Asymmetric carbon nitride catalyst and preparation method and application thereof

Abstract

The present invention relates to the field of photocatalysis technology, and in particular to an asymmetric carbon nitride catalyst and a preparation method and application thereof. The preparation method comprises the following steps: copolymerizing urea and 3-amino-5-mercapto-1,2,4-triazole as raw materials to synthesize an asymmetric carbon nitride material, increasing its crystallinity by post-treatment, and introducing a cyano group. The asymmetric carbon nitride catalyst prepared by the present invention can produce 14.74 mmol g H2O2 under visible light. ‑ 1 h ‑1 , which is about 122.8 times that of bulk carbon nitride materials, and can achieve 70mmol g in eight hours. ‑1 The hydrogen peroxide yield can quickly remove 10 ppm of Rhodamine B dye within 20 s, which almost exceeds the yield of all existing photocatalysts.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalysis, and in particular to an asymmetric carbon nitride catalyst and a preparation method and application thereof. Background Art

[0002] Hydrogen peroxide (H2O2) is an environmentally friendly chemical reagent that is widely used in environmental remediation, chemical synthesis, medical disinfection, and energy storage. However, more than 95% of H2O2 production currently relies on the complex anthraquinone process. Although effective, this process is fraught with safety risks, increases energy consumption, and imposes a heavy cost on the environment. In view of these shortcomings, it is imperative to seek another safe, environmentally friendly, and energy-saving method for producing H2O2. Currently, only abundant renewable water (H2O) and oxygen (O2) on the earth are used as raw materials, and two-electron oxygen reduction (2eO2) is used to produce H2O2. - The photocatalytic production of H2O2 via the ORR (Organic Reactor) route is a method favored by scientists. Although the technology is highly praised for its safety and environmental protection, its multi-step selective reaction results in unsatisfactory H2O2 yield and selectivity. This inherent bottleneck hinders its widespread application and potential in various fields.

[0003] In addition, with the continuous development of social industry, the wanton discharge of various organic pollutants has caused a great burden on the environment. At present, photocatalytic degradation technology and Fenton technology are widely used to remove organic pollutants. However, both methods have obvious disadvantages. Photocatalytic degradation technology: low efficiency, incomplete removal, usually requires at least two hours to achieve about 80% removal of 10ppm rhodamine b. Fenton technology: the large amount of H2O2 raw materials required depends on the complex anthraquinone process. Summary of the invention

[0004] Aiming at the disadvantages that the photocatalytic degradation of organic pollutants in the prior art is slow and the removal is not thorough; the hydrogen peroxide raw materials required by the Fenton oxidation technology all rely on the complex anthraquinone process. The purpose of the present invention is to provide an asymmetric high-crystalline carbon nitride that can provide high-yield H2O2 and achieve the removal of 10ppm rhodamine b within 20 seconds, thereby realizing the organic combination of photocatalytic technology and Fenton oxidation technology.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] In a first aspect, a method for preparing an asymmetric carbon nitride catalyst is provided, comprising the following steps:

[0007] The asymmetric carbon nitride material is synthesized by copolymerization using urea and 3-amino-5-mercapto-1,2,4-triazole as raw materials, and its crystallinity is increased by post-treatment, and a cyano group is introduced.

[0008] Furthermore, the method specifically includes the following steps:

[0009] The urea and 3-amino-5-mercapto-1,2,4-triazole powders are mixed and evenly ground, and heated in air at 500-600°C for 3-5 hours to obtain a yellow mass; the yellow mass is ground into powder, the obtained powder is mixed with KCl / LiCl eutectic salt, and heated in argon at 500-600°C in a tube furnace for 3-5 hours; after cooling to room temperature, the mixture is washed with deionized water for multiple times, and finally dried at 80°C for 24 hours.

[0010] Furthermore, the mass ratio of urea to 3-amino-5-mercapto-1,2,4-triazole powder is 200:1.

[0011] Furthermore, the obtained powder was fully mixed with KCl / LiCl eutectic salt at a mass ratio of 1:5.

[0012] In a second aspect, the invention provides the use of an asymmetric carbon nitride catalyst in producing high-concentration hydrogen peroxide using photocatalytic technology.

[0013] Furthermore, the produced high concentration hydrogen peroxide is used to quickly remove organic pollutants.

[0014] The beneficial effects of the present invention are:

[0015] The present invention uses urea and 3-amino-5-mercapto-1,2,4-triazole as raw materials to copolymerize and synthesize an asymmetric carbon nitride material, and increases its crystallinity by post-treatment, and introduces a cyano group. Under visible light, the H2O2 yield can reach 14.74mmol g -1 h -1 , which is about 122.8 times that of bulk carbon nitride materials, and can achieve 70mmol g in eight hours. -1 The hydrogen peroxide yield can quickly remove 10 ppm of Rhodamine B dye within 20 s, which almost exceeds the yield of all existing photocatalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The molecular structure diagram of asymmetric carbon nitride (MTCN) prepared in Example;

[0017] Figure 2 SEM image of asymmetric carbon nitride (MTCN) prepared in Example;

[0018] Figure 3 Infrared image of asymmetric carbon nitride (MTCN) prepared in Example;

[0019] Figure 4Performance diagram of carbon nitride (BCN) and asymmetric carbon nitride (MTCN) prepared in the examples;

[0020] Figure 5 Long-term performance diagram of asymmetric carbon nitride (MTCN) prepared in Example;

[0021] Figure 6 Schematic diagram of the degradation effect of hydrogen peroxide produced by asymmetric carbon nitride (MTCN) prepared in Example on 10 ppm of rhodamine b. DETAILED DESCRIPTION

[0022] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0023] Example

[0024] Preparation method of carbon nitride (BCN): Grind urea evenly, put it into a crucible, and heat it in air at 550℃ for 4 hours.

[0025] Preparation of asymmetric carbon nitride (MTCN): Mix urea and 3-amino-5-mercapto-1,2,4-triazole powders in a mass ratio of 200:1, grind them evenly, put them in a crucible, and heat them in air at 550°C for 4 hours to obtain yellow lumps. Grind the yellow lumps into powder, mix the obtained powder with KCl / LiCl eutectic salt (molar ratio of 11:9) in a mass ratio of 1:5, and heat them in a tube furnace at 500°C in argon for 4 hours. After cooling to room temperature, wash with deionized water 6 times, and finally dry them in an oven at 80°C for 24 hours.

[0026] like Figure 1-2 As shown, the asymmetric carbon nitride MTCN prepared in this embodiment is a heptazine ring structure with a triazole segment, and is connected to a rich cyano group at the end. The asymmetric carbon nitride MTCN presents an aggregate of small-sized nanosheets.

[0027] like Figure 3 As shown, BCN has an obvious breathing vibration mode belonging to the heptazine part at 810 cm. However, MTCN shows a relatively weakened peak intensity due to the incorporation of the triazole ring. 960-1750cm -1Numerous stretching modes in the range of 100 to 200 cm belong to the CN heterocycle. In MTCN, these vibrational modes show slight deviations compared to BCN, indicating that the insertion of the triazole ring causes a change in the chemical environment. In addition, MTCN has a large number of stretching modes at approximately 998, 1156, and 2180 cm -1 Three different bands appeared at 3200cm -1 The significant signal at the x ), which is significantly reduced in MTCN, because MTCN has better crystallinity than BCN. Compared with BCN, MTCN has a -1 The asymmetric vibration associated with the hydroxyl group (-OH) nearby is significantly enhanced, which is beneficial to the interaction with the adsorbed water molecules of the photocatalyst during the catalytic process and further promotes the generation of H2O2.

[0028] Test example

[0029] The detection of H2O2 is to evenly disperse a certain amount of photocatalyst in 50ml of deionized water containing 10% ethanol, stir in the dark for 30 minutes, and reach adsorption-desorption equilibrium. Then the reaction solution is irradiated with a 420nm cutoff film (λ≥420nm) under a 300W xenon lamp to start the photoreaction test. 4ml of the suspension is taken out every 30 minutes, and its supernatant is subjected to color reaction by iodine titration. Briefly, 2ml of potassium iodide solution (0.1M) and 50μl of ammonium molybdate tetrahydrate solution (0.01M) are added to 500μl of supernatant for color reaction, and then detected with a UV-visible spectrophotometer.

[0030] This test example uses BCN and MTCN prepared in Example 1 for testing. The results show that the basic photocatalytic H2O2 production of BCN nanosheets is 0.12 mmol g -1 h -1 After modification, the H2O2 yield of MTCN reached 14.74mmol g -1 h -1 , which is 122.8 times that of BCN. As the reaction time is further extended, the H2O2 yield of MTCN increases linearly and steadily with time, and the cumulative yield of hydrogen peroxide after 8 hours is 70mmol g -1 ( Figure 4-5 The collected high concentration H2O2 solution was applied to RhB (10 mg L -1 ) color change, through the Fenton reaction, the pollutant can be quickly converted into colorless ( Figure 6 ), has high social value and broad application prospects.

[0031] The present invention uses urea and 3-amino-5-mercapto-1,2,4-triazole as raw materials to copolymerize and synthesize an asymmetric carbon nitride material, and increases its crystallinity by post-treatment, and introduces a cyano group. Under visible light, the H2O2 yield can reach 14.74mmol g -1 h -1 , which is about 122.8 times that of bulk carbon nitride materials, and can achieve 70mmol g in eight hours. -1 The hydrogen peroxide yield can quickly remove 10 ppm of Rhodamine B dye within 20 s, which almost exceeds the yield of all existing photocatalysts.

[0032] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0033] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing an asymmetric carbon nitride catalyst, characterized in that: The following steps are involved: The asymmetric carbon nitride material is synthesized by copolymerization of urea and 3-amino-5-mercapto-1,2,4-triazole as raw materials, and its crystallinity is increased by post-treatment, and a cyano group is introduced; The urea and 3-amino-5-mercapto-1,2,4-triazole powders are mixed and evenly ground, and heated in air at 500-600°C for 3-5 hours to obtain a yellow mass; the yellow mass is ground into powder, the obtained powder is mixed with KCl / LiCl eutectic salt, and heated in argon at 500-600°C in a tube furnace for 3-5 hours; after cooling to room temperature, the mixture is washed with deionized water for multiple times, and finally dried at 80°C for 24 hours.

2. The method for preparing an asymmetric carbon nitride catalyst according to claim 1, characterized in that: The mass ratio of urea to 3-amino-5-mercapto-1,2,4-triazole powder is 200:

1.

3. The method for preparing an asymmetric carbon nitride catalyst according to claim 1, characterized in that: The obtained powder was thoroughly mixed with KCl / LiCl eutectic salt at a mass ratio of 1:

5.

4. An asymmetric carbon nitride catalyst prepared by the method according to any one of claims 1 to 3.

5. Use of the asymmetric carbon nitride catalyst according to claim 4 in producing high-concentration hydrogen peroxide using photocatalytic technology.

6. The use according to claim 5, characterized in that: The high concentration of hydrogen peroxide produced should be used to quickly remove organic pollutants.

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