COF photocatalyst based on precise regulation of benzene ring nitrogen sites and its preparation method and application

Abstract

This invention discloses a COF photocatalyst based on precise regulation of benzene ring nitrogen sites, as well as its preparation method and application, belonging to the technical field of covalent organic framework (COF) materials. The preparation method of the present invention does not require toxic reagents and achieves high reproducibility of the COF structure by precisely controlling the monomer substitution position. By designing COF materials with ortho-, meta-, and para-N substitutions, the photocatalytic activity and stability in acidic environments are significantly improved. In particular, the photocatalytic hydrogen peroxide production rate of oN-COF substituted with ortho-N reaches 3015 μmol·g ‑1 ·h ‑1 , which is significantly higher than the existing technology (such as 1.8 mmol·g reported by Zhang et al. ‑1 ·h ‑1 That is 1800 μmol·g ‑1 ·h ‑1 ), after 5 cycles, the activity remained at 92%. The process of the present invention is green and environmentally friendly and suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of covalent organic framework (COF) materials, and specifically relates to a COF photocatalyst based on precise regulation of the nitrogen sites of the benzene ring, and a preparation method and application thereof. Background Art

[0002] Photocatalysis, which converts solar energy into chemical energy, has become an important approach to addressing energy crises and environmental pollution. As the core of photocatalysis, the performance of photocatalysts directly influences their efficiency. However, traditional inorganic semiconductor materials, such as titanium dioxide, suffer from limitations such as a narrow photoresponse range, low solar energy utilization, and rapid recombination of photogenerated carriers, hindering the further development of photocatalysis.

[0003] Since their discovery, covalent organic framework (COF) materials have become a research hotspot in the field of photocatalysis due to their designable pore structure and tunable electronic properties. COF materials possess a regular pore structure, high specific surface area, tunable electronic properties, and abundant functionalized sites. These properties enable them to efficiently capture and utilize light energy during photocatalysis, promoting the separation and migration of photogenerated charge carriers and thus improving photocatalytic efficiency. For example, strategies such as constructing electron donor-acceptor (DA) structures, introducing metal doping to form heterojunctions, and modifying functional groups have been shown to effectively enhance the photocatalytic performance of COF materials.

[0004] However, existing COF photocatalysts still face many challenges in acidic environments (such as industrial wastewater treatment and proton exchange membrane electrolysis systems):

[0005] 1. Lack of precision in active site design: Currently, researchers mostly improve the activity of COF photocatalysts by randomly introducing heteroatoms (such as N, S). However, the use of random substitution strategies (such as mixed ortho, meta, and para substitutions) does not clearly define the specific effect of heteroatom positions on activity. For example, Zhang et al. ( J. Am. Chem. Soc. 2020, 142, 12367) reported that N-doped COF was used for photocatalytic hydrogen production, but the N substitution position was not distinguished, and the hydrogen production rate was only 1.8 mmol·g -1 ·h -1 Different positions of heteroatom introduction can lead to significant changes in the electronic structure and chemical properties of the material, thereby affecting its photocatalytic performance. For example, introducing nitrogen atoms at different positions on the benzene ring may change the degree of conjugation, electron cloud density distribution, and interaction mode with reactants. However, existing research lacks in-depth systematic research and precise design, resulting in unsatisfactory optimization of active sites.

[0006] 2. Insufficient stability: Under acidic conditions, COF without N substitution is prone to protonation, which leads to skeleton collapse and the loss of photocatalytic activity of the material. (e.g. Adv. Mater. 2022, 34, 2107142). While nitrogen-substituted COFs improve stability to a certain extent, the specific mechanism of action remains unclear. For example, questions remain regarding whether the introduction of nitrogen atoms alters the interaction between COF materials and acidic media, and how it affects the chemical bond stability and structural integrity of the materials. This severely restricts the practical application and long-term stability of COF photocatalysts in acidic environments.

[0007] 3. Ambiguous structure-performance relationship: The synthesis method of COF materials makes it difficult to precisely control the position of substituents, resulting in structural differences between different batches of COF materials, and thus different performance. (e.g. Chem. Mater. 2019, 31, 4817). This large batch-to-batch variability makes it difficult for researchers to accurately establish the relationship between structure and performance, complicating the rational design and performance optimization of COF photocatalysts. For example, differences in the position of substituents can affect the material's pore size distribution, specific surface area, and electron transfer pathways, significantly influencing photocatalytic performance. However, the inability to precisely control the position of substituents makes the relationship between these structural factors and performance complex and ambiguous.

[0008] In view of the above-mentioned key problems of existing COF photocatalysts in acidic environments, the present invention designs four new COF materials (Ph-COF, mN-COF, pN-COF, oN-COF) by precisely controlling the N substitution position on the benzene ring, in order to significantly improve the photocatalytic activity and stability in acidic environments, providing more efficient photocatalytic materials to solve energy crises and environmental pollution problems. Summary of the Invention

[0009] In response to the technical problems of the above-mentioned existing COF photocatalysts such as low yield, poor stability and unclear structure-performance relationship under acidic conditions, the present invention provides a COF photocatalyst based on precise regulation of the nitrogen sites of the benzene ring, as well as its preparation method and application.

[0010] The technical solution adopted in the present invention is:

[0011] A COF photocatalyst based on precise regulation of the nitrogen sites on the benzene ring. The COF benzene ring has a precisely regulated N substitution position, and the N substitution position is a single N substitution at the ortho position, meta position, para position, or no N substitution on the benzene ring. No N substitution on the COF benzene ring corresponds to Ph-COF; single N substitution at the meta position of the benzene ring corresponds to mN-COF; single N substitution at the para position of the benzene ring corresponds to pN-COF; and single N substitution at the ortho position of the benzene ring corresponds to oN-COF.

[0012] Furthermore, the COF photocatalyst is preferably oN-COF obtained by single N substitution at the ortho position of the benzene ring.

[0013] The COF photocatalyst is prepared using a solvothermal method. Differently substituted ammonia monomers and aldehyde monomers are dissolved in a mixed solvent consisting of n-butanol, o-dichlorobenzene, and an aqueous acetic acid solution. The mixture is then placed in a Pyrex tube in a volume ratio of 7-10:1:1. After ultrasonic treatment and a freeze-pump-thaw cycle, the Pyrex tube is sealed under vacuum and placed in an oven at 100-140°C for a solvothermal reaction for 30-100 hours to form a yellow precipitate. The precipitate is then washed sequentially with tetrahydrofuran and acetone to obtain the product Ph-COF, mN-COF, pN-COF, or oN-COF.

[0014] Furthermore, the molar ratio of the ammonia monomer to the aldehyde monomer is 1.5-4:1, preferably 2-3:1.

[0015] Furthermore, the ultrasonic treatment time is 1-5 minutes, preferably 2-4 minutes.

[0016] Furthermore, freeze-pump-thaw cycles were achieved with liquid nitrogen at a temperature of 75-78K.

[0017] Furthermore, the freeze-pump-thaw cycle is performed 2-5 times, preferably 3-4 times.

[0018] Furthermore, the temperature of the solvothermal reaction is preferably 110-130°C, more preferably 115-120°C, and the time is preferably 60-100 hours, more preferably 70-80 hours. Furthermore, when the product is oN-COF, the ammonia monomer is prepared by the following method:

[0019] 2,4-Dibromopyridine, 4-aminophenylboronic acid pinacol ester, tetrakis(triphenylphosphine)palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere with stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is ammonia monomer;

[0020] When the product is Ph-COF, the ammonia monomer is prepared by the following method:

[0021] 1,3-Dibromobenzene, 4-aminophenylboronic acid pinacol ester, tetrakis(triphenylphosphine)palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere and stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is an ammonia monomer;

[0022] When the product is mN-COF, the ammonia monomer is prepared by the following method:

[0023] 2,6-dibromopyridine, 4-aminophenylboronic acid pinacol ester, tetrakistriphenylphosphine palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere with stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is ammonia monomer;

[0024] When the product is pN-COF, the ammonia monomer is prepared by the following method:

[0025] 3,5-Dibromopyridine, 4-aminophenylboronic acid pinacol ester, tetrakis(triphenylphosphine)palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere with stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is the ammonia monomer.

[0026] Furthermore, the aldehyde monomer is prepared by the following method:

[0027] Pd(PPh3)4 was added to a degassed mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole, 5-bromoisophthalaldehyde, K2CO3, 1,4-dioxane and water in a molar ratio of 1:(2-4):(4-7):(1.5×10 -2 -4×10 -2 ), the resulting mixture is heated to 80-120° C. under stirring and nitrogen atmosphere, and maintained for 10-16 hours, the reactant is cooled to room temperature and poured into water, and the residue is washed several times with excess water, methanol, toluene and chloroform to obtain an aldehyde monomer.

[0028] The COF photocatalyst is used for photocatalytic hydrogen production, pollutant degradation or carbon dioxide reduction in an acidic environment with a pH of ≤ 2, and good results can be achieved.

[0029] The beneficial effects of the present invention are:

[0030] (1) The preparation method of the present invention does not require toxic reagents and achieves high reproducibility of COF structure by precisely controlling the monomer substitution position.

[0031] (2) The COF photocatalyst obtained by the present invention has high activity, especially the oN-COF substituted with ortho-N has a photocatalytic hydrogen peroxide production rate of 3015 μmol·g -1 ·h -1 , which is significantly higher than the existing technology (such as 1.8 mmol·g reported by Zhang et al. -1 ·h -1 That is 1800 μmol·g -1 ·h -1 ).

[0032] (3) The COF photocatalyst obtained by the present invention has high stability, especially the oN-COF substituted with ortho-N, which maintains 92% of its activity after 5 cycles.

[0033] (4) The present invention reveals the regulation of the N substitution position on the photocatalytic activity in acidic environment and clarifies the mechanism of the structure-performance relationship. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Figure 2 is the XRD pattern of four COFs, showing sharp absorption peaks, proving good crystallinity.

[0035] Figure 2 This is the SEM image of Ph-COF, showing that COF is a one-dimensional columnar structure.

[0036] Figure 3 The SEM image of mN-COF shows that COF is a one-dimensional columnar structure.

[0037] Figure 4 The SEM image of pN-COF shows that COF is a one-dimensional columnar structure.

[0038] Figure 5 The SEM image of oN-COF shows that COF is a one-dimensional columnar structure.

[0039] Figure 6 This is a comparison chart of the photocatalytic hydrogen peroxide production rate, showing that oN-COF has the highest activity.

[0040] Figure 7Fourier transform infrared spectra of four COFs confirm the formation of imine bond (1627 cm -1 ). DETAILED DESCRIPTION

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0042] Example 1 Preparation of oN-COF (ortho-N substitution)

[0043] Step 1, synthesis of ammonia monomer:

[0044] 2,4-Dibromopyridine (1.19 g, 5.0 mmol), 4-aminophenylboronic acid pinacol ester (2.30 g, 10.5 mmol), tetrakis(triphenylphosphine)palladium (284 mg, 0.25 mmol), and potassium carbonate (2.07 g, 15 mmol) were stirred at reflux in dioxane / water (60 mL / 15 mL) under nitrogen for 72 hours. After cooling to room temperature, the solvent was removed under reduced pressure. The resulting residue was purified by column chromatography on alumina gel (200 mesh) using ethyl acetate / tetrahydrofuran (1 / 1 by volume) as the eluent. The resulting brown powder was ammonia monomer.

[0045] Step 2, synthesis of aldehyde monomer:

[0046] Pd(PPh) (30.0 mg) was added to a degassed mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole (0.20 g, 0.52 mmol), 5-bromoisophthalaldehyde (0.28 g, 1.30 mmol), KCO (0.43 g, 3.12 mmol), 1,4-dioxane (10.0 mL), and HO (10.0 mL). The resulting mixture was heated to 100°C with stirring under a nitrogen atmosphere for 14 hours. The reaction mixture was cooled to room temperature and poured into 100.0 mL of water. The residue was washed several times with excess water, methanol, toluene, and chloroform to obtain the aldehyde monomer.

[0047] Step 3, synthesis of oN-COF:

[0048] A Pyrex tube was charged with the synthesized ammonia monomer (19 mg, 0.08 mmol), aldehyde monomer (15 mg, 0.04 mmol), n-butanol (1.8 mL), o-dichlorobenzene (0.2 mL), and aqueous acetic acid (6 M, 0.2 mL). The tube was sonicated for 2 minutes and then rapidly frozen and degassed using liquid nitrogen at 77 K using three freeze-pump-thaw cycles. The tube was sealed under vacuum and subjected to solvothermal reaction in a 120°C oven for 72 hours, forming a yellow precipitate. The precipitate was isolated by filtration and washed with tetrahydrofuran, acetone, and ethanol, respectively. The sample was then dried in an oven at 60°C for 12 hours to obtain a yellow powder (yield 71%).

[0049] Example 2 Preparation of Ph-COF (without N substitution)

[0050] Step 1, synthesis of ammonia monomer:

[0051] 1,3-Dibromobenzene (1.18 g, 5.0 mmol), 4-aminophenylboronic acid pinacol ester (2.30 g, 10.5 mmol), tetrakis(triphenylphosphine)palladium (284 mg, 0.25 mmol), and potassium carbonate (2.07 g, 15 mmol) were stirred under reflux in dioxane / water (60 mL / 15 mL) under nitrogen for three days. After cooling to room temperature, the solvent was removed under reduced pressure. The resulting residue was purified by column chromatography on alumina gel (200 mesh) using ethyl acetate / tetrahydrofuran (1 / 1 by volume) as the eluent. The resulting brown powder was ammonia monomer.

[0052] Step 2, synthesis of aldehyde monomer:

[0053] Pd(PPh) (30.0 mg) was added to a degassed mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole (0.20 g, 0.52 mmol), 5-bromoisophthalaldehyde (0.28 g, 1.30 mmol), KCO (0.43 g, 3.12 mmol), 1,4-dioxane (10.0 mL), and HO (10.0 mL). The resulting mixture was heated to 100°C with stirring under a nitrogen atmosphere for 14 hours. The reaction mixture was cooled to room temperature and poured into 100.0 mL of water. The residue was washed several times with excess water, methanol, toluene, and chloroform to obtain the aldehyde monomer.

[0054] Step 3, Synthesis of Ph-COF:

[0055] A Pyrex tube was charged with the synthesized ammonia monomer (19 mg, 0.08 mmol), aldehyde monomer (15 mg, 0.04 mmol), n-butanol (1.8 mL), o-dichlorobenzene (0.2 mL), and aqueous acetic acid (6 M, 0.2 mL). The tube was sonicated for 2 minutes and then rapidly frozen and degassed using liquid nitrogen at 77 K using three freeze-pump-thaw cycles. The tube was sealed under vacuum and then subjected to solvothermal reaction in a 120°C oven for 72 hours, forming a brown precipitate. The precipitate was isolated by filtration and washed with tetrahydrofuran, acetone, and ethanol, respectively. The sample was then dried in an oven at 60°C for 12 hours to obtain a brown powder (83% yield).

[0056] Example 3 Preparation of mN-COF (meta-position N substitution)

[0057] Step 1, synthesis of ammonia monomer:

[0058] 2,6-Dibromopyridine (1.19 g, 5.0 mmol), 4-aminophenylboronic acid pinacol ester (2.30 g, 10.5 mmol), tetrakis(triphenylphosphine)palladium (284 mg, 0.25 mmol), and potassium carbonate (2.07 g, 15 mmol) were stirred under reflux in dioxane / water (60 mL / 15 mL) under nitrogen for 72 hours. After cooling to room temperature, the solvent was removed under reduced pressure. The resulting residue was purified by column chromatography on alumina gel (100-200 mesh) using ethyl acetate / petroleum ether (1 / 1) as eluent. The resulting brown powder was ammonia monomer.

[0059] Step 2, synthesis of aldehyde monomer:

[0060] Pd(PPh) (30.0 mg) was added to a degassed mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole (0.20 g, 0.52 mmol), 5-bromoisophthalaldehyde (0.28 g, 1.30 mmol), KCO (0.43 g, 3.12 mmol), 1,4-dioxane (10.0 mL), and HO (10.0 mL). The resulting mixture was heated to 100°C with stirring under a nitrogen atmosphere for 14 hours. The reaction mixture was cooled to room temperature and poured into 100.0 mL of water. The residue was washed several times with excess water, methanol, toluene, and chloroform to obtain the aldehyde monomer.

[0061] Step 3, synthesis of mN-COF:

[0062] A Pyrex tube was charged with the synthesized ammonia monomer (19 mg, 0.08 mmol), aldehyde monomer (15 mg, 0.04 mmol), n-butanol (1.8 mL), o-dichlorobenzene (0.2 mL), and aqueous acetic acid (6 M, 0.2 mL). The tube was sonicated for 2 minutes and then rapidly frozen and degassed using liquid nitrogen at 77 K using three freeze-pump-thaw cycles. The tube was sealed under vacuum and then subjected to solvothermal reaction in a 120°C oven for 72 hours. A yellow precipitate formed, which was isolated by filtration and washed with tetrahydrofuran, acetone, and ethanol, respectively. The sample was then dried in a 60°C oven for 12 hours to obtain a yellow powder (yield 65%).

[0063] Example 4 Preparation of pN-COF (para-N substitution)

[0064] Step 1, synthesis of ammonia monomer:

[0065] 3,5-Dibromopyridine (1.19 g, 5.0 mmol), 4-aminophenylboronic acid pinacol ester (2.30 g, 10.5 mmol), tetrakis(triphenylphosphine)palladium (284 mg, 0.25 mmol), and potassium carbonate (2.07 g, 15 mmol) were stirred under reflux in dioxane / water (60 mL / 15 mL) under nitrogen for 72 hours. After cooling to room temperature, the solvent was removed under reduced pressure. The resulting residue was purified by column chromatography on alumina gel (100-200 mesh) using ethyl acetate / petroleum ether (2 / 1) as the eluent. The resulting brown powder was ammonia monomer.

[0066] Step 2, synthesis of aldehyde monomer:

[0067] Pd(PPh) (30.0 mg) was added to a degassed mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole (0.20 g, 0.52 mmol), 5-bromoisophthalaldehyde (0.28 g, 1.30 mmol), KCO (0.43 g, 3.12 mmol), 1,4-dioxane (10.0 mL), and HO (10.0 mL). The resulting mixture was heated to 100°C with stirring under a nitrogen atmosphere for 14 hours. The reaction mixture was cooled to room temperature and poured into 100.0 mL of water. The residue was washed several times with excess water, methanol, toluene, and chloroform to obtain the aldehyde monomer.

[0068] Step 3, synthesis of pN-COF:

[0069] A Pyrex tube was charged with the synthesized ammonia (19 mg, 0.08 mmol), aldehyde (15 mg, 0.04 mmol), n-butanol (1.8 mL), o-dichlorobenzene (0.2 mL), and aqueous acetic acid (6 M, 0.2 mL). The tube was sonicated for 2 minutes and then rapidly frozen and degassed using liquid nitrogen at 77 K using three freeze-pump-thaw cycles. The tube was sealed under vacuum and subjected to solvothermal reaction in a 120°C oven for 72 hours, forming a yellow precipitate. The precipitate was isolated by filtration and washed with tetrahydrofuran, acetone, and ethanol, respectively. The sample was then dried in a 60°C oven for 12 hours to obtain a yellow powder (yield 78%).

[0070] The XRD patterns of the four COFs are as follows: Figure 1 As shown, from Figure 1 It can be seen that there is a very sharp absorption peak between 2 and 10°, proving the successful preparation of COF.

[0071] Scanning electron microscope (SEM) images of four COFs are shown below: Figures 2 to 5 As shown in the figure, it can be seen that the prepared COFs are all one-dimensional columnar.

[0072] Under acidic test conditions (pH = 2), the photocatalytic hydrogen peroxide production rates of the four COFs under visible light irradiation are shown in Table 1 and Figure 6 As shown by Figure 6 It can be seen that oN-COF reached an astonishing 3015 μmol·g -1 ·h -1 , surpassing most of the currently reported COF photocatalysts and showing excellent photocatalytic activity. This is because oN-COF has large and strong interfacial contacts, excellent visible light absorption ability, porous structure, spatially separated redox sites, and rapid separation of photoinduced charge carriers. The adjacent N forms a local charge center, which can significantly promote H + Adsorption.

[0073] Fourier infrared spectra of four COFs are shown in Figure 2. Figure 7 As shown, from Figure 7 Aldehyde groups (1700 cm -1 ) disappears, and the absorption peak of the imine bond (1627 cm -1 ) formation.

[0074] Table 1 Performance comparison of four groups of catalysts under the same acid test conditions (pH=2)

[0075]

[0076] Comparative Example 1 (Random N-substituted COF)

[0077] Synthesis method:

[0078] The ammonia monomers obtained in Examples 1, 3, and 4 were mixed in a molar ratio of 1:1:1, and then mixed in a molar ratio of 2:1 between the ammonia monomer and the aldehyde monomer. The solvothermal reaction conditions were the same as in Example 1 (120°C / 72 hours). The resulting product was a mixed N-substituted COF (denoted as mixN-COF).

[0079] Performance testing:

[0080] Photocatalytic hydrogen peroxide production rate: 1420 μmol·g -1 ·h -1 (pH=2).

[0081] Cycling stability: The activity dropped to 65% after 5 cycles.

[0082] Experimental results show that mixed N substitution leads to disordered COF structure, low efficiency of photogenerated carrier separation, and significantly lower activity and stability than precisely controlled oN-COF.

[0083] Comparative Example 2 (Stability of COF without N Substitution under Acidic Conditions)

[0084] Test method:

[0085] Ph-COF (without N substitution) was placed in an acidic solution with pH = 1 and continuously exposed to light for 12 hours to observe the structural changes and activity decay.

[0086] Test results:

[0087] Initial activity: hydrogen peroxide production rate of 580 μmol·g -1 ·h -1 .

[0088] After 12 hours: the material skeleton collapsed and the activity dropped to 305 μmol·g -1 ·h -1 , and cannot be recovered.

[0089] Meanwhile, in acidic conditions at pH = 1, the stability of COFs with other N substitutions (especially the ortho position) is hardly affected.

[0090] Experimental results show that COF without N substitution is more susceptible to protonation as the acidity further increases, resulting in poor skeleton stability, while N substitution (especially at the ortho position) effectively inhibits protonation and improves stability through local charge regulation.

Claims

1. A COF photocatalyst based on precise regulation of benzene ring nitrogen sites, characterized in that: The COF benzene ring has a precisely controlled N substitution position, which is a single N substitution at the ortho position, meta position, or para position of the benzene ring; a single N substitution at the meta position of the benzene ring corresponds to mN-COF; a single N substitution at the para position of the benzene ring corresponds to pN-COF; a single N substitution at the ortho position of the benzene ring corresponds to oN-COF; The method for preparing a COF photocatalyst based on precise regulation of the nitrogen site of the benzene ring adopts a solvothermal method. Differently substituted ammonia monomers and aldehyde monomers are dissolved in a mixed solvent consisting of n-butanol, o-dichlorobenzene, and an aqueous acetic acid solution. The mixture is then placed in a Pyrex tube in a volume ratio of n-butanol, o-dichlorobenzene, and an aqueous acetic acid solution of 7-10:1:

1. After ultrasonic treatment and a freeze-pump-thaw cycle, the Pyrex tube is sealed under vacuum and placed in an oven at 100-140°C for a solvothermal reaction for 30-100 hours to form a yellow precipitate. The product mN-COF, pN-COF, or oN-COF is then washed sequentially with tetrahydrofuran and acetone. When the product is oN-COF, the ammonia monomer is prepared by the following method: 2,4-Dibromopyridine, 4-aminophenylboronic acid pinacol ester, tetrakis(triphenylphosphine)palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere with stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is ammonia monomer; When the product is mN-COF, the ammonia monomer is prepared by the following method: 2,6-dibromopyridine, 4-aminophenylboronic acid pinacol ester, tetrakistriphenylphosphine palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere with stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is ammonia monomer; When the product is pN-COF, the ammonia monomer is prepared by the following method: 3,5-Dibromopyridine, 4-aminophenylboronic acid pinacol ester, tetrakis(triphenylphosphine)palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere with stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is ammonia monomer; The aldehyde monomer is prepared by the following method: Pd(PPh3)4 was added to a degassed mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole, 5-bromoisophthalaldehyde, K2CO3, 1,4-dioxane and water in a molar ratio of 1:(2-4):(4-7):(1.5×10 -2 -4×10 -2 ), heating the resulting mixture to 80-120° C. under stirring and nitrogen atmosphere and maintaining for 10-16 hours, cooling the reactant to room temperature and pouring into water, and washing the residue with excess water, methanol, toluene and chloroform several times to obtain an aldehyde monomer; The molar ratio of the ammonia monomer to the aldehyde monomer is 1.5-4:

1.

2. The COF photocatalyst based on precise regulation of benzene ring nitrogen sites according to claim 1, characterized in that: The COF photocatalyst is oN-COF obtained by single N substitution at the ortho position of the benzene ring.

3. The method for preparing a COF photocatalyst based on precise regulation of benzene ring nitrogen sites according to claim 1 or 2, characterized in that: The preparation method is a solvothermal method. Differently substituted ammonia monomers and aldehyde monomers are dissolved in a mixed solvent consisting of n-butanol, o-dichlorobenzene, and aqueous acetic acid. The mixture is then placed in a Pyrex tube in a volume ratio of 7-10:1:

1. After ultrasonic treatment and freeze-pump-thaw cycles, the Pyrex tube is sealed under vacuum and placed in an oven at 100-140°C for solvothermal reaction for 30-100 hours to form a yellow precipitate. The product mN-COF, pN-COF, or oN-COF is then washed with tetrahydrofuran and acetone, respectively. When the product is oN-COF, the ammonia monomer is prepared by the following method: 2,4-Dibromopyridine, 4-aminophenylboronic acid pinacol ester, tetrakis(triphenylphosphine)palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere with stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is ammonia monomer; When the product is mN-COF, the ammonia monomer is prepared by the following method: 2,6-dibromopyridine, 4-aminophenylboronic acid pinacol ester, tetrakistriphenylphosphine palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere with stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is ammonia monomer; When the product is pN-COF, the ammonia monomer is prepared by the following method: 3,5-Dibromopyridine, 4-aminophenylboronic acid pinacol ester, tetrakis(triphenylphosphine)palladium, and potassium carbonate are dissolved in a dioxane-water mixed solvent at a molar ratio of 1:1.5-2.5:0.01-0.03:2-4, followed by reflux reaction under nitrogen atmosphere with stirring for 40-80 hours. After completion of the reaction, the mixture is cooled to room temperature, the solvent is removed under reduced pressure, and the resulting residue is purified by column chromatography to obtain a brown powder, which is ammonia monomer; The aldehyde monomer is prepared by the following method: Pd(PPh3)4 was added to a degassed mixture of 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole, 5-bromoisophthalaldehyde, K2CO3, 1,4-dioxane and water in a molar ratio of 1:(2-4):(4-7):(1.5×10 -2 -4×10 -2 ), heating the resulting mixture to 80-120° C. under stirring and nitrogen atmosphere and maintaining for 10-16 hours, cooling the reactant to room temperature and pouring into water, and washing the residue with excess water, methanol, toluene and chloroform several times to obtain an aldehyde monomer; The molar ratio of the ammonia monomer to the aldehyde monomer is 1.5-4:

1.

4. The preparation method according to claim 3, characterized in that The duration of ultrasonic treatment is 1-5 minutes.

5. The preparation method according to claim 3, characterized in that Freeze-pump-thaw cycles were achieved with liquid nitrogen at a temperature of 75-78 K, and freeze-pump-thaw cycles were repeated 2-5 times.

6. The preparation method according to claim 3, characterized in that The temperature of the solvent thermal reaction is 110-130°C and the time is 60-100 hours.

7. Use of the COF photocatalyst based on precise control of benzene ring nitrogen sites according to claim 1 or 2, or the COF photocatalyst based on precise control of benzene ring nitrogen sites obtained by the preparation method according to any one of claims 3 to 6 in photocatalytic hydrogen production, pollutant degradation or carbon dioxide reduction in an acidic environment with a pH ≤ 2.

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