Chemically bonded heterostructure photocatalyst based on pyrenyl covalent organic framework, preparation method and application

Abstract

The invention relates to a chemical bonding type heterostructure photocatalyst based on a pyrenyl covalent organic framework as well as a preparation method and application of the chemical bonding type heterostructure photocatalyst based on the pyrenyl covalent organic framework. The catalyst is prepared from the following raw materials: 1, 3, 6, 8-tetra (p-aminophenyl) pyrene, 2, 5-dimethoxy terephthalaldehyde or terephthalaldehyde or 4, 4 '-biphenyldicarboxaldehyde and g-C3N4; the expression of the obtained catalyst is as follows: XTAPPy-DMTP-CN or XTAPPy-TPA-CN or XTAPPy-BPDA-CN, X is the mass fraction of TAPPy-DMTP-COF or TAPPy-TPA-COF or TAPPy-BPDA-COF, and the numerical range of X is 10 to 50 percent; according to the technical scheme, the interface driving force can be improved, the charge transfer path is optimized, and the photocatalytic performance of the material is further improved by introducing the pyrenyl unit and the oxidation-reduction active sites.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalytic materials, and particularly relates to a TAPPy-DMTP-COF / g-C 3 N 4 composite photocatalyst prepared by an in-situ growth method and its application in the oxidation of low-concentration (ppb level) nitrogen oxides (NO). This technology is widely used in the fields of air pollution control, environmental purification, photocatalytic oxidation reactions, etc. Background Art

[0002] Nitrogen oxides (NOx) are one of the main components of air pollution, and their harm to human health and the environment is significant, including inducing respiratory diseases, forming acid rain, and consuming ozone. Although many technologies such as adsorption, catalytic reduction, and photocatalysis have been used for NOx treatment, there are still problems of insufficient efficiency when dealing with low-concentration NO (ppb level). Photocatalytic technology has received extensive attention due to its advantages of high efficiency, environmental friendliness, and low energy consumption, especially showing potential in the oxidation of low-concentration NO. However, the performance of traditional photocatalytic materials is still limited by the rapid recombination of electron-hole pairs, limited light absorption ability, and insufficient reactive sites, and there is an urgent need to further optimize the material design and preparation process.

[0003] Graphitic carbon nitride (g-C 3 N 4 ) has been widely used in photocatalytic research due to its moderate bandgap (~2.7 eV), high chemical stability, and low synthesis cost. However, its performance is limited by inherent defects such as high electron-hole recombination rate, low specific surface area, and limited light absorption ability. For example, the g-C 3 N 4 prepared by a simple calcination method has a removal efficiency of only 25.1% in the photocatalytic oxidation of 800 ppb NO, far from meeting the actual application requirements. Therefore, researchers have tried to improve its photocatalytic performance through defect engineering, element doping, and heterostructure construction.

[0004] Constructing heterostructures has been proven to be an effective means to improve the performance of g-C 3 N 4 For example, Wu et al. constructed a Z-scheme heterojunction by combining g-C 3 N 4 with BiOIO 3 to increase the photocatalytic efficiency to 46.9%. However, the interface of such heterojunctions is usually dominated by van der Waals forces, and the interface driving force is weak, resulting in limited separation efficiency of photo-generated carriers. In addition, the electron transfer path between materials in the heterostructure is long, further hindering the improvement of the catalytic reaction efficiency.

[0005] Covalent organic frameworks (COFs) have emerged as novel materials in the field of photocatalysis due to their high specific surface area, tunable electronic structure, and excellent chemical stability. In recent years, by introducing specific functional groups (such as carbonyl and amino groups) into COF materials and optimizing the pore structure, their photocatalytic performance has been significantly improved. For example, Dong et al. reported a pyridine-based COF material, whose efficiency in photocatalytic hydrogen production was enhanced by introducing oxygen atoms. In addition, the application of in-situ growth technology further optimized the interfacial connection of COF composites, enabling them to bind to the substrate material through chemical bonds, thereby enhancing the separation efficiency of photo-generated carriers and the light absorption ability. Summary of the Invention

[0006] Aiming at the above deficiencies of the prior art, this application provides a chemical-bonded heterostructure photocatalyst based on pyrene-based covalent organic frameworks, which can improve the interfacial driving force and optimize the charge transfer path, and further enhance the photocatalytic performance of the material by introducing pyrene units and redox active sites.

[0007] To solve the above technical problems, the technical solution adopted in this application is as follows: A chemical-bonded heterostructure photocatalyst based on pyrene-based covalent organic frameworks, the preparation raw materials of the catalyst include: 1,3,6,8-tetra(4-aminophenyl)pyrene, 2,5-dimethoxyterephthalaldehyde (DMTP) or terephthalaldehyde (TPA) or 4,4'-biphenyldicarboxaldehyde (BPDA), g-C 3 N 4 ; The obtained catalyst is expressed as: XTAPPy-DMTP-CN or XTAPPy-TPA-CN or XTAPPy-BPDA-CN, where X is the mass fraction of TAPPy-DMTP-COF or TAPPy-TPA-COF or TAPPy-BPDA-COF in the catalyst (that is, the mass fraction of TAPPy-DMTP-COF or TAPPy-TPA-COF or TAPPy-BPDA-COF in the corresponding catalyst TAPPy-DMTP-CN or TAPPy-TPA-CN or TAPPy-BPDA-CN), and the value range of X is 10-50%.

[0008] Further, the obtained catalyst is expressed as: XTAPPy-DMTP-CN, where X is the mass fraction of TAPPy-DMTP-COF, and the value range of X is 10-50%.

[0009] This application also provides a preparation method of the above chemical-bonded heterostructure photocatalyst based on pyrene-based covalent organic frameworks, and the process includes:

[0010] (1) g-C 3 N4 (CN) Preparation: Put melamine into an aluminum oxide crucible, heat it to 500 - 600 °C and maintain for 3 - 5 hours;

[0011] (2) Preparation of TAPPy - DMTP - CN or XTAPPy - TPA - CN or XTAPPy - BPDA - CN: Mix 1,3,6,8 - tetra(4 - aminophenyl)pyrene (TAPPy), 2,5 - dimethoxyterephthalaldehyde (DMTP) or terephthalaldehyde (TPA) or 4,4'-biphenyldicarboxaldehyde (BPDA), g - C 3 N 4 Mix; dissolve the mixture in a mixed solution of N,N - dimethylacetamide (DMAc) and o - dichlorobenzene (o - DCB), then add acetic acid, and ultrasonically treat at room temperature for 20 - 40 minutes; after three freeze - pump - thaw cycles, heat to 110 - 130 °C and maintain for 60 - 80 hours; the obtained product is washed with tetrahydrofuran, subjected to Soxhlet extraction, and vacuum - dried. The expression of the obtained catalyst is: XTAPPy - DMTP - CN or XTAPPy - TPA - CN or XTAPPy - BPDA - CN, where X is the mass fraction of TAPPy - DMTP - COF or TAPPy - TPA - COF or TAPPy - BPDA - COF, and the value range of X is 10 - 50%.

[0012] Furthermore, the molar ratio of 1,3,6,8 - tetra(4 - aminophenyl)pyrene (TAPPy) to 2,5 - dimethoxyterephthalaldehyde (DMTP) or terephthalaldehyde (TPA) or 4,4'-biphenyldicarboxaldehyde (BPDA) described in step (2) is 1:1 - 3.

[0013] Even further, the molar ratio of 1,3,6,8 - tetra(4 - aminophenyl)pyrene (TAPPy) to 2,5 - dimethoxyterephthalaldehyde (DMTP) or terephthalaldehyde (TPA) or 4,4'-biphenyldicarboxaldehyde (BPDA) described in step (2) is 1:1.5 - 2.5.

[0014] Furthermore, the volume ratio of N,N - dimethylacetamide to o - dichlorobenzene (o - DCB) described in step (2) is 2 - 4:1.

[0015] Furthermore, the acetic acid described in step (2) is a 5 - 7 mol / L acetic acid solution.

[0016] Furthermore, the ultrasonication treatment at room temperature described in step (2) is for 25 - 35 minutes.

[0017] Furthermore, heat to 115 - 125 °C and maintain for 70 - 75 hours in step (2).

[0018] Further, the Soxhlet extraction in step (2) is carried out for 22 - 25 hours.

[0019] Further, the expression of the catalyst in step (2) is: XTAPPy - DMTP - CN, where X is the mass fraction of TAPPy - DMTP - COF, and the numerical range of X is 10 - 50%.

[0020] Further, the molar ratio of 1,3,6,8 - tetrakis(4 - aminophenyl)pyrene (TAPPy) to g - C 3 N 4 in step (2) is 1:10 - 52.

[0021] This application also provides an application of the obtained chemical - bond - type heterostructure photocatalyst based on pyrene - based covalent organic framework in the photocatalytic oxidation of NO.

[0022] Advantages and beneficial effects of this application:

[0023] 1. In this application, by compounding a COF material with multi - pores and high specific surface area on the surface of g - C 3 N 4 the light absorption range of the overall material and the adsorption capacity for NO are improved; by optimizing the COF structure, introducing additional - OCH 3 functional groups and optimizing the COF structural units, the photocatalytic oxidation efficiency of the pyrene - based COF material for NO is enhanced; through the principle of Schiff - base reaction, - NH 3 N 4 on g - C 2 condenses with - CHO on the COF to generate - H - C = N - H chemical bonds, thereby constructing a stable chemical - bond - type heterostructure and enhancing the interfacial driving force and electron communication ability.

[0024] 2. This application first optimizes the structural units of the pyrene - based COF material. During the synthesis process, by replacing the TPA monomer with the monomer DMTP with an additional - OCH 3 group, an additional - OCH 3 functional group is introduced, and by replacing BPDA with TPA with a smaller molecular structure to optimize the structural unit length, the best - performing pyrene - based COF material (TAPPy - DMTP - COF) is determined; the main reason is - OCH 3The functional group has a strong electron-withdrawing ability, which can regulate the electron distribution of COF, improve the separation efficiency of photo-generated charges, and provide more active adsorption sites for NO, enhancing its oxidation activity. In addition, COF with shorter structural units has a higher specific surface area and a more uniform pore distribution, which is conducive to the rapid adsorption, diffusion, and reaction of NO molecules, significantly improving its photocatalytic efficiency. Finally, by in-situ growing TAPPy-DMTP-COF on the surface of g-C 3 N 4 A type II heterojunction connected by chemical bonds was constructed, further improving the photocatalytic degradation efficiency of NO. The effects and advantages are as follows:

[0025] (2.1) Optimized pyrene-based COF material: Through experimental results, it was determined that the COF material with shorter unit structures can reduce the electron transport distance, thereby enhancing the electron communication between COF and g-C 3 N 4 composite material; The additional -OCH 3 functional group can serve as an additional NO adsorption and reaction site, further enhancing the photocatalytic oxidation of NO;

[0026] (2.2) Significantly improved photocatalytic performance: The 40DAPPy-DMTP-COF / g-C 3 N 4 heterostructure had a photocatalytic removal efficiency of 45.8% under 800 ppb NO conditions, significantly higher than that of pure g-C 3 N 4 (25.1%) and single COF material (38.2%); Due to its ability to regulate the electronic structure and reaction path, first, the -OCH 3 functional group can promote the generation of reactive oxygen species (such as O 2 - · and ·OH) by adjusting the electron density on the COF surface, and these species tend to oxidize NO to a more stable NO 3 - form rather than intermediate products (such as NO 2 ); Second, the COF with short structural units provides more uniform and active reaction sites, restricting the occurrence of side reactions and preferentially forming NO 3 - products; At the same time, the regular pore structure of COF optimizes the mass transfer of NO and oxidation intermediates, making the reaction path more inclined to selective oxidation to NO 3 - ; Therefore, its selectivity for NO 3 -The selectivity reached 97.4%, much higher than that of traditional catalysts; after 600 minutes of continuous light irradiation, the photocatalytic efficiency decreased by less than 5%, indicating that the composite material has excellent stability and reusability;

[0027] (2.3) Optimized heterojunction interface: Chemical bond-connected heterojunction: During the photocatalytic process, electrons are transmitted through the -H-C=N-H- bond, making the electron transmission more accurate and rapid, and further strengthening the electron communication ability between composite materials; Interface growth: The porous COF material grows in-situ on g-C 3 N 4 to make up for the shortcomings of g-C 3 N 4 and enhance the light / NO absorption ability of the composite material. Brief Description of the Drawings

[0028] Figure 1 Molecular structures of TAPPy-TPA-COF, TAPPy-DMTP-COF, and TAPPy-BPDA-COF.

[0029] Figure 2 (a) Schematic illustration of the synthesis process of TAPPy-DMTP-COF, (b) experimental and simulated PXRD patterns of TAPPy-DMTP-COF, (c) PXRD patterns of CN, TAPPy-DMTP-COF, and 40TAPPy-DMTP-CN, and (d) FT-IR results.

[0030] Figure 3 (a) SEM results of CN, (b) TAPPy-DMTP-COF, (c) 40TAPPy-DMTP-CN, and (d) structural diagram of TAPPy-DMTP-COF.

[0031] Figure 4 (a) Efficiency comparison among TAPPy-DMTP-COF, TAPPy-TPA-COF, and TAPPy-BPDA-COF, and (b) efficiency comparison of TAPPy-DMTP-CN with different mass fractions of TAPPy-DMTP-COF. (c) Selectivity of CN, TAPPy-DMTP-COF, and 40TAPPy-DMTP-CN. (d) Cycling experiment results of 40TAPPy-DMTP-CN. (e) X-ray diffraction (PXRD) results of 40TAPPy-DMTP-CN before and after the reaction. (f) Trapping experiment results of 40TAPPy-DMTP-CN. Detailed Description of the Invention

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments and the accompanying drawings. Obviously, the described embodiments are only preferred embodiments, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0033] The g-C 3 N 4 (CN) used in the following examples of the present application can be obtained by the following method: Put 4 grams of melamine into a 30-milliliter aluminum oxide crucible (alumina crucible) with a lid, then heat it to 550 °C and maintain it for 4 hours to obtain the final sample; heat it during the use process, and the obtained powder is ground for standby.

[0034] Example 1:

[0035] 50TAPPy-DMTP-CN: Mix 28.33 mg of 1,3,6,8-tetra(4-aminophenyl)pyrene (TAPPy) (0.05 mmol), 19.41 mg of 2,5-dimethoxyterephthalaldehyde (DMTP) (0.1 mmol) and 47.74 mg of g-C 3 N 4 ; Dissolve the mixture in 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of ortho-dichlorobenzene (o-DCB), then add 0.2 mL of 6 mol / L acetic acid, and ultrasonically treat it at room temperature for 30 minutes; then after three freeze-pump-thaw cycles (this process is to freeze the mixed solution and raw materials, then evacuate to reduce the pressure in the reaction vessel, and then thaw. When thawing, the gas dissolved in the solution will bubble out, and then freeze, evacuate, and thaw again. Three operations can suck out those gases to ensure that there is no oxygen in the whole synthesis process), heat the reaction tube to 120 °C and maintain it for 72 hours. The obtained COF is washed with tetrahydrofuran, extracted by Soxhlet extraction for 24 hours, and dried in vacuum at 60 °C to obtain a 50% mass fraction of TAPPy-DMTP-COF composite material, which is denoted as 50TAPPy-DMTP-CN.

[0036] Example 2:

[0037] 30TAPPy-DMTP-CN: Mix 28.33 mg of 1,3,6,8-tetra(4-aminophenyl)pyrene (TAPPy) (0.05 mmol), 19.41 mg of 2,5-dimethoxyterephthalaldehyde (DMTP) (0.1 mmol) and 79.57 mg of g-C 3 N 4Mixing. The mixture was dissolved in 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of ortho-dichlorobenzene (o-DCB), then 0.2 mL of 6 mol / L acetic acid was added, and the mixture was sonicated at room temperature for 30 minutes. After three freeze-pump-thaw cycles, the reaction tube was heated to 120 °C and maintained for 72 hours. The obtained COF was washed with tetrahydrofuran, Soxhlet extracted for 24 hours, and vacuum dried at 60 °C to obtain a 30% mass fraction of TAPPy-DMTP-COF composite material, denoted as 30TAPPy-DMTP-CN.

[0038] Example 3:

[0039] 40TAPPy-DMTP-CN: 28.33 mg of 1,3,6,8-tetra(4-aminophenyl)pyrene (TAPPy) (0.05 mmol) was mixed with 19.41 mg of 2,5-dimethoxyterephthalaldehyde (DMTP) (0.1 mmol) and 59.68 mg of g-C 3 N 4 Mixing. The mixture was dissolved in 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of ortho-dichlorobenzene (o-DCB), then 0.2 mL of 6 mol / L acetic acid was added, and the mixture was sonicated at room temperature for 30 minutes. After three freeze-pump-thaw cycles, the reaction tube was heated to 120 °C and maintained for 72 hours. The obtained COF was washed with tetrahydrofuran, Soxhlet extracted for 24 hours, and vacuum dried at 60 °C to obtain a 50% mass fraction of TAPPy-DMTP-COF composite material, denoted as 40TAPPy-DMTP-CN.

[0040] Comparative Example 1:

[0041] Preparation of TAPPy-DMTP-COF: 28.33 mg of 1,3,6,8-tetra(4-aminophenyl)pyrene (TAPPy) (0.05 mmol) was mixed with 19.41 mg of 2,5-dimethoxyterephthalaldehyde (DMTP) (0.1 mmol). The mixture was dissolved in 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of ortho-dichlorobenzene (o-DCB), then 0.2 mL of 6 mol / L acetic acid was added, and the mixture was sonicated at room temperature for 30 minutes. After three freeze-pump-thaw cycles, the reaction tube was heated to 120 °C and maintained for 72 hours. The obtained COF was washed with tetrahydrofuran, Soxhlet extracted for 24 hours, and vacuum dried at 60 °C to obtain TAPPy-DMTP-COF.

[0042] Comparative Example 2:

[0043] Preparation of TAPPy-TPA-COF: 28.33 mg of TAPPy (0.05 mmol) was mixed with 13.41 mg of terephthalaldehyde (TPA) (0.1 mmol). The mixture was dissolved in 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of o-dichlorobenzene (o-DCB), then 0.2 mL of 6 mol / L acetic acid was added, and the mixture was sonicated for 30 minutes at room temperature. After three freeze-pump-thaw cycles, the reaction tube was heated to 120 °C and maintained for 72 hours. The obtained COF was washed with tetrahydrofuran, extracted by Soxhlet extraction for 24 hours, and dried in vacuo at 60 °C to obtain TAPPy-TPA-COF.

[0044] Subsequently, the photocatalytic oxidation activity test of NO was carried out according to the procedure of Example 1.

[0045] Comparative Example 3:

[0046] Preparation of TAPPy-BPDA-COF: 28.33 mg of TAPPy (0.05 mmol) was mixed with 21.02 mg of 4,4'-biphenyldicarboxaldehyde (BPDA) (0.1 mmol). The mixture was dissolved in 1.5 mL of N,N-dimethylacetamide (DMAc) and 0.5 mL of o-dichlorobenzene (o-DCB), then 0.2 mL of 6 mol / L acetic acid was added, and the mixture was sonicated for 30 minutes at room temperature. After three freeze-pump-thaw cycles, the reaction tube was heated to 120 °C and maintained for 72 hours. The obtained COF was washed with tetrahydrofuran, extracted by Soxhlet extraction for 24 hours, and dried in vacuo at 60 °C to obtain TAPPy-BPDA-COF. Product activity detection method:

[0047] The activity of the catalyst for photocatalytic oxidation of NO was evaluated in a continuous-flow cubic reactor. The reactor was made of quartz (20×15×10 cm) and covered with aluminum foil on all sides except the top. Before each experiment, 0.2 g of the prepared catalyst was mixed with 15 mL of deionized water and sonicated for 15 minutes. Then, the mixture was placed in a glass dish with a diameter of 12 cm and dried in vacuo at 60 °C for 6 hours. After that, the glass dish was placed at the center of the cubic reactor. The light source was a 300 W xenon lamp equipped with a 420 nm cut-off filter, which was vertically placed 20 cm above the catalyst surface. During the photocatalytic reaction, from the compressed gas cylinder (N 2The 50 ppm NO provided by the [equilibrium] was diluted to 800 ppb by a pure air stream and flowed through the sample surface. The total flow rate in the reactor was 2 L / min. When the adsorption-desorption equilibrium between NO and the catalyst was reached, the xenon lamp was turned on to initiate the photocatalytic NO oxidation reaction. The light intensity measured with a power meter placed vertically 20 cm below the lamp was 1.516 W. During the entire reaction process, the concentrations of NO and NO 2 were measured and recorded by a NOx analyzer, and the photocatalytic efficiency of NO was calculated according to the following formula: where, C 0 (ppb) is the NO concentration at the start of the reaction, and C (ppb) is the NO concentration at a given time.

[0048] For the test results of the examples and comparative examples of this application, specifically refer to the attached Figures 1-4 .

[0049] Figure 1 are the molecular structures of TAPPy-TPA-COF, TAPPy-DMTP-COF, and TAPPy-BPDA-COF prepared for the comparative examples of the application.

[0050] Figure 2 (a) Explanation of the synthesis process of TAPPy-DMTP-COF, (b) experimental and simulated PXRD patterns of TAPPy-DMTP-COF, (c) PXRD patterns of CN, TAPPy-DMTP-COF, and 40TAPPy-DMTP-CN, and (d) FT-IR results; the phase structures of CN, TAPPy-DMTP-COF, and TAPPy-DMTP-CN were analyzed by powder X-ray diffraction (PXRD). As Figure 2 (b) shows, the PXRD pattern is in good agreement with the simulated results of DFT calculations, indicating the minimum structural change and confirming the successful synthesis of the conjugated structure of TAPPy-DMTP-COF. Among them, TAPPy-DMTP-COF shows characteristic peaks at 3.9°, 4.8°, and 7.7°, corresponding to the (100), (110), and (001) planes, respectively. In addition, it was observed that the PXRD pattern of CN is in good agreement with the reference pattern of CN (PDF 87-1526#), indicating that the structural integrity of CN is maintained; further research was extended to the composite sample TAPPy-DMTP-CN, and its PXRD pattern was compared with those of pure CN and TAPPy-DMTP-COF, as Figure 2(c) As shown; it is worth noting that the PXRD pattern of the composite material shows peaks of both the COF and CN components simultaneously, indicating that the combination process maintains the structural integrity of the two materials; therefore, the PXRD results clearly confirm the successful synthesis of the TAPPy-DMTP-CN composite material; the observed integrated structural stability emphasizes the effectiveness of the in-situ growth method in retaining the inherent structures of TAPPy-DMTP-COF and CN, thus promoting the formation of a binary heterostructure with good photocatalytic potential; the Fourier transform infrared spectroscopy results show the transmittance peak spectra of different samples; as Figure 2 (d) shown, the spectra of CN, TAPPy-DMTP-COF, and 40TAPPy-DMTP-CN are basically similar; all spectra show a broader transmittance in the 3100 - 3700 cm -1 region, which may correspond to the N-H stretching vibration of amine or amide groups. There is an obvious peak at 1576 cm -1 , which is a typical C=C stretching vibration of aromatic compounds, while there is an obvious peak near 1285 cm -1 , which is a characteristic peak of C-N stretching vibration of aromatic amines; in addition, there is an obvious peak at 1644 cm -1 , which is consistent with the C=N stretching vibration and is usually found in Schiff base or imine compounds; these findings confirm the presence of graphite and aromatic nitrogen compounds in the synthesized materials and emphasize the successful in-situ growth of CN with the newly synthesized TAPPy-DMTP-COF to form the TAPPy-DMTP-CN composite material.

[0051] Figure 3 (a) SEM results of CN, (b) TAPPy-DMTP-COF, (c) 40TAPPy-DMTP-CN, and (d) structural diagram of TAPPy-DMTP-COF; SEM analysis shows that the synthesized samples have obvious morphological characteristics. Figure 3 (a)'s SEM image shows the typical smooth nanosheet structure of CN, indicating a uniform crystal structure and confirming the successful synthesis of CN. In contrast, Figure 3 (b) shows that the morphology of TAPPy-DMTP-COF is significantly different, characterized by many clusters. After in-situ growth of TAPPy-DMTP-COF on CN, Figure 3 (c) highlights the hybrid structure of the composite material, with TAPPy-DMTP-COF clusters growing on the smooth nanosheets of CN. This interface indicates the successful formation of a heterojunction, potentially providing a synergistic effect beneficial to photocatalytic activity. The SEM images provide strong evidence for the successful synthesis of TAPPy-DMTP-CN, retaining the crystal structure and indicating possible interactions between components.

[0052] Figure 4 (a) Efficiency comparison among TAPPy-DMTP-COF, TAPPy-TPA-COF and TAPPy-BPDA-COF, and (b) efficiency comparison of TAPPy-DMTP-CN with different mass fractions of TAPPy-DMTP-COF; (c) selectivity of CN, TAPPy-DMTP-COF and 40TAPPy-DMTP-CN; (d) cyclic experiment results of 40TAPPy-DMTP-CN; (e) X-ray diffraction (PXRD) results of 40TAPPy-DMTP-CN before and after reaction; (f) capture experiment results of 40TAPPy-DMTP-CN; Integrate CN with the previously optimized TAPPy-DMTP-COF to explore its synergistic effect on the photocatalytic oxidation efficiency of NO; As Figure 4 (b) shows that the photocatalytic efficiency of pure g-C 3 N 4 is 25.1%, while the efficiency of single TAPPy-DMTP-COF is 38.2%; Subsequently, TAPPy-DMTP-COF was mixed with CN, and the photocatalytic efficiency of the obtained composite exceeded that of the single component. When the mass fraction of TAPPy-DMTP-COF was 40%, the photocatalytic efficiency of the composite reached 45.8%; This significant increase is attributed to the strong interaction between TAPPy-DMTP-COF and CN, which enhances charge separation and transfer; However, when the mass fraction exceeds 40%, its efficiency will decrease; This phenomenon may be due to the aggregation of excessive TAPPy-DMTP-COF, which hinders the interaction interface between components and thus hinders the key charge transfer process; Therefore, the CN composite of 40% TAPPy-DMTP-COF (40TAPPy-DMTP-CN) is the most effective photocatalyst; Compared with the previous g-C 3 N 4 -based photocatalysts, 40TAPPy-DMTP-CN shows significantly higher efficiency, demonstrating its strong potential for photocatalytic oxidation of NO by in-situ growth of COF on g-C 3 N 4 nanosheets; The chemically bonded composite not only optimizes the heterostructure interface between g-C 3 N 4 and TAPPy-DMTP-CN, but also provides a porous structure for the active sites on g-C 3 N 4 , improving the photocatalytic performance of g-C 3 N 4 ; In the selectivity study, as Figure 4 (c) shows, we found that the composite 40TAPPy-DMTP-CN not only has the best photocatalytic efficiency, but also has the best performance for NO3 - The formation also has better selectivity, with a selectivity of 97.4%; the high selectivity of the composite material indicates that it can effectively inhibit competitive side reactions, thus directing the photocatalytic pathway towards the production of nitrate; this enhancement of selectivity can be attributed to the synergistic interaction within the composite material, where the TAPPy-DMTP-COF component may selectively adsorb and convert NO 2 and provide additional active sites; in addition, the intimate interface between TAPPy-DMTP-COF and CN promotes carrier dynamics, which may play a role in improving selectivity, and the formation of the heterostructure ensures that sufficient photo-generated electrons participate in the photocatalytic reaction. Figure 4 (d) shows the stability results. It is found that after five consecutive cycles, the photocatalytic efficiency slightly decreases, from the initial 45.8% to 40.8%; the catalyst prepared in this application is mainly aimed at the photocatalytic removal of indoor NO. For example, when cooking in the kitchen or using a coal-burning fireplace, the indoor NO is higher than 600 ppb, and this concentration exceeds the health standard; through this example, the catalyst prepared in this application can reduce the concentration of NO at 600 ppb to more than 300 ppb, greatly reducing the long-term harm of low-concentration NO to humans.

Claims

1. A chemically bonded heterostructure photocatalyst based on a pyrene-based covalent organic framework, characterized in that: The catalyst is prepared by raw materials comprising: 1,3,6,8-tetrakis(p-aminophenyl)pyrene, 2,5-dimethoxyterephthalaldehyde or terephthalaldehyde or 4,4'-biphenyldicarboxaldehyde, and g-C3N4; the obtained catalyst is expressed as: XTAPPy-DMTP-CN or XTAPPy-TPA-CN or XTAPPy-BPDA-CN, wherein X is the mass fraction of TAPPy-DMTP-COF or TAPPy-TPA-COF or TAPPy-BPDA-COF, and the numerical range of X is 10-50%.

2. The chemically bonded heterostructure photocatalyst based on a pyrene-based covalent organic framework according to claim 1, characterized in that: The obtained catalyst is expressed as: XTAPPy-DMTP-CN, wherein X is the mass fraction of TAPPy-DMTP-COF, and the numerical range of X is 10-50%.

3. A method for preparing a chemically bonded heterostructure photocatalyst based on a pyrene-based covalent organic framework according to any one of claims 1 to 2, characterized in that: The process includes: (1) Preparation of g-C3N4(CN): Melamine was placed in an aluminum oxide crucible, heated to 500-600°C and maintained for 3-5 hours; (2) Preparation of TAPPy-DMTP-CN or XTAPPy-TPA-CN or XTAPPy-BPDA-CN: 1,3,6,8-tetrakis(p-aminophenyl)pyrene, 2,5-dimethoxyterephthalaldehyde or terephthalaldehyde or 4,4'-biphenyldicarboxaldehyde, and g-C3N4 were mixed; the mixture was dissolved in a mixture of N,N-dimethylacetamide and o-dichlorobenzene, and then acetic acid was added and ultrasonicated at room temperature for 20-40 minutes; after three freeze-pump-thaw cycles, The reaction tube is heated to 110-130° C. and maintained for 60-80 hours; the obtained product is washed with tetrahydrofuran, extracted with Soxhlet, and dried in vacuo. The expression of the obtained catalyst is: XTAPPy-DMTP-CN or XTAPPy-TPA-CN or XTAPPy-BPDA-CN, wherein X is the mass fraction of TAPPy-DMTP-COF or TAPPy-TPA-COF or TAPPy-BPDA-COF, and the numerical range of X is 10-50%.

4. The method for preparing the chemically bonded heterostructure photocatalyst based on the pyrene-based covalent organic framework according to claim 3, characterized in that: The molar ratio of the 1,3,6,8-tetrakis(p-aminophenyl)pyrene in step (2) to the 2,5-dimethoxyterephthalaldehyde or terephthalaldehyde or 4,4'-biphenyldicarboxaldehyde is 1:1-3.

5. The method for preparing the chemically bonded heterostructure photocatalyst based on the pyrene-based covalent organic framework according to claim 4, characterized in that: The molar ratio of the 1,3,6,8-tetrakis(p-aminophenyl)pyrene to the 2,5-dimethoxyterephthalaldehyde or terephthalaldehyde or 4,4'-biphenyldicarboxaldehyde in step (2) is 1:1.5-2.

5.

6. The method for preparing the chemically bonded heterostructure photocatalyst based on the pyrene-based covalent organic framework according to claim 3, characterized in that: The volume ratio of N,N-dimethylacetamide and 0-o-dichlorobenzene described in step (2) is 2-4:

1.

7. The method for preparing a chemically bonded heterostructure photocatalyst based on a pyrene-based covalent organic framework according to claim 3, characterized in that: The acetic acid in step (2) is a 5-7 mol / L acetic acid solution; the ultrasonic treatment in step (2) is performed at room temperature for 25-35 minutes; the reaction tube in step (2) is heated to 115-125° C. and maintained for 70-75 hours; the Soxhlet extraction in step (2) is performed for 22-25 hours.

8. The method for preparing a chemically bonded heterostructure photocatalyst based on a pyrene-based covalent organic framework according to claim 3, characterized in that: The expression of the catalyst in step (2) is: XTAPPy-DMTP-CN, X is the mass fraction of TAPPy-DMTP-COF, and the numerical range of X is 10-50%.

9. The method for preparing a chemically bonded heterostructure photocatalyst based on a pyrene-based covalent organic framework according to claim 3, characterized in that: The molar ratio of 1,3,6,8-tetrakis(p-aminophenyl)pyrene described in step (2) to the g-C3N4 described is 1:10-52.

10. Application of a chemically bonded heterostructure photocatalyst based on a pyrene-based covalent organic framework in the photocatalytic oxidation of NO.

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