Carbon-doped carbon nitride photocatalyst, and preparation method and application thereof

Abstract

This invention provides a method for preparing a carbon-doped carbon nitride photocatalyst, comprising the following steps: (1) melamine, cyanuric acid, and 2,4,6-triaminopyrimidine are mixed in a solvent, ultrasonically dispersed, and stirred for 12–36 h. The mixture is then washed, centrifuged, and dried. After grinding and sieving, a solid supramolecular precursor is obtained. (2) The solid supramolecular precursor obtained in step (1) is placed in air, heated to 300°C–500°C, and calcined for 2–6 h to form a mixture of carbon-doped melamine, cyanuric acid, and their oligomers. (3) The mixture obtained in step (2) is thoroughly mixed with molten salt, calcined at 500°C–600°C for 2–6 h, cooled, and thoroughly washed with deionized water to remove the mixed salt. The solid residue is separated and dried to obtain the carbon-doped carbon nitride photocatalyst. The prepared carbon-doped carbon nitride photocatalyst is simple to synthesize, structurally stable, and exhibits excellent separation and migration efficiency of photogenerated carriers, as well as excellent photocatalytic hydrogen peroxide production performance.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, and specifically relates to a method for preparing carbon-doped carbon nitride photocatalyst, its products, and applications. Background Technology

[0002] Hydrogen peroxide (H2O2), as a green oxidant and potential energy carrier, has a global annual demand of 4 million tons, which is expected to increase to 5.7 million tons by 2027. It is widely used in chemical synthesis, environmental remediation, medical disinfection, and new energy development. Currently, over 95% of H2O2 is produced through the anthraquinone auto-oxidation process. This technology has been used for over 70 years since its industrialization in 1953, and its core process is "alkyl anthraquinone hydrogenation → hydrogen anthraquinone oxidation → hydrogen peroxide extraction → anthraquinone recycling". However, this process has three major structural defects that seriously conflict with carbon neutrality goals and green chemical engineering concepts: First, it is energy-intensive and costly, relying on high-pressure hydrogenation (0.3-0.5 MPa), precious metal Pd catalysts, large amounts of hydrogen and organic solvents, and requiring large-scale equipment; second, it causes serious environmental pollution, generating wastewater and waste residue containing heavy metals and organic matter, and the volatilization of organic solvents causes pollutant emissions; third, it poses significant safety risks involving hydrogen, high pressure, and flammable and explosive organic materials, with potential leakage and explosion hazards during storage and transportation.

[0003] Photocatalysis, using green and renewable sunlight as an energy source and semiconductor materials as catalysts, can produce hydrogen peroxide under mild reaction conditions. It boasts significant advantages such as environmental friendliness, low energy consumption, and no secondary pollution, making it a crucial technological pathway for the green synthesis of hydrogen peroxide. In the field of photocatalytic hydrogen peroxide production, developing semiconductor catalytic materials with suitable band gaps, matched redox capabilities, and excellent stability has always been a key research focus and hot topic. These semiconductor materials must meet core requirements such as excellent light absorption performance, high photogenerated carrier separation efficiency, and sufficient catalytic active sites to efficiently drive the photocatalytic reaction. Compared to traditional metal-based semiconductor catalytic materials, graphitic carbon nitride (g-C3N4, hereinafter referred to as carbon nitride) has significant advantages: its preparation process is simple, raw material sources are abundant and inexpensive, its physicochemical properties can be flexibly adjusted by regulating preparation parameters, and it possesses good resistance to acid and alkali corrosion and chemical stability. Therefore, it has received widespread attention and in-depth research in the field of photocatalysis, becoming one of the preferred semiconductor materials for photocatalytic hydrogen peroxide production. However, in current industrial and laboratory settings, bulk carbon nitride is typically prepared via direct thermal polymerization using nitrogen-containing small molecules such as melamine, urea, and dicyandiamine as precursors. Bulk carbon nitride prepared by this method generally suffers from inherent defects: a small specific surface area, resulting in a limited number of catalytically active sites; a rapid recombination rate of photogenerated electrons and holes, leading to reduced quantum utilization; and weak absorption of visible light, further limiting its photocatalytic performance. These defects mean that the catalytic activity of bulk carbon nitride in the photocatalytic production of hydrogen peroxide often fails to meet practical application requirements.

[0004] Therefore, in order to overcome the above-mentioned defects of existing bulk carbon nitride, significantly improve its photocatalytic activity in the preparation of hydrogen peroxide, and expand its practical application scenarios, modifying carbon nitride materials has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned shortcomings by providing a method for preparing carbon-doped carbon nitride photocatalysts, as well as their products and applications.

[0006] This invention provides a method for preparing a carbon-doped carbon nitride photocatalyst, the specific steps of which are as follows: (1) Melamine, cyanuric acid and 2,4,6-triaminopyrimidine are mixed in a solvent, ultrasonically dispersed and stirred for 12-36 hours. After washing, centrifugation and drying, the solid supramolecular precursor is obtained by grinding and sieving. (2) Place the solid supramolecular precursor obtained in step (1) in air, heat it to 300℃~500℃, and calcine it for 2~6h to form a mixture of carbon-doped melamine, cyanuric acid and its oligomers. (3) After the mixture obtained in step (2) is thoroughly mixed with molten salt, it is calcined at 500℃~600℃ for 2~6h, cooled and thoroughly washed with deionized water to remove the mixed salt, separate the solid residue, and dry to obtain carbon-doped carbon nitride photocatalyst.

[0007] The method provided by this invention first prepares a solid supramolecular precursor, which can specifically address the shortcomings of traditional thermal polymerization methods. It has the advantages of controllable structure, excellent photocatalytic performance, simple and green preparation, strong adaptability and stability, and good reproducibility. It can efficiently enhance the photocatalytic application potential of carbon nitride. Then, by calcining it at high temperature with molten salt, the synthesis energy consumption and difficulty can be reduced by taking advantage of the low eutectic properties, and the product structure and photocatalytic performance can be optimized. The preparation process is green and simple, the molten salt can be recycled, and it can be adapted to subsequent applications by parameter adjustment. It specifically addresses the shortcomings of traditional preparation methods. It can not only obtain a rich pore structure, improve the material's absorption of sunlight and adsorption capacity of reactant molecules, but also improve the crystallinity of the material, improve its photogenerated carrier separation and transport efficiency, reduce recombination, increase catalytic active sites, and thus improve the efficiency, selectivity and material stability of photocatalytic hydrogen peroxide production.

[0008] Furthermore, in step (3), the heating rate is 5°C·min. -1 .

[0009] Further, in step (1), the mass ratio of melamine, cyanuric acid and 2,4,6-triaminopyrimidine is 1.26:1.29:0.02 to 0.1.

[0010] Furthermore, in step (1), the mass ratio of melamine, cyanuric acid and 2,4,6-triaminopyrimidine is 1.26:1.29:0.06.

[0011] Furthermore, in step (1), the solvent is dimethyl sulfoxide.

[0012] Furthermore, in step (1), the volume of the solvent is 60 mL.

[0013] Furthermore, in step (3), the molten salt is a combination of KCl and LiCl, and the mass ratio of the mixture, KCl and LiCl is 1:7:7.

[0014] A second aspect of the present invention also provides a carbon-doped carbon nitride photocatalyst prepared by the above-described preparation method.

[0015] A third aspect of the present invention also provides an application of the above-mentioned carbon-doped carbon nitride photocatalyst in the photocatalytic production of hydrogen peroxide.

[0016] Furthermore, the application involves using ultrapure water as the reaction medium and reactants, carbon-doped carbon nitride photocatalyst as the photocatalyst, a xenon lamp as the light source, oxygen as the oxygen source, and isopropanol as the sacrificial agent to form a reaction system for the preparation of hydrogen peroxide.

[0017] Furthermore, the reaction conditions are as follows: the reaction temperature is controlled at 25℃, the reaction time is 1–3 h, the reaction system contains 36 mL of ultrapure water, 4 mL of isopropanol, and the concentration of carbon nitride photocatalyst is 0.25 g·L⁻¹. -1 .

[0018] Beneficial effects of this invention:

[0019] (1) Doping with TAP can introduce pyrimidine rings into the carbon nitride framework, break the symmetry structure of the carbon nitride heptaazine framework, excite n→π* transitions, and broaden the photoresponse range of the material; at the same time, carbon doping is also beneficial to the migration and separation of photogenerated carriers, thereby improving photocatalytic efficiency.

[0020] (2) Supramolecular self-assembly makes the material structure controllable, with excellent performance, simple preparation, good stability and reproducibility.

[0021] (3) The addition of molten salt reduces the energy consumption and difficulty of synthesis, optimizes the product structure and photocatalytic properties, and the preparation process is green and simple, and the molten salt can be recycled. Attached Figure Description

[0022] Figure 1 The photoluminescence spectra of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 3 are shown below. Figure 2 Fourier transform infrared spectra of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 3; Figure 3 The graph shows the photocatalytic hydrogen peroxide production performance of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 3 over one hour. Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification. Unless otherwise specified, the methods described are conventional methods, and the original photocatalysts can be obtained from publicly available commercial sources unless otherwise specified.

[0024] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0025] The preparation method of the carbon-doped carbon nitride photocatalyst provided by this invention includes the following specific steps: (1) Melamine, cyanuric acid and 2,4,6-triaminopyrimidine are mixed in a solvent, ultrasonically dispersed and stirred for 12-36 hours. After washing, centrifugation and drying, the solid supramolecular precursor is obtained by grinding and sieving. (2) Place the solid supramolecular precursor obtained in step (1) in air, heat it to 300℃~500℃, and calcine it for 2~6h to form a mixture of carbon-doped melamine, cyanuric acid and its oligomers. (3) After the mixture obtained in step (2) is thoroughly mixed with molten salt, it is calcined at 500℃~600℃ for 2~6h, cooled and thoroughly washed with deionized water to remove the mixed salt, separate the solid residue, and dry to obtain carbon-doped carbon nitride photocatalyst.

[0026] The following examples illustrate the specific amounts of raw materials and reaction conditions.

[0027] Example 1

[0028] CCN Li,K Preparation of photocatalysts: (1) Mix 1.26g melamine, 1.29g cyanuric acid and 0.06g 2,4,6-triaminopyrimidine in 60mL dimethyl sulfoxide, disperse by ultrasonication and stir for 12h, wash, centrifuge three times and dry in a vacuum oven at 60℃, and then grind thoroughly in a mortar to obtain a solid supramolecular precursor; (2) Transfer the solid supramolecular precursor obtained in step (1) into a crucible and calcine it at 350°C for 3 hours (heating rate of 5°C·min). -1 This forms a mixture of carbon-doped melamine, cyanuric acid, and their oligomers. (3) The mixture (0.1 g) obtained in step (2) was uniformly mixed with KCl (0.7 g) and LiCl (0.7 g) and then transferred to a covered crucible. It was calcined at 550 °C for 2 h in air atmosphere (heating rate of 5 °C·min⁻¹). After natural cooling, it was thoroughly washed with deionized water to remove the mixed salts, and the solid residue was separated. After drying, a carbon-doped carbon nitride photocatalyst CCN with uniformly distributed homogeneous junctions was obtained. Li,K .

[0029] Compare with Example 1 Preparation of carbon nitride (CN) photocatalysts: (1) Mix 1.26g melamine and 1.29g cyanuric acid in 60mL dimethyl sulfoxide, disperse by ultrasonication, stir for 12h, wash, centrifuge three times and dry in a vacuum oven at 60℃, and then grind thoroughly in a mortar to obtain a solid supramolecular precursor. (2) Transfer the solid supramolecular precursor obtained in step (1) into a crucible and calcine it at 350°C for 3 hours (heating rate of 5°C·min). -1 This forms a mixture of melamine, cyanuric acid, and their oligomers. (3) The mixture obtained in step (2) is thoroughly washed with deionized water to separate the solid residue, and then dried to obtain carbon nitride photocatalyst CN.

[0030] Compare with Example 2 Preparation of carbon-doped carbon nitride (CCN) photocatalysts: (1) Mix 1.26g melamine, 1.29g cyanuric acid and 0.06g 2,4,6-triaminopyrimidine in 60mL dimethyl sulfoxide, disperse by ultrasonication and stir for 12h, wash, centrifuge three times and dry in a vacuum oven at 60℃, and then grind thoroughly in a mortar to obtain a solid supramolecular precursor; (2) Transfer the solid supramolecular precursor obtained in step (1) into a crucible and calcine it at 350°C for 3 hours (heating rate of 5°C·min). -1 This forms a mixture of carbon-doped melamine, cyanuric acid, and their oligomers. (3) The mixture obtained in step (2) is thoroughly washed with deionized water to separate the solid residue. After drying, carbon-doped carbon nitride photocatalyst CCN is obtained.

[0031] Compare with Example 3 Molten salt carbon nitride (CN) Li,k Preparation of photocatalysts: (1) Mix 1.26g melamine and 1.29g cyanuric acid in 60mL dimethyl sulfoxide, disperse by ultrasonication, stir for 12h, wash, centrifuge three times and dry in a vacuum oven at 60℃, and then grind thoroughly in a mortar to obtain a solid supramolecular precursor. (2) Transfer the solid supramolecular precursor obtained in step (1) into a crucible and calcine it at 350°C for 3 hours (heating rate of 5°C·min). -1 This forms a mixture of melamine, cyanuric acid, and their oligomers. (3) The mixture (0.1 g) obtained in step (2) was uniformly mixed with KCl (0.7 g) and LiCl (0.7 g) and then transferred to a covered crucible. It was calcined at 550 °C for 2 h in air (heating rate of 5 °C·min⁻¹). After natural cooling, it was thoroughly washed with deionized water to remove the mixed salts, and the solid residue was separated. After drying, a carbon-doped carbon nitride photocatalyst with a uniformly distributed homogeneous junction, CN, was obtained. Li,K .

[0032] Figure 1 The images show the photoluminescence spectra of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 3. CN exhibits the highest peak intensity; the high PL intensity can be attributed to the shortened conjugation length, which limits exciton separation. After molten salt treatment, the peak intensity decreases, while the lowest peak intensity is observed when molten salt treatment is combined with carbon doping. This indicates that charge carriers within CN are prone to recombination, and molten salt treatment and carbon doping can effectively reduce this recombination rate. The reduction in electron-hole recombination rate is beneficial for improving charge carrier separation and migration efficiency; therefore, molten salt treatment and carbon doping have a positive effect on improving charge separation.

[0033] Figure 2 The Fourier transform infrared (FTIR) spectra of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 3 are shown below. The FTIR spectra of the carbon nitride catalysts show that each sample is within the range of 810 cm⁻¹. -1 A peak is observed at 1200-1700 cm⁻¹, which is a stretching vibration peak caused by the triazine structure. This indicates that the structure of carbon nitride was not disrupted after using the molten salt method and carbon doping. -1 The peaks in the 2900-3500 cm⁻¹ originate from the stretching vibrations of aromatic CN heterocycles. Additionally, the peaks in the 2900-3500 cm⁻¹ range... -1 The broad peak at this point is due to the vibrations of residual NH and OH, which may be caused by the amino groups at the edge of carbon nitride and absorbed water molecules. Comparing CN and CCN, CCN... Li,K There are two obvious differences, one is CCN Li,K Located at 2172cm -1 A new peak appears, which is the vibrational peak of the cyano group; another is the decreased intensity of the NH vibrational peak. These two differences indicate that some of the edge amino groups in the modified carbon nitride are converted into cyano groups.

[0034] Test case The carbon nitride photocatalysts obtained in the above examples and comparative examples were used as catalysts to carry out the photocatalytic hydrogen peroxide production reaction. The specific reaction methods are as follows: Take 10 mg of each of the carbon nitride photocatalyst powders obtained in the above examples and comparative examples, and ultrasonically disperse them uniformly in 36 mL of ultrapure water. Add 10% (4 mL) of isopropanol and pour into a quartz reactor, then ultrasonically disperse for 5 min. Continuously purge with oxygen for 10 min in darkness. Use a Xe lamp light source with a wavelength greater than 420 nm, control the reaction temperature at 25 °C, and the reaction time for 1 h. Hydrogen peroxide concentration test method: Every 15 minutes, take 2 mL of the reaction solution and remove the photocatalyst using a 0.22 μm microporous filter. Add 1 mL of 0.4 mol / L potassium iodide solution and 1 mL of 0.1 mol / L potassium hydrogen phthalate aqueous solution to 2 mL of the above solution, and then keep in the dark for 30 min. Due to the reaction of iodide ions and hydrogen peroxide, the colorless solution shows color and exhibits strong absorption near 350 nm. Measure the absorbance at 350 nm using UV-Vis spectroscopy to calculate the total amount of hydrogen peroxide produced during the photocatalytic reaction. The results are as follows: Figure 3 As shown.

[0035] Figure 3 The image shows the photocatalytic performance of various catalysts in producing hydrogen peroxide. After one hour of illumination, CCN... Li,K The concentration of hydrogen peroxide produced by photocatalysis reached 1267 μmol / L, CN Li,K The yields of CCN and CN reached 670 μmol / L, 112 μmol / L, and 83 μmol / L, respectively. (CCN) Li,K The photocatalytic performance is 15 times better than CN, 11 times better than CCN, and better than CN. Li,K The performance improved by 1.9 times. This improvement in photocatalytic performance is attributed to the synergistic effect of the molten salt method and carbon doping. These two modification strategies enhance the performance of CCN. Li,K It has high efficiency in separating and transferring photogenerated carriers.

[0036] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a carbon-doped carbon nitride photocatalyst, characterized in that, Including the following steps: (1) Melamine, cyanuric acid and 2,4,6-triaminopyrimidine are mixed in a solvent, ultrasonically dispersed and stirred for 12-36 hours. After washing, centrifugation and drying, the solid supramolecular precursor is obtained by grinding and sieving. (2) Place the solid supramolecular precursor obtained in step (1) in air, heat it to 300℃~500℃, and calcine it for 2~6h to form a mixture of carbon-doped melamine, cyanuric acid and its oligomers. (3) After the mixture obtained in step (2) is thoroughly mixed with molten salt, it is calcined at 500℃~600℃ for 2~6h, cooled and thoroughly washed with deionized water to remove the mixed salt, separate the solid residue, and dry to obtain carbon-doped carbon nitride photocatalyst.

2. A method for preparing the carbon-doped carbon nitride photocatalyst according to claim 1, characterized in that, In step (3), the heating rate is 5°C·min. -1 .

3. The method for preparing the carbon-doped carbon nitride photocatalyst as described in claim 1, characterized in that, In step (1), the mass ratio of melamine, cyanuric acid and 2,4,6-triaminopyrimidine is 1.26:1.29:0.02 to 0.

1.

4. The preparation method of the carbon-doped carbon nitride photocatalyst as described in claim 3, characterized in that, In step (1), the mass ratio of melamine, cyanuric acid and 2,4,6-triaminopyrimidine is 1.26:1.29:0.

06.

5. The method for preparing the carbon-doped carbon nitride photocatalyst as described in claim 1, characterized in that, In step (1), the solvent is dimethyl sulfoxide.

6. The method for preparing the carbon-doped carbon nitride photocatalyst as described in claim 1, characterized in that, In step (1), the volume of the solvent is 60 mL.

7. The method for preparing the carbon-doped carbon nitride photocatalyst as described in claim 2, characterized in that, In step (3), the molten salt is a combination of KCl and LiCl, and the mass ratio of the mixture, KCl and LiCl is 1:7:

7.

8. A carbon-doped carbon nitride photocatalyst, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

9. The application of the carbon-doped carbon nitride photocatalyst as described in claim 8 in the photocatalytic production of hydrogen peroxide.

10. The application of the carbon-doped carbon nitride photocatalyst as described in claim 9 in the photocatalytic production of hydrogen peroxide, characterized in that, Hydrogen peroxide was prepared by using ultrapure water as the reaction medium and reactants, carbon-doped carbon nitride photocatalyst as the photocatalyst, xenon lamp as the light source, oxygen as the oxygen source, and isopropanol as the sacrificial agent to form a reaction system.

11. The application of the carbon-doped carbon nitride photocatalyst as described in claim 10 in the photocatalytic production of hydrogen peroxide, characterized in that, The reaction conditions were as follows: the reaction temperature was controlled at 25℃, the reaction time was 1–3 h, the reaction system contained 36 mL of ultrapure water, 4 mL of isopropanol, and the concentration of carbon nitride photocatalyst was 0.25 g·L⁻¹. -1 .

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