A photocatalyst with photo-induced self-sacrificial exfoliation and a preparation method and application thereof

Abstract

The application discloses a kind of photo-induced self-sacrificial peeling photocatalyst and its preparation method and application, and belongs to the technical field of catalyst, wherein, the preparation method of photocatalyst includes the following steps: 2,4,6-trimethylpyridine is reacted with halogenated alkyl in first solvent, to obtain monomer ETMP-X;X is any one of Cl, Br and I;Monomer ETMP-X, TAPB and base catalyst are placed in second solvent under inert atmosphere, and heated to 100-150 DEG C to react, to obtain photocatalyst.The photocatalyst prepared by the application is ion covalent organic framework material, with high crystallinity and long-range order, which can significantly reduce the particle size and thickness of the material when subjected to photo-induced self-sacrificial peeling, and successfully realize the peeling process of the material.In addition, the peeled material is used for photocatalytic production of hydrogen peroxide and coupled with benzyl alcohol compound aerobic oxidation, achieving ultra-high hydrogen peroxide generation rate and high benzyl alcohol compound conversion selectivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a photocatalyst capable of self-sacrificial peeling under light and a preparation method and application thereof. BACKGROUND

[0002] Covalent organic frameworks (COFs) with periodic crystalline structure connected by strong covalent bonds have become an ideal platform material in sustainable development fields such as adsorption and separation, catalysis, optoelectronic functional devices and drug delivery, due to their predictable structure, adjustable function, permanent porosity, high specific surface area and excellent chemical stability. For two-dimensional COF (2D COF), it extends in the two-dimensional plane to form a network layer, and these network layers are further arranged along the third dimension direction through non-covalent interactions such as π-π stacking to form highly ordered extended channels. This honeycomb structure endows the material with excellent molecular sieving, separation and transport properties; however, the strong interlayer stacking limits the accessibility of active sites inside the framework, thereby restricting the full play of the material performance. Therefore, under the premise of maintaining the covalent connection and structural integrity of the COF in the plane, effectively weakening the π-π stacking out of the plane has become a key strategy to release the active sites.

[0003] Compared with discrete small molecules, the π-π interaction between layers in two-dimensional COF is more intense, and essentially requires external force to achieve efficient interlayer dissociation. This external force needs to selectively destroy non-covalent interactions while maintaining the integrity of the covalent bond network, and ultimately achieve effective peeling of the COF. In recent years, efficient peeling strategies suitable for different structures of covalent organic frameworks (COFs) have been developed, mainly including mechanical peeling based on ultrasonic or grinding, self-peeling achieved by constructing ion covalent organic frameworks using charge repulsion effect, chemical peeling based on post-synthesis modification, and electrochemical peeling relying on electrochemical anode and cathode reactions.

[0004] Mechanical peeling, self-peeling and chemical peeling are difficult to accurately control the peeling degree, thereby bringing challenges to the controllable preparation of COF materials with a specified number of layers. The electrochemical peeling process is severely dependent on the intrinsic conductivity of the material, which is undoubtedly extremely favorable for conductive materials such as graphene, while most COFs have poor conductivity, which greatly limits the wide application of this strategy in COFs.

[0005] In summary, COF has shown broad application prospects in the fields of adsorption, catalysis and energy storage due to its adjustable structure, long-range order, good chemical stability and low toxicity, and has become a hot spot in the research of sustainable advanced materials. However, traditional two-dimensional COF usually depends on non-covalent interaction stacking, resulting in low accessibility of interlayer active sites and limiting the full play of its performance. SUMMARY

[0006] The present application aims to provide a preparation method of a photocatalyst with photo-induced self-sacrificial exfoliation to solve the problems in the background art.

[0007] To achieve the above object, the embodiments of the present application provide the following technical solutions.

[0008] A preparation method of a photocatalyst with photo-induced self-sacrificial exfoliation, comprising the following steps:

[0009] 2,4,6-trimethylpyridine and halogenated alkane are placed in a first solvent to react, to obtain a monomer ETMP-X; X is any one of Cl, Br and I;

[0010] The monomer ETMP-X, TAPB and a base catalyst are placed in a second solvent under an inert atmosphere, and heated to 100-150 DEG C to react, to obtain the photocatalyst.

[0011] Preferably, the step of placing 2,4,6-trimethylpyridine and halogenated alkane in a first solvent to react to obtain a monomer ETMP-X specifically comprises:

[0012] 2,4,6-trimethylpyridine and iodoethane or bromoethane are placed in a first solvent to reflux to react, to obtain a monomer ETMP-I or ETMP-Br;

[0013] Or the monomer ETMP-I and AgCl are mixed in deionized water, and then reacted in the dark to obtain a monomer ETMP-Cl.

[0014] Preferably, the first solvent is acetonitrile.

[0015] Preferably, the molar ratio of the monomer ETMP-X, TAPB and the base catalyst is 1:1:(5-7).

[0016] Preferably, the base catalyst is dimethylamine.

[0017] Preferably, the second solvent is a mixed solvent of N,N-dimethylformamide and o-dichlorobenzene.

[0018] Preferably, the volume ratio of N,N-dimethylformamide and o-dichlorobenzene is (5-8):(2-5).

[0019] Another object of the present application is to provide a photocatalyst with photo-induced self-sacrificial exfoliation prepared by the above preparation method.

[0020] Another object of the present application is to provide an application of the above photocatalyst with photo-induced self-sacrificial exfoliation in photocatalytic production of hydrogen peroxide.

[0021] Preferably, the photocatalytic reaction of hydrogen peroxide is coupled with the aerobic oxidation reaction of benzyl alcohol compounds.

[0022] The photocatalyst prepared by the present invention is an ionic covalent organic framework material with high crystallinity and long-range order. Photo-induced self-sacrificial exfoliation significantly reduces the particle size and thickness of the material, successfully achieving the exfoliation process. Furthermore, the exfoliated material is used for photocatalytic hydrogen peroxide production and coupled with aerobic oxidation of benzyl alcohols, achieving an ultra-high hydrogen peroxide generation rate and high selectivity for benzyl alcohol conversion. Under practical conditions, this method can achieve efficient separation of high-concentration hydrogen peroxide and organic products and supports the recycling of materials. Therefore, the photocatalyst provided by the present invention not only fills the gap in photocontrolled exfoliation technology but also provides a material and methodological foundation for the application of two-dimensional materials in sustainable energy and catalysis. Attached Figure Description

[0023] Figure 1 A schematic diagram of the synthesis route of the photocatalyst for photoinduced self-sacrificial exfoliation provided by the present invention.

[0024] Figure 2 X-ray diffraction (XRD) spectra, XRD photoelectron spectroscopy (XPS) spectra, and N2 adsorption-desorption curves of the three photocatalysts prepared in this invention are shown in the figures. In the figures, a is the XRD spectra of iCOF-Cl; b is the XRD spectra of iCOF-Br; c is the XRD spectra of iCOF-I; d is the XRD spectra of iCOF-Cl; e is the XRD spectra of iCOF-Br; f is the XRD spectra of iCOF-I; g is the N2 adsorption-desorption curve of iCOF-Cl; h is the N2 adsorption-desorption curve of iCOF-Br; and i is the N2 adsorption-desorption curve of iCOF-I.

[0025] Figure 3 Thermogravimetric diagrams of the three photocatalysts prepared in this invention are shown.

[0026] Figure 4 The figures show the particle size and Zeta potential of the three photocatalysts prepared in this invention; in the figures, a is iCOF-Cl; b is iCOF-Br; and c is iCOF-I.

[0027] Figure 5 The diagram shows the performance of the photocatalyst iCOF-I prepared in this invention in the simultaneous photocatalytic production of hydrogen peroxide and the oxidation of benzyl alcohol compounds.

[0028] Figure 6 The figure shows a comparison of the photoelectric properties of the three photocatalysts prepared in this invention; in the figure, a is the photocurrent test; b is the impedance test.

[0029] Figure 7 The image shows a comparison of the XRD and infrared spectra of the photocatalyst iCOF-I prepared in this invention before and after illumination; in the image, a is the XRD and b is the infrared spectrum. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] The photo-induced self-sacrificial exfoliation method proposed in this invention not only achieves controllable and precise exfoliation, significantly increasing the accessibility of active sites and fully demonstrating the intrinsic catalytic activity of the material, but also fills a research gap in photocontrolled exfoliation strategies. More importantly, this method provides a more applicable exfoliation route for COF materials with a wide spectral absorption range constructed from multiple conjugated units.

[0032] Specifically, such as Figure 1 As shown, in one embodiment of the present invention, a method for preparing a photocatalyst for photoinduced self-sacrificial exfoliation is provided, comprising the following steps:

[0033] S1. 2,4,6-Trimethylpyridine is reacted with a haloalkane in a first solvent to obtain the monomer ETMP-X; X is any one of Cl, Br and I;

[0034] S2. Under an inert atmosphere, monomer ETMP-X, TAPB and alkaline catalyst are placed in a second solvent and heated to 100-150℃ to react and obtain ionic covalent organic framework material iCOF-X.

[0035] It is worth noting that, in the embodiments of the present invention, the ionic covalent organic framework material prepared above can be directly used as a photocatalyst; alternatively, the ionic covalent organic framework material can be photo-induced self-sacrificial exfoliation first, and then the exfoliated material can be used as a photocatalyst. The photo-induced self-sacrificial exfoliation method involves placing the ionic covalent organic framework material in a liquid medium and exfoliating it under illumination. Preferably, the liquid medium is water, and the illumination is provided by a xenon lamp, but it is not limited thereto.

[0036] Further, the step of reacting 2,4,6-trimethylpyridine with a haloalkane in a first solvent to obtain the monomer ETMP-X specifically includes:

[0037] 2,4,6-Trimethylpyridine was reacted with iodoethane or bromoethane in a first solvent under reflux to obtain the monomers ETMP-I or ETMP-Br.

[0038] Alternatively, monomers ETMP-I and AgCl can be mixed in deionized water and then reacted under dark conditions to obtain monomer ETMP-Cl.

[0039] Specifically, the first solvent is acetonitrile; the molar ratio of monomer ETMP-X, TAPB and base catalyst is 1:1:(5-7); the base catalyst is dimethylamine; the second solvent is a mixed solvent of N,N-dimethylformamide (DMF) and o-dichlorobenzene (o-DCB); the volume ratio of N,N-dimethylformamide and o-dichlorobenzene is (5-8):(2-5).

[0040] Example 1: This example provides a method for preparing a photocatalyst that undergoes photoinduced self-sacrificial exfoliation, comprising the following steps:

[0041] S1. 2,4,6-Trimethylpyridine (1.25 mL, 10.00 mmol) and iodoethane (3.20 mL, 40.00 mmol) were sequentially added to acetonitrile (50 mL) to obtain a reaction mixture; the reaction mixture was refluxed at 100 °C for 12 hours; then, after removing the solvent under reduced pressure, the resulting yellow solid was recrystallized from ethyl acetate to obtain pale yellow crystals ETMP-I (yield: 80.39%). Structural characterization data are as follows: [ 1 H NMR (400 MHz, CDCl3): 7.55 (s, 2H), 4.75-4.69 (q, 2H), 2.96 (s, 6H), 2.55 (s, 3H), 1.55-1.49 (t, 3H)].

[0042] S2. ETMP-I (500 mg, 1.80 mmol) and AgCl (500 mg, 3.50 mmol) were mixed in deionized water (10 mL) to ensure complete dispersion. The reaction was then carried out in the dark for 4 hours. After cooling to room temperature, the solid residue was removed by filtration. The resulting filtrate was recrystallized three times consecutively from acetone and then evaporated under reduced pressure to give the desired product, a white crystalline solid ETMP-Cl (yield: 74.1%). The structural characterization data are as follows: [ 1 H NMR (400 MHz, CDCl3): 7.56 (s, 2H), 4.90-4.82 (q, 2H), 2.99 (s, 6H), 2.53 (s, 3H), 1.53-1.48 (t, 3H)].

[0043] S3. The reaction was carried out in a pre-dried Pyrex tube under an inert atmosphere: specifically, the tube was first evacuated and purged with argon (3 cycles). Then, ETMP-Cl (37.02 mg, 0.20 mmol), TAPB (78.20 mg, 0.20 mmol), anhydrous THF solution of 2M dimethylamine (600 μL, 1.20 mmol), 5 mL DMF, and 5 mL o-DCB were added sequentially while maintaining argon protection. The mixture was sonicated for 10 minutes to ensure homogeneity, then sealed and heated at 120 °C for 72 hours. The product was collected by filtration, washed sequentially with methanol, tetrahydrofuran, and dichloromethane, and then dried under vacuum overnight at 60 °C to obtain a yellow solid, which was the photocatalyst iCOF-Cl (yield: 87.51%).

[0044] Example 2: This example provides a method for preparing a photocatalyst that undergoes photoinduced self-sacrificial exfoliation, comprising the following steps:

[0045] S1. At room temperature, 2,4,6-trimethylpyridine (1.25 mL, 10.0 mmol) and bromoethane (3.01 mL, 40.0 mmol) were added dropwise to acetonitrile (50 mL), and the mixture was stirred overnight at 100 °C. The mixture was evaporated to form a white solid, which was purified by recrystallization from ethyl acetate to give pale pink crystals ETMP-Br. Yield: 67.9%. Structural characterization data are as follows: [ 1 H NMR (400 MHz, CDCl3): 7.50 (s, 2H), 4.83-4.78 (q, 2H), 2.91 (s, 6H), 2.54 (s, 3H), 1.53-1.48 (t, 3H)].

[0046] S2. First, the dried Pyrex tube was cooled in a vacuum and purged with argon for 10 minutes. Then, under an argon atmosphere, ETMP-Br (9.20 mg, 0.04 mmol), TAPB (15.62 mg, 0.04 mmol), anhydrous THF solution of 2M dimethylamine (120 μL, 0.24 mmol), 1 mL DMF, and 1 mL o-DCB were added sequentially to the Pyrex tube. Gas exchange was then rapidly performed under vacuum with argon, followed by ultrasonic treatment for ten minutes. Finally, the Pyrex tube was heated at 120 °C for 3 days in a thermostatic aluminum block. The precipitate was washed with methanol, tetrahydrofuran, and acetone, and dried under vacuum at 60 °C to obtain a pale yellow solid, which was the photocatalyst iCOF-Br. Yield: 89.1%.

[0047] Example 3: This example provides a method for preparing a photocatalyst for photoinduced self-sacrificial exfoliation, comprising the following steps:

[0048] S1. 2,4,6-Trimethylpyridine (1.25 mL, 10.00 mmol) and iodoethane (3.20 mL, 40.00 mmol) were sequentially added to acetonitrile (50 mL) to obtain a reaction mixture; the reaction mixture was refluxed at 100 °C for 12 hours; then, after removing the solvent under reduced pressure, the resulting yellow solid was recrystallized from ethyl acetate to obtain pale yellow crystals ETMP-I (yield: 80.39%). Structural characterization data are as follows: [ 1 H NMR (400 MHz, CDCl3): 7.55 (s, 2H), 4.75-4.69 (q, 2H), 2.96 (s, 6H), 2.55 (s, 3H), 1.55-1.49 (t, 3H)].

[0049] S2. The reaction was carried out in a pre-dried Pyrex tube under an inert atmosphere: specifically, the tube was first evacuated and purged with argon (3 cycles). Then, ETMP-I (55.50 mg, 0.20 mmol), TAPB (78.20 mg, 0.20 mmol), anhydrous THF solution of 2M dimethylamine (600 μL, 1.20 mmol), 5 mL DMF, and 5 mL o-DCB were added sequentially while maintaining argon protection. The mixture was sonicated for 10 minutes to ensure homogeneity, then sealed and heated at 120 °C for 72 hours. The resulting product was collected by filtration, washed sequentially with methanol, tetrahydrofuran, and dichloromethane, and then dried under vacuum overnight at 60 °C to obtain a yellow solid, which was the photocatalyst iCOF-I (yield: 89.36%).

[0050] Application Experiments: I. Electrochemical Measurements: Electrochemical impedance spectroscopy (EIS) and transient photocurrent response (it) measurements were performed using a standard three-electrode system on a CHI650D electrochemical workstation. The working electrode was prepared by dispersing 10 mg of the photocatalyst prepared above in 2 mL of a water-isopropanol mixture (1:1 v / v) containing 100 μL of Nafion solution (5 wt%), sonicating for 20 minutes, and then dropping the homogeneous slurry onto an FTO conductive glass (1 × 1 cm⁻¹). 2 The electrode was prepared on an active surface. Pt foil was used as the counter electrode, Ag / AgCl (saturated KCl) was used as the reference electrode, and 0.5M Na2SO4 aqueous solution was used as the electrolyte.

[0051] II. Photocatalytic Production of Hydrogen Peroxide: Photocatalytic production of hydrogen peroxide was carried out in a 30 mL aqueous suspension containing 2 mg of the above photocatalyst. Before irradiation, the suspension was saturated with oxygen by bubbling in the dark for 5 minutes. A 300 W xenon lamp (100 mW·cm⁻¹) equipped with a 420 nm cutoff filter was used. -2The reaction system was irradiated, and the reaction temperature was maintained at 15°C by a circulating water bath. The generation of hydrogen peroxide was studied by iodometric titration.

[0052] III. Organic Reaction Conversion: The reaction system for the production of hydrogen peroxide via organic coupling is maintained under the same conditions as the pure water system. Only 10 mL of BnOH or 1-PEOH needs to be added before irradiation, and the reaction temperature adjusted to 25°C. Liquid NMR is used to test the conversion rate and selectivity of the organic reactants.

[0053] IV. Hydrogen peroxide decomposition experiment: 2 mg of photocatalyst was added to 30 mL of hydrogen peroxide solution (10 mmol). Argon gas was purged through the solution by bubbling for 30 minutes to ensure complete removal of O2. The concentration of hydrogen peroxide was measured at 0, 20, 40, and 60 minutes of irradiation. The concentration of hydrogen peroxide before the reaction is denoted as C0, and the concentration after the reaction is denoted as C. The decomposition of hydrogen peroxide follows first-order kinetics, and the decomposition rate constant (Kd, min) is given by... -1 The following formula can be used to calculate:

[0054] ;

[0055] The theoretical formation rate constant of hydrogen peroxide (K) f , μM·min -1 ) Use the following formula to calculate:

[0056] ;

[0057] In the formula, C H2O2 t represents the concentration of hydrogen peroxide; t represents the reaction time.

[0058] The above experimental results are as follows Figures 2-7 As shown.

[0059] from Figure 2 It can be seen that the strong diffraction peak at 5.44° can be attributed to the (100) crystal plane. By comparing the XRD refinement results, it was found that all three materials adopt the AA stacking method. Combining X-ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption experiments, the presence of Cl, Br, and I elements can be clearly observed in the XPS spectrum. In the N2 adsorption-desorption experiment, the BET values ​​of the three materials are all in the range of 500-600 m. 2 ·g -1 This demonstrates the successful synthesis of iCOF-X (X = Cl, Br, I) and its good long-range order.

[0060] from Figure 3 As can be seen from the figure, iCOF-X has high thermal stability, with a weight loss of only about 10% at temperatures as high as 400°C in nitrogen.

[0061] from Figure 4 As can be seen, with the extension of light exposure time, the particle size of the three photocatalysts prepared in the embodiments of the present invention gradually decreases, and the absolute value of the Zeta potential gradually increases, which proves the photoexfoliation characteristics of the material.

[0062] from Figure 5 As can be seen, the photocatalyst iCOF-I prepared in the embodiments of the present invention not only exhibits an ultra-high hydrogen peroxide generation rate, but also shows an ultra-high selectivity of 98% in the oxidation of benzyl alcohol compounds.

[0063] from Figure 6 It can be seen that since the structural differences of the three photocatalysts prepared in the embodiments of the present invention are only in the different counter ions, their photoelectric properties are similar.

[0064] from Figure 7 It can be seen that after illumination, the peak of the (100) crystal plane of the photocatalyst iCOF-I in XRD decreased significantly. This is due to the decrease in crystallinity caused by exfoliation. However, in the infrared spectrum, the chemical structure of the photocatalyst iCOF-I did not change.

[0065] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification.

Claims

1. The application of a photocatalyst for photocatalytic self-sacrificial stripping in the photocatalytic production of hydrogen peroxide, characterized in that, The photocatalytic reaction of hydrogen peroxide is coupled with the aerobic oxidation reaction of benzyl alcohol compounds; The preparation method of the photocatalyst includes the following steps: 2,4,6-Trimethylpyridine was reacted with a haloalkane in a first solvent to give the monomer ETMP-X; X was either Br or I. Under an inert atmosphere, monomers ETMP-X, TAPB, and an alkaline catalyst are placed in a second solvent and heated to 100-150°C to react and obtain a photocatalyst. Alternatively, the preparation method of the photocatalyst may include the following steps: 2,4,6-Trimethylpyridine was reacted with iodoethane in a first solvent under reflux to obtain the monomer ETMP-I; The monomers ETMP-I and AgCl were mixed in deionized water and then reacted under dark conditions to obtain the monomer ETMP-Cl. Under an inert atmosphere, monomers ETMP-Cl, TAPB, and an alkaline catalyst are placed in a second solvent and heated to 100-150°C to react and obtain a photocatalyst.

2. The application according to claim 1, characterized in that, The first solvent is acetonitrile.

3. The application according to claim 1, characterized in that, The molar ratio of the monomer ETMP-X, TAPB, and the base catalyst is 1:1:(5-7).

4. The application according to claim 1 or 3, characterized in that, The alkaline catalyst is dimethylamine.

5. The application according to claim 1, characterized in that, The second solvent is a mixture of N,N-dimethylformamide and o-dichlorobenzene.

6. The application according to claim 5, characterized in that, The volume ratio of N,N-dimethylformamide to o-dichlorobenzene is (5-8):(2-5).

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