Doped modified polyheptazinyl imide as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalytic materials, in particular to doped modified polyheptazinyl imide as well as a preparation method and application thereof. The preparation method of the doped modified polyheptazinyl imide comprises the following steps: carrying out thermal polymerization reaction on a carbon nitride precursor to obtain polymer carbon nitride; and carrying out thermal polymerization reaction on the polymer carbon nitride in the presence of a dopant in the presence of a chloride fused salt as an eutectic salt template to obtain the doped modified polyheptazinamide. The doped modified polyheptazinyl imide prepared by the preparation method has a wide spectral response range, the light absorption range of a photocatalytic material is greatly widened, and sunlight is expected to be utilized to the maximum extent, so that high activity of photocatalytic decomposition of water to produce hydrogen is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and particularly relates to a doped and modified poly(heptazine imide) and a preparation method and application thereof. Background Art

[0002] Poly(heptazine imide) (PHI), as a novel carbon nitride photocatalyst, forms a highly delocalized π-conjugated system with its long-range ordered heptazine ring structure, and has more excellent photogenerated charge separation efficiency compared with traditional carbon nitride materials. However, the wide bandgap characteristic (~2.7 eV) of PHI results in its ability to absorb only sunlight below 460 nm, and only about 10% of solar energy can be utilized, which greatly limits its large-scale application in the field of energy photocatalysis.

[0003] Therefore, the prior art still needs to be improved and developed. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a doped and modified poly(heptazine imide) and a preparation method and application thereof, aiming to solve the problems of narrow light response range and low solar energy utilization rate of the existing PHI photocatalyst.

[0005] The technical solution of the present invention is as follows:

[0006] In the first aspect of the present invention, a preparation method of a doped and modified poly(heptazine imide) is provided, which includes the steps of:

[0007] Performing a thermal polymerization reaction on a carbon nitride precursor to obtain polymeric carbon nitride;

[0008] Performing a thermal polymerization reaction on the polymeric carbon nitride under the conditions of a chloride molten salt as a eutectic salt template and the presence of a dopant to obtain a doped and modified poly(heptazine imide).

[0009] Optionally, the carbon nitride precursor is one of urea, cyanamide, dicyandiamide, thiourea, and melamine.

[0010] Optionally, the chloride in the chloride molten salt is at least two of potassium chloride, sodium chloride, and lithium chloride.

[0011] Optionally, the mass ratio of the polymeric carbon nitride, the chloride molten salt, and the dopant is between 1:1:0.01 and 1:20:5.

[0012] Optionally, the temperature for performing the thermal polymerization reaction on the polymeric carbon nitride under the conditions of a chloride molten salt as a eutectic salt template and the presence of a dopant is between 500 and 650 °C.

[0013] Optionally, the time for the thermal polymerization reaction of the polymeric carbon nitride under the condition of the chloride molten salt as the eutectic salt template and the dopant is between 3 and 12 h.

[0014] Optionally, the dopant is carbon, nitrogen, boron, malonic acid, pyrimidine, phloroglucinol or oxamide.

[0015] In the second aspect of the present invention, a doped and modified polyheptazine imide is provided, which is prepared by the method described in the present invention.

[0016] In the third aspect of the present invention, an application of the doped and modified polyheptazine imide described in the present invention as a photocatalyst is provided.

[0017] Optionally, the photocatalyst is used for photocatalytic water splitting to produce hydrogen.

[0018] Beneficial effects: The polymeric carbon nitride prepared from the carbon nitride precursor in the present invention undergoes a thermal polymerization reaction under the condition of the chloride molten salt as the eutectic salt template and the dopant, so that the light absorption of the doped and modified polyheptazine imide is extended from 460 nm to 900 nm. Using the doped and modified polyheptazine imide with a wide spectral response range as a photocatalyst in the present invention can maximize the utilization of sunlight and obtain high photocatalytic water splitting hydrogen production activity in the visible light and near-infrared regions. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the mechanism for the extension of the light absorption of boron-doped polyheptazine imide in the present invention.

[0020] Figure 2 It is a schematic diagram for preparing boron-doped polyheptazine imide in Example 1 of the present invention, where brown / blue-gray / dark green / light pink represent C / N / B / H atoms respectively.

[0021] Figure 3 In it, a and b are the solid UV diffuse reflectance spectra of boron-doped polyheptazine imide and carbon-doped polyheptazine imide prepared in Example 1 and Example 2 of the present invention respectively.

[0022] Figure 4 In it, a, b, c, d are the XRD (X-ray diffraction) patterns and TEM (transmission electron microscope) images of Example 1 and Example 2 of the present invention.

[0023] Figure 5 In it, a, b, c, d are the photocatalytic water splitting hydrogen production performance diagrams of Example 1, Example 2 and Example 3 of the present invention with wavelengths greater than 420 nm and greater than 500 nm. Detailed Embodiments

[0024] The present invention provides a doped and modified polyheptazine imide and its preparation method and application. To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] Traditional PHI photocatalysts have a narrow light response range and low solar energy utilization rate, and cannot meet the minimum requirements for solar energy-hydrogen conversion efficiency.

[0026] Based on this, the inventors have found through research that by controllably preparing a doped and modified polyheptazine imide, for example, by introducing B atoms into the PHI structure, the charge of PHI is redistributed, and an intermediate energy level is introduced between the bottom of the conduction band and the top of the valence band. This intermediate energy level is mainly contributed by the B 2p orbitals, providing an additional transition path for electrons, that is, from the top of the valence band to the intermediate energy level, which is beneficial to the expansion of the light absorption range from 460 nm to 900 nm. The doped and modified polyheptazine imide exhibits good photocatalytic hydrogen production activity under light illumination greater than 500 nm. In addition, using chloride molten salt as a solvent and template to promote the mass transfer process and the thermal polymerization of unreacted amino groups, the regulation of the degree of polymerization and light absorption of the doped and modified polyheptazine imide is realized. When the light response range of the doped and modified polyheptazine imide is above 900 nm and the quantum efficiency reaches 40%, the minimum requirements for solar energy-hydrogen conversion efficiency can be met, thus realizing the industrial application value.

[0027] Specifically, an embodiment of the present invention provides a preparation method of a doped and modified polyheptazine imide, which includes the steps of:

[0028] Performing a thermal polymerization reaction on a carbon nitride precursor to obtain polymer carbon nitride (abbreviated as CN);

[0029] Performing a thermal polymerization reaction on the CN in the presence of a chloride molten salt as a eutectic salt template and a dopant to obtain a doped and modified polyheptazine imide.

[0030] An embodiment of the present invention uses CN to perform a thermal polymerization reaction in the presence of a chloride molten salt as a eutectic salt template and a dopant to prepare a doped and modified polyheptazine imide with a broad spectral response. Specifically, in combination with Figure 1As shown in a, b, c, and d, taking boron doping as an example, boron atoms form B-N and B-C bonds by substituting C and N atoms in the PHI structure, resulting in the redistribution of PHI charges and introducing an intermediate energy level between the valence band top and the conduction band bottom. This intermediate energy level is mainly contributed by the B 2p orbitals, providing an additional transition path for electrons, that is, from the valence band top to the intermediate energy level, which is beneficial to expanding the light absorption range from 460 nm to 900 nm and achieving the maximum utilization of sunlight. In the embodiment of the present invention, the doped and modified polyheptazine imide with broad spectral response is used as a photocatalyst, which can maximize the utilization of sunlight and obtain high photocatalytic hydrogen production activity for water splitting.

[0031] Currently, doped and modified carbon nitride is mainly prepared by high-temperature polycondensation of precursors such as urea, cyanamide, or melamine in the presence of a dopant. However, the resulting materials have defects such as disordered structure and low doping efficiency, leading to limited expansion of light absorption. In contrast, in the embodiment of the present invention, polymer carbon nitride (g-CN, CN) is used as a precursor, and doped PHI is prepared in a molten salt system of chloride salts in the presence of a dopant. The highly dispersed anchoring of doped atoms can be achieved by utilizing its regular pore channels. While maintaining the integrity of the crystal structure, the doping uniformity and doping efficiency are improved, and the light absorption range of doped PHI is extended to the near-infrared region.

[0032] In one embodiment, the carbon nitride precursor is one of urea, cyanamide, dicyandiamide, thiourea, melamine, etc., but is not limited thereto.

[0033] In one embodiment, the temperature for the thermal polymerization reaction of the carbon nitride precursor is between 500 and 600 °C (such as 550 °C), and the time is between 1 and 6 h (such as 3 h). These conditions ensure the full decomposition and polymerization of the precursor, forming polymer carbon nitride with good crystallinity and stable structure.

[0034] In one embodiment, the chloride salts in the molten salt of chloride salts are at least two of potassium chloride, sodium chloride, and lithium chloride, but are not limited thereto. Preferably, the chloride salts in the molten salt of chloride salts are potassium chloride and lithium chloride, which can ensure the effective formation of a molten salt template and promote the formation of a uniform pore structure of CN.

[0035] In one embodiment, the dopant is carbon, nitrogen, boron, malonic acid, pyrimidine, phloroglucinol, or oxamide, but is not limited thereto.

[0036] In one embodiment, the mass ratio of the CN, chloride molten salt, and dopant is between 1:1:0.01 and 1:20:5. Within this ratio range, the chloride can effectively form a molten salt template to promote the formation of a uniform pore structure of CN, thereby increasing the specific surface area and performance of the material. Taking CN, the chloride molten salt template being potassium chloride and lithium chloride, and the dopant being boron as an example, the optimal mass ratio for photocatalytic hydrogen production activity is 1:10:0.05.

[0037] In one embodiment, the temperature for the thermal polymerization reaction of the polymeric carbon nitride in the presence of a chloride molten salt as a eutectic salt template and a dopant is between 500 and 650 °C. Within this temperature range, the pyrolysis and polymerization reactions of CN can proceed effectively, promoting the formation of an aromatic structure while avoiding high-temperature side reactions and structural collapse. This temperature range can not only ensure the structural integrity and performance optimization of the material but also effectively remove impurities, which is an ideal condition for preparing doped and modified polyheptazine imide with extended light absorption. Taking CN, the chloride molten salt template being potassium chloride and lithium chloride, and the doping element being boron as an example, the optimal temperature for the thermal polymerization reaction for photocatalytic hydrogen production activity is 600 °C.

[0038] In one embodiment, the time for the thermal polymerization reaction of the polymeric carbon nitride in the presence of a chloride molten salt as a eutectic salt template and a dopant is between 3 and 12 h, such as 3 h, 4 h, 7 h, 10 h, 11 h, 12 h, etc. This time range can effectively balance the completion of the reaction, the structural optimization of the material, and the performance improvement. Taking CN, the chloride molten salt template being potassium chloride and lithium chloride, and the doping element being boron as an example, the optimal time for the thermal polymerization reaction for photocatalytic hydrogen production activity is 3 h.

[0039] In the examples of the present invention, the polymeric carbon nitride (abbreviated as CN) prepared from a carbon nitride precursor is used as a precursor for a thermal polymerization reaction in the presence of a chloride molten salt as a eutectic salt template and a dopant to obtain a doped and modified polyheptazine imide. This method dopes the dopant into CN and uses the eutectic salt template to prepare the doped and modified polyheptazine imide. Compared with the method of using melamine / urea, etc. as precursors and dopants to prepare highly crystalline carbon nitride, the method of the examples of the present invention has the following technical advantages: (1) When synthesizing polyheptazine imide in the eutectic salt template of CN, the generation of incomplete polycondensation by-products (such as unclosed amino groups) can be reduced; (2) The interference of intermediates can be avoided, and the doping uniformity and doping efficiency can be improved.

[0040] The examples of the present invention provide a doped and modified polyheptazine imide, wherein the doped and modified polyheptazine imide is prepared by the method as described above in the examples of the present invention.

[0041] The examples of the present invention provide an application of the doped and modified polyheptazine imide as a photocatalyst.

[0042] Specifically, the application of the doped and modified polyheptazine imide as a photocatalyst in photocatalytic water splitting for hydrogen production, carbon dioxide reduction, nitrogen fixation, and organic synthesis. Preferably, the application of the doped and modified polyheptazine imide as a photocatalyst in photocatalytic water splitting for hydrogen production.

[0043] The present invention will be described in detail below through specific examples.

[0044] Taking CN, potassium chloride and lithium chloride as eutectic salt templates, and boron, 2,4,6-triaminopyrimidine or phloroglucinol as dopants as examples, boron-doped, carbon-doped and benzene-ring-doped polyheptazine imides can be obtained respectively. The specific preparation methods are as follows.

[0045] Example 1

[0046] The schematic diagram for preparing boron-doped polyheptazine imide in this example is as Figure 2 shown.

[0047] Using urea as a precursor, thermopolymerization reaction is carried out at 550 °C for 3 h to obtain polymer carbon nitride (CN). 1 g of CN, 0.05 g of boron powder, 5.5 g of potassium chloride and 4.5 g of lithium chloride are placed in a crucible, and then transferred to a muffle furnace and kept at 600 °C for 3 h, with a heating rate of 2 °C / minute. After the insulation is completed, it is naturally cooled to room temperature. The obtained powder sample is filtered and washed with deionized water for many times. The washed powder sample is vacuum dried at 70 °C to prepare boron-doped polyheptazine imide (denoted as BCCN).

[0048] Figure 3 In a, the solid ultraviolet diffuse reflection spectra of boron-doped polyheptazine imides obtained by adding different amounts of boron (0 g, 0.025 g, 0.05 g, 0.075 g, 0.1 g respectively) are shown. From Figure 3 a in it, it can be seen that with the increase of the boron addition amount, the visible light absorption edge is significantly enhanced and extended to 900 nm.

[0049] Example 2

[0050] This example prepares carbon-doped polyheptazine imide.

[0051] It is basically the same as Example 1, except that: 0.05 g of boron powder is changed to 0.1 g of 2,4,6-triaminopyrimidine, and finally carbon-doped polyheptazine imide (denoted as TCCN) is prepared.

[0052] Figure 3 In b, the solid ultraviolet diffuse reflection spectra of carbon-doped polyheptazine imides obtained by adding different amounts of 2,4,6-triaminopyrimidine (0 g, 0.01 g, 0.05 g, 0.1 g, 0.2 g respectively) are shown. FromFigure 3 As can be seen from Figure b, the visible light absorption edge is significantly extended from 460 nm to 900 nm, and there is also obvious light absorption in the near-infrared region. The color of the product gradually transitions from light yellow to orange-red and red.

[0053] Figure 4 XRD diffraction patterns of boron-doped polyheptazine imide and carbon-doped polyheptazine imide prepared using the same molten salt as the eutectic salt template in Examples 1-2 (Figures a and b in Figure 4 respectively) and transmission electron microscope images (Figures c and d in Figure 4 respectively). It can be seen that the carbon nitride still maintains good crystallinity.

[0054] Example 3

[0055] In this example, benzene ring-doped polyheptazine imide is prepared.

[0056] It is basically the same as Example 1, except that: 0.05 g of boron powder is changed to 0.01 g of phloroglucinol, and finally benzene ring-doped polyheptazine imide (denoted as MBCCN) is prepared.

[0057] Example 4

[0058] Using triethanolamine as a hole sacrificial agent, the photocatalytic water splitting hydrogen production reaction is as follows:

[0059] 50 mg of the prepared boron-doped polyheptazine imide (prepared in Example 1), carbon-doped polyheptazine imide (prepared in Example 2), and benzene ring-doped polyheptazine imide (prepared in Example 3) are respectively taken as photocatalysts, 50 mL of a triethanolamine solution with a volume fraction of 10% is measured as the hole sacrificial agent solution, and it is transferred to a quartz glass reaction tank and ultrasonically treated for 30 minutes. Subsequently, chloroplatinic acid solution is added to the quartz glass reaction tank, and 3.0 wt% of platinum (Pt) nanoparticles are loaded by xenon lamp irradiation as a co-catalyst. An online hydrogen production system is used, and under the irradiation conditions of a 300 W xenon lamp and UVCUT-420 nm and UVCUT-500 nm filters, the amount of hydrogen produced is measured by an online gas chromatograph to characterize the hydrogen production performance of the photocatalyst.

[0060] Figure 5 Figures a and b are the photocatalytic water splitting hydrogen production performance diagrams of boron-doped polyheptazine imide with wavelengths greater than 420 nm and 500 nm respectively, and Figures c and d are the photocatalytic water splitting hydrogen production performance diagrams of carbon-doped and benzene ring-doped polyheptazine imide with wavelengths greater than 500 nm respectively. From Figure 5It can be seen that the photocatalytic activity of the boron-doped polyheptazine imide BCCN-0.05 prepared in Example 1 is 127.0 μmol / h. Compared with the undoped CCN (53.3 μmol / h), the hydrogen production activity is increased by about 2.4 times. The photocatalytic activities of the carbon-doped and benzene-ring-doped polyheptazine imides prepared in Examples 2 and 3 are increased by nearly 11 times at wavelengths greater than 500 nm.

[0061] In summary, the present invention provides a doped and modified polyheptazine imide, its preparation method and application. By carrying out a thermal polymerization reaction of CN in a molten chloride salt as a eutectic salt template and a dopant, a doped and modified polyheptazine imide is prepared, which solves the problem of low light absorption and utilization rate of traditional PHI photocatalysts. The doped and modified polyheptazine imide photocatalyst prepared by the present invention has advantages such as broad spectral response, can make the most of sunlight, and obtain high photocatalytic water splitting hydrogen production activity.

[0062] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of doped and modified polyheptazine imide, characterized in that, Including the steps: Performing thermal polymerization reaction on a carbon nitride precursor to obtain polymeric carbon nitride; Performing thermal polymerization reaction on the polymeric carbon nitride under the conditions that a chloride molten salt serves as an eutectic salt template and a dopant exists to obtain doped and modified polyheptazine imide.

2. The preparation method of the doped and modified polyheptazine imide according to claim 1, characterized in that, The carbon nitride precursor is one of urea, cyanamide, dicyandiamide, thiourea, and melamine.

3. The preparation method of the doped and modified polyheptazine imide according to claim 1, wherein, The chloride in the chloride molten salt is at least two of potassium chloride, sodium chloride, and lithium chloride.

4. The preparation method of the doped and modified polyheptazine imide according to claim 3, characterized in that, The mass ratio of the polymeric carbon nitride, the chloride molten salt, and the dopant is between 1:1:0.01 and 1:20:

5.

5. The preparation method of the doped and modified polyheptazine imide according to claim 1, wherein, The temperature for performing the thermal polymerization reaction on the polymeric carbon nitride under the conditions that a chloride molten salt serves as an eutectic salt template and a dopant exists is between 500 and 650 °C.

6. The preparation method of the doped and modified polyheptazine imide according to claim 1, wherein, The time for performing the thermal polymerization reaction on the polymeric carbon nitride under the conditions that a chloride molten salt serves as an eutectic salt template and a dopant exists is between 3 and 12 h.

7. The preparation method of the doped and modified polyheptazine imide according to claim 1, wherein, The dopant is carbon, nitrogen, boron, malonic acid, pyrimidine, phloroglucinol, or oxamide.

8. A doped and modified polyheptazine imide, characterized in that, Prepared by using the method according to any one of claims 1-7.

9. Use of the doped and modified polyheptazine imide according to claim 8 as a photocatalyst.

10. The application according to claim 9, characterized in that The photocatalyst is used for photocatalytic water splitting to produce hydrogen.

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