Preparation method of nano covalent organic framework and application of nano covalent organic framework in photocatalytic hydrogen evolution
By controlling the synthesis of covalent organic framework nanoparticles using polyvinylpyrrolidone, the problem of easy aggregation of COFs was solved, resulting in a significant improvement in the efficient photocatalytic hydrogen evolution performance and a substantial increase in the hydrogen production rate.
Patent Information
- Application Number
- CN202511352286.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-22
- Publication Date
- 2026-01-23
AI Technical Summary
Existing covalent organic framework (COF) nanocrystals are prone to aggregation, resulting in large light energy loss and insufficient photogenerated exciton diffusion length in photocatalytic applications, which limits the improvement of photocatalytic efficiency. Furthermore, traditional nano-sizing methods have low yields or limited applicability.
Using polyvinylpyrrolidone (PVP) as a surfactant, the generation of COF nanoparticles was controlled through a bottom-up synthesis strategy, which suppressed π–π interactions and covalent crosslinking to form a stable colloidal solution, thus achieving the controllable synthesis of nanoparticles.
It significantly improved light absorption capacity and exciton separation efficiency, boosting photocatalytic hydrogen production performance by two orders of magnitude, with a hydrogen production rate of 5854.8 mmol g⁻¹ h⁻¹, while reducing material usage and energy consumption costs.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a kind of nanometer covalent organic framework photocatalyst and its application in photocatalytic hydrogen evolution, in porous organic material and photocatalysis field. BACKGROUND
[0002] As a key path for clean energy transformation, photocatalytic water splitting can directly convert solar energy into hydrogen energy. Although inorganic semiconductor photocatalysts have been intensively studied since the last century, the fine tuning of related properties, including band matching, carrier separation and migration, has not been completely solved. Based on the advantages of designable band gap and rich chemical space, organic semiconductor systems, including linear polymers, graphite phase carbon nitride and organic frameworks, have been proposed as important alternatives. Among them, covalent organic frameworks (COFs) are widely considered as a powerful candidate for solar-driven hydrogen production due to their ordered and designable framework, high chemical / thermal stability and permanent pore structure.
[0003] In existing synthesis routes, COFs are usually obtained through solvothermal conditions: high-concentration monomers are dissolved in organic solvents, and then polymerization and crystallization are promoted simultaneously at high temperatures. Limited by large-sized aromatic units and highly reactive functional groups, the initially generated nanocrystals often undergo irreversible aggregation under strong π-π interactions and covalent cross-linking, and then form bulk COFs mainly in micrometer scale.
[0004] Such bulk morphology constitutes a substantial limitation for photocatalytic applications: first, the high molar extinction coefficient limits the effective depth of light incidence (usually only tens to hundreds of nanometers), resulting in significant light energy loss; second, the diffusion length of photo-generated excitons is usually less than 20 nm, which easily leads to bulk or interface recombination, restricting the improvement of quantum efficiency. Although there have been attempts to obtain nano-COFs through liquid-assisted exfoliation, common problems include low yield or low product concentration (often less than 20%); cases of achieving high-yield nanomization mostly rely on ionic building units, with limited scope of application. Therefore, it is still an urgent and unsolved challenge to develop a general and scalable synthesis strategy for high-yield nano-COF photocatalysts. SUMMARY
[0005] The present application aims to overcome the limitations of traditional synthesis methods of covalent organic frameworks, and provides a preparation method of covalent organic framework nanoparticles and its photocatalytic hydrogen production application.
[0006] The preparation method of the covalent organic framework comprises the following steps:
[0007] 1) Dissolve p-phenylenediamine and polyvinylpyrrolidone in an organic solvent and mix uniformly to obtain solution amine solution A.
[0008] 2) Disperse 2,4,6-trihydroxy-1,3,5-benztrialdehyde in an organic solvent solution to obtain solution B.
[0009] 3) Add solution B dropwise to solution A, mix well, add acetic acid, and heat at high temperature to prepare the solution.
[0010] The above preparation method utilizes the steric stabilizing effect of the surfactant polyvinylpyrrolidone to control the reaction process, inhibiting further strong π–π interactions and covalent cross-linking after the formation of COF nanocrystals, thereby suppressing aggregation. A COF nanoparticle solution is obtained. Controlling the morphology and size of COFs effectively avoids light energy loss and holds promise for improving the photocatalytic hydrogen evolution performance.
[0011] Preferably, the polyvinylpyrrolidone has a number average molecular weight of 10,000 to 360,000 and a content of 0.25 to 3 wt%.
[0012] Preferably, the molar ratio of 2,4,6-trihydroxy-1,3,5-benzyltrialdehyde to p-phenylenediamine is 1:(1~2), and the concentration of 2,4,6-trihydroxy-1,3,5-benzyltrialdehyde is 0.002~0.01 mol / L.
[0013] Preferably, the reaction is carried out under negative pressure at 90-120 °C for 2-24 hours.
[0014] Preferably, the concentration of acetic acid is 0.1~2 mol / L.
[0015] Preferably, the solvent includes N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.
[0016] The covalent organic framework photocatalyst obtained by the method for preparing covalent organic framework nanoparticles.
[0017] Application of the covalent organic framework photocatalyst in photocatalytic hydrogen evolution.
[0018] 1. A bottom-up polymer-assisted synthesis strategy is proposed to achieve the controllable construction of COF nanoparticles. The resulting PVP / nano TPPA can spontaneously form a stable colloidal solution and can be directly used in photocatalytic reactions without complex post-processing.
[0019] 2. This strategy effectively regulates the morphology of COF, which is a key factor in improving photocatalytic efficiency, thereby improving the accessibility of active sites and the processability of the system from the source.
[0020] 3. Compared with the Bulk TPPA obtained by traditional methods, PVP / nano TPPA exhibits significantly enhanced light absorption and effectively suppresses exciton recombination.
[0021] 4. The photocatalytic hydrogen production performance of PVP / nano TPPA is improved by two orders of magnitude compared to bulk TPPA, with a hydrogen production rate of up to 5854.8 mmol g. -1 h -1 (1024.6 μmol h) -1 This is among the highest levels reported so far, significantly reducing the material usage and energy consumption costs per unit of hydrogen production. Attached Figure Description
[0022] Figure 1 This is a schematic diagram of the process described in this invention.
[0023] Figure 2 This is the powder X-ray diffraction pattern of PVP / nano TPPA in this invention.
[0024] Figure 3 This is the Fourier transform infrared spectrum of PVP / nano TPPA and p-phenylenediamine, 2,4,6-trihydroxy-1,3,5-benzenetrialdehyde in this invention.
[0025] Figure 4 This is the solid powder NMR spectrum of PVP / nano TPPA in this invention.
[0026] Figure 5 This is a dynamic light scattering diagram of the PVP / nano TPPA in this invention.
[0027] Figure 6 These are scanning electron microscope images of the PVP / nano TPPA and the Bulk TPPA prepared in Comparative Example 1 in this invention.
[0028] Figure 7 These are the UV-Vis transmittance spectra of the PVP / nano TPPA and the Bulk TPPA prepared in Comparative Example 1 in this invention.
[0029] Figure 8 These are the electron paramagnetic resonance spectra of the PVP / nano TPPA and the Bulk TPPA prepared in Comparative Example 1 in this invention.
[0030] Figure 9 These are the transient photocurrent response spectra of the PVP / nano TPPA and the Bulk TPPA prepared in Comparative Example 1 in this invention.
[0031] Figure 10These are the photocatalytic water splitting hydrogen production time spectra of PVP / nano TPPA and Bulk TPPA prepared in Comparative Example 1 in this invention.
[0032] Figure 11 This is a feed amount spectrum of PVP / nano TPPA photocatalytic water splitting for hydrogen production in this invention.
[0033] Figure 12 This is a stability test of the PVP / nano TPPA photocatalytic water splitting to produce hydrogen using time-frequency spectra in this invention.
[0034] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as a limitation of the present invention. Detailed Implementation Plan
[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to specific embodiments and comparative examples. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0036] Unless otherwise specified, all equipment used in this embodiment is conventional experimental equipment, and all materials and reagents used are commercially available unless otherwise specified. Experimental methods without special instructions are also conventional experimental methods. Example
[0037] PVP / nano TPPA synthesis p-Phenylenediamine (3.2 mg, 0.03 mmol) and polyvinylpyrrolidone (PVP, 40 mg, 55 kDa) were dissolved in 1 mL of N,N-dimethylformamide. Separately, 2,4,6-trihydroxy-1,3,5-benzenetrialdehyde (4.2 mg, 0.02 mmol) was dissolved in 1 mL of N,N-dimethylformamide. The two solutions were then mixed, and 50 μL of acetic acid was added. The resulting mixture was sonicated for 1 min. The mixture was transferred to a Pyrex glass tube (outer diameter × inner diameter = 10 × 8 mm²), rapidly frozen in a liquid nitrogen bath, and degassed by three freeze-evacuation-melt cycles, followed by evacuation to an internal pressure of 100 mtorr. The glass tube was sealed and heated at 120 °C for 4 h. After cooling to room temperature, a red solution was obtained. This nano-covalent organic framework solution can be directly used for the photocatalytic hydrogen evolution reaction. Comparative Example
[0038] Bulk TPPA Synthesis 2,4,6-Trihydroxy-1,3,5-benzenetrialdehyde (63.0 mg, 0.30 mmol), p-phenylenediamine (48.0 mg, 0.45 mmol), mesitylene (1.5 mL), 1,4-dioxane (1.5 mL), and 3 M aqueous acetic acid (0.5 mL) were added to a Pyrex glass tube. The mixture was sonicated for 5 min, followed by rapid freezing in a liquid nitrogen bath and degassing through three freeze-vacuum-melt cycles, after which the internal pressure was increased to 100 mtorr. The glass tube was sealed and heated at 120 °C for 72 h. The resulting precipitate was separated by filtration. To activate the crude product, solvent replacement was performed sequentially with DMF (20 mL × 12), methanol (20 mL × 6), and THF (20 mL × 6). The product was then vacuum dried at 60 °C for 12 h to obtain a light red bulk covalent organic framework powder. Experiments and Data
[0039] The PVP / naon TPPA prepared in Example 1 was subjected to Fourier transform infrared spectroscopy, powder X-ray diffraction, solid powder nuclear magnetic resonance spectroscopy, and dynamic light scattering. It was compared with the Bulk TPPA in Comparative Example 1 by electron microscopy, UV-Vis transmittance, paramagnetic resonance spectroscopy, transient photocurrent response, and photocatalytic hydrogen production rate. The results of the aforementioned tests and analyses are as follows:
[0040] (1) Powder X-ray diffraction detection like Figure 2 As shown, the powder X-ray diffraction (PXRD) pattern of PVP / nano TPPA shows clear diffraction peaks at 2θ of 4.7°, 8.1° and 27°, corresponding to the (100), (110) and (001) crystal planes, respectively, indicating that PVP / nano TPPA has crystallinity.
[0041] (2) Fourier transform infrared test Figure 2 As shown, the 1637 cm⁻¹ corresponding to 2,4,6-trihydroxy-1,3,5-benzenetrialdehyde and p-phenylenediamine was not observed in the PVP / nano TPPA sample. -1 C=O or 3372 cm at the location -1 With 3301 cm -1 N–H stretching vibration at 1580 cm -1 With 1256 cm -1 The appearance of new characteristic vibrational peaks corresponding to C=C and CN indicates that the monomer has completely undergone Schiff base condensation and formed a framework structure.
[0042] (3) Solid powder nuclear magnetic resonance detection like Figure 4 As shown, the solid powder nuclear magnetic resonance (SS-NMR) spectrum of PVP / nano TPPA shows both peaks of polyvinylpyrrolidone and structural characteristic peaks of COF, indicating that COF and polyvinylpyrrolidone undergo a certain degree of physical cross-linking.
[0043] (4) Dynamic light scattering detection Depend on Figure 5 It can be seen that the particle size of the nanoparticles in the PVP / nano TPPA solution is 78 nm, and the polydispersity is relatively low at 0.19, indicating that the nanoparticles in the synthesized colloidal solution have small particle size and uniform size distribution.
[0044] (5) Electron microscopy observation Depend on Figure 6 It can be seen that, Figure 6 (a) corresponds to the Bulk TPPA microstructure being a fibrous mass aggregate with an average size greater than 1 μm; while Figure 6 (b) corresponds to the microstructure of PVP / nano TPPA, which consists of uniformly dispersed rice-grain-like nanoparticles with a particle size of less than 100 nm. This indicates that the optimization of the preparation method successfully controlled the scale of the generated COF, reducing it from the micrometer scale to below 100 nm.
[0045] (6) Ultraviolet-visible transmittance detection As Figure 7 As shown, when both COFs were dispersed at the same concentration (10 μg / mL) in an aqueous suspension, Bulk TPPA exhibited a transmittance exceeding 85% in the 300–700 nm wavelength range. In contrast, the transmittance of PVP / nano TPPA was significantly reduced, reaching as low as 10–25% in the 350–550 nm range, indicating a significant improvement in light utilization. This superior light-harvesting ability is widely considered crucial for promoting photocatalytic hydrogen evolution.
[0046] (7) Electron paramagnetic resonance spectroscopy detection like Figure 8As shown, the presence of these charges can be indicated by the signal quenching of TEMPO (2,2,6,6-tetramethyl-1-piperidinoxy, nitroxide radical), because the free charges generated by COF under illumination are captured by TEMPO and reduced to tetramethylpiperidine (TEMP). Under the same irradiation conditions, PVP / nano TPPA exhibited more significant TEMPO signal quenching compared to the blank control group. Furthermore, the TEMPO signal of the PVP / nano TPPA group was significantly lower than that of the bulk TPPA group, indicating that this nano-COF system can generate more photogenerated free charges (i.e., electrons and holes) under visible light irradiation.
[0047] (8) Transient photocurrent response detection like Figure 9 As shown, when the two materials are prepared with the same concentration solution, the transient photocurrent response is as follows: the photocurrent of PVP / nanoTPPA is higher than that of Bulk TPPA, indicating that its charge separation is more efficient.
[0048] (9) Photocatalytic hydrogen production rate test like Figure 10 As shown, the synthesized PVP / nano TPPA solution was diluted with water and directly used for photocatalytic testing. To ensure accuracy, the photocatalytic activity of each experimental condition was measured at least three times. Under visible light irradiation with a 300 W xenon lamp (λ > 420 nm), 2.5 mg of Bulk TPPA COF powder produced 115.8 μmol of hydrogen gas in 4 hours, corresponding to a hydrogen evolution rate (HER) of 28.9 μmol·h⁻¹. Notably, using only 0.35 mL of diluted PVP / nano TPPA colloidal solution (containing only 0.175 mg of COF), 4098.4 μmol of hydrogen gas was produced in the same time, with an HER of 1024.6 μmol·h⁻¹. Although the catalyst amount was only 1 / 14 of that of Bulk TPPA, this rate was still more than 35 times higher than the latter.
[0049] Figure 11This invention also investigated the effect of photocatalyst dosage on light absorption capacity (which directly affects light absorption). As the dosage of PVP / nano TPPA catalyst was gradually increased from 0.05 mg to 0.125, 0.175, and 0.25 mg, the hydrogen evolution rate (HER) gradually increased. The highest average mass-normalized HER was observed at the lowest dosage of 0.05 mg, at 7599.5 mmol·g⁻¹·h⁻¹ (1519.9 μmol H₂ generated in 4 hours). An optimal balance was achieved between HER and average mass-normalized HER at a catalyst dosage of 0.175 mg (HER: 957.3 μmol·h⁻¹; average mass-normalized HER: 5470.6 mmol·g⁻¹·h⁻¹). However, further increasing the dosage to 0.5 mg led to a decrease in HER, dropping to 765.5 μmol·h⁻¹. This test demonstrates that a sufficient amount of hydrogen can be produced with extremely low photocatalyst usage, significantly reducing the material usage and energy consumption cost per unit of hydrogen production.
[0050] Figure 12 As shown, a cyclic photocatalytic hydrogen evolution experiment was set up to evaluate the photocatalytic stability of the PVP / nano TPPA nanocatalyst. Each cycle consisted of 4 hours of irradiation, followed by ascorbic acid supplementation and degassing of the system. This process was repeated for five consecutive cycles. Throughout the test, the hydrogen evolution rate (HER) remained stable, with an average value of 716.7 μmol·h⁻¹. In the last cycle, the HER remained at 85.4% of that in the first cycle, indicating good photocatalytic stability.
[0051] The method for evaluating the photocatalytic hydrogen evolution activity in water splitting provided by this invention is as follows: Changes in hydrogen release can be used as an indicator of photocatalytic activity. The cumulative amount of gas released was monitored every 60 minutes using a gas chromatograph (Agilent GC7890) equipped with a thermal conductivity detector (TCD). COF was dispersed in 25 mL of pure water. The system contained ascorbic acid as a sacrificial electron donor and H₂PtCl₆·6H₂O as a co-catalyst during the reaction. The light source was a 300 W xenon lamp (Perfect Light PLS-SXE300) equipped with a cutoff filter (>420 nm, 100 mWcm⁻¹). -2 Before the photoreaction, nitrogen gas is introduced into the system to completely remove air and dissolved oxygen. The reaction temperature is maintained at 20 °C.
Claims
1. A method for preparing covalent organic framework nanoparticles for photocatalytic water splitting and hydrogen evolution, characterized in that, The preparation method of the covalent organic framework includes the following steps: 1) p-Phenylenediamine and polyvinylpyrrolidone are dissolved in an organic solvent and mixed evenly to obtain solution amine solution A; 2) Disperse 2,4,6-trihydroxy-1,3,5-benztrialdehyde in an organic solvent solution to obtain solution B; 3) Add solution B dropwise to solution A, mix well, add acetic acid, and heat at high temperature to prepare the solution.
2. The method for preparing covalent organic framework nanoparticles according to claim 1, characterized in that, The number average molecular weight of polyvinylpyrrolidone is 10,000 to 360,000, and the content is 0.25 to 3 wt%.
3. The method for preparing covalent organic framework nanoparticles according to claim 1, characterized in that, The molar ratio of 2,4,6-trihydroxy-1,3,5-benzyltrialdehyde to p-phenylenediamine is 1:(1~2), and the concentration of 2,4,6-trihydroxy-1,3,5-benzyltrialdehyde is 0.002~0.01 mol / L.
4. The method for preparing covalent organic framework nanoparticles according to claim 1, characterized in that, The reaction is carried out under negative pressure at 90~120 °C for 2~24 hours.
5. The method for preparing covalent organic framework nanoparticles according to claim 1, characterized in that, The concentration of acetic acid is 0.1~2 mol / L.
6. The method for preparing covalent organic framework nanoparticles according to claim 1, characterized in that, The solvents include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetonitrile, and dimethyl sulfoxide.
7. The covalent organic framework photocatalyst obtained by the preparation method of covalent organic framework nanoparticles according to any one of claims 1 to 6.
8. The application of the covalent organic framework photocatalyst according to claim 7 in photocatalytic hydrogen evolution.