Photoinduced self-sacrifice stripping photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a photo-induced self-sacrifice stripping photocatalyst and a preparation method and application thereof, and belongs to the technical field of catalysts.The preparation method of the photocatalyst comprises the following steps that 2, 4, 6-trimethylpyridine and alkyl halide are placed in a first solvent for a reaction, and a monomer ETMP-X is obtained; x is any one of Cl, Br and I; and in an inert atmosphere, putting the monomer ETMP-X, TAPB and a base catalyst into a second solvent, and heating to 100-150 DEG C for reaction to obtain the photocatalyst. The prepared photocatalyst is an ionic covalent organic framework material and has high crystallinity and long-range orderliness, the particle size and thickness of the material can be remarkably reduced by conducting photoinduced self-sacrifice stripping on the photocatalyst, and the stripping process of the material is successfully achieved; in addition, the stripped material is applied to the field of photocatalytic hydrogen peroxide production and is coupled with aerobic oxidation of the benzyl alcohol compound, so that ultrahigh hydrogen peroxide generation rate and higher conversion selectivity of the benzyl alcohol compound are realized.

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.

[0007] To achieve the above object, the embodiments of the present application provide the following technical solutions. The preparation method of the photocatalyst with photo-induced self-sacrificial exfoliation comprises the following steps: The 2,4,6-trimethylpyridine and the 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; The monomer ETMP-X, TAPB and the 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.

[0008] Preferably, the step of placing the 2,4,6-trimethylpyridine and the halogenated alkane in the first solvent to react to obtain the monomer ETMP-X specifically comprises: The 2,4,6-trimethylpyridine and the iodoethane or bromoethane are placed in the first solvent to reflux to react, to obtain the monomer ETMP-I or ETMP-Br; Or the monomer ETMP-I and AgCl are mixed in deionized water, and then reacted in the dark to obtain the monomer ETMP-Cl.

[0009] Preferably, the first solvent is acetonitrile.

[0010] Preferably, the molar ratio of the monomer ETMP-X, TAPB and the base catalyst is 1:1:(5-7).

[0011] Preferably, the base catalyst is dimethylamine.

[0012] Preferably, the second solvent is a mixed solvent of N,N-dimethylformamide and o-dichlorobenzene.

[0013] Preferably, the volume ratio of the N,N-dimethylformamide and the o-dichlorobenzene is (5-8):(2-5).

[0014] Another object of the present application is to provide a photocatalyst with photo-induced self-sacrificial exfoliation prepared by the above preparation method.

[0015] 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.

[0016] Preferably, the photocatalytic reaction of hydrogen peroxide is coupled with aerobic oxidation reaction of a benzyl alcohol compound.

[0017] The application provides a preparation method of a photocatalyst for photo-induced self-sacrificial peeling, and the prepared photocatalyst is an ion covalent organic framework material, has high crystallinity and long-range order, and can be subjected to photo-induced self-sacrificial peeling, so that the particle size and thickness of the material can be significantly reduced, and the peeling process of the material is successfully realized; in addition, the peeled material is subjected to photo-catalytic production of hydrogen peroxide and coupling of benzyl alcohol compound aerobic oxidation, so that an ultrahigh hydrogen peroxide production rate and high benzyl alcohol compound conversion selectivity are realized. In actual working conditions, the method can realize efficient separation of high-concentration hydrogen peroxide and organic products, and supports recycling of the material. Therefore, the photocatalyst for photo-induced self-sacrificial peeling provided by the application not only fills the gap of photo-controlled peeling technology, but also provides a material and methodological basis for application of two-dimensional materials in the fields of sustainable energy and catalysis. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The synthesis route of the photocatalyst for photo-induced self-sacrificial peeling provided by the application is shown in the figure.

[0019] Figure 2 X-ray diffraction spectra, X-ray photoelectron spectra and N2 adsorption-desorption curves of three photocatalysts prepared by the application are shown in the figure; in the figure, a is the X-ray diffraction spectrum of iCOF-Cl; b is the X-ray diffraction spectrum of iCOF-Br; c is the X-ray diffraction spectrum of iCOF-I; d is the X-ray photoelectron spectrum of iCOF-Cl; e is the X-ray photoelectron spectrum of iCOF-Br; f is the X-ray photoelectron spectrum 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.

[0020] Figure 3 The thermogravimetric diagrams of the three photocatalysts prepared by the application are shown in the figure.

[0021] Figure 4 The particle size and Zeta potential diagrams of the three photocatalysts prepared by the application are shown in the figure; in the figure, a is iCOF-Cl; b is iCOF-Br; and c is iCOF-I.

[0022] Figure 5 The performance diagram of the photocatalyst iCOF-I prepared by the application in photo-catalytic production of hydrogen peroxide while coupling benzyl alcohol compound oxidation is shown in the figure.

[0023] Figure 6 The comparison diagram of photoelectric property tests of the three photocatalysts prepared by the application is shown in the figure; in the figure, a is a photoelectric current test; and b is an impedance test.

[0024] Figure 7The 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

[0025] 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.

[0026] 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.

[0027] 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: 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; 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.

[0028] 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.

[0029] Further, the step of reacting 2,4,6-trimethylpyridine with a haloalkane in a first solvent to obtain the monomer ETMP-X specifically includes: 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. or mixing monomer ETMP-I and AgCl in deionized water, and then reacting in dark conditions to obtain monomer ETMP-Cl.

[0030] 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).

[0031] Example 1: The embodiment provides a preparation method of a photocatalyst for photo-induced self-sacrificial peeling, comprising the following steps: 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 obtained yellow solid was purified by recrystallization from ethyl acetate to obtain light yellow crystals of ETMP-I (yield: 80.39%). The structure 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)].

[0032] 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. Then, the reaction was carried out in dark conditions for 4 hours. After cooling to room temperature, the solid residue was removed by filtration. The obtained filtrate was recrystallized from acetone for three times, and then evaporated under reduced pressure to obtain the desired product, a white crystalline solid of ETMP-Cl (yield: 74.1%). The structure 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)].

[0033] S3, The reaction was carried out in a pre-dried Pyrex tube under inert atmosphere: Specifically, the tube was first evacuated and purged with argon (3 cycles). Then ETMP-CI (37.02 mg, 0.20 mmol), TAPB (78.20 mg, 0.20 mmol), 2M dimethylamine in anhydrous THF (600 μL, 1.20 mmol), 5 mL DMF and 5 mL o-DCB were sequentially charged 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, sequentially washed with methanol, tetrahydrofuran and dichloromethane, then dried under vacuum at 60 °C overnight to obtain a yellow solid, which is the photocatalyst iCOF-CI (yield: 87.51%).

[0034] Example 2: This example provides a method for preparing a photocatalyst for photo-induced self-sacrificial exfoliation, comprising the following steps: S1, At room temperature, 2,4,6-trimethylpyridine (1.25 mL, 10.0 mmol) and bromoethane (3.01 mL, 40.0 mmol) were sequentially dropped into acetonitrile (50 mL), then stirred at 100 °C overnight. The mixed solution was evaporated to form a white solid, which was purified by recrystallization in ethyl acetate to obtain light pink crystals of ETMP-Br. Yield: 67.9%. The structural characterization data are as follows: 1 H NMR (400 MHz, CDC13): 7.50 (s, 2H) 4.83-4.78 (q, 2H), 2.91 (s, 6H), 2.54 (s, 3H), 1.53-1.48 (t, 3H)].

[0035] S2, First, a dry Pyrex tube was cooled in vacuum and purged with argon for 10 minutes. Then ETMP-Br (9.20 mg, 0.04 mmol), TAPB (15.62 mg, 0.04 mmol), 2M dimethylamine in anhydrous THF (120 μL, 0.24 mmol), 1 mL DMF and 1 mL o-DCB were sequentially charged into the Pyrex tube under argon atmosphere. Then, a gas exchange was performed by vacuum argon and sonicated for ten minutes. Finally, the Pyrex tube was heated at 120 °C for 3d in a thermostatic aluminum block. The precipitate was washed with methanol, tetrahydrofuran and acetone, and dried under vacuum at 60 °C to obtain a light yellow solid, which is the photocatalyst iCOF-Br. Yield: 89.1%.

[0036] Example 3: This example provides a method for preparing a photocatalyst for photo-induced self-sacrificial exfoliation, comprising the following steps: S1, 2,4,6-trimethylpyridine (1.25 mL, 10.00 mmol) and iodoethane (3.20 mL, 40.00 mmol) were added sequentially into acetonitrile (50 mL) to obtain a reaction mixture; the reaction mixture was refluxed at 100 °C for 12 h; then, after removing the solvent under reduced pressure, the resulting yellow solid was purified by recrystallization from ethyl acetate to obtain light yellow crystals of ETMP-I (yield: 80.39%). The structural characterization data are as follows: 1 H NMR (400 MHz, CDC13): 7.55 (s, 2H), 4.75-4.69 (q, 2H), 2.96 (s, 6H), 2.55 (s, 3H), 1.55-1.49 (t, 3H)].

[0037] 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), 2M dimethylamine in anhydrous THF (600 μL, 1.20 mmol), 5 mL of DMF and 5 mL of o-DCB were loaded sequentially while maintaining argon protection. The mixture was sonicated for 10 min to ensure homogeneity, then sealed and heated at 120 °C for 72 h. The resulting product was collected by filtration, washed sequentially with methanol, tetrahydrofuran and dichloromethane, then dried under vacuum at 60 °C overnight to obtain a yellow solid, which was photocatalyst iCOF-I (yield: 89.36%).

[0038] Application experiment: I. Electrochemical measurement: Electrochemical impedance spectroscopy (EIS) and transient photocurrent response (i-t) measurements were performed on a CHI650D electrochemical workstation using a standard three-electrode system. The working electrode was prepared by dispersing 10 mg of the above-prepared photocatalyst in 2 mL of a water-isopropyl alcohol mixed solvent (1:1 v / v) containing 100 μL of a Nafion solution (5 wt%) for 20 min by ultrasonication, then dropping the uniform slurry onto an FTO conductive glass (1 x 1 cm 2 (active area). A Pt foil was used as the counter electrode, Ag / AgCl (saturated KCl) as the reference electrode, and a 0.5 M Na2S04 aqueous solution as the electrolyte.

[0039] II. Photocatalytic hydrogen peroxide production: Photocatalytic production of hydrogen peroxide was carried out in a 30 mL aqueous suspension containing 2 mg of the above photocatalyst. The suspension was filled with oxygen by bubbling in the dark for 5 min before irradiation. A 300 W xenon lamp (100 mW-cm -2The reaction system was irradiated while maintaining the reaction temperature at 15°C by a circulating water bath. The production of hydrogen peroxide was studied by iodometric method.

[0040] III. Organic reaction conversion: The reaction system of organic coupling hydrogen peroxide production was maintained the same condition as the pure water system, except that 10 mL of BnOH or 1-PEOH was added extra before irradiation and the reaction temperature was adjusted to 25°C. The conversion and selectivity of the organic reactant were tested by liquid NMR.

[0041] IV. Hydrogen peroxide decomposition experiment: 2 mg of photocatalyst was added to 30 mL of hydrogen peroxide solution (10 mmol). Argon 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 was C0, and the concentration after the reaction was represented as C. The decomposition of hydrogen peroxide followed first-order kinetics, and the decomposition rate constant (Kd, min -1 ) can be calculated using the following formula: ; The theoretical formation rate constant of hydrogen peroxide (K f , μM·min -1 ) was calculated using the following formula: ; Where C H2O2 is the concentration of hydrogen peroxide; t is the reaction time.

[0042] The experimental results are shown in Figures 2-7 .

[0043] As can be seen from Figure 2 , a 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 adopt the AA stacking mode. Combined with 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, and the BET of the three materials is 500-600 m 2 ·g -1 , proving the successful synthesis of iCOF-X (X = Cl, Br, I) and good long-range order.

[0044] As can be seen from Figure 3 , the figure shows that iCOF-X has very high thermal stability, and the weight loss in nitrogen is only about 10% at 400°C.

[0045] As can be seen from Figure 4It can be seen that the particle size of the three photocatalysts prepared by the embodiment of the present application gradually decreases and the absolute value of Zeta potential gradually increases with the extension of illumination time, which proves the photo-induced exfoliation property of the material.

[0046] From Figure 5 It can be seen that the photocatalyst iCOF-I prepared by the embodiment of the present application not only shows an ultra-high hydrogen peroxide generation rate but also shows an ultra-high selectivity of 98% in the process of oxidizing benzyl alcohol compounds.

[0047] From Figure 6 It can be seen that the photoelectric properties of the three photocatalysts prepared by the embodiment of the present application are similar because the structural difference of the three photocatalysts is only in the different counter ions.

[0048] From Figure 7 It can be seen that the peak of the (100) crystal plane of the XRD of the photocatalyst iCOF-I significantly decreases after illumination, which is caused by the decrease of crystallinity due to exfoliation, and the chemical structure of the photocatalyst iCOF-I does not change in the infrared spectrum.

[0049] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents in the specification.

Claims

1. A method for preparing a photocatalyst for photoinduced self-sacrificial exfoliation, characterized in that, 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 any one of Cl, Br and 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.

2. The method for preparing the photocatalyst for photoinduced self-sacrificial exfoliation according to claim 1, characterized in that, The step of reacting 2,4,6-trimethylpyridine with a haloalkane in a first solvent to obtain the monomer ETMP-X specifically includes: 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. Alternatively, monomers ETMP-I and AgCl can be mixed in deionized water and then reacted under dark conditions to obtain monomer ETMP-Cl.

3. The method for preparing the photocatalyst for photoinduced self-sacrificial exfoliation according to claim 1 or 2, characterized in that, The first solvent is acetonitrile.

4. The method for preparing the photocatalyst for photoinduced self-sacrificial exfoliation 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).

5. The method for preparing the photocatalyst for photoinduced self-sacrificial exfoliation according to claim 1 or 4, characterized in that, The alkaline catalyst is dimethylamine.

6. The method for preparing the photocatalyst for photoinduced self-sacrificial exfoliation according to claim 1, characterized in that, The second solvent is a mixture of N,N-dimethylformamide and o-dichlorobenzene.

7. The method for preparing the photocatalyst for photoinduced self-sacrificial exfoliation according to claim 6, characterized in that, The volume ratio of N,N-dimethylformamide to o-dichlorobenzene is (5-8):(2-5).

8. A photocatalyst for photoinduced self-sacrificial exfoliation prepared by any one of claims 1-7.

9. The application of the photocatalyst for photocatalytic self-sacrificial stripping as described in claim 8 in the photocatalytic production of hydrogen peroxide.

10. The application according to claim 9, characterized in that, The photocatalytic reaction of hydrogen peroxide is coupled with the aerobic oxidation reaction of benzyl alcohol compounds.

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