Preparation method and application of a dual-site regulated covalent organic framework

Abstract

This invention discloses methods for preparing pyridyl covalent organic frameworks (COFs) and their antimony (Sb) coordination compounds (TAPB-BTTA, TAPT-BTTA, TAPB-BTTA-Sb, and TAPT-BTTA-Sb), as well as the application of these compounds in photocatalytic hydrogen peroxide (H2O2), belonging to the field of photocatalysis technology. This invention utilizes a molecular engineering strategy, using specific amine and aldehyde monomers as raw materials, to prepare TAPB-BTTA and TAPT-BTTA with pyridyl-imine bidentate chelate sites via a Schiff base reaction. Then, through a post-modification synthesis strategy, the main group metal Sb atom is precisely anchored to the pyridyl-imine coordination sites of the COF framework, forming atomically dispersed Sb-coordinated COF compounds. These materials, through bi-level regulation of nitrogen and Sb metal sites, optimize the H2O2 generation pathway into a highly efficient one-step two-electron oxygen reduction reaction (2e... ‑ The ORR pathway significantly improves the separation efficiency and catalytic activity of photogenerated carriers, with the H2O2 generation rate of TAPT-BTTA-Sb reaching as high as 18399.72 μmol h⁻¹. ‑1 g ‑1 It also has excellent stability and oxygen utilization, providing efficient materials and preparation methods for solar-driven clean H2O2 synthesis.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, specifically to the preparation methods of pyridylimine covalent organic frameworks (TAPB-BTTA, TAPT-BTTA) and their antimony coordination compounds (TAPB-BTTA-Sb, TAPT-BTTA-Sb), and the application of these compounds in the photocatalytic generation of hydrogen peroxide (H2O2). Background Technology

[0002] Hydrogen peroxide (H2O2), as a green and environmentally friendly oxidant and energy carrier, has wide applications in chemical synthesis, wastewater treatment, and medical disinfection. Traditional industrial production of H2O2 mainly relies on the anthraquinone process, which suffers from problems such as complex processes, high energy consumption, and the generation of toxic byproducts, failing to meet the requirements of sustainable development. Solar-driven photocatalytic oxygen reduction reaction (ORR) for H2O2 synthesis, using water and oxygen as raw materials, offers advantages such as mild conditions and environmental friendliness, making it a current research hotspot.

[0003] Covalent organic frameworks (COFs), as a novel class of crystalline porous materials, possess characteristics such as tunable structure, large specific surface area, and well-defined functional sites, demonstrating great potential in the field of photocatalysis. By designing donor-acceptor (DA) structures, the electronic structure and photogenerated carrier separation efficiency of COFs can be optimized. However, existing COF-based photocatalysts still have the following shortcomings: 1) The chemical environment of active sites is difficult to control, leading to insufficient optimization of the adsorption behavior of reaction intermediates; 2) Most COF catalysts follow a two-step single-electron ORR pathway, requiring passage through superoxide radicals (O2) which easily initiate side reactions. ·- 1) The efficiency and selectivity of H2O2 generation are limited; 2) There are few studies on the atomic-level dispersion and coordination regulation of main group metals in COF, which fails to give full play to the synergistic catalytic effect of metal sites and COF framework.

[0004] Therefore, developing COF-based photocatalysts with precisely regulated active sites and the ability to achieve a highly efficient one-step two-electron ORR pathway is of great significance for improving the photocatalytic production of H2O2. Summary of the Invention

[0005] The primary objective of this invention is to provide pyridylimine COFs (TAPB-BTTA, TAPT-BTTA) with well-defined structures and controllable active sites, and their preparation methods; secondly, to provide high-performance photocatalytic materials (TAPB-BTTA-Sb, TAPT-BTTA-Sb) formed by coordination of the above-mentioned COFs with Sb, and their preparation methods; finally, to provide the application of this type of Sb-coordinated COF compound in the photocatalytic production of H2O2, solving the problems of low H2O2 synthesis efficiency, unreasonable pathways, and insufficient catalyst stability in the prior art.

[0006] Using TAPB or TAPT as amine monomers and BTTA as an aldehyde monomer, a Schiff base condensation reaction is carried out in a mixed solvent with acetic acid as a catalyst to form a two-dimensional layered COF (TAPB-BTTA or TAPT-BTTA) with pyridine-imine bidentate chelate sites. This COF optimizes the electronic structure by replacing the traditional triazine unit with a pyridine unit, laying the foundation for subsequent metal coordination and reaction pathway regulation. Through post-synthetic modification strategies, Sb ions are precisely anchored to the pyridine-imine bidentate chelate sites of TAPB-BTTA or TAPT-BTTA, forming atomically dispersed Sb coordination compounds. The synergistic effect of the Sb metal center and the COF framework further optimizes the carrier separation efficiency and the ORR reaction pathway.

[0007] Using Sb-coordinated COF compounds as photocatalysts, H2O2 is efficiently generated from water and air / oxygen under visible light irradiation. Among them, TAPT-BTTA-Sb exhibits an H2O2 generation rate as high as 18399.72 μmol h⁻¹ g⁻¹, which is significantly better than existing COF-based photocatalysts.

[0008] The prepared TAPB-BTTA and TAPT-BTTA exhibit high crystallinity, large specific surface area, and well-defined pyridine-imine bidentate chelating sites, providing a stable support for the precise anchoring of metal atoms. The coordination of Sb with COF forms atomically dispersed active centers, which, in synergy with the pyridine-imine units, transform the H2O2 generation pathway from a two-step single-electron ORR pathway to a highly efficient one-step two-electron ORR pathway, avoiding side reactions initiated by the O2·- intermediate.

[0009] These Sb-coordinated COF compounds exhibit excellent photogenerated carrier separation efficiency, electron transport rate, and oxygen utilization. They also demonstrate high photocatalytic activity and good stability in H2O2 production, showing no significant performance degradation after four cycles. The preparation method is simple, controllable, and operates under mild conditions, requiring no complex equipment and facilitating large-scale production. This provides a new material system and technical solution for solar-driven clean H2O2 synthesis. Attached Figure Description

[0010] The following is a brief explanation of the content depicted in the accompanying drawings:

[0011] Figure 1 The reaction pathway of COFs in the embodiments of the present invention;

[0012] Figure 2 This is a synthesis route diagram of COFs in an embodiment of the present invention;

[0013] Figure 3 The PXRD patterns of COFs and their corresponding Sb coordination compounds in the embodiments of the present invention are shown below.

[0014] Figure 4 The TEM image and EDS elemental distribution diagram of TAPT-BTTA-Sb in this embodiment of the invention are shown below.

[0015] Figure 5 The UV-visDRS and Tauc-plot spectra of COFs and Sb coordination compounds in the embodiments of the present invention are shown.

[0016] Figure 6 The figures show a comparison of the photocatalytic H2O2 production rates of different COF materials in the embodiments of the present invention and a cycle stability test figure of TAPT-BTTA-Sb. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] The following provides a detailed description of the COFs, their coordinated metal COFs, their preparation methods, and their applications provided in the embodiments of the present invention.

[0019] This invention provides a method for preparing a dual-site regulated imine covalent organic framework and its application. Please refer to [reference needed]. Figure 1 2. This includes the following steps:

[0020] (1) Preparation of TAPB-BTTA: 1.1 Weigh 0.1 mmol of 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 0.1 mmol of 1,3,5-tris(2-formylpyridin-5-yl)benzene (BTTA) and add them to a 25 mL pressure-resistant reaction tube. 1.2 Add 6 ml of 1,4-dioxane and 6 ml of mesitylene to the reaction tube, and sonicate for 10 minutes to ensure complete dissolution of the monomer; add 1 ml of 6 mol / L... -1 Using an acetic acid solution as a catalyst, the mixture was sonicated again for 5 minutes. 1.3 After sealing the reaction tube, place it in an oven at 120℃ for 3 days. After the reaction, cool to room temperature, centrifuge to collect the precipitate, wash it three times successively with N,N-dimethylformamide and ethanol, and dry it in a vacuum oven at 60℃ for 12 hours to obtain a yellow powder, TAPB-BTTA.

[0021] (2) Preparation of TAPT-BTTA: Weigh 50 mg of TAPT-BTTA prepared in Example 2 and disperse it in 20 mL of ethanol, then sonicate for 30 minutes. Weigh 0.03 mmol of antimony trichloride (SbCl3) and dissolve it in 5 mL of ethanol, stirring until completely dissolved. Slowly add the antimony salt solution dropwise to the TAPT-BTTA suspension, and stir at 700 rpm for 20 hours at room temperature. After the reaction is complete, centrifuge at 8000 rpm for 10 minutes, collect the precipitate, wash it four times alternately with ethanol and deionized water, and dry it in a vacuum oven at 60 °C for 12 hours to obtain orange-red powder TAPT-BTTA-Sb.

[0022] Example 1 This invention provides a method for preparing a dual-site regulated imine covalent organic framework and its application, comprising the following steps:

[0023] Weigh 50 mg of TAPB-BTTA prepared in (1) and disperse it in 20 mL of N,N-dimethylformamide (DMF). Sonicate the dispersion for 30 minutes to form a uniform suspension. Weigh 0.03 mmol of antimony trichloride (SbCl3) and dissolve it in 5 mL of DMF. Stir until completely dissolved. Slowly add the antimony salt solution to the TAPB-BTTA suspension and stir at 600 rpm for 18 hours at room temperature. After the reaction is complete, centrifuge at 8000 rpm for 10 minutes, collect the precipitate, wash it 4 times with DMF and ethanol alternately, and dry it in a vacuum oven at 60℃ for 12 hours to obtain a dark yellow powder TAPB-BTTA-Sb.

[0024] Weigh 50 mg of TAPT-BTTA prepared in (2) and disperse it in 20 mL of ethanol. Sonicate the dispersion for 30 minutes. Weigh 0.03 mmol of antimony trichloride (SbCl3) and dissolve it in 5 mL of ethanol. Stir until completely dissolved. Slowly add the antimony salt solution to the TAPT-BTTA suspension and stir at 700 rpm for 20 hours at room temperature. After the reaction is complete, centrifuge at 8000 rpm for 10 minutes, collect the precipitate, wash it 4 times alternately with ethanol and deionized water, and dry it in a vacuum oven at 60 °C for 12 hours to obtain orange-red powder TAPT-BTTA-Sb.

[0025] Experimental Example 1 The material prepared in Example 1 was subjected to powder X-ray diffraction analysis, and the results are as follows: Figure 3 As shown. TAPB-BTTA and TAPT-BTTA exhibit characteristic diffraction peaks at ~4.12°, ~6.94°, ~8.28° and ~10.78°, indicating a highly ordered two-dimensional layered structure; after Sb coordination, the positions of the characteristic diffraction peaks are basically preserved, and the (100) peak shifts to a lower angle, confirming that Sb is successfully anchored to the COF framework without destroying the crystal structure.

[0026] TEM images of TAPT-BTTA-Sb show that it retains the layered structure of COF, and EDS elemental distribution maps show that C, N, and Sb elements are uniformly distributed, confirming that Sb exists in an atomically dispersed form. Figure 4 ).

[0027] UV-visDRS spectra show that the absorption edge of the material undergoes a red shift after Sb coordination, and the band gap narrows. Figure 5 ).

[0028] Experimental Example 2

[0029] Test conditions: A 300W xenon lamp (equipped with a 420nm filter) was used as the light source, 50mL of deionized water was used as the reaction system, and the catalyst concentration was 0.125g / L. -1 Air is introduced (flow rate of 20 mL / min). -1 The reaction time was 1 hour, and the yield of H2O2 was determined by iodometric titration.

[0030] Test results: The photocatalytic H2O2 production rate of TAPT-BTTA is 8488.36 μmol / h. -1 g -1 ; The photocatalytic H2O2 production rate of TAPB-BTTA is 5920.53 μmol h⁻¹ g⁻¹. The photocatalytic H2O2 production rate of TAPB-BTTA-Sb is 11242.86 μmol / h. -1 g -1 ; The photocatalytic H2O2 production rate of TAPT-BTTA-Sb is 18399.72 μmol / h. -1 g -1 .

[0031] Cyclic stability test: TAPT-BTTA-Sb was reused 4 times. After each reaction, the catalyst was recovered by centrifugation, washed, and dried before the next test. The results showed that its H2O2 formation rate decreased by less than 5%, indicating excellent stability. Figure 5 ).

[0032] The reaction pathway was investigated using quenching experiments: The addition of an electron scavenger (KBrO3) significantly reduced the H2O2 formation rate of Sb-coordinated COF, confirming that photogenerated electrons are the core driving force of the reaction; the addition of a superoxide radical scavenger (p-BQ) did not significantly change the activity, indicating that the reaction follows a one-step two-electron ORR pathway and does not involve O2. ·- Intermediates are used to avoid side reactions.

[0033] In summary, this invention has successfully prepared high-performance Sb-coordinated pyridylimine COF compounds through precise nitrogen site engineering and main group metal coordination regulation. These compounds exhibit high activity, high selectivity, and high stability in photocatalytic H2O2 production and have broad application prospects.

[0034] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A pyridylimine covalent organic framework (COF), characterized in that, The COF is TAPB-BTTATAPT-BTTA, possessing pyridine-imine bidentate chelating active sites, and has a two-dimensional layered crystal structure with a BET specific surface area of ​​1045.1 m². 2 g -1 and 1656.1m 2 g -1 .

2. The method for preparing the pyridylimine COFs according to claim 1, characterized in that, The process includes the following steps: using 1,3,5-tris(4-aminophenyl)benzene (TAPB) or tris(4-aminophenyl)amine (TAPT) as an amine monomer and 1,3,5-tris(2-formylpyridin-5-yl)benzene (BTTA) as an aldehyde monomer, a Schiff base condensation reaction is carried out in a mixed solvent of 1,4-dioxane / trimethylbenzene with acetic acid as a catalyst. After the reaction, TAPB-BTTA or TAPT-BTTA is obtained by separation and purification.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the amine monomer to the aldehyde monomer is 1:1; the volume ratio of 1,4-dioxane to mesitylene in the mixed solvent is 1:1; the concentration of acetic acid is 6 mol / L, and the amount used is 10%-20% of the volume of the mixed solvent; the condensation reaction temperature is 120-150℃, and the reaction time is 3-5 days.

4. An antimony-coordinated pyridylimine COF compound, characterized in that, The compound is TAPB-BTTA-Sb or TAPT-BTTA-Sb, formed by the pyridyl imine COF of claim 1 and Sb ions through coordination bonds, wherein Sb is anchored in an atomically dispersed form at the pyridyl-imine bidentate chelation site of COF.

5. The method for preparing the antimony-coordinated pyridylimine COF compound according to claim 4, characterized in that, The process includes the following steps: dispersing the TAPB-BTTA or TAPT-BTTA described in claim 1 in an organic solvent, adding an antimony salt solution, stirring and reacting at room temperature for 12-24 hours, and obtaining TAPB-BTTA-Sb or TAPT-BTTA-Sb after centrifugation, washing, and drying.

6. The preparation method according to claim 5, characterized in that, The organic solvent is N,N-dimethylformamide (DMF) or ethanol; the antimony salt is antimony trichloride (SbCl3), and the molar ratio of antimony salt to COF is 0.5-1:1; the stirring speed is 500-800 rpm.

7. The antimony-coordinated pyridylimine COF compound according to claim 4, characterized in that, The photocatalytic H2O2 production rate of the TAPT-BTTA-Sb is 18399.72 μmol / h. -1 g -1 The photocatalytic H2O2 production rate of TAPB-BTTA-Sb was 11242.86 μmol / h. -1 g -1 .

8. The application of the antimony-coordinated pyridylimine COF compound of claim 4 in the photocatalytic generation of hydrogen peroxide.

9. The application according to claim 8, characterized in that, The application conditions are as follows: visible light (λ≥420nm) as the light source, pure water as the hydrogen source, air or oxygen as the oxygen source, and catalyst concentration of 0.5-0.75 g / L. -1 The reaction system is neutral or weakly acidic.

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