Electron trap type covalent triazine framework nanosheet as well as preparation method and application thereof

Abstract

The invention discloses an electron trap type covalent triazine framework nanosheet as well as a preparation method and application thereof, and belongs to the technical field of preparation of covalent organic framework materials. The electron trap type covalent triazine framework nanosheet is synthesized by adopting terephthalonitrile and bis (trimethylsilyl) lithium amide to synthesize a monomer 1, adopting p-bromobenzaldehyde, ethylene glycol, p-toluenesulfonic acid monohydrate, magnesium powder and phosphorus trichloride to synthesize a monomer 2, and then adopting the monomer 1, the monomer 2 and terephthalaldehyde to synthesize the electron trap type covalent triazine framework nanosheet. A non-planar triphenylphosphine oxide structural unit with a strong electron withdrawing effect is introduced in the polymerization process of a traditional CTFs material, the visible light catalytic hydrogen production activity of the electron trap type covalent triazine framework nanosheet is remarkably improved, the catalytic hydrogen production rate can reach 15988 mu mol / h / g and is 4.8 times that of a pure unmodified covalent triazine framework material, and the catalytic hydrogen production efficiency is greatly improved. And the bottom-to-top synthesis strategy is also beneficial to the development and research of large-scale production of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of covalent organic framework materials, and particularly relates to an electron-trapping covalent triazine framework nanosheet, a preparation method thereof, and an application thereof. Background Art

[0002] Covalent triazine framework materials (CTFs) belong to a branch of covalent organic framework materials (COFs), which specifically refer to COFs materials with a triazine ring structure. CTFs materials are generally constructed by connecting different organic monomers with triazine rings as linking groups, and the carbon-nitrogen bonds in the triazine structure endow CTFs materials with high chemical stability. As an orderly arranged crystalline organic semiconductor material, CTFs have the advantages of rich N content, ordered conjugate structure, large specific surface area, and diverse monomer selection, etc., making CTFs materials have great application potential in the field of photocatalysis. However, unmodified CTFs materials have the disadvantages of high probability of photo-generated carrier recombination, tight stacking of layers leading to difficult exposure of active sites, and long diffusion distance of photo-generated excitons from the bulk to the surface, which seriously limit the development of the application of CTFs materials in the field of photocatalysis. Currently, the improvement strategy usually adopts a chemical method to exfoliate bulk crystalline materials into single-layer or few-layer nanosheets. On the one hand, this can expose more surface active sites, and on the other hand, it can shorten the migration path of photo-generated excitons from the bulk to the surface and reduce the recombination probability. However, most of these "top-down" exfoliation strategies require the use of strong acid reagents, which are not environmentally friendly; and the yield of nano-sheet materials is low and the structure is easily damaged. Summary of the Invention

[0003] In view of this, the present invention provides an electron-trapping covalent triazine framework nanosheet, a preparation method thereof, and an application thereof, aiming to provide a "bottom-up" CTFs modification strategy, by introducing a non-planar and strongly electron-withdrawing monomer during the polymerization process to construct a novel CTFs nanosheet with a non-planar structure and containing electron traps, thereby significantly improving the photocatalytic water splitting hydrogen production performance of CTFs materials.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] One of the technical solutions of the present invention: An electron-trapping covalent triazine framework nanosheet, characterized in that the structural formula is as shown in formula (Ⅰ):

[0006]

[0007] Another technical solution of the present invention: A preparation method of the electron-trapping covalent triazine framework nanosheet according to the above, comprising the following steps:

[0008] Synthesis of Monomer 1: Dissolve terephthalonitrile in an organic solvent to obtain a terephthalonitrile solution; dissolve lithium bis(trimethylsilyl)amide in an organic solvent to obtain a lithium bis(trimethylsilyl)amide solution; then add the lithium bis(trimethylsilyl)amide solution to the terephthalonitrile solution, add a hydrochloric acid / ethanol solution to the resulting mixed solution, wash the obtained reactant, recrystallize it in a water / ethanol solution, filter to separate the solid, and dry it to obtain Monomer 1; the synthesis route of Monomer 1 is shown in Formula (Ⅱ):

[0009]

[0010] Synthesis of Monomer 2: Mix p-bromobenzaldehyde, ethylene glycol, p-toluenesulfonic acid monohydrate with toluene or benzene, heat to 110 - 120 °C and reflux with stirring for 20 - 30 h, and dry to obtain 2-(4-bromophenyl)-1,3-dioxolane; then add 2-(4-bromophenyl)-1,3-dioxolane and magnesium powder to an organic solvent to prepare a Grignard reagent at 0 °C; add phosphorus trichloride to an organic solvent to obtain a phosphorus trichloride solution; add the phosphorus trichloride solution to the Grignard reagent, heat to 60 - 80 °C and reflux for 3 - 8 h, then cool to 0 °C; extract the mixture, collect the organic phase and distill it under reduced pressure to obtain white crystals; mix the white crystals, hydrochloric acid and an organic solvent, heat to 60 - 80 °C and reflux for 15 - 30 min, cool and extract, collect the organic phase, evaporate the solvent, and purify the crude product by column chromatography to obtain Monomer 2; the synthesis route of Monomer 2 is shown in Formula (Ⅲ):

[0011]

[0012] Synthesis of Electron Trap-Type Covalent Triazine Framework Nanosheets: Add Monomer 1 and cesium carbonate to an organic solvent, heat, denoted as Solution A; add Monomer 2 to an organic solvent to obtain a solution of Monomer 2, denoted as Solution B; add Solution B to Solution A and keep it warm, denoted as Liquid A; separately dissolve Monomer 1, terephthalaldehyde and cesium carbonate in an organic solvent, denoted as Liquid B; add Liquid B to Liquid A, continue to keep it warm, and then raise the temperature for reaction to obtain the electron trap-type covalent triazine framework nanosheets; the synthesis route is shown in Formula (Ⅳ):

[0013]

[0014] As a preferred embodiment of the present invention, in the synthesis step of monomer 1, the organic solvents are all tetrahydrofuran; the concentration of the terephthalonitrile solution is 0.3 - 0.7 mol / L, the concentration of the lithium bis(trimethylsilyl)amide solution is 1.0 mol / L, and the molar ratio of terephthalonitrile to lithium bis(trimethylsilyl)amide is 1:(1.5 - 2.5); in the hydrochloric acid / ethanol solution, the concentration of hydrochloric acid is 5 - 7 mol / L, and the volume ratio of the hydrochloric acid / ethanol solution to the terephthalonitrile solution is (1.8 - 2.5):1.

[0015] As a preferred embodiment of the present invention, in the synthesis step of monomer 2, the organic solvents are all tetrahydrofuran; the extraction is all carried out with dichloromethane; the column chromatography purification uses dichloromethane as the mobile phase and neutral alumina as the stationary phase.

[0016] As a preferred embodiment of the present invention, in the synthesis step of monomer 2, the mass ratio of p-bromobenzaldehyde, ethylene glycol and p-toluenesulfonic acid monohydrate is 1:(3 - 5):(0.8 - 1.2), and the mass-volume ratio of p-bromobenzaldehyde to toluene is 1 g:(8 - 12) mL; the mass-volume ratio of 2-(4-bromophenyl)-1,3-dioxolane, magnesium powder and phosphorus trichloride is (20 - 26) g:(2 - 3.5) g:(2.5 - 3.5) mL; the concentration of the hydrochloric acid aqueous solution is 1.5 - 2.5 mol / L, and the mass-volume ratio of the white crystal to the hydrochloric acid aqueous solution is (10 - 12) g:(35 - 45) mL.

[0017] As a preferred embodiment of the present invention, in the synthesis step of the electron trap type covalent triazine framework nanosheets, the organic solvents are all dimethyl sulfoxide; the molar ratio of monomer 1 to monomer 2 in solution A is 1.5 - 2.5, and the molar ratio of monomer 2 to terephthalaldehyde in solution B is 0.1 - 0.4; the mass ratio of monomer 1 to cesium carbonate in solution A is (0.32 - 1.30):1, and the mass ratio of monomer 1, terephthalaldehyde and cesium carbonate in solution B is (3 - 4):(1 - 2):10; the temperature for heat preservation is 90 - 130 °C, and the time is 10 - 15 h; the temperature for the temperature-raising reaction is 150 - 200 °C, and the time is 36 - 60 h.

[0018] As a preferred embodiment of the present invention, after the temperature-raising reaction, it further includes the steps of cooling to room temperature, filtering to obtain a crude product solid, washing the crude product solid with hydrochloric acid and deionized water, and drying.

[0019] The third technical solution of the present invention: An application of the electron trap type covalent triazine framework nanosheets as described above in the preparation of a photocatalyst.

[0020] Fourth technical solution of the present invention: An electron-trapping covalent triazine framework nanosheet photocatalyst is prepared by using the above-mentioned electron-trapping covalent triazine framework nanosheets.

[0021] Fifth technical solution of the present invention: A preparation method of an electron-trapping covalent triazine framework nanosheet photocatalyst according to the above, which is prepared by an in-situ photodeposition method, and includes the following steps: In a reactor equipped with a xenon lamp and a cut-off ultraviolet light filter, sequentially add the electron-trapping covalent triazine framework nanosheets, deionized water containing triethanolamine, and chloroplatinic acid hexahydrate, evacuate, turn on the xenon lamp, stir, and obtain the electron-trapping covalent triazine framework nanosheet photocatalyst.

[0022] As a preferred embodiment of the present invention, it is prepared by an in-situ photodeposition method, specifically including the following steps: In a 250-1000 mL top-illuminated glass reactor (with a diameter of 10-50 cm) equipped with a xenon lamp with a power of 300 W and a cut-off ultraviolet light filter (λ>420 nm), sequentially add 0.01-0.05 g, preferably 0.02 g of electron-trapping covalent triazine framework nanosheet material, 50.00-200 mL of deionized water containing triethanolamine (volume fraction 10-20%) and 122.00-150 μL, 0.02-0.05 mol / L chloroplatinic acid hexahydrate. Circulating water is passed through the reactor jacket to maintain the temperature at 10-20 °C. Evacuate for 30-60 min to remove the air in the system, turn on the xenon lamp, and stir for 30-60 min to obtain an electron-trapping covalent triazine framework nanosheet photocatalyst containing platinum.

[0023] Sixth technical solution of the present invention: An application of an electron-trapping covalent triazine framework nanosheet photocatalyst according to the above in visible light catalytic hydrogen production.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] In the polymerization process of traditional CTFs materials, the present invention introduces a non-planar and strongly electron-withdrawing triphenylphosphine oxide structural unit. (1) The introduction of the non-planar structure weakens the π-π interaction between the layers of CTFs materials, reduces the stacking layers, makes the material morphology show a nanosheet shape, and increases the specific surface area, pore volume, and average pore diameter of the material. (2) The nanosheet morphology shortens the migration path of photo-generated excitons from the bulk phase to the surface, reducing the recombination probability of photo-generated excitons. (3) Due to the introduction of the non-planar structure during the polymerization process, the synthesized nanosheet material has a complete structure compared with the "top-down" exfoliation strategy. (4) The introduced triphenylphosphine oxide group can act as an electron trap, promoting the separation of photo-generated excitons and prolonging the lifetime of photo-generated electrons and photo-generated holes by capturing photo-generated electrons.

[0026] The combined effects of the above four aspects significantly improve the visible-light photocatalytic hydrogen production activity of the electron-trapping covalent triazine framework nanosheets, enabling the visible-light photocatalytic hydrogen production rate of the Tppo-CTF prepared in this invention to reach 15988 μmol / h / g, which is 4.8 times that of the simple unmodified covalent triazine framework material. Moreover, the "bottom-up" synthesis strategy is also conducive to the development and research of large-scale production of the material. Description of the Drawings

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0028] Figure 1 Structural formula of 0.15-Tppo-CTF prepared in Example 1;

[0029] Figure 2 Solid-state nuclear magnetic carbon-13 spectrum of 0.15-Tppo-CTF and CTF prepared in Example 1;

[0030] Figure 3 Solid-state nuclear magnetic phosphorus-31 spectrum of 0.15-Tppo-CTF prepared in Example 1;

[0031] Figure 4 Fourier transform infrared spectrum of 0.15-Tppo-CTF and CTF prepared in Example 1;

[0032] Figure 5 Powder X-ray diffraction pattern of 0.15-Tppo-CTF and CTF prepared in Example 1;

[0033] Figure 6 Transmission electron microscope image of 0.15-Tppo-CTF prepared in Example 1;

[0034] Figure 7 Atomic force microscope image of 0.15-Tppo-CTF prepared in Example 1;

[0035] Figure 8 Visible-light photocatalytic hydrogen production rate diagram of the photocatalysts prepared from the electron-trapping covalent triazine framework nanosheet materials of Examples 1 to 4 and the covalent triazine framework CTF of Comparative Example 1;

[0036] Figure 9Comparison chart of visible-light photocatalytic hydrogen production rates of photocatalysts prepared using the electron trap-type covalent triazine framework nanosheet materials of Examples 1 to 4 and the covalent triazine framework CTF of Comparative Example 1;

[0037] Figure 10 Comparison chart of visible-light photocatalytic hydrogen production rates of photocatalysts prepared using the covalent triazine framework nanosheet materials of Example 1 and Comparative Examples 1 to 3;

[0038] Figure 11 Test result chart of the visible-light photocatalytic hydrogen production stability of the photocatalyst prepared using the electron trap-type covalent triazine framework nanosheet material of Example 1;

[0039] Figure 12 Test result chart of the visible-light photocatalytic hydrogen production stability of the photocatalyst prepared using the traditional CTF material of Comparative Example 1. Detailed implementation manners

[0040] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention.

[0041] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0042] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0043] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0044] Regarding the terms "comprising", "including", "having", "containing", etc. used in this article, they are all open-ended terms, meaning including but not limited to.

[0045] In the following examples, "room temperature" refers to 20 - 35 °C, and will not be repeatedly described below.

[0046] Example 1

[0047] The polymerization method of electron trap-type covalent triazine framework nanosheets is as follows:

[0048] (1) Synthesis of monomer 1: Weigh 1.28 g of terephthalonitrile and dissolve it in 20.0 mL of tetrahydrofuran. Separately take 40.0 mL of lithium bis(trimethylsilyl)amide / tetrahydrofuran solution (1.00 mol / L) and slowly add it to the above solution within 1 h while stirring. After the addition is complete, add 40.0 mL of hydrochloric acid / ethanol solution (hydrochloric acid concentration 6.00 mol / L) to the mixed solution. The obtained reactant is washed with anhydrous ether, recrystallized in a water / ethanol solution, the solid is separated by filtration, and after drying, monomer 1 (2.18 g, yield 96.4%) is obtained;

[0049] (2) Synthesis of monomer 2 (Tppo): Mix p-bromobenzaldehyde (20.0 g), ethylene glycol (80.0 g), p-toluenesulfonic acid monohydrate (2.0 g) with toluene (200 mL). Heat to 115 °C and reflux with stirring for 24 h. After drying, 2-(4-bromophenyl)-1,3-dioxolane is obtained. Then, 2-(4-bromophenyl)-1,3-dioxolane (24.8 g) and magnesium powder (2.85 g) are used to prepare a Grignard reagent in tetrahydrofuran (200 mL) at 0 °C, and then phosphorus trichloride (3.14 mL) in tetrahydrofuran (10 mL) is added. The above mixture is heated to 70 °C and refluxed for 5 h, and then cooled to 0 °C. The mixture is extracted with dichloromethane (150 mL), the organic phase is collected and distilled under reduced pressure to obtain white crystals. The white crystals obtained from the reaction (11.3 g), 2 mol / L hydrochloric acid aqueous solution (42 mL), and tetrahydrofuran (200 mL) are mixed and heated to 70 °C and refluxed for 20 min. After cooling, it is extracted with dichloromethane (100 mL). After collecting the organic phase, the solvent is evaporated, and the crude product is purified by column chromatography (dichloromethane as the mobile phase and neutral alumina as the stationary phase) to obtain monomer 2 (5.1 g, yield 66.6%);

[0050] (3) Synthesis of electron trap type covalent triazine framework nanosheets (Tppo-CTF): Weigh a certain mass of monomer 1 (the molar ratio of monomer 1 to monomer 2 is equal to 2, and monomer 1 is 0.00015 mol) and 0.5000 g of cesium carbonate and add them to 20 mL of dimethyl sulfoxide solution. After heating the above mixed solution to 120 °C, slowly add 10 mL of dimethyl sulfoxide solution containing a certain mass of monomer 2 (the molar ratio of monomer 2 to terephthalaldehyde is 0.15, monomer 2 is 0.000075 mol, and the final product is denoted as X-Tppo-CTF with this molar ratio, where X is the molar ratio value) to the above mixed solution, and continue to maintain it at 120 °C for 12 h, denoted as solution A. Separately, fixedly weigh 0.1622 g of monomer 1, 0.0671 g of terephthalaldehyde, and 0.5000 g of cesium carbonate, and dissolve them in 10 mL of dimethyl sulfoxide solution, denoted as solution B. Slowly add solution B to solution A under the condition of 120 °C, maintain it at 120 °C for 12 h, then raise the temperature to 180 °C and maintain it for 48 h. After the reaction is completed, cool it to room temperature, filter to obtain a solid, and wash the obtained solid with hydrochloric acid and deionized water, and dry it to obtain the final product 0.15-Tppo-CTF.

[0051] Comparative Example 1

[0052] The synthesis of traditional covalent triazine framework CTF is as follows:

[0053] Weigh 0.1622 g of monomer 1 and 0.5000 g of cesium carbonate, and add them to 10.0 mL of dimethyl sulfoxide. Heat to 100 °C, slowly add 5.0 mL of dimethyl sulfoxide solution containing 0.0671 g of terephthalaldehyde to the above solution, continue to maintain it at 120 °C for 12 h, then raise the temperature to 180 °C and maintain it for 48 h. After the reaction is completed, cool it to room temperature, filter to obtain a solid, and wash the obtained solid with hydrochloric acid and deionized water, and dry it to obtain the final product CTF.

[0054] The specific surface area, pore volume, and average pore diameter of 0.15-Tppo-CTF prepared in Example 1 are increased from 761 m 2 / g, 0.87 cm 3 / g, and 4.60 nm of the traditional CTFs material prepared in Comparative Example 1 to 865 m 2 / g, 1.21 cm 3 / g, and 5.62 nm. Figure 1 is the structural formula of 0.15-Tppo-CTF prepared in Example 1, where the green part is the electron trap structure and the purple part is the covalent triazine framework structure. Figure 2 is the solid state nuclear magnetic carbon-13 spectrum of 0.15-Tppo-CTF prepared in Example 1 and the traditional CTF prepared in Comparative Example 1, Figure 3Solid-state nuclear magnetic phosphorus-31 spectrum of 0.15-Tppo-CTF prepared in Example 1 Figure 4 Fourier transform infrared spectra of 0.15-Tppo-CTF and CTF prepared in Example 1 Figure 5 Powder X-ray diffraction patterns of 0.15-Tppo-CTF and CTF prepared in Example 1 Figure 6 Transmission electron microscope image of 0.15-Tppo-CTF prepared in Example 1 Figure 7 Atomic force microscope image of 0.15-Tppo-CTF prepared in Example 1

[0055] From Figure 2 It can be seen that the chemical shift δ = 170 ppm can be attributed to the sp2 hybridized C in the triazine ring, and the two characteristic peaks at δ = 138 and 128 ppm can be attributed to the sp2 hybridized carbon in the benzene ring. The nuclear magnetic resonance carbon spectrum of the 0.15-Tppo-CTF nanosheets is consistent with that of the traditional CTF material. From Figure 3 It can be seen that a sharp peak appears at the chemical shift δ = 27.5 ppm, which can be attributed to P=O in triphenylphosphine oxide, and the weak shoulder peak at the chemical shift δ = 10.3 ppm can be attributed to P-OH. This result indicates that the phosphorus in triphenylphosphine oxide in monomer 2 is oxidized to the P=O structure during the synthesis process and mainly exists in the final product in the form of triphenylphosphine oxide O=PPh3. From Figure 4 It can be seen that both the 0.15-Tppo-CTF nanosheets and the traditional CTF material show characteristic absorption peaks at 1510 cm -1 and 1350 cm -1 which can be attributed to the stretching vibrations of -C=N- and -C-N= groups in the triazine ring structure respectively; the broad peak in the range of 3030 - 3610 cm -1 can be attributed to the characteristic vibration absorption of the amidine group (H2N-CR=NH), indicating that a small amount of the amidine group in monomer 1 did not undergo condensation reaction and remained at the end of the material. From Figure 5 It can be seen that the 0.15-Tppo-CTF and the traditional CTF material have two characteristic diffraction peaks at 2θ = 7.3° and 26.1°, which can be attributed to the diffraction of the {100} and {001} crystal planes respectively. Compared with the traditional CTF, the diffraction peak of the {001} crystal plane of 0.15-Tppo-CTF shifts to a smaller angle, indicating an increase in the interlayer spacing of the 0.15-Tppo-CTF material. From Figure 6 It can be seen that the morphology of the 0.15-Tppo-CTF material shows irregular thin sheets stacked in layers. From Figure 7 It can be seen that the average thickness of the traditional CTF material is 13.8 nm, while the average thickness of the 0.15-Tppo-CTF material is only 4.2 nm.

[0056] Examples 2 to 4

[0057] Same as Example 1, except that the molar ratio of monomer 2 to terephthalaldehyde in step (3) of Example 1 was changed, and the molar ratios of the two were 0.1, 0.3, and 0.4, respectively. The finally prepared products were denoted as: 0.1-Tppo-CTF, 0.3-Tppo-CTF, and 0.4-Tppo-CTF, respectively.

[0058] The specific surface area, pore volume, and average pore diameter of the materials prepared in Examples 2 to 4 were comparable to those of Example 1, with a difference within ±5%.

[0059] Comparative Example 2

[0060] Steps (1) and (2) were the same as those in Example 1, except that step (3) was different. The step (3) of this comparative example was as follows:

[0061] (3) Weigh a certain mass of monomer 1 (the molar ratio of monomer 1 to monomer 2 was equal to 2, and monomer 1 was 0.00015 mol) and 0.5000 g of cesium carbonate and add them to 20 mL of dimethyl sulfoxide solution. After the above mixed solution was heated to 120 °C, 10 mL of dimethyl sulfoxide solution containing a certain mass of monomer 2 (the molar ratio of monomer 2 to terephthalaldehyde was 0.15, and monomer 2 was 0.000075 mol. The finally obtained product was denoted as X-Tppo-CTF with this molar ratio, and X was the molar ratio value) was slowly added to the above mixed solution, denoted as solution A. Separately, 0.1622 g of monomer 1, 0.0671 g of terephthalaldehyde, and 0.5000 g of cesium carbonate were weighed and dissolved in 10 mL of dimethyl sulfoxide solution, denoted as solution B. Solution B was slowly added to solution A at 120 °C and maintained at 120 °C for 12 h, then heated to 180 °C and maintained for 48 h. After the reaction was completed, it was cooled to room temperature, and the solid was filtered. The obtained solid was washed with hydrochloric acid and deionized water and dried to obtain the final product.

[0062] Comparative Example 3

[0063] Steps (1) and (2) were the same as those in Example 1, except that step (3) was different. The step (3) of this comparative example was as follows:

[0064] (3) Synthesis of electron trap type covalent triazine framework nanosheets (Tppo-CTF): Weigh a certain mass of monomer 1 (the molar ratio of monomer 1 to monomer 2 is equal to 2, and monomer 1 is 0.00015 mol) and 0.5000 g of cesium carbonate and add them to 20 mL of dimethyl sulfoxide solution. After heating the above mixed solution to 120 °C, slowly add 10 mL of dimethyl sulfoxide solution containing a certain mass of monomer 2 (the molar ratio of monomer 2 to terephthalaldehyde is 0.15, and monomer 2 is 0.000075 mol, and the final product obtained is denoted as X-Tppo-CTF with this molar ratio, where X is the molar ratio value) to the above mixed solution, and continue to keep it at 120 °C for 12 h, denoted as solution A. Separately, fix and weigh 0.1622 g of monomer 1, 0.0671 g of terephthalaldehyde, and 0.5000 g of cesium carbonate, and dissolve them in 10 mL of dimethyl sulfoxide solution, denoted as solution B. Under the condition of 120 °C, slowly add solution B to solution A, then raise the temperature to 180 °C and keep it for 48 h. After the reaction is completed, cool it to room temperature, filter to obtain a solid, and wash the obtained solid with hydrochloric acid and deionized water, and dry it to obtain the final product.

[0065] Effect verification

[0066] Preparation of electron trap type covalent triazine framework nanosheet photocatalyst, the steps are as follows:

[0067] Prepared by in-situ photodeposition method. In a 250 mL top-illuminated glass reactor (with a diameter of 10 cm) equipped with a xenon lamp with a power of 300 w and a cut-off ultraviolet light filter (λ>420 nm), sequentially add 0.02 g of the electron trap type covalent triazine framework nanosheet materials prepared in Examples 1-4 and Comparative Examples 2-3, the covalent triazine framework CTF prepared in Comparative Example 1, 50.00 mL of deionized water containing triethanolamine (volume fraction 10%) and 122.00 μL of 0.02 mol / L chloroplatinic acid hexahydrate. Circulating water is passed through the reactor jacket to keep the temperature at 10 °C, evacuate for 30 min to remove the air in the system, turn on the xenon lamp, and stir for 30 min to obtain an electron trap type covalent triazine framework nanosheet photocatalyst containing platinum and a traditional covalent triazine framework nanosheet photocatalyst. (In Figures 8 - 9 , 0.15-Tppo-CTF, 0.1-Tppo-CTF, 0.3-Tppo-CTF, 0.4-Tppo-CTF and CTF are used to represent the photocatalysts prepared from the electron trap type covalent triazine framework nanosheet materials in Examples 1-4 and the covalent triazine framework CTF in Comparative Example 1 respectively).

[0068] Visible-light photocatalytic hydrogen production application of the above-mentioned electron trap-type covalent triazine framework nanosheet photocatalyst: In a 250 mL top-illuminated glass reactor (diameter 10 cm) equipped with a 300 W xenon lamp and a cut-off ultraviolet light filter (λ>420 nm), 0.02 g of the above-prepared electron trap-type covalent triazine framework nanosheet photocatalyst and the traditional covalent triazine framework nanosheet photocatalyst were dispersed in 50.00 mL of deionized water containing triethanolamine (volume fraction 10%). Circulating water was passed through the reactor jacket to maintain the temperature at 10 °C. The system was evacuated for 30 min to remove the air in the system. The xenon lamp was turned on. Every 30 min during the reaction, the hydrogen production amount of the reaction system was measured with a gas chromatograph equipped with a thermal conductivity detector. The chromatographic column was 5A molecular sieve, and argon was used as the carrier gas. After the reaction for 2 h, the xenon lamp was turned off, and the reaction system was evacuated for 30 min to remove the gas products. The xenon lamp was turned on again, and the above operation steps were repeated to measure the cyclic reaction stability of the photocatalytic hydrogen production of the catalyst.

[0069] Figure 8 Photocatalytic hydrogen production rate diagrams of the visible light of the electron trap-type covalent triazine framework nanosheet materials of Examples 1-4 and the photocatalysts prepared from the covalent triazine framework CTF of Comparative Example 1. Figure 9 Comparison diagrams of the photocatalytic hydrogen production rates of the visible light of the electron trap-type covalent triazine framework nanosheet materials of Examples 1-4 and the photocatalysts prepared from the covalent triazine framework CTF of Comparative Example 1. Figure 10 Comparison diagrams of the photocatalytic hydrogen production rates of the visible light of the photocatalysts prepared from the covalent triazine framework nanosheet materials of Example 1 and Comparative Examples 1-3. Figure 11 Photocatalytic hydrogen production stability test result diagram of the photocatalyst prepared from the electron trap-type covalent triazine framework nanosheet material of Example 1. Figure 12 Photocatalytic hydrogen production stability test result diagram of the photocatalyst prepared from the traditional CTF material of Comparative Example 1.

[0070] It can be seen from Figure 8 and Figure 9 that the photocatalytic hydrogen production activity of the traditional CTF material is low, while the photocatalytic hydrogen production activity of X-Tppo-CTF is significantly higher than that of the traditional CTF material. Among them, the photocatalytic hydrogen production rate of the optimal 0.15-Tppo-CTF is 4.6 times that of the traditional CTF material. It can be seen from Figure 10It can be seen that the photocatalytic hydrogen production activity of Example 1 is significantly better than that of Comparative Examples 1-3, indicating that the synthesis strategy of stepwise polymerization and the introduction of triphenylphosphine oxide monomers can effectively improve the photocatalytic performance of the material. Among them, compared with Example 1, Comparative Example 1 lacks triphenylphosphine oxide monomers and cannot form electron traps to promote the separation of photo-generated carriers and inhibit the recombination of photo-generated carriers, resulting in weak photocatalytic hydrogen production performance. Compared with Example 1, Comparative Examples 2-3 lack the stepwise polymerization process, which may lead to the disordered arrangement of the introduced triphenylphosphine oxide monomers in the material, thus unable to form effective electron traps. Although there are triphenylphosphine oxide monomers, the improvement of photocatalytic hydrogen production performance is not obvious. From Figure 11 It can be seen that the photocatalytic hydrogen production rate of the 0.15-Tppo-CTF material after multiple cyclic photocatalytic hydrogen production experiments only decreased slightly starting from the third time. From Figure 12 It can be seen that the photocatalytic hydrogen production rate of the traditional CTF material started to decrease from the third cycle, which is basically consistent with the decreasing trend of 0.15-Tppo-CTF.

[0071] As mentioned above, the above are only the preferred specific embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. An electron-trapping covalent triazine framework nanosheet, characterized in that, The structural formula is as shown in Formula (Ⅰ):

2. The preparation method of the electron trap type covalent triazine framework nanosheet according to claim 1, characterized in that, It includes the following steps: Synthesis of monomer 1: Dissolve terephthalonitrile in an organic solvent to obtain a terephthalonitrile solution; dissolve lithium bis(trimethylsilyl)amide in an organic solvent to obtain a lithium bis(trimethylsilyl)amide solution; then add the lithium bis(trimethylsilyl)amide solution to the terephthalonitrile solution, add a hydrochloric acid / ethanol solution to the resulting mixed solution, wash the resulting reactant, recrystallize it in a water / ethanol solution, filter and separate the solid, and obtain monomer 1 after drying; the synthesis route of monomer 1 is as shown in Formula (Ⅱ): Synthesis of monomer 2: Mix p-bromobenzaldehyde, ethylene glycol, p-toluenesulfonic acid monohydrate with toluene or benzene, heat under reflux and stir, and obtain 2-(4-bromophenyl)-1,3-dioxolane after drying; then add 2-(4-bromophenyl)-1,3-dioxolane and magnesium powder to an organic solvent to prepare a Grignard reagent; add phosphorus trichloride to an organic solvent to obtain a phosphorus trichloride solution; add the phosphorus trichloride solution to the Grignard reagent, heat under reflux, and then cool; extract the mixture, collect the organic phase and distill it under reduced pressure to obtain white crystals; mix the white crystals, hydrochloric acid and an organic solvent, heat under reflux, cool and then extract, collect the organic phase, evaporate the solvent, and purify the crude product by column chromatography to obtain monomer 2; the synthesis route of monomer 2 is as shown in Formula (Ⅲ): Synthesis of electron trap-type covalent triazine framework nanosheets: Add monomer 1 and cesium carbonate to an organic solvent, heat, and denote it as solution a; add monomer 2 to an organic solvent to obtain a solution of monomer 2, denoted as solution b; add solution b to solution a and keep warm, denoted as solution A; separately dissolve monomer 1, terephthalaldehyde and cesium carbonate in an organic solvent, denoted as solution B; add solution B to solution A, continue to keep warm, and then raise the temperature for reaction to obtain the electron trap-type covalent triazine framework nanosheets; the synthesis route is as shown in Formula (Ⅳ):

3. The preparation method of the electron trap type covalent triazine framework nanosheets according to claim 2, wherein, In the synthesis step of monomer 1, the organic solvents are all tetrahydrofuran; the concentration of the terephthalonitrile solution is 0.3 - 0.7 mol / L, the concentration of the lithium bis(trimethylsilyl)amide solution is 1.0 mol / L, and the molar ratio of terephthalonitrile to lithium bis(trimethylsilyl)amide is 1:(1.5 - 2.5); in the hydrochloric acid / ethanol solution, the concentration of hydrochloric acid is 5 - 7 mol / L, and the volume ratio of the hydrochloric acid / ethanol solution to the terephthalonitrile solution is (1.8 - 2.5):

1.

4. The preparation method of the electron trap type covalent triazine framework nanosheet according to claim 2, characterized in that, In the synthesis step of monomer 2, the organic solvents are all tetrahydrofuran; the extraction is all carried out with dichloromethane; the column chromatography purification uses dichloromethane as the mobile phase and neutral alumina as the stationary phase.

5. The preparation method of the electron trap type covalent triazine framework nanosheet according to claim 2, wherein, In the synthesis step of monomer 2, the mass ratio of p-bromobenzaldehyde, ethylene glycol and p-toluenesulfonic acid monohydrate is 1:(3-5):(0.8-1.2), and the mass-volume ratio of p-bromobenzaldehyde to toluene is 1 g:(8-12) mL; the mass-volume ratio of 2-(4-bromophenyl)-1,3-dioxolane, magnesium powder and phosphorus trichloride is (20-26) g:(2-3.5) g:(2.5-3.5) mL; the concentration of the hydrochloric acid aqueous solution is 1.5-2.5 mol / L, and the mass-volume ratio of the white crystal to the hydrochloric acid aqueous solution is (10-12) g:(35-45) mL.

6. The preparation method of the electron trap type covalent triazine framework nanosheets according to claim 2, wherein, In the synthesis step of the electron trap type covalent triazine framework nanosheets, the organic solvents are all dimethyl sulfoxide; the molar ratio of monomer 1 to monomer 2 in solution A is 1.5-2.5, and the molar ratio of monomer 2 to terephthalaldehyde in solution B is 0.1-0.4; the mass ratio of monomer 1 to cesium carbonate in solution A is (0.32-1.30):1, and the mass ratio of monomer 1, terephthalaldehyde and cesium carbonate in solution B is (3-4):(1-2):10; the temperature for heat preservation is 90-130 °C, and the time is 10-15 h; the temperature for the temperature-rising reaction is 150-200 °C, and the time is 36-60 h.

7. Use of the electron trap type covalent triazine framework nanosheets according to claim 1 in the preparation of a photocatalyst.

8. An electronic trap type covalent triazine framework nanosheet photocatalyst, characterized in that, Prepared by using the electron trap type covalent triazine framework nanosheets according to claim 1.

9. A preparation method of the electron trap-type covalent triazine framework nanosheet photocatalyst according to claim 8, characterized in that, Prepared by an in-situ photodeposition method, including the following steps: in a reactor equipped with a xenon lamp and a cut-off ultraviolet light filter, sequentially add the electron trap type covalent triazine framework nanosheets, deionized water containing triethanolamine and chloroplatinic acid hexahydrate, evacuate, turn on the xenon lamp, and stir to obtain the electron trap type covalent triazine framework nanosheet photocatalyst.

10. Use of the electron trap type covalent triazine framework nanosheet photocatalyst according to claim 8 in visible light photocatalytic hydrogen production.

Images