Carbon nitride catalyst, preparation method thereof and high-efficiency pollutant degradation method

Abstract

The application discloses a carbon nitride catalyst and a preparation method and a pollutant efficient degradation method thereof, and the preparation method comprises the following steps: S1: mixing a ferric nitrate nine hydrate solution and a potassium tricyanomethanide solution to form a mixed solution, fully complexing the two in the mixed solution, and obtaining a complex solution; S2: adding the complex solution into a mixed solution containing a nitrogen precursor and an additive at a certain rate drop by drop, fully stirring and removing water, and obtaining a catalyst precursor; and S3: grinding the catalyst precursor, placing the catalyst precursor into an oxygen isolation environment, and performing high-temperature treatment to obtain the carbon nitride catalyst. In the application, iron is doped into carbon nitride molecules in an atomic form, the band gap width of the carbon nitride is reduced, the absorption range of visible light is expanded, the recombination rate of electron-hole pairs is reduced, and the photocatalytic activity of the catalyst is enhanced, and the catalyst can efficiently remove trace organic pollutants in water under visible light.

Description

Technical Field

[0001] This invention relates to the field of water treatment, specifically to a carbon nitride catalyst, its preparation method, and a method for efficient degradation of pollutants. Background Technology

[0002] Pharmaceutical and personal care products (PPCPs) are commonly detected in urban wastewater, posing potential ecological and health risks and representing a significant challenge for wastewater reuse. However, conventional wastewater treatment processes are insufficient to completely remove PPCPs. To effectively eliminate PPCPs from wastewater and minimize their risks to human health and ecosystems, advanced treatment processes need to be added to traditional wastewater treatment methods.

[0003] Photocatalytic oxidation is a novel advanced oxidation technology that utilizes photocatalysts to generate highly oxidizing active substances under the influence of light to degrade organic matter. However, current photocatalytic oxidation faces key challenges such as low light energy utilization, especially low visible light utilization, high electron-hole reactivation rate, and low production of active species, limiting its application in practical water treatment. Summary of the Invention

[0004] To address the problems of high recombination rate of photogenerated carriers, low visible light utilization, and low generation of active species in existing photocatalytic materials, which affect their catalytic effect in practical applications, this invention proposes a carbon nitride catalyst, its preparation method, and a method for efficient degradation of pollutants.

[0005] The technical problem of this invention is solved by the following technical solution:

[0006] A method for preparing a carbon nitride catalyst includes the following steps:

[0007] S1: Mix ferric nitrate nonahydrate solution with potassium tricyanomethanide solution to form a mixed solution, and allow the two to fully complex in the mixed solution to obtain a complex solution;

[0008] S2: The complex solution is added dropwise to the mixture of nitrogen-containing precursor and additive at a certain rate, and the mixture is stirred thoroughly and the water is removed to obtain the catalyst precursor.

[0009] S3: The catalyst precursor is placed in an oxygen-isolated environment and subjected to high-temperature treatment to obtain a carbon nitride catalyst.

[0010] In some embodiments, in step S1, the molar ratio of ferric nitrate in the ferric nitrate nonahydrate solution to potassium tricyanomethanide in the potassium tricyanomethanide solution is 1:5.

[0011] In some embodiments, in step S2, the nitrogen-containing precursor is dicyandiamide and the additive is ammonium chloride.

[0012] In some embodiments, in step S2, the mixture of nitrogen-containing precursor and additive is composed of dicyandiamide, ammonium chloride and ultrapure water, wherein the mass ratio of dicyandiamide to ammonium chloride is 1:5.

[0013] In some embodiments, in step S2, the certain rate is 1 to 2 drops per minute, and the thorough stirring and removal of water involves placing dicyandiamide, ammonium chloride, and ultrapure water in a beaker and stirring continuously for 4-6 hours until they are mixed evenly. Then, the complex solution obtained in step S1 is added dropwise, and the mixture is stirred continuously at 65-75°C until the water evaporates.

[0014] In some embodiments, in step S3, the catalyst precursor is in a dry state, the catalyst precursor is in solid form, and the catalyst precursor is ground and then subjected to high-temperature treatment.

[0015] In some embodiments, in step S3, the step of placing the catalyst precursor in an oxygen-isolated environment for high-temperature treatment is to place it in an inert gas environment, raise it to the target temperature range at a designed rate in a heating device, and keep it at a constant temperature for a certain period of time. The heating device is a covered corundum boat, the designed rate is 2-5℃ / min, the target temperature range is 500-600℃, and the constant temperature heating for a certain period of time is 2-3 hours. The step of washing and drying is to wash and dry with ultrapure water.

[0016] The present invention also proposes a carbon nitride catalyst, characterized in that the carbon nitride catalyst is prepared by the method described above.

[0017] In some embodiments, iron atoms in the carbon nitride catalyst are anchored to the support by coordinating with nitrogen atoms of the support to form an Fe-N4 structure, and the iron atoms in the carbon nitride catalyst are uniformly distributed in the form of single atoms, and there are no iron particles in the carbon nitride catalyst.

[0018] In some embodiments, the carbon nitride catalyst is an ultrathin carbon nitride catalyst doped with iron single atoms, wherein the carbon nitride is in the form of thin sheets with a thickness of less than 5 layers.

[0019] The present invention also proposes a method for efficient degradation of pollutants, comprising the following steps: under simulated visible light conditions, using a carbon nitride catalyst as described above to degrade the pollutants, wherein the pollutants are typical pharmaceutical pollutants.

[0020] The beneficial effects of this invention include:

[0021] This invention proposes a carbon nitride catalyst, its preparation method, and a method for efficient degradation of pollutants. By specifying the preparation materials, method, and chemical ratios, the carbon nitride catalyst is prepared. This achieves the formation of Fe-N4 by chemically coordinating iron with nitrogen atoms in the carbon nitride lattice, resulting in a uniform anchorage of iron as a single atom on the carbon nitride support. This maximizes the exposure of active sites and enhances catalytic activity. Simultaneously, the chemical coordination structure allows for stable loading of iron single atoms onto the carbon nitride support, resulting in good catalyst stability. This invention significantly reduces catalyst preparation costs by using non-precious metal iron as the dopant. Furthermore, iron doping significantly reduces the fluorescence emission intensity of the catalyst, suppressing electron-hole recombination and effectively solving the problem of high photogenerated carrier recombination rate, thus enhancing photocatalytic activity. In this invention, iron doping increases the catalyst's adsorption of O2, reducing the adsorption energy from -0.18 eV to -3.10 eV, which is beneficial for the adsorption of the active species superoxide anion (O2). ·- The generation of ) can efficiently degrade organic pollutants, especially typical pharmaceutical pollutants in water.

[0022] In addition, some embodiments also have the following beneficial effects:

[0023] By controlling the molar ratio of ferric nitrate in the ferric nitrate nonahydrate solution to potassium tricyanomethanide in the potassium tricyanomethanide solution to 1:5, the iron ions in the mixed solution are fully complexed, which is beneficial to the uniform dispersion of iron in the prepared catalyst. The present invention also incorporates ammonium chloride, which generates sufficient gas during calcination to exfoliate the blocky carbon nitride, forming a thin and porous carbon nitride structure. This increases the specific surface area of ​​the carbon nitride catalyst and helps to improve its photocatalytic activity.

[0024] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0025] Figure 1a This is a high-angle annular dark-field scanning transmission image of Fe-UTCN in an embodiment of the present invention.

[0026] Figure 1b This is a high-angle annular dark-field image of the Fe-UTCN elemental scanning region in an embodiment of the present invention.

[0027] Figure 1c This is a Fe-UTCN elemental scan C element distribution map in an embodiment of the present invention.

[0028] Figure 1d This is a Fe-UTCN elemental scan distribution map of Fe element in an embodiment of the present invention.

[0029] Figure 1eThis is a Fe-UTCN elemental scan N element distribution diagram in an embodiment of the present invention.

[0030] Figure 2 This is a comparison of the ultraviolet-visible diffuse reflectance spectra of Fe-UTCN and UTCN in an embodiment of the present invention.

[0031] Figure 3 This is a comparison of the fluorescence spectra of Fe-UTCN and UTCN at an excitation wavelength of 350 nm in an embodiment of the present invention.

[0032] Figure 4 This is a schematic diagram illustrating the principle of Fe-UTCN generating various active substances under visible light excitation in an embodiment of the present invention.

[0033] Figure 5 This is a comparison chart of the degradation effects of different catalysts on APAP under light conditions in Experiment Example 1 of this invention.

[0034] Figure 6 This is a schematic diagram of the photocatalytic degradation performance of the Fe-UTCN catalyst in Experimental Example 2 of this invention after multiple cycles.

[0035] Figure 7 This is a schematic diagram showing the degradation effect of the Fe-UTCN catalyst under different water quality conditions in Experimental Example 4 of this invention. Detailed Implementation

[0036] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0037] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0038] This invention provides a method for preparing a carbon nitride catalyst, comprising the following steps:

[0039] S1: Mix ferric nitrate nonahydrate solution with potassium tricyanomethanide solution to form a mixed solution, and allow the two to fully complex in the mixed solution to obtain a complex solution;

[0040] S1-1: A mixed solution is formed by mixing ferric nitrate nonahydrate solution with potassium tricyanomethanide solution, wherein the molar ratio of ferric nitrate component in ferric nitrate nonahydrate solution to potassium tricyanomethanide component in potassium tricyanomethanide solution is 1:5;

[0041] S2: The complex solution is added dropwise to the mixture of nitrogen-containing precursor and additive at a certain rate, and the mixture is stirred thoroughly and the water is removed to obtain the catalyst precursor.

[0042] S2-1: Place dicyandiamide, ammonium chloride, and ultrapure water in a beaker and stir continuously for 4-6 hours until they are mixed evenly. The mass ratio of dicyandiamide to ammonium chloride is 1:5.

[0043] S2-2: Then, the complex solution obtained in step S1 is added dropwise. The amount of complex solution added is preferably 6% of the volume of the mixed solution in S2-1, specifically 0.3 mL. The mixture is stirred continuously at 65-75°C until the water evaporates to dryness, thus obtaining the catalyst precursor.

[0044] S3: The catalyst precursor is ground and then placed in an oxygen-isolated environment for high-temperature treatment to obtain a carbon nitride catalyst.

[0045] S3-1: Grind the catalyst precursor obtained in step S2 into powder, place it in a covered corundum boat, heat it to 500-600℃ under an argon atmosphere, and maintain it for 2-3 hours. The heating program is set to 2-5℃ / min.

[0046] S3-2: Collect the solid after heating, grind and sieve it to make the catalyst uniformly dispersed to remove large particles in the powder, wash with ultrapure water and dry to obtain an ultrathin carbon nitride supported iron single-atom catalyst, denoted as Fe-UTCN.

[0047] This invention relates to an ultrathin Fe-UTCN carbon nitride catalyst doped with iron single atoms, formed by thermal polymerization. In step S1, the molar ratio of Fe(NO3)3 to C4KN3 is 1:5, ensuring sufficient complexation of iron ions and facilitating uniform dispersion of iron in the prepared catalyst. In step S2, the nitrogen-containing precursor is preferably dicyandiamide, but other cyanamide-based organic compounds can also be used. The additive is preferably ammonium chloride, but other ammonium salts can also be used. The mixture of the nitrogen-containing precursor and the additive consists of dicyandiamide, ammonium chloride, and ultrapure water, with a mass ratio of dicyandiamide to ammonium chloride of 1:5. Subsequently, a one-step thermal polymerization method anchors iron in single-atom form onto the carbon nitride support, maximizing the exposure of active sites. The iron atoms form chemical coordination (Fe-N4) with the four nitrogen atoms in the carbon nitride lattice, ensuring the stable existence of the iron atoms without detachment. Simultaneously, the formed Fe-N4 structure provides a favorable adsorption site for O2, reducing the adsorption energy between O2 and the catalyst and promoting the adsorption of superoxide anions (O2). ·- The prepared catalyst exhibits significantly enhanced photocatalytic activity and good stability.

[0048] This invention also proposes a carbon nitride catalyst, which is prepared by the above method. In the carbon nitride catalyst, iron atoms are anchored on the support by coordinating with nitrogen atoms of the support to form an Fe-N4 structure. In the carbon nitride catalyst, iron is uniformly distributed in the form of single atoms. There are no iron particles in the carbon nitride catalyst. The carbon nitride catalyst is an ultrathin carbon nitride catalyst doped with iron single atoms. The carbon nitride is in the form of thin sheets with a thickness of less than 5 layers.

[0049] This invention also proposes a method for the efficient degradation of pollutants, comprising the following steps: under simulated visible light conditions, using a carbon nitride catalyst as described above to degrade the pollutants, wherein the pollutants are typical pharmaceutical pollutants.

[0050] In this embodiment of the invention, a solution of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) and a solution of potassium tricyanomethanide (C4KN3) are mixed at a molar ratio of 1:5 and heated in a water bath to allow for sufficient complexation. The complex is then added dropwise to a mixture of dicyandiamide and ammonium chloride, stirred thoroughly, and the water is removed. The dried mixture is then ground and calcined under an inert gas atmosphere to form an iron-doped ultrathin carbon nitride catalyst (Fe-UTCN) through thermal polymerization. The preparation method is characterized by a 1:5 molar ratio of Fe(NO3)3·9H2O to C4KN3 to ensure sufficient complexation of iron ions. Dicyandiamide is used as a nitrogen-containing precursor, and ammonium chloride is added. The amount of ammonium chloride added is 5-6 times the mass of dicyandiamide; the mixture is calcined at 500-600℃ for 2-3 hours under inert gas protection; during the heating process, iron atoms are anchored to carbon nitride in single-atom form through thermal polymerization. Therefore, the carbon nitride formed in this embodiment of the invention has thinner sheets (<5 layers) and a richer porous structure compared with conventional graphitic carbon nitride. This structure is formed because NH3 and HCl gases are released during the heating process, resulting in thinner sheets and more pores in the catalyst. At the same time, iron doping reduces the band gap of the ultrathin carbon nitride from 2.50 eV to 2.33 eV, improving the absorption and utilization rate of visible light by the catalyst. Iron atom doping significantly reduces the fluorescence emission intensity of the catalyst, thereby greatly suppressing electron-hole pair recombination. When the catalyst prepared in this embodiment of the invention is applied to the photocatalytic degradation of organic matter, the catalyst is mixed with a water sample containing organic pollutants, and then irradiated with 800W xenon lamp with a 420nm cutoff filter to simulate visible sunlight. Under simulated visible light conditions, the catalyst in this embodiment of the invention can efficiently degrade acetaminophen, a typical pharmaceutical pollutant, with a reaction rate that is more than 90% higher than that of the undoped iron single-atom carbon nitride catalyst. At the same time, experimental studies show that the catalyst in this embodiment of the invention does not decay its catalytic activity after multiple cycles of use and can be applied to a variety of different actual water quality conditions.

[0051] The embodiments of the present invention have at least the following beneficial effects:

[0052] (1) In the embodiments of the present invention, the catalyst is ultrathin carbon nitride. The thin and porous structure increases the specific surface area, which helps to improve photocatalytic activity at the physical level.

[0053] (2) In the embodiments of the present invention, non-precious metal iron is used as the doping metal, which greatly reduces the cost of catalyst preparation;

[0054] (3) See Figures 1a-1e As can be seen in the embodiments of the present invention, iron forms Fe-N4 through chemical coordination with nitrogen atoms in the carbon nitride lattice, and is uniformly anchored on the carbon nitride support in the form of single atoms, which can maximize the exposure of active sites and enhance catalytic activity. At the same time, the chemical coordination structure enables the iron single atoms to be stably supported on the carbon nitride support, and the catalyst has good stability.

[0055] (4) See Figure 2 As can be seen, in the embodiments of the present invention, iron doping reduces the band gap of carbon nitride from 2.50 eV to 2.33 eV, thereby improving the catalyst's utilization range of visible light and enabling it to drive photocatalytic reactions more effectively under visible light conditions, thus improving the reaction rate and efficiency.

[0056] (5) See Figure 3 As can be seen, iron atom doping in the embodiments of the present invention significantly reduces the fluorescence emission intensity of the catalyst, inhibits the recombination of electron-hole pairs, and enhances photocatalytic activity.

[0057] (6) See Figure 4 As can be seen, in the embodiments of the present invention, the ultrathin carbon nitride supported iron single-atom catalyst forms a variety of active substances under light irradiation, including superoxide anions, singlet oxygen and hydroxyl radicals, which promote the photocatalytic degradation effect.

[0058] (7) Iron doping increased the catalyst's adsorption of O2, reducing the adsorption energy from -0.18 eV to -3.10 eV, which is beneficial for the active species superoxide anion (O2). ·- The generation of ).

[0059] Specifically, in this embodiment of the invention, (1) Fe(NO3)3·9H2O solution (17.4g / L, 9mL) and C4KN3 solution (41.7g / L, 6mL) are mixed (i.e., the molar ratio of AgNO3 to C4KN3 is 1:5) to cause complexation between the two; (2) Dicyandiamide (1g), ammonium chloride (5g) and ultrapure water (4.7mL) are placed in a beaker and stirred continuously for 4-6h until they are mixed evenly. Then, 0.3mL of the complex solution obtained in step (1) is added dropwise and stirred continuously at 75°C until the water evaporates; (3) The solid mixture obtained in step (2) is ground into powder, placed in a covered corundum boat, heated to 550°C under an argon atmosphere, and kept for 3 hours. The heating program is set to 2.8°C / min. The solid after heating was collected, ground and sieved, washed with ultrapure water and dried to obtain an ultrathin carbon nitride supported iron single-atom catalyst, denoted as Fe-UTCN.

[0060] In the following experimental examples, undoped iron-free ultrathin carbon nitride (UTCN) was synthesized using the same steps as described above, but without the addition of the complex solution in step (1). Bulk carbon nitride (g-C3N4) was obtained by directly heating dicyandiamide, with the heating procedure being consistent with the method described above.

[0061] Experimental Example 1

[0062] Irradiation with visible sunlight was simulated using an 800W xenon lamp with a 420nm cutoff filter. A mixture (40 mL) containing 0.4 mg / L acetaminophen (APAP) and 5 mM phosphate buffer (pH 7.0) was irradiated in a cylindrical high-transparency quartz tube. The Fe-UTCN dosage was 300 mg / L. Before irradiation, the reaction system was stirred in the dark for 30 minutes to reach catalyst adsorption-desorption equilibrium. The solution was continuously stirred during irradiation. Small samples (0.6 mL) were taken out for analysis at regular intervals. Figure 5 The figure shown is a comparison of the degradation effects of different catalysts on APAP under light conditions in Experimental Example 1 of this invention. The degradation effect of iron-supported ultrathin carbon nitride (Fe-UTCN) on APAP is shown in the figure. Figure 5 In the Chinese, it is represented by "Fe-UTCN"; Comparative Example 1 (in Figure 5 Ultrathin carbon nitride (represented by "UTCN"): The difference from Example 1 is that UTCN without iron atoms is used as the photocatalyst. From the above comparison, it can be seen that Fe-UTCN achieves a degradation rate of over 90% for APAP, exceeding the 60% degradation rate of UTCN for APAP. The introduction of iron atoms is beneficial to improving the photocatalytic activity of the catalyst.

[0063] Experiment Example 2

[0064] like Figure 6The diagram shows the photocatalytic degradation performance of the Fe-UTCN catalyst in Experimental Example 2 of this invention after multiple cycles. Under the same experimental conditions, the Fe-UTCN catalyst was used multiple times to degrade APAP. After each round of degradation experiments, the remaining catalyst was filtered through a 0.22 μm filter membrane, washed three times with ultrapure water, and then dried in a vacuum drying oven. The remaining experimental conditions were the same as in Example 1. The concentration of APAP in the water sample was measured at different reaction times, and the ratio of the APAP concentration at different times to the initial concentration (C / C0) was obtained. Figure 6 The results show that after being reused 5 times, the Fe-UTCN catalyst still has a degradation rate of over 70% for APAP, indicating that the catalyst has good stability and repeatability.

[0065] Experimental Example 3

[0066] like Figure 7 The diagram shows the degradation effect of the Fe-UTCN catalyst under different water quality conditions in Experiment 3 of this invention. The photocatalytic degradation effect of Fe-UTCN on APAP was tested in ultrapure water, phosphate buffer, tap water, and river water (taken from a river in Shenzhen, Guangdong). Except for the water quality conditions, other conditions were the same as in Example 1. The concentration of APAP in each water sample was measured at different reaction times, and the ratio of APAP concentration at different times to the initial concentration (C / C0) was obtained. Figure 7 This indicates that Fe-UTCN exhibits good photocatalytic degradation ability under different water quality conditions.

[0067] The above description, in conjunction with specific / preferred embodiments, provides a further detailed explanation of the present invention and should not be construed as limiting the specific implementation of the invention to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the inventive concept, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, references to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention.

[0068] In this specification, the illustrative expressions of the terms used do not necessarily refer to the same embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Those skilled in the art can combine and integrate the different embodiments or examples described herein, as well as the features of different embodiments or examples, without contradiction. Although embodiments of the invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for preparing a carbon nitride catalyst, characterized in that, Includes the following steps: S1: Mix ferric nitrate nonahydrate solution with potassium tricyanomethanide solution to form a mixed solution, and allow the two to fully complex in the mixed solution to obtain a complex solution. The molar ratio of ferric nitrate component in the ferric nitrate nonahydrate solution to potassium tricyanomethanide component in the potassium tricyanomethanide solution is 1:

5. S2: The complex solution is added dropwise to the mixture of nitrogen-containing precursor and additive at a rate of 1 to 2 drops per minute, and the mixture is stirred thoroughly and the water is removed to obtain the catalyst precursor; the nitrogen-containing precursor is dicyandiamide and the additive is ammonium chloride; S3: The catalyst precursor is placed in an oxygen-isolated environment and subjected to high-temperature treatment to obtain a carbon nitride catalyst.

2. The method for preparing the carbon nitride catalyst according to claim 1, characterized in that, In step S2, the mixture of nitrogen-containing precursor and additive is composed of dicyandiamide, ammonium chloride and ultrapure water, wherein the mass ratio of dicyandiamide to ammonium chloride is 1:

5.

3. The method for preparing the carbon nitride catalyst as described in claim 2, characterized in that, In step S2, the thorough stirring and removal of water involves placing dicyandiamide, ammonium chloride, and ultrapure water in a beaker and stirring continuously for 4-6 hours until they are mixed evenly. Then, the complex solution obtained in step S1 is added dropwise, and the mixture is stirred continuously at 65-75°C until the water evaporates.

4. The method for preparing the carbon nitride catalyst according to claim 1, characterized in that, In step S3, the catalyst precursor is in a dry state, the catalyst precursor is in solid form, and the catalyst precursor is ground and then subjected to high-temperature treatment.

5. The method for preparing the carbon nitride catalyst according to claim 1, characterized in that, In step S3, the step of placing the catalyst precursor in an oxygen-isolated environment for high-temperature treatment involves placing it in an inert gas environment, heating it to the target temperature range at a designed rate in a heating device, and then heating it at a constant temperature for a certain period of time. The heating device is a covered corundum boat, the designed rate is 2-5 ℃ / min, the target temperature range is 500-600 ℃, and the constant temperature heating time is 2-3 hours.

6. A carbon nitride catalyst, characterized in that, The carbon nitride catalyst is prepared by the method described in any one of claims 1-5.

7. The carbon nitride catalyst according to claim 6, characterized in that, In the carbon nitride catalyst, iron atoms are anchored to the support by coordinating with nitrogen atoms of the support to form an Fe-N4 structure. The iron atoms in the carbon nitride catalyst are uniformly distributed in the form of single atoms, and there are no iron particles in the carbon nitride catalyst.

8. The carbon nitride catalyst according to claim 6, characterized in that, The carbon nitride catalyst is an ultrathin carbon nitride catalyst doped with iron single atoms, and the carbon nitride is in the form of thin sheets with a thickness of less than 5 layers.

9. A method for efficiently degrading pollutants, characterized in that, Includes the following steps: Under simulated visible light conditions, the pollutant is degraded using the carbon nitride catalyst as described in any one of claims 6-8, wherein the pollutant is a typical pharmaceutical pollutant.

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