High-specific-surface-area porous carbon nitride, preparation method and equipment thereof, application of high-specific-surface-area porous carbon nitride and air filtering device

Abstract

The invention discloses high-specific-surface-area porous carbon nitride, a preparation method and equipment thereof, application of the high-specific-surface-area porous carbon nitride and an air filtering device. The preparation method comprises the following steps: step 1, preparing phosphorus-doped graphite-phase carbon nitride; and 2, carrying out nitrogen vacancy modification on the phosphorus-doped carbon nitride in the step 1. According to the carbon nitride prepared through the method, phosphorus and nitrogen vacancies are introduced into the material at the same time, the types of active sites are effectively increased, the carbon nitride has the high specific surface area and the multi-stage pore channels, a huge containing space and a rapid transportation channel are provided for pollutant molecules, and the adsorption efficiency of the carbon nitride is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of environmental pollution control materials technology, specifically to a high specific surface area porous carbon nitride, its preparation method and equipment, its uses, and air filter components. Background Technology

[0002] Graphitic carbon nitride, as a non-metallic polymer semiconductor, exhibits potential application value in catalysis and adsorption due to its unique graphene-like layered structure and abundant nitrogen element. Typically, its most basic preparation method involves direct high-temperature thermal polymerization (e.g., calcination at 500-600°C for several hours) of nitrogen-containing precursors such as melamine and urea in an air atmosphere. However, the bulk g-C3N4 obtained by this traditional method suffers from inherent defects that severely affect its adsorption performance:

[0003] Extremely low specific surface area: Due to the intense condensation and accumulation of the precursors during thermal polymerization, the resulting blocky structure is dense, and its BET specific surface area is typically less than 10 m². 2 / g. This directly results in a scarcity of exposed active sites on the material, making its physical adsorption capacity for pollutants far lower than that of traditional adsorbents such as commercial activated carbon.

[0004] Lack of pore structure: The material itself lacks a well-developed pore system, especially mesopores and macropores. This non-porous or closed-pore structure severely hinders the diffusion and transport of airborne pollutant molecules within the material, resulting in slow adsorption kinetics and failing to meet the requirements for rapid pollutant capture in air filtration.

[0005] The surface chemical properties were not effectively utilized: Although the nitrogen atoms in the g-C3N4 framework can theoretically serve as polar adsorption sites, most of the atoms are encased in a dense bulk phase and cannot effectively contact pollutant molecules, resulting in the failure to demonstrate its specific adsorption capacity for polar small molecules such as formaldehyde.

[0006] This is because the traditional "one-step thermal polymerization method" thermodynamically tends to form a stable bulk phase structure with the lowest energy and dense packing, but lacks effective means of pore formation and structure control.

[0007] To improve the performance of g-C3N4, researchers have explored elemental doping strategies, with phosphorus doping attracting attention due to its ability to modulate the material's electronic structure. A typical improvement method involves solid-state mixing of melamine with a phosphorus-containing compound (such as diammonium hydrogen phosphate) followed by co-thermal polymerization. While this method successfully introduces phosphorus into the carbon-nitrogen framework, it still suffers from the following drawbacks: ① Limited structural improvement: The introduction of phosphorus may have partially suppressed excessive grain growth during heat treatment, but it failed to fundamentally overturn its dense layered stacking pattern. Although the specific surface area of ​​the resulting phosphorus-doped g-C3N4 was improved, it still remained in the tens of m² range. 2 At the level of / g, it is difficult to achieve a breakthrough in order of magnitude, and the ceiling for improving physical adsorption capacity is obvious.

[0008] ② Inhomogeneous doping: The uniformity of solid-state mixing is highly dependent on the grinding process, making it difficult to ensure uniform dispersion of phosphorus source at the molecular level, which may lead to uneven local properties of the material and discontinuous distribution of active sites.

[0009] ③ Limited "individual combat" effect: Single phosphorus doping mainly changes the surface electron cloud density of the material, enhancing its affinity for specific pollutants. However, without high specific surface area and well-developed pores as support, these modified surface chemical sites are like "islands," unable to be effectively reached by pollutant molecules, and their advantages cannot be fully realized.

[0010] Therefore, existing phosphorus doping methods only solve the problem of regulating the "chemical composition" of g-C3N4, but do not truly solve the problem of reconstructing the "physical structure" of graphitic carbon nitride.

[0011] To further activate the intrinsic activity of g-C3N4, vacancy engineering (such as introducing nitrogen vacancies) has become an effective strategy. In existing technologies, methods such as high-temperature ammonia treatment or ammonium chloride etching are commonly used to create nitrogen vacancies in g-C3N4. However, these methods have the following process or performance drawbacks: ① Process complexity and structural damage risk: High-temperature ammonia treatment requires complex gas path control and safety protection, and the strong reducing atmosphere may cause excessive etching, destroying the long-range ordered structure of the carbon-nitrogen framework, resulting in decreased material crystallinity and poor stability. On the other hand, directly using ammonium chloride and g-C3N4 for physical mixing and heat treatment results in a violent and uncontrollable etching reaction, which can easily cause the pore structure to collapse, forming a disordered and unstable porous structure.

[0012] ② Vacancy type and concentration are difficult to control precisely: The above methods lack fine control over the formation location and concentration of nitrogen vacancies (Nv), which may generate a large number of inactive bulk vacancies instead of the active vacancies exposed on the surface that contribute the most to adsorption.

[0013] ③ Limited functionality and lack of synergistic design: Existing vacancy engineering focuses primarily on creating vacancies themselves, failing to systematically and integratedly design "chemical doping" and "vacancy construction" in a synergistic manner. Simple nitrogen vacancy modification materials (N... VThe specific surface area of ​​nitrogen-doped materials (CN) is typically limited, and their surface chemical properties are relatively simple. More importantly, existing technologies have failed to consciously retain and utilize previously doped elements (such as phosphorus), thus failing to achieve the synergistic enhancement effect between the electronic regulation of phosphorus and the unsaturated dangling bonds of nitrogen vacancies. This limits both the broad-spectrum adsorption capacity of the material for complex mixtures of pollutants and its strong capture capacity for specific polar molecules. Summary of the Invention

[0014] To overcome the above-mentioned shortcomings, the present invention aims to provide a method for preparing porous carbon nitride with high specific surface area, which can simultaneously and controllably improve the physical structure and optimize the surface chemical properties of g-C3N4 material, so that it has both high specific surface area and multi-level channels, and has multiple active sites.

[0015] Includes the following steps: Step 1: Preparation of phosphorus-doped graphitic carbon nitride; Step 2: Modify the phosphorus-doped carbon nitride from Step 1 with nitrogen vacancies. The high specific surface area described in this application can be 200 m² / s. 2 / g and above, for example, 210m 2 / g and above, 230m 2 / g and above, 240m 2 / g and above, 255m 2 / g and above, 265m 2 / g and above, 275m 2 / g and above.

[0016] The present invention has the following beneficial effects: ① This invention introduces phosphorus and nitrogen vacancies into the material simultaneously through phosphorus doping in step 1 and nitrogen etching in step 2, effectively increasing the types of active sites. Furthermore, the formation of nitrogen vacancies after phosphorus doping ensures that nitrogen vacancies are formed at sites adjacent to the doped phosphorus atoms. Thus, phosphorus atoms and adjacent nitrogen vacancies form "active site pairs" with a synergistic enhancement effect. Moreover, while creating nitrogen vacancies, the phosphorus element introduced in the first step is retained to the maximum extent, achieving the coexistence of two active centers.

[0017] ② The carbon nitride prepared by this invention maintains the integrity of the basic network structure of g-C3N4, while forming nitrogen vacancies on the basis of phosphorus-doped carbon nitride, thereby giving carbon nitride a high specific surface area and multi-level channels, providing a huge storage space and fast transport channels for pollutant molecules.

[0018] ③ The carbon nitride material prepared by the method of the present invention utilizes the electron-withdrawing effect of phosphorus sites and the high activity of nitrogen vacancies with unpaired electrons. Therefore, it can produce a stronger chemical adsorption effect on polar pollutants such as formaldehyde. For example, it can achieve a stronger adsorption effect on such pollutants by forming stronger dipole-dipole interactions or even chemical bonds with polar pollutants.

[0019] ④ Further, step 1 includes the following steps: Step 1.1: Physically blend and grind melamine and inorganic phosphate in a mass ratio of 10:0.5-5 to ensure that the two phases are uniformly mixed at the molecular level. Step 1.2: Transfer the ground powder to a crucible with a sealed lid; Step 1.3: Place the crucible in a muffle furnace and heat it to 400-600℃ in a static air atmosphere. Then, calcine it at this temperature for 3-6 hours to ensure complete polymerization and crystallization of the precursor. Step 1.4: After the reaction in step 1.3 is completed, allow the furnace to cool naturally to room temperature, remove the generated orange product, grind it again, and you will get phosphorus-doped carbon nitride (PCN) powder.

[0020] Furthermore, step 2 includes the following steps: Step 2.1: Take an appropriate amount of the PCN powder obtained in Step 1 and place it in a quartz boat; Step 2.2: Place ammonium chloride in another quartz boat, with a mass ratio of ammonium chloride to PCN of 4-10:1; Step 2.3: Seal the tubular furnace and introduce high-purity nitrogen into the furnace for 20-60 minutes to completely remove air; Step 2.4: While maintaining a nitrogen flow, heat to 500-800℃ and hold at this temperature for 1 hour to complete gradient annealing and pore structure reconstruction; Step 2.5: After the reaction system cools naturally to room temperature, the sample is removed and washed several times with deionized water and ethanol to remove byproducts. It is then vacuum dried at 40-70℃ for 5-8 hours to obtain high specific surface area porous carbon nitride (PN). VCN. This application uses ammonium chloride as the raw material for forming nitrogen vacancies. It utilizes the sublimation of ammonium chloride to produce HCl and NH3, which attack and break the relatively unstable CN bond in the g-C3N4 skeleton, removing the -NH2 or =N- groups, thereby creating nitrogen vacancies. Moreover, ammonium chloride and its decomposition products (HCl and NH3) are in the gaseous state under the reaction temperature and inert atmosphere, and can be completely removed in the subsequent cooling and washing process. This ensures that no metal ions or other impurity elements (such as S, P, etc.) are introduced into the final product, thus ensuring the purity of the product.

[0021] Furthermore, another quartz boat containing ammonium chloride is placed upstream of the gas flow in the tube furnace, while the boat containing PCN is placed downstream. This spatially separated design of the two boats is crucial, as it allows for the precise transport of the etching gases generated from the upstream decomposition to the downstream sample surface using the flowing carrier gas. Compared to placing both ammonium chloride and PCN powders in the same quartz boat, this avoids the violent and uncontrollable reactions caused by direct physical mixing, resulting in a gentler and safer process. It also allows for precise control of the etching degree and provides a longer contact time and opportunity between the etching gases generated from the decomposition of ammonium chloride and PCN, ensuring optimal performance of the PCN sample. V High concentrations of nitrogen vacancies are formed in CN.

[0022] Furthermore, step 1 includes the following steps: Step 1.1: Physically blend and grind melamine and inorganic phosphate in a mass ratio of 10:1-3 solid powder for 20-30 minutes to ensure that the two phases are uniformly mixed at the molecular level; Step 1.2: Transfer the ground powder into an alumina crucible with a sealed lid; Step 1.3: Place the crucible in a muffle furnace and heat it to 500-550°C in a static air atmosphere. Then, calcine it at this temperature for 3-5 hours to ensure complete polymerization and crystallization of the precursor. Step 1.4: After the reaction in Step 1.3 is completed, allow the furnace to cool naturally to room temperature, remove the generated orange product, grind it again, and you will get phosphorus-doped carbon nitride powder (PCN).

[0023] Furthermore, step 2 includes the following steps: Step 2.1: Take an appropriate amount of the PCN powder obtained in Step 1 and place it in a quartz boat; Step 2.2: Place ammonium chloride in another quartz boat with a mass ratio of ammonium chloride to PCN of 6-8:1. Place the quartz boat containing ammonium chloride upstream of the gas flow in the tube furnace, while place the quartz boat containing PCN downstream of the gas flow. Step 2.3: Seal the tubular furnace and introduce high-purity nitrogen into the furnace at a flow rate of 40-60 mL / min for 30 minutes to completely remove air; Step 2.4: While maintaining a nitrogen flow, heat to 600-700℃ and hold at this temperature for 1 hour to complete gradient annealing and pore structure reconstruction; Step 2.5: After the reaction system cools naturally to room temperature, the sample is removed and washed several times with deionized water and ethanol to remove byproducts. It is then vacuum dried at 60°C for 5-7 hours to obtain high specific surface area porous carbon nitride (PN). V CN.

[0024] The present invention also provides a high specific surface area porous carbon nitride, which is prepared by the aforementioned preparation method.

[0025] The present invention also provides an apparatus for implementing the aforementioned preparation method, wherein a first quartz boat for placing ammonium chloride and a second quartz boat for placing PCN are sequentially arranged in a tube furnace along the flow direction of the carrier gas flow.

[0026] This invention also provides an air filter comprising high specific surface area porous carbon nitride prepared by the aforementioned method. The air filter can be used to remove at least one of volatile organic compounds (VOCs), polar molecules (such as aldehydes), and ozone. Because the high specific surface area porous carbon nitride of this invention has significantly improved specific surface area and adsorption capacity, it can effectively improve the highly selective adsorption and strong binding energy for substances such as VOCs and polar molecules. Furthermore, it has potentially superior resistance to humidity interference.

[0027] The present invention also provides a use of the high specific surface area porous carbon nitride prepared by the aforementioned method or the aforementioned high specific surface area porous carbon nitride for catalytic degradation of organic pollutants in waste gas or wastewater. Attached Figure Description

[0028] Figure 1 (a) is a scanning electron microscope image of CN; Figure 1 (b) is N V Scanning electron microscope image of CN; Figure 1 (c) is N V Another scanning electron microscope image from CN; Figure 1 (d) is a scanning electron microscope image of the PCN; Figure 1 (e) is PN V Scanning electron microscope image of CN; Figure 1 (f) is PNV Another scanning electron microscope image from CN; Figure 2(a) shows PN V Scanning electron microscope image of CN; Figure 2(b) shows PN V Scanning electron microscope image of carbon in CN; Figure 2(c) shows PN V Scanning electron microscope image of nitrogen in CN; Figure 2(d) shows PN V Scanning electron microscope image of phosphorus in CN; Figure 3 For CN and PN V The aperture distribution curve of CN; Figure 4 The N2 adsorption-desorption isotherm curves are shown. Figure 5 X-ray diffraction (XRD) patterns of CN, PCN, NVCN, and PNVCN; Figure 6 Fourier transform infrared (FTIR) spectra of CN, PCN, NVCN, and PNVCN; Figure 7 For CN, PCN, N V CN and PN V X-ray photoelectron spectroscopy analysis of C1s high-resolution core-level spectra in CN; Figure 8 For CN, PCN, N V CN and PN V High-resolution core-level spectra of N1s obtained by X-ray photoelectron spectroscopy analysis of CN. Figure 9 For CN, PCN, N V CN and PN V X-ray photoelectron spectroscopy analysis of high-resolution core-level spectra of P2p in CN; Figure 10 For PCN and PN V Electron paramagnetic resonance (EPR) spectrum of CN. Detailed Implementation

[0029] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0030] Reagent source information: The melamine, diammonium hydrogen phosphate, ammonium chloride, and diammonium hydrogen phosphate used in the examples were all of analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd.

[0031] Example 1.1: Preparation of graphitic carbon nitride (CN) Weigh 5.0g of melamine precursor and grind it in a mortar for 10-15 minutes until it is thoroughly homogenized. Transfer the ground powder to an alumina crucible with a sealed lid. This sealed environment allows the precursor to generate its own pressure during thermal polymerization, which is beneficial for forming a layered structure. Subsequently, place the crucible in a muffle furnace and heat it to 550℃ at a precise programmed heating rate of 5℃ / min under static air atmosphere. Calcinate at this temperature for 4 hours to ensure complete polymerization and crystallization of the precursor. After the reaction is complete, allow the furnace to cool naturally to room temperature. Remove the resulting light yellow blocky product, grind it again to obtain basic graphitic carbon nitride powder, denoted as CN.

[0032] Example 1.2: Preparation of phosphorus-doped graphitic carbon nitride (PCN) 5.0 g of melamine and 0.5 g of diammonium hydrogen phosphate solid powder were physically blended and ground for 20-30 minutes to ensure uniform mixing at the molecular level. Here, diammonium hydrogen phosphate served as both a phosphorus source and a precursor. The uniformly mixed powder was transferred to a covered alumina crucible and then processed under the same thermal polymerization conditions as in Example 1.1. After natural cooling, an orange phosphorus-doped carbon nitride solid was obtained, which was then ground to obtain a powder sample, denoted as PCN.

[0033] Example 1.3: Co-modified carbon nitride (PN) with nitrogen vacancies and phosphorus elements V Preparation of CN) This embodiment employs a two-step method to prepare porous co-modified carbon nitride for nitrogen vacancy construction and phosphorus retention. The first step involves preparing a PCN precursor using the method described in Example 1.2. The second step involves atmosphere-assisted gradient annealing. a) Take 0.5g of the PCN powder obtained in the first step and place it in a quartz boat.

[0034] b) Place another quartz boat containing 3.0g of ammonium chloride upstream of the gas flow in the tube furnace, while place the quartz boat containing PCN downstream. This spatial separation of the two boats avoids the violent and uncontrollable reactions caused by direct physical mixing, resulting in a gentler and safer process. It also allows for precise control of the etching degree and provides a longer contact time and opportunity between the etching gases generated from the decomposition of ammonium chloride and PCN, ensuring optimal performance in the PN furnace. V High concentrations of nitrogen vacancies are formed in CN.

[0035] c) After sealing the tube furnace, introduce high-purity nitrogen into the furnace at a flow rate of 50 mL / min for 30 minutes to completely remove air and create an oxygen-free inert protective atmosphere.

[0036] d) While maintaining a nitrogen flow, heat to 600°C at a heating rate of 5°C / min and hold at this temperature for 1 hour to complete gradient annealing and pore structure reconstruction.

[0037] e) After the reaction system cools naturally to room temperature, the sample is removed and washed several times with deionized water and ethanol to remove byproducts. It is then vacuum dried at 60°C for 6 hours to finally obtain the porous carbon nitride target product rich in nitrogen vacancies and retaining phosphorus elements, denoted as PN. V CN.

[0038] Comparative Example 1: Preparation of nitrogen-vacancy-modified carbon nitride Except for replacing the precursor in the second step of the atmosphere treatment in Example 1.3 with an equal amount of CN prepared in Example 1.1, all other steps, including the dual-boat design, atmosphere, temperature program, and post-treatment, are exactly the same as in Example 1.3. The resulting sample is denoted as N. V CN.

[0039] Experimental Example 1: Comparison of Morphological Characterization The morphology of the prepared materials (CN, PCN, NvCN, PNvCN) was characterized using scanning electron microscopy. Figure 1 (a)- Figure 1 As shown in (f), significant morphological differences exist between the samples. Compared to the bulk CN sample, the PCN sample exhibits a porous structure with visible cavities. This porous structure originates from the "pore-forming effect" generated by the thermal decomposition of diammonium hydrogen phosphate during calcination: the gases such as NH3 and H2O released by DAP decomposition effectively inhibit the dense packing of the melamine precursor, and may also generate carbon vacancies, thereby promoting the incorporation of phosphorus dopants.

[0040] In contrast, PN subjected to two NH4Cl vapor phase etching processes V CN and N V The CN sample exhibited a significantly altered morphology. The mixed gas released from the decomposition of NH4Cl strongly etched both NVCN and PNVCN, resulting in a densely distributed, irregular channel structure on the material surface. However, the two samples displayed different morphological characteristics: the N sample obtained by etching from bulk CN as a precursor... V CN exhibits a curled rod-like morphology. Figure 1 (b) and Figure 1 (c) lacks the pre-formed porous structure in PCN; while PN obtained by etching using pre-doped PCN as a precursor V CN forms a unique coral-like porous structure. Figure 1 (e) and Figure 1(f) consists of interconnected columnar structures. This indicates that the initially present porous structure in the PCN, together with phosphorus doping, influences the etching path, ultimately forming a more complex and open three-dimensional structure.

[0041] This application first utilizes phosphorus doping to induce a porous structure in carbon nitride before forming nitrogen vacancies, resulting in a unique, regular, coral-like porous structure. However, if nitrogen vacancies are first formed in carbon nitride to obtain N... V After CN, since the formation location of nitrogen vacancies is random, the pore structure of the prepared carbon nitride material will be uneven, affecting the functional stability of the material.

[0042] Furthermore, through PN V Elemental surface distribution analysis of CN confirmed the coexistence and uniform spatial distribution of carbon, nitrogen, and phosphorus in the material system. Scanning electron microscopy (SEM) was used to scan and photograph carbon, nitrogen, and phosphorus, as shown in Figure 2. The results demonstrate that the phosphorus dopant is uniformly dispersed in the material.

[0043] Experimental Example 2: Comparison of Pore Size Distribution The adsorption isotherm of the prepared material was analyzed using the Barrett-Joyner-Halenda (BJH) model, and the pore size distribution curve was obtained. Figure 3 ) shows that PN V CN exhibits a distinct peak at approximately 13 nm. Notably, in all samples, PN... V CN exhibits its highest peak intensity at this pore size, further demonstrating its well-developed porous structure. The synergistic effect of nitrogen vacancies and phosphorus doping reduces diffusion resistance, enabling rapid adsorption, and is equally effective for macromolecular pollutants. The specific surface area of ​​the adsorbent is the decisive factor in its physical adsorption capacity, and the pore size distribution, especially the mesopores of 2-50 nm, is crucial for reducing mass transfer resistance and achieving rapid adsorption of pollutants. Therefore, the PN of this application... V CN can effectively improve its adsorption effect on pollutants by significantly increasing the number of pores within this range.

[0044] Experimental Example 3: Adsorption Performance Comparison The effect of etching on the adsorption properties of materials was quantitatively evaluated using nitrogen adsorption-desorption testing. For example... Figure 4 As shown, Brunauer-Emmett-Teller (BET) analysis confirms the successful fabrication of a porous structure via etching, and compared to the bulk CN, PN... V CN exhibits significantly improved specific surface area and pore volume, with a maximum adsorption capacity reaching 1700 cm³. 3 g -1 And N VThe highest adsorption capacity of CN and PCN is only about 900 cm⁻¹. 3 g -1 and 500cm 3 g -1 Therefore, it is evident that phosphorus doping followed by nitrogen vacancy treatment has a synergistic effect on increasing the adsorption capacity of carbon nitride. PN V CN's BET specific surface area reaches 275.53m². 2 / g ( Figure 4 ), significantly higher than CN's 10.581m 2 / g. The significant increase in specific surface area is due to PN V CN provides more adsorption sites, thus significantly improving its adsorption efficiency.

[0045] Experiment Example 4: Comparison of Structural Characterization of Adsorbents 4.1 Comparison of Phase Structure Characterization of Adsorbents The phase structure of the adsorbent was characterized using X-ray diffraction (XRD). Figure 5 As shown, the diffraction peak at 13.0° corresponds to the (100) crystal plane of graphitic carbon nitride (g-C3N4, JCPDS card number 87-1526), ​​which belongs to the in-plane repeating structure of trihomogeneous triazine units. The characteristic peak at 27.5° is attributed to the (002) crystal plane, reflecting the interlayer stacking characteristics of the conjugated aromatic system.

[0046] It is worth noting that, compared to the bulk CN, PN V The intensities of the (100) and (002) diffraction peaks in the CN sample were significantly weakened, accompanied by a marked peak broadening phenomenon (increased half-width at half-maximum). This attenuation and broadening of peak intensity indicates a decrease in the stacking order between material layers, and structural defects and porosity may have been introduced during heat treatment. These structural modifications likely disrupt the hydrogen bond network within the triazine unit plane and weaken the long-range periodicity of the g-C3N4 framework. Furthermore, PN V The characteristic peak intensity of CN is significantly weaker than that of CN and PCN, indicating that phosphorus doping may induce a decrease in crystal order and an increase in the interlayer spacing, thereby promoting the formation of a large number of structural defects during the secondary calcination process. It is worth noting that no characteristic diffraction peaks of the phosphide crystal phase were detected in the spectrum, which further confirms that phosphorus enters the g-C3N4 lattice in the form of doping without changing its basic framework structure.

[0047] 4.2 Comparison of Chemical Structure Characterization CN, PCN, and N were analyzed using Fourier transform infrared spectroscopy (FTIR). V CN and PN V The chemical structure of CN ( Figure 6Analysis was performed. All samples exhibited the characteristic absorption band of g-C3N4: located at 1200-1650 cm⁻¹. -1 The characteristic peak within the interval (specifically 1236 cm) -1 1315cm -1 1401cm -1 1461cm -1 and 1630cm -1 This belongs to the stretching vibrations of CN and C=N bonds in the heterocyclic aromatic system (trisimilar triazine unit); 806 cm⁻¹ -1 The sharp peak at 3000-3400 cm⁻¹ corresponds to the characteristic respiratory vibration pattern of the triazine ring; while at 3000-3400 cm⁻¹... -1 The broadened absorption bands appearing within this range originate from the stretching vibrations of residual N–H groups. PCN, N V CN and PN V The continued presence of these characteristic peaks in CN confirms that the basic network structure of g-C3N4 remains intact after phosphorus doping and defect engineering modification.

[0048] 4.3 Comparison of Surface Chemical State and Elemental Composition Analysis CN, PCN, and N were analyzed using X-ray photoelectron spectroscopy (XPS). V CN and PN V Surface chemical state and elemental composition of CN. Figure 7 The peaks can be fitted into three characteristic peaks with binding energies at 284.5 eV, 286.1 eV, and 288.0 eV, respectively, which are attributed to adsorbed contaminating carbon (CC / C=C), C-NH4+, and C-NH4+ adsorbed in the environment. x The group and the sp² hybrid carbon (NC=N) in the tris(triazine) ring.

[0049] N1s spectrum analyzed by X-ray photoelectron spectroscopy (XPS) Figure 8 The sample exhibits four independent components: pyridine nitrogen (C=NC) at 398.5 eV, tricoordinate nitrogen N-(C)3 (graphite nitrogen) at 400.0 eV, pyrrole nitrogen (CNH) at 401.1 eV, and a charged effect or π excited state at approximately 404.2 eV.

[0050] The structural evolution of the adsorbent was analyzed based on quantitative analysis of peak area integral: the proportion of the key NC=N component in PCN decreased from 63% in the original CN to 60%, indicating the loss of some carbon atoms during phosphorus doping. This decreasing trend is observed in PN... V The most significant change was observed in CN, where the NC=N content plummeted to 49%, indicating substantial disruption of the NC=N bonding network. Furthermore, the proportion of pyridine nitrogen (C=NC) decreased from 49% in CN to N.V CN was 39%, and further decreased to PN. V CN is 35%. This progressive decrease also proves the formation of nitrogen vacancies, mainly located at pyridine nitrogen sites. This is corroborated by PN. V The C1s and N1s binding energies of CN show positive shifts compared to CN, indicating a decrease in local electron density around these atoms. This electron loss phenomenon is attributed to the electron-withdrawing effect of neighboring highly electronegative phosphorus atoms.

[0051] Through the P2p spectrum ( Figure 9 This confirmed the existence of PN bonds formed by the substitution of carbon atoms in the trihomocyzine ring by doped phosphorus atoms. In the relationship between PCN and PN... V A distinct characteristic peak at 133.7 eV was observed in both CN and N, corresponding to PN bonding. V This peak is completely absent in CN. It is worth noting that PN... V The intensity of the PN characteristic peak in CN is significantly weakened compared to PCN. This attenuation phenomenon further indicates that nitrogen vacancies preferentially form at sites adjacent to the phosphorus atom, implying a close correlation between phosphorus atoms and vacancy defects. This achieves a synergistic effect of phosphorus doping and nitrogen vacancies in the carbon nitride treatment process.

[0052] Elemental analysis based on XPS full spectrum showed that the nitrogen-to-carbon ratio (N / C) of the original CN was 1.30, consistent with the theoretical value of g-C3N4. Compared to CN, PCN had a similar nitrogen content but a lower carbon content, resulting in an increased N / C ratio of 1.43. This increase in ratio is consistent with the mechanism of phosphorus atoms replacing carbon atoms in the tris(triazine) framework. Although PN V The phosphorus content of CN is similar to that of PCN, but its nitrogen content is significantly lower. This evidence collectively confirms the formation of nitrogen vacancy structures during the secondary calcination step.

[0053] Furthermore, electron paramagnetic resonance (EPR) spectroscopy further verified the PN. V The presence of nitrogen vacancies in CN. PCN and PN. V CN all exhibit a Lorentz-shaped EPR signal at g=2.0039. Figure 10 This signal characteristic originates from the unpaired electrons localized on the carbon atoms of the triazine ring. However, the EPR signal intensity of PCN is relatively weak, indicating a low concentration of unpaired electrons, i.e., very few nitrogen vacancies. In stark contrast, PN... V CN exhibits a significantly enhanced paramagnetic absorption signal, indicating a substantial increase in the number of unpaired electrons. This significant enhancement of the EPR signal confirms the presence of PN... V The presence of high concentrations of nitrogen vacancies in CN is consistent with the findings of XPS analysis.

[0054] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing porous carbon nitride with high specific surface area, characterized in that, Includes the following steps: Step 1: Preparation of phosphorus-doped graphitic carbon nitride; Step 2: Modify the phosphorus-doped carbon nitride from Step 1 with nitrogen vacancies.

2. The method for preparing high specific surface area porous carbon nitride according to claim 1, characterized in that, Step 1 includes the following steps: Step 1.1: Physically blend and grind melamine and inorganic phosphate in a mass ratio of 10:0.5-5 to ensure that the two phases are uniformly mixed at the molecular level. Step 1.2: Transfer the ground powder to a crucible with a sealed lid; Step 1.3: Place the crucible in a muffle furnace and heat it to 400-600℃ in a static air atmosphere. Then, calcine it at this temperature for 3-6 hours to ensure complete polymerization and crystallization of the precursor. Step 1.4: After the reaction in step 1.3 is completed, allow the furnace to cool naturally to room temperature, remove the generated orange product, grind it again, and you will get phosphorus-doped carbon nitride (PCN) powder.

3. The method for preparing high specific surface area porous carbon nitride according to claim 1, characterized in that, Step 2 includes the following steps: Step 2.1: Take an appropriate amount of the PCN powder obtained in Step 1 and place it in a quartz boat; Step 2.2: Place ammonium chloride in another quartz boat, with a mass ratio of ammonium chloride to PCN of 4-10:1; Step 2.3: Seal the tubular furnace and introduce high-purity nitrogen into the furnace for 20-60 minutes to completely remove air; Step 2.4: While maintaining a nitrogen flow, heat to 500-800℃ and hold at this temperature for 1 hour to complete gradient annealing and pore structure reconstruction; Step 2.5: After the reaction system cools naturally to room temperature, the sample is removed and washed several times with deionized water and ethanol to remove byproducts. It is then vacuum dried at 40-70℃ for 5-8 hours to obtain high specific surface area porous carbon nitride (PN). V CN.

4. The method for preparing high specific surface area porous carbon nitride according to claim 3, characterized in that, Another quartz boat containing ammonium chloride is placed upstream of the gas flow in the tube furnace, while the boat containing PCN is placed downstream of the gas flow.

5. The method for preparing high specific surface area porous carbon nitride according to claim 2, characterized in that, Step 1 includes the following steps: Step 1.1: Physically blend and grind melamine and inorganic phosphate in a mass ratio of 10:1-3 solid powder for 20-30 minutes to ensure that the two phases are uniformly mixed at the molecular level; Step 1.2: Transfer the ground powder into an alumina crucible with a sealed lid; Step 1.3: Place the crucible in a muffle furnace and heat it to 500-550°C in a static air atmosphere. Then, calcine it at this temperature for 3-5 hours to ensure complete polymerization and crystallization of the precursor. Step 1.4: After the reaction in step 1.3 is completed, allow the furnace to cool naturally to room temperature, remove the generated orange product, grind it again, and you will get phosphorus-doped carbon nitride (PCN) powder.

6. The method for preparing high specific surface area porous carbon nitride according to claim 3, characterized in that, Step 2 includes the following steps: Step 2.1: Take an appropriate amount of the PCN powder obtained in Step 1 and place it in a quartz boat; Step 2.2: Place ammonium chloride in another quartz boat with a mass ratio of ammonium chloride to PCN of 6-8:

1. Place the quartz boat containing ammonium chloride upstream of the gas flow in the tube furnace, while place the quartz boat containing PCN downstream of the gas flow. Step 2.3: Seal the tubular furnace and introduce high-purity nitrogen into the furnace at a flow rate of 40-60 mL / min for 30 minutes to completely remove air; Step 2.4: While maintaining a nitrogen flow, heat to 600-700℃ and hold at this temperature for 1 hour to complete gradient annealing and pore structure reconstruction; Step 2.5: After the reaction system cools naturally to room temperature, the sample is removed and washed several times with deionized water and ethanol to remove byproducts. It is then vacuum dried at 60°C for 5-7 hours to obtain high specific surface area porous carbon nitride (PN). V CN.

7. A porous carbon nitride with high specific surface area, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. An apparatus for implementing the preparation method according to any one of claims 1-6, characterized in that, Inside the tubular furnace, along the flow direction of the carrier gas, there are a first quartz boat for holding ammonium chloride and a second quartz boat for holding PCN, arranged sequentially.

9. An air filter device, characterized in that, High specific surface area porous carbon nitride prepared by the preparation method of any one of claims 1-6.

10. The use of the high specific surface area porous carbon nitride prepared by any one of claims 1-6 or the high specific surface area porous carbon nitride as described in claim 7, characterized in that, Used for catalytic degradation of organic pollutants in waste gas or wastewater.

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