A thiazole ring connection-based covalent organic framework material and a preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalytic materials, and particularly relates to a covalent organic framework material based on a thiadiazole ring connection and a preparation method and application thereof. The application proposes a locking enhancement combined sulfuration strategy for C=N bridges, acylhydrazone bonds in covalent organic frameworks (COFs) connected by acylhydrazone bonds are sulfurated, cyclized and oxidized by using Lawesson reagent as a thio reagent, and the COFs based on the thiadiazole ring connection are synthesized, asymmetric electron distribution is realized by introducing S heteroatoms to form a thiadiazole ring, and it is found through the research of the application that the new COFs used as a photocatalyst realize excellent photocatalytic hydrogen peroxide generation and photocatalytic aerobic oxidation coupling of benzylamine.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a covalent organic framework material based on thiadiazole ring linkage, its preparation method, and its application. Background Technology

[0002] Photocatalytic aerobic oxidation technology, following the principles of green chemistry, has been widely applied in the oxidation reactions of substances such as sulfides, alcohols, secondary amines, and benzyl halides. In the field of photochemistry, reactive oxygen species (ROS) can be generated through photocatalysis; this reaction method is not only highly efficient but also environmentally friendly. Therefore, photocatalysis has become an ideal choice for aerobic oxidation. Currently, researchers have devoted considerable effort to developing various photocatalysts, including novel materials such as transition metal-based composites, polyoxometalates, and coordination complexes, to achieve highly efficient aerobic oxidation reactions.

[0003] Covalent organic frameworks (COFs) are a new class of crystalline porous polymers characterized by lightweight organic backbone structures linked by covalent bonds. These materials have attracted considerable attention due to their tunable band gaps, abundant catalytic sites, and excellent photochemical stability, making them ideal candidates for photocatalytic aerobic oxidation reactions. According to existing research, nitrogen atoms typically play a crucial role as active sites in catalytic processes. Therefore, designing and modifying nitrogen atoms is an effective strategy for improving photocatalytic efficiency.

[0004] In recent years, imine-linked COFs have been widely used in photocatalysis due to their simple synthesis, high crystallinity, and multifunctional tunability. However, the imine covalent organic framework has only one N site as the main active site, fundamentally limiting the improvement of the catalytic activity of imine COFs. In contrast, hydrazone-linked COFs connected by C=N bonds have two nitrogen active sites in each unit. Studies have shown that, under comparable structural configurations, their photocatalytic activity is superior to that of imine-based COFs. However, the reversibility of the C=N bond poses a challenge to its chemical stability, and the strong polarization of the C=N bond hinders the delocalization of π electrons, leading to discontinuous π-conjugated structures within the COFs. To address these challenges, introducing functional molecular units into C=N bonded COFs through chemical locking has been recognized as an effective strategy, transforming reversible bonds into stable and functional covalent bonds within the COFs. For example, post-functionalization of COFs via multi-component Povarov reactions or three-component Doebner reactions has been reported to obtain stable COFs linked to quinoline, thereby enhancing hydrogen peroxide photosynthetic efficiency. Another study reported a novel strategy for C=N bridge locking via rhodium-catalyzed [4+2] cyclization to improve photocatalytic aerobic oxidation efficiency. Although these strategies have significantly improved the stability of COFs, efficient reaction sites and efficient reaction kinetics are still lacking. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a locking-enhanced sulfidation strategy targeting C=N bridges. By using Lawesson's reagent as a sulfidating agent to perform sulfidation, cyclization, and oxidation reactions on the acylhydrazone-linked COFs, COFs based on thiadiazole rings are synthesized. This achieves asymmetric electronic distribution by introducing S heteroatoms to form thiadiazole rings. Research in this invention has revealed that these novel COFs, when used as photocatalysts, achieve excellent photocatalytic hydrogen peroxide generation and photocatalytic aerobic oxidative coupling of benzylamine.

[0006] Specifically, in a first aspect, the present invention provides a method for preparing a covalent organic framework material based on thiadiazole ring linkages, comprising the following steps:

[0007] (1) A covalent organic framework with acylhydrazone bonds is formed by dehydration condensation reaction of ligands with aldehyde groups and ligands with acylhydrazine groups;

[0008] (2) Acylhydrazone bonds are converted into thiadiazole rings through thiolation, cyclization and oxidation reactions to obtain covalent organic framework materials based on thiadiazole ring linkages;

[0009] The ligand containing the hydrazide is 2,5-diethoxyterephthalohydrazide.

[0010] Further, the ligand having an aldehyde group is benzo[1,2-b:3,4-b:5,6-b'']trithiophene-2,5,8-trialdehyde, 1,3,5-tris(4-formylphenyl)triazine, or 1,3,5-triformylbenzene.

[0011] Further, the dehydration condensation reaction described in step (1) is carried out as follows: the ligand with an aldehyde group and the ligand with an acylhydrazine group are subjected to a solvothermal reaction in a reaction solvent under the action of acid.

[0012] Furthermore, the molar ratio of the ligand with the aldehyde group to the ligand with the hydrazide group is 2:3.

[0013] Furthermore, the reaction solvent is one or a mixture of several of the following: dioxane, mesitylene, N,N-dimethylformamide, N,N-dimethylacetamide, 1,2-dichlorobenzene, 1,3-dimethyl-2-imidazolium ketone, n-butanol, benzyl alcohol, methanol, ethanol, dimethyl sulfoxide, acetonitrile, and cyclohexane.

[0014] Furthermore, the acid is acetic acid at a concentration of 3-6 mol / L.

[0015] Furthermore, the solvothermal reaction is carried out at 120-180°C for 3-7 days.

[0016] Furthermore, the solvothermal reaction is carried out under degassing and sealing conditions.

[0017] Furthermore, the degassing includes three cryogenic degassing cycles, for example, rapid freezing using a liquid nitrogen bath followed by three cryogenic pump-thawing cycles for degassing.

[0018] Furthermore, the preparation method further includes ultrasonic treatment of the reaction system before the start of the solvothermal reaction to ensure that the reaction raw materials are dispersed and mixed uniformly.

[0019] Furthermore, the preparation method also includes washing and drying the reaction product after the solvothermal reaction is completed.

[0020] Furthermore, the washing process includes washing with acetone and tetrahydrofuran.

[0021] Furthermore, the drying process includes vacuum drying.

[0022] Further, the thiolation, cyclization and oxidation reactions in step (2) are carried out as follows: the covalent organic framework obtained in step (1) is refluxed in an organic solvent under the action of a thiolation reagent and a catalyst.

[0023] Furthermore, the thiolation reagent is a Lawesson reagent.

[0024] Furthermore, the organic solvent is toluene, THF, or pyridine.

[0025] Furthermore, the catalyst is 4-(dimethylamino)pyridine.

[0026] Furthermore, step (2) also includes washing and drying the reaction product after the reflux reaction is complete.

[0027] Furthermore, the washing includes washing with N,N-dimethylformamide (DMF) and tetrahydrofuran (THF).

[0028] Furthermore, the drying process includes vacuum drying.

[0029] In a second aspect, the present invention provides a covalent organic framework material based on thiadiazole ring linkages, obtained by the preparation method described herein.

[0030] In a third aspect, the present invention provides an application of a covalent organic framework material based on thiadiazole ring linkages as described herein as a photocatalyst.

[0031] Furthermore, the covalent organic framework material is used for photocatalytic hydrogen peroxide generation and photocatalytic benzylamine coupling.

[0032] Beneficial effects of the present invention

[0033] This invention proposes a locking-enhanced sulfidation strategy targeting the C=N bridge. It utilizes Lawesson's reagent (LR) as the sulfidation agent for a post-cyclization reaction to achieve excellent photocatalytic hydrogen peroxide generation and benzylamine coupling. Overall, the novel COFs prepared by this strategy exhibit three unique structural advantages: 1) the thiodiazole framework significantly enhances intramolecular polarity and the DA structure; 2) the locked-in coplanar structure of TDA-BTT-COF endows it with rapid exciton dissociation along the extended effective (-conjugated plane) direction, thereby promoting rapid charge transfer; 3) the introduction of S heteroatoms to form a heteropolyaromatic covalent organic framework significantly improves chemical stability, thus enhancing its intrinsic photocatalytic activity. Therefore, compared with the original hydrazone-linked covalent organic framework structure, this novel COF exhibits significant chemical stability, high in-plane conjugation, and excellent photocatalytic and photoelectric properties in harsh environments. For example, the TDA-BTT-COF prepared in Example 1 achieves a photosynthetic hydrogen peroxide generation rate of up to 5270 μmol g in pure water. -1 h -1 Compared to the original imine-linked covalent organic framework (1878 μmol g), -1 h -1 This represents a three-fold increase and surpasses many advanced organic and inorganic photocatalysts. More importantly, thanks to the extended π-conjugated structure, the novel COFs constructed exhibit extremely high activity in photocatalytic aerobic oxidation. For example, the TDA-BTT-COF in Example 1 can achieve 100% photocatalytic conversion efficiency of benzylamine within 1 hour under 5W blue LED irradiation, which is far higher than that of hydrazone-based covalent organic frameworks. Attached Figure Description

[0034] Figure 1 The chemical structure characteristics of the photocatalytic COFs prepared in Example 1 are shown. (a) Top view of the unit cell of HZ-BTT-COF. (b) Pawley refinement of the experimental PXRD pattern of HZ-BTT-COF. (c) N2 adsorption-desorption isotherm of HZ-BTT-COF, with the pore size distribution in the inset. (d) Top view of the unit cell of TDA-BTT-COF. (e) Pawley refinement of the experimental PXRD pattern of TDA-BTT-COF. (f) N2 adsorption-desorption isotherm of TDA-BTT-COF, with the pore size distribution in the inset. (g) FTIR spectra of HZ-BTT-COF and TDA-BTT-COF. (h) 13Css NMR confirmed that the imine bond had been converted to the corresponding thiadiazole. (i) Chemical stability test of HZ-BTT-COF and TDA-BTT-COF after treatment with 3M hydrochloric acid, 3M sodium hydroxide and 1.0 M hydrogen peroxide for 12 hours. The experiment was independently repeated three times (Figs. b, c, e, f, g, h, i) and the results were consistent. In Figs. b, e, g, h, i, au represents any unit.

[0035] Figure 2 The photophysical characterization and photocatalytic hydrogen peroxide generation performance of the photocatalytic COFs prepared in Example 1 are shown. (a) Solid-state UV-Vis diffuse reflectance spectra and Tauc plots used for bandgap calculation. (b) Band structure diagrams of HZ-BTT-COF and TDA-BTT-COF. (c) Photocurrent response of HZ-BTT-COF and TDA-BTT-COF. (d) Steady-state photoluminescence (PL) measurements of HZ-BTT-COF and TDA-BTT-COF. (e) Time-resolved fluorescence spectra of HZ-BTT-COF and TDA-BTT-COF under 370 nm excitation. (f) Electron paramagnetic resonance (EPR) spectra of HZ-BTT-COF and TDA-BTT-COF under darkness and visible light irradiation. (g) Photocatalytic activity of HZ-BTT-COF and TDA-BTT-COF in hydrogen peroxide generation (5 mg COFs dissolved in 25 mL of deionized water and seawater, temperature 25°C, 300 W xenon lamp, λ>420 nm). (h) Photocatalytic activity of HZ-BTT-COF and TDA-BTT-COF in hydrogen peroxide generation (5 mg COFs dissolved in 25 mL of deionized water and seawater, temperature 25°C, 300 W xenon lamp, λ>420 nm). (i) PXRD patterns of HZ-BTT-COF and TDA-BTT-COF before and after four cycles (COFs were regenerated by washing with acetone and methanol). The experiment was independently repeated three times (Figs. a, c, d, e, f, g, h, i), and the results were consistent. In Figs. a, c, d, f, i, au represents arbitrary units.

[0036] Figure 3 The reaction pathway and mechanism of hydrogen peroxide photosynthesis of photocatalytic COFs prepared in Example 1 are shown. (a) Photocatalytic hydrogen peroxide production of TDA-BTT-COF was carried out in methanol (10% by volume, as a hole scavenger), where hydrogen peroxide was generated in nitrogen and reacted with silver nitrate (0.01 M). Experimental conditions: water (25 mL), catalyst (5 mg), 300 W xenon lamp, λ > 420 nm. (b) By 18O2 isotope experiments to investigate the source of hydrogen peroxide. (c) Electron paramagnetic resonance signals of the reaction solution under dark and visible light irradiation in the presence of DMPO as a spin trapping reagent. (df) In-situ DRIFT spectrum of TDA-BTT-COF. (gi) In-situ DRIFT spectrum of HZ-BTT-COF. The experiment was independently repeated three times (Figure ai), and the results were consistent. In Figures b, c, d, e, g, and h, au represents arbitrary units.

[0037] Figure 4 The photocatalytic performance of the photocatalytic COFs prepared in Example 1 for the oxidative coupling of benzylamine is shown. (a) Benzylamine conversion of HZ-BTT-COF and TDA-BTT-COF at different time points. (b) Reusability of HZ-BTT-COF and TDA-BTT-COF. Reaction conditions: photocatalyst (8 mg), benzylamine (0.2 mmol), blue LED (460 nm, 5 W), acetonitrile (2 mL), O2 (1 atm), reaction time 1 h. (c) Evaluation of different ROS effects during the oxidation process using different quenchers. (d) Photocatalytic results of HZ-BTT-COF and TDA-BTT-COF in benzylamine coupling. (e) Proposed benzylamine coupling mechanism. The experiment was independently repeated three times (Figures a and b), with similar results.

[0038] Figure 5 The universality of thiadiazole functionalization was demonstrated. (a) A scheme for preparing TDA-COFs via hydrazone-to-thiadiazole linkage conversion. (b) PXRD patterns of the six COFs. (c) PXRD patterns of the six COFs. 13 Css NMR spectra. (d) Photocatalytic activity of the six COFs for hydrogen peroxide production. (e) Benzylamine conversion of the six COFs. The experiment was independently repeated three times (Figures be), and the results were similar. Detailed Implementation

[0039] This invention first prepares hydrazone-based covalent organic frameworks (COFs) by reacting an aldehyde-containing ligand (e.g., benzo[1,2-b:3,4-b:5,6-b'']trithiophene-2,5,8-trialdehyde) with an acylhydrazine-containing ligand (e.g., 2,5-diethoxyterephthalohydrazide) via hydrothermal condensation. Subsequently, the hydrazone-based COFs are transformed into thiadiazole-linked COFs through a post-cyclization reaction with elemental sulfur. This hydrazone-linked framework undergoes a series of thiolation, cyclization, and oxidation reactions in toluene using Lawesson's reagent (LR), ultimately yielding fully conjugated COFs with thiadiazole rings. This is a novel method for preparing heteropolyaromatic covalent organic frameworks with customized electronic properties and enhanced stability.

[0040] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0041] Example 1: Synthesis of TDA-BTT-COF

[0042] Synthesis of HZ-BTT-COF: Benzo[1,2-b:3,4-b:5,6-b'']trithiophene-2,5,8-trialdehyde (20.0 mg, 0.06 mmol) and 2,5-diethoxyterephthalohydrazide (25.7 mg, 0.09 mmol) were added to a polytetrafluoroethylene tube. Subsequently, 1,2-dichlorobenzene (1.3 mL), 1,3-dimethyl-2-imidazolium ketone (0.86 mL), and 6 M aqueous acetic acid (0.125 mL) were added. The resulting mixture was sonicated for 10 minutes, followed by degassing through three lyophilization-thawing cycles and sealing under vacuum. After the temperature reached room temperature, the sealed tube was heated at 180 °C and allowed to stand for 3 days. The solid was separated by filtration and washed with anhydrous tetrahydrofuran and anhydrous acetone. After vacuum drying at 60°C for 12 hours (41.2 mg, yield 97%), a covalent organic framework with acylhydrazone linkages was obtained and named HZ-BTT-COF.

[0043] Synthesis of TDA-BTT-COF: Lawesson's reagent (100 mg) and toluene (20 mL) were added to HZ-BTT-COF (40 mg), followed by the addition of 4-(dimethylamino)pyridine (44 mg). After refluxing the mixture for 24 hours, the solid product was obtained by filtration, washed with DMF and THF, and dried in a vacuum oven at 70 °C. Next, the solid was redispersed in 20 mL of toluene, followed by the addition of equal volumes of Lawesson's reagent and 4-(dimethylamino)pyridine, and refluxed for 24 hours. The solid obtained by filtration, washed with DMF and THF, and dried under vacuum at 70 °C yielded a covalent organic framework material based on a thiadiazole ring, named TDA-BTT-COF (38 mg, 95%).

[0044] Example 1: Synthesis of TDA-BTT-COF

[0045] Synthesis of HZ-BTT-COF: Benzo[1,2-b:3,4-b:5,6-b'']trithiophene-2,5,8-trialdehyde (20.0 mg, 0.06 mmol) and 2,5-diethoxyterephthalohydrazide (25.7 mg, 0.09 mmol) were added to a polytetrafluoroethylene tube. Subsequently, 1,2-dichlorobenzene (1.3 mL), 1,3-dimethyl-2-imidazolium ketone (0.86 mL), and 6 M aqueous acetic acid (0.125 mL) were added. The resulting mixture was sonicated for 10 minutes, followed by degassing through three lyophilization-thawing cycles and sealing under vacuum. After the temperature reached room temperature, the sealed tube was heated at 180 °C and allowed to stand for 3 days. The solid was separated by filtration and washed with anhydrous tetrahydrofuran and anhydrous acetone. After vacuum drying at 60°C for 12 hours, a covalent organic framework with acylhydrazone linkages was obtained and named HZ-BTT-COF (41.2 mg, yield 97%).

[0046] Synthesis of TDA-BTT-COF: Lawesson's reagent (100 mg) and toluene (20 mL) were added to HZ-BTT-COF (40 mg), followed by the addition of 4-(dimethylamino)pyridine (44 mg). After refluxing the mixture for 24 hours, the solid product was obtained by filtration, washed with DMF and THF, and dried in a vacuum oven at 70 °C. Next, the solid was redispersed in 20 mL of toluene, followed by the addition of equal volumes of Lawesson's reagent and 4-(dimethylamino)pyridine, and refluxed for 24 hours. The solid obtained by filtration was washed with DMF and THF and dried under vacuum at 70 °C to obtain a covalent organic framework material based on a thiadiazole ring, named TDA-BTT-COF (38 mg, yield 95%).

[0047] Example 2: Synthesis of TDA-TTA-COF

[0048] Synthesis of HZ-TTA-COF: 1,3,5-tris(4-formylphenyl)triazine (TTA) (39.3 mg, 0.1 mmol) and 2,5-diethoxyterephthalohydrazide (42.5 mg, 0.15 mmol) were added to a polyester tube. Subsequently, dimethyl sulfoxide (3 mL), anhydrous dioxane (1 mL), and 6 M aqueous acetic acid (0.4 mL) were added. The resulting mixture was sonicated for 10 minutes, degassed by three cycles of lyophilization-vacuum drying-thawing, and then sealed in a vacuum environment. After the temperature reached room temperature, the sealed tube was heated at 120 °C and allowed to stand for 3 days. The solid was separated by filtration and washed with anhydrous tetrahydrofuran and anhydrous acetone. Finally, after vacuum drying at 60 °C for 12 hours, a covalent organic framework linked by acylhydrazone bonds was obtained, named HZ-TTA-COF (74.5 mg, 98% yield).

[0049] Synthesis of TDA-TTA-COF: Lawesson's reagent (100 mg) and toluene (20 mL) were added to HZ-TTA-COF (40 mg), followed by the addition of 4-(dimethylamino)pyridine (44 mg). The resulting mixture was refluxed for 24 hours, filtered to obtain a solid product, washed with DMF and THF, and dried under vacuum at 70 °C. The above steps were repeated twice, with a total reaction time of 72 hours, to obtain a covalent organic framework material based on a thiadiazole ring, named TDA-TTA-COF (37 mg, yield 93%).

[0050] Example 3: Synthesis of TDA-TFB-COF

[0051] Synthesis of HZ-TFB-COF: 1,3,5-tricarboxyphenyl (TFB) (16.2 mg, 0.1 mmol) and 2,5-diethoxyterephthalohydrazide (42.5 mg, 0.15 mmol) were added to a polytetrafluoroethylene tube. Subsequently, dimethyl sulfoxide (3 mL), anhydrous dioxane (1 mL), and 6 M aqueous acetic acid (0.4 mL) were added. The resulting mixture was sonicated for 10 minutes, degassed by three lyophilization-thawing cycles, and then vacuum-sealed. After returning to room temperature, the sealed tube was heated at 120 °C and allowed to stand for 3 days. The solid was separated by filtration and washed with anhydrous tetrahydrofuran and anhydrous acetone. After vacuum drying at 60 °C for 12 hours, a covalent organic framework linked by acylhydrazone bonds was obtained, named HZ-TFB-COF (51.4 mg, 96% yield).

[0052] Synthesis of TDA-TFB-COF: Lawesson's reagent (100 mg) and toluene (20 mL) were added to HZ-TFB-COF (40 mg), followed by the addition of 4-(dimethylamino)pyridine (44 mg). The resulting mixture was refluxed for 24 hours, filtered to obtain a solid product, washed with DMF and THF, and dried under vacuum at 70 °C. The above steps were repeated twice, with a total reaction time of 72 hours, to obtain a covalent organic framework material based on a thiadiazole ring, named TDA-TFB-COF (38 mg, yield 95%).

[0053] Test Example 1: Structural Characterization of Covalent Organic Framework Materials

[0054] Figure 1 a and Figure 1 Figure d shows the schematic structures of HZ-BTT-COF and TDA-BTT-COF prepared in Example 1, respectively.

[0055] This invention employed powder X-ray diffraction (PXRD) analysis to conduct a detailed study of the crystal properties and structural framework of HZ-BTT-COF and TDA-BTT-COF. Both materials exhibited significant and sharp diffraction peaks in their PXRD patterns, indicating high crystallinity. To determine the lattice parameters, this invention performed detailed Pawley refinement on the experimental PXRD data. Figure 1 (b, e). Both COFs crystallize in the same hexagonal P6 / M space group, and the AA stacking model provides a good fit. XRD data from TDA-BTT-COF, after Pawley refinement, yielded cell parameters a=b=37.78 Å, c=3.5 Å, a low Rwp value of 4.25%, and an Rp value of 2.95%.

[0056] The porous properties of HZ-BTT-COF and TDA-BTT-COF were further evaluated using nitrogen adsorption isotherms, such as... Figure 1 As shown in c and f, the Brunauer-Emmett-Teller (BET) specific surface areas of HZ-BTT-COF and TDA-BTT-COF were measured to be 1176 m². 2 g -1 and 808 m 2 g -1 Pore ​​size distribution analysis using a nonlocal density functional theory model revealed that the average pore size of HZ-BTT-COF is approximately 2.89 nm, while that of TDA-BTT-COF is 2.79 nm. Furthermore, scanning electron microscopy (SEM / TEM) observation showed that HZ-BTT-COF and TDA-BTT-COF exhibit similar rod-like morphologies. Elemental dispersion spectroscopy (EDS) confirmed the uniform distribution of carbon, nitrogen, oxygen, and sulfur within the covalent organic framework matrix, demonstrating the homogeneous integration of sulfur within the covalent organic framework scaffold. This comprehensive structural characterization highlights the successful synthesis of TDA-BTT-COF, laying the foundation for its superior performance in photocatalytic applications.

[0057] The successful synthesis of HZ-BTT-COF with hydrazone bond structure was preliminarily confirmed by Fourier transform infrared spectroscopy (FTIR). The results were obtained at 1670 and 1610 cm⁻¹. -1 The characteristic C=O and N=CH vibrational peaks at the site provide clear evidence for hydrazone bond formation. Figure 1 g). With the disappearance of hydrazone bond vibration and 1641 and 653 cm -1The appearance of novel N=C and CS vibrational peaks specific to the thiadiazole ring further confirms the transformation of HZ-BTT-COF to TDA-BTT-COF. Compared with the HZ-BTT-COF precursor, the solid-state nuclear magnetic resonance (ssNMR) spectrum of TDA-BTT-COF shows significant and clear structural changes. Figure 1 h). In the 13C NMR spectrum of HZ-BTT-COF, the characteristic peaks at 159.7 ppm and 149.8 ppm correspond to C=O and hydrazone-N bonded carbon atoms, respectively. After the cyclization reaction, TDA-BTT-COF shows two new peaks at 161.9 and 156.8 ppm, which are attributed to the carbon atoms of the thiadiazole ring, indicating that the imine has been successfully converted into a thiadiazole ring.

[0058] X-ray photoelectron spectroscopy (XPS) further confirmed the formation of thiadiazole bonds in TDA-BTT-COF. One advantage of thiadiazole bonds is their higher chemical stability compared to hydrazone bonds. To demonstrate the chemical stability of TDA-BTT-COF, this invention subjected the activated sample to rigorous aqueous solution tests: 3 M hydrochloric acid (pH < 0), 3 M sodium hydroxide (pH > 14), and 1 M hydrogen peroxide (a strong oxidizing agent). After 12 hours of exposure, the PXRD pattern still retained the same sharp peak shape as the original sample, proving that the crystallinity of TDA-BTT-COF did not change after immersion. In contrast, HZ-BTT-COF only maintained its crystallinity in the 1 M hydrogen peroxide test. Figure 1 i), highlighting the excellent stability conferred by the thiadiazole ring to TDA-BTT-COF. This detailed characterization not only verifies the successful synthesis and structural integrity of the heteropolyaromatic TDA-BTT-COF, but also emphasizes its outstanding chemical stability, a key attribute for its application in harsh chemical environments and photocatalytic processes.

[0059] Test Example 2: Photocatalytic hydrogen peroxide generation activity of covalent organic framework materials

[0060] After confirming the synthesis of HZ-BTT-COF and TDA-BTT-COF through comprehensive characterization, this invention further investigated their light absorption properties and band structure. Ultraviolet-visible diffuse reflectance spectroscopy (DRS) showed that both materials exhibited effective light absorption in the visible spectral range. Figure 2 a). Notably, TDA-BTT-COF exhibits a wider absorption range in the 550 nm to 600 nm wavelength range, which is attributed to the enhanced conjugation effect provided by the thiadiazole bonding. This absorption characteristic is consistent with... Figure 2The yellow hue of HZ-BTT-COF and the orange hue of TDA-BTT-COF in sample a are highly consistent. The Kubelka-Munk equation derived from the Tauktu method in DRS analysis indicates that the optical bandgap (Eg) of HZ-BTT-COF is 2.51 eV, while that of TDA-BTT-COF is slightly lower to 2.31 eV. Figure 2 a). Using the Mott-Schottky plot, the flat band potential of HZ-BTT-COF was determined to be -1.03 V, and that of TDA-BTT-COF was -0.69 V. By integrating the optical band gap with the Mott-Schottky data, this invention deduces the band structure configuration ( Figure 2 b). Based on flat-band potential calculations, the conduction band (CB) of HZ-BTT-COF and TDA-BTT-COF are -0.83 V and -0.49 V, respectively (relative to the standard hydrogen electrode NHE). Subsequently, according to the relationship ECB = EV(B) - Eg, the valence band (VB) is estimated to be 1.68 V and 1.82 V, respectively (relative to NHE). Given that the CB sites of HZ-BTT-COF and TDA-BTT-COF are higher than 2e - The oxygen reduction reaction (ORR, indirect ORR is -0.33 V, direct ORR is 0.68 V, relative to NHE at pH=0) has a more negative redox potential; thermodynamically, it can be mediated by direct or indirect 2e⁻. - Hydrogen peroxide is generated via the ORR pathway. Meanwhile, the VB site of TDA-BTT-COF is higher than that of 2e. - From a thermodynamic perspective, the water oxidation reaction (WOR, 1.76 vs. NHE) can proceed via 2e⁻. - Hydrogen peroxide is generated via the WOR pathway. However, HZ-BTT-COF does not possess this capability.

[0061] This invention investigates the separation and migration dynamics of photogenerated charges in HZ-BTT-COF and TDA-BTT-COF materials using transient photocurrent response measurements. Under alternating illumination conditions, both materials exhibit continuous and stable photocurrent responses. Figure 2 c). The photocurrent of TDA-BTT-COF is significantly higher than that of HZ-BTT-COF, indicating its superior efficiency in photoinduced charge separation and transport. Furthermore, electrochemical impedance spectroscopy (EIS) analysis of charge transfer resistance revealed that TDA-BTT-COF exhibits a smaller semicircle radius in the Nyquist plot, indicating faster charge transport. Steady-state photoluminescence (PL) spectroscopy showed that TDA-BTT-COF exhibits a significant quenching phenomenon compared to HZ-BTT-COF. Figure 2d), indicating a low charge recombination efficiency. Time-resolved fluorescence spectroscopy, highly sensitive to photogenerated carriers, was used to acquire fluorescence decay curves at a pump wavelength of 370 nm. Figure 2 e). The average fluorescence lifetime of HZ-BTT-COF was measured to be 0.161 nanoseconds, while that of TDA-BTT-COF was 0.422 nanoseconds. The longer fluorescence lifetime of TDA-BTT-COF indicates a slower photoinduced carrier recombination rate, a result consistent with steady-state PL measurements. Furthermore, the generation of photoinduced carriers was characterized using electron paramagnetic resonance (EPR) spectroscopy. Specifically, the EPR signal intensity of TDA-BTT-COF at g=2.0083 (corresponding to the signal intensity of delocalized unpaired electrons within the conjugated COF framework) was higher than that of HZ-BTT-COF under both dark and illuminated conditions (e.g., ...). Figure 2 (as shown in f). The enhanced charge separation and transfer efficiency in TDA-BTT-COF is attributed to the heteropolyaromatic structure formed by the thiadiazole ring, which enhances the (-electron delocalization of the framework and creates new electron donor-acceptor sites, thereby promoting the effectiveness of photocatalytic performance.

[0062] This invention conducted photocatalytic experiments at room temperature (25°C) using deionized water and natural seawater as the reaction medium, without adding any sacrificial agents, and with continuous oxygen supply. The reaction mixture was irradiated with a xenon lamp with a wavelength greater than 420 nm, and the amount of hydrogen peroxide generated was determined by iodometric titration. Both HZ-BTT-COF and TDA-BTT-COF showed a significant linear correlation between hydrogen peroxide generation and light exposure, highlighting their photocatalytic performance. In deionized water with oxygen supply, the hydrogen peroxide generation rate of TDA-BTT-COF was measured to be 5270 μmol g / L. -1 h -1 This is superior to other organic porous catalysts in the prior art. In contrast, the formation rate of HZ-BTT-COF is significantly lower, at only 1878 μmol g. -1 h -1 This highlights the crucial role of thiadiazole bonding in enhancing photocatalytic efficiency. Figure 2 g). Notably, this heteropolyaromatic covalent organic framework can directly generate hydrogen peroxide from seawater without the use of sacrificial reagents. This property is crucial because it facilitates large-scale, practical photosynthesis with lower costs and simpler processes. Figure 2 As shown in g, the hydrogen peroxide yields of HZ-BTT-COF and TDA-BTT-COF in natural seawater are slightly lower than those in deionized water. This is because seawater contains various ions that may interfere with hydrogen peroxide formation or cause its decomposition.

[0063] Furthermore, the photocatalyst of this invention exhibits multifunctionality under various conditions. Photocatalytic experiments of TDA-BTT-COF with different sacrificial agents show that benzyl alcohol (BnOH) performs best as a sacrificial agent (12500 μmol g). -1 h -1 This indicates that the two-phase reaction system composed of water and BnOH can effectively inhibit the decomposition of hydrogen peroxide—because the active sites of COFs remain in the BnOH phase, while the generated hydrogen peroxide rapidly diffuses into the water. Under an O2 atmosphere, the apparent quantum yield (AQY) of TDA-BTT-COF in deionized water at a wavelength of 450 nm was measured to be 9.5%. Furthermore, the solar chemical conversion (SCC) efficiency of TDA-BTT-COF reached 0.27%, exceeding the typical photosynthetic efficiency of 0.10% for plants. These findings highlight the superior photocatalytic performance of TDA-BTT-COF, emphasizing its application potential in artificial photosynthesis and environmental remediation, with efficient hydrogen peroxide generation being crucial.

[0064] The final concentration of hydrogen peroxide depends on the duration of the dynamic equilibrium between hydrogen peroxide formation and decomposition on the catalyst. After 1 hour of continuous irradiation, the hydrogen peroxide concentration of HZ-BTT-COF and TDA-BTT-COF remained above 95%. One advantage of heterogeneous catalysts compared to homogeneous catalysts is their recyclability. To evaluate this, the present invention conducted four continuous cycle experiments on COFs, each including a 1-hour hydrogen peroxide formation run (…). Figure 2 h). After only one cycle, the hydrogen peroxide formation rate of HZ-BTT-COF decreased sharply, accompanied by the loss of some of its crystal structure, which was confirmed by weakened diffraction peaks in the PXRD pattern. In contrast, the formation rate of TDA-BTT-COF was almost unaffected after four cycles, and its crystallinity remained intact. This finding demonstrates the inherent superior stability of TDA-BTT-COF (h). Figure 2 i). Furthermore, FTIR analysis showed that the chemical composition of TDA-BTT-COF remained unchanged after four cycles. These results collectively demonstrate the robust stability and cyclicability of TDA-BTT-COF, reinforcing its potential as a photocatalyst for sustainable hydrogen peroxide production.

[0065] To elucidate the photocatalytic mechanism of hydrogen peroxide generation in this study, a series of experiments were conducted, including active intermediate capture, electron paramagnetic resonance (EPR), rotating disk electrode (RDE), and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements and isotope labeling measurements. When holes are captured in the presence of methanol and oxygen ( Figure 3a) The hydrogen peroxide production of TDA-BTT-COF showed a decreasing trend, while that of HZ-BTT-COF showed an increasing trend. This phenomenon suggests that the holes generated in HZ-BTT-COF may not directly participate in the photocatalytic generation of hydrogen peroxide. When oxygen was replaced by nitrogen in the reaction system, the hydrogen peroxide yield of both COFs decreased significantly. Compared with pure nitrogen conditions, the hydrogen peroxide yield of TDA-BTT-COF increased after adding an electron scavenger (silver nitrate) in the presence of nitrogen. However, under the same conditions, the hydrogen peroxide concentration of HZ-BTT-COF was almost undetectable. This result indicates that 4e-2 electrons may have been generated in HZ-BTT-COF. - WOR process (2H2O + 4h) + →O2 + 4H + ), while 2e may have occurred in TDA-BTT-COF. - WOR process (2H2O + 2h) + → Hydrogen peroxide + 2H + In addition, it has been passed 18 O2 isotope experiments verified the ORR and WOR processes ( Figure 3 b). COFs in H2 16 O and 18 Irradiation with O2 gas for 4 hours. After removing unreacted gases with argon, manganese dioxide was added to the reaction system to decompose hydrogen peroxide and release O2. The escaped gases were analyzed by gas chromatography-mass spectrometry. The decomposition products of photogenerated hydrogen peroxide reacting with manganese dioxide were... 18 O2 and 16 The ratio of hydrogen peroxide to oxygen in the O2 is close to 1:1, indicating that the hydrogen peroxide photosynthetic process in TDA-BTT-COF simultaneously undergoes 2e2O2 oxidation. - ORR and 2e - WOR has two pathways. However, for HZ-BTT-COF, it was observed that... 18 O2 and 16 The ratio of O2 is much higher, which indicates that H2 18 O2 is from 18 The main product of O2 reduction was confirmed, and 4e in HZ-BTT-COF was also confirmed. - WOR process.

[0066] EPR analysis and RDE assays were then employed to further elucidate the reaction pathway of ORR. EPR measurements were performed in methanol using 5,5-dimethyl-1-pyrrolidone N-oxide (DMPO) as a radical spin trap. Figure 3 As shown in c, TDA-BTT-COF exhibits superoxide radical (•O2) activity. -The typical six-line characteristic peak of ) is observed, while the corresponding peak intensity of HZ-BTT-COF is slightly lower, indicating that the induction of thiadiazole significantly promotes the induction of •O2. - The generation of hydroxyl radicals (•OH) and singlet oxygen (•OH) was not detected in EPR measurements. 1 The presence of O2) excludes 1e - The possibility of the WOR process and 1 The involvement of O2 in the hydrogen peroxide photosynthesis process in TDA-BTT-COF. Furthermore, this invention used RDE to measure the linear sweep voltammetry (LSV) curves of HZ-BTT-COF and TDA-BTT-COF at different rotational speeds (100 rpm to 900 rpm). Curves were plotted using the Kutk-Levich method, and the average electron transfer numbers for HZ-BTT-COF and TDA-BTT-COF were calculated to be 1.23 and 1.87, respectively. The results indicate that HZ-BTT-COF mainly derives its photosynthesis through direct 2e- ... - Pathway (O2+2e) - + 2H + →H2O2) reduces O2, while stepwise 1e - The pathway contributes more to hydrogen peroxide photosynthesis (O2+e) in the TDA-BTT-COF-based photocatalytic system. - →•O2 - •O2 - +2H + +e - → Hydrogen peroxide).

[0067] To further support the formation of reaction intermediates and the photocatalytic pathway, this invention conducted in-situ DRIFT tests on HZ-BTT-COF and TDA-BTT-COF in oxygen and steam environments. Figure 3 (di). It is worth noting that the 2,820 cm corresponding to the bending of hydrogen peroxide (OH) -1 Chufeng ( Figure 3 The gradual increase in e and h with light irradiation time indicates the formation of hydrogen peroxide. Originating from the CSC stretching BTT unit (985 cm⁻¹) -1 The peak intensity of CO (1,398 cm⁻¹) also changed with light irradiation time, suggesting that it participates in the reaction as an active site in the reaction pathway. Corresponding to CO (1,398 cm⁻¹) -1 •O2 - (1,165 cm -1 ) and O−O (872 cm -1 The peak intensity also increases over time. Figure 3(d, g), indicating the presence of O2 adsorption and the occurrence of a two-step single-electron pathway in the COF-based photocatalytic system. Finally, C−OH (1,049 cm⁻¹) was observed in in-situ DRIFT spectroscopy. -1 ) and OH (1,262 cm -1 The signal indicates that water adsorbed on the surface of the covalent organic framework can dissociate into *OH. Furthermore, as... Figure 3 As shown in f and i, under the same conditions, the peak changes of HZ-BTT-COF are not as significant as those of TDA-BTT-COF, which further explains why TDA-BTT-COF exhibits superior photocatalytic performance. These experimental insights provide a solid foundation for optimizing the photocatalytic performance of COFs in hydrogen peroxide generation and other related applications.

[0068] Test Example 3: Photocatalytic performance of benzylamine oxidative coupling in covalent organic framework materials

[0069] This study systematically evaluated the photocatalytic activities of HZ-BTT-COF and TDA-BTT-COF in the aerobic oxidation of benzylamine. Acetonitrile (CH3CN) was used as the solvent, and benzylamine and its derivatives were used as model substrates for performance testing. The photocatalytic performance data of benzylamine oxidative coupling (…) Figure 4 a) It is evident that TDA-BTT-COF can completely convert benzylamine to N-benzylbenzaldehyde imine in just 1 hour, while HZ-BTT-COF only achieves a 72% conversion rate in the same hour. This indicates that the introduction of thiadiazole can effectively improve photocatalytic performance. Kinetic curve analysis shows that the reactions of both HZ-BTT-COF and TDA-BTT-COF conform to zero-order kinetics.

[0070] Regarding the reusability of the benzylamine coupling reaction, the experimental results are similar to the above observations, that is, TDA-BTT-COF can still maintain its high photocatalytic activity in four reaction cycles. Figure 4 (b) , while HZ-BTT-COF showed a significant performance loss. Simultaneously, Fourier transform infrared spectroscopy was used to assess the framework stability of TDA-BTT-COF. The spectra of the recovered TDA-BTT-COF sample showed good consistency with the synthesized sample before the benzylamine coupling reaction. These results not only demonstrate the high stability of thiadiazole-linked TDA-BTT-COF but also confirm that photoactive covalent organic frameworks can be used as effective recyclable photocatalysts under relatively harsh conditions.

[0071] To investigate the coupling reaction mechanism, this invention added consumable reagents to the system for experiments. Control experiments showed that the blue LED light source, oxidant O2 source, and TDA-BTT-COF are indispensable conditions for this photocatalytic reaction; without these components, only trace amounts of imine products could be detected. A series of reactive oxygen species (ROS) quenching experiments were used to evaluate the main intermediates in the oxidation process, revealing that the addition of isopropanol had a negligible effect on the yield, confirming that hydroxyl radicals (•OH) did not participate in this photocatalytic process. When L-histidine (L-his) or p-benzoquinone (BQ) was added as... 1 O2 and •O2 − When the cleaning agent was used, the conversion rate was observed to drop sharply from 100% to 45% and 15%. Therefore, 1 O2 and •O2 − It is the key free radical in this reaction. Silver nitrate reacts with O2. − As a photogenerated electron (e - When the receptor for α is added, the formation of the target product is inhibited. Potassium iodide is used as a hole (h + When using a scavenging agent, the conversion rate of N-benzylbenzaldehyde is only 18%. Therefore, e - and h + It also plays an important role in this selective coupling reaction. Figure 4 c). Subsequently, the photocatalytic activity of HZ-BTT-COF and TDA-BTT-COF was investigated by expanding the substrate scope. Under the same optimal conditions as the benzylamine coupling reaction, different substituted benzylamines could generate the product in higher yields than the hydrazone-linked HZ-BTT-COF catalyst. Figure 4 (d) This indicates that the thiadiazole bonding in these photoactive COFs not only enhances the stability of the framework structure but also improves photoactivity. To verify the generation of reactive oxygen species (ROS), electron paramagnetic resonance (EPR) spectroscopy analysis was performed on the formonitrile solution of TDA-BTT-COF. No obvious signal was detected in the dark in an oxygen environment. After 5 minutes of illumination, •O2 appeared in the DMPO system. - The signal indicates that TDA-BTT-COF can rapidly activate oxygen molecules into superoxide radicals under light conditions. Singlet oxygen was also detected in the presence of TEMP. 1 O2), but singlet oxygen was not detected in the HZ-BTT-COF system, which may be the main reason why the catalytic coupling efficiency of benzylamine by HZ-BTT-COF is lower than that by TDA-BTT-COF. According to the experimental results, the photocatalytic coupling reaction mechanism of benzylamine is as follows: Figure 4 As shown in e.

[0072] Furthermore, to demonstrate that the proposed lock-in enhanced binding sulfurization strategy is a general modification strategy, this invention also prepared two additional types of covalent organic frameworks to prove that sulfur addition reactions can also convert hydrazone bonds in other COFs into thiadiazole bonds, thereby enhancing their photocatalytic performance. For example, a hydrazone-linked triazine covalent organic framework (HZ-TTA-COF) and a hydrazone-linked tricarboxyphenyl covalent organic framework (HZ-TFB-COF) were synthesized via solvothermal reaction. Subsequently, TDA-TTA-COF and TDA-TFB-COF (a thiadiazole ring-linked triazine covalent organic framework and a thiadiazole ring-linked tricarboxyphenyl covalent organic framework) were prepared under conditions similar to those of TDA-BTT-COF. Figure 5 a). PXRD, FTIR and 13 Css NMR analysis confirmed that the hydrazone bond was successfully converted into a thiadiazole bond ( Figure 5 b, c). Although the values ​​obtained were lower compared to TDA-BTT-COF (ranked as TDA-BTT-COF > TDA-TTA-COF > TDA-TFB-COF), both TDA-TTA-COF and TDA-TFB-COF showed good efficiency in photocatalytic hydrogen peroxide generation and photocatalytic performance for benzylamine oxidative coupling. Figure 5 (d, e). This result indicates that the photocatalytic performance can be significantly improved by forming heteropolyaromatic thiadiazole bonds.

[0073] In summary, this study proposes a synthetic strategy for thiodiazole heteropolyaromatic TDA-COFs that combines C=N bridge locking enhancement with a sulfidation strategy. The post-cyclization reaction is performed using Lawesson's reagent (LR) as the sulfidation agent to achieve excellent photocatalytic hydrogen peroxide generation and benzylamine coupling. Overall, this TDA-BTT-COF exhibits three unique structural advantages: 1) the thiodiazole framework significantly enhances intramolecular polarity and the DA structure; 2) the locked-in coplanar structure of TDA-BTT-COF endows it with rapid exciton dissociation along the extended effective (-conjugated plane) direction, thereby promoting rapid charge transfer; 3) the introduction of S heteroatoms to form a heteropolyaromatic covalent organic framework significantly improves chemical stability, thus enhancing its intrinsic photocatalytic activity. Therefore, compared with the original hydrazone-linked covalent organic framework structure, this TDA-BTT-COF achieves a photocatalytic hydrogen peroxide generation rate of up to 5270 μmol g in pure water. -1 h -1 Compared to the original imine-linked covalent organic framework (1878 μmol g), -1 h -1The efficiency was improved by three times, surpassing many advanced organic and inorganic photocatalysts. These findings provide a new perspective for the design and development of chemically stable COFs and highlight their practical application value in photocatalytic reactions.

[0074] More importantly, thanks to the extended π-conjugated structure, the constructed photocatalyst TDA-BTT-COF exhibits the highest activity in photocatalytic aerobic oxidation, achieving 100% photocatalytic conversion efficiency of benzylamine within one hour under 5W blue LED irradiation, which is far superior to hydrazone-based covalent organic frameworks. In summary, the strategy proposed in this invention paves the way for the synthesis of a new generation of heteropolyaromatic covalent organic frameworks via an efficient and universal route, and provides new ideas for developing covalent organic framework materials with customized properties. These materials can be used for large-scale production and have wide applications in photocatalysis, electrocatalysis, and many other fields.

[0075] The measurement methods used in the test examples are as follows.

[0076] Hydrogen peroxide detection method (iodometric method): The content of hydrogen peroxide is analyzed by iodometric titration. 1 mL of 0.1 mol∙L⁻¹ -1 Potassium hydrogen phthalate (C8H5KO4) aqueous solution and 1 mL 0.4 mol∙L -1 A potassium iodide (KI) aqueous solution was added to 0.2 mL of solution taken from the catalytic system, mixed, and allowed to stand for 30 minutes. Hydrogen peroxide molecules react with iodide ions (I₂) under acidic conditions. − The reaction produces triiodide ions (I3). − This substance exhibits strong absorption characteristics around 350 nm. I3 was determined using a UV spectrophotometer (UV-6100S). − The absorbance at 350 nm was used to calculate the amount of hydrogen peroxide generated by the photocatalytic reaction.

[0077] Preparation of photocatalytic hydrogen peroxide: The experiment was conducted in a 50 mL vial containing 5 mg of COFs and 25 mL of ultrapure water. The suspension was stirred in the dark for 10 minutes, followed by bubbling with oxygen for 20 minutes. The reaction system was irradiated with a xenon lamp (CEL-HXF300-T3, China Education Golden Light Co., Ltd., λ>420 nm, equipped with circulating water), and oxygen was continuously bubbled into the vial. The concentration of hydrogen peroxide was determined using a UV-Vis spectrophotometer.

[0078] Photocatalytic oxidative coupling of benzylamine: The photocatalytic experimental procedure was as follows: 8 mg of photocatalyst was dispersed in 2 mL of acetonitrile containing 0.2 mmol of benzylamine (placed in a 10 mL quartz reactor). The mixture was then bubbled with O2 for 10 minutes, and the reactor was sealed. An LED light source (total power 5 W) was used in conjunction with an O2 balloon as the light source. The reaction temperature was controlled at 298 K by circulating cooling water. After the reaction, the solution was collected, centrifuged, and filtered through a 0.22 μm syringe filter to remove catalyst particles. The product in the filtrate was identified by gas chromatography (GC-2010 Pro AF) equipped with a flame ionization detector (FID), and the conversion and selectivity were analyzed by GC. Other benzylamine derivatives were tested using the same concentration and the experimental method was similar to the above procedure.

[0079] Photoelectrochemical measurements: The Mott-Schottky curves, photocurrent response, and electrochemical impedance of the catalyst were measured using an electrochemical workstation (Gamry Reference 600, USA). A 300-watt xenon lamp (wavelength λ > 420 nm, average intensity: 100 mW·cm⁻¹) was used as the light source. −2 The photocurrent was measured using a sodium sulfate aqueous solution (0.5 M, pH=7) as the supporting electrolyte. The working electrode was an ITO glass plate coated with the catalyst slurry; the counter electrode was a platinum foil, and a saturated silver / silver chloride solution was used as the reference electrode. Mott-Schottky curves were measured at AC frequencies of 500 Hz, 1000 Hz, and 1500 Hz. Working electrode preparation: 10 mg of photocatalyst, 1 mL of ethanol, and 10 μL of Nafion were mixed and sonicated for 20 min. 50 μL of the slurry was uniformly coated onto an ITO glass plate (1 × 1 cm²). −2 And then dried under infrared irradiation.

[0080] Hydrogen peroxide decomposition: Considering the accelerated decomposition of hydrogen peroxide under irradiation, the stability of the generated hydrogen peroxide was evaluated by measuring its degradation behavior during the sample preparation process. Hydrogen peroxide (1 mM, 20 mL) was reacted with a photocatalyst (0.5 mg / mL). -1 The mixture was sonicated for 2 minutes, followed by purging the system with argon. The light source was then turned on, and the residual hydrogen peroxide concentration was measured every 15 minutes to assess its stability.

[0081] It should be noted that while the preferred embodiments of the present invention are given in the specification and accompanying drawings, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are not intended to impose additional limitations on the content of the present invention; their purpose is to provide a more thorough and comprehensive understanding of the disclosure of the present invention. Furthermore, the above-described technical features can be combined with each other to form various embodiments not listed above, all of which are considered to be within the scope of the present invention specification. Moreover, those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a covalent organic framework material based on thiadiazole ring linkages, characterized in that, Includes the following steps: (1) A covalent organic framework with acylhydrazone bonds is formed by dehydration condensation reaction of ligands with aldehyde groups and ligands with acylhydrazine groups; (2) Acylhydrazone bonds are converted into thiadiazole rings through thiolation, cyclization and oxidation reactions to obtain covalent organic framework materials based on thiadiazole ring linkages; The ligand containing the hydrazide is 2,5-diethoxyterephthalohydrazide; The ligand with the aldehyde group is benzo[1,2-b:3,4-b:5,6-b'']trithiophene-2,5,8-trialdehyde.

2. The preparation method according to claim 1, characterized in that, The dehydration condensation reaction described in step (1) is carried out as follows: the ligand with an aldehyde group and the ligand with an acylhydrazine group are subjected to a solvothermal reaction in a reaction solvent under the action of acid.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the ligand with the aldehyde group to the ligand with the hydrazide group is 2:

3.

4. The preparation method according to claim 2, characterized in that, The reaction solvent is one or a mixture of several of the following: dioxane, mesitylene, N,N-dimethylformamide, N,N-dimethylacetamide, 1,2-dichlorobenzene, 1,3-dimethyl-2-imidazolium ketone, n-butanol, benzyl alcohol, methanol, ethanol, dimethyl sulfoxide, acetonitrile, and cyclohexane. The acid is acetic acid at a concentration of 3-6 mol / L.

5. The preparation method according to claim 1, characterized in that, The thiolation, cyclization and oxidation reactions described in step (2) are carried out as follows: the covalent organic framework obtained in step (1) is refluxed in an organic solvent under the action of a thiolation reagent and a catalyst.

6. The preparation method according to claim 5, characterized in that, The thiolation reagent is a Lawesson reagent; The organic solvent is toluene, THF, or pyridine; The catalyst is 4-(dimethylamino)pyridine.

7. A covalent organic framework material based on thiadiazole ring linkage obtained by the preparation method according to any one of claims 1-6.

8. The application of the covalent organic framework material based on thiadiazole ring linkage as described in claim 7 as a photocatalyst.

9. The application according to claim 8, characterized in that, The covalent organic framework material is used for photocatalytic hydrogen peroxide generation and photocatalytic benzylamine coupling.

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