source, turn off the nitrogen, and introduce ammonia and water vapor into the reactor for activation. The activation duration is 120 minutes; the flow rates of ammonia and water vapor are both 75 mL / min;

[0053] Step S4: After activation, turn off the ammonia and water vapor gas sources, and turn on the nitrogen gas source at the same time, cool to room temperature under a nitrogen atmosphere with a nitrogen flow rate of 80 mL / min, and 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, the shaking speed was set to 200 r / min, 100 mL of 20 mg / L acetaminophen (ACT) solution was added to the conical flask, and then 15 mg of TNS-800 prepared in step 1 was added as a catalyst (0.15 g / L) and 92 mg of PMS (1.5 mmol / L) were added at the same time. The reaction was started, and 1 mL of the reaction solution was 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 membrane, 1 mL of chromatographic grade methanol was added to terminate the reaction and the concentration of ACT was determined.

[0057] The concentration of ACT was determined by high performance liquid chromatography (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) produced by Agilent Technologies, Inc., USA. The detection conditions were: column temperature 25°C, mobile phase acetonitrile: ultrapure water = 20:80, flow rate 0.8 mL / min, injection volume 10 μL, detection wavelength 257 nm. The pH of the solution did not need to be adjusted before the reaction started, and the initial pH value 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 catalytic degradation of TOC in water, the specific steps are as follows: At 25°C in the dark, add 300mL of 20mg / L acetaminophen solution into a brown conical flask, add 45mg TNS-800 catalyst (0.15g / L) and 276mg PMS (1.5mmol / L), and set the water bath shaker speed to 200r / min. The reaction starts timing, and 10mL of the reaction solution is taken at 10, 20, 30, 40, 50 and 60 minutes, respectively, filtered through a 0.22μm polytetrafluoroethylene filter membrane, and then injected into the TOC analyzer, automatically detected three times and the average value is taken to calculate the TOC content.

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

[0063] TOC0: initial TOC value of 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 isotherm.

[0067] The specific surface area and pore size distribution of TNS-800 were measured by nitrogen adsorption-desorption isotherm experiment. The instrument used was ASAP2020PLUS physical adsorption instrument produced by Micromeritics, USA. 0.1g of the prepared nitrogen-doped oxygen-enriched graded porous carbon material was weighed in a special quartz tube, and liquid nitrogen was used as the adsorption medium. The adsorption volume of TNS-800 for N2 at different relative pressures (0.0-1.0) was tested at 77K to obtain the adsorption isotherm of nitrogen-doped oxygen-enriched graded 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 by the adsorption amount at the relative pressure of 0.99 of 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 example were determined by elemental analysis and XPS. Elemental analysis tests the overall composition and content of the material, while XPS can only test the elemental composition and content within a depth of 10 nm from the surface of the sample, and cannot measure 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 using a VARIOELcube elemental analyzer (Elementar, Germany).

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

[0071] The infrared testing process is as follows: grind TNS-800 to 200 mesh, mix it with KBr and press it into tablets, use Nicolet IS50 infrared spectrometer produced by Thermo Fisher Scientific, USA to scan 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. Test conditions: material TNS-800 was placed on a carrier plate, and after gold spraying, it was placed in an electron microscope for observation and photography. The electron microscope scanning photos were taken at a magnification of 1000 times, the acceleration voltage was 0.02~30kV, 10V step continuously adjustable, and the working distance was 8.5mm.

[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 graphite nitrogen content of 3.90at.%, and carbonyl content of 2.29at.%.

[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 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 a nitrogen-doped oxygen-rich graded porous carbon material, with specific reference to Example 1. The difference between this comparative example 1 and Example 1 is step S3: after reaching 800°C, switch the gas source, turn off the nitrogen, and simultaneously introduce pure ammonia into the reactor, 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 those in Example 1.

[0078] Referring to the test method provided in Example 1, the nitrogen doping amount of the nitrogen-doped oxygen-rich graded 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 a nitrogen-doped oxygen-rich graded porous carbon material, with specific reference to Example 1. The difference between this comparative example 1 and Example 1 is step S3: after reaching 800°C, switch the gas source, turn off the nitrogen, and simultaneously introduce pure water vapor into the reactor, and 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 those in 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 graphite nitrogen content of 3.90 at% and a carbonyl (C=O) content of 2.29 at%, wherein the graphite nitrogen regulates the electron distribution of the carbon-based material by doping, enhances the adsorption capacity of PMS and promotes the cleavage of its OO bond, and the carbonyl group accelerates the electron transfer between the catalyst and PMS by virtue of its high electron affinity, synergistically activates 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 diffusion efficiency of reactants. 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), and the total organic carbon removal rate reached 61.2%. The reaction rate constant reached a maximum value of 0.144 min -1 .

[0084] Figure 5 The degradation rate diagram 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; 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 3.90at.%, carbonyl content 2.29at.%). This structural feature allows the active sites to be fully exposed and the mass transfer resistance to be significantly reduced, thus giving it the most outstanding catalytic activity.

[0085] Comparative Example 1 is a nitrogen-oxygen co-doped material. Its performance is limited mainly because: the nitrogen doping amount is only 4.22wt.%, resulting in a lower active site density than in the example; the pore structure is poor (specific surface area 406m 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, 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 in 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 minimizing its catalytic activity.

[0087] Depend on Figure 5 It can be seen that the TNS-800 prepared in Example 1 has the 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.%), which gives it the highest catalytic activity. 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 have insufficient 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, nor is it conducive to mass transfer during the reaction, so that its catalytic activity is weaker than that of the embodiment. Comparative Example 2 is only oxygen doped, lacks key nitrogen active sites, and its pore structure is the least developed, making it difficult to effectively expose its limited active sites. The large mass transfer resistance during the reaction greatly reduces its diffusion efficiency, making its catalytic activity the weakest.

[0088] Figure 6The TOC removal rate diagram of the porous carbon material prepared by Example 1, Comparative Example 1 and Comparative Example 2 at different reaction times; Total organic carbon (TOC for short), 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 its degradation removal rate law. The embodiment has the most outstanding catalytic performance among the three samples. It can activate potassium peroxymonosulfate (PMS) to produce more active oxygen components, and achieve 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 is 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 7000rpm 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 7000rpm 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 diagram 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, and the values ​​are 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 The removal effect diagram of the TNS-800 / PMS system composed of TNS-800 and PMS prepared in Example 1 on bisphenol A, tetracycline, sulfadiazine and methyl orange. Within 60 minutes, the removal rates of bisphenol A, tetracycline, sulfadiazine and methyl orange were 100%, 85.3%, 87.6% and 91.8%, and the corresponding total organic carbon (TOC) removal rates were 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 has a significant degradation efficiency for ACT at a pH of 3.43, and has outstanding versatility for 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 also can be extended 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 to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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. A method for preparing nitrogen-doped oxygen-rich graded porous carbon, characterized in that: The following steps are involved: Step S1: vacuum drying the gallic tannin precursor at 80° C. for 12 hours, and sieving through a standard sieve, and the precursor passing through the sieve is subjected to the next activation treatment; Step S2: placing the screened precursor in a porcelain boat, placing the porcelain boat in a horizontal tube furnace, and performing a programmed temperature increase to a specified temperature under a nitrogen atmosphere; Step S3: After reaching the specified temperature, switch the gas source, turn off the nitrogen, and introduce ammonia and water vapor into the reactor for activation; Step S4: After the activation is completed, the ammonia and water vapor gas sources are turned off, and the nitrogen gas source is turned on at the same time, and the mixture is cooled to room temperature under a nitrogen atmosphere to obtain nitrogen-doped oxygen-rich porous carbon.

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

3. The method for preparing nitrogen-doped oxygen-rich graded porous carbon according to claim 1, characterized in that: In step S2, the designated temperature is one of 600°C, 700°C, 800°C, 900°C, and 1000°C.

4. The method for preparing nitrogen-doped oxygen-rich hierarchical porous carbon according to claim 1, characterized in that: The heating rate in step S2 is 5°C / min.

5. The method for preparing nitrogen-doped oxygen-rich graded porous carbon according to claim 1, characterized in that: In step S2, the nitrogen flow rate is 50-150 mL / min.

6. The method for preparing nitrogen-doped oxygen-rich hierarchical porous carbon according to claim 1, characterized in that: The activation duration in step S3 is 60 to 180 minutes, preferably 120 minutes.

7. The method for preparing nitrogen-doped oxygen-rich graded porous carbon according to claim 1, characterized in that: In step S3, the flow ratio of ammonia gas to water vapor is 1-2:1-2.

8. The method for preparing nitrogen-doped oxygen-rich graded porous carbon according to claim 1, characterized in that: In step S3, the flow rate of ammonia gas is 50-150 mL / min.

9. Use of nitrogen-doped oxygen-rich hierarchical porous carbon prepared by any one of claims 1 to 8, characterized in that: The prepared nitrogen-doped oxygen-rich hierarchical porous carbon was used to catalytically degrade organic pollutants in water.

10. The use according to claim 9, characterized in that: Nitrogen-doped oxygen-rich graded porous carbon was used to activate persulfate and then used for catalytic degradation of organic pollutants in water.

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