Tin polyheptazinyl imide as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalytic materials, in particular to tin polyheptazinyl imide as well as a preparation method and application thereof. The preparation method of the tin polyheptazine imide comprises the following steps: carrying out thermal polymerization reaction on a carbon nitride precursor to obtain polymer carbon nitride; the preparation method comprises the following steps: carrying out thermal polymerization reaction on polymer carbon nitride under the condition that chloride fused salt is used as a fused salt template, and then acidifying by hydrochloric acid to obtain tin polyheptazinamide; wherein the chlorate molten salt comprises anhydrous tin dichloride molten salt. The tin polyheptazine imide prepared by the preparation method disclosed by the invention has high crystallinity and wide spectral response range, greatly widens the light absorption range of a photocatalytic material, is expected to realize efficient near-infrared light activity, and can utilize sunlight to the maximum extent, thereby obtaining high activity of photocatalytic decomposition of water to produce hydrogen.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalytic materials, and in particular to a tin polyheptazinonimide and a preparation method and application thereof. Background Art

[0002] Poly(heptazine imide) (PHI) is a crystalline carbon nitride material composed of heptazine ring units connected by imide bonds, forming a long-range ordered crystal structure. This structure gives PHI a larger π-conjugated system, which is conducive to the separation and transmission of photogenerated charges. Therefore, it has received widespread attention in the field of photocatalytic water decomposition and hydrogen production. However, due to its specific energy band structure, its utilization range of sunlight is limited to 480nm, and it can only utilize about 10% of solar energy, which seriously restricts the large-scale application of PHI in the field of energy photocatalysis. The conversion efficiency of solar energy to hydrogen energy must reach at least 10% to have industrial application value. Due to the narrow photoactivity range and low solar energy conversion efficiency, the solar energy-hydrogen energy conversion efficiency of PHI is still a long way from the goal of achieving industrialization. Therefore, expanding the photoactivity range of PHI and improving the solar energy conversion efficiency are of urgent practical significance for realizing its industrial application.

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

[0004] In view of the problems of narrow light response range and low solar energy utilization rate of traditional PHI, the purpose of the present invention is to provide a method for preparing tin polyheptazinonimide with wide spectrum response and activated near-infrared photocatalytic activity, aiming to solve the problem of low light absorption utilization efficiency of existing PHI photocatalysts.

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

[0006] The first aspect of the present invention provides a method for preparing tin polyheptazinonimide, which comprises the steps of:

[0007] subjecting the carbon nitride precursor to a thermal polymerization reaction to obtain polymer carbon nitride;

[0008] The polymer carbon nitride is subjected to a thermal polymerization reaction under the condition of a chloride molten salt as a molten salt template, and then acidified with hydrochloric acid to obtain tin polyheptazinonimide; wherein the chloride molten salt includes anhydrous tin dichloride molten salt.

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

[0010] The temperature of the thermal polymerization reaction of the carbon nitride precursor is between 500 and 600° C., and the time is between 3 and 6 hours.

[0011] Optionally, the chloride molten salt is anhydrous tin dichloride molten salt;

[0012] Alternatively, the chloride molten salt is composed of one or more of the MCl molten salts and anhydrous tin dichloride molten salt, wherein M is one of K, Na, and Li, and the mass ratio of the one or more of the MCl molten salts to the anhydrous tin dichloride molten salt is 1:19 to 19:1.

[0013] Optionally, the mass ratio of the polymer carbon nitride to the chloride molten salt is between 1:1 and 1:20.

[0014] Optionally, the temperature of the thermal polymerization reaction of the polymer carbon nitride under the condition of chloride molten salt as molten salt template is between 500 and 600°C.

[0015] Optionally, the polymer carbon nitride is subjected to thermal polymerization reaction under the condition of chloride molten salt as molten salt template for a time of between 1 and 12 hours.

[0016] Optionally, the concentration of the hydrochloric acid is 0.1-1.0M.

[0017] Optionally, the hydrochloric acid acidification time is 1 to 24 hours.

[0018] In a second aspect of the present invention, a tin polyheptazoline imide is provided, wherein the tin polyheptazoline imide comprises polyheptazoline imide and Sn 2+ Ion, Sn 2+ The ions form coordination bonds with the nitrogen atoms in the polyheptadiazine imide; and / or, the tin polyheptadiazine imide is prepared by the method described in the present invention.

[0019] The third aspect of the present invention provides a use of the tin polyheptazinonimide of the present invention as a photocatalyst in photocatalytic decomposition of water to produce hydrogen.

[0020] Beneficial effect: The polymer carbon nitride prepared by the present invention using the carbon nitride precursor is subjected to a thermal polymerization reaction under the condition of a chloride molten salt as a molten salt template, and then subjected to hydrochloric acid acidification to obtain tin polyheptazinonimide. The tin polyheptazinonimide prepared by the present invention has high crystallinity and a wide spectral response range. Using the tin polyheptazinonimide with high crystallinity and a wide spectral response range as a photocatalyst, sunlight can be utilized to the maximum extent, high photocatalytic decomposition of water to produce hydrogen activity can be obtained, and effective utilization and capture of sunlight can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The schematic diagram of the preparation of tin polyheptazinonimide according to the present invention is shown.

[0022] Figure 2Solid ultraviolet diffuse reflectance spectra of Examples 1 and 2 of the present invention using different molten salt templates.

[0023] Figure 3 a, b, and c are XRD (X-ray diffraction) images and TEM (transmission electron microscope) images of Examples 1 and 2 of the present invention.

[0024] Figure 4 In the figure, a, b, and c are the photolysis water hydrogen production performance diagrams at wavelengths greater than 500 nm and greater than 700 nm, and the apparent quantum efficiency diagrams at different wavelengths of Example 1 and Example 2 of the present invention, respectively. DETAILED DESCRIPTION

[0025] The present invention provides a tin polyheptazinonimide and a preparation method and application thereof. In order to make the purpose, technical scheme and effect of the present invention clearer and more specific, 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.

[0026] Conventional PHI photocatalysts have a narrow photoresponse range and low solar energy utilization, and are unable to meet the minimum requirements for solar-to-hydrogen conversion efficiency.

[0027] Based on this, the inventors have found that by controlling the preparation of tin polyhepta-azinonimide with near-infrared light activity, its absorption range is extended from 480nm to 900nm, and tin polyhepta-azinonimide exhibits obvious photocatalytic hydrogen production activity under light greater than 700nm. In addition, by regulating the melting point and Lewis acidity of the molten salt system, the mass transfer and deamination reaction kinetics during the polymerization process are accelerated to achieve the regulation of the polymerization degree, crystallinity and light absorption of tin polyhepta-azinonimide. When the light response range of tin polyhepta-azinonimide is above 900nm and the quantum efficiency reaches 40%, it can meet the minimum requirements for solar energy-hydrogen conversion efficiency, thereby realizing the value of industrial application.

[0028] Specifically, an embodiment of the present invention provides a method for preparing tin polyheptazinonimide, which comprises the steps of:

[0029] The carbon nitride precursor is subjected to a thermal polymerization reaction to obtain polymer carbon nitride (abbreviated as CN);

[0030] The CN is subjected to a thermal polymerization reaction under the condition of a chloride molten salt as a molten salt template, and then acidified with hydrochloric acid to obtain tin polyheptazinonimide; wherein the chloride molten salt includes anhydrous tin dichloride molten salt.

[0031] In the embodiment of the present invention, CN is used to perform a thermal polymerization reaction under the condition of a chloride molten salt as a molten salt template, and then subjected to hydrochloric acid acidification to obtain a tin polyheptazinonimide with high crystallinity and wide spectral response. By introducing Sn into the PHI structure2+ Ion, Sn 2+ The formation of coordination bonds with the four surrounding nitrogen atoms leads to a redistribution of the PHI charge, resulting in an intermediate energy level between the bottom of the conduction band and the top of the valence band. This intermediate energy level is mainly contributed by the Sn 5p orbital, allowing the electrons at the top of the valence band to directly transition to this energy level, greatly narrowing the band gap, thereby extending the light absorption to the near-infrared region, and its absorption range extends from 480nm to 900nm, thereby activating near-infrared light activity. The embodiment of the present invention uses tin polyheptazinonimide with high crystallinity and wide spectral response as a photocatalyst, which can maximize the use of sunlight, obtain high photocatalytic water decomposition hydrogen production activity, and realize the effective use and capture of sunlight.

[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 of the thermal polymerization reaction of the carbon nitride precursor is between 500 and 600° C. (such as 550° C.) and the time is between 3 and 6 hours (such as 4 hours). Under these conditions, the carbon nitride precursor can be fully decomposed and polymerized to form a polymer carbon nitride with good crystallinity and stable structure.

[0034] In one embodiment, the chloride salt molten salt is anhydrous tin dichloride molten salt.

[0035] In one embodiment, the chloride molten salt is composed of one or more of the MCl molten salts and anhydrous tin dichloride molten salt, wherein M is one of K, Na, and Li, and the mass ratio of one or more of the MCl molten salts to the anhydrous tin dichloride molten salt is 1:19 to 19:1, such as 1:19, 3:1, 7:1, 10:1, 13:1, 16:1, 17:1, 19:1, etc.

[0036] Compared with anhydrous tin dichloride alone as a molten salt template, using MCl and anhydrous tin dichloride as a molten salt template, the molten salt system can disperse the reactants more evenly, thereby improving the purity and crystallinity of the product. In addition, the addition of MCl can reduce the oxidation of anhydrous tin dichloride, thereby reducing the generation of impurities.

[0037] In one embodiment, the mass ratio of CN to chloride molten salt is between 1:1 and 1:20, such as 1:1, 1:2, 1:4, 1:5, 1:8, 1:10, 1:12, 1:15, 1:20, etc. Within this ratio range, the chloride can effectively form a molten salt template, promote the formation of a uniform pore structure of carbon nitride, and thus improve the specific surface area and performance of the material. Taking CN, anhydrous tin dichloride and potassium chloride molten salt template as an example, the mass ratio with the best photocatalytic hydrogen production activity is 1:10:10.

[0038] In one embodiment, the temperature of the thermal polymerization reaction of the polymer carbon nitride under the condition of chloride molten salt as a molten salt template is between 500 and 600 ° C. In this temperature range, the pyrolysis and polymerization reactions of CN can be effectively carried out, promoting the formation of aromatization 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 the preparation of tin polyseptazinonimide. Taking CN and anhydrous tin dichloride as molten salt templates as an example, the thermal polymerization reaction temperature with the best photocatalytic hydrogen production activity is 550 ° C.

[0039] In one embodiment, the thermal polymerization reaction time is between 1 and 12 hours, such as 2 hours, 4 hours, 7 hours, 10 hours, 11 hours, 12 hours, etc. This time range can effectively balance the completion of the reaction, the structural optimization of the material, and the performance improvement. Taking CN and anhydrous tin dichloride as molten salt templates as an example, the thermal polymerization reaction time with the best photocatalytic hydrogen production activity is 4 hours.

[0040] In one embodiment, the concentration of the hydrochloric acid is 0.1 to 1.0 M, such as 0.1 M, 0.5 M, 0.7 M, 0.8 M, 0.9 M, 1.0 M, etc. The main function of pickling is to remove impurities remaining from the reaction (such as unreacted anhydrous tin dichloride or its hydrolysis product), while optimizing the pore structure of the tin polyseptazinonimide and increasing the specific surface area and stability of the material. Pickling can also prevent side reactions caused by hydrolysis to ensure purity and performance.

[0041] In one embodiment, the hydrochloric acid acidification time is 1 to 24 hours, such as 2 hours, 4 hours, 7 hours, 10 hours, 11 hours, 12 hours, 14 hours, 17 hours, 20 hours, 22 hours, 24 hours, etc. This acid pickling time range can ensure that impurities are completely removed and prevent structural damage or performance degradation caused by excessive acidification, and is an ideal choice for balancing reaction efficiency and material performance.

[0042] In one embodiment, the preparation method of the tin polyheptazinonimide specifically comprises the steps of:

[0043] CN and chloride salt are placed in a crucible, and then transferred to a muffle furnace, with a heating rate of 2 to 5°C / min, and kept at 250°C for 5 to 10 hours to achieve initial thermal polymerization and structural transformation of CN, promote molecular dehydration condensation, and form a stable polymer network, followed by keeping at 500 to 600°C for 1 to 12 hours, cooling, washing and drying to obtain an intermediate product; wherein the chloride salt molten salt includes anhydrous tin dichloride molten salt;

[0044] The intermediate product is acidified with hydrochloric acid having a concentration of 0.1 to 1.0 M for 1 to 24 hours, and then the acidified solution is washed and dried to obtain tin polyheptazinonimide.

[0045] The embodiment of the present invention provides a tin polyheptadiazine imide, wherein the tin polyheptadiazine imide comprises polyheptadiazine imide and Sn 2+ Ion, Sn 2+ The ions form coordination bonds with nitrogen atoms in the polyheptazinonimide; and / or, are prepared by the method described in the embodiments of the present invention.

[0046] The embodiment of the present invention provides a use of the tin polyheptazinimidamide as a photocatalyst.

[0047] Specifically, the tin polyheptazinonimide is used as a photocatalyst in photocatalytic decomposition of water to produce hydrogen, carbon dioxide reduction, nitrogen fixation and organic synthesis. Preferably, the tin polyheptazinonimide is used as a photocatalyst in photocatalytic decomposition of water to produce hydrogen.

[0048] The present invention is described in detail below through specific embodiments.

[0049] Taking CN, anhydrous tin dichloride or anhydrous tin dichloride and potassium chloride, sodium chloride, and lithium chloride as molten salt templates as examples, tin polyheptazinonimide was prepared respectively. The specific preparation methods are as follows:

[0050] Example 1

[0051] The schematic diagram of the tin polyheptazinonimide prepared in this embodiment is as follows Figure 1 shown.

[0052] Urea was thermally polymerized at 550°C for 3h to obtain polymer carbon nitride (CN). 1g CN and 10g anhydrous tin dichloride were placed in a crucible and then transferred to a muffle furnace. The heating rate was 2°C / min, and the mixture was kept at 250°C for 10h, then kept at 550°C for 4h, and cooled naturally to room temperature. The obtained powder sample was filtered and washed with deionized water for many times. The powder sample obtained after washing was vacuum dried at 70°C, and 1g of the vacuum dried powder sample was acidified with 1M hydrochloric acid for 24h, and then the acidified solution was filtered and washed with deionized water for many times. Finally, the powder sample obtained after washing was vacuum dried at 70°C to obtain tin polyheptazinonimide.

[0053] Example 2

[0054] The method is basically the same as Example 1, except that 10 g of anhydrous tin dichloride is replaced by 10 g of anhydrous tin dichloride and 10 g of potassium chloride. The final product is recorded as K-tin polyheptadiazine imide.

[0055] Figure 2The solid ultraviolet diffuse reflectance spectra of the tin polyheptadiazine imide and K-tin polyheptadiazine imide prepared in different molten salt templates in Examples 1-2 are shown in FIG. Figure 2 It can be seen that the visible light absorption edge is significantly extended from 480nm to 900nm, and there is also obvious light absorption in the near-infrared region. The colors of tin polyheptadiazine imide and K-tin polyheptadiazine imide are both brown.

[0056] Figure 3 The XRD diffraction patterns of the tin polyheptadiazine imide and K-tin polyheptadiazine imide prepared in Examples 1-2 using different molten salt templates are shown in FIG. Figure 3 a) and transmission electron microscopy image ( Figure 3 b and c), it can be seen that the carbon nitride maintains very good crystallinity and has an ultra-thin layer structure.

[0057] Example 3

[0058] Using triethanolamine as a hole sacrificial agent, the photocatalytic decomposition of water to produce hydrogen is as follows:

[0059] Take 50mg of the prepared tin polyhepta-azinonimide (prepared in Example 1) and K-tin polyhepta-azinonimide (prepared in Example 2) as photocatalysts, measure 50mL of a 20% volume fraction of triethanolamine solution as a hole sacrificial agent solution, and transfer it to a quartz glass reaction tank. Subsequently, the solution was ultrasonically treated for 30 minutes to ensure that the solution was evenly dispersed. Then, chloroplatinic acid solution was added to the quartz glass reaction tank, and xenon light was used to illuminate, and 3.0wt% of platinum (Pt) nanoparticles were loaded as co-catalysts. An online hydrogen production system was used, and the amount of hydrogen produced was determined by an online gas chromatograph under the irradiation conditions of a 300W xenon lamp and a UVCUT-700nm filter, thereby characterizing the hydrogen production performance of the photocatalyst.

[0060] Figure 4 a and b are the photocatalytic water decomposition and hydrogen production performance diagrams of tin polyheptadiazine imide and K-tin polyheptadiazine imide with a size larger than 500nm and 700nm, respectively. Figure 4 c is the apparent quantum efficiency diagram of K-tin polyheptazinonimide, from Figure 4 It can be seen that the near-infrared hydrogen production activity of K-tin polyheptazine imide is significantly improved, and the apparent quantum efficiency at 420nm reaches 25.66%. However, traditional PHI usually does not have near-infrared photocatalytic activity. This is because its band gap is wide, mainly absorbing ultraviolet light and part of visible light, and it is difficult to effectively absorb near-infrared light.

[0061] In summary, the present invention provides a tin polyheptazinonimide and a preparation method and application thereof, wherein CN is used to perform a thermal polymerization reaction under the condition of a chloride molten salt as a molten salt template, and then subjected to hydrochloric acid acidification to obtain tin polyheptazinonimide, which solves the problems of narrow light response range and low solar energy utilization rate of traditional PHI photocatalysts. The tin polyheptazinonimide photocatalyst prepared by the present invention has the advantages of high crystallinity and wide spectral response, and can maximize the use of sunlight to obtain high photocatalytic water decomposition hydrogen production activity.

[0062] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing tin polyheptazinonimide, characterized in that: Includes steps: subjecting the carbon nitride precursor to a thermal polymerization reaction to obtain polymer carbon nitride; The polymer carbon nitride is subjected to a thermal polymerization reaction under the condition of a chloride molten salt as a molten salt template, and then acidified with hydrochloric acid to obtain tin polyheptazinonimide; wherein the chloride molten salt includes anhydrous tin dichloride molten salt.

2. The method for preparing tin polyheptazinonimide according to claim 1, characterized in that: The carbon nitride precursor is one of urea, cyanamide, dicyandiamide, thiourea and melamine; The temperature of the thermal polymerization reaction of the carbon nitride precursor is between 500 and 600° C., and the time is between 3 and 6 hours.

3. The method for preparing tin polyheptazinonimide according to claim 1, characterized in that: The chloride molten salt is anhydrous tin dichloride molten salt; Alternatively, the chloride molten salt is composed of one or more of the MCl molten salts and anhydrous tin dichloride molten salt, wherein M is one of K, Na, and Li, and the mass ratio of the one or more of the MCl molten salts to the anhydrous tin dichloride molten salt is 1:19 to 19:

1.

4. The method for preparing tin polyheptazinonimide according to claim 3, characterized in that: The mass ratio of the polymer carbon nitride to the chloride molten salt is between 1:1 and 1:

20.

5. The method for preparing tin polyheptazinonimide according to claim 1, characterized in that: The temperature of the thermal polymerization reaction of the polymer carbon nitride under the condition of using chloride molten salt as a molten salt template is between 500 and 600°C.

6. The method for preparing tin polyheptazinimides according to claim 1, characterized in that: The polymer carbon nitride is subjected to thermal polymerization reaction under the condition that chloride molten salt is used as a molten salt template for a time period between 1 and 12 hours.

7. The method for preparing tin polyheptazinonimide according to claim 1, characterized in that: The concentration of the hydrochloric acid is 0.1-1.0M.

8. The method for preparing tin polyheptazinonimide according to claim 1, characterized in that: The hydrochloric acid acidification time is 1 to 24 hours.

9. A tin polyheptazinonimide, characterized in that: The tin polyheptadiazine imide comprises polyheptadiazine imide and Sn 2+ Ion, Sn 2+ The ions form coordination bonds with nitrogen atoms in the polyheptadiazine imide; and / or, the tin polyheptadiazine imide is prepared by the method according to any one of claims 1 to 8.

10. Use of the tin polyheptazinimidamide according to claim 9 as a photocatalyst in photocatalytic decomposition of water to produce hydrogen.

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