Vinyl-linked donor-pi-receptor COFs as well as preparation method and application thereof

Abstract

The invention belongs to the field of photocatalysis, and particularly relates to vinyl-linked donor-pi-receptor COFs as well as a preparation method and application thereof. The vinyl-linked donor-pi-acceptor COFs comprises an electron donor, an electron acceptor A and a pi-conjugate connecting bridge, the electron donor is a benzene ring, a naphthalene ring or a derivative thereof; the electron acceptor is 2, 4, 6-trimethyl-1, 3, 5-triazine; and the pi-conjugate connecting bridge is vinyl and is used for covalently connecting the electron donor and the electron acceptor to form a conjugate skeleton with a donor-pi-acceptor electron structure. According to the invention, a precious insight is provided for application of customized COFs by illuminating a structure-performance relationship of bifunctional photocatalysis in a D-pi-A system. The key effect of an electron donating motif in adjusting charge kinetics and reaction pathways is emphasized, which is crucial for enhancing H2O2 production and reactive oxygen species generation so as to realize efficient pollutant remediation.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a vinyl-linked donor-π-acceptor COFs, its preparation method, and its application. Background Technology

[0002] Energy crisis and environmental pollution are key bottlenecks restricting sustainable social development. Hydrogen peroxide (H2O2), as an environmentally friendly green oxidant and energy carrier, has wide applications in chemical synthesis, pollution control, energy storage, and sterilization. However, its industrial-scale production still heavily relies on the energy-intensive and carbon-emission anthraquinone process, making it difficult to meet the requirements of green and low-carbon development. At the same time, the accumulation of recalcitrant organic pollutants (such as sulfonamide antibiotics) in water bodies poses a serious threat to ecology and public health, necessitating the development of efficient and green degradation technologies.

[0003] Photocatalysis technology can directly convert solar energy into chemical energy, providing an ideal pathway for the green synthesis of H2O2 and the efficient degradation of pollutants. Under light irradiation, photocatalysts (such as modified TiO2, g-C3N4, covalent organic frameworks, etc.) are excited to generate electron-hole pairs. Conduction band electrons can reduce oxygen to H2O2, while valence band holes can oxidize water or pollutant molecules, and can further generate reactive oxygen species (such as ·OH, O2·). - This technology aims to achieve efficient degradation of organic pollutants. However, it still faces challenges such as high recombination rate of photogenerated carriers, limited utilization of sunlight, insufficient catalyst stability, and competition between H2O2 synthesis and degradation pathways, which limit its practical application effectiveness.

[0004] Covalent organic frameworks (COFs), as a class of crystalline porous materials with designable structures, ordered channels, and high specific surface areas, have shown great potential in the field of photocatalysis. Donor-π-acceptor (D-π-A) type COFs, by precisely constructing the push-pull electronic structure between electron donor (D) and electron acceptor (A) units, can effectively narrow the material band gap, expand the light absorption range, and promote the separation and migration of photogenerated electron-hole pairs through a built-in electric field. In this type of material, the π-bridge structure has a significant impact on charge transport performance. Traditional aromatic π-bridges often suffer from limited carrier migration rates due to insufficient molecular planar rigidity and steric hindrance effects. Summary of the Invention

[0005] The purpose of this invention is to provide a vinyl-linked donor-π-acceptor COF, its preparation method and application, thereby overcoming the shortcomings of the prior art and providing a new strategy for the application of vinyl-linked D-π-A COF in environmental remediation and H2O2 production.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a vinyl-linked donor-π-acceptor COF, comprising an electron donor, an electron acceptor A, and a π-conjugated connecting bridge; The electron donor is a benzene ring, a naphthalene ring, or a derivative thereof; The electron acceptor is 2,4,6-trimethyl-1,3,5-triazine; The π-conjugated linker is a vinyl group used to covalently connect the electron donor and the electron acceptor, forming a conjugated framework with a donor-π-acceptor electronic structure.

[0007] This invention utilizes a benzene / naphthalene ring (donor, D) to provide an abundant electron cloud, acting as an electron donor. The naphthalene ring has a larger conjugated system than the benzene ring, resulting in a stronger electron-donating ability and allowing for further tuning of the band structure. The triazine ring (acceptor, A) has strong electron-deficient properties, serving as an electron-trapping center. The vinyl group (π-bridge): as a highly efficient electron channel, its rigid planar structure greatly facilitates the directional migration of electrons from the donor to the acceptor. By selecting different donors (benzene rings or naphthalene rings with larger conjugations), the band gap of the COF can be finely tuned (e.g., the band gap of naphthyl COFs is typically narrower than that of phenyl COFs). This allows the light absorption range to be extended into the visible and even near-infrared regions, significantly improving the utilization efficiency of sunlight.

[0008] In some other embodiments, when the electron donor is a benzene ring structure, the structure shown in formula (I) is used as the structural repeating unit: When the electron donor is a naphthalene ring structure, the structure shown in equation (II) is used as the structural repeating unit: .

[0009] In a second aspect, the present invention provides a method for preparing the vinyl-linked donor-π-acceptor COFs described in the first aspect, comprising the following steps: Electron donor, electron acceptor and catalyst are added to an organic solvent, ultrasonically mixed and degassed, and then heated to react. After the reaction is completed, the mixture is cooled to room temperature, filtered to collect the precipitate, and then washed and dried to obtain the final product.

[0010] In some other embodiments, the electron acceptor is 2,4,6-trimethyl-1,3,5-triazine; the electron donor is terephthalaldehyde or naphthalene-2,6-dicarboxaldehyde; and the catalyst is an acid catalyst or a base catalyst.

[0011] In some other embodiments, the molar ratio of electron acceptor to electron donor is (0.3-0.6):(0.5-0.8); In organic solvents, the concentration of electron acceptor is 0.04-0.05 mol·L⁻¹. -1 ; The heating reaction is carried out at a temperature of 110-160 ℃ for 70-80 h.

[0012] In some other embodiments, the organic solvent is one or more selected from n-butanol, 1,2-dichlorobenzene, mesitylene, 1,4-dioxane, and acetonitrile; The solvent used for washing is one or more of methanol, tetrahydrofuran, acetone, and dichloromethane; Drying is performed under vacuum at 110-130℃ for 10-15 hours.

[0013] Specifically, when the electron donor is a benzene ring structure, the prepared vinyl-linked donor-π-acceptor COFs are labeled as TMT-DB. The preparation method is as follows: 2,4,6-trimethyl-1,3,5-triazine, terephthalaldehyde and an alkaline catalyst are dissolved in an organic solvent, ultrasonically treated and degassed, then heated and reacted. After cooling to room temperature, the precipitate is collected by filtration, and then thoroughly washed and dried with an organic solvent to obtain the final product.

[0014] More specifically, the molar ratio of 2,4,6-trimethyl-1,3,5-triazine, terephthalaldehyde, and the base catalyst is 0.5:(0.7-0.8):(1.4-1.6); the base catalyst is one or more of triethylamine, sodium carbonate, potassium carbonate, KOH, and NaOH; the organic solvent is a mixture of n-butanol and 1,2-dichlorobenzene, wherein the volume ratio of n-butanol to 1,2-dichlorobenzene is (2-3):1; the reaction temperature is 115-125℃, and the time is 70-75 h; the washing is performed sequentially with methanol, tetrahydrofuran, acetone, and dichloromethane; the drying is performed under vacuum at 110-120℃ for 10-15 h.

[0015] Specifically, when the electron donor is a naphthalene ring structure, the prepared vinyl-linked donor-π-acceptor COFs are labeled as TMT-NA. The preparation method is as follows: 2,4,6-trimethyl-1,3,5-triazine, naphthalene-2,6-dicarboxaldehyde and acid catalyst are dissolved in an organic solvent, ultrasonically treated and degassed, then heated to react, cooled to room temperature, filtered to collect the precipitate, and thoroughly washed and dried with an organic solvent to obtain the final product.

[0016] More specifically, the molar ratio of 2,4,6-trimethyl-1,3,5-triazine and naphthalene-2,6-dicarboxaldehyde is 0.4:(0.55-0.65); the acid catalyst is trifluoroacetic acid; and the organic solvent is a mixture of mesitylene, 1,4-dioxane and acetonitrile, wherein the volume ratio of mesitylene, 1,4-dioxane and acetonitrile is 1:1:(1-1.5). The heating reaction is carried out at a temperature of 145-155℃ for 70-75 hours. The washing solvents are methanol and tetrahydrofuran; the drying is carried out at 110-120℃ under vacuum for 10-15 hours.

[0017] Thirdly, the present invention provides the application of the vinyl-linked donor-π-acceptor COFs described in the first aspect in the photocatalytic production of hydrogen peroxide and the photocatalytic degradation of pollutants. The D-π-A structure ensures that the oxidation and reduction reactions occur at spatially different sites, avoiding competition between reactants, thereby simultaneously achieving efficient synthesis of H2O2 and efficient degradation of pollutants.

[0018] This invention synthesizes two highly crystalline COFs with specific structures. TMT-NA (using naphthalene as a donor) exhibits stronger visible light absorption and a narrower band gap due to the extended π-conjugated structure in the naphthalene ring, while TMT-DB (using benzene as a donor) shows faster charge carrier mobility and lower electron-hole recombination efficiency. The results show that TMT-NA outperforms TMT-DB in long-term photocatalytic H2O2 production, achieving a photocatalytic H2O2 production rate as high as 1593 μmol·h⁻¹. -1 ·g -1 This is 1.4 times that of TMT-DB. Meanwhile, TMT-DB performs better in short-term rapid pollutant degradation processes. Its degradation rate constant for sulfadiazine (SMT) under visible light irradiation is 1.127 min. - ¹, significantly higher than TMT-NA (0.109 min) -1 The stepwise single-electron oxygen reduction pathway was identified as the main mechanism for H2O2 generation. DFT calculations revealed that O2 molecules in TMT-NA adsorb onto the carbon atoms of vinyl and naphthalene rings via Yeager-type adsorption, while in TMT-DB, Pauling-type adsorption is dominant. The main reactive species responsible for SMT degradation was identified as O2• - and 1 O2.

[0019] Fourthly, the present invention provides a method for photocatalytic production of hydrogen peroxide, wherein the vinyl-linked donor-π-acceptor COFs described in the first aspect are dispersed in water as a photocatalyst, and hydrogen peroxide is generated by irradiation with visible light under ambient air conditions. Each gram of photocatalyst is dispersed in 6-7 mL of water; the visible light irradiation time is 2-60 min.

[0020] Fifthly, the present invention provides a method for photocatalytic degradation of pollutants, wherein the vinyl-linked donor-π-acceptor COFs described in the first aspect are dispersed as photocatalysts in a sample containing pollutants, the sample is first stirred and mixed in the dark, and then photocatalytically degraded using visible light irradiation.

[0021] In some other embodiments, each gram of photocatalyst is dispersed in 6-7 mL of an antibiotic-containing sample; the visible light irradiation time is 1-15 min; The contaminants are one or more of sulfamethoxazole, sulfathiazole, sulfapyridine, sulfadimethoxypyrimidine, and sulfadimethoxypyrimidine.

[0022] The beneficial effects of this invention are: (1) This invention successfully constructed two well-defined D-π-A type covalent organic framework materials (TMT-DB and TMT-NA) by using benzene rings and naphthalene rings as electron donors, triazine units as electron acceptors, and vinyl groups as conjugated π-bridges, respectively. The benzene rings and naphthalene rings, acting as electron donors, form a strong push-pull electron system with the triazine acceptor units through vinyl π-bridges, effectively narrowing the material band gap and extending the photoresponse range into the visible light region. The vinyl bridges enhance intralayer conjugation and interlayer π-π stacking, significantly improving carrier mobility and fundamentally improving the separation efficiency of photogenerated electron-hole pairs. The vinyl linkages endow the COFs framework with higher chemical and thermal stability, allowing it to maintain structural integrity during photocatalytic cycling; the materials possess high specific surface area and ordered pore structure, providing abundant mass transfer channels and active sites for reactants.

[0023] (2) The D-π-A type covalent organic framework material prepared in this invention exhibits high electron utilization efficiency and selectivity in the photocatalytic synthesis of hydrogen peroxide (H2O2), significantly improving the H2O2 yield. In the degradation of sulfonamide antibiotics, the material achieves efficient removal of pollutants by generating reactive oxygen species and effectively inhibits the accumulation of harmful intermediates, reducing ecotoxicity. This provides a new strategy for developing green catalytic technologies based on D-π-A type COFs, promoting their application in environmental remediation and clean energy production. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 The diagrams above show the structural characterization of the TMT-DB and TMT-NA catalysts in Example 1 of this invention. Specifically, a is a schematic diagram of the synthesis of TMT-DB and TMT-NA; b is the PXRD pattern and Pawley refined image of TMT-DB; c is the PXRD pattern and Pawley refined image of TMT-NA; d is the FE-SEM image of TMT-DB; e is the TEM image of TMT-DB; f is the FE-SEM image of TMT-NA; g is the TEM image of TMT-NA; and h is the solid-state image of TMT-DB and TMT-NA. 13C NMR spectrum, i is the FT-IR spectrum of TMT-DB and TMT-NA; Figure 2 In Example 1 of this invention, the optical properties of two COFs (TMT-DB and TMT-NA) were evaluated using solid-state ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). Here, a is the solid-state UV-Vis DRS, b is the Tauc plot, c is the VB-XPS, d is the band alignment, e is the steady-state PL spectrum, f is the PL decay spectrum, g is the transient photocurrent response, h is the EIS Nyquist plot, and i is the DFT-optimized molecular orbital plots (HOMO and LUMO, orbital isosurface = 0.04) of TMT-DB and TMT-NA. Figure 3 The graph shows the photocatalytic performance of TMT-DB and TMT-NA in H2O2 production in Example 1 of this invention. In the graph, a represents the photocatalytic H2O2 production of different COFs, b represents the effect of various scavengers on H2O2 production, and c represents DMPO-O2 under dark and light conditions (3 min). • ESR spectrum, d is the O2-TPD spectrum of TMT-DB and TMT-NA, e is the in-situ DRIFT spectrum of TMT-DB during the H2O2 generation process, and f is the in-situ DRIFT spectrum of TMT-NA during the H2O2 generation process. Figure 4 This is a diagram illustrating the reaction pathway and potential active sites identified in Example 1 of the present invention. In this diagram, a represents the optimized adsorption sites and configurations of O2 on TMT-DB and TMT-NA; b represents the calculated O2 adsorption energy for each configuration; c represents the Pauling-type O2 adsorption configuration in TMT-DB and the Yeager-type O2 adsorption configuration in TMT-NA; and d represents the two-step 1e process at site 4. - Free energy diagram of ORR generating H2O2; Figure 5 This diagram illustrates the photocatalytic performance of two COFs in evaluating the degradation of SMT under visible light irradiation in Example 1 of this invention. In the diagram, a shows the photocatalytic degradation curves of SMT in the TMT-DB / Vis and TMT-NA / Vis systems, along with the corresponding pseudo-first-order kinetic constants (inset); b shows the effect of different scavengers on the SMT degradation in the TMT-DB / Vis system; and c shows the O2 content in the TMT-DB / Vis and TMT-NA / Vis systems. •- and 1 The concentration of O2, d represents DMPO-•OH and DMPO-O2 in the TMT-DB / Vis and TMT-DB / Vis / SMT systems. •- and TEMP- 1The ESR spectrum of O2, e represents the degradation rate of SMT by TMT-DB under natural sunlight, f represents the degradation curve of SMT in actual water matrix, g represents the recyclability of TMT-DB in multiple runs, and h represents the degradation efficiency of the TMT-DB / Vis system for different SAs and the corresponding degradation efficiency. k obs ; Figure 6 This is a diagram showing the possible degradation pathways of SMT and SMX in the TMT-DB / Vis system in Example 1 of the present invention, where a represents SMT and b represents SMX; Figure 7 This is a diagram illustrating the photocatalytic mechanism of TMT-DB and TMT-NA in H2O2 production and SAs degradation in Example 1 of this invention. Figure 8 This is a graph showing the effects of catalyst loading, pH, ion species, and HA on the degradation of SMT by TMT-DB / Vis in Example 1 of this invention. In this graph, a represents the catalyst loading, b represents pH, and c represents Cl. - CO3 2- SO4 2- NO3 - d represents the effect of HA on the degradation of SMT by TMT-DB / Vis; Figure 9 This is a predicted acute and chronic toxicity diagram of SMT, SMX and their degradation intermediates in Example 1 of the present invention, where a represents the acute toxicity of SMT and its degradation intermediates to various aquatic organisms, b represents the chronic toxicity of SMT and its degradation intermediates to various aquatic organisms, c represents the acute toxicity of SMX and its degradation intermediates to various aquatic organisms, and d represents the chronic toxicity of SMX and its degradation intermediates to various aquatic organisms. Detailed Implementation

[0026] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products.

[0027] Example 1 1 Materials and Instruments Detailed information on chemical reagents and characterization materials is shown below: (1) Chemical reagents Naphthalene-2,6-dicarboxaldehyde (NA) and 2,4,6-trimethyl-1,3,5-triazine (TMT) were purchased from Bidex Pharmaceuticals Co., Ltd. (Shanghai, China). Terephthalaldehyde (DB), sulfadiazine (SDZ), sulfadimethoxypyrimidine (SDM), sulfadiazine (SMT), potassium bromate (KBrO3), catalase (CAT), nitrotetrazole blue chloride (NBT), and mesitylene were purchased from Maclean Biochemical Technology Co., Ltd. (Shanghai, China). Sulfamethoxazole (SMX) and sulfathiazole (STZ) were purchased from Heinz Biochemical Technology Co., Ltd. (Tianjin, China). Trifluoroacetic acid (TFAA), 1,2-dichlorobenzene (oDCB), and sulfapyridine (SPY) were purchased from Aladdin Reagent Co., Ltd. (Shanghai, China). Acetonitrile, 1,4-dioxane, methanol (MeOH), tetrahydrofuran (THF), acetone, dichloromethane, sulfuric acid (H2SO4), sodium hydroxide (NaOH), furfuryl alcohol (FFA), 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), 4-amino-2,2,6,6-tetramethylpiperidine (TEMP), potassium hydroxide (KOH), n-butanol (nBuOH), disodium ethylenediaminetetraacetate (EDTA-2Na), p-benzoquinone ( p -BQ), potassium dichromate (K2Cr2O7), sodium chloride (NaCl), sodium sulfate (Na2SO4), sodium carbonate (Na2CO3), sodium nitrate (NaNO3), potassium iodide (KI), potassium hydrogen phthalate (C8H5KO4) and humic acid (HA) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

[0028] (2) HPLC determination conditions for pollutants and HPLC-MS identification of degradation products The HPLC (UltiMate 3000) determination conditions for contaminants were as follows: C18 column (Agilent, 5 μm, 4.6 × 250 mm). Table 1 below details the conditions for determining contaminants using the HPLC method. Degradation intermediates of sulfadiazine (SMT) were identified using an Agilent 1100-Thermos TSQ Quantum Ultra AM LC-MS system equipped with an Anpu Technology Xtimate C18 column (100 × 2.1 mm, 3 μm). The injection volume was 10 μL, and the column temperature was 295 K. Detection was performed using UV absorption at a wavelength of 254 nm. Data acquisition was performed in ESI positive ion mode, with ESI source conditions set as follows: ion source temperature 450 °C, spray voltage 3000 V. The mass range of the eluted compounds detected was between m / z 50 and 600. The mobile phase consisted of H2O (0.1% formic acid) and acetonitrile (mobile phase B), with a flow rate of 0.5 mL / min. -¹. Intermediate identification was performed in positive ion mode. Mobile phase gradient settings: B% was 2% before 10 min, B% was 93% from 10 min to 10.5 min, and B% was 2% at 10.51 min.

[0029] Table 1. Conditions for determining pollutants using HPLC.

[0030] 2. Synthesis of TMT-DB and TMT-NA In a typical synthesis, 2,4,6-trimethyl-1,3,5-triazine (TMT) and an aromatic dialdehyde are dissolved in a mixture of organic solvents in a Schlenk tube. For TMT-DB, TMT (61.58 mg, 0.50 mmol), terephthalaldehyde (DB, 100.60 mg, 0.75 mmol), and KOH (84.15 mg, 1.5 mmol) are dissolved in a mixture of n-butanol (7 mL) and 1,2-dichlorobenzene (3 mL). For TMT-NA, TMT (49.5 mg, 0.4 mmol) and naphthalene-2,6-dicarboxaldehyde (NA, 111 mg, 0.6 mmol) are mixed in a solvent system consisting of mesitylene (4.5 mL), 1,4-dioxane (4.5 mL), and acetonitrile (0.5 mL). After sonication, trifluoroacetic acid (TFAA, 2 mL) is added. In both cases, the mixture was sonicated for 15 min and degassed by three freeze-pump-thaw cycles. The resulting solutions (TMT-DB was pale yellow, TMT-NA was white) were then heated under controlled conditions: TMT-DB at 120 °C for 72 h, and TMT-NA at 150 °C for 72 h. After cooling to room temperature, the precipitates were collected by filtration and thoroughly washed with organic solvents. TMT-DB was washed sequentially with methanol, tetrahydrofuran, acetone, and dichloromethane; TMT-NA was purified using methanol and tetrahydrofuran. Finally, the products were dried under vacuum at 120 °C for 12 h to obtain TMT-DB and TMT-NA, respectively.

[0031] The structures of the prepared TMT-DB and TMT-NA catalysts were characterized, and the results are as follows: Figure 1 As shown, a is a schematic diagram of the synthesis of TMT-DB and TMT-NA; b is the PXRD pattern and Pawley refined image of TMT-DB; c is the PXRD pattern and Pawley refined image of TMT-NA; d is the FE-SEM image of TMT-DB; e is the TEM image of TMT-DB; f is the FE-SEM image of TMT-NA; g is the TEM image of TMT-NA; and h is the solid-state image of TMT-DB and TMT-NA. 13C NMR spectrum, i is the FT-IR spectrum of TMT-DB and TMT-NA.

[0032] The target COFs, denoted as TMT-DB and TMT-NA, were synthesized via a Knoevenagel condensation reaction under solvothermal conditions, using 2,4,6-trimethyl-1,3,5-triazine (TMT) reacted with terephthalaldehyde (DB) and naphthalene-2,6-dicarboxaldehyde (NA), respectively. Figure 1 (a) The crystal structure of the synthesized COFs was comprehensively characterized by powder X-ray diffraction (PXRD) combined with theoretical simulation. TMT-DB showed major diffraction peaks at 4.7°, 8.1°, 9.4°, 12.6°, and 26.6°, corresponding to the (100), (110), (200), (210), and (001) crystal planes, respectively. Figure 1 (b) Similarly, TMT-NA showed significant peaks at 4.0°, 7.0°, 8.1°, 10.7°, and 25.3°, which can be attributed to the (100), (110), (200), (210), and (001) crystal planes, respectively. An overlapping AA stacking model was constructed using Materials Studio software, and the experimental PXRD patterns matched the model with negligible deviation. The Pawley refinement results also showed excellent agreement with the observed diffraction data. The morphology of the COFs was examined using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Figure 1 As shown in the diagram, TMT-DB exhibits an interlaced structure composed of dendritic nanoribbons. In contrast, TMT-NA ( Figure 1 The fg in the two materials consists of spherical nanoparticles with an average particle size of 2.05 μm. The permanent porosity of both materials was evaluated by nitrogen adsorption measurements at 77 K. Both TMT-DB and TMT-NA exhibited typical type I isotherms and rapid nitrogen absorption at low relative pressures, indicating a microporous structure. The calculated Brunauer-Emmett-Teller (BET) specific surface area was 942 m² for TMT-DB. 2 / g, TMT-NA is 907m 2 / g, corresponding to pore sizes of 4.1 nm and 2.0 nm, respectively.

[0033] Through solid 13 C10 NMR spectroscopy further confirmed the chemical structures of TMT-DB and TMT-NA. Figure 1As shown in h, both compounds exhibit two common signals: one at approximately 170 ppm, originating from a carbon atom in the triazine ring (denoted as 1); and another at 141 ppm, attributed to a carbon atom in the newly formed olefin group (3). In TMT-DB, a clearly resolved peak at 136 ppm corresponds to the phenyl carbon linked to the olefin (4), while the strongest signal at 126 ppm belongs to an olefin carbon (2) and a hydrogen-bonded aromatic carbon (5). In contrast, TMT-NA shows a distinct peak at 132 ppm, corresponding to the naphthalene ring carbon linked to the olefin (4) and two intermediate carbon atoms in the naphthalene ring (6 and 9). Furthermore, the signal at 128 ppm in TMT-NA belongs to an olefin carbon (2) and multiple carbon atoms in the naphthalene ring (5, 7, and 8). Figure 1 The Fourier transform infrared (FT-IR) spectrum of i in the image is shown at 1518 cm⁻¹. -1 and 1372 cm -1 An absorption peak is observed at 1631 cm⁻¹, which is related to the -C=N- stretching vibration in the triazine ring of TMT-DB and TMT-NA. -1 and 977 cm -1 The peak at 750-900 cm⁻¹ is consistent with the stretching vibration of the -C=C- group in the newly formed trans configuration, confirming the formation of the -CH=CH- linkage and thus proving the success of the Knoevenagel condensation reaction between TMT and the aldehyde (DB or NA). Both materials show peaks at 750-900 cm⁻¹. -1 Several sharp peaks were observed within the range, corresponding to the out-of-plane bending vibrations of the CH bonds in the aromatic ring. Due to the larger conjugated system of naphthalene, TMT-NA showed more and more complex CH out-of-plane vibration peaks than TMT-DB, further reflecting the structural differences between the two COFs. Contact angle measurements recorded 143.4° for TMT-NA and 147.5° for TMT-DB, indicating significant hydrophobicity in both materials. The elemental chemical states of TMT-DB and TMT-NA were investigated by X-ray photoelectron spectroscopy. For the TMT-DB COF, the high-resolution C 1s spectrum fitted three peaks centered at 284.8, 286.9, and 288.8 eV, attributed to C=C / C--C bonds, NC=N bonds, and π--π* transitions, respectively. Furthermore, the N 1s spectrum showed a single component at 399.3 eV, consistent with the nitrogen atom in the triazine ring. Additionally, the O 1s spectrum shows a peak at 532.0 eV, which is attributed to adsorbed O2 or H2O.

[0034] The optical properties of two COFs (TMT-DB and TMT-NA) were evaluated using solid-state UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), and the results are as follows: Figure 2As shown, a is the solid-state UV-Vis DRS, b is the Tauc plot, c is the VB-XPS, d is the band arrangement, e is the steady-state PL spectrum, f is the PL decay spectrum, g is the transient photocurrent response, h is the EIS Nyquist plot, and i is the DFT optimized molecular orbital plots (HOMO and LUMO, orbital isosurface = 0.04) of TMT-DB and TMT-NA.

[0035] like Figure 2 As shown in Figure a, both COFs (TMT-DB and TMT-NA) exhibit excellent absorption in the visible light region. Compared to TMT-DB, TMT-NA shows a wider absorption range and a significant redshift at the absorption edge, which can be attributed to the extended π-conjugation imparted by the naphthalene ring, thereby enhancing its visible light trapping ability. The Tauc diagram obtained using the Kubelka-Munk transform (…) Figure 2 In section b), the optical bandgap was estimated. The bandgap of TMT-DB was 2.72 eV, while that of TMT-NA was narrower at 2.22 eV. Valence band X-ray photoelectron spectroscopy (VB-XPS) was used. Figure 2 c) in the equation determines the valence band potential (E). VB TMT-DB and TMT-NA's E VB The values ​​relative to NHE are estimated to be 1.61 V and 1.85 V, respectively. According to the formula Eg = E VB - E CB The calculated conduction band potential (E) VB For TMT-DB, it is -1.11 V, and for TMT-NA, it is -0.37 V (relative to NHE). (Summary follows) Figure 2 In the d-mode, the flat band potential (E) of TMT-DB and TMT-NA. fb The values ​​are -0.44 V and -0.54 V (relative to Ag / AgCl), respectively. The positive slope of the curves confirms their n-type semiconductor characteristics. Figure 2 The energy level diagram in d shows the E levels of the two COFs. CB The value is higher than 2e directly. - ORR pathway (+0.68 V vs. NHE) and stepwise 1e - The ORR pathway (-0.33 V vs. NHE) requires a more negative potential. Meanwhile, E VB The value is sufficiently positive to drive the water oxidation reaction (+1.23 V vs. NHE). These results indicate that both TMT-DB and TMT-NA are thermodynamically capable of photocatalytic H2O2 production via oxygen reduction without the need for a sacrificial agent. Furthermore, the more negative conduction band of TMT-DB suggests that its photogenerated electrons have a stronger reducing power than those of TMT-NA.

[0036] In addition, photoluminescence (PL) spectra were measured to evaluate the photoinduced charge separation efficiency. Figure 2 As shown in e, the PL intensity of TMT-DB is significantly lower than that of TMT-NA, indicating that TMT-DB has a higher photogenerated charge separation efficiency. To further confirm this finding, transient fluorescence lifetime decay measurements were performed. The fitted average fluorescence lifetime was 6.47 ns for TMT-DB and 1.62 ns for TMT-NA. Figure 2 (f in the text). Compared to TMT-NA, TMT-DB's longer fluorescence lifetime and significantly quenched PL emission indicate more efficient charge separation and longer exciton diffusion. The photocurrent response of COFs was also investigated. Figure 2 As shown in g, TMT-DB exhibits a much stronger transient photocurrent than TMT-NA, indicating its superior charge generation and separation capabilities under light irradiation, thus demonstrating greater potential for constructing highly efficient photocatalytic systems. Furthermore, electrochemical impedance spectroscopy (EIS) was performed to investigate charge transfer resistance. Figure 2 The Nyquist plot in h shows that TMT-DB has a smaller arc radius, indicating lower interfacial charge transfer resistance and faster charge migration, which is consistent with its enhanced photocurrent response.

[0037] Based on density functional theory (DFT) calculations, the spatial distributions of the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of two COFs were analyzed. Figure 2 As shown in i, a similar distribution trend was observed: HOMOs were mainly localized on benzene / naphthalene rings and -CH=CH- links, while LUMOs were mainly concentrated on triazine-containing units. This spatial separation of orbitals confirms the electron-donating effect of aromatic olefin motifs and the electron-accepting nature of triazine groups. This separation helps to suppress electron-hole recombination and improve photocatalytic efficiency. DFT calculations of the band structure show that the band gaps of TMT-DB and TMT-NA are 2.02 eV and 1.86 eV, respectively, consistent with experimental results. Figure 2 (d) The density of states (DOS) was also calculated to investigate the elemental orbital contributions to the band structure. The DOS contributions for TMT-DB and TMT-NA were similar. VBM and CBM were primarily dominated by hybridized C 2p and N 2p orbitals. The contribution of C orbitals was greater than that of N, thus C was the dominant element in constructing the electronic structure. N orbitals made significant contributions near the Fermi level (from -1 eV to 1 eV), indicating that the triazine ring could serve as an active site in photocatalysis.

[0038] 3. Photocatalytic production of H2O2 A total of 3 mg of photocatalyst was dispersed in 20 mL of pure water using ultrasonication. All photocatalytic reactions were carried out under ambient air conditions using a 300 W xenon lamp (CEL-HXF300-T3, Beijing, China) equipped with a 400 nm cutoff filter. At specific time points before and during illumination, 1 mL of the reaction solution was collected and mixed with 1 mL of 0.4 M potassium iodide (KI) aqueous solution and 1 mL of 0.1 M potassium hydrogen phthalate (C8H5KO4) aqueous solution. The resulting mixture was allowed to stand in the dark for 1 h, and its absorbance at 351 nm was measured using a UV-Vis spectrophotometer. This method is based on the reaction of H2O2 with iodide ions (I₂O₂). - Under acidic conditions, it reacts to produce triiodide ions (I3). - It exhibits strong absorption near 351 nm. In the scavenger experiments, the following concentrations were used: potassium bromate (KBrO3) at 2 mM, and p-benzoquinone (… p The concentration of EDTA-2Na was 0.5 mM (-BQ) and 10 mM (EDTA-2Na).

[0039] Based on the characterized optical properties, the photocatalytic performance of TMT-DB and TMT-NA in H2O2 production was further evaluated. The photocatalytic reaction was carried out in an air environment using pure water, without the addition of any additional sacrificial agents. The results are as follows: Figure 3 As shown, a represents the photocatalytic H2O2 production of different COFs, b represents the effect of various scavengers on H2O2 production, and c represents the DMPO-O2 production under dark and light conditions (3 min). • ESR spectrum, d is the O2-TPD spectrum of TMT-DB and TMT-NA, e is the in-situ DRIFT spectrum of TMT-DB during the H2O2 generation process, and f is the in-situ DRIFT spectrum of TMT-NA during the H2O2 generation process.

[0040] like Figure 3 As shown in Figure a, under dark conditions, no H2O2 was detected in either TMT-DB or TMT-NA. Under light irradiation, the H2O2 concentration produced by TMT-DB increased rapidly within the first 10 minutes, reaching 137 μmol / L, and then gradually plateaued. In contrast, the H2O2 production on TMT-NA increased almost linearly with irradiation time. Notably, after 30 minutes, the H2O2 concentration in the TMT-NA system exceeded that of TMT-DB, reaching 239 μmol / L after 1 hour. The calculated average H2O2 production rate of the TMT-NA COF was approximately 1593 μmol / L per hour. -1 g -1 Compared to TMT-DB COF (1138 μmol h)-1 g -1 The efficiency is approximately 1.4 times higher. This also surpasses many previously reported COF photocatalysts. This indicates that TMT-DB exhibits superior performance in short-term photocatalytic H2O2 production, while TMT-NA demonstrates advantages in long-term reactions.

[0041] To further elucidate the reaction pathway and identify the reactive oxygen species involved, quenching experiments were conducted to investigate intermediates contributing to H₂O₂ production. Specifically, using... p -BQ, EDTA-2Na, and KBrO3 act as superoxide radicals (O2) and other free radicals, respectively. •- ), hole (h + ) and electrons (e - ( ) cleaning agents. For example Figure 3 As shown in b, add p -BQ significantly inhibited H2O2 generation in both TMT-DB and TMT-NA, indicating that O2 • It is a key intermediate and suggests that the stepwise one-electron oxygen reduction reaction (ORR) pathway is involved in the formation of H2O2. Further electron spin resonance (ESR) spectroscopy, using 5,5-dimethyl-1-pyrrolline N-oxide (DMPO) as a spin trapper, was employed to confirm the presence of O2. • The generation of . For example Figure 3 As shown in c, no characteristic signal was detected under dark conditions. However, after 3 minutes of visible light irradiation, a signal corresponding to O2 was observed in both the TMT-DB and TMT-NA systems. • The obvious signal confirms O2 • The photogenerated signal of TMT-DB is stronger than that of TMT-NA, indicating that its O2... • The formation efficiency is higher. Furthermore, for TMT-DB, adding KBrO3 (e... - The scavenger) inhibited H2O2 production, while EDTA-2Na (h + The scavenger enhanced H2O2 production, supporting an electron-mediated photocatalytic mechanism. In contrast, KBrO3 and EDTA-2Na both reduced the H2O2 yield of TMT-NA, indicating that both photogenerated electrons and holes contribute to the redox reaction. These results, compared with previously determined E2 values ​​for TMT-DB and TMT-NA, suggest that both photogenerated electrons and holes contribute to the redox reaction. CB E VB Location( Figure 2Combining d) with the redox potential associated with H2O2 formation, we can conclude that H2O2 production on both COFs mainly follows the process centered on O2. • The intermediate is obtained through a two-step single-electron ORR pathway (O2→O2). • → H2O2).

[0042] The O2 adsorption capacity of TMT-DB and TMT-NA was evaluated using oxygen-programmed temperature desorption (O2-TPD). Figure 3 As shown in d, compared with TMT-NA, TMT-DB exhibits a larger desorption peak and a higher desorption temperature (approximately 350 °C), indicating its stronger chemisorption capacity for O2. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to reveal the kinetics of the reaction process by real-time monitoring of intermediate species. Figure 3 The figure shows the in-situ DRIFT spectra of TMT-DB and TMT-NA over time under O2 saturated atmosphere, water vapor, and visible light irradiation. The DRIFT spectra of both materials in the first 30 minutes under dark conditions show only very weak vibrational peaks, confirming no reaction in the absence of light. Under visible light irradiation, the DRIFT spectrum of TMT-DB at 858 cm⁻¹... -1 839 cm at the location and TMT-NA -1 Characteristic bands associated with OO bending were observed at 1450 cm⁻¹, indicating the presence of adsorbed O₂. In the TMT-DB spectrum, at 1450 cm⁻¹... -1 (CO) and 1300 cm -1 A vibrational peak appeared at (C=CO), indicating that O2 was adsorbed onto the carbon atoms of the aromatic ring, triazine, and vinyl group. Furthermore, a vibrational peak appeared at 1183 cm⁻¹. -1 (TMT-NA is 1145 cm) -1 A band appeared at the position indicating that the adsorbed O2 was reduced by electrons to form superoxide radicals (O2). • The intermediate was found, thus confirming the existence of the stepwise single-electron ORR pathway. 1339 cm -1 and 1396 cm -1 The vibrational peaks at these locations are attributed to the adsorbed OOH. ad and HOOH ad The formation of intermediates. For TMT-DB, these are related to O2. •- OOH ad and HOOH ad The relevant peak intensity gradually increased with reaction time and was significantly higher than that observed by TMT-NA. Furthermore, at 1551 cm⁻¹... -1(C=N vibration) and 1606 cm - ¹(C=NH + The characteristic peak at ) is attributed to protonated triazine (Tz-H) + This confirms the proton-coupled electron transfer mechanism in photocatalysis.

[0043] DFT calculations were performed, allowing for a deeper understanding of reaction pathways and the identification of potential active sites at the atomic level. The results are as follows: Figure 4 As shown, a represents the optimized adsorption sites and configurations of O2 on TMT-DB and TMT-NA, b represents the calculated O2 adsorption energy for each configuration, c represents the Pauling-type O2 adsorption configuration in TMT-DB and the Yeager-type O2 adsorption configuration in TMT-NA, and d represents the two-step 1e adsorption at site 4. - Free energy diagram of ORR generating H2O2.

[0044] Figure 4 Figure 'a' shows the optimized adsorption configuration of O2 at different sites in two COFs. The results indicate that O2 can form intermolecular hydrogen bonds with hydrogen atoms on aromatic structures and -CH=CH- groups (site 1), and it can also adsorb above aromatic rings (benzene or naphthalene rings, site 2) or above triazine rings (site 3). Figure 4 As shown in b, TMT-DB exhibits a higher O2 adsorption energy than TMT-NA in all three configurations. However, the adsorption energies of all these configurations are significantly lower than the O2 adsorption energy near the -CH=CH- group (site 4), indicating that the -CH=CH- site in both COFs exhibits stronger oxygen adsorption. Furthermore, the optimal O2 adsorption energy of TMT-NA (-0.845 eV) is more negative than that of TMT-DB (-0.305 eV), indicating that TMT-NA has a stronger adsorption affinity for O2. Figure 4 Analysis of the adsorption structure in TMT-NA reveals that in TMT-NA, a specific carbon atom (near the triazine ring) in the -CH=CH- linker and a carbon atom in the naphthalene ring synergistically interact with O2 molecules to form an internal peroxide species (COOC), consistent with the Yeager-type adsorption configuration. Furthermore, O2 can form hydrogen bonds with the hydrogen atoms on these carbon atoms, further enhancing oxygen adsorption. In contrast, for TMT-DB, O2 molecules only bind to the terminal carbon of the -CH=CH- group, forming COO peroxides. The carbon atoms in the benzene ring are too far apart to participate in adsorption, thus preventing the formation of the Yeager-type structure and instead resulting in the Pauling-type adsorption configuration.

[0045] The Gibbs free energy curve of the stepwise single-electron ORR process leading to H2O2 production at site 4 was further examined using DFT calculations. Figure 4 As shown in d, for TMT-NA, the rate determination step (O2+ e) - The Gibbs free energy change of → O2*) is 0.467 eV, much lower than that of TMT-DB (0.942 eV), indicating that the naphthalene ring in TMT-NA promotes the two-step 1e-wave process for photocatalytic H2O2 generation. - The ORR pathway. For TMT-NA, OOH (O2* + H) is formed. + + e - → The Gibbs free energy change of *OOH is 0.292 eV, which is 0.175 eV lower than that of the O2* formation step, indicating that the conversion from O2* to *OOH is thermodynamically favorable. Subsequently, *OOH accepts an additional electron and a proton to break the -OOH bond, forming H2O2(*OOH + e) + H + → H2O2), the energy barriers for both processes are lower for TMT-NA than for TMT-DB, indicating that at site 4, TMT-NA exhibits higher oxygen affinity and higher oxygen reduction activity compared to TMT-DB.

[0046] 4. Photocatalytic degradation experiment In the standard photocatalytic degradation procedure, 3 mg of photocatalyst was added to 20 mL of an aqueous solution of sulfadiazine (SMT) with an initial concentration (C0) of 10 mg / L. Before irradiation, the mixture was magnetically stirred in the dark for 30 min to reach adsorption-desorption equilibrium. The reaction was carried out under visible light generated by a 300 W xenon lamp (CEL-HXF300-T3, Beijing, China) equipped with a 400 nm cutoff filter. Throughout the experiment, the temperature was maintained at 25.0 ± 0.2 °C with continuous magnetic stirring. At specified time intervals, 1 mL samples were taken and immediately quenched with 0.3 mL of methanol. The quenched samples were then filtered through a 0.22 μm filter membrane to remove catalyst particles. The remaining concentration of SMT was analyzed by high-performance liquid chromatography (HPLC). In the scavenger experiment, the following concentrations were used: tert-butanol (TBA) at 10 mM. p -BQ is 1 mM, EDTA-2Na is 10 mM, furfuryl alcohol (FFA) is 10 mM, potassium dichromate (K2Cr2O7) is 1 mM, and catalase (CAT) is 200 units / mL.

[0047] The photocatalytic performance of two COFs was evaluated by monitoring the degradation of SMT under visible light irradiation. The results are as follows: Figure 5As shown in the figure, a represents the photocatalytic degradation curves of SMT in the TMT-DB / Vis and TMT-NA / Vis systems and the corresponding pseudo-first-order kinetic constants (inset); b represents the effect of different scavengers on the SMT degradation in the TMT-DB / Vis system; and c represents the O2 content in the TMT-DB / Vis and TMT-NA / Vis systems. •- and 1 The concentration of O2, d represents DMPO-•OH and DMPO-O2 in the TMT-DB / Vis and TMT-DB / Vis / SMT systems. •- and TEMP- 1 The ESR spectrum of O2, e represents the degradation rate of SMT by TMT-DB under natural sunlight, f represents the degradation curve of SMT in actual water matrix, g represents the recyclability of TMT-DB in multiple runs, and h represents the degradation efficiency of the TMT-DB / Vis system for different SAs and the corresponding degradation efficiency. k obs .

[0048] like Figure 5 As shown in a, the degradation efficiency of SMT in the TMT-DB / Vis system reaches 100% after 15 min, and the corresponding degradation rate constant ( k obs The time was 1.127 min. -1 This performance significantly surpasses that of the TMT-NA / Vis system (90%, 0.109 min). -1 This is in contrast to many other reported photocatalysts for SA degradation. These results clearly demonstrate that TMT-DB exhibits superior catalytic activity compared to TMT-NA in the rapid, short-term degradation of pollutants. To identify the major active species involved in the photocatalytic process, TBA was used in quenching experiments. p -BQ, FFA, K2Cr2O7, EDTA-2Na and CAT were respectively used as • OH, O2 • , 1 O2, e , h + , and H2O2 scavengers. Figure 5 Figure b shows that in the TMT-DB / Vis system, the degradation process of SMT is almost unaffected by the addition of CAT, indicating that the concurrently generated H2O2 hardly participates in the degradation reaction. In contrast, the introduction of TBA, K2Cr2O7, and EDTA-2Na resulted in a moderate degree of inhibition of degradation, indicating that •OH and e-coated H2O2 are largely inhibited. - and h + Participated in the reaction, of which e - The effect of •OH and h +More significantly. It is worth noting that, in p The reaction is strongly inhibited in the presence of -BQ and FFA, which means that O2 •- and 1 O2 is the main active species responsible for SMT degradation in the TMT-DB / Vis system. Furthermore, purging the reaction solution with pure N2 gas slightly inhibited the reaction, while an O2 atmosphere slightly enhanced degradation, confirming the important role of molecular oxygen in the photocatalytic process. In the TMT-NA / Vis system, 1 O2, O2 •- H₂O₂ and H₂O₂ are the main active substances responsible for the degradation of SMT. Meanwhile, •OH and e⁻... - and h + They also participated in the reaction to varying degrees.

[0049] The quenching method was used to determine the concentration of ions in the TMT-DB / Vis system. 1 The steady-state concentration of O2 was determined to be approximately 4.5 × 10⁻⁶. -12 M is higher than the concentration in the TMT-NA / Vis system (2.1 × 10⁻⁶). -12 M)( Figure 5 c). O2 was assessed using the nitroblue tetrazolium (NBT) assay. •- The concentrations of NBT and O2 •- The reaction produces blue formazan. The O2 concentration in the TMT-DB / Vis system was estimated by monitoring the change in NBT absorbance over time. • The concentration is approximately 2.02 × 10⁻⁶. -4 M. In contrast, in the TMT-NA / Vis system, the NBT concentration remained essentially constant, indicating that the O2 concentration in this catalytic system was relatively stable. •- It was not effectively captured by NBT. This may be attributed to the steric hindrance generated by the naphthalene ring in TMT-NA. The superior degradation efficiency of SMT observed in the TMT-DB / Vis system can be attributed to its higher reactive oxygen species concentration. Figure 5 The ESR spectrum of d in the image shows that after 3 min of illumination, the corresponding DMPO-•OH and DMPO-O2 were observed. •- and TEMP- 1 The obvious signals of O2 indicate the presence of • OH, O2 • and 1 O2. The intensity of these signals decreased significantly in the presence of SMT, confirming the involvement of these active species in the degradation process. Notably, the VB sites of TMT-DB are insufficient to directly generate •OH via water oxidation. These detected •OH signals likely originate from the decomposition of H2O2.

[0050] In addition to operating effectively under artificial xenon lamp irradiation, TMT-DB also exhibits high catalytic activity for SMT degradation under natural sunlight in ambient air. Figure 5 (e). Under clear conditions (solar radiation intensity of 230 W / m²). 2 ), k obs Reached 0.4 min -1 Even on a cloudy day (when solar radiation intensity is 178 W / m²), 2 ), k obs Still as high as 0.3 min - ¹ indicates that TMT-DB has high practical efficiency under real-world conditions.

[0051] Figure 8 The graph shows the effects of catalyst loading, pH, ion species, and HA on the degradation of SMT by TMT-DB / Vis. In this graph, a represents catalyst loading, b represents pH, and c represents Cl. - CO3 2- SO4 2- NO3 - d represents the effect of HA on the degradation of SMT by TMT-DB / Vis. Figure 8 Figure a shows that as the catalyst dosage increased from 0.05 g / L to 0.225 g / L, the degradation efficiency of SMT increased from 72.2% to 100%. Figure 8 Figure b shows that the degradation efficiency of SMT does not change much within the initial pH range of 3 to 9, indicating that the catalytic system has a wide applicable pH range. Figure 8 The 'c' in the figure shows that several inorganic anions, such as SO42-, are present. 2- NO3 - , and Cl - The impact on SMT degradation is negligible, while CO3 2- It exhibits a strong inhibitory effect, which may be due to alkaline conditions caused by increased pH. Figure 8 The presence of high concentrations (20 mg / L) of humic acid (HA) in the water partially inhibited degradation. Natural aquatic substrates, including tap water and groundwater, had the least impact on SMT degradation. Figure 5 (f in the text). In contrast, seawater significantly inhibited degradation, possibly due to the high salt content quenching the active species. Figure 5The g-index shows that TMT-DB maintained a degradation efficiency of 89% after four photocatalytic degradation cycles, demonstrating excellent recyclability. After four photocatalytic degradation cycles, the intensity of the main XRD diffraction peak of TMT-DB decreased, and a carbonyl-related absorption peak appeared in the FT-IR spectrum. The oxygen atom content in the XPS spectrum increased slightly from 5.25% to 8.29%. These results indicate that during long-term photocatalysis, the structure of TMT-DB may have undergone the breaking of -CH=CH- bonds under the attack of active species. Furthermore, the TMT-DB / Vis system demonstrates broad applicability in the efficient degradation of various sulfonamide antibiotics. Figure 5 The h-values ​​in the data show that the degradation efficiencies of sulfamethoxazole (SMX), sulfathiazole (STZ), sulfapyridine (SPY), sulfadiazine (SDZ), and sulfadimethoxypyrimidine (SDM) within 15 min were 98.4%, 100%, 99.8%, 99.9%, and 96.1%, respectively. k obs The results were 1.09, 1.60, 1.14, 1.33 and 0.95 min respectively. -1 .

[0052] To elucidate the transformation pathways of sulfonamide antibiotics in the TMT-DB / Vis system, degradation intermediates of SMT and SMX were identified using LC-MS. Complete chromatograms of degradation samples at different time points were obtained. Based on spectral analysis, five and nine major intermediates of SMT and SMX, respectively, were identified. Figure 6 The possible degradation pathways of SMT and SMX in the TMT-DB / Vis system are shown, where a represents SMT and b represents SMX.

[0053] Figure 6 Figure 'a' illustrates the proposed degradation pathway of SMT. Based on the identified intermediates and previous reports, three main pathways (I, II, and III) are proposed. In pathway I, the α-carbon adjacent to the sulfonamide group readily forms an aniline cationic intermediate due to its strong positive charge. This triggers a nucleophilic attack from the pyrimidine nitrogen, initiating an intramolecular Smiles-type rearrangement, leading to SO2 extrusion and the formation of product P1 (C). 12 H 14 N4), m / z = 215.06. Pathway II involves the breaking of the NS and SC bonds under attack by the active species, leading to SO2 elimination and the formation of intermediate P2 (C 12 H 14 N4, m / z = 214.99). In pathway III, the terminal amino group (-NH2) is replaced by •OH, O2. • and 1 O2 and other reactive species are oxidized to nitro (-NO2), generating P3 (C12 H 12 N4O4S, m / z = 308.93). P3 subsequently undergoes N-S and S-S bond breaking and SO2 extrusion to form P4 (C). 12 H 12 N4O2, m / z = 245.03). P2 and P4 were further oxidized and underwent CN bond cleavage to form P5 (C6H9N3, m / z = 124.04), which is mainly composed of pyrimidine ring structures. Similarly, Figure 6 b in section b proposes a possible degradation pathway for SMX. Pathway I involves the oxidation of the terminal -NH2 group to -NO2, generating P1(C 10 H9N3O5S, m / z = 283.79). Subsequently, the oxidation of the isoxazole ring in P1 leads to P2 (C 10 H9N3O6S, m / z = 299.78). Pathway II refers to the cleavage of the SC bond under attack by the active species, leading to the formation of P3 (C4H6N2O4S, m / z = 178.80). In Pathway III, the hydroxylation of the SMX benzene ring produces P4 (C9N3O6S, m / z = 299.78). 10 H 12 N3O4S, m / z = 269.84). Pathway IV involves the breaking of the N-N bond, generating P5 (C4H6N2O, m / z = 98.95) and C6H7NO3S; the latter is further oxidized at the -NH2 group to form P6 (C6H5NO5S, m / z = 202.04). P5 can also be formed via other pathways, such as the breaking of the S-N bond in P3 or P4. After further oxidation, the isoxazole ring of P5 undergoes a ring-opening reaction to generate P8 (C2H4NO, m / z = 60.05) and P9 (C4H7NO, m / z = 84.91). P6 may also be formed via the breaking of the N-N bond in P1 or P2. Finally, pathway V involves the coupling of the N-central radical to form the dimer P7 (C3O4S, m / z = 269.84). 20 H 18 N6O6S2, m / z = 502.9).

[0054] Using the Ecosystem Structure-Activity Relationship (ECOSAR) model, we predicted and analyzed the acute and chronic toxicity of SMT, SMX and their degradation intermediates to various aquatic organisms based on molecular structure. Figure 9 The predicted acute and chronic toxicities of SMT, SMX and their degradation intermediates are given, where a represents the acute toxicity of SMT and its degradation intermediates to various aquatic organisms, b represents the chronic toxicity of SMT and its degradation intermediates to various aquatic organisms, c represents the acute toxicity of SMX and its degradation intermediates to various aquatic organisms, and d represents the chronic toxicity of SMX and its degradation intermediates to various aquatic organisms.

[0055] For SMT, acute toxicity to daphnia and green algae was observed, while its degradation intermediates showed different toxicity characteristics; intermediate P1 was classified as highly toxic to green algae, and P5 was highly toxic to daphnia. Figure 9 (a) Regarding chronic toxicity, SMT itself is highly toxic to Daphnia. Several degradation intermediates exhibit increased chronic toxicity—P1, P2, P4, and P5 are all highly toxic to fish and Daphnia. Figure 9 (b) Effective control of these toxic intermediates during degradation is crucial for minimizing overall ecological risk. For SMX, most degradation intermediates exhibited lower acute toxicity compared to the parent compound. Only P6 showed higher acute toxicity than SMX (b). Figure 9 (c) Regarding chronic toxicity, intermediates P1, P4, and P7 are highly toxic to fish, and P6 is highly toxic to daphnia ( Figure 9 (d) These intermediates exhibited high toxicity to one of the three aquatic species, similar to SMX. In contrast, intermediates P3, P5, and P8 were classified as “harmless” to all three aquatic species in both acute and chronic toxicity assessments. These findings suggest that the TMT-DB / Vis process can effectively reduce the overall practical toxicity of sulfonamide antibiotics. However, some transformation products still exhibit ecotoxicity, highlighting the need for continued monitoring of their environmental impact.

[0056] 5. Photocatalytic mechanism The photocatalytic mechanism of TMT-DB and TMT-NA for H2O2 production and SAs degradation, such as Figure 7 As shown, both COF materials generate photogenerated electron-hole pairs under visible light irradiation. Thanks to their D-π-A structural configuration, electrons rapidly migrate from the aromatic ring unit to the triazine ring via vinyl π-bridges, achieving directional charge transfer and promoting efficient electron-hole separation. Optimized AA stacking enhances vertical electron transport, while vinyl linkages further promote the continuity and efficiency of electron conduction. TMT-DB and TMT-NA primarily generate H2O2 through a two-step single-electron ORR: first, photogenerated electrons react with adsorbed O2 to form O2. • Then O2 • It accepts an extra electron to generate H2O2. During this process, a portion of the O2... • It can also be with h + Interaction generation 1 O2. The generated H2O2 can further accept electrons to form •OH. In the presence of pollutants, these reactive species, including O2... • , 1 O2, • OH, H2O2 and h+ They jointly attack SA molecules, causing them to degrade and eventually mineralize into small organic molecules, CO2, and H2O.

[0057] Regarding photocatalytic performance, the faster charge transfer and lower electron-hole recombination in TMT-DB enable photogenerated electrons to be used rapidly and efficiently in the reaction. Therefore, TMT-DB exhibits superior performance in the rapid removal of organic pollutants and the rapid generation of H2O2 in the short term. In contrast, the slower charge transfer and higher electron-hole recombination in TMT-NA limit its initial photocatalytic activity, but its naphthalene-based extended π-conjugated system provides a wider spectral response range and a larger delocalized electron pool, which is beneficial for maintaining the photocatalytic performance of H2O2 production over a longer period. Therefore, TMT-DB is more suitable for processes requiring high initial activity and fast reaction rates, while TMT-NA is more suitable for long-term reaction systems requiring stable catalytic performance.

[0058] In summary, this invention successfully regulated vinyl-linked D-π-A COFs through electron donor engineering to elucidate their differences in photocatalytic performance and mechanisms in H2O2 generation and pollutant degradation. Differences in structure and electronic properties between two highly crystalline COFs with specific structures lead to different advantages in various photocatalytic applications. TMT-NA exhibits stronger visible light absorption and a narrower band gap due to its extended π-conjugation, resulting in superior long-term photocatalytic H2O2 production compared to TMT-DB. The average H2O2 production rate of TMT-NA is 1.4 times that of TMT-DB. In contrast, TMT-DB possesses faster charge migration, lower charge recombination, and a more negative conduction band position, endowing it with stronger photogenerated electron reduction capabilities. These properties explain the superior performance of TMT-DB in rapid pollutant degradation, with its SMT degradation rate constant under visible light being ten times that of TMT-NA. Mechanistic studies indicate that H2O2 generation is primarily mediated by O2. • The ORR process is a sequential, stepwise, single-electron approach for key intermediates. O2 • and 1O2 was identified as the primary reactive species responsible for SMT degradation. Yeager-type and Pauling-type oxygen adsorption structures likely reside at the active sites of TMT-NA and TMT-DB, respectively. Furthermore, TMT-DB exhibited excellent structural stability and broad environmental compatibility in cyclic operation tests and various aquatic matrices, and it also demonstrated highly efficient removal of various SAs from water. This study elucidates the structure-performance relationship of bifunctional photocatalysis in the D-π-A system, providing valuable insights for the application of customized COFs. It highlights the crucial role of electron-donating motifs in regulating charge kinetics and reaction pathways, which is essential for enhancing H2O2 production and reactive oxygen species generation to achieve efficient pollutant remediation.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A vinyl-linked donor-π-acceptor COF, characterized in that, comprising an electron donor, an electron acceptor and a π-conjugated connecting bridge; wherein the electron donor is a benzene ring, a naphthalene ring or a derivative thereof; the electron acceptor is 2,4,6-trimethyl-1,3,5-triazine; the π-conjugated connecting bridge is a vinyl group, used for covalently connecting the electron donor and the electron acceptor to form a conjugated skeleton with a donor-π-acceptor electronic structure.

2. The vinyl-linked donor-π-acceptor COF according to claim 1, wherein when the electron donor is a benzene ring structure, a structure represented by formula (I) is used as a structural repeating unit: when the electron donor is a naphthalene ring structure, a structure represented by formula (II) is used as a structural repeating unit: comprising the following steps: 。 3. A process for the preparation of the ethenyl-linked donor-π-acceptor COFs of claim 1 or 2, characterized in that, adding the electron donor, the electron acceptor and a catalyst into an organic solvent, ultrasonic mixing and degassing, then heating reaction; after the reaction is completed, cooling to room temperature, collecting the precipitate by filtration, and washing and drying to obtain the product. the electron acceptor is 2,4,6-trimethyl-1,3,5-triazine; the electron donor is p-xylylene glycol or naphthalene-2,6-dimethyl glycol; and the catalyst is an acid catalyst or a base catalyst.

4. The method for preparing vinyl-linked donor-π-acceptor COFs according to claim 3, characterized in that, the molar ratio of the electron acceptor to the electron donor is (0.3-0.6):(0.5-0.8); 5. The method for preparing vinyl-linked donor-π-acceptor COFs according to claim 3, characterized in that, the heating reaction is carried out at a temperature of 110-160 ℃ for 70-80 h. The concentration of the electron acceptor in the organic solvent is 0.04-0.05 mol-L -1 ; the organic solvent is one or more of n-butanol, 1,2-dichlorobenzene, mesitylene, 1,4-dioxane and acetonitrile; 6. The method for preparing vinyl-linked donor-π-acceptor COFs according to claim 3, characterized in that, the solvent used for washing is one or more of methanol, tetrahydrofuran, acetone and dichloromethane; the drying is carried out under vacuum at 110-130 ℃ for 10-15 h.

7. Use of the vinyl-linked donor-π-acceptor COF according to claim 1 or 2 in photocatalytic production of hydrogen peroxide and photocatalytic degradation of pollutants. The vinyl-linked donor-π-acceptor COF according to claim 1 or 2 is dispersed in water as a photocatalyst, and visible light is used for irradiation under ambient air conditions to produce hydrogen peroxide; 8. A method for photocatalytic production of hydrogen peroxide, characterized by, 6-7 mL of water is used for dispersing 1 g of the photocatalyst; the time for visible light irradiation is 2-60 min. The vinyl-linked donor-π-acceptor COF according to claim 1 or 2 is dispersed in a sample containing pollutants as a photocatalyst, and is first stirred and mixed in the dark, and then visible light is used for irradiation to photocatalytically degrade the pollutants.

9. A method of photocatalytic degradation of pollutants, characterized in that, 6-7 mL of a sample containing antibiotics is used for dispersing 1 g of the photocatalyst; the time for visible light irradiation is 1-15 min; 10. The method of photocatalytic degradation of pollutants according to claim 9, characterized in that, the pollutants are one or more of sulfamethoxazole, sulfathiazole, sulfapyridine, sulfadiazine and sulfisomidine. ​

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