Covalent organic framework materials for photocatalytic splitting of water vapor and methods of making the same
By constructing a one-dimensional ultraporous covalent organic framework material, the problems of low stability and low absorption efficiency of traditional photocatalysts in water vapor cracking were solved, and a highly efficient photocatalytic hydrogen production effect was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- JIANGNAN UNIV
- Filing Date
- 2023-07-08
- Publication Date
- 2026-04-17
AI Technical Summary
Existing photocatalysts suffer from poor stability and low light absorption efficiency in pyrolysis liquid water, and traditional COFs materials cannot achieve a uniform microporous structure, which limits water vapor adsorption and photocatalytic performance.
One-dimensional covalent organic framework materials with ultra-small pores were constructed using symmetric V-shaped two-connector blocks and planar four-connector blocks. Using pyrene tetraamine derivatives and nonlinear dialdehyde derivatives with hydrophilic sites as raw materials, COFs materials with light absorption capacity and rapid carrier separation were prepared by solvothermal reaction.
Efficient photocatalytic hydrogen production under water vapor conditions was achieved. The material has good water vapor adsorption capacity and photogenerated charge separation performance, providing stable photocatalytic performance.
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Figure CN116925307B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of covalent organic framework materials, specifically relating to a method for preparing a covalent organic framework material for photocatalytic splitting of water vapor. Technical Background
[0002] Photocatalytic water splitting for hydrogen production is considered one of the most effective methods for solving the energy and environmental crisis. However, current research on photocatalytic hydrogen production largely focuses on liquid water, facing challenges such as demanding reaction systems, photocatalyst decomposition in flowing water, and the potential for freezing and disruption of the reaction system. In contrast, photocatalytic hydrogen production via water vapor splitting offers advantages in improving photocatalyst stability and providing greater scalability, but adsorbing water vapor into the photocatalyst is a highly challenging task. Therefore, current research on photocatalytic water vapor splitting for hydrogen production mainly focuses on inorganic photocatalyst composites composed of water adsorbents. These materials exhibit poor performance due to low water vapor adsorption capacity and low light absorption efficiency, limiting their practical applications.
[0003] Covalent organic frameworks (COFs) have recently been recognized as a new generation of crystalline organic semiconductors. The band structures and reactive sites of COFs can be engineered at the molecular level, and their conjugated structure prevents recombination of photogenerated electrons and holes. Furthermore, COFs have proven to be highly promising materials for atmospheric water vapor harvesting (AWH) due to their large specific surface area, diverse pore volumes, tunable structures, and good stability. Therefore, COFs demonstrate the feasibility of simultaneously achieving AWH and photocatalytic water vapor splitting for hydrogen production.
[0004] To design hygrophilic COFs for photocatalytic hydrogen production from water vapor, the following points should be considered: (i) good light absorption, appropriate band structure, and rapid carrier separation to achieve efficient photocatalysis; (ii) abundant hydrophilic sites, such as hydroxyl groups and N sites in pyridine, for rapid nucleation of water molecules; and (iii) uniform microporous channels to enable rapid adsorption and transport of water molecules. However, conventional photocatalytic COFs cannot achieve such uniform microporous channels. Summary of the Invention
[0005] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a method for preparing a covalent organic framework material for photocatalytic water vapor splitting. This method is based on symmetrical V-shaped two-connector blocks and planar four-connector blocks to construct one-dimensional ultrapores, thereby enhancing the micropore filling of AWH (autoclave-air-hydrogenation). Using light-absorbing conjugated pyrene tetraamine derivatives and a series of nonlinear (60° or 120°) dialdehyde derivatives with hydrophilic sites as raw materials, a one-dimensional covalent organic framework material for photocatalytic water vapor splitting is obtained through a solvothermal reaction.
[0006] To achieve the above objectives, the present invention adopts the following technical solution:
[0007] A covalent organic framework material for photocatalytic splitting of water vapor, the material having the following structural formula:
[0008]
[0009] The second objective of this invention is to provide a method for preparing a covalent organic framework material for photocatalytic splitting of water vapor. The preparation method includes the following steps: dissolving a pyrene tetraamine derivative and a nonlinear dialdehyde derivative with hydrophilic sites in a reaction solvent and reacting them under a catalyst.
[0010] In one embodiment, the pyrene tetraamine derivative comprises:
[0011]
[0012] In this context, the R atoms are independent of each other and represent halogen atoms such as H, F, Cl, and Br.
[0013] In one embodiment, the nonlinear dialdehyde derivative includes a 60° or 120° dialdehyde derivative.
[0014] In one embodiment, the nonlinear dialdehyde derivative having hydrophilic sites includes:
[0015]
[0016] In this context, X represents H, C, N, O, and S respectively; R represents halogen atoms such as H, F, Cl, and Br, hydrophilic oxygen-containing groups such as hydroxyl, aldehyde, and carboxyl groups, and C1-C3 alkyl or alkoxy groups respectively.
[0017] The molecular formula of the 120° dialdehyde derivative with hydrophilic sites is as follows:
[0018]
[0019] The molecular formula of the 60° dialdehyde derivative with hydrophilic sites is as follows:
[0020]
[0021] In this context, X represents H, C, N, O, and S respectively; R represents halogen atoms such as H, F, Cl, and Br, hydrophilic oxygen-containing groups such as hydroxyl, aldehyde, and carboxyl groups, and C1-C3 alkyl or alkoxy groups respectively.
[0022] In one embodiment, the molar ratio of the pyrene tetraamine derivative to the nonlinear dialdehyde derivative having hydrophilic sites is 1:3 to 3:1; the catalyst is 10 to 20% of the volume of the reaction solvent.
[0023] In one embodiment, the reaction solvent is dioxane and mesitylene.
[0024] In one embodiment, the volume ratio of dioxane to mesitylene is 1:1 to 5:1.
[0025] In one embodiment, the catalyst comprises acetic acid.
[0026] In one embodiment, the concentration of acetic acid is 3 to 6 mol / L.
[0027] In one embodiment, the reaction is carried out at 110–150°C for 3–7 days.
[0028] In one embodiment, the reaction is carried out in a reaction vessel.
[0029] In one embodiment, after the reaction is completed, the mixture is cooled to room temperature and the solid is collected by filtration, followed by repeated washing, purification, and drying processes.
[0030] In one embodiment, the washing is performed using an organic solvent.
[0031] In one embodiment, the organic solvent includes one or two of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF).
[0032] In one embodiment, the drying conditions are vacuum and 70–100°C.
[0033] In one embodiment, the purification method includes Soxhlet extraction.
[0034] A third objective of this invention is to provide an application of covalent organic framework materials for photocatalytic hydrogen production under steam conditions. This application includes the following steps: photodepositing a metal cocatalyst using the prepared covalent organic framework material, adding a sacrificial agent, and then performing photocatalytic hydrogen production under steam conditions.
[0035] In one embodiment, the photodeposited metal cocatalyst is H2PtCl6, with a mass fraction of 1 to 10 wt% of the catalyst.
[0036] In one embodiment, the sacrificial agent is ascorbic acid, and the mass ratio of the sacrificial agent to the photocatalyst is 1:10 to 10:1.
[0037] In one embodiment, the light source is a 300W xenon lamp with wavelengths including AM1.5G and λ>420nm.
[0038] In one embodiment, the light intensity range is 10–200 mW / cm². -2 .
[0039] Beneficial effects
[0040] This invention ingeniously combines air-based water collection with photocatalysis, and through a rational design based on geometric principles, constructs a one-dimensional covalent organic framework photocatalytic material with air-absorbing properties. Using the method provided by this invention, a one-dimensional covalent organic framework material for photocatalytically splitting water vapor to produce hydrogen can be prepared. Its one-dimensional framework structure with ultra-small pores satisfies the micropore filling requirements of water molecules under low humidity conditions. Furthermore, the abundant hydrophilic groups such as -OH in the pores not only promote rapid nucleation of water molecules but also enhance the separation of photogenerated charges, thus achieving the first-ever photocatalytic hydrogen production from water vapor using COFs materials, and proposing a new strategy for converting solar energy into hydrogen. Attached Figure Description
[0041] Figure 1 This is a schematic diagram illustrating the synthesis of the covalent organic framework material for photocatalytic water vapor splitting prepared in Example 1.
[0042] Figure 2 The images shown are electron microscope (EM) images of the covalent organic framework material for photocatalytic water vapor splitting prepared in Example 1, with a and e representing EEM images from different angles.
[0043] Figure 3 Transmission electron microscopy (TEM) images of the covalent organic framework material for photocatalytic water vapor splitting prepared in Example 1, with a and c representing TEM images from different angles.
[0044] Figure 4 The powder X-ray diffraction pattern of the covalent organic framework material for photocatalytic water vapor splitting prepared in Example 1;
[0045] Figure 5 Nitrogen adsorption / desorption isotherms of the covalent organic framework material for photocatalytic water vapor splitting prepared in Example 1;
[0046] Figure 6The first image shows the photocatalytic performance of the covalent organic framework material prepared in Example 1 for photocatalytic splitting of water vapor; a is a graph showing the relationship between photocatalytic hydrogen production performance and time; b is a graph showing the photocatalytic hydrogen production cycle test. Detailed Implementation
[0047] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.
[0048] Example 1
[0049] The preparation method of the covalent organic framework material for photocatalytic water vapor splitting in this embodiment is as follows:
[0050] (1) 0.3 mmol of pyrene tetramine (PyTTA) and 0.6 mmol of resorcinol dialdehyde (HMPA) were reacted (see schematic diagram of synthesis). Figure 1 Add it to a mixture of 1 mL dioxane and 1 mL mesitylene as a reaction solvent, and disperse it evenly by ultrasonication.
[0051] (2) Add 0.2 mL of 6 mol / L acetic acid to the uniformly dispersed solution as a catalyst, put it into the reaction vessel, and after ultrasonic dispersion, put it into the reaction vessel.
[0052] (3) The reaction vessel was kept at a constant temperature of 110°C for 5 days. After the reaction was completed, it was cooled to room temperature and the solid was collected by filtration.
[0053] (4) Wash the collected solids by centrifugation with DMF and THF for 10 mL × 5 times, and collect the solids again.
[0054] (5) After Soxhlet extraction of solid THF for 24 hours, vacuum drying at 80°C for 23 hours yielded a brownish-red powder, which is the covalent organic framework material used for photocatalytic cracking of water vapor, labeled as Py-HMPA.
[0055] Figure 2 The image shows a scanning electron microscope (SEM) image of the covalent organic framework material for photocatalytic water vapor splitting obtained in step 5 of this embodiment. It can be seen that it is composed of stacked layers. Figure 3 The image shows a transmission electron microscope (TEM) image of the covalent organic framework material for photocatalytic water vapor splitting obtained in step 5 of this embodiment, revealing the crystalline layered structure of the material. Figure 4 The powder X-ray diffraction image of the covalent organic framework material for photocatalytic water vapor splitting obtained in step 5 of this embodiment shows that it has good crystallinity when compared with the simulated value. Figure 5 The image shows the nitrogen adsorption / desorption isotherm of the covalent organic framework material for photocatalytic water vapor splitting obtained in step 5 of this embodiment. It can be seen that it has a high specific surface area.
[0056] Photocatalytic cracking of water vapor to produce hydrogen experiment
[0057] First, 7 wt% Pt cocatalyst was loaded onto Py-HMPA prepared in this example via in-situ photodeposition of H2PtCl6. Then, 30 mg of photodeposited Pt Py-HMPA and 100 mg of ascorbic acid were dispersed in 5 mL of ethanol. Catalyst ink was coated onto the top of a glass column (2 cm in diameter) and allowed to dry naturally to form a thin film. The glass column was placed in the center of the photoreactor, and liquid water was added to the reactor below the glass column as a source of water vapor.
[0058] Visible light illumination (λ>420nm, 100mW cm⁻¹) is achieved using a 300W xenon lamp source with a cutoff filter. -2 The amount of H2 produced was determined by gas chromatography.
[0059] like Figure 6 As shown in Figure a, when water vapor is used as the photocatalytic condition, Py-HMPA exhibits a stable and continuously increasing hydrogen production rate, and retains its photocatalytic performance even after multiple cycles. Figure 6 b) Therefore, Py-HMPA can serve as a novel covalent organic framework material for photocatalytic cracking of water vapor.
[0060] Example 2
[0061] The preparation method of the covalent organic framework material for photocatalytic water vapor splitting in this embodiment is as follows:
[0062] (1) 0.3 mmol of pyrene tetramine (PyTTA) and 0.5 mmol of resorcinol dialdehyde (HMPA) were reacted (see schematic diagram of synthesis). Figure 1 Add it to a mixture of 2 mL dioxane and 1 mL mesitylene as a reaction solvent, and disperse it evenly by ultrasonication.
[0063] (2) Add 0.4 mL of 5 mol / L acetic acid to the uniformly dispersed solution as a catalyst, put it into the reaction vessel, and after ultrasonic dispersion, put it into the reaction vessel.
[0064] (3) The reaction vessel was kept at a constant temperature of 120°C for 6 days. After the reaction was completed, it was cooled to room temperature and the solid was collected by filtration.
[0065] (4) Wash the collected solids by centrifugation with DMF and THF for 15 mL × 6 times, and collect the solids again.
[0066] (5) After Soxhlet extraction of solid THF for 24 hours, vacuum drying at 90°C for 24 hours yields brown-red powder, which is the covalent organic framework material used for photocatalytic cracking of water vapor.
[0067] Tests showed that the covalent organic framework material prepared in this embodiment has the same photocatalytic performance for splitting water vapor to produce hydrogen as the covalent organic framework material prepared in Example 1.
[0068] Example 3
[0069] The preparation method of the covalent organic framework material for photocatalytic water vapor splitting in this embodiment is as follows:
[0070] (1) 0.3 mmol of pyrene tetramine (PyTTA) and 0.3 mmol of resorcinol dialdehyde (HMPA) were reacted (see schematic diagram of synthesis). Figure 1 Add it to a mixture of 3 mL dioxane and 1 mL mesitylene as a reaction solvent, and disperse it evenly by ultrasonication.
[0071] (3) Add 0.5 mL of 4 mol / L acetic acid to the uniformly dispersed solution as a catalyst, put it into the reaction vessel, and after ultrasonic dispersion, put it into the reaction vessel.
[0072] (4) The reaction vessel was kept at a constant temperature of 115°C for 6 days. After the reaction was completed, it was cooled to room temperature and the solid was collected by filtration.
[0073] (5) Wash the collected solids by centrifugation with DMF and THF for 20 mL × 7 times, and collect the solids again.
[0074] (6) After Soxhlet extraction of solid THF for 24 hours, vacuum drying at 95°C for 24 hours yields a brownish-red powder, which is the covalent organic framework material used for photocatalytic cracking of water vapor.
[0075] Tests showed that the covalent organic framework material prepared in this embodiment has the same photocatalytic performance for splitting water vapor to produce hydrogen as the covalent organic framework material prepared in Example 1.
[0076] Example 4
[0077] The preparation method of the covalent organic framework material for photocatalytic water vapor splitting in this embodiment is as follows:
[0078] (1) 0.3 mmol of pyrene tetramine (PyTTA) and 0.2 mmol of resorcinol dialdehyde (HMPA) were reacted (see schematic diagram of synthesis). Figure 1 Add it to a mixture of 4 mL dioxane and 1 mL mesitylene as a reaction solvent, and disperse it evenly by ultrasonication.
[0079] (2) Add 1 mL of 5.5 mol / L acetic acid to the uniformly dispersed solution as a catalyst, put it into the reaction vessel, and after ultrasonic dispersion, put it into the reaction vessel.
[0080] (3) The reaction vessel was kept at a constant temperature of 112°C for 5 days. After the reaction was completed, it was cooled to room temperature and the solid was collected by filtration.
[0081] (4) Wash the collected solids by centrifugation with DMF and THF for 18 mL × 8 times, and collect the solids again.
[0082] (5) After Soxhlet extraction of solid THF for 24 hours, vacuum drying at 98°C for 24 hours yields a yellow powder, which is the covalent organic framework material used for photocatalytic cracking of water vapor.
[0083] Tests showed that the covalent organic framework material prepared in this embodiment has the same photocatalytic performance for splitting water vapor to produce hydrogen as the covalent organic framework material prepared in Example 1.
[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. Use of a covalent organic framework material for photocatalytic splitting of water vapour, characterized in that, The application method includes the following steps: photodepositing a covalent organic framework material with a metal cocatalyst, adding a sacrificial agent, and then performing photocatalytic hydrogen production under water vapor conditions. The photodeposited metal cocatalyst is H2PtCl6, with a mass fraction of 1-10 wt% of the catalyst. The structural formula of the covalent organic framework material is as follows: 、 、 、 。 2. Use of a covalent organic framework material for photocatalytic splitting of water vapour according to claim 1, characterized in that, The preparation method of the covalent organic framework material includes the following steps: using pyrene tetraamine derivatives and nonlinear dialdehyde derivatives with hydrophilic sites as raw materials, dissolving them in a reaction solvent, and reacting them under a catalyst to obtain the material.
3. Use of a covalent organic framework material for photocatalytic splitting of water vapour according to claim 2, characterized in that, The molar ratio of the pyrene tetraamine derivative to the nonlinear dialdehyde derivative with hydrophilic sites is 1:3 to 3:1; the catalyst is 10 to 20% of the volume of the reaction solvent.
4. The use of a covalent organic framework material for photocatalytic splitting of water vapour according to claim 2, characterised in that, The reaction solvent is dioxane and mesitylene, the volume ratio of dioxane to mesitylene is 1:1 to 5:1, and the reaction conditions are 110 to 150°C and standing for 3 to 7 days.
5. The use of a covalent organic framework material for photocatalytic splitting of water vapour according to claim 2 or 3, characterised in that, The catalyst includes acetic acid, and the concentration of the acetic acid is 3~6 mol / L.
6. The use of a covalent organic framework material for photocatalytic splitting of water vapour according to claim 2, characterised in that, After the reaction is complete, the mixture is cooled to room temperature and the solid is collected by filtration. The washing, purification and drying processes are repeated. The washing is performed with an organic solvent, which includes one or two of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF). The drying conditions are vacuum and 70-100°C. The purification method includes Soxhlet extraction.
7. The use of a covalent organic framework material for photocatalytic splitting of water vapour according to claim 1, characterised in that, The sacrificial agent includes ascorbic acid, and the mass ratio of the sacrificial agent to the photocatalyst is 1:10 to 10:1; the light source includes a 300W xenon lamp, the wavelength of which includes AM 1.5G and λ > 420nm, and the light intensity range is 10~200 mW cm⁻¹. -2 .