A porous carbon nitride photocatalyst and a preparation method and application thereof

Abstract

The application provides a porous carbon nitride photocatalyst and a preparation method and application thereof, and the porous carbon nitride photocatalyst is prepared by the following steps: uniformly mixing and grinding a nitrogen-rich organic material precursor and a gaseous template agent ammonium chloride; performing high-temperature treatment on the mixed precursor by using a microwave-assisted thermal polymerization method, and cooling to room temperature after the reaction is completed; and grinding, washing and drying the obtained product to collect the GCN. The method uses a one-step microwave-assisted thermal polymerization method to make melamine and the mixed precursor of ammonium chloride react, and the rapid thermal shock effect of the microwave field is used to induce the material to form a porous structure; the ammonium chloride is decomposed at high temperature to generate a bubble effect, which effectively inhibits the excessive stacking of carbon-nitrogen planes, induces the formation of a hierarchical porous structure and introduces rich edge defects. The degradation rate constant of the catalyst for cephalosporin antibiotics can reach 4.16 times that of pure g-C3N4, the catalyst has extremely excellent specific removal capacity for tetracycline, has good chemical stability and broad applicability, and can efficiently realize the deep purification of pollutants in water.

Description

Technical Field

[0001] This application belongs to the field of photocatalyst technology, and particularly relates to a porous carbon nitride photocatalyst, its preparation method and application. Background Technology

[0002] With technological advancements and intensified human activities, environmental degradation and energy depletion have become common problems urgently needing solutions for all humanity. In water pollution control, photocatalytic oxidation technology, as an environmentally friendly, cost-effective, and universally applicable solution, has gained widespread favor in academia. This technology utilizes photoexcitation to generate active free radicals, effectively degrading recalcitrant organic pollutants and providing a new direction for solving environmental pollution.

[0003] Among numerous photocatalytic materials, g-C3N4 is considered a highly promising candidate due to its excellent chemical stability, unique electronic structure, and responsiveness in the visible light region. However, pure g-C3N4 suffers from drawbacks such as a wide band gap, low visible light utilization, and low efficiency in separating photogenerated electron-hole pairs, which significantly restricts its large-scale application. Therefore, finding efficient and stable modification methods to optimize its microstructure and improve charge transfer efficiency has become a key focus of current research.

[0004] Patent CN 112495412 A discloses a porous thin-layer graphitic carbon nitride, its preparation method, and its applications. Using ammonium chloride as a bubble template, porous thin-layer graphitic carbon nitride is directly obtained through a simple one-step calcination method. On one hand, the porous thin-layer structure has a high specific surface area, providing more active sites. On the other hand, the formation of the porous structure leads to the loss of electron-donating groups, reducing the recombination sites of photogenerated electrons, solving the problem of easy recombination of photogenerated carriers, and further improving photocatalytic activity. However, the prepared porous material still has defects such as low visible light utilization, insufficient band structure control, uneven pore size distribution, limited structural stability and surface reactivity, unsatisfactory photogenerated carrier separation efficiency, and insufficient ability to generate active species such as free radicals. Consequently, its ability to degrade organic matter in wastewater is poor, especially its low degradation rate constant for cephalosporin antibiotics, making it difficult to achieve deep purification of pollutants in water. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and its purpose is to provide a porous g-C3N4 photocatalytic material prepared by modifying carbon nitride with ammonium chloride as a sacrificial gas-phase template agent through a one-step microwave-assisted thermal polymerization method for the degradation of cephalosporin antibiotics.

[0006] The first aspect of this application provides a method for preparing a porous carbon nitride photocatalyst, the steps of which include: mixing and grinding a nitrogen-rich organic precursor with a gaseous template agent ammonium chloride; subjecting the mixed precursor to high-temperature treatment using a microwave-assisted thermal polymerization method, and cooling to room temperature after the reaction is completed; grinding, washing and drying the obtained product, and collecting the modified porous graphitic carbon nitride.

[0007] In any embodiment, the nitrogen-rich organic precursor is melamine.

[0008] In any embodiment, the mass ratio of the nitrogen-rich organic precursor to ammonium chloride is 1:0.85 to 1:1.15.

[0009] In any embodiment, the microwave-assisted thermal polymerization involves placing the mixed powder in a covered graphite crucible, heating it to 520-570°C and holding it at that temperature for 25-35 minutes under microwave power of 2kW-4kW.

[0010] In any embodiment, the introduced defect sites, acting as electron trapping centers, effectively block the direct recombination of electrons and holes, thus extending carrier lifetime. Free radical trapping experiments confirm that superoxide radicals (·O2) in this system... - ) is the most critical active species that dominates degradation.

[0011] In any embodiment, the modified porous graphitic carbon nitride has a loose, porous honeycomb structure with a specific surface area of ​​26.09 m². 2 / g, pore volume is 0.190 cm³ 3 / g。 .

[0012] A second aspect of this application also provides a porous carbon nitride photocatalyst prepared using the above method.

[0013] A third aspect of this application provides the use of porous carbon nitride photocatalysts for the degradation of organic pollutants in water bodies under visible light-driven conditions.

[0014] In any embodiment, the organic pollutant is a cephalosporin antibiotic or a tetracycline antibiotic; In any embodiment, the cephalosporin antibiotic is ceftiofur sodium (CFS), cephalexin (CEL), cefuroxime (CXM), cefotaxime (CTX), cefepime (CEFEP), tetracycline (TC), ciprofloxacin (CIP), metronidazole (MTZ), and sulfamethoxazole (SMZ).

[0015] In any embodiment, during the degradation of the organic pollutant, for a pollutant solution with a concentration of 20 mg / L, the dosage of the catalyst to the pollutant solution is 1 mg: 5 ml, the reaction time is 20-60 min, and the light source is visible light.

[0016] The beneficial effects of this application are: 1) High efficiency and low energy consumption in the process: This invention adopts a one-step microwave-assisted thermal polymerization method, which utilizes the rapid thermal shock effect of the microwave field to complete the thermal condensation reaction of the precursor within a very short holding time, significantly improving the synthesis efficiency. At the same time, ammonium chloride, as a sacrificial gaseous template agent, can spontaneously decompose and release gas during the preparation process. The process is simple, the raw materials are inexpensive and readily available, and there is no need for complicated post-processing stripping steps, making it suitable for large-scale production.

[0017] 2) Significantly Enhanced Photocatalytic Degradation Performance: The modified GCN material exhibits a significantly increased specific surface area (approximately 2.35 times that of pure g-C3N4) and abundant mesoporous structure. Edge defects introduced through the bubble effect and the presence of hydrophilic hydroxyl groups on the surface not only optimize the band structure of the material but also significantly suppress the recombination of photogenerated carriers. Under visible light irradiation, the degradation rate constant of the GCN sample for cephalosporin antibiotics (k = 0.03242 min) is significantly improved. -1 It is approximately 4.16 times that of pure g-C3N4, exhibiting excellent catalytic activity.

[0018] 3) Wide range of substrates and high environmental safety: The catalyst prepared by this invention exhibits excellent broad-spectrum degradation ability, with a stable removal rate of cephalosporin antibiotics between 85% and 95%; and has extremely excellent specific removal ability for tetracycline (TC), with a degradation rate as high as 95%. Attached Figure Description

[0019] Figure 1 XRD patterns of pure g-C3N4 and GCN prepared in the examples and comparative examples; Figure 2 SEM and EDS images of GCN prepared in Example 1 of this application; Figure 3 FTIR spectra of pure g-C3N4 and GCN prepared in the examples and comparative examples; Figure 4 The XPS total spectrum of GCN prepared in Example 1 of this application; Figure 5 XPS fine spectrum of GCN prepared in Example 1 of this application; Figure 6 Adsorption curves of pure g-C3N4 and GCN prepared in Example 1 of this application; Figure 7TPR curves of pure g-C3N4 and GCN prepared in Example 1 of this application; Figure 8 EIS curves of pure g-C3N4 and GCN prepared in Example 1 of this application; Figure 9 CV curves of pure g-C3N4 and GCN prepared in Example 1 of this application; Figure 10 Photocatalytic degradation curves of ceftiofur sodium by pure g-C3N4 and GCN prepared in the examples and comparative examples; Figure 11 The efficiency curves of photocatalytic degradation of ceftiofur sodium by pure g-C3N4 and GCN prepared in the examples and comparative examples are shown. Figure 12 Rate constants for the photocatalytic degradation of ceftiofur sodium by pure g-C3N4 and GCN prepared in the examples and comparative examples; Figure 13 The graph shows the efficiency of GCN photocatalytic degradation of other cephalosporin antibiotics prepared in Example 1 of this application. Figure 14 The efficiency diagram of GCN photocatalytic degradation of other antibiotics prepared in Example 1 of this application; Figure 15 The figure shows the effect of different free radical quenchers on the degradation efficiency of 10g-GCN catalyst. Detailed Implementation

[0020] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the porous carbon nitride photocatalyst, its preparation method, and its applications. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0021] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0022] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0023] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0024] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0025] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0026] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0027] In one embodiment of this application, a method for preparing a porous carbon nitride photocatalyst is proposed, comprising the following steps: mixing and grinding a nitrogen-rich organic precursor with a gaseous template agent ammonium chloride; subjecting the mixed precursor to high-temperature treatment using a microwave-assisted thermal polymerization method, and cooling to room temperature after the reaction is completed; grinding, washing and drying the obtained product, and collecting the modified porous graphitic carbon nitride.

[0028] This catalyst uses microwave-prepared g-C3N4 as a substrate and is modified by introducing ammonium chloride (NH4Cl) as a gas-phase template agent during the thermal polycondensation process. A one-step microwave-assisted thermal polymerization method is used to react melamine with the ammonium chloride mixed precursor. The rapid thermal shock effect of the microwave field induces the formation of a porous structure in the material. Microwave-assisted thermal polymerization is a high-energy microwave method with electromagnetic field effects, unlike ordinary thermal polycondensation which lacks a thermal magnetic field. At high temperatures, ammonium chloride decomposes, releasing NH3 and HCl gases, generating a bubble effect that effectively suppresses excessive stacking of carbon and nitrogen planes, inducing a hierarchical porous structure and introducing abundant edge defects.

[0029] In some embodiments, the nitrogen-rich organic precursor is melamine.

[0030] In some embodiments, the mass ratio of the nitrogen-rich organic precursor to ammonium chloride is 1:0.85 to 1:1.15.

[0031] The core reason why the material exhibits excellent photocatalytic degradation performance within this range is that this ratio achieves synergistic optimization of the material's pore structure, doping degree, lattice defects, band structure, and carrier separation efficiency. This allows the material's photocatalytic properties to be highly compatible with the degradation requirements of pollutants. If the ratio deviates from this range, structural and performance imbalances will occur, leading to a significant decrease in catalytic activity. During the high-temperature calcination preparation process, ammonium chloride undergoes a thermal decomposition reaction to generate ammonia and hydrogen chloride gases. These two gases play key regulatory roles. Ammonia can act as a dynamic bubble template to create and expand pores in the material, while simultaneously supplementing the nitrogen source, regulating the degree of carbon nitride condensation, and inducing the formation of active defects such as nitrogen vacancies and cyano groups. Hydrogen chloride, on the other hand, enables in-situ doping of chlorine, gently etching the material's stacked structure under an acidic atmosphere to peel off ultrathin nanosheets, weakening the interlayer stacking effect, and effectively shortening the diffusion path of photogenerated carriers, thus laying the structural foundation for efficient photocatalytic reactions.

[0032] When the ratio of ammonium chloride to precursor is within the suitable range of 1:0.85–1:1.15, the amount of gas decomposition is moderate, which can fully modify the carbon nitride material without destroying the inherent crystal framework of the material. This ultimately results in an ultrathin nanosheet morphology with abundant mesoporous structure, significantly improving the specific surface area and pore volume of the material. If the amount of ammonium chloride is lower than this ratio range, the gas template effect and etching modification effect are insufficient. The prepared carbon nitride is mostly a dense bulk structure with few pores and insufficient active sites. At the same time, the chlorine doping amount is too low, and the number of intrinsic defects is scarce, making it impossible to effectively optimize the band structure of the material. Visible light utilization is low, photogenerated electrons and holes recombine easily, making it difficult to generate sufficient active free radicals, resulting in extremely poor catalytic degradation effect.

[0033] Conversely, when the ammonium chloride content exceeds the upper limit of the 1:1.15 ratio, excessive ammonia and hydrogen chloride will over-etch the carbon nitride framework, completely destroying the material's intact triazine ring crystal structure and conjugated electron transport system, resulting in lattice fragmentation. Simultaneously, excessively high chlorine doping concentrations and excessive structural defects no longer improve catalytic performance; instead, they become recombination centers for photogenerated carriers, accelerating electron-hole annihilation, significantly reducing the generation of active free radicals, and ultimately leading to a precipitous drop in the material's photocatalytic activity. The optimal ratio range allows for moderate chlorine doping, effectively narrowing the carbon nitride bandgap, broadening the visible light response range, and improving light energy utilization. Simultaneously, it precisely controls the density of defects such as nitrogen vacancies and cyano groups, allowing defects to fully function as electron traps, effectively suppressing carrier recombination, extending carrier lifetime, and significantly increasing the yield of highly oxidizing active groups such as superoxide radicals and hydroxyl radicals.

[0034] In some embodiments, the microwave-assisted thermal polymerization involves placing the mixed powder in a covered graphite crucible, heating it to 520-570°C and holding it at a microwave power of 2kW-4kW for 25-35 minutes; after the reaction is complete and the mixture is naturally cooled to room temperature, collecting the pale yellow blocky product and grinding it into powder, rinsing it 3-5 times with pure water, and then drying it for later use.

[0035] Excessive power can easily cause localized overheating and temperature spikes, resulting in a product with an outer layer of charred material and an inner layer of brittle material, leading to extremely uneven crystallinity. Conversely, insufficient power will result in slow heating, causing the template agent ammonium chloride to decompose and escape prematurely before the precursor has polymerized, leading to pore-forming failure. A wide range of power and heating programs (such as stepped heating) can ensure uniform heating of the material as a whole.

[0036] The formation of graphitic carbon nitride is extremely temperature-sensitive. At excessively low temperatures, the precursor polymerization is incomplete, resulting in a discontinuous conjugated network, poor crystallinity, and easy recombination of photogenerated carriers. Furthermore, ammonium chloride decomposes inadequately, making it difficult to form interconnected channels. At excessively high temperatures, carbon nitride undergoes violent thermal decomposition, leading to framework collapse. While the specific surface area is large, the defects are numerous, and mass loss is severe (extremely low yield). Finding the optimal "polymerization-pore-forming" balance between high crystallinity and high porosity within the range of 520–570℃ is fundamental to obtaining highly active materials.

[0037] The holding time directly controls the reaction depth. If the time is too short, the reaction is incomplete, and the remaining uncondensed intermediates become numerous complexation centers; if the time is too long, beneficial nitrogen vacancies will further evolve into large-scale structural defects, or even burn out the pores. By controlling the time (especially in combination with temperature and power), the concentration of nitrogen vacancies and the content of edge amino groups can be precisely controlled, thereby fine-tuning the band gap width and conduction band / valence band potential, allowing the catalyst to be adapted to specific redox reactions (such as hydrogen production requiring a more negative conduction band, and degradation requiring stronger oxidizing power).

[0038] Through precise control, the temperature can be slightly lower near 550℃ with a longer holding time (e.g., 520℃, 35min), or the temperature can be rapidly increased to 550℃ with a slightly higher power and held for a short time (e.g., 4kW, 570℃, 25min). This allows for the simultaneous maintenance of high condensation degree (high crystallinity, good π-conjugation of benzene rings) while utilizing template gas impact to fully create pores, resulting in an ideal product with high crystallinity and high specific surface area. Carrier mobility and the number of reaction sites are maximized simultaneously, achieving a "double high" in crystallinity and specific surface area.

[0039] By adjusting the combination of temperature and time, the C / N ratio and nitrogen vacancy concentration of the product can be precisely controlled, achieving a continuously tunable band gap between approximately 2.5 and 2.8 eV, and a light absorption edge that can be redshifted from 460 nm to approximately 500 nm or even further. This means that you can prepare a series of catalysts with broader visible light response and customizable redox capabilities in the same system.

[0040] By controlling the power and heating rate, the intensity of gas release can be influenced. Slow heating combined with a longer holding time tends to form more micropores and small mesopores; rapid heating to a high temperature followed by a short holding time, on the other hand, is conducive to the formation of some macropores and more open mesopores. This provides complete controllability for constructing an ideal hierarchical porous structure with "micropores enriching active sites and mesopores and macropores enhancing mass transfer".

[0041] In some embodiments, the introduced defect sites act as electron trapping centers, effectively blocking the direct recombination of electrons and holes (see reference). Figure 2 This extends the carrier lifetime. Free radical capture experiments confirm that superoxide radicals (·O2) in this system... -) is the most critical active species that dominates degradation (see reference) Figure 15 ).

[0042] The prepared GCN catalyst exhibits excellent photocatalytic performance. The porous structure constructed within the material by the gas released from the decomposition of ammonium chloride shortens the charge transport path, and the introduced defect sites act as electron trapping centers, effectively blocking the direct recombination of electrons and holes and extending the carrier lifetime. Free radical trapping experiments confirm that superoxide radicals (·O2) in this system... - ) is the most critical active species that dominates degradation.

[0043] In some embodiments, the modified porous graphitic carbon nitride has a loose, porous honeycomb structure with a specific surface area of ​​26.09 m². 2 / g, pore volume is 0.190 cm³ 3 / g.

[0044] The modified GCN exhibits a loose, honeycomb-like porous structure with abundant pores and a larger pore volume. Experimental results show that the specific surface area of ​​the modified sample increased by approximately 2.35 times, with its BET specific surface area increasing from 11.09 m² of the original g-C₃N₄. 2 / g increased to 26.09m 2 / g. The specific surface area of ​​the original g-C3N4 is 11.09 m². 2 / g, pore volume is 0.116 cm³ 3 The specific surface area of ​​10 g-GCN increased significantly to 26.09 m². 2 / g, pore volume increased to 0.190 cm³ 3 / g.

[0045] In one embodiment of this application, a porous carbon nitride photocatalyst prepared by the above method is proposed.

[0046] In one embodiment of this application, the application of a porous carbon nitride photocatalyst is proposed for the degradation of organic pollutants in water bodies under visible light-driven conditions.

[0047] In some embodiments, the organic pollutant is a cephalosporin antibiotic or a tetracycline antibiotic.

[0048] In some embodiments, the cephalosporin antibiotics are ceftiofur sodium (CFS), cephalexin (CEL), cefuroxime (CXM), cefotaxime (CTX), cefepime (CEFEP), tetracycline (TC), ciprofloxacin (CIP), metronidazole (MTZ), and sulfamethoxazole (SMZ).

[0049] This catalyst exhibits excellent degradation activity for cephalosporin antibiotics (such as ceftiofur sodium CFS), with a degradation rate constant up to 4.16 times that of pure g-C3N4. Furthermore, this material demonstrates exceptionally high specificity in the removal of tetracycline (TC) (removal rate up to 95%).

[0050] The exceptionally high specificity for tetracycline removal is due to the large number of planar π-conjugated systems and edge defects exposed after vapor-phase exfoliation of GCN. These features enable strong π-stacking and polydentate hydrogen bonding interactions with the highly conjugated tetracyclic skeleton and abundant polar groups in the TC molecule. This highly efficient and specific adsorption significantly shortens the interfacial mass transfer distance, allowing TC to preferentially occupy the catalytic active site.

[0051] In some embodiments, during the degradation of the organic pollutant, for a pollutant solution with a concentration of 20 mg / L, the dosage of the catalyst to the pollutant solution is 1 mg: 5 ml, the reaction time is 20-60 min, and the light source is visible light.

[0052] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0053] Example 1 Accurately weigh 10g of melamine precursor and 10g of ammonium chloride modifier, place them in a mortar, mix thoroughly, and grind evenly. Place the mixed powder in a graphite crucible and center it in the cavity of an industrial high-energy microwave oven. Heat to 550℃ and hold for 30 minutes at a microwave power of 3kW. The ammonium chloride decomposes at high temperature, producing a vapor-phase etching effect that induces the formation of a porous structure in the material. After the sample cools naturally to room temperature, remove the pale yellow, loose product, grind it thoroughly, wash it 3-5 times with deionized water to remove residual impurities, and finally dry and collect it to obtain the porous modified sample, named GCN.

[0054] Photocatalytic degradation test: The GCN sample prepared in Example 1 was used as a photocatalyst to test the degradation performance of ceftiofur sodium (CFS) and tetracycline (TC). Specifically, a 300W xenon lamp was used as the light source, the amount of catalyst was 10 mg, the initial concentration of pollutant solution was 20 mg / L, and the solution volume was 50 mL.

[0055] After adding the photocatalyst, a 1-hour light-shielded adsorption equilibration treatment was performed. Then, the light source was turned on, and the reaction was irradiated for 60 minutes. Samples were taken at regular intervals, filtered through a 0.45 μm filter membrane, and the absorbance was measured. The degradation rate was calculated based on the concentration changes.

[0056] Within 60 minutes, the catalyst prepared in Example 1 achieved a degradation rate of approximately 88% for CFS, with an apparent rate constant k of 0.03242 min. -1 It is approximately 4.16 times that of pure g-C3N4; at the same time, the degradation rate of TC in this sample is as high as 95%.

[0057] Comparative Example Comparative Example 1 10g of melamine and 10g of ammonium chloride were mixed and placed in a ceramic crucible. The temperature was raised to 550 °C in a muffle furnace and held for 2 h. After the sample cooled naturally to room temperature, the pale yellow blocky product was removed, ground into powder, and collected for later use. This sample was designated MGCN.

[0058] Photocatalytic degradation test: The pure g-C3N4 prepared in Comparative Example 1 was used as a photocatalyst to test the degradation performance of a 20 mg / L ceftiofur sodium (CFS) solution.

[0059] After 60 minutes of light exposure, the degradation rate was 79% under the same conditions.

[0060] Comparative Example 2 (1) Preparation of mixed precursors: Accurately weigh 10 g of melamine precursor and 2.5 g of ammonium chloride modifier, place them in a mortar and mix thoroughly and grind evenly.

[0061] (2) Preparation process: The same microwave-assisted thermal polymerization method as in Example 1 was used for preparation. The mixed powder was placed in a graphite crucible and heated to 550 °C under microwave power of 3 kW and held for 30 min. After naturally cooling to room temperature, it was taken out, ground, washed and dried to obtain 2.5 g of sample-GCN.

[0062] Degradation tests were conducted on CFS at a concentration of 20 mg / L under the same illumination conditions. Due to the low amount of ammonium chloride added, the vapor-phase etching effect was limited, resulting in a low degree of porosity in the material. Within 60 min, the degradation efficiency of this sample for CFS was 71%, significantly lower than that in Example 1, demonstrating that low-dose vapor-phase template agents cannot adequately optimize the microstructure of carbon nitride.

[0063] Comparative Example 3 (1) Preparation of mixed precursors: Accurately weigh 10 g of melamine precursor and 5 g of ammonium chloride modifier, place them in a mortar and mix thoroughly and grind evenly.

[0064] (2) Preparation process: The same microwave-assisted thermal polymerization method as in Example 1 was used for preparation. After naturally cooling to room temperature, the sample was taken out, ground, washed and dried to obtain 5g of GCN sample.

[0065] Photocatalytic degradation of 20 mg / L CFS was tested. The degradation efficiency of ceftiofur sodium was 77%, which was an improvement compared to 2.5 g-GCN. However, compared to Example 1 (10 g addition), the separation efficiency of photogenerated carriers still needs optimization and did not achieve optimal redox performance.

[0066] Comparative Example 4 (1) Preparation of mixed precursors: Accurately weigh 10 g of melamine precursor and 7.5 g of ammonium chloride modifier, place them in a mortar and mix thoroughly and grind evenly.

[0067] (2) Preparation process: The same microwave-assisted thermal polymerization method as in Example 1 was used for preparation. After naturally cooling to room temperature, the sample was taken out, ground, washed and dried to obtain 7.5g of GCN.

[0068] Photocatalytic degradation tests were conducted on 20 mg / L CFS. Experimental data showed that as the proportion of ammonium chloride increased further, the remaining concentration of CFS continued to decrease, and the final degradation rate was 81%, indicating that the catalytic activity increased with the degree of modification. However, considering both the kinetic constant k value and the final degradation rate, its actual performance was still slightly inferior to the 10 g-GCN sample in Example 1.

[0069] Comparative Example 5 (1) Preparation of mixed precursors: Accurately weigh 10 g of melamine precursor and 10 g of ammonium chloride modifier, place them in a mortar and mix thoroughly and grind evenly.

[0070] (2) Preparation process: The heating power was 3 kW to 450℃ and kept at that temperature for 30 min. After naturally cooling to room temperature, the sample was taken out, ground, washed and dried to obtain sample 450-10g-GCN. The prepared material was white-yellow.

[0071] Photocatalytic degradation tests were conducted on 20 mg / L CFS. The results showed that the catalyst had a degradation efficiency of 30% for 20 mg / L CFS solution within 60 min, indicating that the reaction temperature was too low, the prepared material had poor crystallinity, and the reaction was incomplete.

[0072] Comparative Example 6 (1) Preparation of mixed precursors: Accurately weigh 10 g of melamine precursor and 10 g of ammonium chloride modifier, place them in a mortar and mix thoroughly and grind evenly.

[0073] (2) Preparation process: The heating power was 3 kW to 600 ℃ and held for 30 min. After naturally cooling to room temperature, it was taken out, ground, washed and dried to obtain sample 600-10g-GCN. The prepared material was brownish-yellow.

[0074] Photocatalytic degradation tests were conducted on 20 mg / L CFS. The results showed that the catalyst had a degradation efficiency of 69% for 20 mg / L CFS solution within 60 min, indicating that the reaction temperature was too high and the prepared material underwent excessive polycondensation, resulting in thermal decomposition.

[0075] Comparative Example 7 (1) Preparation of mixed precursors: Accurately weigh 10 g of melamine precursor and 10 g of ammonium chloride modifier, place them in a mortar and mix thoroughly and grind evenly.

[0076] (2) Preparation process: The heating power was 3 kW to 550 ℃ and held for 60 min. After naturally cooling to room temperature, the sample was taken out, ground, washed and dried to obtain 60-10g-GCN. The prepared material was light brown.

[0077] Photocatalytic degradation tests were conducted on 20 mg / L CFS. The results showed that the catalyst had a degradation efficiency of 57% for 20 mg / L CFS solution within 60 min, indicating that the prepared material decomposed if the reaction time was too long.

[0078] Comparative Example 8 (1) Preparation of mixed precursors: Accurately weigh 10 g of melamine precursor and 10 g of ammonium chloride modifier, place them in a mortar and mix thoroughly and grind evenly.

[0079] (2) Preparation process: The heating power was 3 kW to 550 ℃ and held for 15 min. After naturally cooling to room temperature, the sample was taken out, ground, washed and dried to obtain 15-10g-GCN. The prepared material was yellowish-white.

[0080] Photocatalytic degradation tests were conducted on 20 mg / L CFS. The results showed that the catalyst had a degradation efficiency of 63% for 20 mg / L CFS solution within 60 min, indicating that the reaction time was too short, the polymerization was incomplete, and the crystallinity was poor.

[0081] Figure 1 XRD diffraction patterns of pure g-C3N4 and porous GCN samples prepared by different methods are shown in the figure. As can be seen from the figure, all samples retain the typical (100) and (002) characteristic diffraction peaks of g-C3N4. After modification with ammonium chloride, the intensity of the (002) peak decreased and the full width at half maximum (FWHM) increased slightly. This indicates that the decomposition and release of the gaseous template weakened the orderliness of the interlayer stacking, promoted the formation of thin-layer structures, and did not change the graphite phase crystal characteristics of the material.

[0082] Figure 2 The images show the SEM and EDS morphology of the GCN catalyst. As can be seen from the figures, compared to the dense structure of the original bulk g-C3N4, the GCN prepared in this invention exhibits a significantly loose, honeycomb-like porous structure. This bubble effect generated by the decomposition of ammonium chloride forms abundant hierarchical pores, significantly increasing the specific surface area of ​​the material (from 11.09 m² / g to 26.09 m² / g), which is beneficial for the diffusion of reactant molecules and the exposure of active sites.

[0083] Figure 3 The image shows the FTIR spectrum of the GCN catalyst. As can be seen from the figure, the modified sample exhibits high FTIR at 810 cm⁻¹. -1 and 1200-1650 cm -1 The characteristic vibrational peaks of the region are consistent with those of pure g-C3N4, confirming that its main heptaazine ring framework structure remains stable during microwave-assisted vapor etching.

[0084] Figure 4 This is the XPS spectrum of the GCN catalyst. Full-spectrum analysis shows that the sample mainly contains C, N elements, and a small amount of O. In the C 1s spectrum, the peak at 288.1 eV is attributed to the NC=N structure; the peak at 398.5 eV in the N 1s spectrum is attributed to sp² hybrid nitrogen (CN=C). The modified O content is slightly increased, mainly existing in the form of surface hydroxyl groups, which helps to enhance the dispersibility and hydrophilicity of the material in aqueous solution.

[0085] Depend on Figure 4 The full spectrum shows that the sample is mainly composed of C, N and O elements, and no other impurities were detected. Figure 5 For XPS fine-grained maps, among which Figure 5 (a) The strong peak at 287.8 eV in the C 1s high-resolution spectrum corresponds to sp 2 Hybridized NC=N bonds; Figure 5 (b) The N 1s spectrum shows characteristic peaks such as CN=C (398.1 eV) in the corresponding triazine ring, confirming the integrity of the skeletal structure. Figure 5 (c) The single peak at 531.8 eV in the O 1s spectrum corresponds to oxygen-containing functional groups such as C=O or -OH introduced during the etching process. These hydrophilic groups help improve the interfacial contact performance of the catalyst.

[0086] Figure 6 The BET pore size distribution and nitrogen adsorption-desorption curves of GCN are shown. The curves exhibit typical type IV isotherm characteristics and a type H3 hysteresis loop, confirming the existence of the mesoporous structure of the material. After modification, the pore volume increased from 0.054 cm³ / g to 0.190 cm³ / g, and this optimized pore structure is a key factor in improving the photocatalytic kinetics performance.

[0087] Figure 7 The transient photocurrent response (TPR) spectra of pure g-C3N4 and the optimally modified sample 10g-GCN are shown. As can be seen from the figure, all samples exhibit rapid and reversible photoelectric response characteristics, with 10g-GCN showing a significantly enhanced photocurrent density. This confirms that the porous structure constructed by the ammonium chloride vapor-phase template method and the introduced lattice defects effectively shorten the charge transport path and, acting as shallow trapping centers, suppress the recombination of photogenerated electrons and holes, thereby significantly extending the carrier lifetime.

[0088] Figure 8 The image shows the electrochemical impedance spectroscopy (EIS) spectrum of the samples. In the Nyquist plot, the impedance arc radius of the 10g-GCN sample is significantly smaller than that of the pure g-C3N4. This result indicates that the morphological evolution induced by NH4Cl effectively reduces the interfacial charge transport impedance, which is conducive to the rapid migration of photogenerated electrons from the bulk phase to the surface, providing a kinetic guarantee for the enhancement of photocatalytic activity.

[0089] Figure 9 The image shows the cyclic voltammetry (CV) curves of the sample. Compared to the original g-C3N4, the CV curves of the modified 10g-GCN sample exhibit a larger closed-loop area and a higher response current density. This indicates that treatment with ammonium chloride significantly improves the specific surface area and conductivity of the material, thereby exposing more surface active sites and promoting interfacial redox reactions.

[0090] Figure 10 The degradation curves of ceftiofur sodium (CFS) by GCN samples with different NH4Cl doping levels under visible light irradiation are shown.

[0091] Figure 11 The figures show the degradation efficiency curves of ceftiofur sodium (CFS) by GCN samples with different NH4Cl doping amounts under visible light irradiation. The experimental data show that the degradation rate of pure g-C3N4 is only about 37.8%. After modification with NH4Cl, the activity of all samples was significantly improved, with 10 g-GCN achieving a degradation rate of 88% within 60 min.

[0092] Figure 12 The degradation rate constant k of ceftiofur sodium (CFS) by GCN samples with different NH4Cl doping levels under visible light irradiation is 0.03242 min. -1 It is approximately 4.16 times that of pure g-C3N4.

[0093] Figure 13This is a graph showing the general degradation efficiency of GCN samples for different generations of cephalosporin antibiotics. The results show that the catalyst achieved removal rates of 85% to 95% for cefalexin (CEL), cefuroxime (CXM), cefotaxime (CTX), and cefepime (CEFEP). Although the degradation rate slightly decreased with increasing molecular steric hindrance due to different antibiotic generations, GCN still maintained a degradation efficiency of over 85% for the most resistant fourth-generation cefepime.

[0094] Figure 14 The graph shows the degradation efficiency of GCN samples for four typical non-cephalosporin antibiotics. The catalyst exhibits significant selective degradation characteristics, demonstrating exceptional removal efficiency for tetracycline (TC), with a degradation rate as high as 95%. For ciprofloxacin (CIP), metronidazole (MTZ), and sulfamethoxazole (SMZ), the degradation efficiency remained between 45% and 52%, confirming the broad applicability of this modified material in the remediation of complex antibiotic wastewater and its specific advantage against tetracyclines.

[0095] Figure 15 The effect of different free radical quenchers on the degradation efficiency of 10 g GCN catalyst was investigated. The degradation rate in the uncatalyzed group was only 7%, ruling out the dominant influence of photolysis. In the control group without any scavenging agent, the degradation rate of CFS was as high as 88%. Subsequently, different chemical scavengers were introduced to identify the key free radicals involved in the reaction. When IPA was added, the degradation rate decreased to 59%, indicating that ·OH plays a minor role in this reaction system. In contrast, the degradation efficiency decreased to 76% after the addition of EDTA, indicating that h + It participated in part of the oxidation process. The addition of PBQ severely inhibited the photocatalytic activity of the system, with the degradation rate dropping sharply to 42%. This phenomenon strongly demonstrates that ·O2 - It is the most critical active species driving CFS degradation. Experimental results show that the contribution order of active species in this photocatalytic system is: ·O2 - >·OH>h + This indicates that the catalyst generates O2. - And ·OH is the main pathway that causes CFS degradation.

[0096] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a porous carbon nitride photocatalyst, characterized by, The steps include: mixing and grinding a nitrogen-rich organic precursor with a gaseous template agent ammonium chloride; treating the mixed precursor at high temperature using a microwave-assisted thermal polymerization method, and cooling it to room temperature after the reaction is completed; grinding, washing and drying the obtained product, and collecting the modified porous graphitic carbon nitride.

2. The method according to claim 1, wherein, The nitrogen-rich organic precursor is melamine.

3. The method for preparing a porous carbon nitride photocatalyst according to claim 1 or 2, characterized by, The mass ratio of the nitrogen-rich organic precursor to ammonium chloride is 1:0.85 to 1:1.

15.

4. The method according to claim 1, wherein, The microwave-assisted thermal polymerization involves placing the mixed powder in a covered graphite crucible, heating it to 520-570℃ and holding it at that temperature for 25-35 minutes under microwave power of 2kW-4kW.

5. The method according to claim 1, wherein, The modified porous graphite phase carbon nitride has a loose porous honeycomb structure, a specific surface area of 26.09 m 2 / g, and a pore volume of 0.190 cm 3 / g.

6. A porous carbon nitride photocatalyst, characterized by, Porous carbon nitride photocatalysts obtained by any one of the preparation methods of claims 1-5.

7. Use of a porous carbon nitride photocatalyst, characterized in that, The catalyst obtained by any one of the preparation methods of claims 1-5 or the catalyst of claim 6 is used for the degradation of organic pollutants in water under visible light-driven conditions.

8. The use of a porous carbon nitride photocatalyst according to claim 7, characterized in that, The organic pollutants mentioned are cephalosporin antibiotics or tetracycline antibiotics.

9. The use of a porous carbon nitride photocatalyst according to claim 8, characterized in that, The cephalosporin antibiotics mentioned are ceftiofur sodium, cefalexin, cefuroxime, cefotaxime, cefepime, tetracycline, ciprofloxacin, metronidazole, and sulfamethoxazole.

10. Use of a porous carbon nitride photocatalyst according to claim 7 or 8, characterized in that, In the degradation of the organic pollutants, for a pollutant solution with a concentration of 20 mg / L, the dosage of catalyst to pollutant solution is 1 mg: 5 ml, and the light source is visible light.

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