High-crystallinity carbon nitride nanosheet based on heterogeneous fused salt interface as well as preparation method and application of high-crystallinity carbon nitride nanosheet

Abstract

The invention discloses a high-crystallinity carbon nitride nanosheet based on a heterogeneous fused salt interface as well as a preparation method and application thereof, and belongs to the technical field of photocatalysis. The preparation method comprises the following steps: carrying out hydrothermal reaction on a melamine solution or a melamine mixed solution to obtain a supramolecular precursor; mixing the supramolecular precursor with heterogeneous molten salt, and calcining in a protective atmosphere to obtain the high-crystallinity carbon nitride nanosheet; the heterogeneous molten salt is a mixture of potassium thiocyanate and potassium chloride. The heterogeneous fused salt interface is used as a reaction environment, ideal interface driving force is provided for directional assembly of a precursor and formation of a high-crystallization carbon nitride nanosheet, then preparation of a carbon nitride photocatalytic material with a controllable structure and excellent performance is achieved, and an illumination reaction is carried out in an air environment to catalyze production of hydrogen peroxide.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a highly crystalline carbon nitride nanosheet based on a heterogeneous molten salt interface, its preparation method, and its application. Background Technology

[0002] Graphitic carbon nitride, as a metal-free polymer photocatalyst, has attracted widespread attention due to its excellent thermal stability, chemical stability, and suitable band gap. However, the application potential of carbon nitride is limited by many factors, including its low specific surface area, insufficient crystallinity, low carrier separation efficiency, and limited light absorption capacity.

[0003] To overcome the aforementioned drawbacks, controlling the crystallinity of carbon nitride is an effective strategy. Highly crystalline carbon nitride has a smaller interlayer spacing, which facilitates the interlayer crossing of internal electrons, thereby improving carrier mobility and separation efficiency. Furthermore, two-dimensional nanosheet structures, due to their larger specific surface area and faster carrier transport rate, can significantly enhance their photocatalytic activity.

[0004] However, current methods for synthesizing highly crystalline carbon nitride via molten salt mainly rely on homogeneous molten salt systems. In these systems, the reactions and crystallization processes of the precursors are relatively random, making it difficult to achieve the precise spatial confinement and interface guidance required for the anisotropic growth of nanosheets. This restricts the orderliness of the structure and limits its applications. Summary of the Invention

[0005] To address the significant randomness, spatial confinement, and poor interface guidance inherent in current molten salt methods during reaction and crystallization, this invention provides a method for preparing highly crystalline carbon nitride nanosheets based on a heterogeneous molten salt interface, along with its applications. By utilizing the heterogeneous molten salt interface as a reaction environment, it provides an ideal interfacial driving force for the directional assembly of precursors and the formation of highly crystalline carbon nitride nanosheets, thereby achieving a structurally controllable and high-performance carbon nitride photocatalytic material.

[0006] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing highly crystalline carbon nitride nanosheets based on a heterogeneous molten salt interface, comprising the following steps: (1) A melamine solution or a melamine mixture is subjected to a hydrothermal reaction, followed by centrifugation and drying to obtain a supramolecular precursor; (2) The supramolecular precursor in step (1) is mixed with the heterogeneous molten salt and calcined under a protective atmosphere. The reaction microenvironment is controlled by the heterogeneous molten salt interface to obtain highly crystalline carbon nitride nanosheets. The heterogeneous molten salt is a mixture of potassium thiocyanate and potassium chloride; the heterogeneous molten salt used can provide an ideal interfacial driving force for the directional assembly of precursors and the anisotropic crystallization formation of carbon nitride nanosheets.

[0007] Further, in the melamine solution or melamine mixed solution mentioned in step (1), the mass ratio of melamine to water is 1:30~50.

[0008] Further, the hydrothermal reaction conditions in step (1) are: reaction at 180-220℃ for 10-15 h; the melamine solution undergoes a hydrothermal reaction, causing some of the melamine to decompose into cyanuric acid, which then reacts with the remaining melamine to form a supramolecular precursor.

[0009] Furthermore, in step (2), the mass ratio of supramolecular precursor to heterogeneous molten salt is 1:1~5.

[0010] Furthermore, in step (2), the calcination is a two-stage calcination, with the first stage calcination at 300-400 ℃ and the second stage calcination at 450-550 ℃, and the heating rate is 2-6 ℃ / min.

[0011] Furthermore, in step (2), the mass ratio of potassium thiocyanate to potassium chloride is 1:0.5~2.

[0012] Furthermore, in step (1), the melamine mixed solution can be a melamine-boric acid solution, a melamine-triaminopyrimidine solution, a melamine-cyanuric acid solution, a melamine-phosphoric acid solution, or a melamine-thiocyanic acid solution, which can be used to prepare boron-doped, carbon-doped, oxygen-doped, phosphorus-doped, and sulfur-doped highly crystalline carbon nitride nanosheets.

[0013] Furthermore, the product obtained from calcination in step (2) needs to be washed with water and dried.

[0014] In a second aspect, the present invention provides highly crystalline carbon nitride nanosheets prepared by the above-described preparation method.

[0015] In a third aspect, the present invention provides the application of the above-mentioned highly crystalline carbon nitride nanosheets in photocatalytic hydrogen peroxide production; specifically, the highly crystalline carbon nitride nanosheets are dispersed in water, wherein the mass ratio of the material to water is 0.5-2:5-15; and a photocatalytic reaction is carried out in an air environment to catalytically produce hydrogen peroxide.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: This invention utilizes a heterogeneous molten salt interface as a reaction environment to provide an ideal interfacial driving force for the directional assembly of precursors and the formation of highly crystalline carbon nitride nanosheets, thereby realizing the preparation of carbon nitride photocatalytic materials with controllable structure and excellent performance, and carrying out photocatalytic reaction in an air environment to catalyze the production of hydrogen peroxide. Attached Figure Description

[0017] Figure 1 XRD powder diffraction patterns of carbon nitride in Comparative Examples 1, 2, 3 and Example 1; Figure 2 Transmission electron microscope (TEM) images of carbon nitride in Comparative Examples 1, 2, 3 and Example 1, where A is Comparative Example 1, B is Comparative Example 2, C is Comparative Example 3, and D is Example 1. Figure 3 Cyclic stability test results for visible light photocatalytic hydrogen peroxide production from highly crystalline carbon nitride nanosheets. Detailed Implementation

[0018] The present invention is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods not specifically described in the following examples are generally performed under conventional conditions or as recommended by the manufacturer.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. All reagents and materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods in the art or as per the product instructions.

[0020] Example 1 (1) At room temperature, 2 g of melamine was added to 70 mL of deionized water and stirred for 30 min to obtain a melamine solution; (2) The melamine solution was transferred to a polytetrafluoroethylene reactor, heated to 200 °C, and reacted for 12 h. After the reaction was completed, the mixture was cooled, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular precursor was mixed with potassium thiocyanate and potassium chloride in a mass ratio of 1:1:1. The mixture was heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h. The temperature was then increased to 500°C and held for 4 h. After cooling, the mixture was centrifuged, washed and dried to obtain highly crystalline carbon nitride nanosheets.

[0021] Example 2 (1) At room temperature, 2 g of melamine was added to 70 mL of deionized water and stirred for 30 min to obtain a melamine solution; (2) The melamine solution was transferred to a polytetrafluoroethylene reactor, heated to 200 °C, and reacted for 12 h. After the reaction was completed, the mixture was cooled, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular precursor was mixed with potassium thiocyanate and potassium chloride in a mass ratio of 1:2:1. The mixture was heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h. The temperature was then increased to 500°C and held for 4 h. After cooling, the mixture was centrifuged, washed and dried to obtain highly crystalline carbon nitride nanosheets.

[0022] Example 3 (1) At room temperature, 2 g of melamine was added to 70 mL of deionized water and stirred for 30 min to obtain a melamine solution; (2) Transfer the melamine solution to a polytetrafluoroethylene reactor, heat it to 200 °C, react for 12 h, cool it after the reaction is completed, centrifuge to obtain the supramolecular precursor, and dry it at 60 °C for later use. (3) The above supramolecular precursor was mixed with potassium thiocyanate and potassium chloride in a mass ratio of 1:1:2. The mixture was heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h. The temperature was then increased to 500°C and held for 4 h. After cooling, the mixture was centrifuged, washed and dried to obtain highly crystalline carbon nitride nanosheets.

[0023] Example 4 (1) At room temperature, 2 g of melamine and 500 mg of boric acid were added to 70 mL of deionized water and stirred for 30 min to obtain a melamine mixed solution; (2) The melamine mixed solution was transferred to a polytetrafluoroethylene reactor and heated to 200 °C for 12 h. After the reaction was completed, the mixture was cooled, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular precursor was mixed with potassium thiocyanate and potassium chloride in a mass ratio of 1:1:1. The mixture was heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h. The temperature was then increased to 500°C and held for 4 h. After cooling, the mixture was centrifuged, washed and dried to obtain highly crystalline carbon nitride nanosheets (boron-doped carbon nitride nanosheets).

[0024] Example 5 (1) At room temperature, 2 g of melamine and 500 mg of triaminopyrimidine were added to 70 mL of deionized water and stirred for 30 min to obtain a melamine mixed solution. (2) The melamine mixed solution was transferred to a polytetrafluoroethylene reactor and heated to 200 °C for 12 h. After the reaction was completed, the mixture was cooled, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular precursor was mixed with potassium thiocyanate and potassium chloride in a mass ratio of 1:1:1. The mixture was heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h. The temperature was then increased to 500°C and held for 4 h. After cooling, the mixture was centrifuged, washed and dried to obtain highly crystalline carbon nitride nanosheets (carbon-doped carbon nitride nanosheets).

[0025] Example 6 (1) At room temperature, 2 g of melamine and 500 mg of cyanuric acid were added to 70 mL of deionized water and stirred for 30 min to obtain a melamine mixed solution. (2) The melamine mixed solution was transferred to a polytetrafluoroethylene reactor, heated to 200 °C, reacted for 12 h, cooled after the reaction was completed, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular precursor was mixed with potassium thiocyanate and potassium chloride in a mass ratio of 1:1:1. The mixture was heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h. The temperature was then increased to 500°C and held for 4 h. After cooling, the mixture was centrifuged, washed and dried to obtain highly crystalline carbon nitride nanosheets (oxygen-doped carbon nitride nanosheets).

[0026] Example 7 (1) At room temperature, add 2 g of melamine and 500 mg of phosphoric acid to 70 mL of deionized water and stir for 30 min; (2) The melamine mixed solution was transferred to a polytetrafluoroethylene reactor, heated to 200 °C, reacted for 12 h, cooled after the reaction was completed, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular mixture was mixed with potassium thiocyanate and potassium chloride in a mass ratio of 1:1:1. The mixture was heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h. The temperature was then increased to 500°C and held for 4 h. After cooling, the mixture was centrifuged, washed and dried to obtain highly crystalline carbon nitride nanosheets (phosphorus-doped carbon nitride nanosheets).

[0027] Example 8 (1) At room temperature, 2 g of melamine and 500 mg of thiocyanate were added to 70 mL of deionized water and stirred for 30 min to obtain a melamine mixed solution. (2) The melamine mixed solution was transferred to a polytetrafluoroethylene reactor, heated to 200 °C, reacted for 12 h, cooled after the reaction was completed, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular precursor was mixed with potassium thiocyanate and potassium chloride in a mass ratio of 1:1:1. The mixture was heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h. The temperature was then increased to 500°C and held for 4 h. After cooling, the mixture was centrifuged, washed and dried to obtain highly crystalline carbon nitride nanosheets (sulfur-doped carbon nitride nanosheets).

[0028] Comparative Example 1 (1) At room temperature, 2 g of melamine was added to 70 mL of deionized water and stirred for 30 min to obtain a melamine solution; (2) The melamine solution was transferred to a polytetrafluoroethylene reactor, heated to 200 °C, and reacted for 12 h. After the reaction was completed, the mixture was cooled, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular precursor was heated to 400°C in an argon atmosphere at a rate of 5°C / min and held for 1 h. The temperature was then increased to 500°C and held for 4 h. After cooling, the precursor was centrifuged, washed and dried to obtain carbon nitride nanosheets.

[0029] Comparative Example 2 (1) At room temperature, add 2 g of melamine to 70 mL of deionized water and stir for 30 min; (2) The melamine solution was transferred to a polytetrafluoroethylene reactor, heated to 200 °C, and reacted for 12 h. After the reaction was completed, the mixture was cooled, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular precursor was mixed with potassium thiocyanate at a mass ratio of 1:2, heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h, then heated to 500°C and held for 4 h, cooled, centrifuged, washed and dried to obtain carbon nitride nanosheets.

[0030] Comparative Example 3 (1) At room temperature, 2 g of melamine was added to 70 mL of deionized water and stirred for 30 min to obtain a melamine solution; (2) The melamine solution was transferred to a polytetrafluoroethylene reactor and heated to 200 °C for 12 h. After the reaction was completed, the mixture was cooled, centrifuged, and dried at 60 °C to obtain the supramolecular precursor. (3) The above supramolecular precursor was mixed with potassium chloride at a mass ratio of 1:2, heated to 400°C at a rate of 5°C / min in an argon atmosphere and held for 1 h, then heated to 500°C and held for 4 h, cooled, centrifuged, washed and dried to obtain carbon nitride nanosheets.

[0031] Material characterization The carbon nitride prepared in Example 1 and Comparative Examples 1, 2, and 3 was characterized by XRD powder diffraction, and the results are as follows: Figure 1 As shown, the highly crystalline carbon nitride nanosheets prepared in Example 1 exhibit obvious diffraction peaks, namely 8° and 28°, corresponding to the in-plane repeating units and interlayer spacing of carbon nitride, respectively. Compared with the comparative examples, the 28° peak in Example 1 is significantly shifted to a higher angle, indicating that the highly crystalline carbon nitride nanosheets prepared in Example 1 have a smaller interlayer spacing, which is beneficial for the interlayer crossing of internal electrons and improves carrier mobility and separation efficiency. The carbon nitrides prepared in Example 1 and Comparative Examples 1, 2, and 3 were characterized by transmission electron microscopy, and the results are shown in Figure 2. A, B, C, and D represent Comparative Examples 1, 2, 3, and Example 1, respectively. The carbon nitrides prepared in Comparative Examples 1-3 and Example 1 all show a plate-like morphology. The comparative examples are all large plate-like structures, while Example 1 shows multiple plate-like structures aggregated together.

[0032] Performance testing The carbon nitride prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to the following performance tests: 10 mg of photocatalyst (carbon nitride) was weighed and dispersed in 10 mL of deionized water. After stirring in the dark in air, the mixture was irradiated with a 40 W LED lamp for 1 h, and the hydrogen peroxide production effect was measured using a UV-Vis spectrophotometer. After the reaction was completed, the remaining reaction solution was centrifuged, the resulting precipitate was washed and dried, and the mass was replenished. The experiment was then conducted under the same conditions as the first time, and this process was repeated 4 times to test the cycle stability of the prepared samples. The test results of the carbon nitride materials prepared in Comparative Example 1 and Example 1 are as follows: Figure 3 As shown, by Figure 3 It can be seen that the highly crystalline carbon nitride nanosheets prepared in Example 1 exhibit excellent performance in visible light photocatalytic hydrogen peroxide production, and still have good stability after 5 cycles.

[0033] The photocatalytic hydrogen peroxide production performance of the carbon nitride materials prepared in Examples 1-6 and Comparative Examples 1-3 was tested, and the results are shown in Table 1 below: Table 1. Test results of photocatalytic hydrogen peroxide production performance of carbon nitride materials. Table 1 shows that the proportion of molten salt has a significant impact on the material properties. Doping with different elements modulates the photocatalytic performance of carbon nitride materials. Among them, the oxygen-doped highly crystalline carbon nitride nanosheets in Example 6 exhibit the best performance, while other doping elements can improve the photocatalytic performance of highly crystalline carbon nitride nanosheets to some extent. The samples in the examples show good cycling stability; after 5 cycles, the photocatalytic hydrogen peroxide production performance remains above 85%.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing highly crystalline carbon nitride nanosheets based on a heterogeneous molten salt interface, characterized in that, Includes the following steps: (1) A melamine solution or a melamine mixture is subjected to a hydrothermal reaction to obtain a supramolecular precursor; (2) The supramolecular precursor in step (1) is mixed with the heterogeneous molten salt and calcined under a protective atmosphere to obtain highly crystalline carbon nitride nanosheets. The heterogeneous molten salt is a mixture of potassium thiocyanate and potassium chloride.

2. The method for preparing highly crystalline carbon nitride nanosheets based on a heterogeneous molten salt interface according to claim 1, characterized in that, In step (1), the mass ratio of melamine to water in the melamine solution or melamine mixed solution is 1:30~50.

3. The method for preparing highly crystalline carbon nitride nanosheets based on a heterogeneous molten salt interface according to claim 1, characterized in that, The hydrothermal reaction conditions in step (1) are: reaction at 180-220℃ for 10-15 h.

4. The method for preparing highly crystalline carbon nitride nanosheets based on a heterogeneous molten salt interface according to claim 1, characterized in that, In step (2), the mass ratio of supramolecular precursor to heterogeneous molten salt is 1:1~5.

5. The method for preparing highly crystalline carbon nitride nanosheets based on a heterogeneous molten salt interface according to claim 1, characterized in that, In step (2), the calcination is a two-stage calcination. The first stage of calcination is carried out at 300-400 ℃, and then the second stage of calcination is carried out at 450-550 ℃. The heating rate is 2-6 ℃ / min.

6. The method for preparing highly crystalline carbon nitride nanosheets based on a heterogeneous molten salt interface according to claim 1, characterized in that, In step (2), the mass ratio of potassium thiocyanate to potassium chloride is 1:0.5~2.

7. The method for preparing highly crystalline carbon nitride nanosheets based on a heterogeneous molten salt interface according to claim 1, characterized in that, In step (1), the melamine mixed solution is melamine-boric acid solution, melamine-triaminopyrimidine solution, melamine-cyanuric acid solution, melamine-phosphoric acid solution, or melamine-thiocyanic acid solution.

8. A highly crystalline carbon nitride nanosheet prepared by the preparation method according to any one of claims 1 to 7.

9. The application of highly crystalline carbon nitride nanosheets prepared by the preparation method according to any one of claims 1 to 7, or the highly crystalline carbon nitride nanosheets according to claim 8, in photocatalytic hydrogen peroxide production.

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