Synthesis method of protonated COFs photocatalyst and application of catalyst in photocatalytic transfer hydrogenation reaction

Abstract

According to the protonated COFs photocatalyst and the synthetic method of the aromatic hydroxylamine derivative thereof, imine B-COF is constructed, an imine bond linker is protonated through a protonation strategy to regulate and control a COFs skeleton microenvironment, so that efficient photocatalytic transfer hydrogenation reaction is realized, and the selectivity of an N-hydroxyaniline product is as high as 99%.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic hydrogenation, and particularly to a method for synthesizing a protonated COFs photocatalyst and the application of the catalyst in photocatalytic transfer hydrogenation reaction. Background Art

[0002] Aryl hydroxylamines are a class of compounds with important industrial application values, playing a key role in multiple fields such as pesticide manufacturing, pharmaceutical synthesis, and fine chemical production. In the pesticide manufacturing industry, the synthesis of many pesticides and herbicides requires aryl hydroxylamines as precursors or intermediates. In the pharmaceutical field, aryl hydroxylamines are important synthetic intermediates for certain anti-cancer drugs, cardiovascular drugs, and nervous system drugs. In addition, in the production of fine chemicals, aryl hydroxylamines are commonly used in the synthesis of pigments, dyes, flame retardants, and other functional materials.

[0003] Currently, the synthesis of aryl hydroxylamines mainly relies on the selective reduction of nitro compounds, and common methods include using Raney nickel or zinc powder as reducing agents. Although these traditional methods can effectively generate the desired hydroxylamine, they are often accompanied by adverse factors. For example, the reaction requires harsh conditions such as high temperature and high pressure, may produce harmful by-products during the process, and involves the use of harmful chemicals, posing potential threats to the safety of operators and the environment.

[0004] In recent years, photocatalytic hydrogenation technology has received extensive attention in the scientific research and industrial circles due to its safety, convenience, and environmental protection characteristics. Its principle is to use a photocatalyst to reduce water to produce active hydrogen, and then transfer the active hydrogen to nitroarene to achieve the reduction reaction of nitroarene. Although photocatalytic hydrogenation technology has significant advantages, it still faces challenges in selectively synthesizing the target product hydroxylamine in practical applications, that is, how to avoid the formation of easily synthesized by-products such as amines or azo.

[0005] Research shows that the optimized microenvironment between the catalyst and the substrate is crucial for improving the efficiency of selective hydrogenation reaction and reducing the reaction barrier. Covalent organic frameworks (COFs) show greater potential in the photocatalytic field than traditional organic and inorganic semiconductors due to their pre-designed structures and customizable functions. By regulating the active sites and framework microenvironment of COFs, precise control of the reaction path and kinetics can be achieved, optimizing the catalytic efficiency and selectivity. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for synthesizing a protonated COFs photocatalyst and the application of the catalyst in photocatalytic transfer hydrogenation reaction. By constructing imine B-COF and protonating the imine bond linker through a protonation strategy to regulate the COFs framework microenvironment, efficient photocatalytic transfer hydrogenation reaction can be achieved, with a selectivity of up to 99% for N-hydroxyaniline products.

[0007] The present invention provides a method for synthesizing a protonated COFs photocatalyst, and the method comprises the following steps: Step 1: Weigh 14.1 mg of 1,3,5-tris(4-aminophenyl)benzene and 6.5 mg of benzene-1,3,5-tricarbaldehyde into a 10 mL glass bottle, and add 5 mL of acetonitrile; Step 2: Use ultrasonic waves to ultrasonicate for 30 min, add 12 M CH 3 COOH 3 , and then seal the glass bottle; Step 3: Place the sealed glass bottle at room temperature and let it stand for reaction for 72 h; Step 4: After the reaction is completed, use a centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide; Step 5: Dry the washed solid in a vacuum oven for 12 h to obtain a light yellow solid powder B-COF catalyst; Step 6: Weigh 50 mg of B-COF into a 100 mL beaker, add 50 m of ascorbic acid aqueous solution, and quickly and vigorously stir the mixture for 20 min; Step 7: Filter the mixture and collect the solid residue; Step 8: Place the solid residue in a vacuum oven and dry it for 10 h to obtain a yellow solid powder B-COF_H.

[0008] Further improvement lies in that: the mass of 1,3,5-tris(4-aminophenyl)benzene and benzene-1,3,5-tricarbaldehyde in the step 1 is 0.04 mmol.

[0009] Further improvement lies in that: the room temperature in the step 3 is 25 °C.

[0010] Further improvement lies in that: the drying temperature of the vacuum drying oven in the step 5 is 70 °C.

[0011] Further improvement lies in that: the light yellow solid powder B-COF catalyst obtained in the step 5 is 13.8 mg.

[0012] Further improvement lies in that: the mass of the ascorbic acid aqueous solution in the step 6 is 0.05 M.

[0013] Further improvement lies in that: the oven temperature in the step 8 is controlled at 50 °C.

[0014] The present invention also provides an application of the protonated COFs photocatalyst prepared by the method for synthesizing a protonated COFs photocatalyst, which is used as a photocatalyst for photocatalytic transfer hydrogenation reaction.

[0015] A further improvement lies in: mixing the protonated COFs photocatalyst with a sacrificial agent ascorbic acid solution and an aqueous solution, performing ultrasonic treatment for uniform dispersion, then adding an acetonitrile solution and a substrate nitro compound, ultrasonic mixing again to be uniformly mixed, continuously introducing nitrogen to remove the dissolved oxygen in the solution, and finally using light irradiation for the reaction to complete the photocatalytic transfer hydrogenation reaction.

[0016] A further improvement lies in: the light irradiation power is 300 W.

[0017] The beneficial effects of the present invention: By constructing imine B-COF and regulating the COFs framework microenvironment by protonating the imine bond linker through a protonation strategy, thus achieving an efficient photocatalytic transfer hydrogenation reaction, with a selectivity of up to 99% for the N-hydroxyaniline product. It is found that protonating the imine-linked B-COF can adjust its local environment, effectively regulate the surface electronic structure, improve the interaction with substrate molecules, and enhance the charge separation performance. The research finds that the protonated B-COF_H material has good stability and the activity of catalytic hydrogenation of aromatic nitro to aromatic hydroxylamine. Description of the Drawings

[0018] Figure 1 It is the synthesis route diagram of B-COF of the present invention.

[0019] Figure 2 It is the synthesis route diagram of B-COF_H of the present invention.

[0020] Figure 3 It is the structure and morphology characterization diagram of B-COF and B-COF_H catalysts of the present invention.

[0021] Figure 4 It is the comparison diagram of the optical and electronic properties of B-COF and B-COF_H catalysts of the present invention.

[0022] Figure 5 It is the schematic diagram of the nitrobenzene hydrogenation reaction of B-COF and B-COF_H catalysts of the present invention.

[0023] Figure 6 It is the schematic diagram of the conversion rate and selectivity of the hydrogenation reaction substrate expansion of B-COF_H photocatalyst of the present invention. Detailed Embodiments

[0024] To deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation to the protection scope of the present invention. Embodiment

[0025] As Figure 1-2As shown in the figure, in this embodiment, the synthesis of the B-COF catalyst: Weigh 1,3,5-tris(4-aminophenyl)benzene (0.04 mmol, 14.1 mg) and benzene-1,3,5-tricarbaldehyde (0.04 mmol, 6.5 mg) into a 10 mL glass bottle, and add acetonitrile (5 mL). Use ultrasonic waves to sonicate for 30 min, and add CH 3 COOH 3 (0.4 mL, 12 M), and then seal the glass bottle. Place it at room temperature (25 °C) and let it stand for reaction for 72 h. After the reaction is completed, centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide. Then dry the collected solid in a vacuum oven at 70 °C for 12 h to obtain about 13.8 mg of light yellow solid powder B-COF.

[0026] Synthesis of B-COF_H catalyst: Weigh 50 mg of B-COF into a 100 mL beaker, then add 50 mL of 0.05 M aqueous solution of ascorbic acid, and quickly stir the mixture vigorously for 20 min. Subsequently, filter the mixture to collect the solid, and dry the solid in a vacuum oven at 50 °C for 10 h to obtain orange solid powder B-COF_H. Example

[0027] As Figure 1-2 shown in the figure, in this embodiment, the synthesis of the B-COF catalyst: Weigh 1,3,5-tris(4-aminophenyl)benzene (0.04 mmol, 14.1 mg) and benzene-1,3,5-tricarbaldehyde (0.04 mmol, 6.5 mg) into a 10 mL glass bottle, and add acetonitrile (5 mL). Use ultrasonic waves to sonicate for 35 min, and add CH 3 COOH 3 (0.4 mL, 9 M), and then seal the glass bottle. Place it at room temperature (28 °C) and let it stand for reaction for 70 h. After the reaction is completed, centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide. Then dry the collected solid in a vacuum oven at 75 °C for 10 h to obtain about 10.4 mg of light yellow solid powder B-COF.

[0028] Synthesis of B-COF_H catalyst: Weigh 50 mg of B-COF into a 100 mL beaker, then add 50 mL of 0.05 M aqueous solution of acetic acid, and quickly stir the mixture vigorously for 22 min. Subsequently, filter the mixture to collect the solid, and dry the solid in a vacuum oven at 55 °C for 12 h to obtain orange solid powder B-COF_H. Example

[0029] As Figure 1-2As shown in the figure, the synthesis of the B-COF catalyst in this example: Weigh 1,3,5-tris(4-aminophenyl)benzene (0.04 mmol, 14.1 mg) and benzene-1,3,5-tricarbaldehyde (0.04 mmol, 6.5 mg) into a 10 mL glass bottle, and add acetonitrile (5 mL). Use ultrasonic waves to sonicate for 25 min, then add CH 3 COOH 3 (0.4 mL, 15 M), and then seal the glass bottle. Place it at room temperature (23 °C) and let it stand for reaction for 69 h. After the reaction is completed, centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide. Then dry the collected solid in a vacuum oven at 68 °C for 14 h to obtain about 13.1 mg of light yellow solid powder B-COF.

[0030] Synthesis of B-COF_H catalyst: Weigh 50 mg of B-COF into a 100 mL beaker, then add 50 mL of 0.05 M aqueous solution of ascorbic acid, and quickly stir the mixture vigorously for 25 min. Subsequently, filter the mixture to collect the solid, and place the solid in a vacuum oven at 58 °C for 9 h to obtain orange-yellow solid powder B-COF_H. Example

[0031] As Figure 1-2 shown in the figure, the synthesis of the B-COF catalyst in this example: Weigh 1,3,5-tris(4-aminophenyl)benzene (0.04 mmol, 14.1 mg) and benzene-1,3,5-tricarbaldehyde (0.04 mmol, 6.5 mg) into a 10 mL glass bottle, and add acetonitrile (5 mL). Use ultrasonic waves to sonicate for 29 min, then add CH 3 COOH 3 (0.4 mL, 12 M), and then seal the glass bottle. Place it at room temperature (26 °C) and let it stand for reaction for 73 h. After the reaction is completed, centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide. Then dry the collected solid in a vacuum oven at 74 °C for 11 h to obtain about 13.8 mg of light yellow solid powder B-COF.

[0032] Synthesis of B-COF_H catalyst: Weigh 50 mg of B-COF into a 100 mL beaker, then add 50 mL of 0.05 M aqueous solution of ascorbic acid, and quickly stir the mixture vigorously for 27 min. Subsequently, filter the mixture to collect the solid, and place the solid in a vacuum oven at 50 °C for 11 h to obtain orange-yellow solid powder B-COF_H. Example

[0033] As Figure 1-2As shown, in this example, the synthesis of the B-COF catalyst: Weigh 1,3,5-tris(4-aminophenyl)benzene (0.04 mmol, 14.1 mg) and benzene-1,3,5-tricarbaldehyde (0.04 mmol, 6.5 mg) into a 10 mL glass bottle, and add acetonitrile (5 mL). Use ultrasonic waves to sonicate for 30 min, and then add CH 3 COOH 3 (0.4 mL, 12 M), and then seal the glass bottle. Place it at room temperature (25 °C) and let it stand for reaction for 72 h. After the reaction is completed, centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide. Then dry the collected solid in a vacuum oven at 70 °C for 12 h to obtain about 13.8 mg of light yellow solid powder B-COF.

[0034] Synthesis of B-COF_H catalyst: Weigh 50 mg of B-COF into a 100 mL beaker, then add 50 mL of 0.05 M acetic acid aqueous solution, and quickly and vigorously stir the mixture for 28 min. Subsequently, filter the mixture to collect the solid, and dry the solid in a vacuum oven at 45 °C for 13 h to obtain orange solid powder B-COF_H. Example

[0035] As Figure 1-2 shown, in this example, the synthesis of the B-COF catalyst: Weigh 1,3,5-tris(4-aminophenyl)benzene (0.04 mmol, 14.1 mg) and benzene-1,3,5-tricarbaldehyde (0.04 mmol, 6.5 mg) into a 10 mL glass bottle, and add acetonitrile (5 mL). Use ultrasonic waves to sonicate for 30 min, and then add CH 3 COOH 3 (0.4 mL, 12 M), and then seal the glass bottle. Place it at room temperature (25 °C) and let it stand for reaction for 72 h. After the reaction is completed, centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide. Then dry the collected solid in a vacuum oven at 70 °C for 12 h to obtain about 13.8 mg of light yellow solid powder B-COF.

[0036] Synthesis of B-COF_H catalyst: Weigh 50 mg of B-COF into a 100 mL beaker, then add 50 mL of 0.05 M dilute hydrochloric acid aqueous solution, and quickly and vigorously stir the mixture for 18 min. Subsequently, filter the mixture to collect the solid, and dry the solid in a vacuum oven at 60 °C for 8 h to obtain orange solid powder B-COF_H. Example

[0037] As Figure 1-2As shown, in this example, the synthesis of the B-COF catalyst: Weigh 1,3,5-tris(4-aminophenyl)benzene (0.04 mmol, 14.1 mg) and benzene-1,3,5-tricarbaldehyde (0.04 mmol, 6.5 mg) into a 10 mL glass bottle, and add acetonitrile (5 mL). Use ultrasonic waves to sonicate for 30 min, then add CH 3 COOH 3 (0.4 mL, 12 M), and then seal the glass bottle. Place it at room temperature (29 °C) and let it stand for reaction for 67 h. After the reaction is completed, centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide. Then dry the collected solid in a vacuum oven at 70 °C for 7 h to obtain about 13.8 mg of light yellow solid powder B-COF.

[0038] Synthesis of the B-COF_H catalyst: Weigh 50 mg of B-COF into a 100 mL beaker, then add 50 mL of 0.05 M aqueous sulfuric acid solution, and quickly and vigorously stir the mixture for 20 min. Subsequently, filter the mixture to collect the solid, and place the solid in a vacuum oven at 60 °C to dry for 9 h to obtain orange solid powder B-COF_H. Example

[0039] As Figure 1-2 shown, in this example, the synthesis of the B-COF catalyst: Weigh 1,3,5-tris(4-aminophenyl)benzene (0.04 mmol, 14.1 mg) and benzene-1,3,5-tricarbaldehyde (0.04 mmol, 6.5 mg) into a 10 mL glass bottle, and add acetonitrile (5 mL). Use ultrasonic waves to sonicate for 30 min, add dilute hydrochloric acid (0.4 mL), and then seal the glass bottle. Place it at room temperature (25 °C) and let it stand for reaction for 72 h. After the reaction is completed, centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide. Then dry the collected solid in a vacuum oven at 70 °C for 12 h, and it is impossible to obtain a formed light yellow solid powder B-COF. Example

[0040] As Figure 1-2 shown, in this example, the synthesis of the B-COF catalyst: Weigh 1,3,5-tris(4-aminophenyl)benzene (0.04 mmol, 14.1 mg) and benzene-1,3,5-tricarbaldehyde (0.04 mmol, 6.5 mg) into a 10 mL glass bottle, and add acetonitrile (5 mL). Use ultrasonic waves to sonicate for 30 min, add dilute sulfuric acid (0.4 mL), and then seal the glass bottle. Place it at room temperature (25 °C) and let it stand for reaction for 72 h. After the reaction is completed, centrifuge to collect the solid, and wash it 3 times with N,N-dimethylformamide. Then dry the collected solid in a vacuum oven at 70 °C for 12 h, and it is impossible to obtain a formed light yellow solid powder B-COF.

[0041] In the above Examples 1 to 7, as Figure 6 shown, the photocatalytic transfer hydrogenation experiment was carried out in a quartz glass reactor. The specific experimental operations are as follows: First, 10 mg of the photocatalyst and the sacrificial agent ascorbic acid (0.01 M) were dispersed in 8 mL of secondary aqueous solution and uniformly dispersed by ultrasonic waves. Then, acetonitrile (2 mL) solution and the substrate nitro compound (0.06 mmol) were added, and ultrasonic mixing was carried out again to make it uniform. The mixture was transferred to a glass reaction cell. After fixing the reaction cell, nitrogen was continuously introduced for 60 min to remove the dissolved oxygen in the solution to ensure that the experiment was carried out in an inert atmosphere. Subsequently, a 300 W Xe lamp was used to simulate sunlight (λ>420 nm) to irradiate the reactor, and the temperature of the reactor was maintained at room temperature by external cooling water. At different time intervals, the conversion of the nitro compound was detected by liquid chromatography. By comparing the peak area with the standard curves of the substrate and product prepared in advance, the conversion rate of the nitro compound, the formation of hydroxylamine and aniline were calculated.

[0042] By constructing imine B-COF and protonating the imine bond linker through a protonation strategy to regulate the microenvironment of the COFs framework, an efficient photocatalytic transfer hydrogenation reaction was achieved, with a selectivity of up to 99% for the N-hydroxyaniline product. It was found that protonating the imine-linked B-COF could adjust its local environment, effectively regulate the surface electronic structure, improve the interaction with the substrate molecules, and enhance the charge separation performance. The study found that the protonated B-COF_H material has good stability and the activity of catalytic hydrogenation of aromatic nitro to aromatic hydroxylamine.

[0043] As Figure 3 shown, a) are the PXRD data of B-COF and B-COF_H; b) are the nitrogen adsorption isotherm curves of B-COF and B-COF_H at 77 K; c) are the solid-state 13 CP-MAS NMR spectra of B-COF; d) is B-COF and e) is the SEM of B-COF_H; f) is B-COF and g) is the TEM image of B-COF_H.

[0044] The crystallinity of the sample was measured by powder X-ray diffraction (PXRD). As shown in 3-a, obvious diffraction peaks appeared in the PXRD pattern of B-COF at positions where 2θ were 5.8°, 9.9° and 11.5° respectively, corresponding to the (100), (110) and (200) crystal planes. The PXRD pattern of the protonated B-COF_H sample showed that the intensity of these peaks decreased slightly, but the positions remained unchanged, indicating its good stability. By N 2The pore structure and specific surface area of the sample were analyzed by the adsorption - desorption isotherm curve (3 - b). The calculation results show that the Brunauer - Emmett - Teller (BET) specific surface area of B - COF is 658 m 2 g –1 . After protonation treatment, the BET specific surface area of B - COF_H decreased to 387 m 2 g –1 . The decrease in the BET specific surface area of B - COF_H may be due to the introduction of ascorbic acid anions into its structure. These anions occupy part of the pore space, reducing the surface area available for adsorption. The structural characteristics of the B - COF material were further analyzed by solid - state nuclear magnetic resonance carbon spectrum ( 13 CP - MAS NMR). As shown in 3 - c, a characteristic signal peak of the new C = N bond appeared at 157.4 ppm, further confirming that the Schiff base reaction occurred effectively during the polycondensation process. When comparing the 13 CP - MAS NMR spectra of B - COF and protonated B - COF_H, it was found that the chemical shift of the imine carbon shifted from 157.4 ppm to 158.5 ppm, while the chemical shift of the benzene - ring carbon atoms remained unchanged. This indicates that the protonation mainly occurred at the imine sites of B - COF, and the benzene - ring carbon atoms were not significantly affected. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the microscopic morphology of the sample before and after protonation in detail. As shown in Figure 3 -d to 3 - g, under precise control of the solvent and catalyst concentrations, the B - COF material with a regular spherical microscopic morphology was successfully synthesized at room temperature. After protonation treatment, the resulting B - COF_H material still maintained its complete spherical structure. These results show that after the protonation process, the microscopic structure and apparent morphology of the material were not damaged, confirming the good structural stability of the B - COF catalyst.

[0045] As shown in Figure 4 , 2.a) shows the UV - Vis DRS spectra of B - COF and B - COF_H and the physical pictures of the two; b) shows the UPS spectra of B - COF and c) shows the UPS spectra of B - COF_H; d) shows the HOMO and LUMO molecular orbits of B - COF and e) shows the HOMO and LUMO molecular orbits of B - COF_H; f) shows the surface potentials of B - COF and B - COF_H; g) shows the built - in electric field (IEF) values of B - COF and B - COF_H; h) shows the transient photocurrent responses of B - COF and B - COF_H.

[0046] The ultraviolet-visible diffuse reflectance spectrum (DRS) of B-COF_H shows an absorption band with an edge at 570 nm, indicating its obvious visible light response characteristics (4-a). Compared with B-COF (450 nm), B-COF_H shows an obvious red shift. Calculated by the Tauc plot, the optical band gaps of B-COF and B-COF_H are 2.73 eV and 2.21 eV, respectively. The work function is an important physical parameter, which directly reflects the minimum energy required to move an electron from the Fermi level to the vacuum. To understand the surface work functions of B-COF and B-COF_H, ultraviolet photoelectron spectroscopy (UPS) was measured. As shown in 4-b and 4-c, the surface work functions of B-COF and B-COF_H are 4.25 eV and 3.81 eV, respectively. Obviously, the work function of B-COF_H decreases significantly after protonation. The lower work function indicates that less energy is required to move electrons to the surface for photocatalytic reactions. To further evaluate the surface electron properties after protonation, density functional theory (DFT) calculations were performed to study the spatial distributions of its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). As shown in 4-d and 4-e, the electronic structure of B-COF_H changes significantly after protonation. Compared with B-COF, the optimization of the orbital distribution after protonation is beneficial to promoting the separation and transfer of photo-generated electrons. Obtained by DFT calculation, the energy differences between HOMO and LUMO of B-COF and B-COF_H are 4.08 eV and 2.01 eV (relative to the vacuum level), respectively. The significant decrease in the energy difference of B-COF_H indicates that it is easier to excite and transfer electrons, which is consistent with the results of the surface work function. To gain in-depth understanding of the enhanced charge separation in B-COF_H, the model developed by Kanata-Kito et al. was used to estimate the internal electric field (IEF). As shown in 4-f, the surface potential differences of B-COF and B-COF_H measured by in-situ Kelvin probe force microscopy (KPFM) are 470.2 mV and 800.1 mV, respectively. Finally, it was calculated that the IEF of -COF_H is 2.0 times stronger than that of B-COF ( Figure 4 -g). 4-h shows the transient photocurrent responses of B-COF and B-COF_H. It can be observed that the photocurrent intensity of B-COF_H significantly exceeds that of B-COF. This result indicates that the photocurrent intensity of B-COF is significantly improved after protonation. Through the study of the optoelectronic properties of the protonated B-COF_H catalyst, it was found that the protonation strategy is an effective means for enhancing the functionality of photocatalytic materials. It promotes the effective separation of electron-hole pairs and increases the carrier lifetime by optimizing the charge dynamics process inside the material, providing a new way to improve the photocatalytic efficiency.

[0047] As Figure 5As shown, 3.a) is a schematic diagram of the hydrogenation reaction of nitrobenzene; b) is the 1 1H-NMR spectrum of the liquid-phase products of photocatalytic hydrogenation of nitrobenzene by B-COF_H at different reaction times; c) is the mass spectrum of the liquid-phase products of photocatalytic hydrogenation of nitrobenzene by B-COF_H after 50 minutes; d) is the catalytic effect of B-COF_H varying with time; e) is the catalytic effect of B-COF varying with time; f) is the catalytic performance of B-COF and B-COF_H after 50 minutes; g) is the cyclic performance test of B-COF_H.

[0048] The selective hydrogenation of nitroarenes is a key reaction for the preparation of high-value-added chemical products. Although some photocatalysts have shown their effectiveness in the hydrogenation reaction of nitroarenes, in most cases, the main products formed are aniline derivatives. During the hydrogenation reaction of nitrobenzene, nitroso benzene, N-phenylhydroxylamine, and finally aniline are formed in sequence. Therefore, it is a challenging task to prevent the thermodynamically favored complete hydrogenation in the hydrogenation reaction and selectively produce industrially important partially hydrogenated products such as N-phenylhydroxylamine. In this example, the focus is on the selective hydrogenation process of nitroarenes, which is carried out under visible light irradiation and in a nitrogen atmosphere. Water is selected as the proton source in the experiment, and ascorbic acid is used as the hole sacrificial agent. As shown in 5-b, through 1 1H NMR analysis confirmed that when the protonated B-COF_H material was used as the photocatalyst, the substrate nitrobenzene could rapidly undergo a hydrogenation reaction and was mainly converted into N-phenylhydroxylamine. After the reaction proceeded for 50 min, the selectivity of N-phenylhydroxylamine could reach as high as 99%. At the same time, the results of mass spectrometry analysis (5-c) showed that only the molecular ion peak of N-phenylhydroxylamine was observed in the sample after 50 min of reaction, while the corresponding molecular ions of nitrobenzene and aniline were not detected. These data indicate that protonated B-COF_H as a catalyst has extremely high efficiency in the selective hydrogenation reaction of nitrobenzene and excellent product selectivity. Further experimental results showed that when the reaction time was extended to 120 min, N-phenylhydroxylamine was not further hydrogenated into aniline, which can be seen from Figure 5 -d. On the other hand, when the unprotonated B-COF was used as the catalyst (5-e), the conversion rate of nitrobenzene was relatively low. At the same time, the selectivity of the generated N-phenylhydroxylamine was greatly reduced. Moreover, the extension of the reaction time would lead to the rapid further conversion of N-phenylhydroxylamine into aniline. In contrast, protonated B-COF_H showed a significant improvement in both the conversion rate of catalytic nitrobenzene and the maintenance of the selectivity of N-phenylhydroxylamine, which can be specifically seen in Figure 5It can be seen from -f. This finding confirms that after protonation, B-COF_H has significant advantages as a photocatalyst in improving catalytic efficiency and optimizing product selectivity. In the field of catalytic reactions, the stability of the catalyst plays a crucial role in its practical application value. Considering this, systematic stability evaluation experiments were carried out on the most excellent B-COF_H catalyst. From Figure 5 The data obtained from -g clearly show that even after six cycles of repeated use of the B-COF_H photocatalyst, there is no significant decrease in its ability to convert the substrate and the selectivity of the product. This result indicates that the B-COF_H catalyst not only has high catalytic activity and excellent selectivity, but more importantly, it exhibits good stability and reusability. For industrial applications, the long-term stability and recyclability of the catalyst are indispensable conditions for continuous production processes in an economical and effective manner. The significant performance demonstrated by the B-COF_H catalyst in these key characteristics indicates great application potential in actual industrial catalytic processes.

Claims

1. A method for synthesizing a protonated COFs photocatalyst, characterized in that: The method comprises the following steps: Step 1: Weigh 14.1 mg of 1,3,5-tris(4-aminophenyl)benzene and 6.5 mg of trimesaldehyde into a 10 mL glass bottle, and add 5 mL of acetonitrile; Step 2: Use ultrasonic sonication for 30 min, add 12 M CH3COOH3, and then seal the glass bottle; Step 3: Place the sealed glass bottle at room temperature and allow to react for 72 hours; Step 4: After the reaction is completed, the solid is collected by centrifugation and washed three times with N,N-dimethylformamide; Step 5: Dry the washed solid in a vacuum oven for 12 h to obtain a light yellow solid powder B-COF catalyst; Step 6: Weigh 50 mg of B-COF into a 100 mL beaker, add 50 mL of ascorbic acid aqueous solution, and stir the mixture rapidly and vigorously for 20 min; Step 7: Filter the mixture and collect the solid residue; Step 8: Place the solid residue in a vacuum oven and dry for 10 h to obtain yellow solid powder B-COF_H.

2. A method for synthesizing a protonated COFs photocatalyst according to claim 1, characterized in that: The mass of 1,3,5-tris(4-aminophenyl)benzene and trimesic acid aldehyde in the step 1 is 0.04 mmol.

3. The method for synthesizing a protonated COFs photocatalyst according to claim 1, characterized in that: The room temperature in step 3 is 25°C.

4. The method for synthesizing a protonated COFs photocatalyst according to claim 1, characterized in that: The drying temperature of the vacuum drying oven in step 5 is 70°C.

5. The method for synthesizing a protonated COFs photocatalyst according to claim 1, characterized in that: The light yellow solid powder B-COF catalyst obtained in step 5 weighs 13.8 mg.

6. The method for synthesizing a protonated COFs photocatalyst according to claim 1, characterized in that: The mass of the ascorbic acid aqueous solution in step 6 is 0.05M.

7. The method for synthesizing a protonated COFs photocatalyst according to claim 1, characterized in that: The oven temperature in step eight is controlled at 50°C.

8. An application of a protonated COFs photocatalyst prepared by the synthesis method of a protonated COFs photocatalyst according to any one of claims 1 to 7, characterized in that: It acts as a photocatalyst for photocatalytic transfer hydrogenation reactions.

9. The use of the protonated COFs photocatalyst prepared by the synthesis method of the protonated COFs photocatalyst according to claim 8, characterized in that: The protonated COFs photocatalyst and the sacrificial agent ascorbic acid solution and aqueous solution are mixed, and ultrasonication is used to evenly disperse them. Then, the acetonitrile solution and the substrate nitro compound are added, and ultrasonication is used to evenly mix them again. Nitrogen is continuously introduced to remove the dissolved oxygen in the solution. Finally, light is used to react to complete the photocatalytic transfer hydrogenation reaction.

10. Use of the protonated COFs photocatalyst prepared by the synthesis method of the protonated COFs photocatalyst according to claim 9, characterized in that: The illumination power is 300W.

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