Preparation method of holmium monatomic doped carbon nitride photocatalytic material and application of holmium monatomic doped carbon nitride photocatalytic material in photocatalytic nitrogen fixation

Abstract

The invention belongs to the technical field of photocatalytic functional materials, and discloses a preparation method of a holmium monatomic doped carbon nitride photocatalytic material and application of the holmium monatomic doped carbon nitride photocatalytic material in photocatalytic nitrogen fixation. According to the invention, potassium chloride and lithium chloride are adopted as high-temperature liquid-phase solvents, and the novel holmium monatomic doped carbon nitride photocatalytic material is obtained through a one-step calcination method. The preparation method has the advantages of simplicity in operation, environment friendliness and the like; compared with a traditional preparation method, the holmium-doped graphite-phase carbon nitride photocatalyst has expanded pi conjugation, higher nitrogen reduction capacity and more effective carrier separation and transfer, so that the photocatalytic nitrogen fixation activity is remarkably improved, and the photocatalytic nitrogen fixation performance of holmium-doped graphite-phase carbon nitride is 271.68 mu mol.g <-1 >. H <-1 >; the photocatalytic nitrogen fixation performance of the pure graphite phase carbon nitride is 40.14 [mu] mol.g <-1 >. H <-1 >; and the performance is improved by about 7 times.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic functional materials, and relates to a method for preparing a holmium single atom-doped carbon nitride photocatalytic material and its application in photocatalytic nitrogen fixation. Background Art

[0002] Ammonia is a clean hydrogen energy carrier and an indispensable raw material for the synthesis of nitrogen fertilizers. Currently, ammonia synthesis relies primarily on the high-temperature, high-pressure Haber-Bosch process. This process suffers from high energy consumption and high carbon dioxide emissions. Therefore, finding a green, clean, low-energy, efficient, and stable nitrogen fixation process to replace the traditional, energy-intensive nitrogen fixation process has become an urgent challenge.

[0003] Solar energy is a clean, pollution-free, and renewable resource, and as such, is attracting increasing attention from researchers. The abundant nitrogen in Earth's atmosphere and the water in the vast hydrosphere provide the natural raw materials for ammonia synthesis. Photocatalytic nitrogen fixation technology leverages solar radiation to reduce the chemical energy required for the reaction through photocatalytic materials, enabling the nitrogen fixation reaction to proceed under milder conditions.

[0004] In recent years, photocatalysis based on graphitic carbon nitride has become a very hot research topic. This material has attracted a large number of scholars and experts to conduct further in-depth research due to its sufficient stability, easy preparation and easy availability, and moderate band gap. Due to the defects of graphitic carbon nitride, such as easy carrier recombination and poor photoresponse, its practical application is limited to a certain extent. Therefore, this has also inspired relevant researchers to develop various modification methods to make up for the existing defects and improve the photocatalytic performance of graphitic carbon nitride. Common modification methods and existing problems are as follows:

[0005] Structural vacancy modification: For example, Yu et al. reported a nitrogen-deficient g-C3N4, in which the introduction of nitrogen defects caused a red shift in the absorption edge of g-C3N4. The magnitude of the shift depended on the KOH-to-precursor ratio. While this facilitated carrier separation to some extent, the introduction of vacancies was difficult to precisely control, which could lead to increased local disorder in the material structure, resulting in a chaotic transmission path for photogenerated carriers, which in turn increased the probability of recombination. Furthermore, the number and distribution of vacancies are difficult to precisely control. When there are too many vacancies, they become carrier recombination centers, reducing photocatalytic efficiency and impacting the overall stability of the material, affecting long-term performance.

[0006] Morphology Modification: Jin et al. modified g-C3N4 by inserting molecules with sulfonic acid and phenyl groups between layers. These inserted molecules successfully disrupted the tightly packed structure of the g-C3N4 laminates. However, the construction of complex morphologies often results in increased surface energy, which can lead to material agglomeration and affect the dispersion of the photocatalytic material, thus reducing the contact area for the photocatalytic reaction. Furthermore, the specific morphology is extremely sensitive to preparation conditions, and even minor process fluctuations can lead to morphological inhomogeneity. Consequently, photocatalytic performance varies significantly across different morphological regions, making it difficult to achieve stable and efficient photocatalysis.

[0007] Although the photocatalytic materials disclosed in existing patent applications CN118988376A and CN119016081A perform well in hydrogen production, they still have significant limitations: lack of structure-performance correlation research: the mechanism of the influence of the electronic structure / lattice defects of rare earth oxides on the efficiency of photogenerated carrier separation has not been deeply analyzed, which restricts the rational optimization of material design; high-cost raw material dependence: the key components use scarce heavy rare earths, which seriously hinders large-scale application; insufficient adaptability to high-energy barrier reactions: the system only verifies hydrogen production performance (breaking HO / HH bonds, bond energy ≤464kJ / mol), but does not involve the more challenging field of photocatalytic nitrogen fixation.

[0008] The fundamental bottleneck facing nitrogen fixation lies in the extreme inertness of the N≡N molecule: the N≡N triple bond energy is as high as 941 kJ / mol, and its molecular symmetry and lack of a permanent dipole moment result in an extremely high adsorption activation barrier. Existing hydrogen production catalyst design strategies (such as shallow-level defect construction and proton reduction site optimization) primarily target low-barrier reactions, making it difficult to address the strong electron injection and N≡N dissociation kinetics required for nitrogen fixation.

[0009] Therefore, efficient photocatalytic nitrogen fixation remains a core challenge in this field, and there is an urgent need to develop new material systems that have strong N2 adsorption capacity, deep energy level hole oxidation properties and anti-HER competitive reaction properties. Summary of the Invention

[0010] In order to overcome the shortcomings of the existing technology, the present invention provides a method for preparing a holmium single atom-doped carbon nitride photocatalytic material and its application in photocatalytic nitrogen fixation. Currently, in the field of photocatalytic nitrogen fixation, although there have been studies on the modification of carbon nitride materials, the existing modification methods have obvious shortcomings: on the one hand, traditional photocatalytic materials such as pure graphite phase carbon nitride have low efficiency in separating photogenerated carriers, resulting in poor photocatalytic nitrogen fixation performance (the photocatalytic nitrogen fixation performance of pure graphite phase carbon nitride is only 40.14μmol·g -1·h-1); On the other hand, some modification strategies have failed to effectively solve the limitations of carbon nitride structure defects on the exposure of catalytic active sites and catalytic reaction kinetics, and have been unable to significantly break through the bottleneck of nitrogen fixation performance. The preparation method of the present invention, holmium single-atom catalysis has uniformly distributed unsaturated sites, which provides a model platform for bridging the gap between heterogeneous and homogeneous catalysis. The specific problems of poor carrier separation and insufficient active sites in the above-mentioned traditional and existing modified photocatalytic materials in photocatalytic nitrogen fixation are solved, and they are applied to the field of photocatalytic nitrogen fixation. The photocatalytic nitrogen fixation performance of holmium-doped graphite phase carbon nitride reaches 271.68μmol·g -1 h-1, improving performance by approximately 7 times compared to pure phase, providing a more efficient material and preparation solution for photocatalytic nitrogen fixation. This invention utilizes single-atom rare earth doping to prepare modified carbon nitride. The bonding formed by the incorporated holmium atoms and nitrogen atoms influences the electronic structure of graphitic carbon nitride, inhibiting the recombination of photogenerated carriers, thereby effectively improving photocatalytic efficiency.

[0011] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0012] A holmium single atom-doped carbon nitride photocatalytic material, the catalytic material is shown in Formula I; its chemical formula is C3N4:Ho, named xHo / PTI; wherein x is the mass ratio of the raw materials melamine and holmium oxide, and x is 5-7;

[0013]

[0014] The present invention also seeks to protect a method for preparing the above-mentioned holmium single atom-doped carbon nitride photocatalytic material, which specifically comprises the following steps:

[0015] S1. Weigh a certain amount of melamine, potassium chloride, lithium chloride, and holmium oxide into an agate mortar and grind them rapidly into a uniform powder. Place the ground powder into a crucible, cover it, and heat treat it in a tube furnace. Then cool it to room temperature to obtain a light yellow powder. The mass ratio of potassium chloride and lithium chloride to melamine and holmium oxide is 2:1; the mass ratio of melamine to holmium oxide is 5-7:1; and the mass ratio of potassium chloride to lithium chloride is 55:45.

[0016] S2. The light yellow powder obtained in step S1 is washed with detergent, centrifuged, and then dried in a drying oven to obtain a holmium single atom-doped carbon nitride photocatalytic material.

[0017] Furthermore, in step S1, the heat treatment conditions are as follows: using a molten salt of potassium chloride and lithium chloride as an inert environment, raising the temperature in a tube furnace at a heating rate of 3 to 5 degrees Celsius per minute to 545 to 550 degrees Celsius for 3 to 4 hours; and naturally cooling to room temperature. Preferably, the tube furnace is heated at a heating rate of 3 degrees Celsius per minute to 550 degrees Celsius for 3 hours; and naturally cooling to room temperature.

[0018] Furthermore, in step S1, the crucible is a square alumina crucible.

[0019] Furthermore, in step S2, the detergent is deionized water at 80 degrees Celsius.

[0020] Furthermore, in step S2, during cleaning, a centrifuge is used as a washing device, and the light yellow powder is placed in a detergent and cleaned under centrifugal conditions.

[0021] Furthermore, in step S2, the centrifugation conditions are: centrifugation at 7000-9000 rpm for 4-6 minutes, repeated 4-6 times. Preferably, the centrifugation conditions are: centrifugation at 8000 rpm for 5 minutes, repeated 5 times.

[0022] Furthermore, in step S2, the drying conditions are: a drying temperature of 70 to 80 degrees Celsius, and a drying time of more than 12 hours. Preferably, the drying conditions are: a drying temperature of 70 degrees Celsius.

[0023] The present invention also requests protection for the application of the holmium single atom-doped carbon nitride photocatalytic material prepared by the above-mentioned preparation method in photocatalytic nitrogen fixation. The specific application is: 20 mg of the photocatalytic material is placed in a centrifuge tube, 40 ml of ultrapure water and 10.0 ml of methanol are added and mixed, and the mixture is transferred to a reactor. Nitrogen is introduced and purged for 30 minutes under dark conditions; the product is collected under irradiation under a xenon lamp equipped with a 420 nm filter for two hours, and the concentration of ammonium chloride produced is detected by an ultraviolet spectrophotometer.

[0024] After application, the specific method for measuring the performance is as follows: 20 mg of the prepared catalytic material Ho / PTI was weighed into a centrifuge tube, 40.0 ml of ultrapure water and 10.0 ml of methanol were added and mixed, and the mixture was transferred to a reactor, and nitrogen was passed through for 30 minutes under dark conditions; a xenon lamp was turned on for photocatalytic nitrogen fixation experiment, and samples were taken once every 30 minutes, and the sampling time was recorded; four samples were taken, and potassium sodium tartrate was added as a masking agent and Nessler's reagent was added as a color developer to the samples taken, and the samples were detected using an ultraviolet spectrophotometer, and the nitrogen fixation performance of the prepared catalytic material was obtained by the change in absorbance at 420 nm.

[0025] The beneficial effects of the present invention compared with the prior art are:

[0026] This invention uses potassium chloride and lithium chloride as high-temperature liquid phase solvents to produce a novel holmium single-atom doped carbon nitride photocatalytic material through a one-step calcination process. This preparation method has the advantages of being simple to operate and environmentally friendly. Compared with traditional preparation methods, it also exhibits extended π conjugation, stronger nitrogen reduction ability, and more effective carrier separation and transfer, resulting in significantly improved photocatalytic nitrogen fixation activity. The photocatalytic nitrogen fixation performance of the holmium-doped graphite-phase carbon nitride is 271.68 μmol·g -1 ·h-1; the photocatalytic nitrogen fixation performance of pure graphite carbon nitride is 40.14μmol·g -1 h-1; performance improved by about 7 times.

[0027] The present invention provides a new technical approach for developing the types and sources of semiconductor photocatalytic materials, which is of great significance for solving the increasingly serious energy problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Transmission electron microscopy image and spherical aberration-corrected high-angle annular dark field image of the holmium single-atom doped carbon nitride photocatalytic material prepared in Example 1 of the present invention. In the figure, A is 200 nm, B is 50 nm, and C is 2 nm.

[0029] Figure 2 This is a comparison chart of the nitrogen fixation rates of the holmium single atom-doped carbon nitride photocatalytic material prepared in Example 1 and the unmodified carbon nitride prepared in Comparative Example 1 under visible light irradiation. DETAILED DESCRIPTION

[0030] The present invention is described in detail below by specific examples, but the scope of protection of the present invention is not limited. Unless otherwise specified, the experimental methods adopted in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0031] The present invention provides a method for preparing a holmium single-atom-doped carbon nitride photocatalytic material. Holmium single atoms are doped into the carbon nitride structure via a one-step molten salt method, and the holmium single-atom-doped carbon nitride photocatalytic material is characterized. Transmission electron microscopy morphology observation reveals the formation of a well-crystalline, two-dimensional, sheet-like catalytic material, demonstrating the successful synthesis of the novel photocatalytic material. The photocatalytic material exhibits good photocatalytic activity in nitrogen fixation applications under visible light. The technical solutions of the present invention are described in detail below through specific embodiments and application examples.

[0032] Example 1

[0033] A method for preparing a holmium single atom-doped carbon nitride photocatalytic material;

[0034] 1.286 grams of melamine, 0.214 grams of holmium oxide, 1.65 grams of sodium chloride, and 1.35 grams of lithium chloride were weighed into an agate mortar and repeatedly and rapidly ground until uniform. This yielded a ground sample. The sample was then placed in a square alumina crucible and placed in a tube furnace. In an inert atmosphere of molten lithium chloride and potassium chloride, the temperature was raised to 550 degrees Celsius at a rate of 3 degrees Celsius per minute for 3 hours. Finally, the sample was allowed to cool naturally to room temperature, yielding a pale yellow powder. The powder was collected, washed with hot deionized water, and centrifuged at 8,000 rpm for 5 minutes. This was repeated five times. The sample was then dried in a drying oven maintained at 70 degrees Celsius for at least 12 hours. This yielded a novel holmium single-atom-doped carbon nitride photocatalytic material. The final catalytic material obtained is carbon nitride doped with holmium single atoms with x=6 (chemical formula C3N4:Ho, abbreviated as xHo / PTI, where x is the mass ratio of melamine and holmium oxide, x=6).

[0035] like Figure 1 As shown, it can be observed through transmission electron microscopy that the morphology of the prepared holmium single atom doped carbon nitride photocatalytic material is a two-dimensional nanosheet structure, and it can be observed through spherical aberration corrected high-angle annular dark field that holmium is uniformly loaded on the carbon nitride surface in the form of single atoms.

[0036] Example 2

[0037] A method for preparing a holmium single atom-doped carbon nitride photocatalytic material;

[0038] The masses of melamine and holmium oxide added in step (1) were adjusted to 1.25 g and 0.25 g, respectively, and the final catalytic material obtained was carbon nitride doped with a single holmium atom, where x=5. Other steps were the same as in Example 1.

[0039] Example 3

[0040] A method for preparing a holmium single atom-doped carbon nitride photocatalytic material;

[0041] The masses of melamine and holmium oxide added in step (1) were adjusted to 1.312 g and 0.188 g, respectively, to finally obtain a catalytic material of carbon nitride doped with holmium single atoms with x=7. Other steps were the same as in Example 1.

[0042] Comparative Example 1

[0043] The masses of melamine and holmium oxide added in step (1) were adjusted to 1.5 g and 0 g, respectively, and the catalytic material finally obtained was pure graphite-phase carbon nitride. Other conditions were the same as in Example 1.

[0044] Application Example 1

[0045] Take 20 mg of the Ho / PTI catalytic material prepared in Example 1, place it in a centrifuge tube, add 40.0 ml of ultrapure water and 10.0 ml of methanol, mix thoroughly, and transfer to a reactor. Set the circulating water temperature to 30 degrees Celsius, and in the dark, pass nitrogen gas into the reactor for 30 minutes; then turn on the xenon lamp to carry out the photocatalytic nitrogen fixation reaction, take samples every 30 minutes, and record the sampling time. A total of four samples were taken, and potassium sodium tartrate as a masking agent and Nessler's reagent as a color developer were added to each sample. The samples were tested using a UV-visible spectrophotometer, and the nitrogen fixation performance of the prepared catalytic material was evaluated by measuring the absorbance change at 420 nm.

[0046] Comparative Application Example 1

[0047] 20 mg of the PTI photocatalytic material prepared in Comparative Example 1 was placed in a centrifuge tube. 40.0 ml of ultrapure water and 10.0 ml of methanol were added, mixed thoroughly, and then transferred to a reactor. The circulating water temperature was set at 30°C. Nitrogen was purged into the reactor in the dark for 30 minutes. A xenon lamp was then used to perform the photocatalytic nitrogen fixation reaction. Samples were taken every 30 minutes and the sampling time was recorded. Four samples were taken, and potassium sodium tartrate as a masking agent and Nessler's reagent as a color developer were added to each sample. The samples were analyzed using a UV-visible spectrophotometer. The nitrogen fixation performance of the prepared catalytic material was evaluated by measuring the absorbance change at 420 nm.

[0048] Application Example 2

[0049] Take 20 mg of the Ho / PTI catalytic material prepared in Example 2, place it in a centrifuge tube, add 40.0 ml of ultrapure water and 10.0 ml of methanol, mix thoroughly, and transfer to a reactor. Set the circulating water temperature to 30 degrees Celsius, and in the dark, pass nitrogen gas into the reactor for 30 minutes; then turn on the xenon lamp for photocatalytic nitrogen fixation, take samples every 30 minutes, and record the sampling time. A total of four samples were taken, and potassium sodium tartrate was added as a masking agent and Nessler's reagent as a color developer to each sample. The samples were tested using a UV-visible spectrophotometer, and the nitrogen fixation performance of the prepared catalytic material was evaluated by measuring the absorbance change at 420 nm.

[0050] Application Comparative Example 2

[0051] 20 mg of the PTI photocatalytic material prepared in Comparative Example 1 was placed in a centrifuge tube, and 40.0 ml of ultrapure water and 10.0 ml of methanol were added. The mixture was thoroughly mixed and then transferred to a reactor. The circulating water temperature was set at 30°C. Nitrogen was purged into the reactor in the dark for 30 minutes. A xenon lamp was then used to perform the photocatalytic nitrogen fixation reaction. Samples were taken every 30 minutes and the sampling time was recorded. Four samples were taken, and potassium sodium tartrate as a masking agent and Nessler's reagent as a color developer were added to each sample. The samples were analyzed using a UV-visible spectrophotometer. The nitrogen fixation performance of the prepared catalytic material was evaluated by measuring the absorbance change at 420 nm.

[0052] Application Example 3

[0053] Take 20 mg of the Ho / PTI catalytic material prepared in Example 3, place it in a centrifuge tube, add 40.0 ml of ultrapure water and 10.0 ml of methanol, mix thoroughly, and transfer to a reactor. Set the circulating water temperature to 30 degrees Celsius, and in the dark, pass nitrogen gas into the reactor for 30 minutes; then turn on the xenon lamp for photocatalytic nitrogen fixation, take samples every 30 minutes, and record the sampling time. A total of four samples were taken, and potassium sodium tartrate was added as a masking agent and Nessler's reagent as a color developer to each sample. The samples were tested using a UV-visible spectrophotometer, and the nitrogen fixation performance of the prepared catalytic material was evaluated by measuring the absorbance change at 420 nm.

[0054] Application Comparative Example 3

[0055] 20 mg of the PTI photocatalytic material prepared in Comparative Example 1 was placed in a centrifuge tube, and 40.0 ml of ultrapure water and 10.0 ml of methanol were added. The mixture was thoroughly mixed and then transferred to a reactor. The circulating water temperature was set at 30°C. Nitrogen was purged into the reactor in the dark for 30 minutes. A xenon lamp was then used to perform the photocatalytic nitrogen fixation reaction. Samples were taken every 30 minutes and the sampling time was recorded. Four samples were taken, and potassium sodium tartrate as a masking agent and Nessler's reagent as a color developer were added to each sample. The samples were analyzed using a UV-visible spectrophotometer. The nitrogen fixation performance of the prepared catalytic material was evaluated by measuring the absorbance change at 420 nm.

[0056] After the specific application of the holmium single atom doped carbon nitride photocatalytic material prepared in Example 1 of the present invention, the hydrogen production rate (271.68 μmol·g -1 h-1) is the pure component carbon nitride (40.14 μmol·g -1 ·h-1). This proves that the holmium single atom-doped carbon nitride photocatalytic material prepared by the present invention has excellent nitrogen fixation performance.

[0057] The above-described embodiments are only preferred embodiments of the present invention, and are not intended to be all feasible embodiments of the present invention. Any obvious modifications made by a person skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A holmium single atom doped carbon nitride photocatalytic material, characterized in that the catalytic The material is shown in Formula I; its chemical formula is C3N4:Ho, named xHo / PTI; wherein x is the mass ratio of the raw materials melamine and holmium oxide, and the value of x is 5-7; 2. The method for preparing a holmium single atom-doped carbon nitride photocatalytic material according to claim 1, wherein: The specific steps include: S1. Weigh a certain amount of melamine, potassium chloride, lithium chloride, and holmium oxide and grind them rapidly into a uniform powder in an agate mortar. Place the ground powder in a covered crucible and heat-treat it in a tube furnace. Then cool it to room temperature to obtain a pale yellow powder. The mass ratio of potassium chloride and lithium chloride to melamine and holmium oxide is 2:1; the mass ratio of melamine to holmium oxide is 5-7:1; and the mass ratio of potassium chloride to lithium chloride is 55:

45. S2. The light yellow powder obtained in step S1 is washed with detergent, centrifuged, and then dried in a drying oven to obtain a holmium single atom-doped carbon nitride photocatalytic material.

3. The method for preparing a holmium single atom-doped carbon nitride photocatalytic material according to claim 2, wherein: In step S1, the heat treatment conditions are: using molten salt of potassium chloride and lithium chloride as an inert environment, raising the temperature to 545-550 degrees Celsius at a heating rate of 3-5 degrees Celsius per minute in a tube furnace for 3-4 hours; and naturally cooling to room temperature.

4. The method for preparing a holmium single atom-doped carbon nitride photocatalytic material according to claim 2, wherein: In step S2, the centrifugation conditions are: centrifugation at 7000-9000 rpm for 4-6 minutes, and repeated centrifugation 4-6 times.

5. The method for preparing a holmium single atom-doped carbon nitride photocatalytic material according to claim 2, wherein: In step S2, the drying conditions are: drying temperature is 70-80 degrees Celsius, and drying time is more than 12 hours.

6. The method for preparing a holmium single atom-doped carbon nitride photocatalytic material according to claim 2, wherein: In step S2, during cleaning, a centrifuge is used as a washing device, and the light yellow powder is placed in a detergent and cleaned under centrifugal conditions.

7. The method for preparing a holmium single atom-doped carbon nitride photocatalytic material according to claim 2, wherein: In step S2, the detergent is deionized water at 80 degrees Celsius.

8. The method for preparing a holmium single atom-doped carbon nitride photocatalytic material according to claim 2, wherein: In step S1 , the crucible is a square alumina crucible.

9. Use of the holmium single atom-doped carbon nitride photocatalytic material prepared by the preparation method according to any one of claims 2 to 8 in photocatalytic nitrogen fixation.

10. The use according to claim 9, characterized in that: The specific application is as follows: 20 mg of photocatalytic material is placed in a centrifuge tube, 40 ml of ultrapure water and 10.0 ml of methanol are added and mixed, then transferred to a reactor and purged with nitrogen for 30 minutes under dark conditions; The product was collected by irradiation under a xenon lamp equipped with a 420 nm filter for two hours, and the concentration of ammonium chloride produced was detected by a UV spectrophotometer.

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