Coumarin-doped graphite phase carbon nitride photocatalyst and preparation method and application thereof

Abstract

This application relates to the field of graphitic carbon nitride photocatalyst technology, and discloses a coumarin-doped graphitic carbon nitride photocatalyst, its preparation method, and its application. The preparation method includes: dissolving dihydroxycoumarin in anhydrous ethanol, ultrasonically dispersing it to obtain a homogeneous solution; mixing the homogeneous solution with urea, and drying it at low temperature to obtain a precursor; grinding the precursor and then calcining it at high temperature to obtain a CM-CN photocatalyst; and subjecting the CM-CN photocatalyst to static oxidation to obtain a coumarin-doped graphitic carbon nitride photocatalyst. This application innovatively proposes a CM-CN-AO photocatalyst prepared by modifying coumarin combined with a unique "oxidation enhancement" process, using urea as a carbon nitride precursor. Through a mild oxidation process under long-term static placement in air, a quinone structure is generated, optimizing its surface electronic structure and increasing photocatalytic active sites, thereby achieving a significant improvement in hydrogen production performance and breaking through the performance limitations of traditional carbon-nitrogen materials.

Description

Technical Field

[0001] This application relates to the field of graphitic carbon nitride photocatalyst technology, and in particular to a coumarin-doped graphitic carbon nitride photocatalyst, its preparation method and application. Background Technology

[0002] Hydrogen energy, as a clean energy source with high energy density and water as its only combustion product, is considered an ideal alternative to fossil fuels in the future. Among the many hydrogen production pathways, semiconductor photocatalytic water splitting technology can directly utilize solar energy to convert water into hydrogen, achieving a green conversion from solar energy to chemical energy. It boasts significant advantages such as low cost, environmental friendliness, and mild operating conditions, demonstrating enormous application potential and strategic significance in addressing the energy crisis and controlling environmental pollution. Developing efficient, stable, and inexpensive visible light-responsive photocatalysts is key to promoting the widespread application of this technology.

[0003] Graphitic carbon nitride (g-C3N4), as a non-metallic polymer semiconductor, has attracted much attention in fields such as photocatalytic water splitting for hydrogen production and environmental pollution control due to its unique band structure, thermal stability, and chemical stability. However, pure g-C3N4 suffers from drawbacks such as small specific surface area, high photogenerated electron-hole recombination rate, and low visible light utilization, limiting its widespread application. To overcome these shortcomings, researchers have employed various modification methods, including elemental doping, copolymerization modification, template preparation, and heterostructure construction. However, while existing patented preparation methods can improve efficiency, they still have significant limitations. For example, patent CN116371441A prepared a sulfur-modified g-C3N4 photocatalytic material by introducing sulfur into the carbon nitride framework, achieving a photocatalytic hydrogen production efficiency of 8.25 mmol·g·h. -1 This material exhibits good reaction stability in short-term cycling tests; however, its performance improvement relies mainly on non-metallic doping, and its ability to improve the separation and migration of photogenerated electron-hole pairs remains limited, with the carrier recombination problem not fundamentally resolved. For example, patent CN117602593B constructs a highly crystalline graphitic carbon nitride photocatalyst material through molecularly induced self-assembly combined with ammonia pretreatment. In real-time photocatalytic performance testing, its photocatalytic hydrogen production performance reaches 1.86 mmol·h⁻¹. -1 ·g -1 Meanwhile, the regular and ordered crystal structure is also beneficial to improving the structural stability during the reaction process. However, the synthesis steps of this method are relatively complex, and the requirements for reaction conditions and equipment are high, which is not conducive to low-cost and large-scale preparation; at the same time, high crystallinity is often accompanied by a decrease in specific surface area, which may limit the full exposure of active sites.

[0004] Existing technologies focus on immediate / short-term photocatalytic performance testing. While the aforementioned patents demonstrate significant activity in initial tests, their design focuses on improving initial efficiency, lacking attention to and assessment of potential surface oxidation during long-term static storage and the resulting degradation of photocatalytic hydrogen production performance. This leaves a research gap in practical application and promotion. Furthermore, the activity of traditional photocatalytic materials typically declines after storage or recycling, and there is currently no effective and simple method to reverse this trend.

[0005] Therefore, how to effectively modify carbon nitride-based photocatalysts to achieve a photocatalytic system with tunable microstructure, excellent stability, and long-term performance optimization has become an urgent scientific problem to be solved. Summary of the Invention

[0006] This application provides a coumarin-doped graphitic carbon nitride photocatalyst, its preparation method, and its application, aiming to solve the technical problems of low catalytic performance and poor long-term stability of existing graphitic carbon nitride photocatalytic materials.

[0007] To achieve the above objectives, the present application adopts the following technical solution.

[0008] A first aspect of this application provides a method for preparing a coumarin-doped graphitic carbon nitride photocatalyst, comprising: S1, Dihydroxycoumarin is dissolved in anhydrous ethanol and ultrasonically dispersed to obtain a homogeneous solution; S2, the homogeneous solution is mixed with urea and dried at low temperature to obtain the precursor; S3, the precursor is ground and then calcined at high temperature to obtain CM-CN photocatalyst; S4, the CM-CN photocatalyst is statically placed and oxidized to obtain a coumarin-doped graphitic carbon nitride photocatalyst, namely the CM-CN-AO photocatalyst.

[0009] Preferably, the dihydroxycoumarin is any one of 5,7-dihydroxycoumarin, 6,7-dihydroxycoumarin, 7,8-dihydroxycoumarin, or 4,7-dihydroxycoumarin.

[0010] Preferably, the temperature for the low-temperature drying is 40~80℃.

[0011] Preferably, the high-temperature calcination temperature is 450~550℃, and the calcination time is 2~3h.

[0012] More preferably, the heating rate to the high-temperature calcination temperature is (3~8℃) / min.

[0013] Preferably, the static oxidation is carried out by sealing and placing the product in air at room temperature, away from light, and in a dry environment for 0.5 to 5 months.

[0014] Preferably, the mass-to-volume ratio of dihydroxycoumarin to anhydrous ethanol is 1 mg / (0.8~1) mL; The mass-to-volume ratio of urea to homogenized solution is 8000 mg / (0.25~2) mL.

[0015] A second aspect of this application provides a coumarin-doped graphitic carbon nitride photocatalyst prepared by the above-described preparation method.

[0016] A third aspect of this application provides the application of the aforementioned coumarin-doped graphitic carbon nitride photocatalyst in photocatalytic water splitting for hydrogen production.

[0017] Preferably, the coumarin-doped graphitic carbon nitride photocatalyst needs to be supported with a co-catalyst accounting for 0.0~3.0 wt% of its mass; The cocatalyst includes chloroplatinic acid.

[0018] Compared with the prior art, the beneficial effects of this application are as follows: This application innovatively proposes a CM-CN-AO photocatalyst prepared by modifying coumarin with a unique "oxidation enhancement" process, using urea as a precursor for carbon nitride. This application generates a quinone structure through a mild oxidation process under long-term static placement in air, optimizing its surface electronic structure and increasing photocatalytic active sites, thereby achieving a significant improvement in hydrogen production performance and overcoming the performance limitations of traditional carbon-nitrogen materials due to their age. The CM-CN-AO photocatalyst of this application has a wide optical absorption range, and its high specific surface area and mesoporous structure provide more active sites, greatly promoting the separation and transport of photogenerated carriers. Compared with carbon nitride synthesized from a single urea precursor, it exhibits a wider visible light response and higher photocatalytic water splitting efficiency for hydrogen production.

[0019] The photocatalyst of this application has unique performance evolution characteristics. After being stored statically in air for several months, its photocatalytic activity is significantly higher than that when it was just prepared. It has high long-term catalytic stability, providing a new breakthrough for the long-term storage and commercial application of non-precious metal photocatalytic materials.

[0020] The CM-CN-AO photocatalyst of this application features both tunable microstructure and excellent stability. By controlling the coumarin doping ratio, the content and distribution of hydroxyl groups can be effectively regulated, thereby modulating its photocatalytic performance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 SEM images of photocatalysts CM-CN1 and CM-CN1-AO-3M; Figure 2 The image shows the EDS spectrum of the photocatalyst CM-CN1. Figure 3 EDS image of photocatalyst CM-CN1-AO-3M; Figure 4 The images show the FT-IR spectra of photocatalysts CM-CN1, CM-CN1-AO-3M, and BCN. Figure 5 XRD patterns of photocatalysts CM-CN1, CM-CN1-AO-3M, and BCN; Figure 6 The graph shows the catalytic hydrogen production effects of photocatalysts CM-CN1, CM-CN1-AO-3M, CM-CN1-AO-0.5M and BCN. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0024] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0025] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0026] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0027] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0028] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0029] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] Firstly, this application provides a method for preparing a coumarin-doped graphitic carbon nitride photocatalyst. Using urea as a precursor for carbon nitride, it innovatively proposes a method for preparing a CM-CN-AO photocatalyst through coumarin modification combined with a unique "oxidation enhancement" process. This application generates a quinone structure through a mild oxidation process under long-term static placement in air, optimizing its surface electronic structure and increasing photocatalytic active sites, thereby achieving a significant improvement in hydrogen production performance and breaking through the performance limitations of traditional carbon-nitrogen materials over time.

[0032] The preparation method specifically includes: S1, Dihydroxycoumarin is dissolved in anhydrous ethanol and ultrasonically dispersed to obtain a homogeneous solution; In this application, the dihydroxycoumarin is any one of 5,7-dihydroxycoumarin, 6,7-dihydroxycoumarin, 7,8-dihydroxycoumarin, or 4,7-dihydroxycoumarin.

[0033] The preferred mass-to-volume ratio of dihydroxycoumarin to anhydrous ethanol is 1 mg / (0.8~1) mL.

[0034] S2, the homogeneous solution is mixed with urea and dried at low temperature to obtain the precursor; The mass-to-volume ratio of urea to homogenized solution is 8000 mg / (0.25~2) mL.

[0035] In this application, the precursor is obtained by drying at 40~80℃ to remove anhydrous ethanol.

[0036] S3, the precursor is ground and then calcined at high temperature to obtain CM-CN photocatalyst; In this application, dihydroxycoumarin and urea are thoroughly mixed by grinding, and then calcined at a heating rate of (3~8℃) / min to 450~550℃ for 2~3h to obtain CM-CN photocatalyst.

[0037] S4, the CM-CN photocatalyst is statically placed and oxidized to obtain a coumarin-doped graphitic carbon nitride photocatalyst, namely the CM-CN-AO photocatalyst.

[0038] Specifically, the static oxidation refers to sealing and storing the photocatalyst in air at room temperature, protected from light, and in a dry environment for 0.5 to 5 months. This application, without using hazardous chemicals or performing complex post-treatment, utilizes long-term static storage in air. After the photocatalyst is excited by natural light, the phenolic hydroxyl groups of dihydroxycoumarin are first converted to ·OH or h... + The attack generates phenolic radicals, which are then captured by O2 to form ortho / para quinone structures. These quinone structures have reversible redox properties and can serve as electron transfer and transport sites. They work in synergy with surface polar functional groups to promote the adsorption and activation of water molecules and protons, thereby enhancing the photocatalytic hydrogen production performance of CM-CN-AO materials.

[0039] Secondly, this application provides a CM-CN-AO photocatalyst prepared by the above-described method. It exhibits a wide optical absorption range, and its high specific surface area and mesoporous structure provide more active sites, greatly promoting the separation and transport of photogenerated carriers. Compared to carbon nitride synthesized from a single precursor, urea, it has a wider visible light response and higher photocatalytic water splitting efficiency for hydrogen production.

[0040] Most importantly, the CM-CN-AO photocatalyst of this application has unique performance evolution characteristics. Its photocatalytic activity is significantly higher than that when it is freshly prepared, and it has high long-term catalytic stability. It provides a brand-new breakthrough for the long-term storage and commercial application of non-precious metal photocatalytic materials.

[0041] Furthermore, the CM-CN-AO photocatalyst of this application possesses both tunable microstructure and excellent stability. By controlling the coumarin doping ratio, the content and distribution of hydroxyl groups can be effectively regulated, thereby modulating its photocatalytic performance.

[0042] The CM-CN-AO photocatalyst of this application, based on its wider visible light response and higher photocatalytic water splitting efficiency for hydrogen production, can be applied to photocatalytic water splitting for hydrogen production.

[0043] To achieve better catalytic performance, the CM-CN-AO photocatalyst of this application needs to be supported with chloroplatinic acid as a co-catalyst; wherein, the amount of chloroplatinic acid is 0.0~3.0 wt% of the CM-CN-AO photocatalyst.

[0044] The present application will be further described below through specific embodiments.

[0045] Example 1 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1, 1 mg of 5,7-dihydroxycoumarin was dissolved in 1 mL of anhydrous ethanol and ultrasonically dispersed to form a golden-yellow homogeneous solution; S2, add 8g of urea to the above homogenized solution, dry in an oven at 60℃ to remove anhydrous ethanol, and obtain the precursor; S3. After cooling the precursor to room temperature, it was transferred to a mortar and ground thoroughly. The ground precursor powder was then transferred to a muffle furnace and heated to 550℃ at a heating rate of 5℃ / min. The temperature was then maintained for 2.5h and cooled to room temperature to obtain the CM-CN photocatalyst, denoted as CM-CN1. S4. CM-CN1 was sealed and placed in a dry place at room temperature and away from light for 3 months to obtain the final CM-CN-AO photocatalyst, denoted as CM-CN1-AO-3M.

[0046] Example 2 The difference between Example 2 and Example 1 is that the placement time in S4 is 1 month, while the rest is the same as in Example 1.

[0047] Example 3 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1, 0.25 mg of 5,7-dihydroxycoumarin was dissolved in 0.25 mL of anhydrous ethanol and ultrasonically dispersed to form a golden-yellow homogeneous solution; S2, add 8g of urea to the above homogenized solution, dry in an oven at 60℃ to remove anhydrous ethanol, and obtain the precursor; S3 is the same as in Example 1; S4. The CM-CN photocatalyst was sealed and placed in a dry place at room temperature in the dark for 2 months to obtain the final CM-CN-AO photocatalyst.

[0048] Example 4 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1, 0.5 mg of 5,7-dihydroxycoumarin was dissolved in 0.5 mL of anhydrous ethanol and ultrasonically dispersed to form a golden-yellow homogeneous solution; S2, add 8g of urea to the above homogenized solution, dry in an oven at 60℃ to remove anhydrous ethanol, and obtain the precursor; S3 is the same as in Example 1; S4. The CM-CN photocatalyst was sealed and placed in a dry place at room temperature in the dark for 2 months to obtain the final CM-CN-AO photocatalyst.

[0049] Example 5 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1, Dissolve 2 mg of 5,7-dihydroxycoumarin in 2 mL of anhydrous ethanol and disperse by ultrasonication to form a golden-yellow homogeneous solution; S2, add 8g of urea to the above homogenized solution, dry in an oven at 60℃ to remove anhydrous ethanol, and obtain the precursor; S3 is the same as in Example 1; S4. The CM-CN photocatalyst was sealed and placed in a dry place at room temperature in the dark for 2 months to obtain the final CM-CN-AO photocatalyst.

[0050] Example 6 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1 is the same as in Example 1; S2 is the same as in Example 1; S3. After cooling the precursor to room temperature, it was transferred to a mortar and ground thoroughly. The ground precursor powder was then transferred to a muffle furnace and heated to 450℃ at a heating rate of 5℃ / min. The temperature was then maintained for 2.5h and cooled to room temperature to obtain the CM-CN photocatalyst. S4. The CM-CN photocatalyst was sealed and placed in a dry place at room temperature in the dark for 2 months to obtain the final CM-CN-AO photocatalyst.

[0051] Example 7 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1 is the same as in Example 1; S2 is the same as in Example 1; S3. After cooling the precursor to room temperature, it was transferred to a mortar and ground thoroughly. The ground precursor powder was then transferred to a muffle furnace and heated to 500℃ at a heating rate of 5℃ / min. The temperature was then maintained for 2.5h and cooled to room temperature to obtain the CM-CN photocatalyst. S4. The CM-CN photocatalyst was sealed and placed in a dry place at room temperature in the dark for 2 months to obtain the final CM-CN-AO photocatalyst.

[0052] Example 8 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1 is the same as in Example 1; S2 is the same as in Example 1; S3. After cooling the precursor to room temperature, it was transferred to a mortar and ground thoroughly. The ground precursor powder was then transferred to a muffle furnace and heated to 550°C at a heating rate of 5°C / min. The temperature was then maintained for 2 hours and cooled to room temperature to obtain the CM-CN photocatalyst. S4. The CM-CN photocatalyst was sealed and placed in a dry place at room temperature in the dark for 2 months to obtain the final CM-CN-AO photocatalyst.

[0053] Example 9 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1 is the same as in Example 1; S2 is the same as in Example 1; S3. After cooling the precursor to room temperature, it was transferred to a mortar and ground thoroughly. The ground precursor powder was then transferred to a muffle furnace and heated to 550°C at a heating rate of 5°C / min. The temperature was then maintained for 3 hours and cooled to room temperature to obtain the CM-CN photocatalyst. S4. The CM-CN photocatalyst was sealed and placed in a dry place at room temperature in the dark for 2 months to obtain the final CM-CN-AO photocatalyst.

[0054] Example 10 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1 is the same as in Example 1; S2 is the same as in Example 1; S3 is the same as in Example 1; S4. The CM-CN photocatalyst was sealed and placed in a dry place at room temperature in the dark for 2 months to obtain the final CM-CN-AO photocatalyst.

[0055] Example 11 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1 is the same as in Example 1; S2 is the same as in Example 1; S3. After cooling the precursor to room temperature, it was transferred to a mortar and ground thoroughly. The ground precursor powder was then transferred to a muffle furnace and heated to 550°C at a heating rate of 5°C / min. The temperature was then maintained for 2 hours and cooled to room temperature to obtain the CM-CN photocatalyst. S4. The CM-CN photocatalyst was sealed and placed in a dry environment at room temperature and away from light for 4 months to obtain the final CM-CN-AO photocatalyst.

[0056] Example 12 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1 is the same as in Example 1; S2 is the same as in Example 1; S3. After cooling the precursor to room temperature, it was transferred to a mortar and ground thoroughly. The ground precursor powder was then transferred to a muffle furnace and heated to 550°C at a heating rate of 5°C / min. The temperature was then maintained for 2 hours and cooled to room temperature to obtain the CM-CN photocatalyst. S4. The CM-CN photocatalyst was sealed and placed in a dry environment at room temperature and away from light for 5 months to obtain the final CM-CN-AO photocatalyst.

[0057] Example 13 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1 differs from Example 1 in that 5,7-dihydroxycoumarin is replaced with 6,7-dihydroxycoumarin; S2 is the same as in Example 1; S3 is the same as in Example 1; S4 is the same as in Example 1.

[0058] Example 14 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1, the difference from Example 1 is that 5,7-dihydroxycoumarin is replaced with 7,8-dihydroxycoumarin; S2 is the same as in Example 1; S3 is the same as in Example 1; S4 is the same as in Example 1.

[0059] Example 15 This embodiment provides a method for preparing a CM-CN-AO photocatalyst, including: S1 is the same as in Example 1; S2 is the same as in Example 1; S3 is the same as in Example 1; S4. The CM-CN photocatalyst was sealed and placed in a dry environment at room temperature and away from light for 0.5 months to obtain the final CM-CN-AO photocatalyst.

[0060] Comparative Example 1 Comparative Example 1 provides a BCN photocatalyst, the preparation method of which includes: 8g of urea was placed in a crucible and heated to 500℃ at a heating rate of 5℃ / min and held for 2h. Then it was annealed for 2h, cooled to room temperature, and ground to obtain BCN photocatalyst.

[0061] Comparative Example 2 Comparative Example 2 provides a CM-CN photocatalyst, the preparation method of which is the same as that of Example 1 except for step S4. The photocatalyst of Comparative Example 2 is the same as the photocatalyst CM-CN1 in Example 1.

[0062] The photocatalysts CM-CN1 and CM-CN1-AO-3M prepared in Example 1 of this application were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results are as follows: Figure 1-3 As shown in Table 1.

[0063] Figure 1 SEM images of two photocatalysts are shown. Figure 1 It can be seen that the surface of the CM-CN1 photocatalyst exhibits thin nanosheet characteristics and has obvious porous nanostructure; while the CM-CN1-AO-3M photocatalyst obviously exhibits more porous structure.

[0064] Figure 2 and Figure 3 The EDS plots for CM-CN1 and CM-CN1-AO-3M are shown in Table 1, and the EDS analysis results are shown in Table 1.

[0065] Table 1. Spectrum of total element distribution

[0066] from Figure 2 As shown in Table 1, the characteristic elements oxygen (O), carbon (C), and nitrogen (N) of the CM-CN1 photocatalyst are uniformly distributed, proving that oxygen was successfully incorporated into the CM-CN1 framework, and the photocatalyst was successfully prepared. Figure 3 As shown in Table 1, the oxygen content on the surface of the CM-CN1-AO-3M sample increased from 3.16 at% in CM-CN1 to 4.24 at%. This is attributed to the slow oxidation reaction between the CM-CN1 material surface and oxygen and water molecules in the air.

[0067] Using the same amount of sample, the FT-IR spectra of the freshly prepared CM-CN1 photocatalyst and CM-CN1-AO-3M photocatalyst of Example 1 or Comparative Example 2, as well as the BCN photocatalyst of Comparative Example 1, were compared. The spectra are shown below. Figure 4 As shown.

[0068] from Figure 4 It can be seen that the distance is between 1250 and 1610 cm. - ¹ In the region, all three samples exhibited broad absorption bands composed of CN and C=N stretching vibrations, indicating that the heterocyclic skeleton of g-C3N4 remained stable during placement. However, CM-CN1-AO-3M showed a different absorption band in the 1650-1750 cm⁻¹ region. - The absorption in region ¹ is significantly enhanced, and this band is attributed to the stretching vibration of the conjugated carbonyl group (C=O). Combined with the hydroxylated aromatic structure present on the surface of the material after coumarin doping, this indicates that some hydroxyl groups on the CM-CN1 surface underwent slow oxidation in an air environment, gradually transforming from a hydroxyl structure to a quinone structure. This change did not introduce new impurity peaks, suggesting that the oxidation was mainly limited to the material surface or edge sites. (3000-3500 cm⁻¹) - ¹ The broad peaks related to -NH / -OH in the region are further enhanced in CM-CN1-AO-3M, indicating that while the quinone structure is formed, a certain number of polar groups are still retained on the surface. These results suggest that CM-CN1 undergoes a mild reconstruction process characterized by the oxidation of surface hydroxyl groups to the quinone structure after being placed in air. This quinone structure has reversible redox properties and can serve as a temporary storage and transfer site for photogenerated electrons, synergistically promoting the adsorption and activation of water molecules and protons with the surface polar functional groups.

[0069] XRD tests were performed on the freshly prepared CM-CN1 photocatalyst of Example 1 or Comparative Example 2, the CM-CN1-AO-3M photocatalyst of Example 1, and the BCN photocatalyst of Comparative Example 1. The results are as follows: Figure 5 As shown.

[0070] Figure 5 Characteristic diffraction peaks at 13.1° (100) and 27.3° (002) are shown, corresponding to the in-plane stacking of heptaazine units and the interlayer stacking of CM-CN1-AO-3M nanosheets, respectively. Compared with the initial CM-CN1 sample, CM-CN1-AO-3M has characteristic diffraction peaks consistent with BCN, corresponding to the (002) crystal plane, indicating the successful preparation of g-C3N4 and that the doping of coumarin does not cause a shift in the diffraction peaks.

[0071] The CM-CN-AO photocatalysts prepared in Examples 2-15 were tested and found to have similar properties to CM-CN1-AO-3M in Example 1.

[0072] Application examples The hydrogen production performance of the CM-CN1-AO-3M photocatalyst prepared in Example 1, the BCN photocatalyst of Comparative Example 1, and the CM-CN1 photocatalyst of Comparative Example 2 was studied. The specific methods are as follows: A xenon lamp was used as the hydrogen production light source with a wavelength range of ≥400 nm. The catalyst dosage was 0.1 g / L, the sacrificial agent was 10 mL of triethanolamine, 1.5 wt% of chloroplatinic acid co-catalyst was added, and 90 mL of water was added. The reaction cell was evacuated, and argon was used as the carrier gas. The H2 generated in the gas chromatography system was detected. The hydrogen production experiment was carried out for 4 hours, and the hydrogen data in the system was collected every 1 hour.

[0073] The photocatalytic hydrogen production effect of CM-CN1 in Example 1 or Comparative Example 2, CM-CN1-AO-3M in Example 1, CM-CN1-AO-0.5M in Example 15, and BCN photocatalyst in Comparative Example 1 under a xenon lamp is shown in the figure. Figure 6 As shown, the horizontal axis represents time, the vertical axis represents hydrogen production, and the upper curve is the curve of hydrogen production of the sample under a xenon lamp with triethanolamine as a sacrificial agent as a function of time.

[0074] from Figure 6 It can be seen that the CM-CN1-AO-3M photocatalyst achieves a hydrogen production rate of 32.57 mmol·g within 4 hours. -1 ·h -1 The hydrogen production rate was significantly higher than that of CM-CN1 (9.75 mmol·g⁻¹). -1 ·h -1 The hydrogen production rate of the CM-CN1-A0-0.5M photocatalyst was 11.97 mmol·g⁻¹. -1 ·h -1 ) and the hydrogen production rate of the BCN photocatalyst (1.64 mmol·g -1 ·h -1The results show that, thanks to the slow oxidation of the material in air, the hydrogen production rate of the photocatalyst prepared in this application is significantly higher than that of graphitic carbon nitride, exhibiting excellent visible light photocatalytic hydrogen production performance and breaking through the performance limitations of traditional carbon-nitrogen materials over time.

[0075] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. A method for preparing a coumarin-doped graphitic carbon nitride photocatalyst, characterized in that, include: S1, Dihydroxycoumarin is dissolved in anhydrous ethanol and ultrasonically dispersed to obtain a homogeneous solution; S2, the homogeneous solution is mixed with urea and dried at low temperature to obtain the precursor; S3, the precursor is ground and then calcined at high temperature to obtain CM-CN photocatalyst; S4, the CM-CN photocatalyst is statically placed and oxidized to obtain a coumarin-doped graphitic carbon nitride photocatalyst, namely the CM-CN-AO photocatalyst.

2. The preparation method according to claim 1, characterized in that, The dihydroxycoumarin is any one of 5,7-dihydroxycoumarin, 6,7-dihydroxycoumarin, 7,8-dihydroxycoumarin, or 4,7-dihydroxycoumarin.

3. The preparation method according to claim 1, characterized in that, The temperature for the low-temperature drying is 40~80℃.

4. The preparation method according to claim 1, characterized in that, The high-temperature calcination temperature is 450~550℃, and the calcination time is 2~3h.

5. The preparation method according to claim 4, characterized in that, The heating rate to the high-temperature calcination temperature is (3~8℃) / min.

6. The preparation method according to claim 1, characterized in that, The static oxidation process involves sealing the product in air at room temperature, away from light, and in a dry environment for 0.5 to 5 months.

7. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of dihydroxycoumarin to anhydrous ethanol is 1 mg / (0.8~1) mL; The mass-to-volume ratio of urea to homogenized solution is 8000 mg / (0.25~2) mL.

8. The coumarin-doped graphitic carbon nitride photocatalyst prepared by the preparation method according to any one of claims 1-7.

9. The application of the coumarin-doped graphitic carbon nitride photocatalyst of claim 8 in photocatalytic water splitting for hydrogen production.

10. The application according to claim 9, characterized in that, The coumarin-doped graphitic carbon nitride photocatalyst requires a co-catalyst comprising 0.0 to 3.0 wt% of its mass; The cocatalyst includes chloroplatinic acid.

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